From: Yufen Yu yuyufen@huawei.com
commit d3b38596875dbc709b4e721a5873f4663d8a9ea2 upstream.
We do test on a virtio scsi device (/dev/sda) and the default mq scheduler is 'none'. We found a IO hung as following:
blk_finish_plug blk_mq_plug_issue_direct scsi_mq_get_budget //get budget_token fail and sdev->restarts=1
scsi_end_request scsi_run_queue_async //sdev->restart=0 and run queue
blk_mq_request_bypass_insert //add request to hctx->dispatch list
//continue to dispath plug list blk_mq_dispatch_plug_list blk_mq_try_issue_list_directly //success issue all requests from plug list
After .get_budget fail, scsi_mq_get_budget will increase 'restarts'. Normally, it will run hw queue when io complete and set 'restarts' as 0. But if we run queue before adding request to the dispatch list and blk_mq_dispatch_plug_list also success issue all requests, then on one will run queue, and the request will be stall in the dispatch list and cannot complete forever.
It is wrong to use last request of plug list to decide if run queue is needed since all the remained requests in plug list may be from other hctxs. To fix the bug, pass run_queue as true always to blk_mq_request_bypass_insert().
Fix-suggested-by: Ming Lei ming.lei@redhat.com Signed-off-by: Yufen Yu yuyufen@huawei.com Reviewed-by: Ming Lei ming.lei@redhat.com Fixes: dc5fc361d891 ("block: attempt direct issue of plug list") Link: https://lore.kernel.org/r/20220803023355.3687360-1-yuyufen@huaweicloud.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/blk-mq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2568,7 +2568,7 @@ static void blk_mq_plug_issue_direct(str break; case BLK_STS_RESOURCE: case BLK_STS_DEV_RESOURCE: - blk_mq_request_bypass_insert(rq, false, last); + blk_mq_request_bypass_insert(rq, false, true); blk_mq_commit_rqs(hctx, &queued, from_schedule); return; default: