[PATCH 6/6] blk-mq: clarify dispatching may not be drained/blocked by stopping queue

[Ming Lei]

BLK_MQ_S_STOPPED may be not observed in other concurrent I/O paths,
we can't guarantee that dispatching won't happen after queue
is stopped.

So clarify the fact and avoid potential misuse.

Signed-off-by: Ming Lei <ming.lei at redhat.com>
---
 block/blk-mq.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 900eb91e0ece..32bed5bac7da 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1240,6 +1240,11 @@ static void __blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx, bool sync)
 	set_bit(BLK_MQ_S_STOPPED, &hctx->state);
 }
 
+/*
+ * Do not expect that dispatching or .queue_rq() can be blocked
+ * after blk_mq_stop_hw_queue() returns. Please use
+ * blk_mq_quiesce_queue() for that requirement.
+ */
 void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx)
 {
 	__blk_mq_stop_hw_queue(hctx, false);
@@ -1255,6 +1260,11 @@ static void __blk_mq_stop_hw_queues(struct request_queue *q, bool sync)
 		__blk_mq_stop_hw_queue(hctx, sync);
 }
 
+/*
+ * Do not expect that dispatching or .queue_rq() can be blocked
+ * after blk_mq_stop_hw_queues() returns. Please use
+ * blk_mq_quiesce_queue() for that requirement.
+ */
 void blk_mq_stop_hw_queues(struct request_queue *q)
 {
 	__blk_mq_stop_hw_queues(q, false);
-- 
2.9.4