diff options
| -rw-r--r-- | kernel/cgroup/cgroup.c | 42 |
1 files changed, 22 insertions, 20 deletions
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 2163054e1aa6..4ca3cb993da2 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -6229,20 +6229,22 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) * cgroup_drain_dying - wait for dying tasks to leave before rmdir * @cgrp: the cgroup being removed * - * The PF_EXITING filter in css_task_iter_advance() hides exiting tasks from - * cgroup.procs so that userspace (e.g. systemd) doesn't see tasks that have - * already been reaped via waitpid(). However, the populated counter - * (nr_populated_csets) is only decremented when the task later passes through + * cgroup.procs and cgroup.threads use css_task_iter which filters out + * PF_EXITING tasks so that userspace doesn't see tasks that have already been + * reaped via waitpid(). However, cgroup_has_tasks() - which tests whether the + * cgroup has non-empty css_sets - is only updated when dying tasks pass through * cgroup_task_dead() in finish_task_switch(). This creates a window where - * cgroup.procs appears empty but cgroup_is_populated() is still true, causing - * rmdir to fail with -EBUSY. + * cgroup.procs reads empty but cgroup_has_tasks() is still true, making rmdir + * fail with -EBUSY from cgroup_destroy_locked() even though userspace sees no + * tasks. + * + * This function aligns cgroup_has_tasks() with what userspace can observe. If + * cgroup_has_tasks() but the task iterator sees nothing (all remaining tasks are + * PF_EXITING), we wait for cgroup_task_dead() to finish processing them. As the + * window between PF_EXITING and cgroup_task_dead() is short, the wait is brief. * - * This function bridges that gap. If the cgroup is populated but all remaining - * tasks have PF_EXITING set, we wait for cgroup_task_dead() to process them. - * Tasks are removed from the cgroup's css_set in cgroup_task_dead() called from - * finish_task_switch(). As the window between PF_EXITING and cgroup_task_dead() - * is short, the number of PF_EXITING tasks on the list is small and the wait - * is brief. + * This function only concerns itself with this cgroup's own dying tasks. + * Whether the cgroup has children is cgroup_destroy_locked()'s problem. * * Each cgroup_task_dead() kicks the waitqueue via cset->cgrp_links, and we * retry the full check from scratch. @@ -6258,7 +6260,7 @@ static int cgroup_drain_dying(struct cgroup *cgrp) lockdep_assert_held(&cgroup_mutex); retry: - if (!cgroup_is_populated(cgrp)) + if (!cgroup_has_tasks(cgrp)) return 0; /* Same iterator as cgroup.threads - if any task is visible, it's busy */ @@ -6273,15 +6275,15 @@ retry: * All remaining tasks are PF_EXITING and will pass through * cgroup_task_dead() shortly. Wait for a kick and retry. * - * cgroup_is_populated() can't transition from false to true while - * we're holding cgroup_mutex, but the true to false transition - * happens under css_set_lock (via cgroup_task_dead()). We must - * retest and prepare_to_wait() under css_set_lock. Otherwise, the - * transition can happen between our first test and - * prepare_to_wait(), and we sleep with no one to wake us. + * cgroup_has_tasks() can't transition from false to true while we're + * holding cgroup_mutex, but the true to false transition happens + * under css_set_lock (via cgroup_task_dead()). We must retest and + * prepare_to_wait() under css_set_lock. Otherwise, the transition + * can happen between our first test and prepare_to_wait(), and we + * sleep with no one to wake us. */ spin_lock_irq(&css_set_lock); - if (!cgroup_is_populated(cgrp)) { + if (!cgroup_has_tasks(cgrp)) { spin_unlock_irq(&css_set_lock); return 0; } |