diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b16b5b807d7c..ae1e953cead7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1893,13 +1893,13 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 {
 	unsigned long flags;
 
+	VM_WARN_ON_ONCE(mem_cgroup_is_root(memcg));
+
 	if (!local_trylock_irqsave(&memcg_stock.stock_lock, flags)) {
 		/*
 		 * In case of unlikely failure to lock percpu stock_lock
 		 * uncharge memcg directly.
 		 */
-		if (mem_cgroup_is_root(memcg))
-			return;
 		page_counter_uncharge(&memcg->memory, nr_pages);
 		if (do_memsw_account())
 			page_counter_uncharge(&memcg->memsw, nr_pages);