workqueue: make it clear that WQ_DRAINING is an internal flag

We're gonna add another internal WQ flag.  Let's make the distinction
clear.  Prefix WQ_DRAINING with __ and move it to bit 16.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>

include/linux/workqueue.h

@@ -294,7 +294,7 @@ enum {
 	WQ_HIGHPRI		= 1 << 4, /* high priority */
 	WQ_CPU_INTENSIVE	= 1 << 5, /* cpu instensive workqueue */
 
-	WQ_DRAINING		= 1 << 6, /* internal: workqueue is draining */
+	__WQ_DRAINING		= 1 << 16, /* internal: workqueue is draining */
 
 	WQ_MAX_ACTIVE		= 512,	  /* I like 512, better ideas? */
 	WQ_MAX_UNBOUND_PER_CPU	= 4,	  /* 4 * #cpus for unbound wq */

kernel/workqueue.c

@@ -1225,7 +1225,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
 	debug_work_activate(work);
 
 	/* if dying, only works from the same workqueue are allowed */
-	if (unlikely(wq->flags & WQ_DRAINING) &&
+	if (unlikely(wq->flags & __WQ_DRAINING) &&
 	    WARN_ON_ONCE(!is_chained_work(wq)))
 		return;
 retry:
@@ -2763,11 +2763,11 @@ void drain_workqueue(struct workqueue_struct *wq)
 	/*
 	 * __queue_work() needs to test whether there are drainers, is much
 	 * hotter than drain_workqueue() and already looks at @wq->flags.
-	 * Use WQ_DRAINING so that queue doesn't have to check nr_drainers.
+	 * Use __WQ_DRAINING so that queue doesn't have to check nr_drainers.
 	 */
 	spin_lock_irq(&workqueue_lock);
 	if (!wq->nr_drainers++)
-		wq->flags |= WQ_DRAINING;
+		wq->flags |= __WQ_DRAINING;
 	spin_unlock_irq(&workqueue_lock);
 reflush:
 	flush_workqueue(wq);
@@ -2795,7 +2795,7 @@ void drain_workqueue(struct workqueue_struct *wq)
 
 	spin_lock(&workqueue_lock);
 	if (!--wq->nr_drainers)
-		wq->flags &= ~WQ_DRAINING;
+		wq->flags &= ~__WQ_DRAINING;
 	spin_unlock(&workqueue_lock);
 
 	local_irq_enable();