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 <gthe...@google.com>
Signed-off-by: Aaron Durbin <adur...@google.com>
---
kernel/cgroup.c | 11 ++++++++---
1 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ece60d4..a0d75bb 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4276,6 +4276,7 @@ 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);
@@ -4330,16 +4331,20 @@ 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;
}
--
1.7.7.3
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