On Mon, Jan 19, 2026 at 7:59 PM <[email protected]> wrote: > > From: Chia-Yu Chang <[email protected]> > > 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 <[email protected]> > > --- > 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.
