[PATCH cgroup/for-3.16] cgroup: fix rcu_read_lock() leak in update_if_frozen()

[Tejun Heo]

While updating cgroup_freezer locking, 68fafb77d827 ("cgroup_freezer:
replace freezer->lock with freezer_mutex") introduced a bug in
update_if_frozen() where it returns with rcu_read_lock() held.  Fix it
by adding rcu_read_unlock() before returning.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reported-by: kbuild test robot <fengguang.wu@xxxxxxxxx>
---
 kernel/cgroup_freezer.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -267,8 +267,10 @@ static void update_if_frozen(struct cgro
 		struct freezer *child = css_freezer(pos);
 
 		if ((child->state & CGROUP_FREEZER_ONLINE) &&
-		    !(child->state & CGROUP_FROZEN))
+		    !(child->state & CGROUP_FROZEN)) {
+			rcu_read_unlock();
 			return;
+		}
 	}
 	rcu_read_unlock();
 
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