From: "Michael S. Tsirkin" <mst@redhat.com>
To: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: Network Development <netdev@vger.kernel.org>,
David Miller <davem@davemloft.net>
Subject: Re: [PATCH net] net/packet: tpacket_rcv: do not increment ring index on drop
Date: Tue, 10 Mar 2020 08:59:01 -0400 [thread overview]
Message-ID: <20200310085437-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CA+FuTSd=oLQhtKet-n5r++3HHmHR+5rMkDqSMyjArOBfF4vsKw@mail.gmail.com>
On Tue, Mar 10, 2020 at 08:49:23AM -0400, Willem de Bruijn wrote:
> On Tue, Mar 10, 2020 at 2:43 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Mon, Mar 09, 2020 at 11:34:35AM -0400, Willem de Bruijn wrote:
> > > From: Willem de Bruijn <willemb@google.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@google.com>
> > >
> > > ---
> > >
> > > I wonder whether it should drop packets with unknown GSO types at all.
> > > This consistently blinds the reader to certain packets, including
> > > recent UDP and SCTP GSO types.
> >
> > Ugh it looks like you have found a bug. Consider a legacy userspace -
> > it was actually broken by adding USD and SCTP GSO. I suspect the right
> > thing to do here is actually to split these packets up, not drop them.
>
> In the main virtio users, virtio_net/tun/tap, the packets will always
> arrive segmented, due to these devices not advertising hardware
> segmentation for these protocols.
Oh right. That's good then, sorry about the noise.
> So the issue is limited to users of tpacket_rcv, which is relatively
> new. There too it is limited on egress to devices that do advertise
> h/w offload. And on r/x to GRO.
>
> The UDP GSO issue precedes the fraglist GRO patch, by the way, and
> goes back to my (argh!) introduction of the feature on the egress
> path.
>
> >
> > > The peer function virtio_net_hdr_to_skb already drops any packets with
> > > unknown types, so it should be fine to add an SKB_GSO_UNKNOWN type and
> > > let the peer at least be aware of failure.
> > >
> > > And possibly add SKB_GSO_UDP_L4 and SKB_GSO_SCTP types to virtio too.
> >
> > This last one is possible for sure, but for virtio_net_hdr_from_skb
> > we'll need more flags to know whether it's safe to pass
> > these types to userspace.
>
> Can you elaborate? Since virtio_net_hdr_to_skb users already returns
> -EINVAL on unknown GSO types and its callers just drop these packets,
> it looks to me that the infra is future proof wrt adding new GSO
> types.
Oh I mean if we do want to add new types and want to pass them to
users, then virtio_net_hdr_from_skb will need to flag so it
knows whether that will or won't confuse userspace.
--
MST
next prev parent reply other threads:[~2020-03-10 12:59 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-09 15:34 [PATCH net] net/packet: tpacket_rcv: do not increment ring index on drop Willem de Bruijn
2020-03-09 15:42 ` Willem de Bruijn
2020-03-09 15:50 ` Willem de Bruijn
2020-03-10 6:46 ` Michael S. Tsirkin
2020-03-10 6:43 ` Michael S. Tsirkin
2020-03-10 12:49 ` Willem de Bruijn
2020-03-10 12:59 ` Michael S. Tsirkin [this message]
2020-03-10 14:16 ` Willem de Bruijn
2020-03-10 14:43 ` Michael S. Tsirkin
2020-03-10 15:38 ` Willem de Bruijn
2020-03-10 16:14 ` Willem de Bruijn
2020-03-10 21:29 ` Michael S. Tsirkin
2020-03-10 21:35 ` Willem de Bruijn
2020-03-10 21:57 ` Michael S. Tsirkin
2020-03-10 23:13 ` Willem de Bruijn
2020-03-11 7:56 ` Michael S. Tsirkin
2020-03-11 14:31 ` Willem de Bruijn
2020-03-11 21:25 ` Michael S. Tsirkin
2020-03-11 21:49 ` Willem de Bruijn
2020-03-12 6:13 ` David Miller
2020-03-12 6:27 ` Michael S. Tsirkin
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