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

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Message-ID: <CA+FuTSfTac=Ut43nFJdB_z605Y-NO7En8AqKT3X8q8=SjFHe6Q@mail.gmail.com>
Date:   Mon, 9 Mar 2020 11:42:40 -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 11:34 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 discussion then explicitly arrived at deciding to fail on an
unknown type (SKB_GSO_FCOE). Which is why I asked the question here
whether we want to revisit that choice or leave as is.