linux-kernel - Re: [PATCH net-next v4 4/4] net: gro: move L3 flush checks to tcp_gro

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Date: Tue, 26 Mar 2024 15:46:35 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Richard Gobert <richardbgobert@...il.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, 
	willemdebruijn.kernel@...il.com, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next v4 4/4] net: gro: move L3 flush checks to tcp_gro_receive

On Tue, Mar 26, 2024 at 3:43 PM Richard Gobert <richardbgobert@...il.com> wrote:
>
> Eric Dumazet wrote:
> > On Mon, Mar 25, 2024 at 7:27 PM Richard Gobert <richardbgobert@...il.com> wrote:
> >>
> >> {inet,ipv6}_gro_receive functions perform flush checks (ttl, flags,
> >> iph->id, ...) against all packets in a loop. These flush checks are used
> >> currently only in tcp flows in GRO.
> >
> > I think this is a bug.
> >
> > GRO should not aggregate packets if their ttl/tos fields do not match.
>
> AFAIU, the only UDP flow where ttl/flush_id need to be checked is when
> udp_gro_receive_segment calls skb_gro_receive - could you confirm / point
> out if there are any other flows to which these flush checks may be
> relevant?
>
> As I've discussed with Willem in v3 I prefer to fix this bug in a separate
> series.

I do not understand this patch 4/4 then.

Why bother moving stuff in net/ipv4/tcp_offload.c if we plan to move
it back to where it belongs ?