Re: [PATCH] blk-mq: run queue after issuing the last request of the plug list

Yufen Yu <yuyufen@xxxxxxxxxx> · Tue, 19 Jul 2022 19:00:15 +0800

On 2022/7/19 17:26, Ming Lei wrote:
On Mon, Jul 18, 2022 at 08:35:28PM +0800, Yufen Yu wrote:
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

Here the issue shouldn't be related with scsi's get budget or
scsi_run_queue_async.

If blk-mq adds request into ->dispatch_list, it is blk-mq core's
responsibility to re-run queue for moving on. Can you investigate a
bit more why blk-mq doesn't run queue after adding request to
hctx dispatch list?

In my IO hung scenario, no one issue any IO any more after calling blk_finish_plug().
There is no chance of run queue.

Thanks,
Yufen