slab: do not panic if we fail to create memcg cache

There is no point in flooding logs with warnings or especially crashing
the system if we fail to create a cache for a memcg.  In this case we
will be accounting the memcg allocation to the root cgroup until we
succeed to create its own cache, but it isn't that critical.
Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slab_common.c

@@ -233,7 +233,14 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size,
 	mutex_unlock(&slab_mutex);
 	put_online_cpus();
 
-	if (err) {
+	/*
+	 * There is no point in flooding logs with warnings or especially
+	 * crashing the system if we fail to create a cache for a memcg. In
+	 * this case we will be accounting the memcg allocation to the root
+	 * cgroup until we succeed to create its own cache, but it isn't that
+	 * critical.
+	 */
+	if (err && !memcg) {
 		if (flags & SLAB_PANIC)
 			panic("kmem_cache_create: Failed to create slab '%s'. Error %d\n",
 				name, err);