Re: [PATCH 1/2] virtio-blk: fix hw_queue stopped on arbitrary error

[Ming Lei]

On Thu, Feb 13, 2020 at 8:38 PM Halil Pasic <pasic@xxxxxxxxxxxxx> wrote:
>
> Since nobody else is going to restart our hw_queue for us, the
> blk_mq_start_stopped_hw_queues() is in virtblk_done() is not sufficient
> necessarily sufficient to ensure that the queue will get started again.
> In case of global resource outage (-ENOMEM because mapping failure,
> because of swiotlb full) our virtqueue may be empty and we can get
> stuck with a stopped hw_queue.
>
> Let us not stop the queue on arbitrary errors, but only on -EONSPC which
> indicates a full virtqueue, where the hw_queue is guaranteed to get
> started by virtblk_done() before when it makes sense to carry on
> submitting requests. Let us also remove a stale comment.

The generic solution may be to stop queue only when there is any
in-flight request
not completed.

Checking -ENOMEM may not be enough, given -EIO can be returned from
virtqueue_add()
too in case of dma map failure.

Thanks,