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Commit 205a872b authored by Greg Thelen's avatar Greg Thelen Committed by Tejun Heo
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cgroup: fix lockdep warning for event_control 



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: default avatarGreg Thelen <gthelen@google.com>
Signed-off-by: default avatarAaron Durbin <adurbin@google.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent fddfb02a

kernel/cgroup.c

+8 −3
Original line number Diff line number Diff line
@@ -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;

}