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 <glommer@parallels.com>
Reported-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f4f41c36e70325c00a56e37cba22f80e7384336d..60d28e36f0e0f9e57379b4cf0003e6073bfb19a6 100644 (file)
--- 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;
 }