Linux-libre 4.9.46-gnu

[librecmc/linux-libre.git] / drivers / md / raid5.c

/*
 * raid5.c : Multiple Devices driver for Linux
 *         Copyright (C) 1996, 1997 Ingo Molnar, Miguel de Icaza, Gadi Oxman
 *         Copyright (C) 1999, 2000 Ingo Molnar
 *         Copyright (C) 2002, 2003 H. Peter Anvin
 *
 * RAID-4/5/6 management functions.
 * Thanks to Penguin Computing for making the RAID-6 development possible
 * by donating a test server!
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * You should have received a copy of the GNU General Public License
 * (for example /usr/src/linux/COPYING); if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 * BITMAP UNPLUGGING:
 *
 * The sequencing for updating the bitmap reliably is a little
 * subtle (and I got it wrong the first time) so it deserves some
 * explanation.
 *
 * We group bitmap updates into batches.  Each batch has a number.
 * We may write out several batches at once, but that isn't very important.
 * conf->seq_write is the number of the last batch successfully written.
 * conf->seq_flush is the number of the last batch that was closed to
 *    new additions.
 * When we discover that we will need to write to any block in a stripe
 * (in add_stripe_bio) we update the in-memory bitmap and record in sh->bm_seq
 * the number of the batch it will be in. This is seq_flush+1.
 * When we are ready to do a write, if that batch hasn't been written yet,
 *   we plug the array and queue the stripe for later.
 * When an unplug happens, we increment bm_flush, thus closing the current
 *   batch.
 * When we notice that bm_flush > bm_write, we write out all pending updates
 * to the bitmap, and advance bm_write to where bm_flush was.
 * This may occasionally write a bit out twice, but is sure never to
 * miss any bits.
 */

#include <linux/blkdev.h>
#include <linux/kthread.h>
#include <linux/raid/pq.h>
#include <linux/async_tx.h>
#include <linux/module.h>
#include <linux/async.h>
#include <linux/seq_file.h>
#include <linux/cpu.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>
#include <linux/nodemask.h>
#include <linux/flex_array.h>
#include <trace/events/block.h>

#include "md.h"
#include "raid5.h"
#include "raid0.h"
#include "bitmap.h"

#define cpu_to_group(cpu) cpu_to_node(cpu)
#define ANY_GROUP NUMA_NO_NODE

static bool devices_handle_discard_safely = false;
module_param(devices_handle_discard_safely, bool, 0644);
MODULE_PARM_DESC(devices_handle_discard_safely,
                 "Set to Y if all devices in each array reliably return zeroes on reads from discarded regions");
static struct workqueue_struct *raid5_wq;
/*
 * Stripe cache
 */

#define NR_STRIPES              256
#define STRIPE_SIZE             PAGE_SIZE
#define STRIPE_SHIFT            (PAGE_SHIFT - 9)
#define STRIPE_SECTORS          (STRIPE_SIZE>>9)
#define IO_THRESHOLD            1
#define BYPASS_THRESHOLD        1
#define NR_HASH                 (PAGE_SIZE / sizeof(struct hlist_head))
#define HASH_MASK               (NR_HASH - 1)
#define MAX_STRIPE_BATCH        8

static inline struct hlist_head *stripe_hash(struct r5conf *conf, sector_t sect)
{
        int hash = (sect >> STRIPE_SHIFT) & HASH_MASK;
        return &conf->stripe_hashtbl[hash];
}

static inline int stripe_hash_locks_hash(sector_t sect)
{
        return (sect >> STRIPE_SHIFT) & STRIPE_HASH_LOCKS_MASK;
}

static inline void lock_device_hash_lock(struct r5conf *conf, int hash)
{
        spin_lock_irq(conf->hash_locks + hash);
        spin_lock(&conf->device_lock);
}

static inline void unlock_device_hash_lock(struct r5conf *conf, int hash)
{
        spin_unlock(&conf->device_lock);
        spin_unlock_irq(conf->hash_locks + hash);
}

static inline void lock_all_device_hash_locks_irq(struct r5conf *conf)
{
        int i;
        local_irq_disable();
        spin_lock(conf->hash_locks);
        for (i = 1; i < NR_STRIPE_HASH_LOCKS; i++)
                spin_lock_nest_lock(conf->hash_locks + i, conf->hash_locks);
        spin_lock(&conf->device_lock);
}

static inline void unlock_all_device_hash_locks_irq(struct r5conf *conf)
{
        int i;
        spin_unlock(&conf->device_lock);
        for (i = NR_STRIPE_HASH_LOCKS; i; i--)
                spin_unlock(conf->hash_locks + i - 1);
        local_irq_enable();
}

/* bio's attached to a stripe+device for I/O are linked together in bi_sector
 * order without overlap.  There may be several bio's per stripe+device, and
 * a bio could span several devices.
 * When walking this list for a particular stripe+device, we must never proceed
 * beyond a bio that extends past this device, as the next bio might no longer
 * be valid.
 * This function is used to determine the 'next' bio in the list, given the sector
 * of the current stripe+device
 */
static inline struct bio *r5_next_bio(struct bio *bio, sector_t sector)
{
        int sectors = bio_sectors(bio);
        if (bio->bi_iter.bi_sector + sectors < sector + STRIPE_SECTORS)
                return bio->bi_next;
        else
                return NULL;
}

/*
 * We maintain a biased count of active stripes in the bottom 16 bits of
 * bi_phys_segments, and a count of processed stripes in the upper 16 bits
 */
static inline int raid5_bi_processed_stripes(struct bio *bio)
{
        atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
        return (atomic_read(segments) >> 16) & 0xffff;
}

static inline int raid5_dec_bi_active_stripes(struct bio *bio)
{
        atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
        return atomic_sub_return(1, segments) & 0xffff;
}

static inline void raid5_inc_bi_active_stripes(struct bio *bio)
{
        atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
        atomic_inc(segments);
}

static inline void raid5_set_bi_processed_stripes(struct bio *bio,
        unsigned int cnt)
{
        atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
        int old, new;

        do {
                old = atomic_read(segments);
                new = (old & 0xffff) | (cnt << 16);
        } while (atomic_cmpxchg(segments, old, new) != old);
}

static inline void raid5_set_bi_stripes(struct bio *bio, unsigned int cnt)
{
        atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
        atomic_set(segments, cnt);
}

/* Find first data disk in a raid6 stripe */
static inline int raid6_d0(struct stripe_head *sh)
{
        if (sh->ddf_layout)
                /* ddf always start from first device */
                return 0;
        /* md starts just after Q block */
        if (sh->qd_idx == sh->disks - 1)
                return 0;
        else
                return sh->qd_idx + 1;
}
static inline int raid6_next_disk(int disk, int raid_disks)
{
        disk++;
        return (disk < raid_disks) ? disk : 0;
}

/* When walking through the disks in a raid5, starting at raid6_d0,
 * We need to map each disk to a 'slot', where the data disks are slot
 * 0 .. raid_disks-3, the parity disk is raid_disks-2 and the Q disk
 * is raid_disks-1.  This help does that mapping.
 */
static int raid6_idx_to_slot(int idx, struct stripe_head *sh,
                             int *count, int syndrome_disks)
{
        int slot = *count;

        if (sh->ddf_layout)
                (*count)++;
        if (idx == sh->pd_idx)
                return syndrome_disks;
        if (idx == sh->qd_idx)
                return syndrome_disks + 1;
        if (!sh->ddf_layout)
                (*count)++;
        return slot;
}

static void return_io(struct bio_list *return_bi)
{
        struct bio *bi;
        while ((bi = bio_list_pop(return_bi)) != NULL) {
                bi->bi_iter.bi_size = 0;
                trace_block_bio_complete(bdev_get_queue(bi->bi_bdev),
                                         bi, 0);
                bio_endio(bi);
        }
}

static void print_raid5_conf (struct r5conf *conf);

static int stripe_operations_active(struct stripe_head *sh)
{
        return sh->check_state || sh->reconstruct_state ||
               test_bit(STRIPE_BIOFILL_RUN, &sh->state) ||
               test_bit(STRIPE_COMPUTE_RUN, &sh->state);
}

static void raid5_wakeup_stripe_thread(struct stripe_head *sh)
{
        struct r5conf *conf = sh->raid_conf;
        struct r5worker_group *group;
        int thread_cnt;
        int i, cpu = sh->cpu;

        if (!cpu_online(cpu)) {
                cpu = cpumask_any(cpu_online_mask);
                sh->cpu = cpu;
        }

        if (list_empty(&sh->lru)) {
                struct r5worker_group *group;
                group = conf->worker_groups + cpu_to_group(cpu);
                list_add_tail(&sh->lru, &group->handle_list);
                group->stripes_cnt++;
                sh->group = group;
        }

        if (conf->worker_cnt_per_group == 0) {
                md_wakeup_thread(conf->mddev->thread);
                return;
        }

        group = conf->worker_groups + cpu_to_group(sh->cpu);

        group->workers[0].working = true;
        /* at least one worker should run to avoid race */
        queue_work_on(sh->cpu, raid5_wq, &group->workers[0].work);

        thread_cnt = group->stripes_cnt / MAX_STRIPE_BATCH - 1;
        /* wakeup more workers */
        for (i = 1; i < conf->worker_cnt_per_group && thread_cnt > 0; i++) {
                if (group->workers[i].working == false) {
                        group->workers[i].working = true;
                        queue_work_on(sh->cpu, raid5_wq,
                                      &group->workers[i].work);
                        thread_cnt--;
                }
        }
}

static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh,
                              struct list_head *temp_inactive_list)
{
        BUG_ON(!list_empty(&sh->lru));
        BUG_ON(atomic_read(&conf->active_stripes)==0);
        if (test_bit(STRIPE_HANDLE, &sh->state)) {
                if (test_bit(STRIPE_DELAYED, &sh->state) &&
                    !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                        list_add_tail(&sh->lru, &conf->delayed_list);
                else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
                           sh->bm_seq - conf->seq_write > 0)
                        list_add_tail(&sh->lru, &conf->bitmap_list);
                else {
                        clear_bit(STRIPE_DELAYED, &sh->state);
                        clear_bit(STRIPE_BIT_DELAY, &sh->state);
                        if (conf->worker_cnt_per_group == 0) {
                                list_add_tail(&sh->lru, &conf->handle_list);
                        } else {
                                raid5_wakeup_stripe_thread(sh);
                                return;
                        }
                }
                md_wakeup_thread(conf->mddev->thread);
        } else {
                BUG_ON(stripe_operations_active(sh));
                if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                        if (atomic_dec_return(&conf->preread_active_stripes)
                            < IO_THRESHOLD)
                                md_wakeup_thread(conf->mddev->thread);
                atomic_dec(&conf->active_stripes);
                if (!test_bit(STRIPE_EXPANDING, &sh->state))
                        list_add_tail(&sh->lru, temp_inactive_list);
        }
}

static void __release_stripe(struct r5conf *conf, struct stripe_head *sh,
                             struct list_head *temp_inactive_list)
{
        if (atomic_dec_and_test(&sh->count))
                do_release_stripe(conf, sh, temp_inactive_list);
}

/*
 * @hash could be NR_STRIPE_HASH_LOCKS, then we have a list of inactive_list
 *
 * Be careful: Only one task can add/delete stripes from temp_inactive_list at
 * given time. Adding stripes only takes device lock, while deleting stripes
 * only takes hash lock.
 */
static void release_inactive_stripe_list(struct r5conf *conf,
                                         struct list_head *temp_inactive_list,
                                         int hash)
{
        int size;
        bool do_wakeup = false;
        unsigned long flags;

        if (hash == NR_STRIPE_HASH_LOCKS) {
                size = NR_STRIPE_HASH_LOCKS;
                hash = NR_STRIPE_HASH_LOCKS - 1;
        } else
                size = 1;
        while (size) {
                struct list_head *list = &temp_inactive_list[size - 1];

                /*
                 * We don't hold any lock here yet, raid5_get_active_stripe() might
                 * remove stripes from the list
                 */
                if (!list_empty_careful(list)) {
                        spin_lock_irqsave(conf->hash_locks + hash, flags);
                        if (list_empty(conf->inactive_list + hash) &&
                            !list_empty(list))
                                atomic_dec(&conf->empty_inactive_list_nr);
                        list_splice_tail_init(list, conf->inactive_list + hash);
                        do_wakeup = true;
                        spin_unlock_irqrestore(conf->hash_locks + hash, flags);
                }
                size--;
                hash--;
        }

        if (do_wakeup) {
                wake_up(&conf->wait_for_stripe);
                if (atomic_read(&conf->active_stripes) == 0)
                        wake_up(&conf->wait_for_quiescent);
                if (conf->retry_read_aligned)
                        md_wakeup_thread(conf->mddev->thread);
        }
}

/* should hold conf->device_lock already */
static int release_stripe_list(struct r5conf *conf,
                               struct list_head *temp_inactive_list)
{
        struct stripe_head *sh;
        int count = 0;
        struct llist_node *head;

        head = llist_del_all(&conf->released_stripes);
        head = llist_reverse_order(head);
        while (head) {
                int hash;

                sh = llist_entry(head, struct stripe_head, release_list);
                head = llist_next(head);
                /* sh could be readded after STRIPE_ON_RELEASE_LIST is cleard */
                smp_mb();
                clear_bit(STRIPE_ON_RELEASE_LIST, &sh->state);
                /*
                 * Don't worry the bit is set here, because if the bit is set
                 * again, the count is always > 1. This is true for
                 * STRIPE_ON_UNPLUG_LIST bit too.
                 */
                hash = sh->hash_lock_index;
                __release_stripe(conf, sh, &temp_inactive_list[hash]);
                count++;
        }

        return count;
}

void raid5_release_stripe(struct stripe_head *sh)
{
        struct r5conf *conf = sh->raid_conf;
        unsigned long flags;
        struct list_head list;
        int hash;
        bool wakeup;

        /* Avoid release_list until the last reference.
         */
        if (atomic_add_unless(&sh->count, -1, 1))
                return;

        if (unlikely(!conf->mddev->thread) ||
                test_and_set_bit(STRIPE_ON_RELEASE_LIST, &sh->state))
                goto slow_path;
        wakeup = llist_add(&sh->release_list, &conf->released_stripes);
        if (wakeup)
                md_wakeup_thread(conf->mddev->thread);
        return;
slow_path:
        local_irq_save(flags);
        /* we are ok here if STRIPE_ON_RELEASE_LIST is set or not */
        if (atomic_dec_and_lock(&sh->count, &conf->device_lock)) {
                INIT_LIST_HEAD(&list);
                hash = sh->hash_lock_index;
                do_release_stripe(conf, sh, &list);
                spin_unlock(&conf->device_lock);
                release_inactive_stripe_list(conf, &list, hash);
        }
        local_irq_restore(flags);
}

static inline void remove_hash(struct stripe_head *sh)
{
        pr_debug("remove_hash(), stripe %llu\n",
                (unsigned long long)sh->sector);

        hlist_del_init(&sh->hash);
}

static inline void insert_hash(struct r5conf *conf, struct stripe_head *sh)
{
        struct hlist_head *hp = stripe_hash(conf, sh->sector);

        pr_debug("insert_hash(), stripe %llu\n",
                (unsigned long long)sh->sector);

        hlist_add_head(&sh->hash, hp);
}

/* find an idle stripe, make sure it is unhashed, and return it. */
static struct stripe_head *get_free_stripe(struct r5conf *conf, int hash)
{
        struct stripe_head *sh = NULL;
        struct list_head *first;

        if (list_empty(conf->inactive_list + hash))
                goto out;
        first = (conf->inactive_list + hash)->next;
        sh = list_entry(first, struct stripe_head, lru);
        list_del_init(first);
        remove_hash(sh);
        atomic_inc(&conf->active_stripes);
        BUG_ON(hash != sh->hash_lock_index);
        if (list_empty(conf->inactive_list + hash))
                atomic_inc(&conf->empty_inactive_list_nr);
out:
        return sh;
}

static void shrink_buffers(struct stripe_head *sh)
{
        struct page *p;
        int i;
        int num = sh->raid_conf->pool_size;

        for (i = 0; i < num ; i++) {
                WARN_ON(sh->dev[i].page != sh->dev[i].orig_page);
                p = sh->dev[i].page;
                if (!p)
                        continue;
                sh->dev[i].page = NULL;
                put_page(p);
        }
}

static int grow_buffers(struct stripe_head *sh, gfp_t gfp)
{
        int i;
        int num = sh->raid_conf->pool_size;

        for (i = 0; i < num; i++) {
                struct page *page;

                if (!(page = alloc_page(gfp))) {
                        return 1;
                }
                sh->dev[i].page = page;
                sh->dev[i].orig_page = page;
        }
        return 0;
}

static void raid5_build_block(struct stripe_head *sh, int i, int previous);
static void stripe_set_idx(sector_t stripe, struct r5conf *conf, int previous,
                            struct stripe_head *sh);

static void init_stripe(struct stripe_head *sh, sector_t sector, int previous)
{
        struct r5conf *conf = sh->raid_conf;
        int i, seq;

        BUG_ON(atomic_read(&sh->count) != 0);
        BUG_ON(test_bit(STRIPE_HANDLE, &sh->state));
        BUG_ON(stripe_operations_active(sh));
        BUG_ON(sh->batch_head);

        pr_debug("init_stripe called, stripe %llu\n",
                (unsigned long long)sector);
retry:
        seq = read_seqcount_begin(&conf->gen_lock);
        sh->generation = conf->generation - previous;
        sh->disks = previous ? conf->previous_raid_disks : conf->raid_disks;
        sh->sector = sector;
        stripe_set_idx(sector, conf, previous, sh);
        sh->state = 0;

        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];

                if (dev->toread || dev->read || dev->towrite || dev->written ||
                    test_bit(R5_LOCKED, &dev->flags)) {
                        printk(KERN_ERR "sector=%llx i=%d %p %p %p %p %d\n",
                               (unsigned long long)sh->sector, i, dev->toread,
                               dev->read, dev->towrite, dev->written,
                               test_bit(R5_LOCKED, &dev->flags));
                        WARN_ON(1);
                }
                dev->flags = 0;
                raid5_build_block(sh, i, previous);
        }
        if (read_seqcount_retry(&conf->gen_lock, seq))
                goto retry;
        sh->overwrite_disks = 0;
        insert_hash(conf, sh);
        sh->cpu = smp_processor_id();
        set_bit(STRIPE_BATCH_READY, &sh->state);
}

static struct stripe_head *__find_stripe(struct r5conf *conf, sector_t sector,
                                         short generation)
{
        struct stripe_head *sh;

        pr_debug("__find_stripe, sector %llu\n", (unsigned long long)sector);
        hlist_for_each_entry(sh, stripe_hash(conf, sector), hash)
                if (sh->sector == sector && sh->generation == generation)
                        return sh;
        pr_debug("__stripe %llu not in cache\n", (unsigned long long)sector);
        return NULL;
}

/*
 * Need to check if array has failed when deciding whether to:
 *  - start an array
 *  - remove non-faulty devices
 *  - add a spare
 *  - allow a reshape
 * This determination is simple when no reshape is happening.
 * However if there is a reshape, we need to carefully check
 * both the before and after sections.
 * This is because some failed devices may only affect one
 * of the two sections, and some non-in_sync devices may
 * be insync in the section most affected by failed devices.
 */
static int calc_degraded(struct r5conf *conf)
{
        int degraded, degraded2;
        int i;

        rcu_read_lock();
        degraded = 0;
        for (i = 0; i < conf->previous_raid_disks; i++) {
                struct md_rdev *rdev = rcu_dereference(conf->disks[i].rdev);
                if (rdev && test_bit(Faulty, &rdev->flags))
                        rdev = rcu_dereference(conf->disks[i].replacement);
                if (!rdev || test_bit(Faulty, &rdev->flags))
                        degraded++;
                else if (test_bit(In_sync, &rdev->flags))
                        ;
                else
                        /* not in-sync or faulty.
                         * If the reshape increases the number of devices,
                         * this is being recovered by the reshape, so
                         * this 'previous' section is not in_sync.
                         * If the number of devices is being reduced however,
                         * the device can only be part of the array if
                         * we are reverting a reshape, so this section will
                         * be in-sync.
                         */
                        if (conf->raid_disks >= conf->previous_raid_disks)
                                degraded++;
        }
        rcu_read_unlock();
        if (conf->raid_disks == conf->previous_raid_disks)
                return degraded;
        rcu_read_lock();
        degraded2 = 0;
        for (i = 0; i < conf->raid_disks; i++) {
                struct md_rdev *rdev = rcu_dereference(conf->disks[i].rdev);
                if (rdev && test_bit(Faulty, &rdev->flags))
                        rdev = rcu_dereference(conf->disks[i].replacement);
                if (!rdev || test_bit(Faulty, &rdev->flags))
                        degraded2++;
                else if (test_bit(In_sync, &rdev->flags))
                        ;
                else
                        /* not in-sync or faulty.
                         * If reshape increases the number of devices, this
                         * section has already been recovered, else it
                         * almost certainly hasn't.
                         */
                        if (conf->raid_disks <= conf->previous_raid_disks)
                                degraded2++;
        }
        rcu_read_unlock();
        if (degraded2 > degraded)
                return degraded2;
        return degraded;
}

static int has_failed(struct r5conf *conf)
{
        int degraded;

        if (conf->mddev->reshape_position == MaxSector)
                return conf->mddev->degraded > conf->max_degraded;

        degraded = calc_degraded(conf);
        if (degraded > conf->max_degraded)
                return 1;
        return 0;
}

struct stripe_head *
raid5_get_active_stripe(struct r5conf *conf, sector_t sector,
                        int previous, int noblock, int noquiesce)
{
        struct stripe_head *sh;
        int hash = stripe_hash_locks_hash(sector);
        int inc_empty_inactive_list_flag;

        pr_debug("get_stripe, sector %llu\n", (unsigned long long)sector);

        spin_lock_irq(conf->hash_locks + hash);

        do {
                wait_event_lock_irq(conf->wait_for_quiescent,
                                    conf->quiesce == 0 || noquiesce,
                                    *(conf->hash_locks + hash));
                sh = __find_stripe(conf, sector, conf->generation - previous);
                if (!sh) {
                        if (!test_bit(R5_INACTIVE_BLOCKED, &conf->cache_state)) {
                                sh = get_free_stripe(conf, hash);
                                if (!sh && !test_bit(R5_DID_ALLOC,
                                                     &conf->cache_state))
                                        set_bit(R5_ALLOC_MORE,
                                                &conf->cache_state);
                        }
                        if (noblock && sh == NULL)
                                break;
                        if (!sh) {
                                set_bit(R5_INACTIVE_BLOCKED,
                                        &conf->cache_state);
                                wait_event_lock_irq(
                                        conf->wait_for_stripe,
                                        !list_empty(conf->inactive_list + hash) &&
                                        (atomic_read(&conf->active_stripes)
                                         < (conf->max_nr_stripes * 3 / 4)
                                         || !test_bit(R5_INACTIVE_BLOCKED,
                                                      &conf->cache_state)),
                                        *(conf->hash_locks + hash));
                                clear_bit(R5_INACTIVE_BLOCKED,
                                          &conf->cache_state);
                        } else {
                                init_stripe(sh, sector, previous);
                                atomic_inc(&sh->count);
                        }
                } else if (!atomic_inc_not_zero(&sh->count)) {
                        spin_lock(&conf->device_lock);
                        if (!atomic_read(&sh->count)) {
                                if (!test_bit(STRIPE_HANDLE, &sh->state))
                                        atomic_inc(&conf->active_stripes);
                                BUG_ON(list_empty(&sh->lru) &&
                                       !test_bit(STRIPE_EXPANDING, &sh->state));
                                inc_empty_inactive_list_flag = 0;
                                if (!list_empty(conf->inactive_list + hash))
                                        inc_empty_inactive_list_flag = 1;
                                list_del_init(&sh->lru);
                                if (list_empty(conf->inactive_list + hash) && inc_empty_inactive_list_flag)
                                        atomic_inc(&conf->empty_inactive_list_nr);
                                if (sh->group) {
                                        sh->group->stripes_cnt--;
                                        sh->group = NULL;
                                }
                        }
                        atomic_inc(&sh->count);
                        spin_unlock(&conf->device_lock);
                }
        } while (sh == NULL);

        spin_unlock_irq(conf->hash_locks + hash);
        return sh;
}

static bool is_full_stripe_write(struct stripe_head *sh)
{
        BUG_ON(sh->overwrite_disks > (sh->disks - sh->raid_conf->max_degraded));
        return sh->overwrite_disks == (sh->disks - sh->raid_conf->max_degraded);
}

static void lock_two_stripes(struct stripe_head *sh1, struct stripe_head *sh2)
{
        local_irq_disable();
        if (sh1 > sh2) {
                spin_lock(&sh2->stripe_lock);
                spin_lock_nested(&sh1->stripe_lock, 1);
        } else {
                spin_lock(&sh1->stripe_lock);
                spin_lock_nested(&sh2->stripe_lock, 1);
        }
}

static void unlock_two_stripes(struct stripe_head *sh1, struct stripe_head *sh2)
{
        spin_unlock(&sh1->stripe_lock);
        spin_unlock(&sh2->stripe_lock);
        local_irq_enable();
}

/* Only freshly new full stripe normal write stripe can be added to a batch list */
static bool stripe_can_batch(struct stripe_head *sh)
{
        struct r5conf *conf = sh->raid_conf;

        if (conf->log)
                return false;
        return test_bit(STRIPE_BATCH_READY, &sh->state) &&
                !test_bit(STRIPE_BITMAP_PENDING, &sh->state) &&
                is_full_stripe_write(sh);
}

/* we only do back search */
static void stripe_add_to_batch_list(struct r5conf *conf, struct stripe_head *sh)
{
        struct stripe_head *head;
        sector_t head_sector, tmp_sec;
        int hash;
        int dd_idx;
        int inc_empty_inactive_list_flag;

        /* Don't cross chunks, so stripe pd_idx/qd_idx is the same */
        tmp_sec = sh->sector;
        if (!sector_div(tmp_sec, conf->chunk_sectors))
                return;
        head_sector = sh->sector - STRIPE_SECTORS;

        hash = stripe_hash_locks_hash(head_sector);
        spin_lock_irq(conf->hash_locks + hash);
        head = __find_stripe(conf, head_sector, conf->generation);
        if (head && !atomic_inc_not_zero(&head->count)) {
                spin_lock(&conf->device_lock);
                if (!atomic_read(&head->count)) {
                        if (!test_bit(STRIPE_HANDLE, &head->state))
                                atomic_inc(&conf->active_stripes);
                        BUG_ON(list_empty(&head->lru) &&
                               !test_bit(STRIPE_EXPANDING, &head->state));
                        inc_empty_inactive_list_flag = 0;
                        if (!list_empty(conf->inactive_list + hash))
                                inc_empty_inactive_list_flag = 1;
                        list_del_init(&head->lru);
                        if (list_empty(conf->inactive_list + hash) && inc_empty_inactive_list_flag)
                                atomic_inc(&conf->empty_inactive_list_nr);
                        if (head->group) {
                                head->group->stripes_cnt--;
                                head->group = NULL;
                        }
                }
                atomic_inc(&head->count);
                spin_unlock(&conf->device_lock);
        }
        spin_unlock_irq(conf->hash_locks + hash);

        if (!head)
                return;
        if (!stripe_can_batch(head))
                goto out;

        lock_two_stripes(head, sh);
        /* clear_batch_ready clear the flag */
        if (!stripe_can_batch(head) || !stripe_can_batch(sh))
                goto unlock_out;

        if (sh->batch_head)
                goto unlock_out;

        dd_idx = 0;
        while (dd_idx == sh->pd_idx || dd_idx == sh->qd_idx)
                dd_idx++;
        if (head->dev[dd_idx].towrite->bi_opf != sh->dev[dd_idx].towrite->bi_opf ||
            bio_op(head->dev[dd_idx].towrite) != bio_op(sh->dev[dd_idx].towrite))
                goto unlock_out;

        if (head->batch_head) {
                spin_lock(&head->batch_head->batch_lock);
                /* This batch list is already running */
                if (!stripe_can_batch(head)) {
                        spin_unlock(&head->batch_head->batch_lock);
                        goto unlock_out;
                }

                /*
                 * at this point, head's BATCH_READY could be cleared, but we
                 * can still add the stripe to batch list
                 */
                list_add(&sh->batch_list, &head->batch_list);
                spin_unlock(&head->batch_head->batch_lock);

                sh->batch_head = head->batch_head;
        } else {
                head->batch_head = head;
                sh->batch_head = head->batch_head;
                spin_lock(&head->batch_lock);
                list_add_tail(&sh->batch_list, &head->batch_list);
                spin_unlock(&head->batch_lock);
        }

        if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                if (atomic_dec_return(&conf->preread_active_stripes)
                    < IO_THRESHOLD)
                        md_wakeup_thread(conf->mddev->thread);

        if (test_and_clear_bit(STRIPE_BIT_DELAY, &sh->state)) {
                int seq = sh->bm_seq;
                if (test_bit(STRIPE_BIT_DELAY, &sh->batch_head->state) &&
                    sh->batch_head->bm_seq > seq)
                        seq = sh->batch_head->bm_seq;
                set_bit(STRIPE_BIT_DELAY, &sh->batch_head->state);
                sh->batch_head->bm_seq = seq;
        }

        atomic_inc(&sh->count);
unlock_out:
        unlock_two_stripes(head, sh);
out:
        raid5_release_stripe(head);
}

/* Determine if 'data_offset' or 'new_data_offset' should be used
 * in this stripe_head.
 */
static int use_new_offset(struct r5conf *conf, struct stripe_head *sh)
{
        sector_t progress = conf->reshape_progress;
        /* Need a memory barrier to make sure we see the value
         * of conf->generation, or ->data_offset that was set before
         * reshape_progress was updated.
         */
        smp_rmb();
        if (progress == MaxSector)
                return 0;
        if (sh->generation == conf->generation - 1)
                return 0;
        /* We are in a reshape, and this is a new-generation stripe,
         * so use new_data_offset.
         */
        return 1;
}

static void
raid5_end_read_request(struct bio *bi);
static void
raid5_end_write_request(struct bio *bi);

static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
{
        struct r5conf *conf = sh->raid_conf;
        int i, disks = sh->disks;
        struct stripe_head *head_sh = sh;

        might_sleep();

        if (r5l_write_stripe(conf->log, sh) == 0)
                return;
        for (i = disks; i--; ) {
                int op, op_flags = 0;
                int replace_only = 0;
                struct bio *bi, *rbi;
                struct md_rdev *rdev, *rrdev = NULL;

                sh = head_sh;
                if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags)) {
                        op = REQ_OP_WRITE;
                        if (test_and_clear_bit(R5_WantFUA, &sh->dev[i].flags))
                                op_flags = WRITE_FUA;
                        if (test_bit(R5_Discard, &sh->dev[i].flags))
                                op = REQ_OP_DISCARD;
                } else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
                        op = REQ_OP_READ;
                else if (test_and_clear_bit(R5_WantReplace,
                                            &sh->dev[i].flags)) {
                        op = REQ_OP_WRITE;
                        replace_only = 1;
                } else
                        continue;
                if (test_and_clear_bit(R5_SyncIO, &sh->dev[i].flags))
                        op_flags |= REQ_SYNC;

again:
                bi = &sh->dev[i].req;
                rbi = &sh->dev[i].rreq; /* For writing to replacement */

                rcu_read_lock();
                rrdev = rcu_dereference(conf->disks[i].replacement);
                smp_mb(); /* Ensure that if rrdev is NULL, rdev won't be */
                rdev = rcu_dereference(conf->disks[i].rdev);
                if (!rdev) {
                        rdev = rrdev;
                        rrdev = NULL;
                }
                if (op_is_write(op)) {
                        if (replace_only)
                                rdev = NULL;
                        if (rdev == rrdev)
                                /* We raced and saw duplicates */
                                rrdev = NULL;
                } else {
                        if (test_bit(R5_ReadRepl, &head_sh->dev[i].flags) && rrdev)
                                rdev = rrdev;
                        rrdev = NULL;
                }

                if (rdev && test_bit(Faulty, &rdev->flags))
                        rdev = NULL;
                if (rdev)
                        atomic_inc(&rdev->nr_pending);
                if (rrdev && test_bit(Faulty, &rrdev->flags))
                        rrdev = NULL;
                if (rrdev)
                        atomic_inc(&rrdev->nr_pending);
                rcu_read_unlock();

                /* We have already checked bad blocks for reads.  Now
                 * need to check for writes.  We never accept write errors
                 * on the replacement, so we don't to check rrdev.
                 */
                while (op_is_write(op) && rdev &&
                       test_bit(WriteErrorSeen, &rdev->flags)) {
                        sector_t first_bad;
                        int bad_sectors;
                        int bad = is_badblock(rdev, sh->sector, STRIPE_SECTORS,
                                              &first_bad, &bad_sectors);
                        if (!bad)
                                break;

                        if (bad < 0) {
                                set_bit(BlockedBadBlocks, &rdev->flags);
                                if (!conf->mddev->external &&
                                    conf->mddev->flags) {
                                        /* It is very unlikely, but we might
                                         * still need to write out the
                                         * bad block log - better give it
                                         * a chance*/
                                        md_check_recovery(conf->mddev);
                                }
                                /*
                                 * Because md_wait_for_blocked_rdev
                                 * will dec nr_pending, we must
                                 * increment it first.
                                 */
                                atomic_inc(&rdev->nr_pending);
                                md_wait_for_blocked_rdev(rdev, conf->mddev);
                        } else {
                                /* Acknowledged bad block - skip the write */
                                rdev_dec_pending(rdev, conf->mddev);
                                rdev = NULL;
                        }
                }

                if (rdev) {
                        if (s->syncing || s->expanding || s->expanded
                            || s->replacing)
                                md_sync_acct(rdev->bdev, STRIPE_SECTORS);

                        set_bit(STRIPE_IO_STARTED, &sh->state);

                        bi->bi_bdev = rdev->bdev;
                        bio_set_op_attrs(bi, op, op_flags);
                        bi->bi_end_io = op_is_write(op)
                                ? raid5_end_write_request
                                : raid5_end_read_request;
                        bi->bi_private = sh;

                        pr_debug("%s: for %llu schedule op %d on disc %d\n",
                                __func__, (unsigned long long)sh->sector,
                                bi->bi_opf, i);
                        atomic_inc(&sh->count);
                        if (sh != head_sh)
                                atomic_inc(&head_sh->count);
                        if (use_new_offset(conf, sh))
                                bi->bi_iter.bi_sector = (sh->sector
                                                 + rdev->new_data_offset);
                        else
                                bi->bi_iter.bi_sector = (sh->sector
                                                 + rdev->data_offset);
                        if (test_bit(R5_ReadNoMerge, &head_sh->dev[i].flags))
                                bi->bi_opf |= REQ_NOMERGE;

                        if (test_bit(R5_SkipCopy, &sh->dev[i].flags))
                                WARN_ON(test_bit(R5_UPTODATE, &sh->dev[i].flags));
                        sh->dev[i].vec.bv_page = sh->dev[i].page;
                        bi->bi_vcnt = 1;
                        bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
                        bi->bi_io_vec[0].bv_offset = 0;
                        bi->bi_iter.bi_size = STRIPE_SIZE;
                        /*
                         * If this is discard request, set bi_vcnt 0. We don't
                         * want to confuse SCSI because SCSI will replace payload
                         */
                        if (op == REQ_OP_DISCARD)
                                bi->bi_vcnt = 0;
                        if (rrdev)
                                set_bit(R5_DOUBLE_LOCKED, &sh->dev[i].flags);

                        if (conf->mddev->gendisk)
                                trace_block_bio_remap(bdev_get_queue(bi->bi_bdev),
                                                      bi, disk_devt(conf->mddev->gendisk),
                                                      sh->dev[i].sector);
                        generic_make_request(bi);
                }
                if (rrdev) {
                        if (s->syncing || s->expanding || s->expanded
                            || s->replacing)
                                md_sync_acct(rrdev->bdev, STRIPE_SECTORS);

                        set_bit(STRIPE_IO_STARTED, &sh->state);

                        rbi->bi_bdev = rrdev->bdev;
                        bio_set_op_attrs(rbi, op, op_flags);
                        BUG_ON(!op_is_write(op));
                        rbi->bi_end_io = raid5_end_write_request;
                        rbi->bi_private = sh;

                        pr_debug("%s: for %llu schedule op %d on "
                                 "replacement disc %d\n",
                                __func__, (unsigned long long)sh->sector,
                                rbi->bi_opf, i);
                        atomic_inc(&sh->count);
                        if (sh != head_sh)
                                atomic_inc(&head_sh->count);
                        if (use_new_offset(conf, sh))
                                rbi->bi_iter.bi_sector = (sh->sector
                                                  + rrdev->new_data_offset);
                        else
                                rbi->bi_iter.bi_sector = (sh->sector
                                                  + rrdev->data_offset);
                        if (test_bit(R5_SkipCopy, &sh->dev[i].flags))
                                WARN_ON(test_bit(R5_UPTODATE, &sh->dev[i].flags));
                        sh->dev[i].rvec.bv_page = sh->dev[i].page;
                        rbi->bi_vcnt = 1;
                        rbi->bi_io_vec[0].bv_len = STRIPE_SIZE;
                        rbi->bi_io_vec[0].bv_offset = 0;
                        rbi->bi_iter.bi_size = STRIPE_SIZE;
                        /*
                         * If this is discard request, set bi_vcnt 0. We don't
                         * want to confuse SCSI because SCSI will replace payload
                         */
                        if (op == REQ_OP_DISCARD)
                                rbi->bi_vcnt = 0;
                        if (conf->mddev->gendisk)
                                trace_block_bio_remap(bdev_get_queue(rbi->bi_bdev),
                                                      rbi, disk_devt(conf->mddev->gendisk),
                                                      sh->dev[i].sector);
                        generic_make_request(rbi);
                }
                if (!rdev && !rrdev) {
                        if (op_is_write(op))
                                set_bit(STRIPE_DEGRADED, &sh->state);
                        pr_debug("skip op %d on disc %d for sector %llu\n",
                                bi->bi_opf, i, (unsigned long long)sh->sector);
                        clear_bit(R5_LOCKED, &sh->dev[i].flags);
                        set_bit(STRIPE_HANDLE, &sh->state);
                }

                if (!head_sh->batch_head)
                        continue;
                sh = list_first_entry(&sh->batch_list, struct stripe_head,
                                      batch_list);
                if (sh != head_sh)
                        goto again;
        }
}

static struct dma_async_tx_descriptor *
async_copy_data(int frombio, struct bio *bio, struct page **page,
        sector_t sector, struct dma_async_tx_descriptor *tx,
        struct stripe_head *sh)
{
        struct bio_vec bvl;
        struct bvec_iter iter;
        struct page *bio_page;
        int page_offset;
        struct async_submit_ctl submit;
        enum async_tx_flags flags = 0;

        if (bio->bi_iter.bi_sector >= sector)
                page_offset = (signed)(bio->bi_iter.bi_sector - sector) * 512;
        else
                page_offset = (signed)(sector - bio->bi_iter.bi_sector) * -512;

        if (frombio)
                flags |= ASYNC_TX_FENCE;
        init_async_submit(&submit, flags, tx, NULL, NULL, NULL);

        bio_for_each_segment(bvl, bio, iter) {
                int len = bvl.bv_len;
                int clen;
                int b_offset = 0;

                if (page_offset < 0) {
                        b_offset = -page_offset;
                        page_offset += b_offset;
                        len -= b_offset;
                }

                if (len > 0 && page_offset + len > STRIPE_SIZE)
                        clen = STRIPE_SIZE - page_offset;
                else
                        clen = len;

                if (clen > 0) {
                        b_offset += bvl.bv_offset;
                        bio_page = bvl.bv_page;
                        if (frombio) {
                                if (sh->raid_conf->skip_copy &&
                                    b_offset == 0 && page_offset == 0 &&
                                    clen == STRIPE_SIZE)
                                        *page = bio_page;
                                else
                                        tx = async_memcpy(*page, bio_page, page_offset,
                                                  b_offset, clen, &submit);
                        } else
                                tx = async_memcpy(bio_page, *page, b_offset,
                                                  page_offset, clen, &submit);
                }
                /* chain the operations */
                submit.depend_tx = tx;

                if (clen < len) /* hit end of page */
                        break;
                page_offset +=  len;
        }

        return tx;
}

static void ops_complete_biofill(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        struct bio_list return_bi = BIO_EMPTY_LIST;
        int i;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        /* clear completed biofills */
        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];

                /* acknowledge completion of a biofill operation */
                /* and check if we need to reply to a read request,
                 * new R5_Wantfill requests are held off until
                 * !STRIPE_BIOFILL_RUN
                 */
                if (test_and_clear_bit(R5_Wantfill, &dev->flags)) {
                        struct bio *rbi, *rbi2;

                        BUG_ON(!dev->read);
                        rbi = dev->read;
                        dev->read = NULL;
                        while (rbi && rbi->bi_iter.bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                rbi2 = r5_next_bio(rbi, dev->sector);
                                if (!raid5_dec_bi_active_stripes(rbi))
                                        bio_list_add(&return_bi, rbi);
                                rbi = rbi2;
                        }
                }
        }
        clear_bit(STRIPE_BIOFILL_RUN, &sh->state);

        return_io(&return_bi);

        set_bit(STRIPE_HANDLE, &sh->state);
        raid5_release_stripe(sh);
}

static void ops_run_biofill(struct stripe_head *sh)
{
        struct dma_async_tx_descriptor *tx = NULL;
        struct async_submit_ctl submit;
        int i;

        BUG_ON(sh->batch_head);
        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                if (test_bit(R5_Wantfill, &dev->flags)) {
                        struct bio *rbi;
                        spin_lock_irq(&sh->stripe_lock);
                        dev->read = rbi = dev->toread;
                        dev->toread = NULL;
                        spin_unlock_irq(&sh->stripe_lock);
                        while (rbi && rbi->bi_iter.bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                tx = async_copy_data(0, rbi, &dev->page,
                                        dev->sector, tx, sh);
                                rbi = r5_next_bio(rbi, dev->sector);
                        }
                }
        }

        atomic_inc(&sh->count);
        init_async_submit(&submit, ASYNC_TX_ACK, tx, ops_complete_biofill, sh, NULL);
        async_trigger_callback(&submit);
}

static void mark_target_uptodate(struct stripe_head *sh, int target)
{
        struct r5dev *tgt;

        if (target < 0)
                return;

        tgt = &sh->dev[target];
        set_bit(R5_UPTODATE, &tgt->flags);
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
        clear_bit(R5_Wantcompute, &tgt->flags);
}

static void ops_complete_compute(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        /* mark the computed target(s) as uptodate */
        mark_target_uptodate(sh, sh->ops.target);
        mark_target_uptodate(sh, sh->ops.target2);

        clear_bit(STRIPE_COMPUTE_RUN, &sh->state);
        if (sh->check_state == check_state_compute_run)
                sh->check_state = check_state_compute_result;
        set_bit(STRIPE_HANDLE, &sh->state);
        raid5_release_stripe(sh);
}

/* return a pointer to the address conversion region of the scribble buffer */
static addr_conv_t *to_addr_conv(struct stripe_head *sh,
                                 struct raid5_percpu *percpu, int i)
{
        void *addr;

        addr = flex_array_get(percpu->scribble, i);
        return addr + sizeof(struct page *) * (sh->disks + 2);
}

/* return a pointer to the address conversion region of the scribble buffer */
static struct page **to_addr_page(struct raid5_percpu *percpu, int i)
{
        void *addr;

        addr = flex_array_get(percpu->scribble, i);
        return addr;
}

static struct dma_async_tx_descriptor *
ops_run_compute5(struct stripe_head *sh, struct raid5_percpu *percpu)
{
        int disks = sh->disks;
        struct page **xor_srcs = to_addr_page(percpu, 0);
        int target = sh->ops.target;
        struct r5dev *tgt = &sh->dev[target];
        struct page *xor_dest = tgt->page;
        int count = 0;
        struct dma_async_tx_descriptor *tx;
        struct async_submit_ctl submit;
        int i;

        BUG_ON(sh->batch_head);

        pr_debug("%s: stripe %llu block: %d\n",
                __func__, (unsigned long long)sh->sector, target);
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));

        for (i = disks; i--; )
                if (i != target)
                        xor_srcs[count++] = sh->dev[i].page;

        atomic_inc(&sh->count);

        init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST, NULL,
                          ops_complete_compute, sh, to_addr_conv(sh, percpu, 0));
        if (unlikely(count == 1))
                tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE, &submit);
        else
                tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE, &submit);

        return tx;
}

/* set_syndrome_sources - populate source buffers for gen_syndrome
 * @srcs - (struct page *) array of size sh->disks
 * @sh - stripe_head to parse
 *
 * Populates srcs in proper layout order for the stripe and returns the
 * 'count' of sources to be used in a call to async_gen_syndrome.  The P
 * destination buffer is recorded in srcs[count] and the Q destination
 * is recorded in srcs[count+1]].
 */
static int set_syndrome_sources(struct page **srcs,
                                struct stripe_head *sh,
                                int srctype)
{
        int disks = sh->disks;
        int syndrome_disks = sh->ddf_layout ? disks : (disks - 2);
        int d0_idx = raid6_d0(sh);
        int count;
        int i;

        for (i = 0; i < disks; i++)
                srcs[i] = NULL;

        count = 0;
        i = d0_idx;
        do {
                int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);
                struct r5dev *dev = &sh->dev[i];

                if (i == sh->qd_idx || i == sh->pd_idx ||
                    (srctype == SYNDROME_SRC_ALL) ||
                    (srctype == SYNDROME_SRC_WANT_DRAIN &&
                     test_bit(R5_Wantdrain, &dev->flags)) ||
                    (srctype == SYNDROME_SRC_WRITTEN &&
                     dev->written))
                        srcs[slot] = sh->dev[i].page;
                i = raid6_next_disk(i, disks);
        } while (i != d0_idx);

        return syndrome_disks;
}

static struct dma_async_tx_descriptor *
ops_run_compute6_1(struct stripe_head *sh, struct raid5_percpu *percpu)
{
        int disks = sh->disks;
        struct page **blocks = to_addr_page(percpu, 0);
        int target;
        int qd_idx = sh->qd_idx;
        struct dma_async_tx_descriptor *tx;
        struct async_submit_ctl submit;
        struct r5dev *tgt;
        struct page *dest;
        int i;
        int count;

        BUG_ON(sh->batch_head);
        if (sh->ops.target < 0)
                target = sh->ops.target2;
        else if (sh->ops.target2 < 0)
                target = sh->ops.target;
        else
                /* we should only have one valid target */
                BUG();
        BUG_ON(target < 0);
        pr_debug("%s: stripe %llu block: %d\n",
                __func__, (unsigned long long)sh->sector, target);

        tgt = &sh->dev[target];
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
        dest = tgt->page;

        atomic_inc(&sh->count);

        if (target == qd_idx) {
                count = set_syndrome_sources(blocks, sh, SYNDROME_SRC_ALL);
                blocks[count] = NULL; /* regenerating p is not necessary */
                BUG_ON(blocks[count+1] != dest); /* q should already be set */
                init_async_submit(&submit, ASYNC_TX_FENCE, NULL,
                                  ops_complete_compute, sh,
                                  to_addr_conv(sh, percpu, 0));
                tx = async_gen_syndrome(blocks, 0, count+2, STRIPE_SIZE, &submit);
        } else {
                /* Compute any data- or p-drive using XOR */
                count = 0;
                for (i = disks; i-- ; ) {
                        if (i == target || i == qd_idx)
                                continue;
                        blocks[count++] = sh->dev[i].page;
                }

                init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST,
                                  NULL, ops_complete_compute, sh,
                                  to_addr_conv(sh, percpu, 0));
                tx = async_xor(dest, blocks, 0, count, STRIPE_SIZE, &submit);
        }

        return tx;
}

static struct dma_async_tx_descriptor *
ops_run_compute6_2(struct stripe_head *sh, struct raid5_percpu *percpu)
{
        int i, count, disks = sh->disks;
        int syndrome_disks = sh->ddf_layout ? disks : disks-2;
        int d0_idx = raid6_d0(sh);
        int faila = -1, failb = -1;
        int target = sh->ops.target;
        int target2 = sh->ops.target2;
        struct r5dev *tgt = &sh->dev[target];
        struct r5dev *tgt2 = &sh->dev[target2];
        struct dma_async_tx_descriptor *tx;
        struct page **blocks = to_addr_page(percpu, 0);
        struct async_submit_ctl submit;

        BUG_ON(sh->batch_head);
        pr_debug("%s: stripe %llu block1: %d block2: %d\n",
                 __func__, (unsigned long long)sh->sector, target, target2);
        BUG_ON(target < 0 || target2 < 0);
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
        BUG_ON(!test_bit(R5_Wantcompute, &tgt2->flags));

        /* we need to open-code set_syndrome_sources to handle the
         * slot number conversion for 'faila' and 'failb'
         */
        for (i = 0; i < disks ; i++)
                blocks[i] = NULL;
        count = 0;
        i = d0_idx;
        do {
                int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);

                blocks[slot] = sh->dev[i].page;

                if (i == target)
                        faila = slot;
                if (i == target2)
                        failb = slot;
                i = raid6_next_disk(i, disks);
        } while (i != d0_idx);

        BUG_ON(faila == failb);
        if (failb < faila)
                swap(faila, failb);
        pr_debug("%s: stripe: %llu faila: %d failb: %d\n",
                 __func__, (unsigned long long)sh->sector, faila, failb);

        atomic_inc(&sh->count);

        if (failb == syndrome_disks+1) {
                /* Q disk is one of the missing disks */
                if (faila == syndrome_disks) {
                        /* Missing P+Q, just recompute */
                        init_async_submit(&submit, ASYNC_TX_FENCE, NULL,
                                          ops_complete_compute, sh,
                                          to_addr_conv(sh, percpu, 0));
                        return async_gen_syndrome(blocks, 0, syndrome_disks+2,
                                                  STRIPE_SIZE, &submit);
                } else {
                        struct page *dest;
                        int data_target;
                        int qd_idx = sh->qd_idx;

                        /* Missing D+Q: recompute D from P, then recompute Q */
                        if (target == qd_idx)
                                data_target = target2;
                        else
                                data_target = target;

                        count = 0;
                        for (i = disks; i-- ; ) {
                                if (i == data_target || i == qd_idx)
                                        continue;
                                blocks[count++] = sh->dev[i].page;
                        }
                        dest = sh->dev[data_target].page;
                        init_async_submit(&submit,
                                          ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST,
                                          NULL, NULL, NULL,
                                          to_addr_conv(sh, percpu, 0));
                        tx = async_xor(dest, blocks, 0, count, STRIPE_SIZE,
                                       &submit);

                        count = set_syndrome_sources(blocks, sh, SYNDROME_SRC_ALL);
                        init_async_submit(&submit, ASYNC_TX_FENCE, tx,
                                          ops_complete_compute, sh,
                                          to_addr_conv(sh, percpu, 0));
                        return async_gen_syndrome(blocks, 0, count+2,
                                                  STRIPE_SIZE, &submit);
                }
        } else {
                init_async_submit(&submit, ASYNC_TX_FENCE, NULL,
                                  ops_complete_compute, sh,
                                  to_addr_conv(sh, percpu, 0));
                if (failb == syndrome_disks) {
                        /* We're missing D+P. */
                        return async_raid6_datap_recov(syndrome_disks+2,
                                                       STRIPE_SIZE, faila,
                                                       blocks, &submit);
                } else {
                        /* We're missing D+D. */
                        return async_raid6_2data_recov(syndrome_disks+2,
                                                       STRIPE_SIZE, faila, failb,
                                                       blocks, &submit);
                }
        }
}

static void ops_complete_prexor(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);
}

static struct dma_async_tx_descriptor *
ops_run_prexor5(struct stripe_head *sh, struct raid5_percpu *percpu,
                struct dma_async_tx_descriptor *tx)
{
        int disks = sh->disks;
        struct page **xor_srcs = to_addr_page(percpu, 0);
        int count = 0, pd_idx = sh->pd_idx, i;
        struct async_submit_ctl submit;

        /* existing parity data subtracted */
        struct page *xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;

        BUG_ON(sh->batch_head);
        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                /* Only process blocks that are known to be uptodate */
                if (test_bit(R5_Wantdrain, &dev->flags))
                        xor_srcs[count++] = dev->page;
        }

        init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
                          ops_complete_prexor, sh, to_addr_conv(sh, percpu, 0));
        tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE, &submit);

        return tx;
}

static struct dma_async_tx_descriptor *
ops_run_prexor6(struct stripe_head *sh, struct raid5_percpu *percpu,
                struct dma_async_tx_descriptor *tx)
{
        struct page **blocks = to_addr_page(percpu, 0);
        int count;
        struct async_submit_ctl submit;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        count = set_syndrome_sources(blocks, sh, SYNDROME_SRC_WANT_DRAIN);

        init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_PQ_XOR_DST, tx,
                          ops_complete_prexor, sh, to_addr_conv(sh, percpu, 0));
        tx = async_gen_syndrome(blocks, 0, count+2, STRIPE_SIZE,  &submit);

        return tx;
}

static struct dma_async_tx_descriptor *
ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
{
        int disks = sh->disks;
        int i;
        struct stripe_head *head_sh = sh;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev;
                struct bio *chosen;

                sh = head_sh;
                if (test_and_clear_bit(R5_Wantdrain, &head_sh->dev[i].flags)) {
                        struct bio *wbi;

again:
                        dev = &sh->dev[i];
                        spin_lock_irq(&sh->stripe_lock);
                        chosen = dev->towrite;
                        dev->towrite = NULL;
                        sh->overwrite_disks = 0;
                        BUG_ON(dev->written);
                        wbi = dev->written = chosen;
                        spin_unlock_irq(&sh->stripe_lock);
                        WARN_ON(dev->page != dev->orig_page);

                        while (wbi && wbi->bi_iter.bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                if (wbi->bi_opf & REQ_FUA)
                                        set_bit(R5_WantFUA, &dev->flags);
                                if (wbi->bi_opf & REQ_SYNC)
                                        set_bit(R5_SyncIO, &dev->flags);
                                if (bio_op(wbi) == REQ_OP_DISCARD)
                                        set_bit(R5_Discard, &dev->flags);
                                else {
                                        tx = async_copy_data(1, wbi, &dev->page,
                                                dev->sector, tx, sh);
                                        if (dev->page != dev->orig_page) {
                                                set_bit(R5_SkipCopy, &dev->flags);
                                                clear_bit(R5_UPTODATE, &dev->flags);
                                                clear_bit(R5_OVERWRITE, &dev->flags);
                                        }
                                }
                                wbi = r5_next_bio(wbi, dev->sector);
                        }

                        if (head_sh->batch_head) {
                                sh = list_first_entry(&sh->batch_list,
                                                      struct stripe_head,
                                                      batch_list);
                                if (sh == head_sh)
                                        continue;
                                goto again;
                        }
                }
        }

        return tx;
}

static void ops_complete_reconstruct(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        int disks = sh->disks;
        int pd_idx = sh->pd_idx;
        int qd_idx = sh->qd_idx;
        int i;
        bool fua = false, sync = false, discard = false;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                fua |= test_bit(R5_WantFUA, &sh->dev[i].flags);
                sync |= test_bit(R5_SyncIO, &sh->dev[i].flags);
                discard |= test_bit(R5_Discard, &sh->dev[i].flags);
        }

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];

                if (dev->written || i == pd_idx || i == qd_idx) {
                        if (!discard && !test_bit(R5_SkipCopy, &dev->flags))
                                set_bit(R5_UPTODATE, &dev->flags);
                        if (fua)
                                set_bit(R5_WantFUA, &dev->flags);
                        if (sync)
                                set_bit(R5_SyncIO, &dev->flags);
                }
        }

        if (sh->reconstruct_state == reconstruct_state_drain_run)
                sh->reconstruct_state = reconstruct_state_drain_result;
        else if (sh->reconstruct_state == reconstruct_state_prexor_drain_run)
                sh->reconstruct_state = reconstruct_state_prexor_drain_result;
        else {
                BUG_ON(sh->reconstruct_state != reconstruct_state_run);
                sh->reconstruct_state = reconstruct_state_result;
        }

        set_bit(STRIPE_HANDLE, &sh->state);
        raid5_release_stripe(sh);
}

static void
ops_run_reconstruct5(struct stripe_head *sh, struct raid5_percpu *percpu,
                     struct dma_async_tx_descriptor *tx)
{
        int disks = sh->disks;
        struct page **xor_srcs;
        struct async_submit_ctl submit;
        int count, pd_idx = sh->pd_idx, i;
        struct page *xor_dest;
        int prexor = 0;
        unsigned long flags;
        int j = 0;
        struct stripe_head *head_sh = sh;
        int last_stripe;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = 0; i < sh->disks; i++) {
                if (pd_idx == i)
                        continue;
                if (!test_bit(R5_Discard, &sh->dev[i].flags))
                        break;
        }
        if (i >= sh->disks) {
                atomic_inc(&sh->count);
                set_bit(R5_Discard, &sh->dev[pd_idx].flags);
                ops_complete_reconstruct(sh);
                return;
        }
again:
        count = 0;
        xor_srcs = to_addr_page(percpu, j);
        /* check if prexor is active which means only process blocks
         * that are part of a read-modify-write (written)
         */
        if (head_sh->reconstruct_state == reconstruct_state_prexor_drain_run) {
                prexor = 1;
                xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (head_sh->dev[i].written)
                                xor_srcs[count++] = dev->page;
                }
        } else {
                xor_dest = sh->dev[pd_idx].page;
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (i != pd_idx)
                                xor_srcs[count++] = dev->page;
                }
        }

        /* 1/ if we prexor'd then the dest is reused as a source
         * 2/ if we did not prexor then we are redoing the parity
         * set ASYNC_TX_XOR_DROP_DST and ASYNC_TX_XOR_ZERO_DST
         * for the synchronous xor case
         */
        last_stripe = !head_sh->batch_head ||
                list_first_entry(&sh->batch_list,
                                 struct stripe_head, batch_list) == head_sh;
        if (last_stripe) {
                flags = ASYNC_TX_ACK |
                        (prexor ? ASYNC_TX_XOR_DROP_DST : ASYNC_TX_XOR_ZERO_DST);

                atomic_inc(&head_sh->count);
                init_async_submit(&submit, flags, tx, ops_complete_reconstruct, head_sh,
                                  to_addr_conv(sh, percpu, j));
        } else {
                flags = prexor ? ASYNC_TX_XOR_DROP_DST : ASYNC_TX_XOR_ZERO_DST;
                init_async_submit(&submit, flags, tx, NULL, NULL,
                                  to_addr_conv(sh, percpu, j));
        }

        if (unlikely(count == 1))
                tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE, &submit);
        else
                tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE, &submit);
        if (!last_stripe) {
                j++;
                sh = list_first_entry(&sh->batch_list, struct stripe_head,
                                      batch_list);
                goto again;
        }
}

static void
ops_run_reconstruct6(struct stripe_head *sh, struct raid5_percpu *percpu,
                     struct dma_async_tx_descriptor *tx)
{
        struct async_submit_ctl submit;
        struct page **blocks;
        int count, i, j = 0;
        struct stripe_head *head_sh = sh;
        int last_stripe;
        int synflags;
        unsigned long txflags;

        pr_debug("%s: stripe %llu\n", __func__, (unsigned long long)sh->sector);

        for (i = 0; i < sh->disks; i++) {
                if (sh->pd_idx == i || sh->qd_idx == i)
                        continue;
                if (!test_bit(R5_Discard, &sh->dev[i].flags))
                        break;
        }
        if (i >= sh->disks) {
                atomic_inc(&sh->count);
                set_bit(R5_Discard, &sh->dev[sh->pd_idx].flags);
                set_bit(R5_Discard, &sh->dev[sh->qd_idx].flags);
                ops_complete_reconstruct(sh);
                return;
        }

again:
        blocks = to_addr_page(percpu, j);

        if (sh->reconstruct_state == reconstruct_state_prexor_drain_run) {
                synflags = SYNDROME_SRC_WRITTEN;
                txflags = ASYNC_TX_ACK | ASYNC_TX_PQ_XOR_DST;
        } else {
                synflags = SYNDROME_SRC_ALL;
                txflags = ASYNC_TX_ACK;
        }

        count = set_syndrome_sources(blocks, sh, synflags);
        last_stripe = !head_sh->batch_head ||
                list_first_entry(&sh->batch_list,
                                 struct stripe_head, batch_list) == head_sh;

        if (last_stripe) {
                atomic_inc(&head_sh->count);
                init_async_submit(&submit, txflags, tx, ops_complete_reconstruct,
                                  head_sh, to_addr_conv(sh, percpu, j));
        } else
                init_async_submit(&submit, 0, tx, NULL, NULL,
                                  to_addr_conv(sh, percpu, j));
        tx = async_gen_syndrome(blocks, 0, count+2, STRIPE_SIZE,  &submit);
        if (!last_stripe) {
                j++;
                sh = list_first_entry(&sh->batch_list, struct stripe_head,
                                      batch_list);
                goto again;
        }
}

static void ops_complete_check(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        sh->check_state = check_state_check_result;
        set_bit(STRIPE_HANDLE, &sh->state);
        raid5_release_stripe(sh);
}

static void ops_run_check_p(struct stripe_head *sh, struct raid5_percpu *percpu)
{
        int disks = sh->disks;
        int pd_idx = sh->pd_idx;
        int qd_idx = sh->qd_idx;
        struct page *xor_dest;
        struct page **xor_srcs = to_addr_page(percpu, 0);
        struct dma_async_tx_descriptor *tx;
        struct async_submit_ctl submit;
        int count;
        int i;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        BUG_ON(sh->batch_head);
        count = 0;
        xor_dest = sh->dev[pd_idx].page;
        xor_srcs[count++] = xor_dest;
        for (i = disks; i--; ) {
                if (i == pd_idx || i == qd_idx)
                        continue;
                xor_srcs[count++] = sh->dev[i].page;
        }

        init_async_submit(&submit, 0, NULL, NULL, NULL,
                          to_addr_conv(sh, percpu, 0));
        tx = async_xor_val(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                           &sh->ops.zero_sum_result, &submit);

        atomic_inc(&sh->count);
        init_async_submit(&submit, ASYNC_TX_ACK, tx, ops_complete_check, sh, NULL);
        tx = async_trigger_callback(&submit);
}

static void ops_run_check_pq(struct stripe_head *sh, struct raid5_percpu *percpu, int checkp)
{
        struct page **srcs = to_addr_page(percpu, 0);
        struct async_submit_ctl submit;
        int count;

        pr_debug("%s: stripe %llu checkp: %d\n", __func__,
                (unsigned long long)sh->sector, checkp);

        BUG_ON(sh->batch_head);
        count = set_syndrome_sources(srcs, sh, SYNDROME_SRC_ALL);
        if (!checkp)
                srcs[count] = NULL;

        atomic_inc(&sh->count);
        init_async_submit(&submit, ASYNC_TX_ACK, NULL, ops_complete_check,
                          sh, to_addr_conv(sh, percpu, 0));
        async_syndrome_val(srcs, 0, count+2, STRIPE_SIZE,
                           &sh->ops.zero_sum_result, percpu->spare_page, &submit);
}

static void raid_run_ops(struct stripe_head *sh, unsigned long ops_request)
{
        int overlap_clear = 0, i, disks = sh->disks;
        struct dma_async_tx_descriptor *tx = NULL;
        struct r5conf *conf = sh->raid_conf;
        int level = conf->level;
        struct raid5_percpu *percpu;
        unsigned long cpu;

        cpu = get_cpu();
        percpu = per_cpu_ptr(conf->percpu, cpu);
        if (test_bit(STRIPE_OP_BIOFILL, &ops_request)) {
                ops_run_biofill(sh);
                overlap_clear++;
        }

        if (test_bit(STRIPE_OP_COMPUTE_BLK, &ops_request)) {
                if (level < 6)
                        tx = ops_run_compute5(sh, percpu);
                else {
                        if (sh->ops.target2 < 0 || sh->ops.target < 0)
                                tx = ops_run_compute6_1(sh, percpu);
                        else
                                tx = ops_run_compute6_2(sh, percpu);
                }
                /* terminate the chain if reconstruct is not set to be run */
                if (tx && !test_bit(STRIPE_OP_RECONSTRUCT, &ops_request))
                        async_tx_ack(tx);
        }

        if (test_bit(STRIPE_OP_PREXOR, &ops_request)) {
                if (level < 6)
                        tx = ops_run_prexor5(sh, percpu, tx);
                else
                        tx = ops_run_prexor6(sh, percpu, tx);
        }

        if (test_bit(STRIPE_OP_BIODRAIN, &ops_request)) {
                tx = ops_run_biodrain(sh, tx);
                overlap_clear++;
        }

        if (test_bit(STRIPE_OP_RECONSTRUCT, &ops_request)) {
                if (level < 6)
                        ops_run_reconstruct5(sh, percpu, tx);
                else
                        ops_run_reconstruct6(sh, percpu, tx);
        }

        if (test_bit(STRIPE_OP_CHECK, &ops_request)) {
                if (sh->check_state == check_state_run)
                        ops_run_check_p(sh, percpu);
                else if (sh->check_state == check_state_run_q)
                        ops_run_check_pq(sh, percpu, 0);
                else if (sh->check_state == check_state_run_pq)
                        ops_run_check_pq(sh, percpu, 1);
                else
                        BUG();
        }

        if (overlap_clear && !sh->batch_head)
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (test_and_clear_bit(R5_Overlap, &dev->flags))
                                wake_up(&sh->raid_conf->wait_for_overlap);
                }
        put_cpu();
}

static struct stripe_head *alloc_stripe(struct kmem_cache *sc, gfp_t gfp,
        int disks)
{
        struct stripe_head *sh;
        int i;

        sh = kmem_cache_zalloc(sc, gfp);
        if (sh) {
                spin_lock_init(&sh->stripe_lock);
                spin_lock_init(&sh->batch_lock);
                INIT_LIST_HEAD(&sh->batch_list);
                INIT_LIST_HEAD(&sh->lru);
                atomic_set(&sh->count, 1);
                for (i = 0; i < disks; i++) {
                        struct r5dev *dev = &sh->dev[i];

                        bio_init(&dev->req);
                        dev->req.bi_io_vec = &dev->vec;
                        dev->req.bi_max_vecs = 1;

                        bio_init(&dev->rreq);
                        dev->rreq.bi_io_vec = &dev->rvec;
                        dev->rreq.bi_max_vecs = 1;
                }
        }
        return sh;
}
static int grow_one_stripe(struct r5conf *conf, gfp_t gfp)
{
        struct stripe_head *sh;

        sh = alloc_stripe(conf->slab_cache, gfp, conf->pool_size);
        if (!sh)
                return 0;

        sh->raid_conf = conf;

        if (grow_buffers(sh, gfp)) {
                shrink_buffers(sh);
                kmem_cache_free(conf->slab_cache, sh);
                return 0;
        }
        sh->hash_lock_index =
                conf->max_nr_stripes % NR_STRIPE_HASH_LOCKS;
        /* we just created an active stripe so... */
        atomic_inc(&conf->active_stripes);

        raid5_release_stripe(sh);
        conf->max_nr_stripes++;
        return 1;
}

static int grow_stripes(struct r5conf *conf, int num)
{
        struct kmem_cache *sc;
        int devs = max(conf->raid_disks, conf->previous_raid_disks);

        if (conf->mddev->gendisk)
                sprintf(conf->cache_name[0],
                        "raid%d-%s", conf->level, mdname(conf->mddev));
        else
                sprintf(conf->cache_name[0],
                        "raid%d-%p", conf->level, conf->mddev);
        sprintf(conf->cache_name[1], "%s-alt", conf->cache_name[0]);

        conf->active_name = 0;
        sc = kmem_cache_create(conf->cache_name[conf->active_name],
                               sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
                               0, 0, NULL);
        if (!sc)
                return 1;
        conf->slab_cache = sc;
        conf->pool_size = devs;
        while (num--)
                if (!grow_one_stripe(conf, GFP_KERNEL))
                        return 1;

        return 0;
}

/**
 * scribble_len - return the required size of the scribble region
 * @num - total number of disks in the array
 *
 * The size must be enough to contain:
 * 1/ a struct page pointer for each device in the array +2
 * 2/ room to convert each entry in (1) to its corresponding dma
 *    (dma_map_page()) or page (page_address()) address.
 *
 * Note: the +2 is for the destination buffers of the ddf/raid6 case where we
 * calculate over all devices (not just the data blocks), using zeros in place
 * of the P and Q blocks.
 */
static struct flex_array *scribble_alloc(int num, int cnt, gfp_t flags)
{
        struct flex_array *ret;
        size_t len;

        len = sizeof(struct page *) * (num+2) + sizeof(addr_conv_t) * (num+2);
        ret = flex_array_alloc(len, cnt, flags);
        if (!ret)
                return NULL;
        /* always prealloc all elements, so no locking is required */
        if (flex_array_prealloc(ret, 0, cnt, flags)) {
                flex_array_free(ret);
                return NULL;
        }
        return ret;
}

static int resize_chunks(struct r5conf *conf, int new_disks, int new_sectors)
{
        unsigned long cpu;
        int err = 0;

        /*
         * Never shrink. And mddev_suspend() could deadlock if this is called
         * from raid5d. In that case, scribble_disks and scribble_sectors
         * should equal to new_disks and new_sectors
         */
        if (conf->scribble_disks >= new_disks &&
            conf->scribble_sectors >= new_sectors)
                return 0;
        mddev_suspend(conf->mddev);
        get_online_cpus();
        for_each_present_cpu(cpu) {
                struct raid5_percpu *percpu;
                struct flex_array *scribble;

                percpu = per_cpu_ptr(conf->percpu, cpu);
                scribble = scribble_alloc(new_disks,
                                          new_sectors / STRIPE_SECTORS,
                                          GFP_NOIO);

                if (scribble) {
                        flex_array_free(percpu->scribble);
                        percpu->scribble = scribble;
                } else {
                        err = -ENOMEM;
                        break;
                }
        }
        put_online_cpus();
        mddev_resume(conf->mddev);
        if (!err) {
                conf->scribble_disks = new_disks;
                conf->scribble_sectors = new_sectors;
        }
        return err;
}

static int resize_stripes(struct r5conf *conf, int newsize)
{
        /* Make all the stripes able to hold 'newsize' devices.
         * New slots in each stripe get 'page' set to a new page.
         *
         * This happens in stages:
         * 1/ create a new kmem_cache and allocate the required number of
         *    stripe_heads.
         * 2/ gather all the old stripe_heads and transfer the pages across
         *    to the new stripe_heads.  This will have the side effect of
         *    freezing the array as once all stripe_heads have been collected,
         *    no IO will be possible.  Old stripe heads are freed once their
         *    pages have been transferred over, and the old kmem_cache is
         *    freed when all stripes are done.
         * 3/ reallocate conf->disks to be suitable bigger.  If this fails,
         *    we simple return a failre status - no need to clean anything up.
         * 4/ allocate new pages for the new slots in the new stripe_heads.
         *    If this fails, we don't bother trying the shrink the
         *    stripe_heads down again, we just leave them as they are.
         *    As each stripe_head is processed the new one is released into
         *    active service.
         *
         * Once step2 is started, we cannot afford to wait for a write,
         * so we use GFP_NOIO allocations.
         */
        struct stripe_head *osh, *nsh;
        LIST_HEAD(newstripes);
        struct disk_info *ndisks;
        int err;
        struct kmem_cache *sc;
        int i;
        int hash, cnt;

        if (newsize <= conf->pool_size)
                return 0; /* never bother to shrink */

        err = md_allow_write(conf->mddev);
        if (err)
                return err;

        /* Step 1 */
        sc = kmem_cache_create(conf->cache_name[1-conf->active_name],
                               sizeof(struct stripe_head)+(newsize-1)*sizeof(struct r5dev),
                               0, 0, NULL);
        if (!sc)
                return -ENOMEM;

        /* Need to ensure auto-resizing doesn't interfere */
        mutex_lock(&conf->cache_size_mutex);

        for (i = conf->max_nr_stripes; i; i--) {
                nsh = alloc_stripe(sc, GFP_KERNEL, newsize);
                if (!nsh)
                        break;

                nsh->raid_conf = conf;
                list_add(&nsh->lru, &newstripes);
        }
        if (i) {
                /* didn't get enough, give up */
                while (!list_empty(&newstripes)) {
                        nsh = list_entry(newstripes.next, struct stripe_head, lru);
                        list_del(&nsh->lru);
                        kmem_cache_free(sc, nsh);
                }
                kmem_cache_destroy(sc);
                mutex_unlock(&conf->cache_size_mutex);
                return -ENOMEM;
        }
        /* Step 2 - Must use GFP_NOIO now.
         * OK, we have enough stripes, start collecting inactive
         * stripes and copying them over
         */
        hash = 0;
        cnt = 0;
        list_for_each_entry(nsh, &newstripes, lru) {
                lock_device_hash_lock(conf, hash);
                wait_event_cmd(conf->wait_for_stripe,
                                    !list_empty(conf->inactive_list + hash),
                                    unlock_device_hash_lock(conf, hash),
                                    lock_device_hash_lock(conf, hash));
                osh = get_free_stripe(conf, hash);
                unlock_device_hash_lock(conf, hash);

                for(i=0; i<conf->pool_size; i++) {
                        nsh->dev[i].page = osh->dev[i].page;
                        nsh->dev[i].orig_page = osh->dev[i].page;
                }
                nsh->hash_lock_index = hash;
                kmem_cache_free(conf->slab_cache, osh);
                cnt++;
                if (cnt >= conf->max_nr_stripes / NR_STRIPE_HASH_LOCKS +
                    !!((conf->max_nr_stripes % NR_STRIPE_HASH_LOCKS) > hash)) {
                        hash++;
                        cnt = 0;
                }
        }
        kmem_cache_destroy(conf->slab_cache);

        /* Step 3.
         * At this point, we are holding all the stripes so the array
         * is completely stalled, so now is a good time to resize
         * conf->disks and the scribble region
         */
        ndisks = kzalloc(newsize * sizeof(struct disk_info), GFP_NOIO);
        if (ndisks) {
                for (i=0; i<conf->raid_disks; i++)
                        ndisks[i] = conf->disks[i];
                kfree(conf->disks);
                conf->disks = ndisks;
        } else
                err = -ENOMEM;

        mutex_unlock(&conf->cache_size_mutex);

        conf->slab_cache = sc;
        conf->active_name = 1-conf->active_name;

        /* Step 4, return new stripes to service */
        while(!list_empty(&newstripes)) {
                nsh = list_entry(newstripes.next, struct stripe_head, lru);
                list_del_init(&nsh->lru);

                for (i=conf->raid_disks; i < newsize; i++)
                        if (nsh->dev[i].page == NULL) {
                                struct page *p = alloc_page(GFP_NOIO);
                                nsh->dev[i].page = p;
                                nsh->dev[i].orig_page = p;
                                if (!p)
                                        err = -ENOMEM;
                        }
                raid5_release_stripe(nsh);
        }
        /* critical section pass, GFP_NOIO no longer needed */

        if (!err)
                conf->pool_size = newsize;
        return err;
}

static int drop_one_stripe(struct r5conf *conf)
{
        struct stripe_head *sh;
        int hash = (conf->max_nr_stripes - 1) & STRIPE_HASH_LOCKS_MASK;

        spin_lock_irq(conf->hash_locks + hash);
        sh = get_free_stripe(conf, hash);
        spin_unlock_irq(conf->hash_locks + hash);
        if (!sh)
                return 0;
        BUG_ON(atomic_read(&sh->count));
        shrink_buffers(sh);
        kmem_cache_free(conf->slab_cache, sh);
        atomic_dec(&conf->active_stripes);
        conf->max_nr_stripes--;
        return 1;
}

static void shrink_stripes(struct r5conf *conf)
{
        while (conf->max_nr_stripes &&
               drop_one_stripe(conf))
                ;

        kmem_cache_destroy(conf->slab_cache);
        conf->slab_cache = NULL;
}

static void raid5_end_read_request(struct bio * bi)
{
        struct stripe_head *sh = bi->bi_private;
        struct r5conf *conf = sh->raid_conf;
        int disks = sh->disks, i;
        char b[BDEVNAME_SIZE];
        struct md_rdev *rdev = NULL;
        sector_t s;

        for (i=0 ; i<disks; i++)
                if (bi == &sh->dev[i].req)
                        break;

        pr_debug("end_read_request %llu/%d, count: %d, error %d.\n",
                (unsigned long long)sh->sector, i, atomic_read(&sh->count),
                bi->bi_error);
        if (i == disks) {
                bio_reset(bi);
                BUG();
                return;
        }
        if (test_bit(R5_ReadRepl, &sh->dev[i].flags))
                /* If replacement finished while this request was outstanding,
                 * 'replacement' might be NULL already.
                 * In that case it moved down to 'rdev'.
                 * rdev is not removed until all requests are finished.
                 */
                rdev = conf->disks[i].replacement;
        if (!rdev)
                rdev = conf->disks[i].rdev;

        if (use_new_offset(conf, sh))
                s = sh->sector + rdev->new_data_offset;
        else
                s = sh->sector + rdev->data_offset;
        if (!bi->bi_error) {
                set_bit(R5_UPTODATE, &sh->dev[i].flags);
                if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                        /* Note that this cannot happen on a
                         * replacement device.  We just fail those on
                         * any error
                         */
                        printk_ratelimited(
                                KERN_INFO
                                "md/raid:%s: read error corrected"
                                " (%lu sectors at %llu on %s)\n",
                                mdname(conf->mddev), STRIPE_SECTORS,
                                (unsigned long long)s,
                                bdevname(rdev->bdev, b));
                        atomic_add(STRIPE_SECTORS, &rdev->corrected_errors);
                        clear_bit(R5_ReadError, &sh->dev[i].flags);
                        clear_bit(R5_ReWrite, &sh->dev[i].flags);
                } else if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
                        clear_bit(R5_ReadNoMerge, &sh->dev[i].flags);

                if (atomic_read(&rdev->read_errors))
                        atomic_set(&rdev->read_errors, 0);
        } else {
                const char *bdn = bdevname(rdev->bdev, b);
                int retry = 0;
                int set_bad = 0;

                clear_bit(R5_UPTODATE, &sh->dev[i].flags);
                atomic_inc(&rdev->read_errors);
                if (test_bit(R5_ReadRepl, &sh->dev[i].flags))
                        printk_ratelimited(
                                KERN_WARNING
                                "md/raid:%s: read error on replacement device "
                                "(sector %llu on %s).\n",
                                mdname(conf->mddev),
                                (unsigned long long)s,
                                bdn);
                else if (conf->mddev->degraded >= conf->max_degraded) {
                        set_bad = 1;
                        printk_ratelimited(
                                KERN_WARNING
                                "md/raid:%s: read error not correctable "
                                "(sector %llu on %s).\n",
                                mdname(conf->mddev),
                                (unsigned long long)s,
                                bdn);
                } else if (test_bit(R5_ReWrite, &sh->dev[i].flags)) {
                        /* Oh, no!!! */
                        set_bad = 1;
                        printk_ratelimited(
                                KERN_WARNING
                                "md/raid:%s: read error NOT corrected!! "
                                "(sector %llu on %s).\n",
                                mdname(conf->mddev),
                                (unsigned long long)s,
                                bdn);
                } else if (atomic_read(&rdev->read_errors)
                         > conf->max_nr_stripes)
                        printk(KERN_WARNING
                               "md/raid:%s: Too many read errors, failing device %s.\n",
                               mdname(conf->mddev), bdn);
                else
                        retry = 1;
                if (set_bad && test_bit(In_sync, &rdev->flags)
                    && !test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
                        retry = 1;
                if (retry)
                        if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags)) {
                                set_bit(R5_ReadError, &sh->dev[i].flags);
                                clear_bit(R5_ReadNoMerge, &sh->dev[i].flags);
                        } else
                                set_bit(R5_ReadNoMerge, &sh->dev[i].flags);
                else {
                        clear_bit(R5_ReadError, &sh->dev[i].flags);
                        clear_bit(R5_ReWrite, &sh->dev[i].flags);
                        if (!(set_bad
                              && test_bit(In_sync, &rdev->flags)
                              && rdev_set_badblocks(
                                      rdev, sh->sector, STRIPE_SECTORS, 0)))
                                md_error(conf->mddev, rdev);
                }
        }
        rdev_dec_pending(rdev, conf->mddev);
        bio_reset(bi);
        clear_bit(R5_LOCKED, &sh->dev[i].flags);
        set_bit(STRIPE_HANDLE, &sh->state);
        raid5_release_stripe(sh);
}

static void raid5_end_write_request(struct bio *bi)
{
        struct stripe_head *sh = bi->bi_private;
        struct r5conf *conf = sh->raid_conf;
        int disks = sh->disks, i;
        struct md_rdev *uninitialized_var(rdev);
        sector_t first_bad;
        int bad_sectors;
        int replacement = 0;

        for (i = 0 ; i < disks; i++) {
                if (bi == &sh->dev[i].req) {
                        rdev = conf->disks[i].rdev;
                        break;
                }
                if (bi == &sh->dev[i].rreq) {
                        rdev = conf->disks[i].replacement;
                        if (rdev)
                                replacement = 1;
                        else
                                /* rdev was removed and 'replacement'
                                 * replaced it.  rdev is not removed
                                 * until all requests are finished.
                                 */
                                rdev = conf->disks[i].rdev;
                        break;
                }
        }
        pr_debug("end_write_request %llu/%d, count %d, error: %d.\n",
                (unsigned long long)sh->sector, i, atomic_read(&sh->count),
                bi->bi_error);
        if (i == disks) {
                bio_reset(bi);
                BUG();
                return;
        }

        if (replacement) {
                if (bi->bi_error)
                        md_error(conf->mddev, rdev);
                else if (is_badblock(rdev, sh->sector,
                                     STRIPE_SECTORS,
                                     &first_bad, &bad_sectors))
                        set_bit(R5_MadeGoodRepl, &sh->dev[i].flags);
        } else {
                if (bi->bi_error) {
                        set_bit(STRIPE_DEGRADED, &sh->state);
                        set_bit(WriteErrorSeen, &rdev->flags);
                        set_bit(R5_WriteError, &sh->dev[i].flags);
                        if (!test_and_set_bit(WantReplacement, &rdev->flags))
                                set_bit(MD_RECOVERY_NEEDED,
                                        &rdev->mddev->recovery);
                } else if (is_badblock(rdev, sh->sector,
                                       STRIPE_SECTORS,
                                       &first_bad, &bad_sectors)) {
                        set_bit(R5_MadeGood, &sh->dev[i].flags);
                        if (test_bit(R5_ReadError, &sh->dev[i].flags))
                                /* That was a successful write so make
                                 * sure it looks like we already did
                                 * a re-write.
                                 */
                                set_bit(R5_ReWrite, &sh->dev[i].flags);
                }
        }
        rdev_dec_pending(rdev, conf->mddev);

        if (sh->batch_head && bi->bi_error && !replacement)
                set_bit(STRIPE_BATCH_ERR, &sh->batch_head->state);

        bio_reset(bi);
        if (!test_and_clear_bit(R5_DOUBLE_LOCKED, &sh->dev[i].flags))
                clear_bit(R5_LOCKED, &sh->dev[i].flags);
        set_bit(STRIPE_HANDLE, &sh->state);
        raid5_release_stripe(sh);

        if (sh->batch_head && sh != sh->batch_head)
                raid5_release_stripe(sh->batch_head);
}

static void raid5_build_block(struct stripe_head *sh, int i, int previous)
{
        struct r5dev *dev = &sh->dev[i];

        dev->flags = 0;
        dev->sector = raid5_compute_blocknr(sh, i, previous);
}

static void raid5_error(struct mddev *mddev, struct md_rdev *rdev)
{
        char b[BDEVNAME_SIZE];
        struct r5conf *conf = mddev->private;
        unsigned long flags;
        pr_debug("raid456: error called\n");

        spin_lock_irqsave(&conf->device_lock, flags);
        clear_bit(In_sync, &rdev->flags);
        mddev->degraded = calc_degraded(conf);
        spin_unlock_irqrestore(&conf->device_lock, flags);
        set_bit(MD_RECOVERY_INTR, &mddev->recovery);

        set_bit(Blocked, &rdev->flags);
        set_bit(Faulty, &rdev->flags);
        set_mask_bits(&mddev->flags, 0,
                      BIT(MD_CHANGE_DEVS) | BIT(MD_CHANGE_PENDING));
        printk(KERN_ALERT
               "md/raid:%s: Disk failure on %s, disabling device.\n"
               "md/raid:%s: Operation continuing on %d devices.\n",
               mdname(mddev),
               bdevname(rdev->bdev, b),
               mdname(mddev),
               conf->raid_disks - mddev->degraded);
}

/*
 * Input: a 'big' sector number,
 * Output: index of the data and parity disk, and the sector # in them.
 */
sector_t raid5_compute_sector(struct r5conf *conf, sector_t r_sector,
                              int previous, int *dd_idx,
                              struct stripe_head *sh)
{
        sector_t stripe, stripe2;
        sector_t chunk_number;
        unsigned int chunk_offset;
        int pd_idx, qd_idx;
        int ddf_layout = 0;
        sector_t new_sector;
        int algorithm = previous ? conf->prev_algo
                                 : conf->algorithm;
        int sectors_per_chunk = previous ? conf->prev_chunk_sectors
                                         : conf->chunk_sectors;
        int raid_disks = previous ? conf->previous_raid_disks
                                  : conf->raid_disks;
        int data_disks = raid_disks - conf->max_degraded;

        /* First compute the information on this sector */

        /*
         * Compute the chunk number and the sector offset inside the chunk
         */
        chunk_offset = sector_div(r_sector, sectors_per_chunk);
        chunk_number = r_sector;

        /*
         * Compute the stripe number
         */
        stripe = chunk_number;
        *dd_idx = sector_div(stripe, data_disks);
        stripe2 = stripe;
        /*
         * Select the parity disk based on the user selected algorithm.
         */
        pd_idx = qd_idx = -1;
        switch(conf->level) {
        case 4:
                pd_idx = data_disks;
                break;
        case 5:
                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                        pd_idx = data_disks - sector_div(stripe2, raid_disks);
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        break;
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        pd_idx = sector_div(stripe2, raid_disks);
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                        pd_idx = data_disks - sector_div(stripe2, raid_disks);
                        *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                        break;
                case ALGORITHM_RIGHT_SYMMETRIC:
                        pd_idx = sector_div(stripe2, raid_disks);
                        *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                        break;
                case ALGORITHM_PARITY_0:
                        pd_idx = 0;
                        (*dd_idx)++;
                        break;
                case ALGORITHM_PARITY_N:
                        pd_idx = data_disks;
                        break;
                default:
                        BUG();
                }
                break;
        case 6:

                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                        pd_idx = raid_disks - 1 - sector_div(stripe2, raid_disks);
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        break;
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        pd_idx = sector_div(stripe2, raid_disks);
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                        pd_idx = raid_disks - 1 - sector_div(stripe2, raid_disks);
                        qd_idx = (pd_idx + 1) % raid_disks;
                        *dd_idx = (pd_idx + 2 + *dd_idx) % raid_disks;
                        break;
                case ALGORITHM_RIGHT_SYMMETRIC:
                        pd_idx = sector_div(stripe2, raid_disks);
                        qd_idx = (pd_idx + 1) % raid_disks;
                        *dd_idx = (pd_idx + 2 + *dd_idx) % raid_disks;
                        break;

                case ALGORITHM_PARITY_0:
                        pd_idx = 0;
                        qd_idx = 1;
                        (*dd_idx) += 2;
                        break;
                case ALGORITHM_PARITY_N:
                        pd_idx = data_disks;
                        qd_idx = data_disks + 1;
                        break;

                case ALGORITHM_ROTATING_ZERO_RESTART:
                        /* Exactly the same as RIGHT_ASYMMETRIC, but or
                         * of blocks for computing Q is different.
                         */
                        pd_idx = sector_div(stripe2, raid_disks);
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        ddf_layout = 1;
                        break;

                case ALGORITHM_ROTATING_N_RESTART:
                        /* Same a left_asymmetric, by first stripe is
                         * D D D P Q  rather than
                         * Q D D D P
                         */
                        stripe2 += 1;
                        pd_idx = raid_disks - 1 - sector_div(stripe2, raid_disks);
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        ddf_layout = 1;
                        break;

                case ALGORITHM_ROTATING_N_CONTINUE:
                        /* Same as left_symmetric but Q is before P */
                        pd_idx = raid_disks - 1 - sector_div(stripe2, raid_disks);
                        qd_idx = (pd_idx + raid_disks - 1) % raid_disks;
                        *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                        ddf_layout = 1;
                        break;

                case ALGORITHM_LEFT_ASYMMETRIC_6:
                        /* RAID5 left_asymmetric, with Q on last device */
                        pd_idx = data_disks - sector_div(stripe2, raid_disks-1);
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_RIGHT_ASYMMETRIC_6:
                        pd_idx = sector_div(stripe2, raid_disks-1);
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_LEFT_SYMMETRIC_6:
                        pd_idx = data_disks - sector_div(stripe2, raid_disks-1);
                        *dd_idx = (pd_idx + 1 + *dd_idx) % (raid_disks-1);
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_RIGHT_SYMMETRIC_6:
                        pd_idx = sector_div(stripe2, raid_disks-1);
                        *dd_idx = (pd_idx + 1 + *dd_idx) % (raid_disks-1);
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_PARITY_0_6:
                        pd_idx = 0;
                        (*dd_idx)++;
                        qd_idx = raid_disks - 1;
                        break;

                default:
                        BUG();
                }
                break;
        }

        if (sh) {
                sh->pd_idx = pd_idx;
                sh->qd_idx = qd_idx;
                sh->ddf_layout = ddf_layout;
        }
        /*
         * Finally, compute the new sector number
         */
        new_sector = (sector_t)stripe * sectors_per_chunk + chunk_offset;
        return new_sector;
}

sector_t raid5_compute_blocknr(struct stripe_head *sh, int i, int previous)
{
        struct r5conf *conf = sh->raid_conf;
        int raid_disks = sh->disks;
        int data_disks = raid_disks - conf->max_degraded;
        sector_t new_sector = sh->sector, check;
        int sectors_per_chunk = previous ? conf->prev_chunk_sectors
                                         : conf->chunk_sectors;
        int algorithm = previous ? conf->prev_algo
                                 : conf->algorithm;
        sector_t stripe;
        int chunk_offset;
        sector_t chunk_number;
        int dummy1, dd_idx = i;
        sector_t r_sector;
        struct stripe_head sh2;

        chunk_offset = sector_div(new_sector, sectors_per_chunk);
        stripe = new_sector;

        if (i == sh->pd_idx)
                return 0;
        switch(conf->level) {
        case 4: break;
        case 5:
                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        if (i > sh->pd_idx)
                                i--;
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                case ALGORITHM_RIGHT_SYMMETRIC:
                        if (i < sh->pd_idx)
                                i += raid_disks;
                        i -= (sh->pd_idx + 1);
                        break;
                case ALGORITHM_PARITY_0:
                        i -= 1;
                        break;
                case ALGORITHM_PARITY_N:
                        break;
                default:
                        BUG();
                }
                break;
        case 6:
                if (i == sh->qd_idx)
                        return 0; /* It is the Q disk */
                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                case ALGORITHM_RIGHT_ASYMMETRIC:
                case ALGORITHM_ROTATING_ZERO_RESTART:
                case ALGORITHM_ROTATING_N_RESTART:
                        if (sh->pd_idx == raid_disks-1)
                                i--;    /* Q D D D P */
                        else if (i > sh->pd_idx)
                                i -= 2; /* D D P Q D */
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                case ALGORITHM_RIGHT_SYMMETRIC:
                        if (sh->pd_idx == raid_disks-1)
                                i--; /* Q D D D P */
                        else {
                                /* D D P Q D */
                                if (i < sh->pd_idx)
                                        i += raid_disks;
                                i -= (sh->pd_idx + 2);
                        }
                        break;
                case ALGORITHM_PARITY_0:
                        i -= 2;
                        break;
                case ALGORITHM_PARITY_N:
                        break;
                case ALGORITHM_ROTATING_N_CONTINUE:
                        /* Like left_symmetric, but P is before Q */
                        if (sh->pd_idx == 0)
                                i--;    /* P D D D Q */
                        else {
                                /* D D Q P D */
                                if (i < sh->pd_idx)
                                        i += raid_disks;
                                i -= (sh->pd_idx + 1);
                        }
                        break;
                case ALGORITHM_LEFT_ASYMMETRIC_6:
                case ALGORITHM_RIGHT_ASYMMETRIC_6:
                        if (i > sh->pd_idx)
                                i--;
                        break;
                case ALGORITHM_LEFT_SYMMETRIC_6:
                case ALGORITHM_RIGHT_SYMMETRIC_6:
                        if (i < sh->pd_idx)
                                i += data_disks + 1;
                        i -= (sh->pd_idx + 1);
                        break;
                case ALGORITHM_PARITY_0_6:
                        i -= 1;
                        break;
                default:
                        BUG();
                }
                break;
        }

        chunk_number = stripe * data_disks + i;
        r_sector = chunk_number * sectors_per_chunk + chunk_offset;

        check = raid5_compute_sector(conf, r_sector,
                                     previous, &dummy1, &sh2);
        if (check != sh->sector || dummy1 != dd_idx || sh2.pd_idx != sh->pd_idx
                || sh2.qd_idx != sh->qd_idx) {
                printk(KERN_ERR "md/raid:%s: compute_blocknr: map not correct\n",
                       mdname(conf->mddev));
                return 0;
        }
        return r_sector;
}

static void
schedule_reconstruction(struct stripe_head *sh, struct stripe_head_state *s,
                         int rcw, int expand)
{
        int i, pd_idx = sh->pd_idx, qd_idx = sh->qd_idx, disks = sh->disks;
        struct r5conf *conf = sh->raid_conf;
        int level = conf->level;

        if (rcw) {

                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];

                        if (dev->towrite) {
                                set_bit(R5_LOCKED, &dev->flags);
                                set_bit(R5_Wantdrain, &dev->flags);
                                if (!expand)
                                        clear_bit(R5_UPTODATE, &dev->flags);
                                s->locked++;
                        }
                }
                /* if we are not expanding this is a proper write request, and
                 * there will be bios with new data to be drained into the
                 * stripe cache
                 */
                if (!expand) {
                        if (!s->locked)
                                /* False alarm, nothing to do */
                                return;
                        sh->reconstruct_state = reconstruct_state_drain_run;
                        set_bit(STRIPE_OP_BIODRAIN, &s->ops_request);
                } else
                        sh->reconstruct_state = reconstruct_state_run;

                set_bit(STRIPE_OP_RECONSTRUCT, &s->ops_request);

                if (s->locked + conf->max_degraded == disks)
                        if (!test_and_set_bit(STRIPE_FULL_WRITE, &sh->state))
                                atomic_inc(&conf->pending_full_writes);
        } else {
                BUG_ON(!(test_bit(R5_UPTODATE, &sh->dev[pd_idx].flags) ||
                        test_bit(R5_Wantcompute, &sh->dev[pd_idx].flags)));
                BUG_ON(level == 6 &&
                        (!(test_bit(R5_UPTODATE, &sh->dev[qd_idx].flags) ||
                           test_bit(R5_Wantcompute, &sh->dev[qd_idx].flags))));

                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (i == pd_idx || i == qd_idx)
                                continue;

                        if (dev->towrite &&
                            (test_bit(R5_UPTODATE, &dev->flags) ||
                             test_bit(R5_Wantcompute, &dev->flags))) {
                                set_bit(R5_Wantdrain, &dev->flags);
                                set_bit(R5_LOCKED, &dev->flags);
                                clear_bit(R5_UPTODATE, &dev->flags);
                                s->locked++;
                        }
                }
                if (!s->locked)
                        /* False alarm - nothing to do */
                        return;
                sh->reconstruct_state = reconstruct_state_prexor_drain_run;
                set_bit(STRIPE_OP_PREXOR, &s->ops_request);
                set_bit(STRIPE_OP_BIODRAIN, &s->ops_request);
                set_bit(STRIPE_OP_RECONSTRUCT, &s->ops_request);
        }

        /* keep the parity disk(s) locked while asynchronous operations
         * are in flight
         */
        set_bit(R5_LOCKED, &sh->dev[pd_idx].flags);
        clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
        s->locked++;

        if (level == 6) {
                int qd_idx = sh->qd_idx;
                struct r5dev *dev = &sh->dev[qd_idx];

                set_bit(R5_LOCKED, &dev->flags);
                clear_bit(R5_UPTODATE, &dev->flags);
                s->locked++;
        }

        pr_debug("%s: stripe %llu locked: %d ops_request: %lx\n",
                __func__, (unsigned long long)sh->sector,
                s->locked, s->ops_request);
}

/*
 * Each stripe/dev can have one or more bion attached.
 * toread/towrite point to the first in a chain.
 * The bi_next chain must be in order.
 */
static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx,
                          int forwrite, int previous)
{
        struct bio **bip;
        struct r5conf *conf = sh->raid_conf;
        int firstwrite=0;

        pr_debug("adding bi b#%llu to stripe s#%llu\n",
                (unsigned long long)bi->bi_iter.bi_sector,
                (unsigned long long)sh->sector);

        /*
         * If several bio share a stripe. The bio bi_phys_segments acts as a
         * reference count to avoid race. The reference count should already be
         * increased before this function is called (for example, in
         * raid5_make_request()), so other bio sharing this stripe will not free the
         * stripe. If a stripe is owned by one stripe, the stripe lock will
         * protect it.
         */
        spin_lock_irq(&sh->stripe_lock);
        /* Don't allow new IO added to stripes in batch list */
        if (sh->batch_head)
                goto overlap;
        if (forwrite) {
                bip = &sh->dev[dd_idx].towrite;
                if (*bip == NULL)
                        firstwrite = 1;
        } else
                bip = &sh->dev[dd_idx].toread;
        while (*bip && (*bip)->bi_iter.bi_sector < bi->bi_iter.bi_sector) {
                if (bio_end_sector(*bip) > bi->bi_iter.bi_sector)
                        goto overlap;
                bip = & (*bip)->bi_next;
        }
        if (*bip && (*bip)->bi_iter.bi_sector < bio_end_sector(bi))
                goto overlap;

        if (!forwrite || previous)
                clear_bit(STRIPE_BATCH_READY, &sh->state);

        BUG_ON(*bip && bi->bi_next && (*bip) != bi->bi_next);
        if (*bip)
                bi->bi_next = *bip;
        *bip = bi;
        raid5_inc_bi_active_stripes(bi);

        if (forwrite) {
                /* check if page is covered */
                sector_t sector = sh->dev[dd_idx].sector;
                for (bi=sh->dev[dd_idx].towrite;
                     sector < sh->dev[dd_idx].sector + STRIPE_SECTORS &&
                             bi && bi->bi_iter.bi_sector <= sector;
                     bi = r5_next_bio(bi, sh->dev[dd_idx].sector)) {
                        if (bio_end_sector(bi) >= sector)
                                sector = bio_end_sector(bi);
                }
                if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
                        if (!test_and_set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags))
                                sh->overwrite_disks++;
        }

        pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
                (unsigned long long)(*bip)->bi_iter.bi_sector,
                (unsigned long long)sh->sector, dd_idx);

        if (conf->mddev->bitmap && firstwrite) {
                /* Cannot hold spinlock over bitmap_startwrite,
                 * but must ensure this isn't added to a batch until
                 * we have added to the bitmap and set bm_seq.
                 * So set STRIPE_BITMAP_PENDING to prevent
                 * batching.
                 * If multiple add_stripe_bio() calls race here they
                 * much all set STRIPE_BITMAP_PENDING.  So only the first one
                 * to complete "bitmap_startwrite" gets to set
                 * STRIPE_BIT_DELAY.  This is important as once a stripe
                 * is added to a batch, STRIPE_BIT_DELAY cannot be changed
                 * any more.
                 */
                set_bit(STRIPE_BITMAP_PENDING, &sh->state);
                spin_unlock_irq(&sh->stripe_lock);
                bitmap_startwrite(conf->mddev->bitmap, sh->sector,
                                  STRIPE_SECTORS, 0);
                spin_lock_irq(&sh->stripe_lock);
                clear_bit(STRIPE_BITMAP_PENDING, &sh->state);
                if (!sh->batch_head) {
                        sh->bm_seq = conf->seq_flush+1;
                        set_bit(STRIPE_BIT_DELAY, &sh->state);
                }
        }
        spin_unlock_irq(&sh->stripe_lock);

        if (stripe_can_batch(sh))
                stripe_add_to_batch_list(conf, sh);
        return 1;

 overlap:
        set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
        spin_unlock_irq(&sh->stripe_lock);
        return 0;
}

static void end_reshape(struct r5conf *conf);

static void stripe_set_idx(sector_t stripe, struct r5conf *conf, int previous,
                            struct stripe_head *sh)
{
        int sectors_per_chunk =
                previous ? conf->prev_chunk_sectors : conf->chunk_sectors;
        int dd_idx;
        int chunk_offset = sector_div(stripe, sectors_per_chunk);
        int disks = previous ? conf->previous_raid_disks : conf->raid_disks;

        raid5_compute_sector(conf,
                             stripe * (disks - conf->max_degraded)
                             *sectors_per_chunk + chunk_offset,
                             previous,
                             &dd_idx, sh);
}

static void
handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh,
                                struct stripe_head_state *s, int disks,
                                struct bio_list *return_bi)
{
        int i;
        BUG_ON(sh->batch_head);
        for (i = disks; i--; ) {
                struct bio *bi;
                int bitmap_end = 0;

                if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                        struct md_rdev *rdev;
                        rcu_read_lock();
                        rdev = rcu_dereference(conf->disks[i].rdev);
                        if (rdev && test_bit(In_sync, &rdev->flags) &&
                            !test_bit(Faulty, &rdev->flags))
                                atomic_inc(&rdev->nr_pending);
                        else
                                rdev = NULL;
                        rcu_read_unlock();
                        if (rdev) {
                                if (!rdev_set_badblocks(
                                            rdev,
                                            sh->sector,
                                            STRIPE_SECTORS, 0))
                                        md_error(conf->mddev, rdev);
                                rdev_dec_pending(rdev, conf->mddev);
                        }
                }
                spin_lock_irq(&sh->stripe_lock);
                /* fail all writes first */
                bi = sh->dev[i].towrite;
                sh->dev[i].towrite = NULL;
                sh->overwrite_disks = 0;
                spin_unlock_irq(&sh->stripe_lock);
                if (bi)
                        bitmap_end = 1;

                r5l_stripe_write_finished(sh);

                if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                        wake_up(&conf->wait_for_overlap);

                while (bi && bi->bi_iter.bi_sector <
                        sh->dev[i].sector + STRIPE_SECTORS) {
                        struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);

                        bi->bi_error = -EIO;
                        if (!raid5_dec_bi_active_stripes(bi)) {
                                md_write_end(conf->mddev);
                                bio_list_add(return_bi, bi);
                        }
                        bi = nextbi;
                }
                if (bitmap_end)
                        bitmap_endwrite(conf->mddev->bitmap, sh->sector,
                                STRIPE_SECTORS, 0, 0);
                bitmap_end = 0;
                /* and fail all 'written' */
                bi = sh->dev[i].written;
                sh->dev[i].written = NULL;
                if (test_and_clear_bit(R5_SkipCopy, &sh->dev[i].flags)) {
                        WARN_ON(test_bit(R5_UPTODATE, &sh->dev[i].flags));
                        sh->dev[i].page = sh->dev[i].orig_page;
                }

                if (bi) bitmap_end = 1;
                while (bi && bi->bi_iter.bi_sector <
                       sh->dev[i].sector + STRIPE_SECTORS) {
                        struct bio *bi2 = r5_next_bio(bi, sh->dev[i].sector);

                        bi->bi_error = -EIO;
                        if (!raid5_dec_bi_active_stripes(bi)) {
                                md_write_end(conf->mddev);
                                bio_list_add(return_bi, bi);
                        }
                        bi = bi2;
                }

                /* fail any reads if this device is non-operational and
                 * the data has not reached the cache yet.
                 */
                if (!test_bit(R5_Wantfill, &sh->dev[i].flags) &&
                    s->failed > conf->max_degraded &&
                    (!test_bit(R5_Insync, &sh->dev[i].flags) ||
                      test_bit(R5_ReadError, &sh->dev[i].flags))) {
                        spin_lock_irq(&sh->stripe_lock);
                        bi = sh->dev[i].toread;
                        sh->dev[i].toread = NULL;
                        spin_unlock_irq(&sh->stripe_lock);
                        if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                                wake_up(&conf->wait_for_overlap);
                        if (bi)
                                s->to_read--;
                        while (bi && bi->bi_iter.bi_sector <
                               sh->dev[i].sector + STRIPE_SECTORS) {
                                struct bio *nextbi =
                                        r5_next_bio(bi, sh->dev[i].sector);

                                bi->bi_error = -EIO;
                                if (!raid5_dec_bi_active_stripes(bi))
                                        bio_list_add(return_bi, bi);
                                bi = nextbi;
                        }
                }
                if (bitmap_end)
                        bitmap_endwrite(conf->mddev->bitmap, sh->sector,
                                        STRIPE_SECTORS, 0, 0);
                /* If we were in the middle of a write the parity block might
                 * still be locked - so just clear all R5_LOCKED flags
                 */
                clear_bit(R5_LOCKED, &sh->dev[i].flags);
        }
        s->to_write = 0;
        s->written = 0;

        if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))
                if (atomic_dec_and_test(&conf->pending_full_writes))
                        md_wakeup_thread(conf->mddev->thread);
}

static void
handle_failed_sync(struct r5conf *conf, struct stripe_head *sh,
                   struct stripe_head_state *s)
{
        int abort = 0;
        int i;

        BUG_ON(sh->batch_head);
        clear_bit(STRIPE_SYNCING, &sh->state);
        if (test_and_clear_bit(R5_Overlap, &sh->dev[sh->pd_idx].flags))
                wake_up(&conf->wait_for_overlap);
        s->syncing = 0;
        s->replacing = 0;
        /* There is nothing more to do for sync/check/repair.
         * Don't even need to abort as that is handled elsewhere
         * if needed, and not always wanted e.g. if there is a known
         * bad block here.
         * For recover/replace we need to record a bad block on all
         * non-sync devices, or abort the recovery
         */
        if (test_bit(MD_RECOVERY_RECOVER, &conf->mddev->recovery)) {
                /* During recovery devices cannot be removed, so
                 * locking and refcounting of rdevs is not needed
                 */
                rcu_read_lock();
                for (i = 0; i < conf->raid_disks; i++) {
                        struct md_rdev *rdev = rcu_dereference(conf->disks[i].rdev);
                        if (rdev
                            && !test_bit(Faulty, &rdev->flags)
                            && !test_bit(In_sync, &rdev->flags)
                            && !rdev_set_badblocks(rdev, sh->sector,
                                                   STRIPE_SECTORS, 0))
                                abort = 1;
                        rdev = rcu_dereference(conf->disks[i].replacement);
                        if (rdev
                            && !test_bit(Faulty, &rdev->flags)
                            && !test_bit(In_sync, &rdev->flags)
                            && !rdev_set_badblocks(rdev, sh->sector,
                                                   STRIPE_SECTORS, 0))
                                abort = 1;
                }
                rcu_read_unlock();
                if (abort)
                        conf->recovery_disabled =
                                conf->mddev->recovery_disabled;
        }
        md_done_sync(conf->mddev, STRIPE_SECTORS, !abort);
}

static int want_replace(struct stripe_head *sh, int disk_idx)
{
        struct md_rdev *rdev;
        int rv = 0;

        rcu_read_lock();
        rdev = rcu_dereference(sh->raid_conf->disks[disk_idx].replacement);
        if (rdev
            && !test_bit(Faulty, &rdev->flags)
            && !test_bit(In_sync, &rdev->flags)
            && (rdev->recovery_offset <= sh->sector
                || rdev->mddev->recovery_cp <= sh->sector))
                rv = 1;
        rcu_read_unlock();
        return rv;
}

/* fetch_block - checks the given member device to see if its data needs
 * to be read or computed to satisfy a request.
 *
 * Returns 1 when no more member devices need to be checked, otherwise returns
 * 0 to tell the loop in handle_stripe_fill to continue
 */

static int need_this_block(struct stripe_head *sh, struct stripe_head_state *s,
                           int disk_idx, int disks)
{
        struct r5dev *dev = &sh->dev[disk_idx];
        struct r5dev *fdev[2] = { &sh->dev[s->failed_num[0]],
                                  &sh->dev[s->failed_num[1]] };
        int i;


        if (test_bit(R5_LOCKED, &dev->flags) ||
            test_bit(R5_UPTODATE, &dev->flags))
                /* No point reading this as we already have it or have
                 * decided to get it.
                 */
                return 0;

        if (dev->toread ||
            (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)))
                /* We need this block to directly satisfy a request */
                return 1;

        if (s->syncing || s->expanding ||
            (s->replacing && want_replace(sh, disk_idx)))
                /* When syncing, or expanding we read everything.
                 * When replacing, we need the replaced block.
                 */
                return 1;

        if ((s->failed >= 1 && fdev[0]->toread) ||
            (s->failed >= 2 && fdev[1]->toread))
                /* If we want to read from a failed device, then
                 * we need to actually read every other device.
                 */
                return 1;

        /* Sometimes neither read-modify-write nor reconstruct-write
         * cycles can work.  In those cases we read every block we
         * can.  Then the parity-update is certain to have enough to
         * work with.
         * This can only be a problem when we need to write something,
         * and some device has failed.  If either of those tests
         * fail we need look no further.
         */
        if (!s->failed || !s->to_write)
                return 0;

        if (test_bit(R5_Insync, &dev->flags) &&
            !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                /* Pre-reads at not permitted until after short delay
                 * to gather multiple requests.  However if this
                 * device is no Insync, the block could only be be computed
                 * and there is no need to delay that.
                 */
                return 0;

        for (i = 0; i < s->failed && i < 2; i++) {
                if (fdev[i]->towrite &&
                    !test_bit(R5_UPTODATE, &fdev[i]->flags) &&
                    !test_bit(R5_OVERWRITE, &fdev[i]->flags))
                        /* If we have a partial write to a failed
                         * device, then we will need to reconstruct
                         * the content of that device, so all other
                         * devices must be read.
                         */
                        return 1;
        }

        /* If we are forced to do a reconstruct-write, either because
         * the current RAID6 implementation only supports that, or
         * or because parity cannot be trusted and we are currently
         * recovering it, there is extra need to be careful.
         * If one of the devices that we would need to read, because
         * it is not being overwritten (and maybe not written at all)
         * is missing/faulty, then we need to read everything we can.
         */
        if (sh->raid_conf->level != 6 &&
            sh->sector < sh->raid_conf->mddev->recovery_cp)
                /* reconstruct-write isn't being forced */
                return 0;
        for (i = 0; i < s->failed && i < 2; i++) {
                if (s->failed_num[i] != sh->pd_idx &&
                    s->failed_num[i] != sh->qd_idx &&
                    !test_bit(R5_UPTODATE, &fdev[i]->flags) &&
                    !test_bit(R5_OVERWRITE, &fdev[i]->flags))
                        return 1;
        }

        return 0;
}

static int fetch_block(struct stripe_head *sh, struct stripe_head_state *s,
                       int disk_idx, int disks)
{
        struct r5dev *dev = &sh->dev[disk_idx];

        /* is the data in this block needed, and can we get it? */
        if (need_this_block(sh, s, disk_idx, disks)) {
                /* we would like to get this block, possibly by computing it,
                 * otherwise read it if the backing disk is insync
                 */
                BUG_ON(test_bit(R5_Wantcompute, &dev->flags));
                BUG_ON(test_bit(R5_Wantread, &dev->flags));
                BUG_ON(sh->batch_head);
                if ((s->uptodate == disks - 1) &&
                    (s->failed && (disk_idx == s->failed_num[0] ||
                                   disk_idx == s->failed_num[1]))) {
                        /* have disk failed, and we're requested to fetch it;
                         * do compute it
                         */
                        pr_debug("Computing stripe %llu block %d\n",
                               (unsigned long long)sh->sector, disk_idx);
                        set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                        set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                        set_bit(R5_Wantcompute, &dev->flags);
                        sh->ops.target = disk_idx;
                        sh->ops.target2 = -1; /* no 2nd target */
                        s->req_compute = 1;
                        /* Careful: from this point on 'uptodate' is in the eye
                         * of raid_run_ops which services 'compute' operations
                         * before writes. R5_Wantcompute flags a block that will
                         * be R5_UPTODATE by the time it is needed for a
                         * subsequent operation.
                         */
                        s->uptodate++;
                        return 1;
                } else if (s->uptodate == disks-2 && s->failed >= 2) {
                        /* Computing 2-failure is *very* expensive; only
                         * do it if failed >= 2
                         */
                        int other;
                        for (other = disks; other--; ) {
                                if (other == disk_idx)
                                        continue;
                                if (!test_bit(R5_UPTODATE,
                                      &sh->dev[other].flags))
                                        break;
                        }
                        BUG_ON(other < 0);
                        pr_debug("Computing stripe %llu blocks %d,%d\n",
                               (unsigned long long)sh->sector,
                               disk_idx, other);
                        set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                        set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                        set_bit(R5_Wantcompute, &sh->dev[disk_idx].flags);
                        set_bit(R5_Wantcompute, &sh->dev[other].flags);
                        sh->ops.target = disk_idx;
                        sh->ops.target2 = other;
                        s->uptodate += 2;
                        s->req_compute = 1;
                        return 1;
                } else if (test_bit(R5_Insync, &dev->flags)) {
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantread, &dev->flags);
                        s->locked++;
                        pr_debug("Reading block %d (sync=%d)\n",
                                disk_idx, s->syncing);
                }
        }

        return 0;
}

/**
 * handle_stripe_fill - read or compute data to satisfy pending requests.
 */
static void handle_stripe_fill(struct stripe_head *sh,
                               struct stripe_head_state *s,
                               int disks)
{
        int i;

        /* look for blocks to read/compute, skip this if a compute
         * is already in flight, or if the stripe contents are in the
         * midst of changing due to a write
         */
        if (!test_bit(STRIPE_COMPUTE_RUN, &sh->state) && !sh->check_state &&
            !sh->reconstruct_state)
                for (i = disks; i--; )
                        if (fetch_block(sh, s, i, disks))
                                break;
        set_bit(STRIPE_HANDLE, &sh->state);
}

static void break_stripe_batch_list(struct stripe_head *head_sh,
                                    unsigned long handle_flags);
/* handle_stripe_clean_event
 * any written block on an uptodate or failed drive can be returned.
 * Note that if we 'wrote' to a failed drive, it will be UPTODATE, but
 * never LOCKED, so we don't need to test 'failed' directly.
 */
static void handle_stripe_clean_event(struct r5conf *conf,
        struct stripe_head *sh, int disks, struct bio_list *return_bi)
{
        int i;
        struct r5dev *dev;
        int discard_pending = 0;
        struct stripe_head *head_sh = sh;
        bool do_endio = false;

        for (i = disks; i--; )
                if (sh->dev[i].written) {
                        dev = &sh->dev[i];
                        if (!test_bit(R5_LOCKED, &dev->flags) &&
                            (test_bit(R5_UPTODATE, &dev->flags) ||
                             test_bit(R5_Discard, &dev->flags) ||
                             test_bit(R5_SkipCopy, &dev->flags))) {
                                /* We can return any write requests */
                                struct bio *wbi, *wbi2;
                                pr_debug("Return write for disc %d\n", i);
                                if (test_and_clear_bit(R5_Discard, &dev->flags))
                                        clear_bit(R5_UPTODATE, &dev->flags);
                                if (test_and_clear_bit(R5_SkipCopy, &dev->flags)) {
                                        WARN_ON(test_bit(R5_UPTODATE, &dev->flags));
                                }
                                do_endio = true;

returnbi:
                                dev->page = dev->orig_page;
                                wbi = dev->written;
                                dev->written = NULL;
                                while (wbi && wbi->bi_iter.bi_sector <
                                        dev->sector + STRIPE_SECTORS) {
                                        wbi2 = r5_next_bio(wbi, dev->sector);
                                        if (!raid5_dec_bi_active_stripes(wbi)) {
                                                md_write_end(conf->mddev);
                                                bio_list_add(return_bi, wbi);
                                        }
                                        wbi = wbi2;
                                }
                                bitmap_endwrite(conf->mddev->bitmap, sh->sector,
                                                STRIPE_SECTORS,
                                         !test_bit(STRIPE_DEGRADED, &sh->state),
                                                0);
                                if (head_sh->batch_head) {
                                        sh = list_first_entry(&sh->batch_list,
                                                              struct stripe_head,
                                                              batch_list);
                                        if (sh != head_sh) {
                                                dev = &sh->dev[i];
                                                goto returnbi;
                                        }
                                }
                                sh = head_sh;
                                dev = &sh->dev[i];
                        } else if (test_bit(R5_Discard, &dev->flags))
                                discard_pending = 1;
                }

        r5l_stripe_write_finished(sh);

        if (!discard_pending &&
            test_bit(R5_Discard, &sh->dev[sh->pd_idx].flags)) {
                int hash;
                clear_bit(R5_Discard, &sh->dev[sh->pd_idx].flags);
                clear_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags);
                if (sh->qd_idx >= 0) {
                        clear_bit(R5_Discard, &sh->dev[sh->qd_idx].flags);
                        clear_bit(R5_UPTODATE, &sh->dev[sh->qd_idx].flags);
                }
                /* now that discard is done we can proceed with any sync */
                clear_bit(STRIPE_DISCARD, &sh->state);
                /*
                 * SCSI discard will change some bio fields and the stripe has
                 * no updated data, so remove it from hash list and the stripe
                 * will be reinitialized
                 */
unhash:
                hash = sh->hash_lock_index;
                spin_lock_irq(conf->hash_locks + hash);
                remove_hash(sh);
                spin_unlock_irq(conf->hash_locks + hash);
                if (head_sh->batch_head) {
                        sh = list_first_entry(&sh->batch_list,
                                              struct stripe_head, batch_list);
                        if (sh != head_sh)
                                        goto unhash;
                }
                sh = head_sh;

                if (test_bit(STRIPE_SYNC_REQUESTED, &sh->state))
                        set_bit(STRIPE_HANDLE, &sh->state);

        }

        if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))
                if (atomic_dec_and_test(&conf->pending_full_writes))
                        md_wakeup_thread(conf->mddev->thread);

        if (head_sh->batch_head && do_endio)
                break_stripe_batch_list(head_sh, STRIPE_EXPAND_SYNC_FLAGS);
}

static void handle_stripe_dirtying(struct r5conf *conf,
                                   struct stripe_head *sh,
                                   struct stripe_head_state *s,
                                   int disks)
{
        int rmw = 0, rcw = 0, i;
        sector_t recovery_cp = conf->mddev->recovery_cp;

        /* Check whether resync is now happening or should start.
         * If yes, then the array is dirty (after unclean shutdown or
         * initial creation), so parity in some stripes might be inconsistent.
         * In this case, we need to always do reconstruct-write, to ensure
         * that in case of drive failure or read-error correction, we
         * generate correct data from the parity.
         */
        if (conf->rmw_level == PARITY_DISABLE_RMW ||
            (recovery_cp < MaxSector && sh->sector >= recovery_cp &&
             s->failed == 0)) {
                /* Calculate the real rcw later - for now make it
                 * look like rcw is cheaper
                 */
                rcw = 1; rmw = 2;
                pr_debug("force RCW rmw_level=%u, recovery_cp=%llu sh->sector=%llu\n",
                         conf->rmw_level, (unsigned long long)recovery_cp,
                         (unsigned long long)sh->sector);
        } else for (i = disks; i--; ) {
                /* would I have to read this buffer for read_modify_write */
                struct r5dev *dev = &sh->dev[i];
                if ((dev->towrite || i == sh->pd_idx || i == sh->qd_idx) &&
                    !test_bit(R5_LOCKED, &dev->flags) &&
                    !(test_bit(R5_UPTODATE, &dev->flags) ||
                      test_bit(R5_Wantcompute, &dev->flags))) {
                        if (test_bit(R5_Insync, &dev->flags))
                                rmw++;
                        else
                                rmw += 2*disks;  /* cannot read it */
                }
                /* Would I have to read this buffer for reconstruct_write */
                if (!test_bit(R5_OVERWRITE, &dev->flags) &&
                    i != sh->pd_idx && i != sh->qd_idx &&
                    !test_bit(R5_LOCKED, &dev->flags) &&
                    !(test_bit(R5_UPTODATE, &dev->flags) ||
                    test_bit(R5_Wantcompute, &dev->flags))) {
                        if (test_bit(R5_Insync, &dev->flags))
                                rcw++;
                        else
                                rcw += 2*disks;
                }
        }
        pr_debug("for sector %llu, rmw=%d rcw=%d\n",
                (unsigned long long)sh->sector, rmw, rcw);
        set_bit(STRIPE_HANDLE, &sh->state);
        if ((rmw < rcw || (rmw == rcw && conf->rmw_level == PARITY_PREFER_RMW)) && rmw > 0) {
                /* prefer read-modify-write, but need to get some data */
                if (conf->mddev->queue)
                        blk_add_trace_msg(conf->mddev->queue,
                                          "raid5 rmw %llu %d",
                                          (unsigned long long)sh->sector, rmw);
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if ((dev->towrite || i == sh->pd_idx || i == sh->qd_idx) &&
                            !test_bit(R5_LOCKED, &dev->flags) &&
                            !(test_bit(R5_UPTODATE, &dev->flags) ||
                            test_bit(R5_Wantcompute, &dev->flags)) &&
                            test_bit(R5_Insync, &dev->flags)) {
                                if (test_bit(STRIPE_PREREAD_ACTIVE,
                                             &sh->state)) {
                                        pr_debug("Read_old block %d for r-m-w\n",
                                                 i);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        set_bit(R5_Wantread, &dev->flags);
                                        s->locked++;
                                } else {
                                        set_bit(STRIPE_DELAYED, &sh->state);
                                        set_bit(STRIPE_HANDLE, &sh->state);
                                }
                        }
                }
        }
        if ((rcw < rmw || (rcw == rmw && conf->rmw_level != PARITY_PREFER_RMW)) && rcw > 0) {
                /* want reconstruct write, but need to get some data */
                int qread =0;
                rcw = 0;
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (!test_bit(R5_OVERWRITE, &dev->flags) &&
                            i != sh->pd_idx && i != sh->qd_idx &&
                            !test_bit(R5_LOCKED, &dev->flags) &&
                            !(test_bit(R5_UPTODATE, &dev->flags) ||
                              test_bit(R5_Wantcompute, &dev->flags))) {
                                rcw++;
                                if (test_bit(R5_Insync, &dev->flags) &&
                                    test_bit(STRIPE_PREREAD_ACTIVE,
                                             &sh->state)) {
                                        pr_debug("Read_old block "
                                                "%d for Reconstruct\n", i);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        set_bit(R5_Wantread, &dev->flags);
                                        s->locked++;
                                        qread++;
                                } else {
                                        set_bit(STRIPE_DELAYED, &sh->state);
                                        set_bit(STRIPE_HANDLE, &sh->state);
                                }
                        }
                }
                if (rcw && conf->mddev->queue)
                        blk_add_trace_msg(conf->mddev->queue, "raid5 rcw %llu %d %d %d",
                                          (unsigned long long)sh->sector,
                                          rcw, qread, test_bit(STRIPE_DELAYED, &sh->state));
        }

        if (rcw > disks && rmw > disks &&
            !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                set_bit(STRIPE_DELAYED, &sh->state);

        /* now if nothing is locked, and if we have enough data,
         * we can start a write request
         */
        /* since handle_stripe can be called at any time we need to handle the
         * case where a compute block operation has been submitted and then a
         * subsequent call wants to start a write request.  raid_run_ops only
         * handles the case where compute block and reconstruct are requested
         * simultaneously.  If this is not the case then new writes need to be
         * held off until the compute completes.
         */
        if ((s->req_compute || !test_bit(STRIPE_COMPUTE_RUN, &sh->state)) &&
            (s->locked == 0 && (rcw == 0 || rmw == 0) &&
            !test_bit(STRIPE_BIT_DELAY, &sh->state)))
                schedule_reconstruction(sh, s, rcw == 0, 0);
}

static void handle_parity_checks5(struct r5conf *conf, struct stripe_head *sh,
                                struct stripe_head_state *s, int disks)
{
        struct r5dev *dev = NULL;

        BUG_ON(sh->batch_head);
        set_bit(STRIPE_HANDLE, &sh->state);

        switch (sh->check_state) {
        case check_state_idle:
                /* start a new check operation if there are no failures */
                if (s->failed == 0) {
                        BUG_ON(s->uptodate != disks);
                        sh->check_state = check_state_run;
                        set_bit(STRIPE_OP_CHECK, &s->ops_request);
                        clear_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags);
                        s->uptodate--;
                        break;
                }
                dev = &sh->dev[s->failed_num[0]];
                /* fall through */
        case check_state_compute_result:
                sh->check_state = check_state_idle;
                if (!dev)
                        dev = &sh->dev[sh->pd_idx];

                /* check that a write has not made the stripe insync */
                if (test_bit(STRIPE_INSYNC, &sh->state))
                        break;

                /* either failed parity check, or recovery is happening */
                BUG_ON(!test_bit(R5_UPTODATE, &dev->flags));
                BUG_ON(s->uptodate != disks);

                set_bit(R5_LOCKED, &dev->flags);
                s->locked++;
                set_bit(R5_Wantwrite, &dev->flags);

                clear_bit(STRIPE_DEGRADED, &sh->state);
                set_bit(STRIPE_INSYNC, &sh->state);
                break;
        case check_state_run:
                break; /* we will be called again upon completion */
        case check_state_check_result:
                sh->check_state = check_state_idle;

                /* if a failure occurred during the check operation, leave
                 * STRIPE_INSYNC not set and let the stripe be handled again
                 */
                if (s->failed)
                        break;

                /* handle a successful check operation, if parity is correct
                 * we are done.  Otherwise update the mismatch count and repair
                 * parity if !MD_RECOVERY_CHECK
                 */
                if ((sh->ops.zero_sum_result & SUM_CHECK_P_RESULT) == 0)
                        /* parity is correct (on disc,
                         * not in buffer any more)
                         */
                        set_bit(STRIPE_INSYNC, &sh->state);
                else {
                        atomic64_add(STRIPE_SECTORS, &conf->mddev->resync_mismatches);
                        if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
                                /* don't try to repair!! */
                                set_bit(STRIPE_INSYNC, &sh->state);
                        else {
                                sh->check_state = check_state_compute_run;
                                set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                                set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                                set_bit(R5_Wantcompute,
                                        &sh->dev[sh->pd_idx].flags);
                                sh->ops.target = sh->pd_idx;
                                sh->ops.target2 = -1;
                                s->uptodate++;
                        }
                }
                break;
        case check_state_compute_run:
                break;
        default:
                printk(KERN_ERR "%s: unknown check_state: %d sector: %llu\n",
                       __func__, sh->check_state,
                       (unsigned long long) sh->sector);
                BUG();
        }
}

static void handle_parity_checks6(struct r5conf *conf, struct stripe_head *sh,
                                  struct stripe_head_state *s,
                                  int disks)
{
        int pd_idx = sh->pd_idx;
        int qd_idx = sh->qd_idx;
        struct r5dev *dev;

        BUG_ON(sh->batch_head);
        set_bit(STRIPE_HANDLE, &sh->state);

        BUG_ON(s->failed > 2);

        /* Want to check and possibly repair P and Q.
         * However there could be one 'failed' device, in which
         * case we can only check one of them, possibly using the
         * other to generate missing data
         */

        switch (sh->check_state) {
        case check_state_idle:
                /* start a new check operation if there are < 2 failures */
                if (s->failed == s->q_failed) {
                        /* The only possible failed device holds Q, so it
                         * makes sense to check P (If anything else were failed,
                         * we would have used P to recreate it).
                         */
                        sh->check_state = check_state_run;
                }
                if (!s->q_failed && s->failed < 2) {
                        /* Q is not failed, and we didn't use it to generate
                         * anything, so it makes sense to check it
                         */
                        if (sh->check_state == check_state_run)
                                sh->check_state = check_state_run_pq;
                        else
                                sh->check_state = check_state_run_q;
                }

                /* discard potentially stale zero_sum_result */
                sh->ops.zero_sum_result = 0;

                if (sh->check_state == check_state_run) {
                        /* async_xor_zero_sum destroys the contents of P */
                        clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
                        s->uptodate--;
                }
                if (sh->check_state >= check_state_run &&
                    sh->check_state <= check_state_run_pq) {
                        /* async_syndrome_zero_sum preserves P and Q, so
                         * no need to mark them !uptodate here
                         */
                        set_bit(STRIPE_OP_CHECK, &s->ops_request);
                        break;
                }

                /* we have 2-disk failure */
                BUG_ON(s->failed != 2);
                /* fall through */
        case check_state_compute_result:
                sh->check_state = check_state_idle;

                /* check that a write has not made the stripe insync */
                if (test_bit(STRIPE_INSYNC, &sh->state))
                        break;

                /* now write out any block on a failed drive,
                 * or P or Q if they were recomputed
                 */
                BUG_ON(s->uptodate < disks - 1); /* We don't need Q to recover */
                if (s->failed == 2) {
                        dev = &sh->dev[s->failed_num[1]];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                if (s->failed >= 1) {
                        dev = &sh->dev[s->failed_num[0]];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                if (sh->ops.zero_sum_result & SUM_CHECK_P_RESULT) {
                        dev = &sh->dev[pd_idx];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                if (sh->ops.zero_sum_result & SUM_CHECK_Q_RESULT) {
                        dev = &sh->dev[qd_idx];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                clear_bit(STRIPE_DEGRADED, &sh->state);

                set_bit(STRIPE_INSYNC, &sh->state);
                break;
        case check_state_run:
        case check_state_run_q:
        case check_state_run_pq:
                break; /* we will be called again upon completion */
        case check_state_check_result:
                sh->check_state = check_state_idle;

                /* handle a successful check operation, if parity is correct
                 * we are done.  Otherwise update the mismatch count and repair
                 * parity if !MD_RECOVERY_CHECK
                 */
                if (sh->ops.zero_sum_result == 0) {
                        /* both parities are correct */
                        if (!s->failed)
                                set_bit(STRIPE_INSYNC, &sh->state);
                        else {
                                /* in contrast to the raid5 case we can validate
                                 * parity, but still have a failure to write
                                 * back
                                 */
                                sh->check_state = check_state_compute_result;
                                /* Returning at this point means that we may go
                                 * off and bring p and/or q uptodate again so
                                 * we make sure to check zero_sum_result again
                                 * to verify if p or q need writeback
                                 */
                        }
                } else {
                        atomic64_add(STRIPE_SECTORS, &conf->mddev->resync_mismatches);
                        if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
                                /* don't try to repair!! */
                                set_bit(STRIPE_INSYNC, &sh->state);
                        else {
                                int *target = &sh->ops.target;

                                sh->ops.target = -1;
                                sh->ops.target2 = -1;
                                sh->check_state = check_state_compute_run;
                                set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                                set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                                if (sh->ops.zero_sum_result & SUM_CHECK_P_RESULT) {
                                        set_bit(R5_Wantcompute,
                                                &sh->dev[pd_idx].flags);
                                        *target = pd_idx;
                                        target = &sh->ops.target2;
                                        s->uptodate++;
                                }
                                if (sh->ops.zero_sum_result & SUM_CHECK_Q_RESULT) {
                                        set_bit(R5_Wantcompute,
                                                &sh->dev[qd_idx].flags);
                                        *target = qd_idx;
                                        s->uptodate++;
                                }
                        }
                }
                break;
        case check_state_compute_run:
                break;
        default:
                printk(KERN_ERR "%s: unknown check_state: %d sector: %llu\n",
                       __func__, sh->check_state,
                       (unsigned long long) sh->sector);
                BUG();
        }
}

static void handle_stripe_expansion(struct r5conf *conf, struct stripe_head *sh)
{
        int i;

        /* We have read all the blocks in this stripe and now we need to
         * copy some of them into a target stripe for expand.
         */
        struct dma_async_tx_descriptor *tx = NULL;
        BUG_ON(sh->batch_head);
        clear_bit(STRIPE_EXPAND_SOURCE, &sh->state);
        for (i = 0; i < sh->disks; i++)
                if (i != sh->pd_idx && i != sh->qd_idx) {
                        int dd_idx, j;
                        struct stripe_head *sh2;
                        struct async_submit_ctl submit;

                        sector_t bn = raid5_compute_blocknr(sh, i, 1);
                        sector_t s = raid5_compute_sector(conf, bn, 0,
                                                          &dd_idx, NULL);
                        sh2 = raid5_get_active_stripe(conf, s, 0, 1, 1);
                        if (sh2 == NULL)
                                /* so far only the early blocks of this stripe
                                 * have been requested.  When later blocks
                                 * get requested, we will try again
                                 */
                                continue;
                        if (!test_bit(STRIPE_EXPANDING, &sh2->state) ||
                           test_bit(R5_Expanded, &sh2->dev[dd_idx].flags)) {
                                /* must have already done this block */
                                raid5_release_stripe(sh2);
                                continue;
                        }

                        /* place all the copies on one channel */
                        init_async_submit(&submit, 0, tx, NULL, NULL, NULL);
                        tx = async_memcpy(sh2->dev[dd_idx].page,
                                          sh->dev[i].page, 0, 0, STRIPE_SIZE,
                                          &submit);

                        set_bit(R5_Expanded, &sh2->dev[dd_idx].flags);
                        set_bit(R5_UPTODATE, &sh2->dev[dd_idx].flags);
                        for (j = 0; j < conf->raid_disks; j++)
                                if (j != sh2->pd_idx &&
                                    j != sh2->qd_idx &&
                                    !test_bit(R5_Expanded, &sh2->dev[j].flags))
                                        break;
                        if (j == conf->raid_disks) {
                                set_bit(STRIPE_EXPAND_READY, &sh2->state);
                                set_bit(STRIPE_HANDLE, &sh2->state);
                        }
                        raid5_release_stripe(sh2);

                }
        /* done submitting copies, wait for them to complete */
        async_tx_quiesce(&tx);
}

/*
 * handle_stripe - do things to a stripe.
 *
 * We lock the stripe by setting STRIPE_ACTIVE and then examine the
 * state of various bits to see what needs to be done.
 * Possible results:
 *    return some read requests which now have data
 *    return some write requests which are safely on storage
 *    schedule a read on some buffers
 *    schedule a write of some buffers
 *    return confirmation of parity correctness
 *
 */

static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s)
{
        struct r5conf *conf = sh->raid_conf;
        int disks = sh->disks;
        struct r5dev *dev;
        int i;
        int do_recovery = 0;

        memset(s, 0, sizeof(*s));

        s->expanding = test_bit(STRIPE_EXPAND_SOURCE, &sh->state) && !sh->batch_head;
        s->expanded = test_bit(STRIPE_EXPAND_READY, &sh->state) && !sh->batch_head;
        s->failed_num[0] = -1;
        s->failed_num[1] = -1;
        s->log_failed = r5l_log_disk_error(conf);

        /* Now to look around and see what can be done */
        rcu_read_lock();
        for (i=disks; i--; ) {
                struct md_rdev *rdev;
                sector_t first_bad;
                int bad_sectors;
                int is_bad = 0;

                dev = &sh->dev[i];

                pr_debug("check %d: state 0x%lx read %p write %p written %p\n",
                         i, dev->flags,
                         dev->toread, dev->towrite, dev->written);
                /* maybe we can reply to a read
                 *
                 * new wantfill requests are only permitted while
                 * ops_complete_biofill is guaranteed to be inactive
                 */
                if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread &&
                    !test_bit(STRIPE_BIOFILL_RUN, &sh->state))
                        set_bit(R5_Wantfill, &dev->flags);

                /* now count some things */
                if (test_bit(R5_LOCKED, &dev->flags))
                        s->locked++;
                if (test_bit(R5_UPTODATE, &dev->flags))
                        s->uptodate++;
                if (test_bit(R5_Wantcompute, &dev->flags)) {
                        s->compute++;
                        BUG_ON(s->compute > 2);
                }

                if (test_bit(R5_Wantfill, &dev->flags))
                        s->to_fill++;
                else if (dev->toread)
                        s->to_read++;
                if (dev->towrite) {
                        s->to_write++;
                        if (!test_bit(R5_OVERWRITE, &dev->flags))
                                s->non_overwrite++;
                }
                if (dev->written)
                        s->written++;
                /* Prefer to use the replacement for reads, but only
                 * if it is recovered enough and has no bad blocks.
                 */
                rdev = rcu_dereference(conf->disks[i].replacement);
                if (rdev && !test_bit(Faulty, &rdev->flags) &&
                    rdev->recovery_offset >= sh->sector + STRIPE_SECTORS &&
                    !is_badblock(rdev, sh->sector, STRIPE_SECTORS,
                                 &first_bad, &bad_sectors))
                        set_bit(R5_ReadRepl, &dev->flags);
                else {
                        if (rdev && !test_bit(Faulty, &rdev->flags))
                                set_bit(R5_NeedReplace, &dev->flags);
                        else
                                clear_bit(R5_NeedReplace, &dev->flags);
                        rdev = rcu_dereference(conf->disks[i].rdev);
                        clear_bit(R5_ReadRepl, &dev->flags);
                }
                if (rdev && test_bit(Faulty, &rdev->flags))
                        rdev = NULL;
                if (rdev) {
                        is_bad = is_badblock(rdev, sh->sector, STRIPE_SECTORS,
                                             &first_bad, &bad_sectors);
                        if (s->blocked_rdev == NULL
                            && (test_bit(Blocked, &rdev->flags)
                                || is_bad < 0)) {
                                if (is_bad < 0)
                                        set_bit(BlockedBadBlocks,
                                                &rdev->flags);
                                s->blocked_rdev = rdev;
                                atomic_inc(&rdev->nr_pending);
                        }
                }
                clear_bit(R5_Insync, &dev->flags);
                if (!rdev)
                        /* Not in-sync */;
                else if (is_bad) {
                        /* also not in-sync */
                        if (!test_bit(WriteErrorSeen, &rdev->flags) &&
                            test_bit(R5_UPTODATE, &dev->flags)) {
                                /* treat as in-sync, but with a read error
                                 * which we can now try to correct
                                 */
                                set_bit(R5_Insync, &dev->flags);
                                set_bit(R5_ReadError, &dev->flags);
                        }
                } else if (test_bit(In_sync, &rdev->flags))
                        set_bit(R5_Insync, &dev->flags);
                else if (sh->sector + STRIPE_SECTORS <= rdev->recovery_offset)
                        /* in sync if before recovery_offset */
                        set_bit(R5_Insync, &dev->flags);
                else if (test_bit(R5_UPTODATE, &dev->flags) &&
                         test_bit(R5_Expanded, &dev->flags))
                        /* If we've reshaped into here, we assume it is Insync.
                         * We will shortly update recovery_offset to make
                         * it official.
                         */
                        set_bit(R5_Insync, &dev->flags);

                if (test_bit(R5_WriteError, &dev->flags)) {
                        /* This flag does not apply to '.replacement'
                         * only to .rdev, so make sure to check that*/
                        struct md_rdev *rdev2 = rcu_dereference(
                                conf->disks[i].rdev);
                        if (rdev2 == rdev)
                                clear_bit(R5_Insync, &dev->flags);
                        if (rdev2 && !test_bit(Faulty, &rdev2->flags)) {
                                s->handle_bad_blocks = 1;
                                atomic_inc(&rdev2->nr_pending);
                        } else
                                clear_bit(R5_WriteError, &dev->flags);
                }
                if (test_bit(R5_MadeGood, &dev->flags)) {
                        /* This flag does not apply to '.replacement'
                         * only to .rdev, so make sure to check that*/
                        struct md_rdev *rdev2 = rcu_dereference(
                                conf->disks[i].rdev);
                        if (rdev2 && !test_bit(Faulty, &rdev2->flags)) {
                                s->handle_bad_blocks = 1;
                                atomic_inc(&rdev2->nr_pending);
                        } else
                                clear_bit(R5_MadeGood, &dev->flags);
                }
                if (test_bit(R5_MadeGoodRepl, &dev->flags)) {
                        struct md_rdev *rdev2 = rcu_dereference(
                                conf->disks[i].replacement);
                        if (rdev2 && !test_bit(Faulty, &rdev2->flags)) {
                                s->handle_bad_blocks = 1;
                                atomic_inc(&rdev2->nr_pending);
                        } else
                                clear_bit(R5_MadeGoodRepl, &dev->flags);
                }
                if (!test_bit(R5_Insync, &dev->flags)) {
                        /* The ReadError flag will just be confusing now */
                        clear_bit(R5_ReadError, &dev->flags);
                        clear_bit(R5_ReWrite, &dev->flags);
                }
                if (test_bit(R5_ReadError, &dev->flags))
                        clear_bit(R5_Insync, &dev->flags);
                if (!test_bit(R5_Insync, &dev->flags)) {
                        if (s->failed < 2)
                                s->failed_num[s->failed] = i;
                        s->failed++;
                        if (rdev && !test_bit(Faulty, &rdev->flags))
                                do_recovery = 1;
                }
        }
        if (test_bit(STRIPE_SYNCING, &sh->state)) {
                /* If there is a failed device being replaced,
                 *     we must be recovering.
                 * else if we are after recovery_cp, we must be syncing
                 * else if MD_RECOVERY_REQUESTED is set, we also are syncing.
                 * else we can only be replacing
                 * sync and recovery both need to read all devices, and so
                 * use the same flag.
                 */
                if (do_recovery ||
                    sh->sector >= conf->mddev->recovery_cp ||
                    test_bit(MD_RECOVERY_REQUESTED, &(conf->mddev->recovery)))
                        s->syncing = 1;
                else
                        s->replacing = 1;
        }
        rcu_read_unlock();
}

static int clear_batch_ready(struct stripe_head *sh)
{
        /* Return '1' if this is a member of batch, or
         * '0' if it is a lone stripe or a head which can now be
         * handled.
         */
        struct stripe_head *tmp;
        if (!test_and_clear_bit(STRIPE_BATCH_READY, &sh->state))
                return (sh->batch_head && sh->batch_head != sh);
        spin_lock(&sh->stripe_lock);
        if (!sh->batch_head) {
                spin_unlock(&sh->stripe_lock);
                return 0;
        }

        /*
         * this stripe could be added to a batch list before we check
         * BATCH_READY, skips it
         */
        if (sh->batch_head != sh) {
                spin_unlock(&sh->stripe_lock);
                return 1;
        }
        spin_lock(&sh->batch_lock);
        list_for_each_entry(tmp, &sh->batch_list, batch_list)
                clear_bit(STRIPE_BATCH_READY, &tmp->state);
        spin_unlock(&sh->batch_lock);
        spin_unlock(&sh->stripe_lock);

        /*
         * BATCH_READY is cleared, no new stripes can be added.
         * batch_list can be accessed without lock
         */
        return 0;
}

static void break_stripe_batch_list(struct stripe_head *head_sh,
                                    unsigned long handle_flags)
{
        struct stripe_head *sh, *next;
        int i;
        int do_wakeup = 0;

        list_for_each_entry_safe(sh, next, &head_sh->batch_list, batch_list) {

                list_del_init(&sh->batch_list);

                WARN_ONCE(sh->state & ((1 << STRIPE_ACTIVE) |
                                          (1 << STRIPE_SYNCING) |
                                          (1 << STRIPE_REPLACED) |
                                          (1 << STRIPE_DELAYED) |
                                          (1 << STRIPE_BIT_DELAY) |
                                          (1 << STRIPE_FULL_WRITE) |
                                          (1 << STRIPE_BIOFILL_RUN) |
                                          (1 << STRIPE_COMPUTE_RUN)  |
                                          (1 << STRIPE_OPS_REQ_PENDING) |
                                          (1 << STRIPE_DISCARD) |
                                          (1 << STRIPE_BATCH_READY) |
                                          (1 << STRIPE_BATCH_ERR) |
                                          (1 << STRIPE_BITMAP_PENDING)),
                        "stripe state: %lx\n", sh->state);
                WARN_ONCE(head_sh->state & ((1 << STRIPE_DISCARD) |
                                              (1 << STRIPE_REPLACED)),
                        "head stripe state: %lx\n", head_sh->state);

                set_mask_bits(&sh->state, ~(STRIPE_EXPAND_SYNC_FLAGS |
                                            (1 << STRIPE_PREREAD_ACTIVE) |
                                            (1 << STRIPE_DEGRADED)),
                              head_sh->state & (1 << STRIPE_INSYNC));

                sh->check_state = head_sh->check_state;
                sh->reconstruct_state = head_sh->reconstruct_state;
                for (i = 0; i < sh->disks; i++) {
                        if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                                do_wakeup = 1;
                        sh->dev[i].flags = head_sh->dev[i].flags &
                                (~((1 << R5_WriteError) | (1 << R5_Overlap)));
                }
                spin_lock_irq(&sh->stripe_lock);
                sh->batch_head = NULL;
                spin_unlock_irq(&sh->stripe_lock);
                if (handle_flags == 0 ||
                    sh->state & handle_flags)
                        set_bit(STRIPE_HANDLE, &sh->state);
                raid5_release_stripe(sh);
        }
        spin_lock_irq(&head_sh->stripe_lock);
        head_sh->batch_head = NULL;
        spin_unlock_irq(&head_sh->stripe_lock);
        for (i = 0; i < head_sh->disks; i++)
                if (test_and_clear_bit(R5_Overlap, &head_sh->dev[i].flags))
                        do_wakeup = 1;
        if (head_sh->state & handle_flags)
                set_bit(STRIPE_HANDLE, &head_sh->state);

        if (do_wakeup)
                wake_up(&head_sh->raid_conf->wait_for_overlap);
}

static void handle_stripe(struct stripe_head *sh)
{
        struct stripe_head_state s;
        struct r5conf *conf = sh->raid_conf;
        int i;
        int prexor;
        int disks = sh->disks;
        struct r5dev *pdev, *qdev;

        clear_bit(STRIPE_HANDLE, &sh->state);
        if (test_and_set_bit_lock(STRIPE_ACTIVE, &sh->state)) {
                /* already being handled, ensure it gets handled
                 * again when current action finishes */
                set_bit(STRIPE_HANDLE, &sh->state);
                return;
        }

        if (clear_batch_ready(sh) ) {
                clear_bit_unlock(STRIPE_ACTIVE, &sh->state);
                return;
        }

        if (test_and_clear_bit(STRIPE_BATCH_ERR, &sh->state))
                break_stripe_batch_list(sh, 0);

        if (test_bit(STRIPE_SYNC_REQUESTED, &sh->state) && !sh->batch_head) {
                spin_lock(&sh->stripe_lock);
                /* Cannot process 'sync' concurrently with 'discard' */
                if (!test_bit(STRIPE_DISCARD, &sh->state) &&
                    test_and_clear_bit(STRIPE_SYNC_REQUESTED, &sh->state)) {
                        set_bit(STRIPE_SYNCING, &sh->state);
                        clear_bit(STRIPE_INSYNC, &sh->state);
                        clear_bit(STRIPE_REPLACED, &sh->state);
                }
                spin_unlock(&sh->stripe_lock);
        }
        clear_bit(STRIPE_DELAYED, &sh->state);

        pr_debug("handling stripe %llu, state=%#lx cnt=%d, "
                "pd_idx=%d, qd_idx=%d\n, check:%d, reconstruct:%d\n",
               (unsigned long long)sh->sector, sh->state,
               atomic_read(&sh->count), sh->pd_idx, sh->qd_idx,
               sh->check_state, sh->reconstruct_state);

        analyse_stripe(sh, &s);

        if (test_bit(STRIPE_LOG_TRAPPED, &sh->state))
                goto finish;

        if (s.handle_bad_blocks) {
                set_bit(STRIPE_HANDLE, &sh->state);
                goto finish;
        }

        if (unlikely(s.blocked_rdev)) {
                if (s.syncing || s.expanding || s.expanded ||
                    s.replacing || s.to_write || s.written) {
                        set_bit(STRIPE_HANDLE, &sh->state);
                        goto finish;
                }
                /* There is nothing for the blocked_rdev to block */
                rdev_dec_pending(s.blocked_rdev, conf->mddev);
                s.blocked_rdev = NULL;
        }

        if (s.to_fill && !test_bit(STRIPE_BIOFILL_RUN, &sh->state)) {
                set_bit(STRIPE_OP_BIOFILL, &s.ops_request);
                set_bit(STRIPE_BIOFILL_RUN, &sh->state);
        }

        pr_debug("locked=%d uptodate=%d to_read=%d"
               " to_write=%d failed=%d failed_num=%d,%d\n",
               s.locked, s.uptodate, s.to_read, s.to_write, s.failed,
               s.failed_num[0], s.failed_num[1]);
        /* check if the array has lost more than max_degraded devices and,
         * if so, some requests might need to be failed.
         */
        if (s.failed > conf->max_degraded || s.log_failed) {
                sh->check_state = 0;
                sh->reconstruct_state = 0;
                break_stripe_batch_list(sh, 0);
                if (s.to_read+s.to_write+s.written)
                        handle_failed_stripe(conf, sh, &s, disks, &s.return_bi);
                if (s.syncing + s.replacing)
                        handle_failed_sync(conf, sh, &s);
        }

        /* Now we check to see if any write operations have recently
         * completed
         */
        prexor = 0;
        if (sh->reconstruct_state == reconstruct_state_prexor_drain_result)
                prexor = 1;
        if (sh->reconstruct_state == reconstruct_state_drain_result ||
            sh->reconstruct_state == reconstruct_state_prexor_drain_result) {
                sh->reconstruct_state = reconstruct_state_idle;

                /* All the 'written' buffers and the parity block are ready to
                 * be written back to disk
                 */
                BUG_ON(!test_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags) &&
                       !test_bit(R5_Discard, &sh->dev[sh->pd_idx].flags));
                BUG_ON(sh->qd_idx >= 0 &&
                       !test_bit(R5_UPTODATE, &sh->dev[sh->qd_idx].flags) &&
                       !test_bit(R5_Discard, &sh->dev[sh->qd_idx].flags));
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (test_bit(R5_LOCKED, &dev->flags) &&
                                (i == sh->pd_idx || i == sh->qd_idx ||
                                 dev->written)) {
                                pr_debug("Writing block %d\n", i);
                                set_bit(R5_Wantwrite, &dev->flags);
                                if (prexor)
                                        continue;
                                if (s.failed > 1)
                                        continue;
                                if (!test_bit(R5_Insync, &dev->flags) ||
                                    ((i == sh->pd_idx || i == sh->qd_idx)  &&
                                     s.failed == 0))
                                        set_bit(STRIPE_INSYNC, &sh->state);
                        }
                }
                if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                        s.dec_preread_active = 1;
        }

        /*
         * might be able to return some write requests if the parity blocks
         * are safe, or on a failed drive
         */
        pdev = &sh->dev[sh->pd_idx];
        s.p_failed = (s.failed >= 1 && s.failed_num[0] == sh->pd_idx)
                || (s.failed >= 2 && s.failed_num[1] == sh->pd_idx);
        qdev = &sh->dev[sh->qd_idx];
        s.q_failed = (s.failed >= 1 && s.failed_num[0] == sh->qd_idx)
                || (s.failed >= 2 && s.failed_num[1] == sh->qd_idx)
                || conf->level < 6;

        if (s.written &&
            (s.p_failed || ((test_bit(R5_Insync, &pdev->flags)
                             && !test_bit(R5_LOCKED, &pdev->flags)
                             && (test_bit(R5_UPTODATE, &pdev->flags) ||
                                 test_bit(R5_Discard, &pdev->flags))))) &&
            (s.q_failed || ((test_bit(R5_Insync, &qdev->flags)
                             && !test_bit(R5_LOCKED, &qdev->flags)
                             && (test_bit(R5_UPTODATE, &qdev->flags) ||
                                 test_bit(R5_Discard, &qdev->flags))))))
                handle_stripe_clean_event(conf, sh, disks, &s.return_bi);

        /* Now we might consider reading some blocks, either to check/generate
         * parity, or to satisfy requests
         * or to load a block that is being partially written.
         */
        if (s.to_read || s.non_overwrite
            || (conf->level == 6 && s.to_write && s.failed)
            || (s.syncing && (s.uptodate + s.compute < disks))
            || s.replacing
            || s.expanding)
                handle_stripe_fill(sh, &s, disks);

        /* Now to consider new write requests and what else, if anything
         * should be read.  We do not handle new writes when:
         * 1/ A 'write' operation (copy+xor) is already in flight.
         * 2/ A 'check' operation is in flight, as it may clobber the parity
         *    block.
         */
        if (s.to_write && !sh->reconstruct_state && !sh->check_state)
                handle_stripe_dirtying(conf, sh, &s, disks);

        /* maybe we need to check and possibly fix the parity for this stripe
         * Any reads will already have been scheduled, so we just see if enough
         * data is available.  The parity check is held off while parity
         * dependent operations are in flight.
         */
        if (sh->check_state ||
            (s.syncing && s.locked == 0 &&
             !test_bit(STRIPE_COMPUTE_RUN, &sh->state) &&
             !test_bit(STRIPE_INSYNC, &sh->state))) {
                if (conf->level == 6)
                        handle_parity_checks6(conf, sh, &s, disks);
                else
                        handle_parity_checks5(conf, sh, &s, disks);
        }

        if ((s.replacing || s.syncing) && s.locked == 0
            && !test_bit(STRIPE_COMPUTE_RUN, &sh->state)
            && !test_bit(STRIPE_REPLACED, &sh->state)) {
                /* Write out to replacement devices where possible */
                for (i = 0; i < conf->raid_disks; i++)
                        if (test_bit(R5_NeedReplace, &sh->dev[i].flags)) {
                                WARN_ON(!test_bit(R5_UPTODATE, &sh->dev[i].flags));
                                set_bit(R5_WantReplace, &sh->dev[i].flags);
                                set_bit(R5_LOCKED, &sh->dev[i].flags);
                                s.locked++;
                        }
                if (s.replacing)
                        set_bit(STRIPE_INSYNC, &sh->state);
                set_bit(STRIPE_REPLACED, &sh->state);
        }
        if ((s.syncing || s.replacing) && s.locked == 0 &&
            !test_bit(STRIPE_COMPUTE_RUN, &sh->state) &&
            test_bit(STRIPE_INSYNC, &sh->state)) {
                md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
                clear_bit(STRIPE_SYNCING, &sh->state);
                if (test_and_clear_bit(R5_Overlap, &sh->dev[sh->pd_idx].flags))
                        wake_up(&conf->wait_for_overlap);
        }

        /* If the failed drives are just a ReadError, then we might need
         * to progress the repair/check process
         */
        if (s.failed <= conf->max_degraded && !conf->mddev->ro)
                for (i = 0; i < s.failed; i++) {
                        struct r5dev *dev = &sh->dev[s.failed_num[i]];
                        if (test_bit(R5_ReadError, &dev->flags)
                            && !test_bit(R5_LOCKED, &dev->flags)
                            && test_bit(R5_UPTODATE, &dev->flags)
                                ) {
                                if (!test_bit(R5_ReWrite, &dev->flags)) {
                                        set_bit(R5_Wantwrite, &dev->flags);
                                        set_bit(R5_ReWrite, &dev->flags);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        s.locked++;
                                } else {
                                        /* let's read it back */
                                        set_bit(R5_Wantread, &dev->flags);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        s.locked++;
                                }
                        }
                }

        /* Finish reconstruct operations initiated by the expansion process */
        if (sh->reconstruct_state == reconstruct_state_result) {
                struct stripe_head *sh_src
                        = raid5_get_active_stripe(conf, sh->sector, 1, 1, 1);
                if (sh_src && test_bit(STRIPE_EXPAND_SOURCE, &sh_src->state)) {
                        /* sh cannot be written until sh_src has been read.
                         * so arrange for sh to be delayed a little
                         */
                        set_bit(STRIPE_DELAYED, &sh->state);
                        set_bit(STRIPE_HANDLE, &sh->state);
                        if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE,
                                              &sh_src->state))
                                atomic_inc(&conf->preread_active_stripes);
                        raid5_release_stripe(sh_src);
                        goto finish;
                }
                if (sh_src)
                        raid5_release_stripe(sh_src);

                sh->reconstruct_state = reconstruct_state_idle;
                clear_bit(STRIPE_EXPANDING, &sh->state);
                for (i = conf->raid_disks; i--; ) {
                        set_bit(R5_Wantwrite, &sh->dev[i].flags);
                        set_bit(R5_LOCKED, &sh->dev[i].flags);
                        s.locked++;
                }
        }

        if (s.expanded && test_bit(STRIPE_EXPANDING, &sh->state) &&
            !sh->reconstruct_state) {
                /* Need to write out all blocks after computing parity */
                sh->disks = conf->raid_disks;
                stripe_set_idx(sh->sector, conf, 0, sh);
                schedule_reconstruction(sh, &s, 1, 1);
        } else if (s.expanded && !sh->reconstruct_state && s.locked == 0) {
                clear_bit(STRIPE_EXPAND_READY, &sh->state);
                atomic_dec(&conf->reshape_stripes);
                wake_up(&conf->wait_for_overlap);
                md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
        }

        if (s.expanding && s.locked == 0 &&
            !test_bit(STRIPE_COMPUTE_RUN, &sh->state))
                handle_stripe_expansion(conf, sh);

finish:
        /* wait for this device to become unblocked */
        if (unlikely(s.blocked_rdev)) {
                if (conf->mddev->external)
                        md_wait_for_blocked_rdev(s.blocked_rdev,
                                                 conf->mddev);
                else
                        /* Internal metadata will immediately
                         * be written by raid5d, so we don't
                         * need to wait here.
                         */
                        rdev_dec_pending(s.blocked_rdev,
                                         conf->mddev);
        }

        if (s.handle_bad_blocks)
                for (i = disks; i--; ) {
                        struct md_rdev *rdev;
                        struct r5dev *dev = &sh->dev[i];
                        if (test_and_clear_bit(R5_WriteError, &dev->flags)) {
                                /* We own a safe reference to the rdev */
                                rdev = conf->disks[i].rdev;
                                if (!rdev_set_badblocks(rdev, sh->sector,
                                                        STRIPE_SECTORS, 0))
                                        md_error(conf->mddev, rdev);
                                rdev_dec_pending(rdev, conf->mddev);
                        }
                        if (test_and_clear_bit(R5_MadeGood, &dev->flags)) {
                                rdev = conf->disks[i].rdev;
                                rdev_clear_badblocks(rdev, sh->sector,
                                                     STRIPE_SECTORS, 0);
                                rdev_dec_pending(rdev, conf->mddev);
                        }
                        if (test_and_clear_bit(R5_MadeGoodRepl, &dev->flags)) {
                                rdev = conf->disks[i].replacement;
                                if (!rdev)
                                        /* rdev have been moved down */
                                        rdev = conf->disks[i].rdev;
                                rdev_clear_badblocks(rdev, sh->sector,
                                                     STRIPE_SECTORS, 0);
                                rdev_dec_pending(rdev, conf->mddev);
                        }
                }

        if (s.ops_request)
                raid_run_ops(sh, s.ops_request);

        ops_run_io(sh, &s);

        if (s.dec_preread_active) {
                /* We delay this until after ops_run_io so that if make_request
                 * is waiting on a flush, it won't continue until the writes
                 * have actually been submitted.
                 */
                atomic_dec(&conf->preread_active_stripes);
                if (atomic_read(&conf->preread_active_stripes) <
                    IO_THRESHOLD)
                        md_wakeup_thread(conf->mddev->thread);
        }

        if (!bio_list_empty(&s.return_bi)) {
                if (test_bit(MD_CHANGE_PENDING, &conf->mddev->flags) &&
                                (s.failed <= conf->max_degraded ||
                                        conf->mddev->external == 0)) {
                        spin_lock_irq(&conf->device_lock);
                        bio_list_merge(&conf->return_bi, &s.return_bi);
                        spin_unlock_irq(&conf->device_lock);
                        md_wakeup_thread(conf->mddev->thread);
                } else
                        return_io(&s.return_bi);
        }

        clear_bit_unlock(STRIPE_ACTIVE, &sh->state);
}

static void raid5_activate_delayed(struct r5conf *conf)
{
        if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD) {
                while (!list_empty(&conf->delayed_list)) {
                        struct list_head *l = conf->delayed_list.next;
                        struct stripe_head *sh;
                        sh = list_entry(l, struct stripe_head, lru);
                        list_del_init(l);
                        clear_bit(STRIPE_DELAYED, &sh->state);
                        if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                                atomic_inc(&conf->preread_active_stripes);
                        list_add_tail(&sh->lru, &conf->hold_list);
                        raid5_wakeup_stripe_thread(sh);
                }
        }
}

static void activate_bit_delay(struct r5conf *conf,
        struct list_head *temp_inactive_list)
{
        /* device_lock is held */
        struct list_head head;
        list_add(&head, &conf->bitmap_list);
        list_del_init(&conf->bitmap_list);
        while (!list_empty(&head)) {
                struct stripe_head *sh = list_entry(head.next, struct stripe_head, lru);
                int hash;
                list_del_init(&sh->lru);
                atomic_inc(&sh->count);
                hash = sh->hash_lock_index;
                __release_stripe(conf, sh, &temp_inactive_list[hash]);
        }
}

static int raid5_congested(struct mddev *mddev, int bits)
{
        struct r5conf *conf = mddev->private;

        /* No difference between reads and writes.  Just check
         * how busy the stripe_cache is
         */

        if (test_bit(R5_INACTIVE_BLOCKED, &conf->cache_state))
                return 1;
        if (conf->quiesce)
                return 1;
        if (atomic_read(&conf->empty_inactive_list_nr))
                return 1;

        return 0;
}

static int in_chunk_boundary(struct mddev *mddev, struct bio *bio)
{
        struct r5conf *conf = mddev->private;
        sector_t sector = bio->bi_iter.bi_sector + get_start_sect(bio->bi_bdev);
        unsigned int chunk_sectors;
        unsigned int bio_sectors = bio_sectors(bio);

        chunk_sectors = min(conf->chunk_sectors, conf->prev_chunk_sectors);
        return  chunk_sectors >=
                ((sector & (chunk_sectors - 1)) + bio_sectors);
}

/*
 *  add bio to the retry LIFO  ( in O(1) ... we are in interrupt )
 *  later sampled by raid5d.
 */
static void add_bio_to_retry(struct bio *bi,struct r5conf *conf)
{
        unsigned long flags;

        spin_lock_irqsave(&conf->device_lock, flags);

        bi->bi_next = conf->retry_read_aligned_list;
        conf->retry_read_aligned_list = bi;

        spin_unlock_irqrestore(&conf->device_lock, flags);
        md_wakeup_thread(conf->mddev->thread);
}

static struct bio *remove_bio_from_retry(struct r5conf *conf)
{
        struct bio *bi;

        bi = conf->retry_read_aligned;
        if (bi) {
                conf->retry_read_aligned = NULL;
                return bi;
        }
        bi = conf->retry_read_aligned_list;
        if(bi) {
                conf->retry_read_aligned_list = bi->bi_next;
                bi->bi_next = NULL;
                /*
                 * this sets the active strip count to 1 and the processed
                 * strip count to zero (upper 8 bits)
                 */
                raid5_set_bi_stripes(bi, 1); /* biased count of active stripes */
        }

        return bi;
}

/*
 *  The "raid5_align_endio" should check if the read succeeded and if it
 *  did, call bio_endio on the original bio (having bio_put the new bio
 *  first).
 *  If the read failed..
 */
static void raid5_align_endio(struct bio *bi)
{
        struct bio* raid_bi  = bi->bi_private;
        struct mddev *mddev;
        struct r5conf *conf;
        struct md_rdev *rdev;
        int error = bi->bi_error;

        bio_put(bi);

        rdev = (void*)raid_bi->bi_next;
        raid_bi->bi_next = NULL;
        mddev = rdev->mddev;
        conf = mddev->private;

        rdev_dec_pending(rdev, conf->mddev);

        if (!error) {
                trace_block_bio_complete(bdev_get_queue(raid_bi->bi_bdev),
                                         raid_bi, 0);
                bio_endio(raid_bi);
                if (atomic_dec_and_test(&conf->active_aligned_reads))
                        wake_up(&conf->wait_for_quiescent);
                return;
        }

        pr_debug("raid5_align_endio : io error...handing IO for a retry\n");

        add_bio_to_retry(raid_bi, conf);
}

static int raid5_read_one_chunk(struct mddev *mddev, struct bio *raid_bio)
{
        struct r5conf *conf = mddev->private;
        int dd_idx;
        struct bio* align_bi;
        struct md_rdev *rdev;
        sector_t end_sector;

        if (!in_chunk_boundary(mddev, raid_bio)) {
                pr_debug("%s: non aligned\n", __func__);
                return 0;
        }
        /*
         * use bio_clone_mddev to make a copy of the bio
         */
        align_bi = bio_clone_mddev(raid_bio, GFP_NOIO, mddev);
        if (!align_bi)
                return 0;
        /*
         *   set bi_end_io to a new function, and set bi_private to the
         *     original bio.
         */
        align_bi->bi_end_io  = raid5_align_endio;
        align_bi->bi_private = raid_bio;
        /*
         *      compute position
         */
        align_bi->bi_iter.bi_sector =
                raid5_compute_sector(conf, raid_bio->bi_iter.bi_sector,
                                     0, &dd_idx, NULL);

        end_sector = bio_end_sector(align_bi);
        rcu_read_lock();
        rdev = rcu_dereference(conf->disks[dd_idx].replacement);
        if (!rdev || test_bit(Faulty, &rdev->flags) ||
            rdev->recovery_offset < end_sector) {
                rdev = rcu_dereference(conf->disks[dd_idx].rdev);
                if (rdev &&
                    (test_bit(Faulty, &rdev->flags) ||
                    !(test_bit(In_sync, &rdev->flags) ||
                      rdev->recovery_offset >= end_sector)))
                        rdev = NULL;
        }
        if (rdev) {
                sector_t first_bad;
                int bad_sectors;

                atomic_inc(&rdev->nr_pending);
                rcu_read_unlock();
                raid_bio->bi_next = (void*)rdev;
                align_bi->bi_bdev =  rdev->bdev;
                bio_clear_flag(align_bi, BIO_SEG_VALID);

                if (is_badblock(rdev, align_bi->bi_iter.bi_sector,
                                bio_sectors(align_bi),
                                &first_bad, &bad_sectors)) {
                        bio_put(align_bi);
                        rdev_dec_pending(rdev, mddev);
                        return 0;
                }

                /* No reshape active, so we can trust rdev->data_offset */
                align_bi->bi_iter.bi_sector += rdev->data_offset;

                spin_lock_irq(&conf->device_lock);
                wait_event_lock_irq(conf->wait_for_quiescent,
                                    conf->quiesce == 0,
                                    conf->device_lock);
                atomic_inc(&conf->active_aligned_reads);
                spin_unlock_irq(&conf->device_lock);

                if (mddev->gendisk)
                        trace_block_bio_remap(bdev_get_queue(align_bi->bi_bdev),
                                              align_bi, disk_devt(mddev->gendisk),
                                              raid_bio->bi_iter.bi_sector);
                generic_make_request(align_bi);
                return 1;
        } else {
                rcu_read_unlock();
                bio_put(align_bi);
                return 0;
        }
}

static struct bio *chunk_aligned_read(struct mddev *mddev, struct bio *raid_bio)
{
        struct bio *split;

        do {
                sector_t sector = raid_bio->bi_iter.bi_sector;
                unsigned chunk_sects = mddev->chunk_sectors;
                unsigned sectors = chunk_sects - (sector & (chunk_sects-1));

                if (sectors < bio_sectors(raid_bio)) {
                        split = bio_split(raid_bio, sectors, GFP_NOIO, fs_bio_set);
                        bio_chain(split, raid_bio);
                } else
                        split = raid_bio;

                if (!raid5_read_one_chunk(mddev, split)) {
                        if (split != raid_bio)
                                generic_make_request(raid_bio);
                        return split;
                }
        } while (split != raid_bio);

        return NULL;
}

/* __get_priority_stripe - get the next stripe to process
 *
 * Full stripe writes are allowed to pass preread active stripes up until
 * the bypass_threshold is exceeded.  In general the bypass_count
 * increments when the handle_list is handled before the hold_list; however, it
 * will not be incremented when STRIPE_IO_STARTED is sampled set signifying a
 * stripe with in flight i/o.  The bypass_count will be reset when the
 * head of the hold_list has changed, i.e. the head was promoted to the
 * handle_list.
 */
static struct stripe_head *__get_priority_stripe(struct r5conf *conf, int group)
{
        struct stripe_head *sh = NULL, *tmp;
        struct list_head *handle_list = NULL;
        struct r5worker_group *wg = NULL;

        if (conf->worker_cnt_per_group == 0) {
                handle_list = &conf->handle_list;
        } else if (group != ANY_GROUP) {
                handle_list = &conf->worker_groups[group].handle_list;
                wg = &conf->worker_groups[group];
        } else {
                int i;
                for (i = 0; i < conf->group_cnt; i++) {
                        handle_list = &conf->worker_groups[i].handle_list;
                        wg = &conf->worker_groups[i];
                        if (!list_empty(handle_list))
                                break;
                }
        }

        pr_debug("%s: handle: %s hold: %s full_writes: %d bypass_count: %d\n",
                  __func__,
                  list_empty(handle_list) ? "empty" : "busy",
                  list_empty(&conf->hold_list) ? "empty" : "busy",
                  atomic_read(&conf->pending_full_writes), conf->bypass_count);

        if (!list_empty(handle_list)) {
                sh = list_entry(handle_list->next, typeof(*sh), lru);

                if (list_empty(&conf->hold_list))
                        conf->bypass_count = 0;
                else if (!test_bit(STRIPE_IO_STARTED, &sh->state)) {
                        if (conf->hold_list.next == conf->last_hold)
                                conf->bypass_count++;
                        else {
                                conf->last_hold = conf->hold_list.next;
                                conf->bypass_count -= conf->bypass_threshold;
                                if (conf->bypass_count < 0)
                                        conf->bypass_count = 0;
                        }
                }
        } else if (!list_empty(&conf->hold_list) &&
                   ((conf->bypass_threshold &&
                     conf->bypass_count > conf->bypass_threshold) ||
                    atomic_read(&conf->pending_full_writes) == 0)) {

                list_for_each_entry(tmp, &conf->hold_list,  lru) {
                        if (conf->worker_cnt_per_group == 0 ||
                            group == ANY_GROUP ||
                            !cpu_online(tmp->cpu) ||
                            cpu_to_group(tmp->cpu) == group) {
                                sh = tmp;
                                break;
                        }
                }

                if (sh) {
                        conf->bypass_count -= conf->bypass_threshold;
                        if (conf->bypass_count < 0)
                                conf->bypass_count = 0;
                }
                wg = NULL;
        }

        if (!sh)
                return NULL;

        if (wg) {
                wg->stripes_cnt--;
                sh->group = NULL;
        }
        list_del_init(&sh->lru);
        BUG_ON(atomic_inc_return(&sh->count) != 1);
        return sh;
}

struct raid5_plug_cb {
        struct blk_plug_cb      cb;
        struct list_head        list;
        struct list_head        temp_inactive_list[NR_STRIPE_HASH_LOCKS];
};

static void raid5_unplug(struct blk_plug_cb *blk_cb, bool from_schedule)
{
        struct raid5_plug_cb *cb = container_of(
                blk_cb, struct raid5_plug_cb, cb);
        struct stripe_head *sh;
        struct mddev *mddev = cb->cb.data;
        struct r5conf *conf = mddev->private;
        int cnt = 0;
        int hash;

        if (cb->list.next && !list_empty(&cb->list)) {
                spin_lock_irq(&conf->device_lock);
                while (!list_empty(&cb->list)) {
                        sh = list_first_entry(&cb->list, struct stripe_head, lru);
                        list_del_init(&sh->lru);
                        /*
                         * avoid race release_stripe_plug() sees
                         * STRIPE_ON_UNPLUG_LIST clear but the stripe
                         * is still in our list
                         */
                        smp_mb__before_atomic();
                        clear_bit(STRIPE_ON_UNPLUG_LIST, &sh->state);
                        /*
                         * STRIPE_ON_RELEASE_LIST could be set here. In that
                         * case, the count is always > 1 here
                         */
                        hash = sh->hash_lock_index;
                        __release_stripe(conf, sh, &cb->temp_inactive_list[hash]);
                        cnt++;
                }
                spin_unlock_irq(&conf->device_lock);
        }
        release_inactive_stripe_list(conf, cb->temp_inactive_list,
                                     NR_STRIPE_HASH_LOCKS);
        if (mddev->queue)
                trace_block_unplug(mddev->queue, cnt, !from_schedule);
        kfree(cb);
}

static void release_stripe_plug(struct mddev *mddev,
                                struct stripe_head *sh)
{
        struct blk_plug_cb *blk_cb = blk_check_plugged(
                raid5_unplug, mddev,
                sizeof(struct raid5_plug_cb));
        struct raid5_plug_cb *cb;

        if (!blk_cb) {
                raid5_release_stripe(sh);
                return;
        }

        cb = container_of(blk_cb, struct raid5_plug_cb, cb);

        if (cb->list.next == NULL) {
                int i;
                INIT_LIST_HEAD(&cb->list);
                for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
                        INIT_LIST_HEAD(cb->temp_inactive_list + i);
        }

        if (!test_and_set_bit(STRIPE_ON_UNPLUG_LIST, &sh->state))
                list_add_tail(&sh->lru, &cb->list);
        else
                raid5_release_stripe(sh);
}

static void make_discard_request(struct mddev *mddev, struct bio *bi)
{
        struct r5conf *conf = mddev->private;
        sector_t logical_sector, last_sector;
        struct stripe_head *sh;
        int remaining;
        int stripe_sectors;

        if (mddev->reshape_position != MaxSector)
                /* Skip discard while reshape is happening */
                return;

        logical_sector = bi->bi_iter.bi_sector & ~((sector_t)STRIPE_SECTORS-1);
        last_sector = bi->bi_iter.bi_sector + (bi->bi_iter.bi_size>>9);

        bi->bi_next = NULL;
        bi->bi_phys_segments = 1; /* over-loaded to count active stripes */

        stripe_sectors = conf->chunk_sectors *
                (conf->raid_disks - conf->max_degraded);
        logical_sector = DIV_ROUND_UP_SECTOR_T(logical_sector,
                                               stripe_sectors);
        sector_div(last_sector, stripe_sectors);

        logical_sector *= conf->chunk_sectors;
        last_sector *= conf->chunk_sectors;

        for (; logical_sector < last_sector;
             logical_sector += STRIPE_SECTORS) {
                DEFINE_WAIT(w);
                int d;
        again:
                sh = raid5_get_active_stripe(conf, logical_sector, 0, 0, 0);
                prepare_to_wait(&conf->wait_for_overlap, &w,
                                TASK_UNINTERRUPTIBLE);
                set_bit(R5_Overlap, &sh->dev[sh->pd_idx].flags);
                if (test_bit(STRIPE_SYNCING, &sh->state)) {
                        raid5_release_stripe(sh);
                        schedule();
                        goto again;
                }
                clear_bit(R5_Overlap, &sh->dev[sh->pd_idx].flags);
                spin_lock_irq(&sh->stripe_lock);
                for (d = 0; d < conf->raid_disks; d++) {
                        if (d == sh->pd_idx || d == sh->qd_idx)
                                continue;
                        if (sh->dev[d].towrite || sh->dev[d].toread) {
                                set_bit(R5_Overlap, &sh->dev[d].flags);
                                spin_unlock_irq(&sh->stripe_lock);
                                raid5_release_stripe(sh);
                                schedule();
                                goto again;
                        }
                }
                set_bit(STRIPE_DISCARD, &sh->state);
                finish_wait(&conf->wait_for_overlap, &w);
                sh->overwrite_disks = 0;
                for (d = 0; d < conf->raid_disks; d++) {
                        if (d == sh->pd_idx || d == sh->qd_idx)
                                continue;
                        sh->dev[d].towrite = bi;
                        set_bit(R5_OVERWRITE, &sh->dev[d].flags);
                        raid5_inc_bi_active_stripes(bi);
                        sh->overwrite_disks++;
                }
                spin_unlock_irq(&sh->stripe_lock);
                if (conf->mddev->bitmap) {
                        for (d = 0;
                             d < conf->raid_disks - conf->max_degraded;
                             d++)
                                bitmap_startwrite(mddev->bitmap,
                                                  sh->sector,
                                                  STRIPE_SECTORS,
                                                  0);
                        sh->bm_seq = conf->seq_flush + 1;
                        set_bit(STRIPE_BIT_DELAY, &sh->state);
                }

                set_bit(STRIPE_HANDLE, &sh->state);
                clear_bit(STRIPE_DELAYED, &sh->state);
                if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                        atomic_inc(&conf->preread_active_stripes);
                release_stripe_plug(mddev, sh);
        }

        remaining = raid5_dec_bi_active_stripes(bi);
        if (remaining == 0) {
                md_write_end(mddev);
                bio_endio(bi);
        }
}

static void raid5_make_request(struct mddev *mddev, struct bio * bi)
{
        struct r5conf *conf = mddev->private;
        int dd_idx;
        sector_t new_sector;
        sector_t logical_sector, last_sector;
        struct stripe_head *sh;
        const int rw = bio_data_dir(bi);
        int remaining;
        DEFINE_WAIT(w);
        bool do_prepare;

        if (unlikely(bi->bi_opf & REQ_PREFLUSH)) {
                int ret = r5l_handle_flush_request(conf->log, bi);

                if (ret == 0)
                        return;
                if (ret == -ENODEV) {
                        md_flush_request(mddev, bi);
                        return;
                }
                /* ret == -EAGAIN, fallback */
        }

        md_write_start(mddev, bi);

        /*
         * If array is degraded, better not do chunk aligned read because
         * later we might have to read it again in order to reconstruct
         * data on failed drives.
         */
        if (rw == READ && mddev->degraded == 0 &&
            mddev->reshape_position == MaxSector) {
                bi = chunk_aligned_read(mddev, bi);
                if (!bi)
                        return;
        }

        if (unlikely(bio_op(bi) == REQ_OP_DISCARD)) {
                make_discard_request(mddev, bi);
                return;
        }

        logical_sector = bi->bi_iter.bi_sector & ~((sector_t)STRIPE_SECTORS-1);
        last_sector = bio_end_sector(bi);
        bi->bi_next = NULL;
        bi->bi_phys_segments = 1;       /* over-loaded to count active stripes */

        prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
        for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
                int previous;
                int seq;

                do_prepare = false;
        retry:
                seq = read_seqcount_begin(&conf->gen_lock);
                previous = 0;
                if (do_prepare)
                        prepare_to_wait(&conf->wait_for_overlap, &w,
                                TASK_UNINTERRUPTIBLE);
                if (unlikely(conf->reshape_progress != MaxSector)) {
                        /* spinlock is needed as reshape_progress may be
                         * 64bit on a 32bit platform, and so it might be
                         * possible to see a half-updated value
                         * Of course reshape_progress could change after
                         * the lock is dropped, so once we get a reference
                         * to the stripe that we think it is, we will have
                         * to check again.
                         */
                        spin_lock_irq(&conf->device_lock);
                        if (mddev->reshape_backwards
                            ? logical_sector < conf->reshape_progress
                            : logical_sector >= conf->reshape_progress) {
                                previous = 1;
                        } else {
                                if (mddev->reshape_backwards
                                    ? logical_sector < conf->reshape_safe
                                    : logical_sector >= conf->reshape_safe) {
                                        spin_unlock_irq(&conf->device_lock);
                                        schedule();
                                        do_prepare = true;
                                        goto retry;
                                }
                        }
                        spin_unlock_irq(&conf->device_lock);
                }

                new_sector = raid5_compute_sector(conf, logical_sector,
                                                  previous,
                                                  &dd_idx, NULL);
                pr_debug("raid456: raid5_make_request, sector %llu logical %llu\n",
                        (unsigned long long)new_sector,
                        (unsigned long long)logical_sector);

                sh = raid5_get_active_stripe(conf, new_sector, previous,
                                       (bi->bi_opf & REQ_RAHEAD), 0);
                if (sh) {
                        if (unlikely(previous)) {
                                /* expansion might have moved on while waiting for a
                                 * stripe, so we must do the range check again.
                                 * Expansion could still move past after this
                                 * test, but as we are holding a reference to
                                 * 'sh', we know that if that happens,
                                 *  STRIPE_EXPANDING will get set and the expansion
                                 * won't proceed until we finish with the stripe.
                                 */
                                int must_retry = 0;
                                spin_lock_irq(&conf->device_lock);
                                if (mddev->reshape_backwards
                                    ? logical_sector >= conf->reshape_progress
                                    : logical_sector < conf->reshape_progress)
                                        /* mismatch, need to try again */
                                        must_retry = 1;
                                spin_unlock_irq(&conf->device_lock);
                                if (must_retry) {
                                        raid5_release_stripe(sh);
                                        schedule();
                                        do_prepare = true;
                                        goto retry;
                                }
                        }
                        if (read_seqcount_retry(&conf->gen_lock, seq)) {
                                /* Might have got the wrong stripe_head
                                 * by accident
                                 */
                                raid5_release_stripe(sh);
                                goto retry;
                        }

                        if (rw == WRITE &&
                            logical_sector >= mddev->suspend_lo &&
                            logical_sector < mddev->suspend_hi) {
                                raid5_release_stripe(sh);
                                /* As the suspend_* range is controlled by
                                 * userspace, we want an interruptible
                                 * wait.
                                 */
                                prepare_to_wait(&conf->wait_for_overlap,
                                                &w, TASK_INTERRUPTIBLE);
                                if (logical_sector >= mddev->suspend_lo &&
                                    logical_sector < mddev->suspend_hi) {
                                        sigset_t full, old;
                                        sigfillset(&full);
                                        sigprocmask(SIG_BLOCK, &full, &old);
                                        schedule();
                                        sigprocmask(SIG_SETMASK, &old, NULL);
                                        do_prepare = true;
                                }
                                goto retry;
                        }

                        if (test_bit(STRIPE_EXPANDING, &sh->state) ||
                            !add_stripe_bio(sh, bi, dd_idx, rw, previous)) {
                                /* Stripe is busy expanding or
                                 * add failed due to overlap.  Flush everything
                                 * and wait a while
                                 */
                                md_wakeup_thread(mddev->thread);
                                raid5_release_stripe(sh);
                                schedule();
                                do_prepare = true;
                                goto retry;
                        }
                        set_bit(STRIPE_HANDLE, &sh->state);
                        clear_bit(STRIPE_DELAYED, &sh->state);
                        if ((!sh->batch_head || sh == sh->batch_head) &&
                            (bi->bi_opf & REQ_SYNC) &&
                            !test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                                atomic_inc(&conf->preread_active_stripes);
                        release_stripe_plug(mddev, sh);
                } else {
                        /* cannot get stripe for read-ahead, just give-up */
                        bi->bi_error = -EIO;
                        break;
                }
        }
        finish_wait(&conf->wait_for_overlap, &w);

        remaining = raid5_dec_bi_active_stripes(bi);
        if (remaining == 0) {

                if ( rw == WRITE )
                        md_write_end(mddev);

                trace_block_bio_complete(bdev_get_queue(bi->bi_bdev),
                                         bi, 0);
                bio_endio(bi);
        }
}

static sector_t raid5_size(struct mddev *mddev, sector_t sectors, int raid_disks);

static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr, int *skipped)
{
        /* reshaping is quite different to recovery/resync so it is
         * handled quite separately ... here.
         *
         * On each call to sync_request, we gather one chunk worth of
         * destination stripes and flag them as expanding.
         * Then we find all the source stripes and request reads.
         * As the reads complete, handle_stripe will copy the data
         * into the destination stripe and release that stripe.
         */
        struct r5conf *conf = mddev->private;
        struct stripe_head *sh;
        sector_t first_sector, last_sector;
        int raid_disks = conf->previous_raid_disks;
        int data_disks = raid_disks - conf->max_degraded;
        int new_data_disks = conf->raid_disks - conf->max_degraded;
        int i;
        int dd_idx;
        sector_t writepos, readpos, safepos;
        sector_t stripe_addr;
        int reshape_sectors;
        struct list_head stripes;
        sector_t retn;

        if (sector_nr == 0) {
                /* If restarting in the middle, skip the initial sectors */
                if (mddev->reshape_backwards &&
                    conf->reshape_progress < raid5_size(mddev, 0, 0)) {
                        sector_nr = raid5_size(mddev, 0, 0)
                                - conf->reshape_progress;
                } else if (mddev->reshape_backwards &&
                           conf->reshape_progress == MaxSector) {
                        /* shouldn't happen, but just in case, finish up.*/
                        sector_nr = MaxSector;
                } else if (!mddev->reshape_backwards &&
                           conf->reshape_progress > 0)
                        sector_nr = conf->reshape_progress;
                sector_div(sector_nr, new_data_disks);
                if (sector_nr) {
                        mddev->curr_resync_completed = sector_nr;
                        sysfs_notify(&mddev->kobj, NULL, "sync_completed");
                        *skipped = 1;
                        retn = sector_nr;
                        goto finish;
                }
        }

        /* We need to process a full chunk at a time.
         * If old and new chunk sizes differ, we need to process the
         * largest of these
         */

        reshape_sectors = max(conf->chunk_sectors, conf->prev_chunk_sectors);

        /* We update the metadata at least every 10 seconds, or when
         * the data about to be copied would over-write the source of
         * the data at the front of the range.  i.e. one new_stripe
         * along from reshape_progress new_maps to after where
         * reshape_safe old_maps to
         */
        writepos = conf->reshape_progress;
        sector_div(writepos, new_data_disks);
        readpos = conf->reshape_progress;
        sector_div(readpos, data_disks);
        safepos = conf->reshape_safe;
        sector_div(safepos, data_disks);
        if (mddev->reshape_backwards) {
                BUG_ON(writepos < reshape_sectors);
                writepos -= reshape_sectors;
                readpos += reshape_sectors;
                safepos += reshape_sectors;
        } else {
                writepos += reshape_sectors;
                /* readpos and safepos are worst-case calculations.
                 * A negative number is overly pessimistic, and causes
                 * obvious problems for unsigned storage.  So clip to 0.
                 */
                readpos -= min_t(sector_t, reshape_sectors, readpos);
                safepos -= min_t(sector_t, reshape_sectors, safepos);
        }

        /* Having calculated the 'writepos' possibly use it
         * to set 'stripe_addr' which is where we will write to.
         */
        if (mddev->reshape_backwards) {
                BUG_ON(conf->reshape_progress == 0);
                stripe_addr = writepos;
                BUG_ON((mddev->dev_sectors &
                        ~((sector_t)reshape_sectors - 1))
                       - reshape_sectors - stripe_addr
                       != sector_nr);
        } else {
                BUG_ON(writepos != sector_nr + reshape_sectors);
                stripe_addr = sector_nr;
        }

        /* 'writepos' is the most advanced device address we might write.
         * 'readpos' is the least advanced device address we might read.
         * 'safepos' is the least address recorded in the metadata as having
         *     been reshaped.
         * If there is a min_offset_diff, these are adjusted either by
         * increasing the safepos/readpos if diff is negative, or
         * increasing writepos if diff is positive.
         * If 'readpos' is then behind 'writepos', there is no way that we can
         * ensure safety in the face of a crash - that must be done by userspace
         * making a backup of the data.  So in that case there is no particular
         * rush to update metadata.
         * Otherwise if 'safepos' is behind 'writepos', then we really need to
         * update the metadata to advance 'safepos' to match 'readpos' so that
         * we can be safe in the event of a crash.
         * So we insist on updating metadata if safepos is behind writepos and
         * readpos is beyond writepos.
         * In any case, update the metadata every 10 seconds.
         * Maybe that number should be configurable, but I'm not sure it is
         * worth it.... maybe it could be a multiple of safemode_delay???
         */
        if (conf->min_offset_diff < 0) {
                safepos += -conf->min_offset_diff;
                readpos += -conf->min_offset_diff;
        } else
                writepos += conf->min_offset_diff;

        if ((mddev->reshape_backwards
             ? (safepos > writepos && readpos < writepos)
             : (safepos < writepos && readpos > writepos)) ||
            time_after(jiffies, conf->reshape_checkpoint + 10*HZ)) {
                /* Cannot proceed until we've updated the superblock... */
                wait_event(conf->wait_for_overlap,
                           atomic_read(&conf->reshape_stripes)==0
                           || test_bit(MD_RECOVERY_INTR, &mddev->recovery));
                if (atomic_read(&conf->reshape_stripes) != 0)
                        return 0;
                mddev->reshape_position = conf->reshape_progress;
                mddev->curr_resync_completed = sector_nr;
                conf->reshape_checkpoint = jiffies;
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                md_wakeup_thread(mddev->thread);
                wait_event(mddev->sb_wait, mddev->flags == 0 ||
                           test_bit(MD_RECOVERY_INTR, &mddev->recovery));
                if (test_bit(MD_RECOVERY_INTR, &mddev->recovery))
                        return 0;
                spin_lock_irq(&conf->device_lock);
                conf->reshape_safe = mddev->reshape_position;
                spin_unlock_irq(&conf->device_lock);
                wake_up(&conf->wait_for_overlap);
                sysfs_notify(&mddev->kobj, NULL, "sync_completed");
        }

        INIT_LIST_HEAD(&stripes);
        for (i = 0; i < reshape_sectors; i += STRIPE_SECTORS) {
                int j;
                int skipped_disk = 0;
                sh = raid5_get_active_stripe(conf, stripe_addr+i, 0, 0, 1);
                set_bit(STRIPE_EXPANDING, &sh->state);
                atomic_inc(&conf->reshape_stripes);
                /* If any of this stripe is beyond the end of the old
                 * array, then we need to zero those blocks
                 */
                for (j=sh->disks; j--;) {
                        sector_t s;
                        if (j == sh->pd_idx)
                                continue;
                        if (conf->level == 6 &&
                            j == sh->qd_idx)
                                continue;
                        s = raid5_compute_blocknr(sh, j, 0);
                        if (s < raid5_size(mddev, 0, 0)) {
                                skipped_disk = 1;
                                continue;
                        }
                        memset(page_address(sh->dev[j].page), 0, STRIPE_SIZE);
                        set_bit(R5_Expanded, &sh->dev[j].flags);
                        set_bit(R5_UPTODATE, &sh->dev[j].flags);
                }
                if (!skipped_disk) {
                        set_bit(STRIPE_EXPAND_READY, &sh->state);
                        set_bit(STRIPE_HANDLE, &sh->state);
                }
                list_add(&sh->lru, &stripes);
        }
        spin_lock_irq(&conf->device_lock);
        if (mddev->reshape_backwards)
                conf->reshape_progress -= reshape_sectors * new_data_disks;
        else
                conf->reshape_progress += reshape_sectors * new_data_disks;
        spin_unlock_irq(&conf->device_lock);
        /* Ok, those stripe are ready. We can start scheduling
         * reads on the source stripes.
         * The source stripes are determined by mapping the first and last
         * block on the destination stripes.
         */
        first_sector =
                raid5_compute_sector(conf, stripe_addr*(new_data_disks),
                                     1, &dd_idx, NULL);
        last_sector =
                raid5_compute_sector(conf, ((stripe_addr+reshape_sectors)
                                            * new_data_disks - 1),
                                     1, &dd_idx, NULL);
        if (last_sector >= mddev->dev_sectors)
                last_sector = mddev->dev_sectors - 1;
        while (first_sector <= last_sector) {
                sh = raid5_get_active_stripe(conf, first_sector, 1, 0, 1);
                set_bit(STRIPE_EXPAND_SOURCE, &sh->state);
                set_bit(STRIPE_HANDLE, &sh->state);
                raid5_release_stripe(sh);
                first_sector += STRIPE_SECTORS;
        }
        /* Now that the sources are clearly marked, we can release
         * the destination stripes
         */
        while (!list_empty(&stripes)) {
                sh = list_entry(stripes.next, struct stripe_head, lru);
                list_del_init(&sh->lru);
                raid5_release_stripe(sh);
        }
        /* If this takes us to the resync_max point where we have to pause,
         * then we need to write out the superblock.
         */
        sector_nr += reshape_sectors;
        retn = reshape_sectors;
finish:
        if (mddev->curr_resync_completed > mddev->resync_max ||
            (sector_nr - mddev->curr_resync_completed) * 2
            >= mddev->resync_max - mddev->curr_resync_completed) {
                /* Cannot proceed until we've updated the superblock... */
                wait_event(conf->wait_for_overlap,
                           atomic_read(&conf->reshape_stripes) == 0
                           || test_bit(MD_RECOVERY_INTR, &mddev->recovery));
                if (atomic_read(&conf->reshape_stripes) != 0)
                        goto ret;
                mddev->reshape_position = conf->reshape_progress;
                mddev->curr_resync_completed = sector_nr;
                conf->reshape_checkpoint = jiffies;
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                md_wakeup_thread(mddev->thread);
                wait_event(mddev->sb_wait,
                           !test_bit(MD_CHANGE_DEVS, &mddev->flags)
                           || test_bit(MD_RECOVERY_INTR, &mddev->recovery));
                if (test_bit(MD_RECOVERY_INTR, &mddev->recovery))
                        goto ret;
                spin_lock_irq(&conf->device_lock);
                conf->reshape_safe = mddev->reshape_position;
                spin_unlock_irq(&conf->device_lock);
                wake_up(&conf->wait_for_overlap);
                sysfs_notify(&mddev->kobj, NULL, "sync_completed");
        }
ret:
        return retn;
}

static inline sector_t raid5_sync_request(struct mddev *mddev, sector_t sector_nr,
                                          int *skipped)
{
        struct r5conf *conf = mddev->private;
        struct stripe_head *sh;
        sector_t max_sector = mddev->dev_sectors;
        sector_t sync_blocks;
        int still_degraded = 0;
        int i;

        if (sector_nr >= max_sector) {
                /* just being told to finish up .. nothing much to do */

                if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery)) {
                        end_reshape(conf);
                        return 0;
                }

                if (mddev->curr_resync < max_sector) /* aborted */
                        bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
                                        &sync_blocks, 1);
                else /* completed sync */
                        conf->fullsync = 0;
                bitmap_close_sync(mddev->bitmap);

                return 0;
        }

        /* Allow raid5_quiesce to complete */
        wait_event(conf->wait_for_overlap, conf->quiesce != 2);

        if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
                return reshape_request(mddev, sector_nr, skipped);

        /* No need to check resync_max as we never do more than one
         * stripe, and as resync_max will always be on a chunk boundary,
         * if the check in md_do_sync didn't fire, there is no chance
         * of overstepping resync_max here
         */

        /* if there is too many failed drives and we are trying
         * to resync, then assert that we are finished, because there is
         * nothing we can do.
         */
        if (mddev->degraded >= conf->max_degraded &&
            test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
                sector_t rv = mddev->dev_sectors - sector_nr;
                *skipped = 1;
                return rv;
        }
        if (!test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
            !conf->fullsync &&
            !bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) &&
            sync_blocks >= STRIPE_SECTORS) {
                /* we can skip this block, and probably more */
                sync_blocks /= STRIPE_SECTORS;
                *skipped = 1;
                return sync_blocks * STRIPE_SECTORS; /* keep things rounded to whole stripes */
        }

        bitmap_cond_end_sync(mddev->bitmap, sector_nr, false);

        sh = raid5_get_active_stripe(conf, sector_nr, 0, 1, 0);
        if (sh == NULL) {
                sh = raid5_get_active_stripe(conf, sector_nr, 0, 0, 0);
                /* make sure we don't swamp the stripe cache if someone else
                 * is trying to get access
                 */
                schedule_timeout_uninterruptible(1);
        }
        /* Need to check if array will still be degraded after recovery/resync
         * Note in case of > 1 drive failures it's possible we're rebuilding
         * one drive while leaving another faulty drive in array.
         */
        rcu_read_lock();
        for (i = 0; i < conf->raid_disks; i++) {
                struct md_rdev *rdev = ACCESS_ONCE(conf->disks[i].rdev);

                if (rdev == NULL || test_bit(Faulty, &rdev->flags))
                        still_degraded = 1;
        }
        rcu_read_unlock();

        bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, still_degraded);

        set_bit(STRIPE_SYNC_REQUESTED, &sh->state);
        set_bit(STRIPE_HANDLE, &sh->state);

        raid5_release_stripe(sh);

        return STRIPE_SECTORS;
}

static int  retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)
{
        /* We may not be able to submit a whole bio at once as there
         * may not be enough stripe_heads available.
         * We cannot pre-allocate enough stripe_heads as we may need
         * more than exist in the cache (if we allow ever large chunks).
         * So we do one stripe head at a time and record in
         * ->bi_hw_segments how many have been done.
         *
         * We *know* that this entire raid_bio is in one chunk, so
         * it will be only one 'dd_idx' and only need one call to raid5_compute_sector.
         */
        struct stripe_head *sh;
        int dd_idx;
        sector_t sector, logical_sector, last_sector;
        int scnt = 0;
        int remaining;
        int handled = 0;

        logical_sector = raid_bio->bi_iter.bi_sector &
                ~((sector_t)STRIPE_SECTORS-1);
        sector = raid5_compute_sector(conf, logical_sector,
                                      0, &dd_idx, NULL);
        last_sector = bio_end_sector(raid_bio);

        for (; logical_sector < last_sector;
             logical_sector += STRIPE_SECTORS,
                     sector += STRIPE_SECTORS,
                     scnt++) {

                if (scnt < raid5_bi_processed_stripes(raid_bio))
                        /* already done this stripe */
                        continue;

                sh = raid5_get_active_stripe(conf, sector, 0, 1, 1);

                if (!sh) {
                        /* failed to get a stripe - must wait */
                        raid5_set_bi_processed_stripes(raid_bio, scnt);
                        conf->retry_read_aligned = raid_bio;
                        return handled;
                }

                if (!add_stripe_bio(sh, raid_bio, dd_idx, 0, 0)) {
                        raid5_release_stripe(sh);
                        raid5_set_bi_processed_stripes(raid_bio, scnt);
                        conf->retry_read_aligned = raid_bio;
                        return handled;
                }

                set_bit(R5_ReadNoMerge, &sh->dev[dd_idx].flags);
                handle_stripe(sh);
                raid5_release_stripe(sh);
                handled++;
        }
        remaining = raid5_dec_bi_active_stripes(raid_bio);
        if (remaining == 0) {
                trace_block_bio_complete(bdev_get_queue(raid_bio->bi_bdev),
                                         raid_bio, 0);
                bio_endio(raid_bio);
        }
        if (atomic_dec_and_test(&conf->active_aligned_reads))
                wake_up(&conf->wait_for_quiescent);
        return handled;
}

static int handle_active_stripes(struct r5conf *conf, int group,
                                 struct r5worker *worker,
                                 struct list_head *temp_inactive_list)
{
        struct stripe_head *batch[MAX_STRIPE_BATCH], *sh;
        int i, batch_size = 0, hash;
        bool release_inactive = false;

        while (batch_size < MAX_STRIPE_BATCH &&
                        (sh = __get_priority_stripe(conf, group)) != NULL)
                batch[batch_size++] = sh;

        if (batch_size == 0) {
                for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
                        if (!list_empty(temp_inactive_list + i))
                                break;
                if (i == NR_STRIPE_HASH_LOCKS) {
                        spin_unlock_irq(&conf->device_lock);
                        r5l_flush_stripe_to_raid(conf->log);
                        spin_lock_irq(&conf->device_lock);
                        return batch_size;
                }
                release_inactive = true;
        }
        spin_unlock_irq(&conf->device_lock);

        release_inactive_stripe_list(conf, temp_inactive_list,
                                     NR_STRIPE_HASH_LOCKS);

        r5l_flush_stripe_to_raid(conf->log);
        if (release_inactive) {
                spin_lock_irq(&conf->device_lock);
                return 0;
        }

        for (i = 0; i < batch_size; i++)
                handle_stripe(batch[i]);
        r5l_write_stripe_run(conf->log);

        cond_resched();

        spin_lock_irq(&conf->device_lock);
        for (i = 0; i < batch_size; i++) {
                hash = batch[i]->hash_lock_index;
                __release_stripe(conf, batch[i], &temp_inactive_list[hash]);
        }
        return batch_size;
}

static void raid5_do_work(struct work_struct *work)
{
        struct r5worker *worker = container_of(work, struct r5worker, work);
        struct r5worker_group *group = worker->group;
        struct r5conf *conf = group->conf;
        int group_id = group - conf->worker_groups;
        int handled;
        struct blk_plug plug;

        pr_debug("+++ raid5worker active\n");

        blk_start_plug(&plug);
        handled = 0;
        spin_lock_irq(&conf->device_lock);
        while (1) {
                int batch_size, released;

                released = release_stripe_list(conf, worker->temp_inactive_list);

                batch_size = handle_active_stripes(conf, group_id, worker,
                                                   worker->temp_inactive_list);
                worker->working = false;
                if (!batch_size && !released)
                        break;
                handled += batch_size;
        }
        pr_debug("%d stripes handled\n", handled);

        spin_unlock_irq(&conf->device_lock);

        async_tx_issue_pending_all();
        blk_finish_plug(&plug);

        pr_debug("--- raid5worker inactive\n");
}

/*
 * This is our raid5 kernel thread.
 *
 * We scan the hash table for stripes which can be handled now.
 * During the scan, completed stripes are saved for us by the interrupt
 * handler, so that they will not have to wait for our next wakeup.
 */
static void raid5d(struct md_thread *thread)
{
        struct mddev *mddev = thread->mddev;
        struct r5conf *conf = mddev->private;
        int handled;
        struct blk_plug plug;

        pr_debug("+++ raid5d active\n");

        md_check_recovery(mddev);

        if (!bio_list_empty(&conf->return_bi) &&
            !test_bit(MD_CHANGE_PENDING, &mddev->flags)) {
                struct bio_list tmp = BIO_EMPTY_LIST;
                spin_lock_irq(&conf->device_lock);
                if (!test_bit(MD_CHANGE_PENDING, &mddev->flags)) {
                        bio_list_merge(&tmp, &conf->return_bi);
                        bio_list_init(&conf->return_bi);
                }
                spin_unlock_irq(&conf->device_lock);
                return_io(&tmp);
        }

        blk_start_plug(&plug);
        handled = 0;
        spin_lock_irq(&conf->device_lock);
        while (1) {
                struct bio *bio;
                int batch_size, released;

                released = release_stripe_list(conf, conf->temp_inactive_list);
                if (released)
                        clear_bit(R5_DID_ALLOC, &conf->cache_state);

                if (
                    !list_empty(&conf->bitmap_list)) {
                        /* Now is a good time to flush some bitmap updates */
                        conf->seq_flush++;
                        spin_unlock_irq(&conf->device_lock);
                        bitmap_unplug(mddev->bitmap);
                        spin_lock_irq(&conf->device_lock);
                        conf->seq_write = conf->seq_flush;
                        activate_bit_delay(conf, conf->temp_inactive_list);
                }
                raid5_activate_delayed(conf);

                while ((bio = remove_bio_from_retry(conf))) {
                        int ok;
                        spin_unlock_irq(&conf->device_lock);
                        ok = retry_aligned_read(conf, bio);
                        spin_lock_irq(&conf->device_lock);
                        if (!ok)
                                break;
                        handled++;
                }

                batch_size = handle_active_stripes(conf, ANY_GROUP, NULL,
                                                   conf->temp_inactive_list);
                if (!batch_size && !released)
                        break;
                handled += batch_size;

                if (mddev->flags & ~(1<<MD_CHANGE_PENDING)) {
                        spin_unlock_irq(&conf->device_lock);
                        md_check_recovery(mddev);
                        spin_lock_irq(&conf->device_lock);
                }
        }
        pr_debug("%d stripes handled\n", handled);

        spin_unlock_irq(&conf->device_lock);
        if (test_and_clear_bit(R5_ALLOC_MORE, &conf->cache_state) &&
            mutex_trylock(&conf->cache_size_mutex)) {
                grow_one_stripe(conf, __GFP_NOWARN);
                /* Set flag even if allocation failed.  This helps
                 * slow down allocation requests when mem is short
                 */
                set_bit(R5_DID_ALLOC, &conf->cache_state);
                mutex_unlock(&conf->cache_size_mutex);
        }

        r5l_flush_stripe_to_raid(conf->log);

        async_tx_issue_pending_all();
        blk_finish_plug(&plug);

        pr_debug("--- raid5d inactive\n");
}

static ssize_t
raid5_show_stripe_cache_size(struct mddev *mddev, char *page)
{
        struct r5conf *conf;
        int ret = 0;
        spin_lock(&mddev->lock);
        conf = mddev->private;
        if (conf)
                ret = sprintf(page, "%d\n", conf->min_nr_stripes);
        spin_unlock(&mddev->lock);
        return ret;
}

int
raid5_set_cache_size(struct mddev *mddev, int size)
{
        struct r5conf *conf = mddev->private;
        int err;

        if (size <= 16 || size > 32768)
                return -EINVAL;

        conf->min_nr_stripes = size;
        mutex_lock(&conf->cache_size_mutex);
        while (size < conf->max_nr_stripes &&
               drop_one_stripe(conf))
                ;
        mutex_unlock(&conf->cache_size_mutex);


        err = md_allow_write(mddev);
        if (err)
                return err;

        mutex_lock(&conf->cache_size_mutex);
        while (size > conf->max_nr_stripes)
                if (!grow_one_stripe(conf, GFP_KERNEL))
                        break;
        mutex_unlock(&conf->cache_size_mutex);

        return 0;
}
EXPORT_SYMBOL(raid5_set_cache_size);

static ssize_t
raid5_store_stripe_cache_size(struct mddev *mddev, const char *page, size_t len)
{
        struct r5conf *conf;
        unsigned long new;
        int err;

        if (len >= PAGE_SIZE)
                return -EINVAL;
        if (kstrtoul(page, 10, &new))
                return -EINVAL;
        err = mddev_lock(mddev);
        if (err)
                return err;
        conf = mddev->private;
        if (!conf)
                err = -ENODEV;
        else
                err = raid5_set_cache_size(mddev, new);
        mddev_unlock(mddev);

        return err ?: len;
}

static struct md_sysfs_entry
raid5_stripecache_size = __ATTR(stripe_cache_size, S_IRUGO | S_IWUSR,
                                raid5_show_stripe_cache_size,
                                raid5_store_stripe_cache_size);

static ssize_t
raid5_show_rmw_level(struct mddev  *mddev, char *page)
{
        struct r5conf *conf = mddev->private;
        if (conf)
                return sprintf(page, "%d\n", conf->rmw_level);
        else
                return 0;
}

static ssize_t
raid5_store_rmw_level(struct mddev  *mddev, const char *page, size_t len)
{
        struct r5conf *conf = mddev->private;
        unsigned long new;

        if (!conf)
                return -ENODEV;

        if (len >= PAGE_SIZE)
                return -EINVAL;

        if (kstrtoul(page, 10, &new))
                return -EINVAL;

        if (new != PARITY_DISABLE_RMW && !raid6_call.xor_syndrome)
                return -EINVAL;

        if (new != PARITY_DISABLE_RMW &&
            new != PARITY_ENABLE_RMW &&
            new != PARITY_PREFER_RMW)
                return -EINVAL;

        conf->rmw_level = new;
        return len;
}

static struct md_sysfs_entry
raid5_rmw_level = __ATTR(rmw_level, S_IRUGO | S_IWUSR,
                         raid5_show_rmw_level,
                         raid5_store_rmw_level);


static ssize_t
raid5_show_preread_threshold(struct mddev *mddev, char *page)
{
        struct r5conf *conf;
        int ret = 0;
        spin_lock(&mddev->lock);
        conf = mddev->private;
        if (conf)
                ret = sprintf(page, "%d\n", conf->bypass_threshold);
        spin_unlock(&mddev->lock);
        return ret;
}

static ssize_t
raid5_store_preread_threshold(struct mddev *mddev, const char *page, size_t len)
{
        struct r5conf *conf;
        unsigned long new;
        int err;

        if (len >= PAGE_SIZE)
                return -EINVAL;
        if (kstrtoul(page, 10, &new))
                return -EINVAL;

        err = mddev_lock(mddev);
        if (err)
                return err;
        conf = mddev->private;
        if (!conf)
                err = -ENODEV;
        else if (new > conf->min_nr_stripes)
                err = -EINVAL;
        else
                conf->bypass_threshold = new;
        mddev_unlock(mddev);
        return err ?: len;
}

static struct md_sysfs_entry
raid5_preread_bypass_threshold = __ATTR(preread_bypass_threshold,
                                        S_IRUGO | S_IWUSR,
                                        raid5_show_preread_threshold,
                                        raid5_store_preread_threshold);

static ssize_t
raid5_show_skip_copy(struct mddev *mddev, char *page)
{
        struct r5conf *conf;
        int ret = 0;
        spin_lock(&mddev->lock);
        conf = mddev->private;
        if (conf)
                ret = sprintf(page, "%d\n", conf->skip_copy);
        spin_unlock(&mddev->lock);
        return ret;
}

static ssize_t
raid5_store_skip_copy(struct mddev *mddev, const char *page, size_t len)
{
        struct r5conf *conf;
        unsigned long new;
        int err;

        if (len >= PAGE_SIZE)
                return -EINVAL;
        if (kstrtoul(page, 10, &new))
                return -EINVAL;
        new = !!new;

        err = mddev_lock(mddev);
        if (err)
                return err;
        conf = mddev->private;
        if (!conf)
                err = -ENODEV;
        else if (new != conf->skip_copy) {
                mddev_suspend(mddev);
                conf->skip_copy = new;
                if (new)
                        mddev->queue->backing_dev_info.capabilities |=
                                BDI_CAP_STABLE_WRITES;
                else
                        mddev->queue->backing_dev_info.capabilities &=
                                ~BDI_CAP_STABLE_WRITES;
                mddev_resume(mddev);
        }
        mddev_unlock(mddev);
        return err ?: len;
}

static struct md_sysfs_entry
raid5_skip_copy = __ATTR(skip_copy, S_IRUGO | S_IWUSR,
                                        raid5_show_skip_copy,
                                        raid5_store_skip_copy);

static ssize_t
stripe_cache_active_show(struct mddev *mddev, char *page)
{
        struct r5conf *conf = mddev->private;
        if (conf)
                return sprintf(page, "%d\n", atomic_read(&conf->active_stripes));
        else
                return 0;
}

static struct md_sysfs_entry
raid5_stripecache_active = __ATTR_RO(stripe_cache_active);

static ssize_t
raid5_show_group_thread_cnt(struct mddev *mddev, char *page)
{
        struct r5conf *conf;
        int ret = 0;
        spin_lock(&mddev->lock);
        conf = mddev->private;
        if (conf)
                ret = sprintf(page, "%d\n", conf->worker_cnt_per_group);
        spin_unlock(&mddev->lock);
        return ret;
}

static int alloc_thread_groups(struct r5conf *conf, int cnt,
                               int *group_cnt,
                               int *worker_cnt_per_group,
                               struct r5worker_group **worker_groups);
static ssize_t
raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
{
        struct r5conf *conf;
        unsigned long new;
        int err;
        struct r5worker_group *new_groups, *old_groups;
        int group_cnt, worker_cnt_per_group;

        if (len >= PAGE_SIZE)
                return -EINVAL;
        if (kstrtoul(page, 10, &new))
                return -EINVAL;

        err = mddev_lock(mddev);
        if (err)
                return err;
        conf = mddev->private;
        if (!conf)
                err = -ENODEV;
        else if (new != conf->worker_cnt_per_group) {
                mddev_suspend(mddev);

                old_groups = conf->worker_groups;
                if (old_groups)
                        flush_workqueue(raid5_wq);

                err = alloc_thread_groups(conf, new,
                                          &group_cnt, &worker_cnt_per_group,
                                          &new_groups);
                if (!err) {
                        spin_lock_irq(&conf->device_lock);
                        conf->group_cnt = group_cnt;
                        conf->worker_cnt_per_group = worker_cnt_per_group;
                        conf->worker_groups = new_groups;
                        spin_unlock_irq(&conf->device_lock);

                        if (old_groups)
                                kfree(old_groups[0].workers);
                        kfree(old_groups);
                }
                mddev_resume(mddev);
        }
        mddev_unlock(mddev);

        return err ?: len;
}

static struct md_sysfs_entry
raid5_group_thread_cnt = __ATTR(group_thread_cnt, S_IRUGO | S_IWUSR,
                                raid5_show_group_thread_cnt,
                                raid5_store_group_thread_cnt);

static struct attribute *raid5_attrs[] =  {
        &raid5_stripecache_size.attr,
        &raid5_stripecache_active.attr,
        &raid5_preread_bypass_threshold.attr,
        &raid5_group_thread_cnt.attr,
        &raid5_skip_copy.attr,
        &raid5_rmw_level.attr,
        NULL,
};
static struct attribute_group raid5_attrs_group = {
        .name = NULL,
        .attrs = raid5_attrs,
};

static int alloc_thread_groups(struct r5conf *conf, int cnt,
                               int *group_cnt,
                               int *worker_cnt_per_group,
                               struct r5worker_group **worker_groups)
{
        int i, j, k;
        ssize_t size;
        struct r5worker *workers;

        *worker_cnt_per_group = cnt;
        if (cnt == 0) {
                *group_cnt = 0;
                *worker_groups = NULL;
                return 0;
        }
        *group_cnt = num_possible_nodes();
        size = sizeof(struct r5worker) * cnt;
        workers = kzalloc(size * *group_cnt, GFP_NOIO);
        *worker_groups = kzalloc(sizeof(struct r5worker_group) *
                                *group_cnt, GFP_NOIO);
        if (!*worker_groups || !workers) {
                kfree(workers);
                kfree(*worker_groups);
                return -ENOMEM;
        }

        for (i = 0; i < *group_cnt; i++) {
                struct r5worker_group *group;

                group = &(*worker_groups)[i];
                INIT_LIST_HEAD(&group->handle_list);
                group->conf = conf;
                group->workers = workers + i * cnt;

                for (j = 0; j < cnt; j++) {
                        struct r5worker *worker = group->workers + j;
                        worker->group = group;
                        INIT_WORK(&worker->work, raid5_do_work);

                        for (k = 0; k < NR_STRIPE_HASH_LOCKS; k++)
                                INIT_LIST_HEAD(worker->temp_inactive_list + k);
                }
        }

        return 0;
}

static void free_thread_groups(struct r5conf *conf)
{
        if (conf->worker_groups)
                kfree(conf->worker_groups[0].workers);
        kfree(conf->worker_groups);
        conf->worker_groups = NULL;
}

static sector_t
raid5_size(struct mddev *mddev, sector_t sectors, int raid_disks)
{
        struct r5conf *conf = mddev->private;

        if (!sectors)
                sectors = mddev->dev_sectors;
        if (!raid_disks)
                /* size is defined by the smallest of previous and new size */
                raid_disks = min(conf->raid_disks, conf->previous_raid_disks);

        sectors &= ~((sector_t)conf->chunk_sectors - 1);
        sectors &= ~((sector_t)conf->prev_chunk_sectors - 1);
        return sectors * (raid_disks - conf->max_degraded);
}

static void free_scratch_buffer(struct r5conf *conf, struct raid5_percpu *percpu)
{
        safe_put_page(percpu->spare_page);
        if (percpu->scribble)
                flex_array_free(percpu->scribble);
        percpu->spare_page = NULL;
        percpu->scribble = NULL;
}

static int alloc_scratch_buffer(struct r5conf *conf, struct raid5_percpu *percpu)
{
        if (conf->level == 6 && !percpu->spare_page)
                percpu->spare_page = alloc_page(GFP_KERNEL);
        if (!percpu->scribble)
                percpu->scribble = scribble_alloc(max(conf->raid_disks,
                                                      conf->previous_raid_disks),
                                                  max(conf->chunk_sectors,
                                                      conf->prev_chunk_sectors)
                                                   / STRIPE_SECTORS,
                                                  GFP_KERNEL);

        if (!percpu->scribble || (conf->level == 6 && !percpu->spare_page)) {
                free_scratch_buffer(conf, percpu);
                return -ENOMEM;
        }

        return 0;
}

static int raid456_cpu_dead(unsigned int cpu, struct hlist_node *node)
{
        struct r5conf *conf = hlist_entry_safe(node, struct r5conf, node);

        free_scratch_buffer(conf, per_cpu_ptr(conf->percpu, cpu));
        return 0;
}

static void raid5_free_percpu(struct r5conf *conf)
{
        if (!conf->percpu)
                return;

        cpuhp_state_remove_instance(CPUHP_MD_RAID5_PREPARE, &conf->node);
        free_percpu(conf->percpu);
}

static void free_conf(struct r5conf *conf)
{
        if (conf->log)
                r5l_exit_log(conf->log);
        if (conf->shrinker.nr_deferred)
                unregister_shrinker(&conf->shrinker);

        free_thread_groups(conf);
        shrink_stripes(conf);
        raid5_free_percpu(conf);
        kfree(conf->disks);
        kfree(conf->stripe_hashtbl);
        kfree(conf);
}

static int raid456_cpu_up_prepare(unsigned int cpu, struct hlist_node *node)
{
        struct r5conf *conf = hlist_entry_safe(node, struct r5conf, node);
        struct raid5_percpu *percpu = per_cpu_ptr(conf->percpu, cpu);

        if (alloc_scratch_buffer(conf, percpu)) {
                pr_err("%s: failed memory allocation for cpu%u\n",
                       __func__, cpu);
                return -ENOMEM;
        }
        return 0;
}

static int raid5_alloc_percpu(struct r5conf *conf)
{
        int err = 0;

        conf->percpu = alloc_percpu(struct raid5_percpu);
        if (!conf->percpu)
                return -ENOMEM;

        err = cpuhp_state_add_instance(CPUHP_MD_RAID5_PREPARE, &conf->node);
        if (!err) {
                conf->scribble_disks = max(conf->raid_disks,
                        conf->previous_raid_disks);
                conf->scribble_sectors = max(conf->chunk_sectors,
                        conf->prev_chunk_sectors);
        }
        return err;
}

static unsigned long raid5_cache_scan(struct shrinker *shrink,
                                      struct shrink_control *sc)
{
        struct r5conf *conf = container_of(shrink, struct r5conf, shrinker);
        unsigned long ret = SHRINK_STOP;

        if (mutex_trylock(&conf->cache_size_mutex)) {
                ret= 0;
                while (ret < sc->nr_to_scan &&
                       conf->max_nr_stripes > conf->min_nr_stripes) {
                        if (drop_one_stripe(conf) == 0) {
                                ret = SHRINK_STOP;
                                break;
                        }
                        ret++;
                }
                mutex_unlock(&conf->cache_size_mutex);
        }
        return ret;
}

static unsigned long raid5_cache_count(struct shrinker *shrink,
                                       struct shrink_control *sc)
{
        struct r5conf *conf = container_of(shrink, struct r5conf, shrinker);

        if (conf->max_nr_stripes < conf->min_nr_stripes)
                /* unlikely, but not impossible */
                return 0;
        return conf->max_nr_stripes - conf->min_nr_stripes;
}

static struct r5conf *setup_conf(struct mddev *mddev)
{
        struct r5conf *conf;
        int raid_disk, memory, max_disks;
        struct md_rdev *rdev;
        struct disk_info *disk;
        char pers_name[6];
        int i;
        int group_cnt, worker_cnt_per_group;
        struct r5worker_group *new_group;

        if (mddev->new_level != 5
            && mddev->new_level != 4
            && mddev->new_level != 6) {
                printk(KERN_ERR "md/raid:%s: raid level not set to 4/5/6 (%d)\n",
                       mdname(mddev), mddev->new_level);
                return ERR_PTR(-EIO);
        }
        if ((mddev->new_level == 5
             && !algorithm_valid_raid5(mddev->new_layout)) ||
            (mddev->new_level == 6
             && !algorithm_valid_raid6(mddev->new_layout))) {
                printk(KERN_ERR "md/raid:%s: layout %d not supported\n",
                       mdname(mddev), mddev->new_layout);
                return ERR_PTR(-EIO);
        }
        if (mddev->new_level == 6 && mddev->raid_disks < 4) {
                printk(KERN_ERR "md/raid:%s: not enough configured devices (%d, minimum 4)\n",
                       mdname(mddev), mddev->raid_disks);
                return ERR_PTR(-EINVAL);
        }

        if (!mddev->new_chunk_sectors ||
            (mddev->new_chunk_sectors << 9) % PAGE_SIZE ||
            !is_power_of_2(mddev->new_chunk_sectors)) {
                printk(KERN_ERR "md/raid:%s: invalid chunk size %d\n",
                       mdname(mddev), mddev->new_chunk_sectors << 9);
                return ERR_PTR(-EINVAL);
        }

        conf = kzalloc(sizeof(struct r5conf), GFP_KERNEL);
        if (conf == NULL)
                goto abort;
        /* Don't enable multi-threading by default*/
        if (!alloc_thread_groups(conf, 0, &group_cnt, &worker_cnt_per_group,
                                 &new_group)) {
                conf->group_cnt = group_cnt;
                conf->worker_cnt_per_group = worker_cnt_per_group;
                conf->worker_groups = new_group;
        } else
                goto abort;
        spin_lock_init(&conf->device_lock);
        seqcount_init(&conf->gen_lock);
        mutex_init(&conf->cache_size_mutex);
        init_waitqueue_head(&conf->wait_for_quiescent);
        init_waitqueue_head(&conf->wait_for_stripe);
        init_waitqueue_head(&conf->wait_for_overlap);
        INIT_LIST_HEAD(&conf->handle_list);
        INIT_LIST_HEAD(&conf->hold_list);
        INIT_LIST_HEAD(&conf->delayed_list);
        INIT_LIST_HEAD(&conf->bitmap_list);
        bio_list_init(&conf->return_bi);
        init_llist_head(&conf->released_stripes);
        atomic_set(&conf->active_stripes, 0);
        atomic_set(&conf->preread_active_stripes, 0);
        atomic_set(&conf->active_aligned_reads, 0);
        conf->bypass_threshold = BYPASS_THRESHOLD;
        conf->recovery_disabled = mddev->recovery_disabled - 1;

        conf->raid_disks = mddev->raid_disks;
        if (mddev->reshape_position == MaxSector)
                conf->previous_raid_disks = mddev->raid_disks;
        else
                conf->previous_raid_disks = mddev->raid_disks - mddev->delta_disks;
        max_disks = max(conf->raid_disks, conf->previous_raid_disks);

        conf->disks = kzalloc(max_disks * sizeof(struct disk_info),
                              GFP_KERNEL);
        if (!conf->disks)
                goto abort;

        conf->mddev = mddev;

        if ((conf->stripe_hashtbl = kzalloc(PAGE_SIZE, GFP_KERNEL)) == NULL)
                goto abort;

        /* We init hash_locks[0] separately to that it can be used
         * as the reference lock in the spin_lock_nest_lock() call
         * in lock_all_device_hash_locks_irq in order to convince
         * lockdep that we know what we are doing.
         */
        spin_lock_init(conf->hash_locks);
        for (i = 1; i < NR_STRIPE_HASH_LOCKS; i++)
                spin_lock_init(conf->hash_locks + i);

        for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
                INIT_LIST_HEAD(conf->inactive_list + i);

        for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
                INIT_LIST_HEAD(conf->temp_inactive_list + i);

        conf->level = mddev->new_level;
        conf->chunk_sectors = mddev->new_chunk_sectors;
        if (raid5_alloc_percpu(conf) != 0)
                goto abort;

        pr_debug("raid456: run(%s) called.\n", mdname(mddev));

        rdev_for_each(rdev, mddev) {
                raid_disk = rdev->raid_disk;
                if (raid_disk >= max_disks
                    || raid_disk < 0 || test_bit(Journal, &rdev->flags))
                        continue;
                disk = conf->disks + raid_disk;

                if (test_bit(Replacement, &rdev->flags)) {
                        if (disk->replacement)
                                goto abort;
                        disk->replacement = rdev;
                } else {
                        if (disk->rdev)
                                goto abort;
                        disk->rdev = rdev;
                }

                if (test_bit(In_sync, &rdev->flags)) {
                        char b[BDEVNAME_SIZE];
                        printk(KERN_INFO "md/raid:%s: device %s operational as raid"
                               " disk %d\n",
                               mdname(mddev), bdevname(rdev->bdev, b), raid_disk);
                } else if (rdev->saved_raid_disk != raid_disk)
                        /* Cannot rely on bitmap to complete recovery */
                        conf->fullsync = 1;
        }

        conf->level = mddev->new_level;
        if (conf->level == 6) {
                conf->max_degraded = 2;
                if (raid6_call.xor_syndrome)
                        conf->rmw_level = PARITY_ENABLE_RMW;
                else
                        conf->rmw_level = PARITY_DISABLE_RMW;
        } else {
                conf->max_degraded = 1;
                conf->rmw_level = PARITY_ENABLE_RMW;
        }
        conf->algorithm = mddev->new_layout;
        conf->reshape_progress = mddev->reshape_position;
        if (conf->reshape_progress != MaxSector) {
                conf->prev_chunk_sectors = mddev->chunk_sectors;
                conf->prev_algo = mddev->layout;
        } else {
                conf->prev_chunk_sectors = conf->chunk_sectors;
                conf->prev_algo = conf->algorithm;
        }

        conf->min_nr_stripes = NR_STRIPES;
        if (mddev->reshape_position != MaxSector) {
                int stripes = max_t(int,
                        ((mddev->chunk_sectors << 9) / STRIPE_SIZE) * 4,
                        ((mddev->new_chunk_sectors << 9) / STRIPE_SIZE) * 4);
                conf->min_nr_stripes = max(NR_STRIPES, stripes);
                if (conf->min_nr_stripes != NR_STRIPES)
                        printk(KERN_INFO
                                "md/raid:%s: force stripe size %d for reshape\n",
                                mdname(mddev), conf->min_nr_stripes);
        }
        memory = conf->min_nr_stripes * (sizeof(struct stripe_head) +
                 max_disks * ((sizeof(struct bio) + PAGE_SIZE))) / 1024;
        atomic_set(&conf->empty_inactive_list_nr, NR_STRIPE_HASH_LOCKS);
        if (grow_stripes(conf, conf->min_nr_stripes)) {
                printk(KERN_ERR
                       "md/raid:%s: couldn't allocate %dkB for buffers\n",
                       mdname(mddev), memory);
                goto abort;
        } else
                printk(KERN_INFO "md/raid:%s: allocated %dkB\n",
                       mdname(mddev), memory);
        /*
         * Losing a stripe head costs more than the time to refill it,
         * it reduces the queue depth and so can hurt throughput.
         * So set it rather large, scaled by number of devices.
         */
        conf->shrinker.seeks = DEFAULT_SEEKS * conf->raid_disks * 4;
        conf->shrinker.scan_objects = raid5_cache_scan;
        conf->shrinker.count_objects = raid5_cache_count;
        conf->shrinker.batch = 128;
        conf->shrinker.flags = 0;
        if (register_shrinker(&conf->shrinker)) {
                printk(KERN_ERR
                       "md/raid:%s: couldn't register shrinker.\n",
                       mdname(mddev));
                goto abort;
        }

        sprintf(pers_name, "raid%d", mddev->new_level);
        conf->thread = md_register_thread(raid5d, mddev, pers_name);
        if (!conf->thread) {
                printk(KERN_ERR
                       "md/raid:%s: couldn't allocate thread.\n",
                       mdname(mddev));
                goto abort;
        }

        return conf;

 abort:
        if (conf) {
                free_conf(conf);
                return ERR_PTR(-EIO);
        } else
                return ERR_PTR(-ENOMEM);
}

static int only_parity(int raid_disk, int algo, int raid_disks, int max_degraded)
{
        switch (algo) {
        case ALGORITHM_PARITY_0:
                if (raid_disk < max_degraded)
                        return 1;
                break;
        case ALGORITHM_PARITY_N:
                if (raid_disk >= raid_disks - max_degraded)
                        return 1;
                break;
        case ALGORITHM_PARITY_0_6:
                if (raid_disk == 0 ||
                    raid_disk == raid_disks - 1)
                        return 1;
                break;
        case ALGORITHM_LEFT_ASYMMETRIC_6:
        case ALGORITHM_RIGHT_ASYMMETRIC_6:
        case ALGORITHM_LEFT_SYMMETRIC_6:
        case ALGORITHM_RIGHT_SYMMETRIC_6:
                if (raid_disk == raid_disks - 1)
                        return 1;
        }
        return 0;
}

static int raid5_run(struct mddev *mddev)
{
        struct r5conf *conf;
        int working_disks = 0;
        int dirty_parity_disks = 0;
        struct md_rdev *rdev;
        struct md_rdev *journal_dev = NULL;
        sector_t reshape_offset = 0;
        int i;
        long long min_offset_diff = 0;
        int first = 1;

        if (mddev->recovery_cp != MaxSector)
                printk(KERN_NOTICE "md/raid:%s: not clean"
                       " -- starting background reconstruction\n",
                       mdname(mddev));

        rdev_for_each(rdev, mddev) {
                long long diff;

                if (test_bit(Journal, &rdev->flags)) {
                        journal_dev = rdev;
                        continue;
                }
                if (rdev->raid_disk < 0)
                        continue;
                diff = (rdev->new_data_offset - rdev->data_offset);
                if (first) {
                        min_offset_diff = diff;
                        first = 0;
                } else if (mddev->reshape_backwards &&
                         diff < min_offset_diff)
                        min_offset_diff = diff;
                else if (!mddev->reshape_backwards &&
                         diff > min_offset_diff)
                        min_offset_diff = diff;
        }

        if (mddev->reshape_position != MaxSector) {
                /* Check that we can continue the reshape.
                 * Difficulties arise if the stripe we would write to
                 * next is at or after the stripe we would read from next.
                 * For a reshape that changes the number of devices, this
                 * is only possible for a very short time, and mdadm makes
                 * sure that time appears to have past before assembling
                 * the array.  So we fail if that time hasn't passed.
                 * For a reshape that keeps the number of devices the same
                 * mdadm must be monitoring the reshape can keeping the
                 * critical areas read-only and backed up.  It will start
                 * the array in read-only mode, so we check for that.
                 */
                sector_t here_new, here_old;
                int old_disks;
                int max_degraded = (mddev->level == 6 ? 2 : 1);
                int chunk_sectors;
                int new_data_disks;

                if (journal_dev) {
                        printk(KERN_ERR "md/raid:%s: don't support reshape with journal - aborting.\n",
                               mdname(mddev));
                        return -EINVAL;
                }

                if (mddev->new_level != mddev->level) {
                        printk(KERN_ERR "md/raid:%s: unsupported reshape "
                               "required - aborting.\n",
                               mdname(mddev));
                        return -EINVAL;
                }
                old_disks = mddev->raid_disks - mddev->delta_disks;
                /* reshape_position must be on a new-stripe boundary, and one
                 * further up in new geometry must map after here in old
                 * geometry.
                 * If the chunk sizes are different, then as we perform reshape
                 * in units of the largest of the two, reshape_position needs
                 * be a multiple of the largest chunk size times new data disks.
                 */
                here_new = mddev->reshape_position;
                chunk_sectors = max(mddev->chunk_sectors, mddev->new_chunk_sectors);
                new_data_disks = mddev->raid_disks - max_degraded;
                if (sector_div(here_new, chunk_sectors * new_data_disks)) {
                        printk(KERN_ERR "md/raid:%s: reshape_position not "
                               "on a stripe boundary\n", mdname(mddev));
                        return -EINVAL;
                }
                reshape_offset = here_new * chunk_sectors;
                /* here_new is the stripe we will write to */
                here_old = mddev->reshape_position;
                sector_div(here_old, chunk_sectors * (old_disks-max_degraded));
                /* here_old is the first stripe that we might need to read
                 * from */
                if (mddev->delta_disks == 0) {
                        /* We cannot be sure it is safe to start an in-place
                         * reshape.  It is only safe if user-space is monitoring
                         * and taking constant backups.
                         * mdadm always starts a situation like this in
                         * readonly mode so it can take control before
                         * allowing any writes.  So just check for that.
                         */
                        if (abs(min_offset_diff) >= mddev->chunk_sectors &&
                            abs(min_offset_diff) >= mddev->new_chunk_sectors)
                                /* not really in-place - so OK */;
                        else if (mddev->ro == 0) {
                                printk(KERN_ERR "md/raid:%s: in-place reshape "
                                       "must be started in read-only mode "
                                       "- aborting\n",
                                       mdname(mddev));
                                return -EINVAL;
                        }
                } else if (mddev->reshape_backwards
                    ? (here_new * chunk_sectors + min_offset_diff <=
                       here_old * chunk_sectors)
                    : (here_new * chunk_sectors >=
                       here_old * chunk_sectors + (-min_offset_diff))) {
                        /* Reading from the same stripe as writing to - bad */
                        printk(KERN_ERR "md/raid:%s: reshape_position too early for "
                               "auto-recovery - aborting.\n",
                               mdname(mddev));
                        return -EINVAL;
                }
                printk(KERN_INFO "md/raid:%s: reshape will continue\n",
                       mdname(mddev));
                /* OK, we should be able to continue; */
        } else {
                BUG_ON(mddev->level != mddev->new_level);
                BUG_ON(mddev->layout != mddev->new_layout);
                BUG_ON(mddev->chunk_sectors != mddev->new_chunk_sectors);
                BUG_ON(mddev->delta_disks != 0);
        }

        if (mddev->private == NULL)
                conf = setup_conf(mddev);
        else
                conf = mddev->private;

        if (IS_ERR(conf))
                return PTR_ERR(conf);

        if (test_bit(MD_HAS_JOURNAL, &mddev->flags)) {
                if (!journal_dev) {
                        pr_err("md/raid:%s: journal disk is missing, force array readonly\n",
                               mdname(mddev));
                        mddev->ro = 1;
                        set_disk_ro(mddev->gendisk, 1);
                } else if (mddev->recovery_cp == MaxSector)
                        set_bit(MD_JOURNAL_CLEAN, &mddev->flags);
        }

        conf->min_offset_diff = min_offset_diff;
        mddev->thread = conf->thread;
        conf->thread = NULL;
        mddev->private = conf;

        for (i = 0; i < conf->raid_disks && conf->previous_raid_disks;
             i++) {
                rdev = conf->disks[i].rdev;
                if (!rdev && conf->disks[i].replacement) {
                        /* The replacement is all we have yet */
                        rdev = conf->disks[i].replacement;
                        conf->disks[i].replacement = NULL;
                        clear_bit(Replacement, &rdev->flags);
                        conf->disks[i].rdev = rdev;
                }
                if (!rdev)
                        continue;
                if (conf->disks[i].replacement &&
                    conf->reshape_progress != MaxSector) {
                        /* replacements and reshape simply do not mix. */
                        printk(KERN_ERR "md: cannot handle concurrent "
                               "replacement and reshape.\n");
                        goto abort;
                }
                if (test_bit(In_sync, &rdev->flags)) {
                        working_disks++;
                        continue;
                }
                /* This disc is not fully in-sync.  However if it
                 * just stored parity (beyond the recovery_offset),
                 * when we don't need to be concerned about the
                 * array being dirty.
                 * When reshape goes 'backwards', we never have
                 * partially completed devices, so we only need
                 * to worry about reshape going forwards.
                 */
                /* Hack because v0.91 doesn't store recovery_offset properly. */
                if (mddev->major_version == 0 &&
                    mddev->minor_version > 90)
                        rdev->recovery_offset = reshape_offset;

                if (rdev->recovery_offset < reshape_offset) {
                        /* We need to check old and new layout */
                        if (!only_parity(rdev->raid_disk,
                                         conf->algorithm,
                                         conf->raid_disks,
                                         conf->max_degraded))
                                continue;
                }
                if (!only_parity(rdev->raid_disk,
                                 conf->prev_algo,
                                 conf->previous_raid_disks,
                                 conf->max_degraded))
                        continue;
                dirty_parity_disks++;
        }

        /*
         * 0 for a fully functional array, 1 or 2 for a degraded array.
         */
        mddev->degraded = calc_degraded(conf);

        if (has_failed(conf)) {
                printk(KERN_ERR "md/raid:%s: not enough operational devices"
                        " (%d/%d failed)\n",
                        mdname(mddev), mddev->degraded, conf->raid_disks);
                goto abort;
        }

        /* device size must be a multiple of chunk size */
        mddev->dev_sectors &= ~(mddev->chunk_sectors - 1);
        mddev->resync_max_sectors = mddev->dev_sectors;

        if (mddev->degraded > dirty_parity_disks &&
            mddev->recovery_cp != MaxSector) {
                if (mddev->ok_start_degraded)
                        printk(KERN_WARNING
                               "md/raid:%s: starting dirty degraded array"
                               " - data corruption possible.\n",
                               mdname(mddev));
                else {
                        printk(KERN_ERR
                               "md/raid:%s: cannot start dirty degraded array.\n",
                               mdname(mddev));
                        goto abort;
                }
        }

        if (mddev->degraded == 0)
                printk(KERN_INFO "md/raid:%s: raid level %d active with %d out of %d"
                       " devices, algorithm %d\n", mdname(mddev), conf->level,
                       mddev->raid_disks-mddev->degraded, mddev->raid_disks,
                       mddev->new_layout);
        else
                printk(KERN_ALERT "md/raid:%s: raid level %d active with %d"
                       " out of %d devices, algorithm %d\n",
                       mdname(mddev), conf->level,
                       mddev->raid_disks - mddev->degraded,
                       mddev->raid_disks, mddev->new_layout);

        print_raid5_conf(conf);

        if (conf->reshape_progress != MaxSector) {
                conf->reshape_safe = conf->reshape_progress;
                atomic_set(&conf->reshape_stripes, 0);
                clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
                clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
                set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
                set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
                mddev->sync_thread = md_register_thread(md_do_sync, mddev,
                                                        "reshape");
        }

        /* Ok, everything is just fine now */
        if (mddev->to_remove == &raid5_attrs_group)
                mddev->to_remove = NULL;
        else if (mddev->kobj.sd &&
            sysfs_create_group(&mddev->kobj, &raid5_attrs_group))
                printk(KERN_WARNING
                       "raid5: failed to create sysfs attributes for %s\n",
                       mdname(mddev));
        md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));

        if (mddev->queue) {
                int chunk_size;
                bool discard_supported = true;
                /* read-ahead size must cover two whole stripes, which
                 * is 2 * (datadisks) * chunksize where 'n' is the
                 * number of raid devices
                 */
                int data_disks = conf->previous_raid_disks - conf->max_degraded;
                int stripe = data_disks *
                        ((mddev->chunk_sectors << 9) / PAGE_SIZE);
                if (mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
                        mddev->queue->backing_dev_info.ra_pages = 2 * stripe;

                chunk_size = mddev->chunk_sectors << 9;
                blk_queue_io_min(mddev->queue, chunk_size);
                blk_queue_io_opt(mddev->queue, chunk_size *
                                 (conf->raid_disks - conf->max_degraded));
                mddev->queue->limits.raid_partial_stripes_expensive = 1;
                /*
                 * We can only discard a whole stripe. It doesn't make sense to
                 * discard data disk but write parity disk
                 */
                stripe = stripe * PAGE_SIZE;
                /* Round up to power of 2, as discard handling
                 * currently assumes that */
                while ((stripe-1) & stripe)
                        stripe = (stripe | (stripe-1)) + 1;
                mddev->queue->limits.discard_alignment = stripe;
                mddev->queue->limits.discard_granularity = stripe;

                /*
                 * We use 16-bit counter of active stripes in bi_phys_segments
                 * (minus one for over-loaded initialization)
                 */
                blk_queue_max_hw_sectors(mddev->queue, 0xfffe * STRIPE_SECTORS);
                blk_queue_max_discard_sectors(mddev->queue,
                                              0xfffe * STRIPE_SECTORS);

                /*
                 * unaligned part of discard request will be ignored, so can't
                 * guarantee discard_zeroes_data
                 */
                mddev->queue->limits.discard_zeroes_data = 0;

                blk_queue_max_write_same_sectors(mddev->queue, 0);

                rdev_for_each(rdev, mddev) {
                        disk_stack_limits(mddev->gendisk, rdev->bdev,
                                          rdev->data_offset << 9);
                        disk_stack_limits(mddev->gendisk, rdev->bdev,
                                          rdev->new_data_offset << 9);
                        /*
                         * discard_zeroes_data is required, otherwise data
                         * could be lost. Consider a scenario: discard a stripe
                         * (the stripe could be inconsistent if
                         * discard_zeroes_data is 0); write one disk of the
                         * stripe (the stripe could be inconsistent again
                         * depending on which disks are used to calculate
                         * parity); the disk is broken; The stripe data of this
                         * disk is lost.
                         */
                        if (!blk_queue_discard(bdev_get_queue(rdev->bdev)) ||
                            !bdev_get_queue(rdev->bdev)->
                                                limits.discard_zeroes_data)
                                discard_supported = false;
                        /* Unfortunately, discard_zeroes_data is not currently
                         * a guarantee - just a hint.  So we only allow DISCARD
                         * if the sysadmin has confirmed that only safe devices
                         * are in use by setting a module parameter.
                         */
                        if (!devices_handle_discard_safely) {
                                if (discard_supported) {
                                        pr_info("md/raid456: discard support disabled due to uncertainty.\n");
                                        pr_info("Set raid456.devices_handle_discard_safely=Y to override.\n");
                                }
                                discard_supported = false;
                        }
                }

                if (discard_supported &&
                    mddev->queue->limits.max_discard_sectors >= (stripe >> 9) &&
                    mddev->queue->limits.discard_granularity >= stripe)
                        queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
                                                mddev->queue);
                else
                        queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD,
                                                mddev->queue);

                blk_queue_max_hw_sectors(mddev->queue, UINT_MAX);
        }

        if (journal_dev) {
                char b[BDEVNAME_SIZE];

                printk(KERN_INFO"md/raid:%s: using device %s as journal\n",
                       mdname(mddev), bdevname(journal_dev->bdev, b));
                r5l_init_log(conf, journal_dev);
        }

        return 0;
abort:
        md_unregister_thread(&mddev->thread);
        print_raid5_conf(conf);
        free_conf(conf);
        mddev->private = NULL;
        printk(KERN_ALERT "md/raid:%s: failed to run raid set.\n", mdname(mddev));
        return -EIO;
}

static void raid5_free(struct mddev *mddev, void *priv)
{
        struct r5conf *conf = priv;

        free_conf(conf);
        mddev->to_remove = &raid5_attrs_group;
}

static void raid5_status(struct seq_file *seq, struct mddev *mddev)
{
        struct r5conf *conf = mddev->private;
        int i;

        seq_printf(seq, " level %d, %dk chunk, algorithm %d", mddev->level,
                conf->chunk_sectors / 2, mddev->layout);
        seq_printf (seq, " [%d/%d] [", conf->raid_disks, conf->raid_disks - mddev->degraded);
        rcu_read_lock();
        for (i = 0; i < conf->raid_disks; i++) {
                struct md_rdev *rdev = rcu_dereference(conf->disks[i].rdev);
                seq_printf (seq, "%s", rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");
        }
        rcu_read_unlock();
        seq_printf (seq, "]");
}

static void print_raid5_conf (struct r5conf *conf)
{
        int i;
        struct disk_info *tmp;

        printk(KERN_DEBUG "RAID conf printout:\n");
        if (!conf) {
                printk("(conf==NULL)\n");
                return;
        }
        printk(KERN_DEBUG " --- level:%d rd:%d wd:%d\n", conf->level,
               conf->raid_disks,
               conf->raid_disks - conf->mddev->degraded);

        for (i = 0; i < conf->raid_disks; i++) {
                char b[BDEVNAME_SIZE];
                tmp = conf->disks + i;
                if (tmp->rdev)
                        printk(KERN_DEBUG " disk %d, o:%d, dev:%s\n",
                               i, !test_bit(Faulty, &tmp->rdev->flags),
                               bdevname(tmp->rdev->bdev, b));
        }
}

static int raid5_spare_active(struct mddev *mddev)
{
        int i;
        struct r5conf *conf = mddev->private;
        struct disk_info *tmp;
        int count = 0;
        unsigned long flags;

        for (i = 0; i < conf->raid_disks; i++) {
                tmp = conf->disks + i;
                if (tmp->replacement
                    && tmp->replacement->recovery_offset == MaxSector
                    && !test_bit(Faulty, &tmp->replacement->flags)
                    && !test_and_set_bit(In_sync, &tmp->replacement->flags)) {
                        /* Replacement has just become active. */
                        if (!tmp->rdev
                            || !test_and_clear_bit(In_sync, &tmp->rdev->flags))
                                count++;
                        if (tmp->rdev) {
                                /* Replaced device not technically faulty,
                                 * but we need to be sure it gets removed
                                 * and never re-added.
                                 */
                                set_bit(Faulty, &tmp->rdev->flags);
                                sysfs_notify_dirent_safe(
                                        tmp->rdev->sysfs_state);
                        }
                        sysfs_notify_dirent_safe(tmp->replacement->sysfs_state);
                } else if (tmp->rdev
                    && tmp->rdev->recovery_offset == MaxSector
                    && !test_bit(Faulty, &tmp->rdev->flags)
                    && !test_and_set_bit(In_sync, &tmp->rdev->flags)) {
                        count++;
                        sysfs_notify_dirent_safe(tmp->rdev->sysfs_state);
                }
        }
        spin_lock_irqsave(&conf->device_lock, flags);
        mddev->degraded = calc_degraded(conf);
        spin_unlock_irqrestore(&conf->device_lock, flags);
        print_raid5_conf(conf);
        return count;
}

static int raid5_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
{
        struct r5conf *conf = mddev->private;
        int err = 0;
        int number = rdev->raid_disk;
        struct md_rdev **rdevp;
        struct disk_info *p = conf->disks + number;

        print_raid5_conf(conf);
        if (test_bit(Journal, &rdev->flags) && conf->log) {
                struct r5l_log *log;
                /*
                 * we can't wait pending write here, as this is called in
                 * raid5d, wait will deadlock.
                 */
                if (atomic_read(&mddev->writes_pending))
                        return -EBUSY;
                log = conf->log;
                conf->log = NULL;
                synchronize_rcu();
                r5l_exit_log(log);
                return 0;
        }
        if (rdev == p->rdev)
                rdevp = &p->rdev;
        else if (rdev == p->replacement)
                rdevp = &p->replacement;
        else
                return 0;

        if (number >= conf->raid_disks &&
            conf->reshape_progress == MaxSector)
                clear_bit(In_sync, &rdev->flags);

        if (test_bit(In_sync, &rdev->flags) ||
            atomic_read(&rdev->nr_pending)) {
                err = -EBUSY;
                goto abort;
        }
        /* Only remove non-faulty devices if recovery
         * isn't possible.
         */
        if (!test_bit(Faulty, &rdev->flags) &&
            mddev->recovery_disabled != conf->recovery_disabled &&
            !has_failed(conf) &&
            (!p->replacement || p->replacement == rdev) &&
            number < conf->raid_disks) {
                err = -EBUSY;
                goto abort;
        }
        *rdevp = NULL;
        if (!test_bit(RemoveSynchronized, &rdev->flags)) {
                synchronize_rcu();
                if (atomic_read(&rdev->nr_pending)) {
                        /* lost the race, try later */
                        err = -EBUSY;
                        *rdevp = rdev;
                }
        }
        if (p->replacement) {
                /* We must have just cleared 'rdev' */
                p->rdev = p->replacement;
                clear_bit(Replacement, &p->replacement->flags);
                smp_mb(); /* Make sure other CPUs may see both as identical
                           * but will never see neither - if they are careful
                           */
                p->replacement = NULL;
                clear_bit(WantReplacement, &rdev->flags);
        } else
                /* We might have just removed the Replacement as faulty-
                 * clear the bit just in case
                 */
                clear_bit(WantReplacement, &rdev->flags);
abort:

        print_raid5_conf(conf);
        return err;
}

static int raid5_add_disk(struct mddev *mddev, struct md_rdev *rdev)
{
        struct r5conf *conf = mddev->private;
        int err = -EEXIST;
        int disk;
        struct disk_info *p;
        int first = 0;
        int last = conf->raid_disks - 1;

        if (test_bit(Journal, &rdev->flags)) {
                char b[BDEVNAME_SIZE];
                if (conf->log)
                        return -EBUSY;

                rdev->raid_disk = 0;
                /*
                 * The array is in readonly mode if journal is missing, so no
                 * write requests running. We should be safe
                 */
                r5l_init_log(conf, rdev);
                printk(KERN_INFO"md/raid:%s: using device %s as journal\n",
                       mdname(mddev), bdevname(rdev->bdev, b));
                return 0;
        }
        if (mddev->recovery_disabled == conf->recovery_disabled)
                return -EBUSY;

        if (rdev->saved_raid_disk < 0 && has_failed(conf))
                /* no point adding a device */
                return -EINVAL;

        if (rdev->raid_disk >= 0)
                first = last = rdev->raid_disk;

        /*
         * find the disk ... but prefer rdev->saved_raid_disk
         * if possible.
         */
        if (rdev->saved_raid_disk >= 0 &&
            rdev->saved_raid_disk >= first &&
            conf->disks[rdev->saved_raid_disk].rdev == NULL)
                first = rdev->saved_raid_disk;

        for (disk = first; disk <= last; disk++) {
                p = conf->disks + disk;
                if (p->rdev == NULL) {
                        clear_bit(In_sync, &rdev->flags);
                        rdev->raid_disk = disk;
                        err = 0;
                        if (rdev->saved_raid_disk != disk)
                                conf->fullsync = 1;
                        rcu_assign_pointer(p->rdev, rdev);
                        goto out;
                }
        }
        for (disk = first; disk <= last; disk++) {
                p = conf->disks + disk;
                if (test_bit(WantReplacement, &p->rdev->flags) &&
                    p->replacement == NULL) {
                        clear_bit(In_sync, &rdev->flags);
                        set_bit(Replacement, &rdev->flags);
                        rdev->raid_disk = disk;
                        err = 0;
                        conf->fullsync = 1;
                        rcu_assign_pointer(p->replacement, rdev);
                        break;
                }
        }
out:
        print_raid5_conf(conf);
        return err;
}

static int raid5_resize(struct mddev *mddev, sector_t sectors)
{
        /* no resync is happening, and there is enough space
         * on all devices, so we can resize.
         * We need to make sure resync covers any new space.
         * If the array is shrinking we should possibly wait until
         * any io in the removed space completes, but it hardly seems
         * worth it.
         */
        sector_t newsize;
        struct r5conf *conf = mddev->private;

        if (conf->log)
                return -EINVAL;
        sectors &= ~((sector_t)conf->chunk_sectors - 1);
        newsize = raid5_size(mddev, sectors, mddev->raid_disks);
        if (mddev->external_size &&
            mddev->array_sectors > newsize)
                return -EINVAL;
        if (mddev->bitmap) {
                int ret = bitmap_resize(mddev->bitmap, sectors, 0, 0);
                if (ret)
                        return ret;
        }
        md_set_array_sectors(mddev, newsize);
        set_capacity(mddev->gendisk, mddev->array_sectors);
        revalidate_disk(mddev->gendisk);
        if (sectors > mddev->dev_sectors &&
            mddev->recovery_cp > mddev->dev_sectors) {
                mddev->recovery_cp = mddev->dev_sectors;
                set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
        }
        mddev->dev_sectors = sectors;
        mddev->resync_max_sectors = sectors;
        return 0;
}

static int check_stripe_cache(struct mddev *mddev)
{
        /* Can only proceed if there are plenty of stripe_heads.
         * We need a minimum of one full stripe,, and for sensible progress
         * it is best to have about 4 times that.
         * If we require 4 times, then the default 256 4K stripe_heads will
         * allow for chunk sizes up to 256K, which is probably OK.
         * If the chunk size is greater, user-space should request more
         * stripe_heads first.
         */
        struct r5conf *conf = mddev->private;
        if (((mddev->chunk_sectors << 9) / STRIPE_SIZE) * 4
            > conf->min_nr_stripes ||
            ((mddev->new_chunk_sectors << 9) / STRIPE_SIZE) * 4
            > conf->min_nr_stripes) {
                printk(KERN_WARNING "md/raid:%s: reshape: not enough stripes.  Needed %lu\n",
                       mdname(mddev),
                       ((max(mddev->chunk_sectors, mddev->new_chunk_sectors) << 9)
                        / STRIPE_SIZE)*4);
                return 0;
        }
        return 1;
}

static int check_reshape(struct mddev *mddev)
{
        struct r5conf *conf = mddev->private;

        if (conf->log)
                return -EINVAL;
        if (mddev->delta_disks == 0 &&
            mddev->new_layout == mddev->layout &&
            mddev->new_chunk_sectors == mddev->chunk_sectors)
                return 0; /* nothing to do */
        if (has_failed(conf))
                return -EINVAL;
        if (mddev->delta_disks < 0 && mddev->reshape_position == MaxSector) {
                /* We might be able to shrink, but the devices must
                 * be made bigger first.
                 * For raid6, 4 is the minimum size.
                 * Otherwise 2 is the minimum
                 */
                int min = 2;
                if (mddev->level == 6)
                        min = 4;
                if (mddev->raid_disks + mddev->delta_disks < min)
                        return -EINVAL;
        }

        if (!check_stripe_cache(mddev))
                return -ENOSPC;

        if (mddev->new_chunk_sectors > mddev->chunk_sectors ||
            mddev->delta_disks > 0)
                if (resize_chunks(conf,
                                  conf->previous_raid_disks
                                  + max(0, mddev->delta_disks),
                                  max(mddev->new_chunk_sectors,
                                      mddev->chunk_sectors)
                            ) < 0)
                        return -ENOMEM;
        return resize_stripes(conf, (conf->previous_raid_disks
                                     + mddev->delta_disks));
}

static int raid5_start_reshape(struct mddev *mddev)
{
        struct r5conf *conf = mddev->private;
        struct md_rdev *rdev;
        int spares = 0;
        unsigned long flags;

        if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
                return -EBUSY;

        if (!check_stripe_cache(mddev))
                return -ENOSPC;

        if (has_failed(conf))
                return -EINVAL;

        rdev_for_each(rdev, mddev) {
                if (!test_bit(In_sync, &rdev->flags)
                    && !test_bit(Faulty, &rdev->flags))
                        spares++;
        }

        if (spares - mddev->degraded < mddev->delta_disks - conf->max_degraded)
                /* Not enough devices even to make a degraded array
                 * of that size
                 */
                return -EINVAL;

        /* Refuse to reduce size of the array.  Any reductions in
         * array size must be through explicit setting of array_size
         * attribute.
         */
        if (raid5_size(mddev, 0, conf->raid_disks + mddev->delta_disks)
            < mddev->array_sectors) {
                printk(KERN_ERR "md/raid:%s: array size must be reduced "
                       "before number of disks\n", mdname(mddev));
                return -EINVAL;
        }

        atomic_set(&conf->reshape_stripes, 0);
        spin_lock_irq(&conf->device_lock);
        write_seqcount_begin(&conf->gen_lock);
        conf->previous_raid_disks = conf->raid_disks;
        conf->raid_disks += mddev->delta_disks;
        conf->prev_chunk_sectors = conf->chunk_sectors;
        conf->chunk_sectors = mddev->new_chunk_sectors;
        conf->prev_algo = conf->algorithm;
        conf->algorithm = mddev->new_layout;
        conf->generation++;
        /* Code that selects data_offset needs to see the generation update
         * if reshape_progress has been set - so a memory barrier needed.
         */
        smp_mb();
        if (mddev->reshape_backwards)
                conf->reshape_progress = raid5_size(mddev, 0, 0);
        else
                conf->reshape_progress = 0;
        conf->reshape_safe = conf->reshape_progress;
        write_seqcount_end(&conf->gen_lock);
        spin_unlock_irq(&conf->device_lock);

        /* Now make sure any requests that proceeded on the assumption
         * the reshape wasn't running - like Discard or Read - have
         * completed.
         */
        mddev_suspend(mddev);
        mddev_resume(mddev);

        /* Add some new drives, as many as will fit.
         * We know there are enough to make the newly sized array work.
         * Don't add devices if we are reducing the number of
         * devices in the array.  This is because it is not possible
         * to correctly record the "partially reconstructed" state of
         * such devices during the reshape and confusion could result.
         */
        if (mddev->delta_disks >= 0) {
                rdev_for_each(rdev, mddev)
                        if (rdev->raid_disk < 0 &&
                            !test_bit(Faulty, &rdev->flags)) {
                                if (raid5_add_disk(mddev, rdev) == 0) {
                                        if (rdev->raid_disk
                                            >= conf->previous_raid_disks)
                                                set_bit(In_sync, &rdev->flags);
                                        else
                                                rdev->recovery_offset = 0;

                                        if (sysfs_link_rdev(mddev, rdev))
                                                /* Failure here is OK */;
                                }
                        } else if (rdev->raid_disk >= conf->previous_raid_disks
                                   && !test_bit(Faulty, &rdev->flags)) {
                                /* This is a spare that was manually added */
                                set_bit(In_sync, &rdev->flags);
                        }

                /* When a reshape changes the number of devices,
                 * ->degraded is measured against the larger of the
                 * pre and post number of devices.
                 */
                spin_lock_irqsave(&conf->device_lock, flags);
                mddev->degraded = calc_degraded(conf);
                spin_unlock_irqrestore(&conf->device_lock, flags);
        }
        mddev->raid_disks = conf->raid_disks;
        mddev->reshape_position = conf->reshape_progress;
        set_bit(MD_CHANGE_DEVS, &mddev->flags);

        clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
        clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
        clear_bit(MD_RECOVERY_DONE, &mddev->recovery);
        set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
        set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
        mddev->sync_thread = md_register_thread(md_do_sync, mddev,
                                                "reshape");
        if (!mddev->sync_thread) {
                mddev->recovery = 0;
                spin_lock_irq(&conf->device_lock);
                write_seqcount_begin(&conf->gen_lock);
                mddev->raid_disks = conf->raid_disks = conf->previous_raid_disks;
                mddev->new_chunk_sectors =
                        conf->chunk_sectors = conf->prev_chunk_sectors;
                mddev->new_layout = conf->algorithm = conf->prev_algo;
                rdev_for_each(rdev, mddev)
                        rdev->new_data_offset = rdev->data_offset;
                smp_wmb();
                conf->generation --;
                conf->reshape_progress = MaxSector;
                mddev->reshape_position = MaxSector;
                write_seqcount_end(&conf->gen_lock);
                spin_unlock_irq(&conf->device_lock);
                return -EAGAIN;
        }
        conf->reshape_checkpoint = jiffies;
        md_wakeup_thread(mddev->sync_thread);
        md_new_event(mddev);
        return 0;
}

/* This is called from the reshape thread and should make any
 * changes needed in 'conf'
 */
static void end_reshape(struct r5conf *conf)
{

        if (!test_bit(MD_RECOVERY_INTR, &conf->mddev->recovery)) {

                spin_lock_irq(&conf->device_lock);
                conf->previous_raid_disks = conf->raid_disks;
                md_finish_reshape(conf->mddev);
                smp_wmb();
                conf->reshape_progress = MaxSector;
                conf->mddev->reshape_position = MaxSector;
                spin_unlock_irq(&conf->device_lock);
                wake_up(&conf->wait_for_overlap);

                /* read-ahead size must cover two whole stripes, which is
                 * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
                 */
                if (conf->mddev->queue) {
                        int data_disks = conf->raid_disks - conf->max_degraded;
                        int stripe = data_disks * ((conf->chunk_sectors << 9)
                                                   / PAGE_SIZE);
                        if (conf->mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
                                conf->mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
                }
        }
}

/* This is called from the raid5d thread with mddev_lock held.
 * It makes config changes to the device.
 */
static void raid5_finish_reshape(struct mddev *mddev)
{
        struct r5conf *conf = mddev->private;

        if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery)) {

                if (mddev->delta_disks > 0) {
                        md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));
                        if (mddev->queue) {
                                set_capacity(mddev->gendisk, mddev->array_sectors);
                                revalidate_disk(mddev->gendisk);
                        }
                } else {
                        int d;
                        spin_lock_irq(&conf->device_lock);
                        mddev->degraded = calc_degraded(conf);
                        spin_unlock_irq(&conf->device_lock);
                        for (d = conf->raid_disks ;
                             d < conf->raid_disks - mddev->delta_disks;
                             d++) {
                                struct md_rdev *rdev = conf->disks[d].rdev;
                                if (rdev)
                                        clear_bit(In_sync, &rdev->flags);
                                rdev = conf->disks[d].replacement;
                                if (rdev)
                                        clear_bit(In_sync, &rdev->flags);
                        }
                }
                mddev->layout = conf->algorithm;
                mddev->chunk_sectors = conf->chunk_sectors;
                mddev->reshape_position = MaxSector;
                mddev->delta_disks = 0;
                mddev->reshape_backwards = 0;
        }
}

static void raid5_quiesce(struct mddev *mddev, int state)
{
        struct r5conf *conf = mddev->private;

        switch(state) {
        case 2: /* resume for a suspend */
                wake_up(&conf->wait_for_overlap);
                break;

        case 1: /* stop all writes */
                lock_all_device_hash_locks_irq(conf);
                /* '2' tells resync/reshape to pause so that all
                 * active stripes can drain
                 */
                conf->quiesce = 2;
                wait_event_cmd(conf->wait_for_quiescent,
                                    atomic_read(&conf->active_stripes) == 0 &&
                                    atomic_read(&conf->active_aligned_reads) == 0,
                                    unlock_all_device_hash_locks_irq(conf),
                                    lock_all_device_hash_locks_irq(conf));
                conf->quiesce = 1;
                unlock_all_device_hash_locks_irq(conf);
                /* allow reshape to continue */
                wake_up(&conf->wait_for_overlap);
                break;

        case 0: /* re-enable writes */
                lock_all_device_hash_locks_irq(conf);
                conf->quiesce = 0;
                wake_up(&conf->wait_for_quiescent);
                wake_up(&conf->wait_for_overlap);
                unlock_all_device_hash_locks_irq(conf);
                break;
        }
        r5l_quiesce(conf->log, state);
}

static void *raid45_takeover_raid0(struct mddev *mddev, int level)
{
        struct r0conf *raid0_conf = mddev->private;
        sector_t sectors;

        /* for raid0 takeover only one zone is supported */
        if (raid0_conf->nr_strip_zones > 1) {
                printk(KERN_ERR "md/raid:%s: cannot takeover raid0 with more than one zone.\n",
                       mdname(mddev));
                return ERR_PTR(-EINVAL);
        }

        sectors = raid0_conf->strip_zone[0].zone_end;
        sector_div(sectors, raid0_conf->strip_zone[0].nb_dev);
        mddev->dev_sectors = sectors;
        mddev->new_level = level;
        mddev->new_layout = ALGORITHM_PARITY_N;
        mddev->new_chunk_sectors = mddev->chunk_sectors;
        mddev->raid_disks += 1;
        mddev->delta_disks = 1;
        /* make sure it will be not marked as dirty */
        mddev->recovery_cp = MaxSector;

        return setup_conf(mddev);
}

static void *raid5_takeover_raid1(struct mddev *mddev)
{
        int chunksect;

        if (mddev->raid_disks != 2 ||
            mddev->degraded > 1)
                return ERR_PTR(-EINVAL);

        /* Should check if there are write-behind devices? */

        chunksect = 64*2; /* 64K by default */

        /* The array must be an exact multiple of chunksize */
        while (chunksect && (mddev->array_sectors & (chunksect-1)))
                chunksect >>= 1;

        if ((chunksect<<9) < STRIPE_SIZE)
                /* array size does not allow a suitable chunk size */
                return ERR_PTR(-EINVAL);

        mddev->new_level = 5;
        mddev->new_layout = ALGORITHM_LEFT_SYMMETRIC;
        mddev->new_chunk_sectors = chunksect;

        return setup_conf(mddev);
}

static void *raid5_takeover_raid6(struct mddev *mddev)
{
        int new_layout;

        switch (mddev->layout) {
        case ALGORITHM_LEFT_ASYMMETRIC_6:
                new_layout = ALGORITHM_LEFT_ASYMMETRIC;
                break;
        case ALGORITHM_RIGHT_ASYMMETRIC_6:
                new_layout = ALGORITHM_RIGHT_ASYMMETRIC;
                break;
        case ALGORITHM_LEFT_SYMMETRIC_6:
                new_layout = ALGORITHM_LEFT_SYMMETRIC;
                break;
        case ALGORITHM_RIGHT_SYMMETRIC_6:
                new_layout = ALGORITHM_RIGHT_SYMMETRIC;
                break;
        case ALGORITHM_PARITY_0_6:
                new_layout = ALGORITHM_PARITY_0;
                break;
        case ALGORITHM_PARITY_N:
                new_layout = ALGORITHM_PARITY_N;
                break;
        default:
                return ERR_PTR(-EINVAL);
        }
        mddev->new_level = 5;
        mddev->new_layout = new_layout;
        mddev->delta_disks = -1;
        mddev->raid_disks -= 1;
        return setup_conf(mddev);
}

static int raid5_check_reshape(struct mddev *mddev)
{
        /* For a 2-drive array, the layout and chunk size can be changed
         * immediately as not restriping is needed.
         * For larger arrays we record the new value - after validation
         * to be used by a reshape pass.
         */
        struct r5conf *conf = mddev->private;
        int new_chunk = mddev->new_chunk_sectors;

        if (mddev->new_layout >= 0 && !algorithm_valid_raid5(mddev->new_layout))
                return -EINVAL;
        if (new_chunk > 0) {
                if (!is_power_of_2(new_chunk))
                        return -EINVAL;
                if (new_chunk < (PAGE_SIZE>>9))
                        return -EINVAL;
                if (mddev->array_sectors & (new_chunk-1))
                        /* not factor of array size */
                        return -EINVAL;
        }

        /* They look valid */

        if (mddev->raid_disks == 2) {
                /* can make the change immediately */
                if (mddev->new_layout >= 0) {
                        conf->algorithm = mddev->new_layout;
                        mddev->layout = mddev->new_layout;
                }
                if (new_chunk > 0) {
                        conf->chunk_sectors = new_chunk ;
                        mddev->chunk_sectors = new_chunk;
                }
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                md_wakeup_thread(mddev->thread);
        }
        return check_reshape(mddev);
}

static int raid6_check_reshape(struct mddev *mddev)
{
        int new_chunk = mddev->new_chunk_sectors;

        if (mddev->new_layout >= 0 && !algorithm_valid_raid6(mddev->new_layout))
                return -EINVAL;
        if (new_chunk > 0) {
                if (!is_power_of_2(new_chunk))
                        return -EINVAL;
                if (new_chunk < (PAGE_SIZE >> 9))
                        return -EINVAL;
                if (mddev->array_sectors & (new_chunk-1))
                        /* not factor of array size */
                        return -EINVAL;
        }

        /* They look valid */
        return check_reshape(mddev);
}

static void *raid5_takeover(struct mddev *mddev)
{
        /* raid5 can take over:
         *  raid0 - if there is only one strip zone - make it a raid4 layout
         *  raid1 - if there are two drives.  We need to know the chunk size
         *  raid4 - trivial - just use a raid4 layout.
         *  raid6 - Providing it is a *_6 layout
         */
        if (mddev->level == 0)
                return raid45_takeover_raid0(mddev, 5);
        if (mddev->level == 1)
                return raid5_takeover_raid1(mddev);
        if (mddev->level == 4) {
                mddev->new_layout = ALGORITHM_PARITY_N;
                mddev->new_level = 5;
                return setup_conf(mddev);
        }
        if (mddev->level == 6)
                return raid5_takeover_raid6(mddev);

        return ERR_PTR(-EINVAL);
}

static void *raid4_takeover(struct mddev *mddev)
{
        /* raid4 can take over:
         *  raid0 - if there is only one strip zone
         *  raid5 - if layout is right
         */
        if (mddev->level == 0)
                return raid45_takeover_raid0(mddev, 4);
        if (mddev->level == 5 &&
            mddev->layout == ALGORITHM_PARITY_N) {
                mddev->new_layout = 0;
                mddev->new_level = 4;
                return setup_conf(mddev);
        }
        return ERR_PTR(-EINVAL);
}

static struct md_personality raid5_personality;

static void *raid6_takeover(struct mddev *mddev)
{
        /* Currently can only take over a raid5.  We map the
         * personality to an equivalent raid6 personality
         * with the Q block at the end.
         */
        int new_layout;

        if (mddev->pers != &raid5_personality)
                return ERR_PTR(-EINVAL);
        if (mddev->degraded > 1)
                return ERR_PTR(-EINVAL);
        if (mddev->raid_disks > 253)
                return ERR_PTR(-EINVAL);
        if (mddev->raid_disks < 3)
                return ERR_PTR(-EINVAL);

        switch (mddev->layout) {
        case ALGORITHM_LEFT_ASYMMETRIC:
                new_layout = ALGORITHM_LEFT_ASYMMETRIC_6;
                break;
        case ALGORITHM_RIGHT_ASYMMETRIC:
                new_layout = ALGORITHM_RIGHT_ASYMMETRIC_6;
                break;
        case ALGORITHM_LEFT_SYMMETRIC:
                new_layout = ALGORITHM_LEFT_SYMMETRIC_6;
                break;
        case ALGORITHM_RIGHT_SYMMETRIC:
                new_layout = ALGORITHM_RIGHT_SYMMETRIC_6;
                break;
        case ALGORITHM_PARITY_0:
                new_layout = ALGORITHM_PARITY_0_6;
                break;
        case ALGORITHM_PARITY_N:
                new_layout = ALGORITHM_PARITY_N;
                break;
        default:
                return ERR_PTR(-EINVAL);
        }
        mddev->new_level = 6;
        mddev->new_layout = new_layout;
        mddev->delta_disks = 1;
        mddev->raid_disks += 1;
        return setup_conf(mddev);
}

static struct md_personality raid6_personality =
{
        .name           = "raid6",
        .level          = 6,
        .owner          = THIS_MODULE,
        .make_request   = raid5_make_request,
        .run            = raid5_run,
        .free           = raid5_free,
        .status         = raid5_status,
        .error_handler  = raid5_error,
        .hot_add_disk   = raid5_add_disk,
        .hot_remove_disk= raid5_remove_disk,
        .spare_active   = raid5_spare_active,
        .sync_request   = raid5_sync_request,
        .resize         = raid5_resize,
        .size           = raid5_size,
        .check_reshape  = raid6_check_reshape,
        .start_reshape  = raid5_start_reshape,
        .finish_reshape = raid5_finish_reshape,
        .quiesce        = raid5_quiesce,
        .takeover       = raid6_takeover,
        .congested      = raid5_congested,
};
static struct md_personality raid5_personality =
{
        .name           = "raid5",
        .level          = 5,
        .owner          = THIS_MODULE,
        .make_request   = raid5_make_request,
        .run            = raid5_run,
        .free           = raid5_free,
        .status         = raid5_status,
        .error_handler  = raid5_error,
        .hot_add_disk   = raid5_add_disk,
        .hot_remove_disk= raid5_remove_disk,
        .spare_active   = raid5_spare_active,
        .sync_request   = raid5_sync_request,
        .resize         = raid5_resize,
        .size           = raid5_size,
        .check_reshape  = raid5_check_reshape,
        .start_reshape  = raid5_start_reshape,
        .finish_reshape = raid5_finish_reshape,
        .quiesce        = raid5_quiesce,
        .takeover       = raid5_takeover,
        .congested      = raid5_congested,
};

static struct md_personality raid4_personality =
{
        .name           = "raid4",
        .level          = 4,
        .owner          = THIS_MODULE,
        .make_request   = raid5_make_request,
        .run            = raid5_run,
        .free           = raid5_free,
        .status         = raid5_status,
        .error_handler  = raid5_error,
        .hot_add_disk   = raid5_add_disk,
        .hot_remove_disk= raid5_remove_disk,
        .spare_active   = raid5_spare_active,
        .sync_request   = raid5_sync_request,
        .resize         = raid5_resize,
        .size           = raid5_size,
        .check_reshape  = raid5_check_reshape,
        .start_reshape  = raid5_start_reshape,
        .finish_reshape = raid5_finish_reshape,
        .quiesce        = raid5_quiesce,
        .takeover       = raid4_takeover,
        .congested      = raid5_congested,
};

static int __init raid5_init(void)
{
        int ret;

        raid5_wq = alloc_workqueue("raid5wq",
                WQ_UNBOUND|WQ_MEM_RECLAIM|WQ_CPU_INTENSIVE|WQ_SYSFS, 0);
        if (!raid5_wq)
                return -ENOMEM;

        ret = cpuhp_setup_state_multi(CPUHP_MD_RAID5_PREPARE,
                                      "md/raid5:prepare",
                                      raid456_cpu_up_prepare,
                                      raid456_cpu_dead);
        if (ret) {
                destroy_workqueue(raid5_wq);
                return ret;
        }
        register_md_personality(&raid6_personality);
        register_md_personality(&raid5_personality);
        register_md_personality(&raid4_personality);
        return 0;
}

static void raid5_exit(void)
{
        unregister_md_personality(&raid6_personality);
        unregister_md_personality(&raid5_personality);
        unregister_md_personality(&raid4_personality);
        cpuhp_remove_multi_state(CPUHP_MD_RAID5_PREPARE);
        destroy_workqueue(raid5_wq);
}

module_init(raid5_init);
module_exit(raid5_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("RAID4/5/6 (striping with parity) personality for MD");
MODULE_ALIAS("md-personality-4"); /* RAID5 */
MODULE_ALIAS("md-raid5");
MODULE_ALIAS("md-raid4");
MODULE_ALIAS("md-level-5");
MODULE_ALIAS("md-level-4");
MODULE_ALIAS("md-personality-8"); /* RAID6 */
MODULE_ALIAS("md-raid6");
MODULE_ALIAS("md-level-6");

/* This used to be two separate modules, they were: */
MODULE_ALIAS("raid5");
MODULE_ALIAS("raid6");