linux-kernel - Re: [PATCH] vhost_net: revert upend

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Date:   Thu, 1 Dec 2022 17:01:58 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Andrey Smetanin <asmetanin@...dex-team.ru>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, yc-core@...dex-team.ru
Subject: Re: [PATCH] vhost_net: revert upend_idx only on retriable error

On Wed, Nov 23, 2022 at 6:24 PM Andrey Smetanin
<asmetanin@...dex-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.

Should we mark head.len as VHOST_DMA_DONE_LEN in this case?

Thanks

>
> Signed-off-by: Andrey Smetanin <asmetanin@...dex-team.ru>
> ---
>  drivers/vhost/net.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 20265393aee7..93e9166039b9 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -934,13 +934,16 @@ 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;
>                         }
> -                       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
>