From 5de73abdb7cfa0b59b5ad8098d9a14478ab24025 Mon Sep 17 00:00:00 2001 From: Muchun Song Date: Tue, 11 Mar 2025 08:51:19 +0900 Subject: [PATCH] block: fix missing dispatching request when queue is started or unquiesced BugLink: https://bugs.launchpad.net/bugs/2101915 commit 2003ee8a9aa14d766b06088156978d53c2e9be3d upstream. Supposing the following scenario with a virtio_blk driver. CPU0 CPU1 CPU2 blk_mq_try_issue_directly() __blk_mq_issue_directly() q->mq_ops->queue_rq() virtio_queue_rq() blk_mq_stop_hw_queue() virtblk_done() blk_mq_try_issue_directly() if (blk_mq_hctx_stopped()) blk_mq_request_bypass_insert() blk_mq_run_hw_queue() blk_mq_run_hw_queue() blk_mq_run_hw_queue() blk_mq_insert_request() return After CPU0 has marked the queue as stopped, CPU1 will see the queue is stopped. But before CPU1 puts the request on the dispatch list, CPU2 receives the interrupt of completion of request, so it will run the hardware queue and marks the queue as non-stopped. Meanwhile, CPU1 also runs the same hardware queue. After both CPU1 and CPU2 complete blk_mq_run_hw_queue(), CPU1 just puts the request to the same hardware queue and returns. It misses dispatching a request. Fix it by running the hardware queue explicitly. And blk_mq_request_issue_directly() should handle a similar situation. Fix it as well. Fixes: d964f04a8fde ("blk-mq: fix direct issue") Cc: stable@vger.kernel.org Cc: Muchun Song Signed-off-by: Muchun Song Reviewed-by: Ming Lei Link: https://lore.kernel.org/r/20241014092934.53630-2-songmuchun@bytedance.com Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman Signed-off-by: Koichiro Den Signed-off-by: Stefan Bader --- block/blk-mq.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index 4eb428a649ad..e2b3d757cf68 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2657,6 +2657,7 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(rq->q)) { blk_mq_insert_request(rq, 0); + blk_mq_run_hw_queue(hctx, false); return; } @@ -2687,6 +2688,7 @@ static blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last) if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(rq->q)) { blk_mq_insert_request(rq, 0); + blk_mq_run_hw_queue(hctx, false); return BLK_STS_OK; }