Commit 9ba52e58 authored by Shaohua Li's avatar Shaohua Li Committed by Jens Axboe

blk-mq: don't lose requests if a stopped queue restarts

Normally if driver is busy to dispatch a request the logic is like below:
block layer:					driver:
	__blk_mq_run_hw_queue
a.						blk_mq_stop_hw_queue
b.	rq add to ctx->dispatch

later:
1.						blk_mq_start_hw_queue
2.	__blk_mq_run_hw_queue

But it's possible step 1-2 runs between a and b. And since rq isn't in
ctx->dispatch yet, step 2 will not run rq. The rq might get lost if
there are no subsequent requests kick in.
Signed-off-by: default avatarShaohua Li <shli@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent b2387ddc
...@@ -858,6 +858,16 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) ...@@ -858,6 +858,16 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
spin_lock(&hctx->lock); spin_lock(&hctx->lock);
list_splice(&rq_list, &hctx->dispatch); list_splice(&rq_list, &hctx->dispatch);
spin_unlock(&hctx->lock); spin_unlock(&hctx->lock);
/*
* the queue is expected stopped with BLK_MQ_RQ_QUEUE_BUSY, but
* it's possible the queue is stopped and restarted again
* before this. Queue restart will dispatch requests. And since
* requests in rq_list aren't added into hctx->dispatch yet,
* the requests in rq_list might get lost.
*
* blk_mq_run_hw_queue() already checks the STOPPED bit
**/
blk_mq_run_hw_queue(hctx, true);
} }
} }
......
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