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Message-Id: <20251201163800.3965-11-chia-yu.chang@nokia-bell-labs.com>
Date: Mon, 1 Dec 2025 17:37:57 +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,
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@...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
Cc: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
Subject: [PATCH v7 net-next 10/13] 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>
---
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 | 4 ++++
net/ipv4/tcp_input.c | 2 ++
net/ipv4/tcp_minisocks.c | 39 ++++++++++++++++++++++++---------
net/ipv4/tcp_output.c | 3 ++-
net/ipv4/tcp_timer.c | 3 +++
5 files changed, 40 insertions(+), 11 deletions(-)
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 97d57c52b9ad..c994a00c83d2 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 +1104,9 @@ 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_accecn_fail_mode_set(tcp_sk(sk_listener),
+ 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 e5c9cf586437..db361daebff8 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6240,6 +6240,8 @@ 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..ff573fad465f 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -749,16 +749,35 @@ 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) {
+ u8 fail_mode = TCP_ACCECN_ACE_FAIL_RECV;
+
+ tcp_accecn_fail_mode_set(tcp_sk(sk),
+ fail_mode);
+ }
+ }
+ if (!tcp_rtx_synack(sk, req)) {
+ u8 fail_mode = TCP_ACCECN_ACE_FAIL_SEND;
+ unsigned long expires = jiffies;
+
+ if (req->num_retrans > 1 &&
+ tcp_rsk(req)->accecn_ok)
+ tcp_accecn_fail_mode_set(tcp_sk(sk),
+ fail_mode);
+
+ 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 c6754854ad09..9489cda7322e 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..8ef2f105cc21 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_accecn_fail_mode_set(tcp_sk(sk), TCP_ACCECN_ACE_FAIL_SEND);
req->num_timeout++;
tcp_update_rto_stats(sk);
if (!tp->retrans_stamp)
--
2.34.1
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