From 9ba52e5812e53f20f23600d79449a3ec05a0254f Mon Sep 17 00:00:00 2001 From: Shaohua Li <shli@fb.com> Date: Mon, 4 May 2015 14:32:48 -0600 Subject: [PATCH] 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: Shaohua Li <shli@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com> --- block/blk-mq.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index 76f460e36f1dd..e68b71b85a7ea 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -858,6 +858,16 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) spin_lock(&hctx->lock); list_splice(&rq_list, &hctx->dispatch); 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); } } -- GitLab