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blk-mq: use QUEUE_FLAG_QUIESCED to quiesce queue

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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>
This commit is contained in:
Ming Lei
2017-06-18 14:24:27 -06:00
committed by Jens Axboe
parent f660174e8b
commit f4560ffe8c
4 changed files with 18 additions and 2 deletions
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4
include/linux/blk-mq.h
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@@ -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);
}