Re: [Qemu-stable] [PATCH 6/6] virtio: zero vq->inuse in virtio_reset()

[Ladi Prosek]

Please ignore, git-publish gone wrong.

On Mon, Jan 2, 2017 at 12:58 PM, Ladi Prosek <address@hidden> wrote:
> From: Stefan Hajnoczi <address@hidden>
>
> vq->inuse must be zeroed upon device reset like most other virtqueue
> fields.
>
> In theory, virtio_reset() just needs assert(vq->inuse == 0) since
> devices must clean up in-flight requests during reset (requests cannot
> not be leaked!).
>
> In practice, it is difficult to achieve vq->inuse == 0 across reset
> because balloon, blk, 9p, etc implement various different strategies for
> cleaning up requests.  Most devices call g_free(elem) directly without
> telling virtio.c that the VirtQueueElement is cleaned up.  Therefore
> vq->inuse is not decremented during reset.
>
> This patch zeroes vq->inuse and trusts that devices are not leaking
> VirtQueueElements across reset.
>
> I will send a follow-up series that refactors request life-cycle across
> all devices and converts vq->inuse = 0 into assert(vq->inuse == 0) but
> this more invasive approach is not appropriate for stable trees.
>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> Cc: qemu-stable <address@hidden>
> Reviewed-by: Michael S. Tsirkin <address@hidden>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> Reviewed-by: Ladi Prosek <address@hidden>
> (cherry picked from commit 4b7f91ed0270a371e1933efa21ba600b6da23ab9)
> Signed-off-by: Ladi Prosek <address@hidden>
> ---
>  hw/virtio.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/hw/virtio.c b/hw/virtio.c
> index eb527d0..7791b28 100644
> --- a/hw/virtio.c
> +++ b/hw/virtio.c
> @@ -570,6 +570,7 @@ void virtio_reset(void *opaque)
>          vdev->vq[i].signalled_used = 0;
>          vdev->vq[i].signalled_used_valid = false;
>          vdev->vq[i].notification = true;
> +        vdev->vq[i].inuse = 0;
>      }
>  }
>
> --
> 2.7.4
>