kernel/cgroup/freezer.c

   1 //SPDX-License-Identifier: GPL-2.0
   2 #include <linux/cgroup.h>
   3 #include <linux/sched.h>
   4 #include <linux/sched/task.h>
   5 #include <linux/sched/signal.h>
   6
   7 #include "cgroup-internal.h"
   8
   9 #include <trace/events/cgroup.h>
  10
  11 /*
  12  * Propagate the cgroup frozen state upwards by the cgroup tree.
  13  */
  14 static void cgroup_propagate_frozen(struct cgroup *cgrp, bool frozen)
  15 {
  16         int desc = 1;
  17
  18         /*
  19          * If the new state is frozen, some freezing ancestor cgroups may change
  20          * their state too, depending on if all their descendants are frozen.
  21          *
  22          * Otherwise, all ancestor cgroups are forced into the non-frozen state.
  23          */
  24         while ((cgrp = cgroup_parent(cgrp))) {
  25                 if (frozen) {
  26                         cgrp->freezer.nr_frozen_descendants += desc;
  27                         if (!test_bit(CGRP_FROZEN, &cgrp->flags) &&
  28                             test_bit(CGRP_FREEZE, &cgrp->flags) &&
  29                             cgrp->freezer.nr_frozen_descendants ==
  30                             cgrp->nr_descendants) {
  31                                 set_bit(CGRP_FROZEN, &cgrp->flags);
  32                                 cgroup_file_notify(&cgrp->events_file);
  33                                 TRACE_CGROUP_PATH(notify_frozen, cgrp, 1);
  34                                 desc++;
  35                         }
  36                 } else {
  37                         cgrp->freezer.nr_frozen_descendants -= desc;
  38                         if (test_bit(CGRP_FROZEN, &cgrp->flags)) {
  39                                 clear_bit(CGRP_FROZEN, &cgrp->flags);
  40                                 cgroup_file_notify(&cgrp->events_file);
  41                                 TRACE_CGROUP_PATH(notify_frozen, cgrp, 0);
  42                                 desc++;
  43                         }
  44                 }
  45         }
  46 }
  47
  48 /*
  49  * Revisit the cgroup frozen state.
  50  * Checks if the cgroup is really frozen and perform all state transitions.
  51  */
  52 void cgroup_update_frozen(struct cgroup *cgrp)
  53 {
  54         bool frozen;
  55
  56         lockdep_assert_held(&css_set_lock);
  57
  58         /*
  59          * If the cgroup has to be frozen (CGRP_FREEZE bit set),
  60          * and all tasks are frozen and/or stopped, let's consider
  61          * the cgroup frozen. Otherwise it's not frozen.
  62          */
  63         frozen = test_bit(CGRP_FREEZE, &cgrp->flags) &&
  64                 cgrp->freezer.nr_frozen_tasks == __cgroup_task_count(cgrp);
  65
  66         if (frozen) {
  67                 /* Already there? */
  68                 if (test_bit(CGRP_FROZEN, &cgrp->flags))
  69                         return;
  70
  71                 set_bit(CGRP_FROZEN, &cgrp->flags);
  72         } else {
  73                 /* Already there? */
  74                 if (!test_bit(CGRP_FROZEN, &cgrp->flags))
  75                         return;
  76
  77                 clear_bit(CGRP_FROZEN, &cgrp->flags);
  78         }
  79         cgroup_file_notify(&cgrp->events_file);
  80         TRACE_CGROUP_PATH(notify_frozen, cgrp, frozen);
  81
  82         /* Update the state of ancestor cgroups. */
  83         cgroup_propagate_frozen(cgrp, frozen);
  84 }
  85
  86 /*
  87  * Increment cgroup's nr_frozen_tasks.
  88  */
  89 static void cgroup_inc_frozen_cnt(struct cgroup *cgrp)
  90 {
  91         cgrp->freezer.nr_frozen_tasks++;
  92 }
  93
  94 /*
  95  * Decrement cgroup's nr_frozen_tasks.
  96  */
  97 static void cgroup_dec_frozen_cnt(struct cgroup *cgrp)
  98 {
  99         cgrp->freezer.nr_frozen_tasks--;
 100         WARN_ON_ONCE(cgrp->freezer.nr_frozen_tasks < 0);
 101 }
 102
 103 /*
 104  * Enter frozen/stopped state, if not yet there. Update cgroup's counters,
 105  * and revisit the state of the cgroup, if necessary.
 106  */
 107 void cgroup_enter_frozen(void)
 108 {
 109         struct cgroup *cgrp;
 110
 111         if (current->frozen)
 112                 return;
 113
 114         spin_lock_irq(&css_set_lock);
 115         current->frozen = true;
 116         cgrp = task_dfl_cgroup(current);
 117         cgroup_inc_frozen_cnt(cgrp);
 118         cgroup_update_frozen(cgrp);
 119         spin_unlock_irq(&css_set_lock);
 120 }
 121
 122 /*
 123  * Conditionally leave frozen/stopped state. Update cgroup's counters,
 124  * and revisit the state of the cgroup, if necessary.
 125  *
 126  * If always_leave is not set, and the cgroup is freezing,
 127  * we're racing with the cgroup freezing. In this case, we don't
 128  * drop the frozen counter to avoid a transient switch to
 129  * the unfrozen state.
 130  */
 131 void cgroup_leave_frozen(bool always_leave)
 132 {
 133         struct cgroup *cgrp;
 134
 135         spin_lock_irq(&css_set_lock);
 136         cgrp = task_dfl_cgroup(current);
 137         if (always_leave || !test_bit(CGRP_FREEZE, &cgrp->flags)) {
 138                 cgroup_dec_frozen_cnt(cgrp);
 139                 cgroup_update_frozen(cgrp);
 140                 WARN_ON_ONCE(!current->frozen);
 141                 current->frozen = false;
 142         } else if (!(current->jobctl & JOBCTL_TRAP_FREEZE)) {
 143                 spin_lock(&current->sighand->siglock);
 144                 current->jobctl |= JOBCTL_TRAP_FREEZE;
 145                 set_thread_flag(TIF_SIGPENDING);
 146                 spin_unlock(&current->sighand->siglock);
 147         }
 148         spin_unlock_irq(&css_set_lock);
 149 }
 150
 151 /*
 152  * Freeze or unfreeze the task by setting or clearing the JOBCTL_TRAP_FREEZE
 153  * jobctl bit.
 154  */
 155 static void cgroup_freeze_task(struct task_struct *task, bool freeze)
 156 {
 157         unsigned long flags;
 158
 159         /* If the task is about to die, don't bother with freezing it. */
 160         if (!lock_task_sighand(task, &flags))
 161                 return;
 162
 163         if (freeze) {
 164                 task->jobctl |= JOBCTL_TRAP_FREEZE;
 165                 signal_wake_up(task, false);
 166         } else {
 167                 task->jobctl &= ~JOBCTL_TRAP_FREEZE;
 168                 wake_up_process(task);
 169         }
 170
 171         unlock_task_sighand(task, &flags);
 172 }
 173
 174 /*
 175  * Freeze or unfreeze all tasks in the given cgroup.
 176  */
 177 static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze)
 178 {
 179         struct css_task_iter it;
 180         struct task_struct *task;
 181
 182         lockdep_assert_held(&cgroup_mutex);
 183
 184         spin_lock_irq(&css_set_lock);
 185         if (freeze)
 186                 set_bit(CGRP_FREEZE, &cgrp->flags);
 187         else
 188                 clear_bit(CGRP_FREEZE, &cgrp->flags);
 189         spin_unlock_irq(&css_set_lock);
 190
 191         if (freeze)
 192                 TRACE_CGROUP_PATH(freeze, cgrp);
 193         else
 194                 TRACE_CGROUP_PATH(unfreeze, cgrp);
 195
 196         css_task_iter_start(&cgrp->self, 0, &it);
 197         while ((task = css_task_iter_next(&it))) {
 198                 /*
 199                  * Ignore kernel threads here. Freezing cgroups containing
 200                  * kthreads isn't supported.
 201                  */
 202                 if (task->flags & PF_KTHREAD)
 203                         continue;
 204                 cgroup_freeze_task(task, freeze);
 205         }
 206         css_task_iter_end(&it);
 207
 208         /*
 209          * Cgroup state should be revisited here to cover empty leaf cgroups
 210          * and cgroups which descendants are already in the desired state.
 211          */
 212         spin_lock_irq(&css_set_lock);
 213         if (cgrp->nr_descendants == cgrp->freezer.nr_frozen_descendants)
 214                 cgroup_update_frozen(cgrp);
 215         spin_unlock_irq(&css_set_lock);
 216 }
 217
 218 /*
 219  * Adjust the task state (freeze or unfreeze) and revisit the state of
 220  * source and destination cgroups.
 221  */
 222 void cgroup_freezer_migrate_task(struct task_struct *task,
 223                                  struct cgroup *src, struct cgroup *dst)
 224 {
 225         lockdep_assert_held(&css_set_lock);
 226
 227         /*
 228          * Kernel threads are not supposed to be frozen at all.
 229          */
 230         if (task->flags & PF_KTHREAD)
 231                 return;
 232
 233         /*
 234          * Adjust counters of freezing and frozen tasks.
 235          * Note, that if the task is frozen, but the destination cgroup is not
 236          * frozen, we bump both counters to keep them balanced.
 237          */
 238         if (task->frozen) {
 239                 cgroup_inc_frozen_cnt(dst);
 240                 cgroup_dec_frozen_cnt(src);
 241         }
 242         cgroup_update_frozen(dst);
 243         cgroup_update_frozen(src);
 244
 245         /*
 246          * Force the task to the desired state.
 247          */
 248         cgroup_freeze_task(task, test_bit(CGRP_FREEZE, &dst->flags));
 249 }
 250
 251 void cgroup_freeze(struct cgroup *cgrp, bool freeze)
 252 {
 253         struct cgroup_subsys_state *css;
 254         struct cgroup *dsct;
 255         bool applied = false;
 256
 257         lockdep_assert_held(&cgroup_mutex);
 258
 259         /*
 260          * Nothing changed? Just exit.
 261          */
 262         if (cgrp->freezer.freeze == freeze)
 263                 return;
 264
 265         cgrp->freezer.freeze = freeze;
 266
 267         /*
 268          * Propagate changes downwards the cgroup tree.
 269          */
 270         css_for_each_descendant_pre(css, &cgrp->self) {
 271                 dsct = css->cgroup;
 272
 273                 if (cgroup_is_dead(dsct))
 274                         continue;
 275
 276                 if (freeze) {
 277                         dsct->freezer.e_freeze++;
 278                         /*
 279                          * Already frozen because of ancestor's settings?
 280                          */
 281                         if (dsct->freezer.e_freeze > 1)
 282                                 continue;
 283                 } else {
 284                         dsct->freezer.e_freeze--;
 285                         /*
 286                          * Still frozen because of ancestor's settings?
 287                          */
 288                         if (dsct->freezer.e_freeze > 0)
 289                                 continue;
 290
 291                         WARN_ON_ONCE(dsct->freezer.e_freeze < 0);
 292                 }
 293
 294                 /*
 295                  * Do change actual state: freeze or unfreeze.
 296                  */
 297                 cgroup_do_freeze(dsct, freeze);
 298                 applied = true;
 299         }
 300
 301         /*
 302          * Even if the actual state hasn't changed, let's notify a user.
 303          * The state can be enforced by an ancestor cgroup: the cgroup
 304          * can already be in the desired state or it can be locked in the
 305          * opposite state, so that the transition will never happen.
 306          * In both cases it's better to notify a user, that there is
 307          * nothing to wait for.
 308          */
 309         if (!applied) {
 310                 TRACE_CGROUP_PATH(notify_frozen, cgrp,
 311                                   test_bit(CGRP_FROZEN, &cgrp->flags));
 312                 cgroup_file_notify(&cgrp->events_file);
 313         }
 314 }