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blk-mq: clarify dispatch may not be drained/blocked by stopping queue 

BLK_MQ_S_STOPPED may not be observed in other concurrent I/O paths,
we can't guarantee that dispatching won't happen after returning
from the APIs of stopping queue.

So clarify the fact and avoid potential misuse.

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 2017-06-06 23:22:09 +08:00 committed by Jens Axboe
parent 1d9e9bc6b5
commit 39a70c76b8
1 changed files with 18 additions and 0 deletions
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18
block/blk-mq.c
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@ -1204,6 +1204,15 @@ static void __blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx, bool sync)
set_bit(BLK_MQ_S_STOPPED, &hctx->state);
}
/*
* This function is often used for pausing .queue_rq() by driver when
* there isn't enough resource or some conditions aren't satisfied, and
* BLK_MQ_RQ_QUEUE_BUSY is usually returned.
*
* We do not guarantee that dispatch can be drained or 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);
@ -1219,6 +1228,15 @@ static void __blk_mq_stop_hw_queues(struct request_queue *q, bool sync)
__blk_mq_stop_hw_queue(hctx, sync);
}
/*
* This function is often used for pausing .queue_rq() by driver when
* there isn't enough resource or some conditions aren't satisfied, and
* BLK_MQ_RQ_QUEUE_BUSY is usually returned.
*
* We do not guarantee that dispatch can be drained or 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);