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From:   Ming Lei <tom.leiming@gmail.com>
Date:   Wed, 19 Feb 2020 09:46:56 +0800
Message-ID: <CACVXFVPBPCzr+sfQ4HOw1DNPGnEfp+5BLqQkXWQgkaBKqr3yVQ@mail.gmail.com>
Subject: Re: [PATCH 1/2] virtio-blk: fix hw_queue stopped on arbitrary error
To:     Halil Pasic <pasic@linux.ibm.com>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        linux-block <linux-block@vger.kernel.org>,
        linux-s390 <linux-s390@vger.kernel.org>,
        Cornelia Huck <cohuck@redhat.com>,
        Ram Pai <linuxram@us.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        "Lendacky, Thomas" <Thomas.Lendacky@amd.com>,
        Viktor Mihajlovski <mihajlov@linux.ibm.com>
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On Tue, Feb 18, 2020 at 8:35 PM Halil Pasic <pasic@linux.ibm.com> wrote:
>
> On Tue, 18 Feb 2020 10:21:18 +0800
> Ming Lei <tom.leiming@gmail.com> wrote:
>
> > On Thu, Feb 13, 2020 at 8:38 PM Halil Pasic <pasic@linux.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.
> >
>
> I think this is a pretty close to that. The queue is stopped only on
> ENOSPC, which means virtqueue is full.
>
> > Checking -ENOMEM may not be enough, given -EIO can be returned from
> > virtqueue_add()
> > too in case of dma map failure.
>
> I'm not checking on -ENOMEM. So the queue would not be stopped on EIO.
> Maybe I'm misunderstanding something In any case, please have another
> look at the diff, and if your concerns persist please help me understand.

Looks I misread the patch, and this patch is fine:

Reviewed-by: Ming Lei <ming.lei@redhat.com>


Thanks,
Ming Lei