[PATCH v2 6/8] blk-mq: don't stop queue for quiescing

Ming Lei
2017-05-27T14:22:40Z

Queue can be started by other blk-mq APIs and can be used in
different cases, this limits uses of blk_mq_quiesce_queue()
if it is based on stopping queue, and make its usage very
difficult, especially users have to use the stop queue APIs
carefully for avoiding to break blk_mq_quiesce_queue().

We have applied the QUIESCED flag for draining and blocking
dispatch, so it isn't necessary to stop queue any more.

After stopping queue is removed, blk_mq_quiesce_queue() can
be used safely and easily, then users won't worry about queue
restarting during quiescing at all.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-mq.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 032045841856..84cce67caee3 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -168,8 +168,6 @@ void blk_mq_quiesce_queue(struct request_queue *q)
unsigned int i;
bool rcu = false;

- __blk_mq_stop_hw_queues(q, true);
-
spin_lock_irq(q->queue_lock);
queue_flag_set(QUEUE_FLAG_QUIESCED, q);
spin_unlock_irq(q->queue_lock);
@@ -198,7 +196,12 @@ void blk_mq_unquiesce_queue(struct request_queue *q)
queue_flag_clear(QUEUE_FLAG_QUIESCED, q);
spin_unlock_irq(q->queue_lock);

- blk_mq_start_stopped_hw_queues(q, true);
+ /*
+ * During quiescing, requests can be inserted
+ * to scheduler's queue or sw queue, so we run
+ * queues for dispatching these requests.
+ */
+ blk_mq_start_hw_queues(q);
}
EXPORT_SYMBOL_GPL(blk_mq_unquiesce_queue);

--
2.9.4