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Message-ID:
<PAXPR07MB7984E2D22D4337CA97EBB9CBA389A@PAXPR07MB7984.eurprd07.prod.outlook.com>
Date: Tue, 20 Jan 2026 18:11:39 +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 v9 net-next 10/15] tcp: accecn: unset ECT if receive or
send ACE=0 in AccECN negotiaion
> -----Original Message-----
> From: Eric Dumazet <edumazet@...gle.com>
> Sent: Tuesday, January 20, 2026 12:05 PM
> To: Chia-Yu Chang (Nokia) <chia-yu.chang@...ia-bell-labs.com>
> Cc: pabeni@...hat.com; parav@...dia.com; linux-doc@...r.kernel.org; corbet@....net; horms@...nel.org; dsahern@...nel.org; kuniyu@...gle.com; bpf@...r.kernel.org; netdev@...r.kernel.org; dave.taht@...il.com; 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 <cheshire@...le.com>; rs.ietf@....at; Jason_Livingood@...cast.com; Vidhi Goel <vidhi_goel@...le.com>
> Subject: Re: [PATCH v9 net-next 10/15] tcp: accecn: unset ECT if receive or send ACE=0 in AccECN negotiaion
>
>
> 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 Mon, Jan 19, 2026 at 7:59 PM <chia-yu.chang@...ia-bell-labs.com> wrote:
> >
> > From: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> >
> > Based on specification:
> > https://tools.ietf.org/id/draft-ietf-tcpm-accurate-ecn-28.txt
> >
> > Based on Section 3.1.5 of AccECN spec (RFC9768), a TCP Server in
> > AccECN mode MUST NOT set ECT on any packet for the rest of the
> > connection, if it has received or sent at least one valid SYN or
> > Acceptable SYN/ACK with (AE,CWR,ECE) = (0,0,0) during the handshake.
> >
> > In addition, a host in AccECN mode that is feeding back the IP-ECN
> > field on a SYN or SYN/ACK MUST feed back the IP-ECN field on the
> > latest valid SYN or acceptable SYN/ACK to arrive.
> >
> > Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> >
> > ---
> > v8:
> > - Add new helper function tcp_accecn_ace_fail_send_set_retrans()
> >
> > v6:
> > - Do not cast const struct request_sock into struct request_sock
> > - Set tcp_accecn_fail_mode after calling tcp_rtx_synack().
> > ---
> > include/net/tcp_ecn.h | 7 +++++++
> > net/ipv4/inet_connection_sock.c | 3 +++
> > net/ipv4/tcp_input.c | 2 ++
> > net/ipv4/tcp_minisocks.c | 36 ++++++++++++++++++++++++---------
> > net/ipv4/tcp_output.c | 3 ++-
> > net/ipv4/tcp_timer.c | 2 ++
> > 6 files changed, 42 insertions(+), 11 deletions(-)
> >
> > diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h index
> > 796c613b5ef3..f5e1f6b1bec3 100644
> > --- a/include/net/tcp_ecn.h
> > +++ b/include/net/tcp_ecn.h
> > @@ -97,6 +97,13 @@ static inline void tcp_accecn_fail_mode_set(struct tcp_sock *tp, u8 mode)
> > tp->accecn_fail_mode |= mode;
> > }
> >
> > +static inline void tcp_accecn_ace_fail_send_set_retrans(struct request_sock *req,
> > + struct
> > +tcp_sock *tp) {
> > + if (req->num_retrans > 1 && tcp_rsk(req)->accecn_ok)
> > + tcp_accecn_fail_mode_set(tp,
> > +TCP_ACCECN_ACE_FAIL_SEND); }
> > +
> > #define TCP_ACCECN_OPT_NOT_SEEN 0x0
> > #define TCP_ACCECN_OPT_EMPTY_SEEN 0x1
> > #define TCP_ACCECN_OPT_COUNTER_SEEN 0x2
> > diff --git a/net/ipv4/inet_connection_sock.c
> > b/net/ipv4/inet_connection_sock.c index 97d57c52b9ad..9d16cb9c3db4
> > 100644
> > --- a/net/ipv4/inet_connection_sock.c
> > +++ b/net/ipv4/inet_connection_sock.c
> > @@ -20,6 +20,7 @@
> > #include <net/tcp_states.h>
> > #include <net/xfrm.h>
> > #include <net/tcp.h>
> > +#include <net/tcp_ecn.h>
> > #include <net/sock_reuseport.h>
> > #include <net/addrconf.h>
> >
> > @@ -1103,6 +1104,8 @@ static void reqsk_timer_handler(struct timer_list *t)
> > (!resend ||
> > !tcp_rtx_synack(sk_listener, req) ||
> > inet_rsk(req)->acked)) {
> > + tcp_accecn_ace_fail_send_set_retrans(req,
> > +
> > + tcp_sk(sk_listener));
>
>
> Ouch.
>
> I think you missed the fact that a listener is shared by many SYN_RECV requests.
>
> Consider it as read-only here.
Hi Eric,
Thanks for the feedback.
Do you mean sk_listener here is read-only despite there is no const here?
Then, could you help to suggest the way please?
Beacuse for AccECN, here we need to set fail flag after retransmitting SYN/ACK > 1 time.
And this was done within tcp_make_synack(), but now move to every place where could retransmit SYN/ACK.
Thanks.
Chia-Yu
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