[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <65ef038e78a8b_20699f29437@willemb.c.googlers.com.notmuch>
Date: Mon, 11 Mar 2024 09:13:50 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Richard Gobert <richardbgobert@...il.com>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>,
Eric Dumazet <edumazet@...gle.com>
Cc: davem@...emloft.net,
kuba@...nel.org,
pabeni@...hat.com,
dsahern@...nel.org,
xeb@...l.ru,
shuah@...nel.org,
idosch@...dia.com,
razor@...ckwall.org,
amcohen@...dia.com,
petrm@...dia.com,
jbenc@...hat.com,
bpoirier@...dia.com,
b.galvani@...il.com,
gavinl@...dia.com,
liujian56@...wei.com,
horms@...nel.org,
linyunsheng@...wei.com,
therbert@...gle.com,
netdev@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next v3 4/4] net: gro: move L3 flush checks to
tcp_gro_receive
Richard Gobert wrote:
> Willem de Bruijn wrote:
> > Richard Gobert wrote:
> >> Eric Dumazet wrote:
> >>> On Sat, Mar 9, 2024 at 4:35 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
> >>>> relevant only to tcp flows, and as such they're used to determine whether
> >>>> the packets can be merged later in tcp_gro_receive.
> >>>>
> >>>> These checks are not relevant to UDP packets.
> >>>
> >>> I do not think this claim is true.
> >>>
> >>> Incoming packets -> GRO -> GSO -> forwarded packets
> >>>
> >>> The {GRO,GSO} step must be transparent, GRO is not LRO.
> >>
> >> Sorry, I should rephrase myself. The patch preserves the
> >> current logic in GRO. These L3 checks (ttl, flags, etc.) are written to
> >> NAPI_GRO_CB(p)->{flush,flush_id}, and NAPI_GRO_CB(skb)->is_atomic - and
> >> all of these are currently used only in tcp_gro_receive.
> >
> > That was perhaps an oversight when adding UDP GRO?
> >
> > Simply because the flush is determined in the innermost callback.
>
> It might have been an oversight. From what I have seen it's only relevant
> to GRO's UDP fraglist path (it was added in 9fd1ff5d ("udp: Support UDP
> fraglist GRO/GSO.")). That's the only UDP path that calls skb_gro_receive -
> which may alter the forwarded packets and make GRO/GSO not transparent.
>
> AFAIU NAPI_GRO_CB(p)->flush value is not overwritten in encapsulation - it
> is determined by both outer and inner callbacks.
Thanks for the context
> I tried to preserve the current behaviour in GRO - if we want to change
> this behaviour I'll gladly do it, although I'd prefer to address it in a
> different patch series. What do you think?
Yes, it's entirely reasonable to leave that out of this series.
Powered by blists - more mailing lists