memcg: fix mutex not unlocked on memcg_create_kmem_cache fail path

Commit 842e2873697e ("memcg: get rid of kmem_cache_dup()") introduced a
mutex for memcg_create_kmem_cache() to protect the tmp_name buffer that
holds the memcg name.  It failed to unlock the mutex if this buffer
could not be allocated.

This patch fixes the issue by appropriately unlocking the mutex if the
allocation fails.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Glauber Costa <glommer@parallels.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 4 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 19d5d4274e22..53385cd4e6f0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3400,7 +3400,7 @@ void mem_cgroup_destroy_cache(struct kmem_cache *cachep)
 static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
                                                   struct kmem_cache *s)
 {
-        struct kmem_cache *new;
+        struct kmem_cache *new = NULL;
         static char *tmp_name = NULL;
         static DEFINE_MUTEX(mutex);     /* protects tmp_name */
 
@@ -3416,7 +3416,7 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
         if (!tmp_name) {
                 tmp_name = kmalloc(PATH_MAX, GFP_KERNEL);
                 if (!tmp_name)
-                        return NULL;
+                        goto out;
         }
 
         rcu_read_lock();
@@ -3426,12 +3426,11 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
 
         new = kmem_cache_create_memcg(memcg, tmp_name, s->object_size, s->align,
                                       (s->flags & ~SLAB_PANIC), s->ctor, s);
-
         if (new)
                 new->allocflags |= __GFP_KMEMCG;
         else
                 new = s;
-
+out:
         mutex_unlock(&mutex);
         return new;
 }