[PATCH 4.8 034/140] dm rq: take request_queue lock while clearing QUEUE_FLAG_STOPPED

[Greg Kroah-Hartman]

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mike Snitzer <snitzer@xxxxxxxxxx>

commit 9dbeaeabacb26260d1621fe58f0f6fdedc8860d4 upstream.

Every call of queue_flag_clear_unlocked() after block device
initialization has finished is wrong if blk_cleanup_queue() can be
called concurrently.  Convert queue_flag_clear_unlocked() into
queue_flag_clear() and protect it by the block layer queue lock.

Also, factor out dm_mq_start_queue().

Reported-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/md/dm-rq.c |   19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -73,15 +73,24 @@ static void dm_old_start_queue(struct re
 	spin_unlock_irqrestore(q->queue_lock, flags);
 }
 
+static void dm_mq_start_queue(struct request_queue *q)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	queue_flag_clear(QUEUE_FLAG_STOPPED, q);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	blk_mq_start_stopped_hw_queues(q, true);
+	blk_mq_kick_requeue_list(q);
+}
+
 void dm_start_queue(struct request_queue *q)
 {
 	if (!q->mq_ops)
 		dm_old_start_queue(q);
-	else {
-		queue_flag_clear_unlocked(QUEUE_FLAG_STOPPED, q);
-		blk_mq_start_stopped_hw_queues(q, true);
-		blk_mq_kick_requeue_list(q);
-	}
+	else
+		dm_mq_start_queue(q);
 }
 
 static void dm_old_stop_queue(struct request_queue *q)