Re: [PATCH 1/2] virtio-blk: set req->state to MQ_RQ_COMPLETE after polling I/O is finished

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Dec 06, 2022 at 11:11:24PM +0900, Suwan Kim wrote:
> Driver should set req->state to MQ_RQ_COMPLETE after it finishes to process
> req. But virtio-blk doesn't set MQ_RQ_COMPLETE after virtblk_poll() handles
> req and req->state still remains MQ_RQ_IN_FLIGHT. Fortunately so far there
> is no issue about it because blk_mq_end_request_batch() sets req->state to
> MQ_RQ_IDLE. This patch properly sets req->state after polling I/O is finished.
> 
> Fixes: 4e0400525691 ("virtio-blk: support polling I/O")
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
>  drivers/block/virtio_blk.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 19da5defd734..cf64d256787e 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -839,6 +839,7 @@ static void virtblk_complete_batch(struct io_comp_batch *iob)
>  	rq_list_for_each(&iob->req_list, req) {
>  		virtblk_unmap_data(req, blk_mq_rq_to_pdu(req));
>  		virtblk_cleanup_cmd(req);
> +		blk_mq_set_request_complete(req);
>  	}
>  	blk_mq_end_request_batch(iob);
>  }

The doc comment for blk_mq_set_request_complete() mentions this being
used in ->queue_rq(), but that's not the case here. Does the doc comment
need to be updated if we're using the function in a different way?

I'm not familiar enough with the Linux block APIs, but this feels weird
to me. Shouldn't blk_mq_end_request_batch(iob) take care of this for us?
Why does it set the state to IDLE instead of COMPLETE?

I think Jens can confirm whether we really want all drivers that use
polling and io_comp_batch to manually call
blk_mq_set_request_complete().

Thanks,
Stefan

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