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cgroup: fix lockdep warning for event_control

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The cgroup_event_wake() function is called with the wait queue head
locked and it takes cgrp->event_list_lock. However, in cgroup_rmdir()
remove_wait_queue() was being called after taking
cgrp->event_list_lock.  Correct the lock ordering by using a temporary
list to obtain the event list to remove from the wait queue.

Signed-off-by: Greg Thelen <gthelen@google.com>
Signed-off-by: Aaron Durbin <adurbin@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Greg Thelen 2012-11-28 13:50:44 -08:00 committed by Tejun Heo
parent fddfb02ad0
commit 205a872bd6
1 changed files with 8 additions and 3 deletions
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11
kernel/cgroup.c
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@ -4277,6 +4277,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
DEFINE_WAIT(wait);
struct cgroup_event *event, *tmp;
struct cgroup_subsys *ss;
LIST_HEAD(tmp_list);
lockdep_assert_held(&d->d_inode->i_mutex);
lockdep_assert_held(&cgroup_mutex);
@ -4331,16 +4332,20 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
/*
* Unregister events and notify userspace.
* Notify userspace about cgroup removing only after rmdir of cgroup
* directory to avoid race between userspace and kernelspace
* directory to avoid race between userspace and kernelspace. Use
* a temporary list to avoid a deadlock with cgroup_event_wake(). Since
* cgroup_event_wake() is called with the wait queue head locked,
* remove_wait_queue() cannot be called while holding event_list_lock.
*/
spin_lock(&cgrp->event_list_lock);
list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
list_splice_init(&cgrp->event_list, &tmp_list);
spin_unlock(&cgrp->event_list_lock);
list_for_each_entry_safe(event, tmp, &tmp_list, list) {
list_del(&event->list);
remove_wait_queue(event->wqh, &event->wait);
eventfd_signal(event->eventfd, 1);
schedule_work(&event->remove);
}
spin_unlock(&cgrp->event_list_lock);
return 0;
}