slub: tidy up initialization ordering

 - free_kmem_cache_nodes() frees the cache node before nulling out a
   reference to it

 - init_kmem_cache_nodes() publishes the cache node before initializing
   it

Neither of these matter at runtime because the cache nodes cannot be
looked up by any other thread.  But it's neater and more consistent to
reorder these.

Link: http://lkml.kernel.org/r/20170707083408.40410-1-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slub.c

@@ -3358,8 +3358,8 @@ static void free_kmem_cache_nodes(struct kmem_cache *s)
 	struct kmem_cache_node *n;
 
 	for_each_kmem_cache_node(s, node, n) {
-		kmem_cache_free(kmem_cache_node, n);
 		s->node[node] = NULL;
+		kmem_cache_free(kmem_cache_node, n);
 	}
 }
 
@@ -3389,8 +3389,8 @@ static int init_kmem_cache_nodes(struct kmem_cache *s)
 			return 0;
 		}
 
-		s->node[node] = n;
 		init_kmem_cache_node(n);
+		s->node[node] = n;
 	}
 	return 1;
 }