1 files changed, 14 insertions, 9 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 014a4f1acf1c..d2da65c4cd84 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3264,6 +3264,12 @@ void memcg_register_cache(struct kmem_cache *s)
         if (is_root_cache(s))
                 return;
 
+        /*
+         * Holding the slab_mutex assures nobody will touch the memcg_caches
+         * array while we are modifying it.
+         */
+        lockdep_assert_held(&slab_mutex);
+
         root = s->memcg_params->root_cache;
         memcg = s->memcg_params->memcg;
         id = memcg_cache_id(memcg);
@@ -3283,6 +3289,7 @@ void memcg_register_cache(struct kmem_cache *s)
          * before adding it to the memcg_slab_caches list, otherwise we can
          * fail to convert memcg_params_to_cache() while traversing the list.
          */
+        VM_BUG_ON(root->memcg_params->memcg_caches[id]);
         root->memcg_params->memcg_caches[id] = s;
 
         mutex_lock(&memcg->slab_caches_mutex);
@@ -3299,6 +3306,12 @@ void memcg_unregister_cache(struct kmem_cache *s)
         if (is_root_cache(s))
                 return;
 
+        /*
+         * Holding the slab_mutex assures nobody will touch the memcg_caches
+         * array while we are modifying it.
+         */
+        lockdep_assert_held(&slab_mutex);
+
         root = s->memcg_params->root_cache;
         memcg = s->memcg_params->memcg;
         id = memcg_cache_id(memcg);
@@ -3312,6 +3325,7 @@ void memcg_unregister_cache(struct kmem_cache *s)
          * after removing it from the memcg_slab_caches list, otherwise we can
          * fail to convert memcg_params_to_cache() while traversing the list.
          */
+        VM_BUG_ON(!root->memcg_params->memcg_caches[id]);
         root->memcg_params->memcg_caches[id] = NULL;
 
         css_put(&memcg->css);
@@ -3464,22 +3478,13 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
                                                   struct kmem_cache *cachep)
 {
         struct kmem_cache *new_cachep;
-        int idx;
 
         BUG_ON(!memcg_can_account_kmem(memcg));
 
-        idx = memcg_cache_id(memcg);
-
         mutex_lock(&memcg_cache_mutex);
-        new_cachep = cache_from_memcg_idx(cachep, idx);
-        if (new_cachep)
-                goto out;
-
         new_cachep = kmem_cache_dup(memcg, cachep);
         if (new_cachep == NULL)
                 new_cachep = cachep;
-
-out:
         mutex_unlock(&memcg_cache_mutex);
         return new_cachep;
 }