Don't do INIT_WORK() repeatedly against the same work_struct. It can

actually lead to a BUG.

Just do it once in initialization.
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memcontrol.c

@@ -1349,8 +1349,8 @@ static void drain_all_stock_async(void)
 	/* This function is for scheduling "drain" in asynchronous way.
 	 * The result of "drain" is not directly handled by callers. Then,
 	 * if someone is calling drain, we don't have to call drain more.
-	 * Anyway, work_pending() will catch if there is a race. We just do
-	 * loose check here.
+	 * Anyway, WORK_STRUCT_PENDING check in queue_work_on() will catch if
+	 * there is a race. We just do loose check here.
 	 */
 	if (atomic_read(&memcg_drain_count))
 		return;
@@ -1359,9 +1359,6 @@ static void drain_all_stock_async(void)
 	get_online_cpus();
 	for_each_online_cpu(cpu) {
 		struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
-		if (work_pending(&stock->work))
-			continue;
-		INIT_WORK(&stock->work, drain_local_stock);
 		schedule_work_on(cpu, &stock->work);
 	}
  	put_online_cpus();
@@ -3327,11 +3324,17 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 
 	/* root ? */
 	if (cont->parent == NULL) {
+		int cpu;
 		enable_swap_cgroup();
 		parent = NULL;
 		root_mem_cgroup = mem;
 		if (mem_cgroup_soft_limit_tree_init())
 			goto free_out;
+		for_each_possible_cpu(cpu) {
+			struct memcg_stock_pcp *stock =
+						&per_cpu(memcg_stock, cpu);
+			INIT_WORK(&stock->work, drain_local_stock);
+		}
 		hotcpu_notifier(memcg_stock_cpu_callback, 0);
 
 	} else {