---

yaml
---
r: 262697
b: refs/heads/master
c: 9f50fad
h: refs/heads/master
i:
  262695: c51ab59
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 47e180d6523081605c970f806572beab8a205537
+refs/heads/master: 9f50fad65b87a8776ae989ca059ad6c17925dfc3

trunk/mm/memcontrol.c

@@ -2091,6 +2091,7 @@ struct memcg_stock_pcp {
 #define FLUSHING_CACHED_CHARGE	(0)
 };
 static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
+static DEFINE_MUTEX(percpu_charge_mutex);
 
 /*
  * Try to consume stocked charge on this cpu. If success, one page is consumed
@@ -2197,8 +2198,7 @@ static void drain_all_stock(struct mem_cgroup *root_mem, bool sync)
 
 	for_each_online_cpu(cpu) {
 		struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
-		if (mem_cgroup_same_or_subtree(root_mem, stock->cached) &&
-				test_bit(FLUSHING_CACHED_CHARGE, &stock->flags))
+		if (test_bit(FLUSHING_CACHED_CHARGE, &stock->flags))
 			flush_work(&stock->work);
 	}
 out:
@@ -2213,14 +2213,22 @@ static void drain_all_stock(struct mem_cgroup *root_mem, bool sync)
  */
 static void drain_all_stock_async(struct mem_cgroup *root_mem)
 {
+	/*
+	 * If someone calls draining, avoid adding more kworker runs.
+	 */
+	if (!mutex_trylock(&percpu_charge_mutex))
+		return;
 	drain_all_stock(root_mem, false);
+	mutex_unlock(&percpu_charge_mutex);
 }
 
 /* This is a synchronous drain interface. */
 static void drain_all_stock_sync(struct mem_cgroup *root_mem)
 {
 	/* called when force_empty is called */
+	mutex_lock(&percpu_charge_mutex);
 	drain_all_stock(root_mem, true);
+	mutex_unlock(&percpu_charge_mutex);
 }
 
 /*