memcg: avoid accessing memcg after releasing reference

This might cause a use-after-free bug.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Cc: Glauber Costa <glommer@parallels.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.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 360464f..c92bcfc 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3215,12 +3215,12 @@ void memcg_release_cache(struct kmem_cache *s)
 
        root = s->memcg_params->root_cache;
        root->memcg_params->memcg_caches[id] = NULL;
-       mem_cgroup_put(memcg);
 
        mutex_lock(&memcg->slab_caches_mutex);
        list_del(&s->memcg_params->list);
        mutex_unlock(&memcg->slab_caches_mutex);
 
+       mem_cgroup_put(memcg);
 out:
        kfree(s->memcg_params);
 }