netdev - Re: [PATCH net] net/packet: tpacket_rcv: do not increment ring index on drop

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Date:   Mon, 9 Mar 2020 11:50:23 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH net] net/packet: tpacket_rcv: do not increment ring index
 on drop

On Mon, Mar 9, 2020 at 11:42 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> On Mon, Mar 9, 2020 at 11:34 AM Willem de Bruijn
> <willemdebruijn.kernel@...il.com> wrote:
> >
> > From: Willem de Bruijn <willemb@...gle.com>
> >
> > In one error case, tpacket_rcv drops packets after incrementing the
> > ring producer index.
> >
> > If this happens, it does not update tp_status to TP_STATUS_USER and
> > thus the reader is stalled for an iteration of the ring, causing out
> > of order arrival.
> >
> > The only such error path is when virtio_net_hdr_from_skb fails due
> > to encountering an unknown GSO type.
> >
> > Signed-off-by: Willem de Bruijn <willemb@...gle.com>
>
>
> Fixes: bfd5f4a3d605 ("packet: Add GSO/csum offload support.")
>
> I forgot to add the Fixes tag, sorry. This goes back to the
> introduction of GSO support for virtio_net.

The problem of blinding receivers to certain packet types goes back to
that commit.

But the specific issue of ring out of order arrival is added later,
when vnet_hdr support is extended to tpacket_rcv:

Fixes: 58d19b19cd99 ("packet: vnet_hdr support for tpacket_rcv")