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

[Cornelia Huck]

On Wed,  7 Sep 2016 11:51:25 -0400
Stefan Hajnoczi <address@hidden> wrote:

> 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>
> ---
>  hw/virtio/virtio.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 74c085c..e8a13a5 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -822,6 +822,7 @@ void virtio_reset(void *opaque)
>          vdev->vq[i].signalled_used_valid = false;
>          vdev->vq[i].notification = true;
>          vdev->vq[i].vring.num = vdev->vq[i].vring.num_default;
> +        vdev->vq[i].inuse = 0;
>      }
>  }
> 

This looks sane as a minimal change, and survives my smoketests.

Reviewed-by: Cornelia Huck <address@hidden>