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Re: [Qemu-stable] [Qemu-devel] [PATCH] virtio: zero vq->inuse in virtio_
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-stable] [Qemu-devel] [PATCH] virtio: zero vq->inuse in virtio_reset() |
Date: |
Wed, 7 Sep 2016 11:54:13 -0400 |
On Wed, Sep 7, 2016 at 11:51 AM, 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;
> }
> }
>
> --
> 2.7.4
CCing qemu-stable
- Re: [Qemu-stable] [Qemu-devel] [PATCH] virtio: zero vq->inuse in virtio_reset(),
Stefan Hajnoczi <=