blk-mq: use QUEUE_FLAG_QUIESCED to quiesce queue

It is required that no dispatch can happen any more once
blk_mq_quiesce_queue() returns, and we don't have such requirement
on APIs of stopping queue.

But blk_mq_quiesce_queue() still may not block/drain dispatch in the
the case of BLK_MQ_S_START_ON_RUN, so use the new introduced flag of
QUEUE_FLAG_QUIESCED and evaluate it inside RCU read-side critical
sections for fixing this issue.

Also blk_mq_quiesce_queue() is implemented via stopping queue, which
limits its uses, and easy to cause race, because any queue restart in
other paths may break blk_mq_quiesce_queue(). With the introduced
flag of QUEUE_FLAG_QUIESCED, we don't need to depend on stopping queue
for quiescing any more.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bart Van Assche <Bart.VanAssche@sandisk.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 787d8a2a2ac6..de6536c14ae7 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -268,6 +268,10 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues);
  */
 static inline void blk_mq_quiesce_queue_nowait(struct request_queue *q)
 {
+	spin_lock_irq(q->queue_lock);
+	queue_flag_set(QUEUE_FLAG_QUIESCED, q);
+	spin_unlock_irq(q->queue_lock);
+
 	blk_mq_stop_hw_queues(q);
 }