Re: [PATCH] virtio_ring: reset IN_ORDER state in virtqueue_init()

[Jason Wang]

On Thu, Sep 10, 2026 at 8:39 PM lirongqing <lirongqing@xxxxxxxxx> wrote:
>
> From: Li RongQing <lirongqing@xxxxxxxxx>
>
> The IN_ORDER feature uses additional software state to track the next
> available descriptor and in-flight descriptor batches.
>
> virtqueue_init() resets the common virtqueue state, but free_head and
> batch_last.id are initialized only when the virtqueue is created. When
> an IN_ORDER virtqueue is reset, these fields can retain state from the
> previous queue instance.
>
> Reset free_head and invalidate batch_last when initializing an IN_ORDER
> virtqueue. Keep this in virtqueue_init() so the state is initialized
> consistently for both newly created and reset virtqueues.
>
> Fixes: f6a15d854986 ("virtio_ring: add in order support")

I think this is needed for -stable.

> Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
> ---
>  drivers/virtio/virtio_ring.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index db678f5..d0dc464 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -559,6 +559,11 @@ static void virtqueue_init(struct vring_virtqueue *vq, u32 num)
>         vq->in_use = false;
>         vq->last_add_time_valid = false;
>  #endif
> +
> +       if (virtqueue_is_in_order(vq)) {
> +               vq->free_head = 0;
> +               vq->batch_last.id = UINT_MAX;
> +       }

I would try to reuse or refactor virtqueue_vring_attach_split() to
reduce code duplication.

Btw have you checked Qemu shadow virtqueue as it might suffer from the
same issue.

Thanks

>  }
>
>
> --
> 2.9.4
>