unify queue_delayed_work() and queue_delayed_work_on()

Change queue_delayed_work() to use queue_delayed_work_on() to avoid the code
duplication (saves 133 bytes).

Q: queue_delayed_work() enqueues &dwork->work directly when delay == 0, why?

[jirislaby@gmail.com: oops fix]
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/workqueue.c

@@ -180,28 +180,11 @@ void delayed_work_timer_fn(unsigned long __data)
 int fastcall queue_delayed_work(struct workqueue_struct *wq,
 			struct delayed_work *dwork, unsigned long delay)
 {
-	int ret = 0;
-	struct timer_list *timer = &dwork->timer;
-	struct work_struct *work = &dwork->work;
-
-	timer_stats_timer_set_start_info(timer);
+	timer_stats_timer_set_start_info(&dwork->timer);
 	if (delay == 0)
-		return queue_work(wq, work);
+		return queue_work(wq, &dwork->work);
 
-	if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
-		BUG_ON(timer_pending(timer));
-		BUG_ON(!list_empty(&work->entry));
-
-		/* This stores cwq for the moment, for the timer_fn */
-		set_wq_data(work,
-			per_cpu_ptr(wq->cpu_wq, raw_smp_processor_id()));
-		timer->expires = jiffies + delay;
-		timer->data = (unsigned long)dwork;
-		timer->function = delayed_work_timer_fn;
-		add_timer(timer);
-		ret = 1;
-	}
-	return ret;
+	return queue_delayed_work_on(-1, wq, dwork, delay);
 }
 EXPORT_SYMBOL_GPL(queue_delayed_work);
 
@@ -227,11 +210,16 @@ int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
 
 		/* This stores cwq for the moment, for the timer_fn */
 		set_wq_data(work,
-			per_cpu_ptr(wq->cpu_wq, raw_smp_processor_id()));
+			per_cpu_ptr(wq->cpu_wq, wq->singlethread ?
+				singlethread_cpu : raw_smp_processor_id()));
 		timer->expires = jiffies + delay;
 		timer->data = (unsigned long)dwork;
 		timer->function = delayed_work_timer_fn;
+
+		if (unlikely(cpu >= 0))
 			add_timer_on(timer, cpu);
+		else
+			add_timer(timer);
 		ret = 1;
 	}
 	return ret;