slab: delete cache from list after __kmem_cache_shutdown succeeds

Currently, on kmem_cache_destroy we delete the cache from the slab_list
before __kmem_cache_shutdown, inserting it back to the list on failure.
Initially, this was done, because we could release the slab_mutex in
__kmem_cache_shutdown to delete sysfs slub entry, but since commit
41a212859a4d ("slub: use sysfs'es release mechanism for kmem_cache") we
remove sysfs entry later in kmem_cache_destroy after dropping the
slab_mutex, so that no implementation of __kmem_cache_shutdown can ever
release the lock.  Therefore we can simplify the code a bit by moving
list_del after __kmem_cache_shutdown.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Pekka Enberg <penberg@kernel.org>
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>

mm/slab_common.c

@@ -346,15 +346,15 @@ void kmem_cache_destroy(struct kmem_cache *s)
 	if (memcg_cleanup_cache_params(s) != 0)
 		goto out_unlock;
 
-	list_del(&s->list);
 	if (__kmem_cache_shutdown(s) != 0) {
-		list_add(&s->list, &slab_caches);
 		printk(KERN_ERR "kmem_cache_destroy %s: "
 		       "Slab cache still has objects\n", s->name);
 		dump_stack();
 		goto out_unlock;
 	}
 
+	list_del(&s->list);
+
 	mutex_unlock(&slab_mutex);
 	if (s->flags & SLAB_DESTROY_BY_RCU)
 		rcu_barrier();