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

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Date:   Tue, 18 Feb 2020 10:21:18 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Ram Pai <linuxram@...ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        Viktor Mihajlovski <mihajlov@...ux.ibm.com>
Subject: Re: [PATCH 1/2] virtio-blk: fix hw_queue stopped on arbitrary error

On Thu, Feb 13, 2020 at 8:38 PM Halil Pasic <pasic@...ux.ibm.com> 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,