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Message-Id: <20260128143435.15708-11-chia-yu.chang@nokia-bell-labs.com>
Date: Wed, 28 Jan 2026 15:34:30 +0100
From: chia-yu.chang@...ia-bell-labs.com
To: pabeni@...hat.com,
edumazet@...gle.com,
parav@...dia.com,
linux-doc@...r.kernel.org,
corbet@....net,
horms@...nel.org,
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netdev@...r.kernel.org,
dave.taht@...il.com,
jhs@...atatu.com,
kuba@...nel.org,
stephen@...workplumber.org,
xiyou.wangcong@...il.com,
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davem@...emloft.net,
andrew+netdev@...n.ch,
donald.hunter@...il.com,
ast@...erby.net,
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rs.ietf@....at,
Jason_Livingood@...cast.com,
vidhi_goel@...le.com
Cc: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
Subject: [PATCH v12 net-next 10/15] tcp: accecn: unset ECT if receive or send ACE=0 in AccECN negotiaion
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>
Reviewed-by: Eric Dumazet <edumazet@...gle.com>
---
v12:
- Change AccECN fail flag setting to request socket
v10:
- Set AccECN error flag on request itself via tcp_rsk() to avoid
changing directly on the listener
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().
---
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 | 3 +++
5 files changed, 36 insertions(+), 11 deletions(-)
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 13372d2cbed5..018e8ffc0717 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)) {
+ if (req->num_retrans > 1 && tcp_rsk(req)->accecn_ok)
+ tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_SEND;
if (req->num_timeout++ == 0)
atomic_dec(&queue->young);
mod_timer(&req->rsk_timer, jiffies + tcp_reqsk_timeout(req));
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index aef6f2bbcd0c..a4d086ccb18a 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6394,6 +6394,8 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
if (th->syn) {
if (tcp_ecn_mode_accecn(tp)) {
accecn_reflector = true;
+ tp->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield &
+ INET_ECN_MASK;
if (tp->rx_opt.accecn &&
tp->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) {
u8 saw_opt = tcp_accecn_option_init(skb, tp->rx_opt.accecn);
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 9776c921d1bb..ec128865f5c0 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -481,6 +481,10 @@ static void tcp_ecn_openreq_child(struct sock *sk,
tp->syn_ect_snt = treq->syn_ect_snt;
tcp_accecn_third_ack(sk, skb, treq->syn_ect_snt);
tp->saw_accecn_opt = treq->saw_accecn_opt;
+ if (treq->accecn_fail_mode & TCP_ACCECN_ACE_FAIL_SEND)
+ tcp_accecn_fail_mode_set(tp, TCP_ACCECN_ACE_FAIL_SEND);
+ if (treq->accecn_fail_mode & TCP_ACCECN_ACE_FAIL_RECV)
+ tcp_accecn_fail_mode_set(tp, TCP_ACCECN_ACE_FAIL_RECV);
tp->prev_ecnfield = treq->syn_ect_rcv;
tp->accecn_opt_demand = 1;
tcp_ecn_received_counters_payload(sk, skb);
@@ -749,16 +753,28 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
*/
if (!tcp_oow_rate_limited(sock_net(sk), skb,
LINUX_MIB_TCPACKSKIPPEDSYNRECV,
- &tcp_rsk(req)->last_oow_ack_time) &&
-
- !tcp_rtx_synack(sk, req)) {
- unsigned long expires = jiffies;
-
- expires += tcp_reqsk_timeout(req);
- if (!fastopen)
- mod_timer_pending(&req->rsk_timer, expires);
- else
- req->rsk_timer.expires = expires;
+ &tcp_rsk(req)->last_oow_ack_time)) {
+ if (tcp_rsk(req)->accecn_ok) {
+ u8 ect_rcv = TCP_SKB_CB(skb)->ip_dsfield &
+ INET_ECN_MASK;
+
+ tcp_rsk(req)->syn_ect_rcv = ect_rcv;
+ if (tcp_accecn_ace(tcp_hdr(skb)) == 0x0)
+ tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_RECV;
+ }
+ if (!tcp_rtx_synack(sk, req)) {
+ unsigned long expires = jiffies;
+
+ if (req->num_retrans > 1 && tcp_rsk(req)->accecn_ok)
+ tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_SEND;
+
+ expires += tcp_reqsk_timeout(req);
+ if (!fastopen)
+ mod_timer_pending(&req->rsk_timer,
+ expires);
+ else
+ req->rsk_timer.expires = expires;
+ }
}
return NULL;
}
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 22728daed436..ed545cb033b6 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -334,7 +334,8 @@ static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
return;
if (tcp_ecn_mode_accecn(tp)) {
- if (!tcp_accecn_ace_fail_recv(tp))
+ if (!tcp_accecn_ace_fail_recv(tp) &&
+ !tcp_accecn_ace_fail_send(tp))
INET_ECN_xmit(sk);
tcp_accecn_set_ace(tp, skb, th);
skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ACCECN;
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 160080c9021d..5a14a53a3c9e 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -22,6 +22,7 @@
#include <linux/module.h>
#include <linux/gfp.h>
#include <net/tcp.h>
+#include <net/tcp_ecn.h>
#include <net/rstreason.h>
static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
@@ -479,6 +480,8 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
* it's not good to give up too easily.
*/
tcp_rtx_synack(sk, req);
+ if (req->num_retrans > 1 && tcp_rsk(req)->accecn_ok)
+ tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_SEND;
req->num_timeout++;
tcp_update_rto_stats(sk);
if (!tp->retrans_stamp)
--
2.34.1
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