slub: fix memcg_propagate_slab_attrs

After creating a cache for a memcg we should initialize its sysfs attrs
with the values from its parent.  That's what memcg_propagate_slab_attrs
is for.  Currently it's broken - we clearly muddled root-vs-memcg caches
there.  Let's fix it up.
Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slub.c

@@ -5071,15 +5071,18 @@ static void memcg_propagate_slab_attrs(struct kmem_cache *s)
 #ifdef CONFIG_MEMCG_KMEM
 	int i;
 	char *buffer = NULL;
+	struct kmem_cache *root_cache;
 
-	if (!is_root_cache(s))
+	if (is_root_cache(s))
 		return;
 
+	root_cache = s->memcg_params->root_cache;
+
 	/*
 	 * This mean this cache had no attribute written. Therefore, no point
 	 * in copying default values around
 	 */
-	if (!s->max_attr_size)
+	if (!root_cache->max_attr_size)
 		return;
 
 	for (i = 0; i < ARRAY_SIZE(slab_attrs); i++) {
@@ -5101,7 +5104,7 @@ static void memcg_propagate_slab_attrs(struct kmem_cache *s)
 		 */
 		if (buffer)
 			buf = buffer;
-		else if (s->max_attr_size < ARRAY_SIZE(mbuf))
+		else if (root_cache->max_attr_size < ARRAY_SIZE(mbuf))
 			buf = mbuf;
 		else {
 			buffer = (char *) get_zeroed_page(GFP_KERNEL);
@@ -5110,7 +5113,7 @@ static void memcg_propagate_slab_attrs(struct kmem_cache *s)
 			buf = buffer;
 		}
 
-		attr->show(s->memcg_params->root_cache, buf);
+		attr->show(root_cache, buf);
 		attr->store(s, buf, strlen(buf));
 	}