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

[Ming Lei <ming.lei@redhat.com>]

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?



Thanks,
Ming