Virtualization - May 2023 - [PATCH v2] vhost_net: revert upend_idx only on retriable error

On Tue, Apr 25, 2023 at 4:44?AM Andrey Smetanin
<asmetanin at yandex-team.ru> wrote:
>
> Fix possible virtqueue used buffers leak and corresponding stuck
> in case of temporary -EIO from sendmsg() which is produced by
> tun driver while backend device is not up.
>
> In case of no-retriable error and zcopy do not revert upend_idx
> to pass packet data (that is update used_idx in corresponding
> vhost_zerocopy_signal_used()) as if packet data has been
> transferred successfully.
>
> v2: set vq->heads[ubuf->desc].len equal to VHOST_DMA_DONE_LEN
> in case of fake successful transmit.
>
> Signed-off-by: Andrey Smetanin <asmetanin at yandex-team.ru>
Acked-by: Jason Wang <jasowang at redhat.com>

Thanks
> ---
>  drivers/vhost/net.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 20265393aee7..0791fbdb3975 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -934,13 +934,18 @@ static void handle_tx_zerocopy(struct vhost_net *net,
struct socket *sock)
>
>                 err = sock->ops->sendmsg(sock, &msg, len);
>                 if (unlikely(err < 0)) {
> +                       bool retry = err == -EAGAIN || err == -ENOMEM ||
err == -ENOBUFS;
> +
>                         if (zcopy_used) {
>                                 if (vq->heads[ubuf->desc].len ==
VHOST_DMA_IN_PROGRESS)
>                                         vhost_net_ubuf_put(ubufs);
> -                               nvq->upend_idx =
((unsigned)nvq->upend_idx - 1)
> -                                       % UIO_MAXIOV;
> +                               if (retry)
> +                                       nvq->upend_idx =
((unsigned)nvq->upend_idx - 1)
> +                                               % UIO_MAXIOV;
> +                               else
> +                                       vq->heads[ubuf->desc].len =
VHOST_DMA_DONE_LEN;
>                         }
> -                       if (err == -EAGAIN || err == -ENOMEM || err ==
-ENOBUFS) {
> +                       if (retry) {
>                                 vhost_discard_vq_desc(vq, 1);
>                                 vhost_net_enable_vq(net, vq);
>                                 break;
> --
> 2.25.1
>