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.
To fix the bug, we run queue after issuing the last request in
function blk_mq_sched_insert_requests.
Signed-off-by: Yufen Yu <yuyufen@xxxxxxxxxx>
---
block/blk-mq-sched.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index a4f7c101b53b..c3ad97ca2753 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -490,8 +490,8 @@ void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
blk_mq_insert_requests(hctx, ctx, list);
}
- blk_mq_run_hw_queue(hctx, run_queue_async);
out:
+ blk_mq_run_hw_queue(hctx, run_queue_async);
percpu_ref_put(&q->q_usage_counter);
}
--
2.31.1
