netdev - RE: [PATCH v15 net-next 12/14] tcp: accecn: AccECN option failure handling

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Message-ID:
 <PAXPR07MB798409A944ED834962D5CED0A33DA@PAXPR07MB7984.eurprd07.prod.outlook.com>
Date: Fri, 22 Aug 2025 10:00:41 +0000
From: "Chia-Yu Chang (Nokia)" <chia-yu.chang@...ia-bell-labs.com>
To: Eric Dumazet <edumazet@...gle.com>
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Subject: RE: [PATCH v15 net-next 12/14] tcp: accecn: AccECN option failure
 handling

> -----Original Message-----
> From: Eric Dumazet <edumazet@...gle.com> 
> Sent: Thursday, August 21, 2025 2:56 PM
> To: Chia-Yu Chang (Nokia) <chia-yu.chang@...ia-bell-labs.com>
> Cc: pabeni@...hat.com; linux-doc@...r.kernel.org; corbet@....net; horms@...nel.org; dsahern@...nel.org; kuniyu@...zon.com; bpf@...r.kernel.org; netdev@...r.kernel.org; jhs@...atatu.com; kuba@...nel.org; stephen@...workplumber.org; xiyou.wangcong@...il.com; jiri@...nulli.us; davem@...emloft.net; andrew+netdev@...n.ch; donald.hunter@...il.com; ast@...erby.net; liuhangbin@...il.com; shuah@...nel.org; linux-kselftest@...r.kernel.org; ij@...nel.org; ncardwell@...gle.com; Koen De Schepper (Nokia) <koen.de_schepper@...ia-bell-labs.com>; g.white@...lelabs.com; ingemar.s.johansson@...csson.com; mirja.kuehlewind@...csson.com; cheshire@...le.com; rs.ietf@....at; Jason_Livingood@...cast.com; vidhi_goel@...le.com
> Subject: Re: [PATCH v15 net-next 12/14] tcp: accecn: AccECN option failure handling
> 
> 
> CAUTION: This is an external email. Please be very careful when clicking links or opening attachments. See the URL nok.it/ext for additional information.
> 
> 
> 
> On Fri, Aug 15, 2025 at 1:40 AM <chia-yu.chang@...ia-bell-labs.com> wrote:
> >
> > From: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> >
> > AccECN option may fail in various way, handle these:
> > - Attempt to negotiate the use of AccECN on the 1st retransmitted SYN
> >         - From the 2nd retransmitted SYN, stop AccECN negotiation
> > - Remove option from SYN/ACK rexmits to handle blackholes
> > - If no option arrives in SYN/ACK, assume Option is not usable
> >         - If an option arrives later, re-enabled
> > - If option is zeroed, disable AccECN option processing
> >
> > This patch use existing padding bits in tcp_request_sock and holes in 
> > tcp_sock without increasing the size.
> >
> > Signed-off-by: Ilpo Järvinen <ij@...nel.org>
> > Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> 
> Truly invasive changes, what can I say....
> 
> Not sure why you CC so many folks which will very unlikely give any feedback.
> 
> What is the purpose of WARN_ON_ONCE() in tcp_accecn_option_init() ?
> 
> Just to feed syzbot ?

Hi Eric,

WARN_ON_ONCE() exists in both tcp_accecn_option_init() and tcp_accecn_process_option().

And the one in tcp_accecn_option_init() is for AccECN option handling during the handshake.

Or is it not preferred to put WARN_ON_ONCE() during TCP handshake?

Chia-Yu