diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6ba4dd988e2e49..67648e6b2ac85e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3661,6 +3661,7 @@ static void memcg_deactivate_kmem(struct mem_cgroup *memcg)
 	 * ordering is imposed by list_lru_node->lock taken by
 	 * memcg_drain_all_list_lrus().
 	 */
+	rcu_read_lock(); /* can be called from css_free w/o cgroup_mutex */
 	css_for_each_descendant_pre(css, &memcg->css) {
 		child = mem_cgroup_from_css(css);
 		BUG_ON(child->kmemcg_id != kmemcg_id);
@@ -3668,6 +3669,8 @@ static void memcg_deactivate_kmem(struct mem_cgroup *memcg)
 		if (!memcg->use_hierarchy)
 			break;
 	}
+	rcu_read_unlock();
+
 	memcg_drain_all_list_lrus(kmemcg_id, parent->kmemcg_id);
 
 	memcg_free_cache_id(kmemcg_id);