Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20200213123728.61216-1-pasic@linux.ibm.com> <20200213123728.61216-2-pasic@linux.ibm.com>
In-Reply-To: <20200213123728.61216-2-pasic@linux.ibm.com>
From:   Ming Lei <tom.leiming@gmail.com>
Date:   Tue, 18 Feb 2020 10:21:18 +0800
Message-ID: <CACVXFVNiADTW_vLVc1bUSa0CoViLbVzoMnSJW4=sx=MCE-xUPw@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>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.

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

Thanks,