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Commit 39a70c76 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

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: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarBart Van Assche <Bart.VanAssche@sandisk.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 1d9e9bc6

block/blk-mq.c

+18 −0
Original line number Diff line number Diff line
@@ -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);