memcg: avoid dangling reference count in creation failure.

When use_hierarchy is enabled, we acquire an extra reference count in
our parent during cgroup creation.  We don't release it, though, if any
failure exist in the creation process.

Signed-off-by: Glauber Costa <[email protected]>
Reported-by: Michal Hocko <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Hiroyuki Kamezawa <[email protected]>
Cc: Johannes Weiner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f4f41c36e703..60d28e36f0e0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6196,6 +6196,8 @@ mem_cgroup_css_online(struct cgroup *cont)
 		 * call __mem_cgroup_free, so return directly
 		 */
 		mem_cgroup_put(memcg);
+		if (parent->use_hierarchy)
+			mem_cgroup_put(parent);
 	}
 	return error;
 }