From 39a70c76b89b81db91a72a86b6c6a9b239013417 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Tue, 6 Jun 2017 23:22:09 +0800 Subject: [PATCH] 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 Reviewed-by: Bart Van Assche Signed-off-by: Jens Axboe --- block/blk-mq.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index dbae586..89cbd02 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -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); -- 2.7.4