list_lru: don't call list_lru_from_kmem if the list_head is empty

If the list_head is empty then we'll have called list_lru_from_kmem for
nothing.  Move that call inside of the list_empty if block.
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/list_lru.c

@@ -99,8 +99,8 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item)
 	struct list_lru_one *l;
 
 	spin_lock(&nlru->lock);
-	l = list_lru_from_kmem(nlru, item);
 	if (list_empty(item)) {
+		l = list_lru_from_kmem(nlru, item);
 		list_add_tail(item, &l->list);
 		l->nr_items++;
 		spin_unlock(&nlru->lock);
@@ -118,8 +118,8 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item)
 	struct list_lru_one *l;
 
 	spin_lock(&nlru->lock);
-	l = list_lru_from_kmem(nlru, item);
 	if (!list_empty(item)) {
+		l = list_lru_from_kmem(nlru, item);
 		list_del_init(item);
 		l->nr_items--;
 		spin_unlock(&nlru->lock);