[PATCH 1/2] workqueue: rescuer_thread() processes all pwqs before exit

[Lai Jiangshan <laijs@cn.fujitsu.com>]

Before the rescuer is picked to running, the works of the @pwq
may be processed by some other workers, and destroy_workqueue()
may called at the same time. This may result a nasty situation
that rescuer may exit with non-empty mayday list.

It is no harm currently, destroy_workqueue() can safely to free
them all(workqueue&pwqs) togerther, since the rescuer is stopped.
No rescuer nor mayday-timer can access the mayday list.

But it is nasty and error-prone in future develop. Fix it.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
 kernel/workqueue.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0ee63af..832125f 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2409,12 +2409,6 @@ static int rescuer_thread(void *__rescuer)
 repeat:
 	set_current_state(TASK_INTERRUPTIBLE);
 
-	if (kthread_should_stop()) {
-		__set_current_state(TASK_RUNNING);
-		rescuer->task->flags &= ~PF_WQ_WORKER;
-		return 0;
-	}
-
 	/* see whether any pwq is asking for help */
 	spin_lock_irq(&wq_mayday_lock);
 
@@ -2459,6 +2453,12 @@ repeat:
 
 	spin_unlock_irq(&wq_mayday_lock);
 
+	if (kthread_should_stop()) {
+		__set_current_state(TASK_RUNNING);
+		rescuer->task->flags &= ~PF_WQ_WORKER;
+		return 0;
+	}
+
 	/* rescuers should never participate in concurrency management */
 	WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));
 	schedule();
-- 
1.7.4.4