slab: clean up kmem_cache_create_memcg() error handling

Currently kmem_cache_create_memcg() backoffs on failure inside
conditionals, without using gotos.  This results in the rollback code
duplication, which makes the function look cumbersome even though on
error we should only free the allocated cache.  Since in the next patch
I am going to add yet another rollback function call on error path
there, let's employ labels instead of conditionals for undoing any
changes on failure to keep things clean.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.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

@@ -171,13 +171,14 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size,
 			struct kmem_cache *parent_cache)
 {
 	struct kmem_cache *s = NULL;
-	int err = 0;
+	int err;
 
 	get_online_cpus();
 	mutex_lock(&slab_mutex);
 
-	if (!kmem_cache_sanity_check(memcg, name, size) == 0)
-		goto out_locked;
+	err = kmem_cache_sanity_check(memcg, name, size);
+	if (err)
+		goto out_unlock;
 
 	/*
 	 * Some allocators will constraint the set of valid flags to a subset
@@ -189,45 +190,38 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size,
 
 	s = __kmem_cache_alias(memcg, name, size, align, flags, ctor);
 	if (s)
-		goto out_locked;
+		goto out_unlock;
 
+	err = -ENOMEM;
 	s = kmem_cache_zalloc(kmem_cache, GFP_KERNEL);
-	if (s) {
-		s->object_size = s->size = size;
-		s->align = calculate_alignment(flags, align, size);
-		s->ctor = ctor;
+	if (!s)
+		goto out_unlock;
 
-		if (memcg_register_cache(memcg, s, parent_cache)) {
-			kmem_cache_free(kmem_cache, s);
-			err = -ENOMEM;
-			goto out_locked;
-		}
+	s->object_size = s->size = size;
+	s->align = calculate_alignment(flags, align, size);
+	s->ctor = ctor;
 
-		s->name = kstrdup(name, GFP_KERNEL);
-		if (!s->name) {
-			kmem_cache_free(kmem_cache, s);
-			err = -ENOMEM;
-			goto out_locked;
-		}
+	s->name = kstrdup(name, GFP_KERNEL);
+	if (!s->name)
+		goto out_free_cache;
 
-		err = __kmem_cache_create(s, flags);
-		if (!err) {
-			s->refcount = 1;
-			list_add(&s->list, &slab_caches);
-			memcg_cache_list_add(memcg, s);
-		} else {
-			kfree(s->name);
-			kmem_cache_free(kmem_cache, s);
-		}
-	} else
-		err = -ENOMEM;
+	err = memcg_register_cache(memcg, s, parent_cache);
+	if (err)
+		goto out_free_cache;
+
+	err = __kmem_cache_create(s, flags);
+	if (err)
+		goto out_free_cache;
+
+	s->refcount = 1;
+	list_add(&s->list, &slab_caches);
+	memcg_cache_list_add(memcg, s);
 
-out_locked:
+out_unlock:
 	mutex_unlock(&slab_mutex);
 	put_online_cpus();
 
 	if (err) {
-
 		if (flags & SLAB_PANIC)
 			panic("kmem_cache_create: Failed to create slab '%s'. Error %d\n",
 				name, err);
@@ -236,11 +230,14 @@ out_locked:
 				name, err);
 			dump_stack();
 		}
-
 		return NULL;
 	}
-
 	return s;
+
+out_free_cache:
+	kfree(s->name);
+	kmem_cache_free(kmem_cache, s);
+	goto out_unlock;
 }
 
 struct kmem_cache *