From: Christian Lamparter Date: Fri, 21 Jun 2019 17:21:30 +0000 (+0200) Subject: kernel: add promising "fix loop discard errors" hack X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=82f3a2b81e72f5d672f599d3dcb2959055f52418;p=oweals%2Fopenwrt.git kernel: add promising "fix loop discard errors" hack This patch adds a promising upstream patch that claims to help for the treated I/O errors happening on f2fs or ext4 on real block devices. |print_req_error: I/O error, dev loop1, sector 1334 Link: Signed-off-by: Christian Lamparter --- diff --git a/target/linux/generic/hack-4.19/550-loop-better-discard-for-block-devices.patch b/target/linux/generic/hack-4.19/550-loop-better-discard-for-block-devices.patch new file mode 100644 index 0000000000..d6f0f3df0a --- /dev/null +++ b/target/linux/generic/hack-4.19/550-loop-better-discard-for-block-devices.patch @@ -0,0 +1,164 @@ +From: Evan Green +Subject: [PATCH v5 0/2] loop: Better discard for block devices +Date: Mon, 6 May 2019 11:27:35 -0700 +Message-Id: <20190506182736.21064-2-evgreen@chromium.org> + +This series addresses some errors seen when using the loop +device directly backed by a block device. + +The first change titled "loop: Better discard for block devices" +plumbs out the correct error message, and the second change prevents +the error from occurring in many cases. + +The errors look like this: +[ 90.880875] print_req_error: I/O error, dev loop5, sector 0 + +The errors occur when trying to do a discard or write zeroes operation +on a loop device backed by a block device that does not support write zeroes. +Firstly, the error itself is incorrectly reported as I/O error, but is +actually EOPNOTSUPP. The first patch plumbs out EOPNOTSUPP to properly +report the error. + +The second patch called "loop: Better discard support for block devices" +prevents these errors from occurring by mirroring the zeroing capabilities +of the underlying block device into the loop device. +Before this change, discard was always reported as being supported, and +the loop device simply turns around and does an fallocate operation on the +backing device. After this change, backing block devices that do support +zeroing will continue to work as before, and continue to get all the +benefits of doing that. Backing devices that do not support zeroing will +fail earlier, avoiding hitting the loop device at all and ultimately +avoiding this error in the logs. + +I can also confirm that this fixes test block/003 in the blktests, when +running blktests on a loop device backed by a block device. + +Signed-off-by: Evan Green +Reviewed-by: Ming Lei +Reviewed-by: Bart Van Assche +Reviewed-by: Martin K. Petersen +Reviewed-by: Gwendal Grignou +Reviewed-by: Chaitanya Kulkarni +--- + +--- a/drivers/block/loop.c ++++ b/drivers/block/loop.c +@@ -416,19 +416,14 @@ out_free_page: + return ret; + } + +-static int lo_discard(struct loop_device *lo, struct request *rq, loff_t pos) ++static int lo_discard(struct loop_device *lo, struct request *rq, ++ int mode, loff_t pos) + { +- /* +- * We use punch hole to reclaim the free space used by the +- * image a.k.a. discard. However we do not support discard if +- * encryption is enabled, because it may give an attacker +- * useful information. +- */ + struct file *file = lo->lo_backing_file; +- int mode = FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE; ++ struct request_queue *q = lo->lo_queue; + int ret; + +- if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) { ++ if (!blk_queue_discard(q)) { + ret = -EOPNOTSUPP; + goto out; + } +@@ -457,7 +452,9 @@ static void lo_complete_rq(struct reques + + if (!cmd->use_aio || cmd->ret < 0 || cmd->ret == blk_rq_bytes(rq) || + req_op(rq) != REQ_OP_READ) { +- if (cmd->ret < 0) ++ if (cmd->ret == -EOPNOTSUPP) ++ ret = BLK_STS_NOTSUPP; ++ else if (cmd->ret < 0) + ret = BLK_STS_IOERR; + goto end_io; + } +@@ -597,8 +594,13 @@ static int do_req_filebacked(struct loop + case REQ_OP_FLUSH: + return lo_req_flush(lo, rq); + case REQ_OP_DISCARD: ++ return lo_discard(lo, rq, ++ FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, pos); ++ + case REQ_OP_WRITE_ZEROES: +- return lo_discard(lo, rq, pos); ++ return lo_discard(lo, rq, ++ FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE, pos); ++ + case REQ_OP_WRITE: + if (lo->transfer) + return lo_write_transfer(lo, rq, pos); +@@ -853,6 +855,21 @@ static void loop_config_discard(struct l + struct file *file = lo->lo_backing_file; + struct inode *inode = file->f_mapping->host; + struct request_queue *q = lo->lo_queue; ++ struct request_queue *backingq; ++ ++ /* ++ * If the backing device is a block device, mirror its zeroing ++ * capability. REQ_OP_DISCARD translates to a zero-out even when backed ++ * by block devices to keep consistent behavior with file-backed loop ++ * devices. ++ */ ++ if (S_ISBLK(inode->i_mode) && !lo->lo_encrypt_key_size) { ++ backingq = bdev_get_queue(inode->i_bdev); ++ blk_queue_max_discard_sectors(q, ++ backingq->limits.max_write_zeroes_sectors); ++ ++ blk_queue_max_write_zeroes_sectors(q, ++ backingq->limits.max_write_zeroes_sectors); + + /* + * We use punch hole to reclaim the free space used by the +@@ -860,22 +877,24 @@ static void loop_config_discard(struct l + * encryption is enabled, because it may give an attacker + * useful information. + */ +- if ((!file->f_op->fallocate) || +- lo->lo_encrypt_key_size) { ++ } else if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) { + q->limits.discard_granularity = 0; + q->limits.discard_alignment = 0; + blk_queue_max_discard_sectors(q, 0); + blk_queue_max_write_zeroes_sectors(q, 0); +- blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q); +- return; +- } + +- q->limits.discard_granularity = inode->i_sb->s_blocksize; +- q->limits.discard_alignment = 0; ++ } else { ++ q->limits.discard_granularity = inode->i_sb->s_blocksize; ++ q->limits.discard_alignment = 0; + +- blk_queue_max_discard_sectors(q, UINT_MAX >> 9); +- blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9); +- blk_queue_flag_set(QUEUE_FLAG_DISCARD, q); ++ blk_queue_max_discard_sectors(q, UINT_MAX >> 9); ++ blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9); ++ } ++ ++ if (q->limits.max_write_zeroes_sectors) ++ blk_queue_flag_set(QUEUE_FLAG_DISCARD, q); ++ else ++ blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q); + } + + static void loop_unprepare_queue(struct loop_device *lo) +@@ -1893,7 +1912,10 @@ static void loop_handle_cmd(struct loop_ + failed: + /* complete non-aio request */ + if (!cmd->use_aio || ret) { +- cmd->ret = ret ? -EIO : 0; ++ if (ret == -EOPNOTSUPP) ++ cmd->ret = ret; ++ else ++ cmd->ret = ret ? -EIO : 0; + blk_mq_complete_request(rq); + } + }