From ae3f31df5722995bbf717fd4ffe7bfa9c2e80826 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Fri, 19 Jan 2024 15:11:58 +0100
Subject: [PATCH 01/24] Modification for ACCECN draft

---
 net/ipv4/tcp_minisocks.c | 39 +++++++++++++++++----------------------
 net/ipv4/tcp_output.c    |  6 ------
 2 files changed, 17 insertions(+), 28 deletions(-)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 8450748d6873..75b919d850c2 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -414,7 +414,11 @@ bool tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
 		if (!TCP_SKB_CB(skb)->sacked) {
 		    inet_rsk(req)->ecn_ok = 0;
 		    tcp_rsk(req)->accecn_ok = 0;
+
 		    tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
+		    tp->prev_ecnfield = treq->syn_ect_rcv;
+		    tp->accecn_opt_demand = 1;
+		    tcp_ecn_received_counters(sk, skb, skb->len - th->doff * 4);
 		    verify_ace = false;
 		}
 		break;
@@ -447,24 +451,20 @@ static void tcp_ecn_openreq_child(struct sock *sk,
 	// [CY] 3.1.5. Implications of AccECN Mode - 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.
-	if (treq->noect) {
-	    tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
-	} else {
-	    if (treq->accecn_ok) {
-		const struct tcphdr *th = (const struct tcphdr *)skb->data;
-		if (tcp_accecn_third_ack(sk, skb, req, treq->syn_ect_snt)) {
-		    tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
-		    tp->syn_ect_snt = treq->syn_ect_snt;
-		    tp->saw_accecn_opt = treq->saw_accecn_opt;
-		    tp->prev_ecnfield = treq->syn_ect_rcv;
-		    tp->accecn_opt_demand = 1;
-		    tcp_ecn_received_counters(sk, skb, skb->len - th->doff * 4);
-		}
-	    } else {
-		tcp_ecn_mode_set(tp, inet_rsk(req)->ecn_ok && !tcp_ca_no_fallback_rfc3168(sk) ?
-				     TCP_ECN_MODE_RFC3168 :
-	 			     TCP_ECN_DISABLED);
+	if (treq->accecn_ok) {
+	    const struct tcphdr *th = (const struct tcphdr *)skb->data;
+	    if (tcp_accecn_third_ack(sk, skb, req, treq->syn_ect_snt)) {
+	        tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
+	        tp->syn_ect_snt = treq->syn_ect_snt;
+	        tp->saw_accecn_opt = treq->saw_accecn_opt;
+	        tp->prev_ecnfield = treq->syn_ect_rcv;
+	        tp->accecn_opt_demand = 1;
+	        tcp_ecn_received_counters(sk, skb, skb->len - th->doff * 4);
 	    }
+	} else {
+	    tcp_ecn_mode_set(tp, inet_rsk(req)->ecn_ok && !tcp_ca_no_fallback_rfc3168(sk) ?
+	    		     TCP_ECN_MODE_RFC3168 :
+	    		     TCP_ECN_DISABLED);
 	}
 }
 
@@ -723,11 +723,6 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 			// the appropriate combination of TCP-ECN flags to feed back the IP-ECN field of this latest SYN)
 			    tcp_sk(sk)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
 
-			// [CY] 3.1.5. Implications of AccECN Mode - 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.
-			    tcp_rsk(req)->noect = 1;
-			    INET_ECN_dontxmit(sk);
 			}
 		    }
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 99ae746753eb..c884210b21cc 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -392,12 +392,6 @@ tcp_ecn_make_synack(struct sock *sk, struct request_sock *req, struct tcphdr *th
 		th->ae  = 0;
 		th->cwr = 0;
 		th->ece = 0;
-
-	// [CY] 3.1.5. Implications of AccECN Mode - 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.
-		tcp_rsk(req)->noect = 1;
-		INET_ECN_dontxmit(sk);
 	}
 }
 

From bb25bcf7350fae2b174666c7c1572ae9ea836460 Mon Sep 17 00:00:00 2001
From: Chia-Yu Chang <125277758+minuscat@users.noreply.github.com>
Date: Fri, 19 Jan 2024 15:23:54 +0100
Subject: [PATCH 02/24] Update kernel.yml

---
 .github/workflows/kernel.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/kernel.yml b/.github/workflows/kernel.yml
index 1c6d3320a606..4c81b75c797e 100644
--- a/.github/workflows/kernel.yml
+++ b/.github/workflows/kernel.yml
@@ -63,7 +63,7 @@ jobs:
     runs-on: ubuntu-20.04
     needs: build
     permissions: write-all
-    if: ${{ github.ref == 'refs/heads/testing' || github.ref == 'refs/heads/ratebase' || github.ref == 'refs/heads/AccECN-2023'}}
+    if: ${{ github.ref == 'refs/heads/testing' || github.ref == 'refs/heads/ratebase' || github.ref == 'refs/heads/AccECN-2023' || github.ref == 'refs/heads/AccECN-2024'}}
     steps:
     - name: Get artifact
       uses: actions/download-artifact@v3

From 12a84bc0a1b5996a20e4e1a627530d0181ca5393 Mon Sep 17 00:00:00 2001
From: Chia-Yu Chang <125277758+minuscat@users.noreply.github.com>
Date: Fri, 19 Jan 2024 15:25:24 +0100
Subject: [PATCH 03/24] Update tcp_minisocks.c

---
 net/ipv4/tcp_minisocks.c | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 75b919d850c2..f78c540f13f2 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -407,20 +407,6 @@ bool tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
 	switch (ace) {
 	case 0x0:
 		tp->ecn_fail = 1;
-		// [CY] 3.2.2.1. ACE Field on the ACK of the SYN/ACK - If the Server is in AccECN mode and in SYN-RCVD 
-		// state, and if it receives a value of zero on a pure ACK with SYN=0 and no SACK blocks, for the rest
-		// of the connection the Server MUST NOT set ECT on outgoing packets and MUST NOT respond to AccECN 
-		// feedback. Nonetheless, as a Data Receiver it MUST NOT disable AccECN feedback.
-		if (!TCP_SKB_CB(skb)->sacked) {
-		    inet_rsk(req)->ecn_ok = 0;
-		    tcp_rsk(req)->accecn_ok = 0;
-
-		    tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
-		    tp->prev_ecnfield = treq->syn_ect_rcv;
-		    tp->accecn_opt_demand = 1;
-		    tcp_ecn_received_counters(sk, skb, skb->len - th->doff * 4);
-		    verify_ace = false;
-		}
 		break;
 	case 0x7:
 	case 0x5:

From 230e7ae791293db96b0696a9e4ac79b839097f4e Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Fri, 19 Jan 2024 18:09:50 +0100
Subject: [PATCH 04/24] Modification for ACCECN draft

---
 net/ipv4/tcp_input.c     | 33 +++++++++++++++++----------------
 net/ipv4/tcp_minisocks.c |  2 +-
 net/ipv4/tcp_output.c    |  6 +++---
 3 files changed, 21 insertions(+), 20 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index fdd58702b736..820330e81eba 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -444,6 +444,7 @@ static void tcp_ecn_rcv_synack(struct sock *sk, const struct sk_buff *skb,
 		tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
 		break;
 	case 0x1:
+	case 0x5:
 		if (tcp_ca_no_fallback_rfc3168(sk))
 		    tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
 		else
@@ -454,22 +455,22 @@ static void tcp_ecn_rcv_synack(struct sock *sk, const struct sk_buff *skb,
 	// = (1,0,1) but it does not have logic specific to such a combination, the Client MUST enable AccECN 
 	// mode as if the SYN/ACK confirmed that the Server supported AccECN and as if it fed back that the 
 	// IP-ECN field on the SYN had arrived unchanged.
-	case 0x5:
-		if (tcp_ecn_mode_pending(tp)) {
-		    tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
-		    tp->syn_ect_rcv = ip_dsfield & INET_ECN_MASK;
-		    if (tp->rx_opt.accecn &&
-			tp->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) {
-			    tp->saw_accecn_opt = tcp_accecn_option_init(skb,
-									tp->rx_opt.accecn);
-				tp->accecn_opt_demand = 2;
-		    }
-		    if (INET_ECN_is_ce(ip_dsfield)) {
-			    tp->received_ce++;
-			    tp->received_ce_pending++;
-		    }
-		}
-		break;
+	//case 0x5:
+	//	if (tcp_ecn_mode_pending(tp)) {
+	//	    tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
+	//	    tp->syn_ect_rcv = ip_dsfield & INET_ECN_MASK;
+	//	    if (tp->rx_opt.accecn &&
+	//		tp->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) {
+	//		    tp->saw_accecn_opt = tcp_accecn_option_init(skb,
+	//								tp->rx_opt.accecn);
+	//			tp->accecn_opt_demand = 2;
+	//	    }
+	//	    if (INET_ECN_is_ce(ip_dsfield)) {
+	//		    tp->received_ce++;
+	//		    tp->received_ce_pending++;
+	//	    }
+	//	}
+	//	break;
 	default:
 		tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
 		tp->syn_ect_rcv = ip_dsfield & INET_ECN_MASK;
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index f78c540f13f2..deacdb22aab3 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -707,7 +707,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 			// [CY] 3.1.5. Implications of AccECN Mode - A TCP Server already in AccECN mode: SHOULD 
 			// acknowledge a valid SYN arriving with (AE,CWR,ECE) =(0,0,0) by emitting an AccECN SYN/ACK (with
 			// the appropriate combination of TCP-ECN flags to feed back the IP-ECN field of this latest SYN)
-			    tcp_sk(sk)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
+			    //tcp_sk(sk)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
 
 			}
 		    }
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c884210b21cc..9237c9f7a4ef 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -389,9 +389,9 @@ tcp_ecn_make_synack(struct sock *sk, struct request_sock *req, struct tcphdr *th
 	// [CY] 3.2.3.2.2. Testing for Loss of Packets Carrying the AccECN Option - If this retransmission times out, 
 	// to expedite connection setup, the TCP Server SHOULD retransmit the SYN/ACK with (AE,CWR,ECE) = (0,0,0) and 
 	// no AccECN Option, but it remains in AccECN feedback mode
-		th->ae  = 0;
-		th->cwr = 0;
-		th->ece = 0;
+		//th->ae  = 0;
+		//th->cwr = 0;
+		//th->ece = 0;
 	}
 }
 

From 472b228b6effa285a9064dfd4bc8df596f723f93 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Sat, 20 Jan 2024 11:04:29 +0100
Subject: [PATCH 05/24] Revert "Modification for ACCECN draft"

This reverts commit 230e7ae791293db96b0696a9e4ac79b839097f4e.
---
 net/ipv4/tcp_input.c     | 33 ++++++++++++++++-----------------
 net/ipv4/tcp_minisocks.c |  2 +-
 net/ipv4/tcp_output.c    |  6 +++---
 3 files changed, 20 insertions(+), 21 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 820330e81eba..fdd58702b736 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -444,7 +444,6 @@ static void tcp_ecn_rcv_synack(struct sock *sk, const struct sk_buff *skb,
 		tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
 		break;
 	case 0x1:
-	case 0x5:
 		if (tcp_ca_no_fallback_rfc3168(sk))
 		    tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
 		else
@@ -455,22 +454,22 @@ static void tcp_ecn_rcv_synack(struct sock *sk, const struct sk_buff *skb,
 	// = (1,0,1) but it does not have logic specific to such a combination, the Client MUST enable AccECN 
 	// mode as if the SYN/ACK confirmed that the Server supported AccECN and as if it fed back that the 
 	// IP-ECN field on the SYN had arrived unchanged.
-	//case 0x5:
-	//	if (tcp_ecn_mode_pending(tp)) {
-	//	    tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
-	//	    tp->syn_ect_rcv = ip_dsfield & INET_ECN_MASK;
-	//	    if (tp->rx_opt.accecn &&
-	//		tp->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) {
-	//		    tp->saw_accecn_opt = tcp_accecn_option_init(skb,
-	//								tp->rx_opt.accecn);
-	//			tp->accecn_opt_demand = 2;
-	//	    }
-	//	    if (INET_ECN_is_ce(ip_dsfield)) {
-	//		    tp->received_ce++;
-	//		    tp->received_ce_pending++;
-	//	    }
-	//	}
-	//	break;
+	case 0x5:
+		if (tcp_ecn_mode_pending(tp)) {
+		    tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
+		    tp->syn_ect_rcv = ip_dsfield & INET_ECN_MASK;
+		    if (tp->rx_opt.accecn &&
+			tp->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) {
+			    tp->saw_accecn_opt = tcp_accecn_option_init(skb,
+									tp->rx_opt.accecn);
+				tp->accecn_opt_demand = 2;
+		    }
+		    if (INET_ECN_is_ce(ip_dsfield)) {
+			    tp->received_ce++;
+			    tp->received_ce_pending++;
+		    }
+		}
+		break;
 	default:
 		tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
 		tp->syn_ect_rcv = ip_dsfield & INET_ECN_MASK;
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index deacdb22aab3..f78c540f13f2 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -707,7 +707,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 			// [CY] 3.1.5. Implications of AccECN Mode - A TCP Server already in AccECN mode: SHOULD 
 			// acknowledge a valid SYN arriving with (AE,CWR,ECE) =(0,0,0) by emitting an AccECN SYN/ACK (with
 			// the appropriate combination of TCP-ECN flags to feed back the IP-ECN field of this latest SYN)
-			    //tcp_sk(sk)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
+			    tcp_sk(sk)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
 
 			}
 		    }
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 9237c9f7a4ef..c884210b21cc 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -389,9 +389,9 @@ tcp_ecn_make_synack(struct sock *sk, struct request_sock *req, struct tcphdr *th
 	// [CY] 3.2.3.2.2. Testing for Loss of Packets Carrying the AccECN Option - If this retransmission times out, 
 	// to expedite connection setup, the TCP Server SHOULD retransmit the SYN/ACK with (AE,CWR,ECE) = (0,0,0) and 
 	// no AccECN Option, but it remains in AccECN feedback mode
-		//th->ae  = 0;
-		//th->cwr = 0;
-		//th->ece = 0;
+		th->ae  = 0;
+		th->cwr = 0;
+		th->ece = 0;
 	}
 }
 

From 2fc01fe6844a2f364600f919b25d09c1e4a6df99 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Sat, 20 Jan 2024 11:33:05 +0100
Subject: [PATCH 06/24] Modification for ACCECN draft

---
 net/ipv4/tcp_minisocks.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index f78c540f13f2..149e12d5c6f6 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -407,6 +407,16 @@ bool tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
 	switch (ace) {
 	case 0x0:
 		tp->ecn_fail = 1;
+		// [CY] 3.2.2.1. ACE Field on the ACK of the SYN/ACK - If the Server is in AccECN mode and in SYN-RCVD 
+		// state, and if it receives a value of zero on a pure ACK with SYN=0 and no SACK blocks, for the rest
+		// of the connection the Server MUST NOT set ECT on outgoing packets and MUST NOT respond to AccECN 
+		// feedback. Nonetheless, as a Data Receiver it MUST NOT disable AccECN feedback.
+		if (!TCP_SKB_CB(skb)->sacked) {
+		    inet_rsk(req)->ecn_ok = 0;
+		    tcp_rsk(req)->accecn_ok = 0;
+		    tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
+		    verify_ace = false;
+		}
 		break;
 	case 0x7:
 	case 0x5:
@@ -443,10 +453,10 @@ static void tcp_ecn_openreq_child(struct sock *sk,
 	        tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
 	        tp->syn_ect_snt = treq->syn_ect_snt;
 	        tp->saw_accecn_opt = treq->saw_accecn_opt;
-	        tp->prev_ecnfield = treq->syn_ect_rcv;
-	        tp->accecn_opt_demand = 1;
-	        tcp_ecn_received_counters(sk, skb, skb->len - th->doff * 4);
 	    }
+	    tp->prev_ecnfield = treq->syn_ect_rcv;
+	    tp->accecn_opt_demand = 1;
+	    tcp_ecn_received_counters(sk, skb, skb->len - th->doff * 4);
 	} else {
 	    tcp_ecn_mode_set(tp, inet_rsk(req)->ecn_ok && !tcp_ca_no_fallback_rfc3168(sk) ?
 	    		     TCP_ECN_MODE_RFC3168 :

From 04b6c9851681024aaa26cc203d0c6a115a9f4285 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Sat, 20 Jan 2024 16:58:40 +0100
Subject: [PATCH 07/24] Modification for ACCECN draft

---
 net/ipv4/tcp_minisocks.c | 11 ++++++++---
 net/ipv4/tcp_output.c    |  5 +++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 149e12d5c6f6..47623c7bc3e8 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -412,8 +412,6 @@ bool tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
 		// of the connection the Server MUST NOT set ECT on outgoing packets and MUST NOT respond to AccECN 
 		// feedback. Nonetheless, as a Data Receiver it MUST NOT disable AccECN feedback.
 		if (!TCP_SKB_CB(skb)->sacked) {
-		    inet_rsk(req)->ecn_ok = 0;
-		    tcp_rsk(req)->accecn_ok = 0;
 		    tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
 		    verify_ace = false;
 		}
@@ -451,9 +449,11 @@ static void tcp_ecn_openreq_child(struct sock *sk,
 	    const struct tcphdr *th = (const struct tcphdr *)skb->data;
 	    if (tcp_accecn_third_ack(sk, skb, req, treq->syn_ect_snt)) {
 	        tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
-	        tp->syn_ect_snt = treq->syn_ect_snt;
 	        tp->saw_accecn_opt = treq->saw_accecn_opt;
+	    } else {
+		tp->saw_accecn_opt = TCP_ACCECN_OPT_FAIL;
 	    }
+	    tp->syn_ect_snt = treq->syn_ect_snt;
 	    tp->prev_ecnfield = treq->syn_ect_rcv;
 	    tp->accecn_opt_demand = 1;
 	    tcp_ecn_received_counters(sk, skb, skb->len - th->doff * 4);
@@ -719,6 +719,11 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 			// the appropriate combination of TCP-ECN flags to feed back the IP-ECN field of this latest SYN)
 			    tcp_sk(sk)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
 
+			// [CY] 3.1.5. Implications of AccECN Mode - 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
+			    tcp_sk(sk)->ecn_fail = 1;
+			    INET_ECN_dontxmit(sk);
 			}
 		    }
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c884210b21cc..5bf109464f6b 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -392,6 +392,11 @@ tcp_ecn_make_synack(struct sock *sk, struct request_sock *req, struct tcphdr *th
 		th->ae  = 0;
 		th->cwr = 0;
 		th->ece = 0;
+	// [CY] 3.1.5. Implications of AccECN Mode - 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.
+		tcp_sk(sk)->ecn_fail = 1;
+		INET_ECN_dontxmit(sk);
 	}
 }
 

From a449debb5c81f55cb04b5fe07e903563294bc581 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Sun, 21 Jan 2024 03:37:15 +0100
Subject: [PATCH 08/24] Modification for ACCECN draft

---
 include/linux/tcp.h      |  4 ++--
 net/ipv4/tcp.c           |  1 +
 net/ipv4/tcp_input.c     |  5 ++---
 net/ipv4/tcp_minisocks.c | 33 +++++++++++++++------------------
 net/ipv4/tcp_output.c    |  2 +-
 5 files changed, 21 insertions(+), 24 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 1557cf0241c8..50f036db09bf 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -126,8 +126,7 @@ struct tcp_request_sock {
 #if IS_ENABLED(CONFIG_MPTCP)
 	bool				drop_req;
 #endif
-	u8				noect : 1,
-					accecn_ok  : 1,
+	u8				accecn_ok  : 1,
 					saw_accecn_opt : 2,
 					syn_ect_snt: 2,
 					syn_ect_rcv: 2;
@@ -234,6 +233,7 @@ struct tcp_sock {
 		syn_ect_snt:2,	/* AccECN ECT memory, only */
 		syn_ect_rcv:2,	/* ... needed durign 3WHS + first seqno */
 		ecn_fail:1;	/* ECN reflector detected path mangling */
+	u8	accecn_no_process:1; /* AccECN no response on feedback */
 	u8	saw_accecn_opt:2,    /* An AccECN option was seen */
 		fast_ack_mode:2, /* which fast ack mode ? */
 		unused:4;
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 9721d7f0db9b..a9ccb83a8548 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3033,6 +3033,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tp->delivered_ce = 0;
 	tp->saw_accecn_opt = 0;
 	tp->ecn_fail = 0;
+	tp->accecn_no_preocess = 0;
 	tcp_accecn_init_counters(tp);
 	tp->prev_ecnfield = 0;
 	tp->accecn_opt_tstamp = 0;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index fdd58702b736..56d2a9a454fd 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -595,7 +595,7 @@ static bool tcp_accecn_process_option(struct tcp_sock *tp,
 	bool order1, res;
 	unsigned int i;
 
-	if (tp->saw_accecn_opt == TCP_ACCECN_OPT_FAIL)
+	if (tp->saw_accecn_opt == TCP_ACCECN_OPT_FAIL || tp->accecn_no_process)
 		return false;
 
 	if (!(flag & FLAG_SLOWPATH) || !tp->rx_opt.accecn) {
@@ -7017,7 +7017,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 
 		tcp_initialize_rcv_mss(sk);
 		if (tcp_ecn_mode_accecn(tp))
-			tcp_accecn_third_ack(sk, skb, req, tp->syn_ect_snt);
+			tcp_accecn_third_ack(sk, skb, tp->syn_ect_snt);
 		tcp_fast_path_on(tp);
 		break;
 
@@ -7218,7 +7218,6 @@ static void tcp_openreq_init(struct request_sock *req,
 	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
 	tcp_rsk(req)->snt_synack = 0;
 	tcp_rsk(req)->last_oow_ack_time = 0;
-	tcp_rsk(req)->noect = 0;
 	tcp_rsk(req)->accecn_ok = 0;
 	tcp_rsk(req)->saw_accecn_opt = 0;
 	tcp_rsk(req)->syn_ect_rcv = 0;
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 47623c7bc3e8..c0a448571ae7 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -397,24 +397,25 @@ void tcp_openreq_init_rwin(struct request_sock *req,
 }
 EXPORT_SYMBOL(tcp_openreq_init_rwin);
 
-bool tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
-		          struct request_sock *req, u8 syn_ect_snt)
+void tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
+		          u8 syn_ect_snt)
 {
 	u8 ace = tcp_accecn_ace(tcp_hdr(skb));
 	struct tcp_sock *tp = tcp_sk(sk);
-	bool verify_ace = true;
 
 	switch (ace) {
 	case 0x0:
-		tp->ecn_fail = 1;
 		// [CY] 3.2.2.1. ACE Field on the ACK of the SYN/ACK - If the Server is in AccECN mode and in SYN-RCVD 
 		// state, and if it receives a value of zero on a pure ACK with SYN=0 and no SACK blocks, for the rest
 		// of the connection the Server MUST NOT set ECT on outgoing packets and MUST NOT respond to AccECN 
 		// feedback. Nonetheless, as a Data Receiver it MUST NOT disable AccECN feedback.
-		if (!TCP_SKB_CB(skb)->sacked) {
-		    tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
-		    verify_ace = false;
-		}
+		tp->ecn_fail = 1;
+		tp->accecn_no_process = 1;
+		//INET_ECN_dontxmit(sk);
+		//if (!TCP_SKB_CB(skb)->sacked) {
+		//    tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
+		//    verify_ace = false;
+		//}
 		break;
 	case 0x7:
 	case 0x5:
@@ -432,14 +433,13 @@ bool tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
 		}
 		break;
 	}
-	return verify_ace;
 }
 
 static void tcp_ecn_openreq_child(struct sock *sk,
-				  struct request_sock *req,
+				  const struct request_sock *req,
 				  const struct sk_buff *skb)
 {
-	struct tcp_request_sock *treq = tcp_rsk(req);
+	const struct tcp_request_sock *treq = tcp_rsk(req);
 	struct tcp_sock *tp = tcp_sk(sk);
 
 	// [CY] 3.1.5. Implications of AccECN Mode - A TCP Server in AccECN mode: MUST NOT set ECT on 
@@ -447,13 +447,10 @@ static void tcp_ecn_openreq_child(struct sock *sk,
 	// SYN or Acceptable SYN/ACK with (AE,CWR,ECE) = (0,0,0) during the handshake.
 	if (treq->accecn_ok) {
 	    const struct tcphdr *th = (const struct tcphdr *)skb->data;
-	    if (tcp_accecn_third_ack(sk, skb, req, treq->syn_ect_snt)) {
-	        tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
-	        tp->saw_accecn_opt = treq->saw_accecn_opt;
-	    } else {
-		tp->saw_accecn_opt = TCP_ACCECN_OPT_FAIL;
-	    }
+	    tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
 	    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;
 	    tp->prev_ecnfield = treq->syn_ect_rcv;
 	    tp->accecn_opt_demand = 1;
 	    tcp_ecn_received_counters(sk, skb, skb->len - th->doff * 4);
@@ -723,7 +720,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 			// 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
 			    tcp_sk(sk)->ecn_fail = 1;
-			    INET_ECN_dontxmit(sk);
+			    //INET_ECN_dontxmit(sk);
 			}
 		    }
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 5bf109464f6b..04313da0783d 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -396,7 +396,7 @@ tcp_ecn_make_synack(struct sock *sk, struct request_sock *req, struct tcphdr *th
 	// 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.
 		tcp_sk(sk)->ecn_fail = 1;
-		INET_ECN_dontxmit(sk);
+		//INET_ECN_dontxmit(sk);
 	}
 }
 

From 0e900e57ac8f015b44f226ef53f78c48586b09a4 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Sun, 21 Jan 2024 08:44:50 +0100
Subject: [PATCH 09/24] Modification for ACCECN draft

---
 Documentation/networking/ip-sysctl.rst |  4 ++--
 include/net/tcp.h                      |  4 ++--
 net/ipv4/tcp_minisocks.c               | 24 ++++++++++++------------
 net/ipv4/tcp_output.c                  |  2 +-
 4 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index dbe87fe8cc56..88c315841f3d 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -433,9 +433,9 @@ tcp_ecn_option - INTEGER
 
 tcp_ecn_option_beacon - INTEGER
         Control Accurate ECN (AccECN) option sending frequency per RTT and it 
-        take effect only when tcp_ecn_option is set to 2.
+        takes effect only when tcp_ecn_option is set to 2.
 
-        Default: 3 (AccECN will be send at least 3 times per RTT)
+        Default: 1 (AccECN will be send at least 1 time per RTT)
 
 tcp_ecn_fallback - BOOLEAN
 	If the kernel detects that ECN connection misbehaves, enable fall
diff --git a/include/net/tcp.h b/include/net/tcp.h
index f26a931d2ae2..6745b64ca705 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -432,8 +432,8 @@ static inline int tcp_accecn_extract_syn_ect(u8 ace)
 }
 
 bool tcp_accecn_validate_syn_feedback(struct sock *sk, u8 ace, u8 sent_ect);
-bool tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
-                          struct request_sock *req, u8 syn_ect_snt);
+void tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
+			  u8 syn_ect_snt);
 u8 tcp_accecn_option_init(const struct sk_buff *skb, u8 opt_offset);
 void tcp_ecn_received_counters(struct sock *sk, const struct sk_buff *skb,
 			       u32 payload_len);
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index c0a448571ae7..95a4bfdb189e 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -398,7 +398,7 @@ void tcp_openreq_init_rwin(struct request_sock *req,
 EXPORT_SYMBOL(tcp_openreq_init_rwin);
 
 void tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
-		          u8 syn_ect_snt)
+			  u8 syn_ect_snt)
 {
 	u8 ace = tcp_accecn_ace(tcp_hdr(skb));
 	struct tcp_sock *tp = tcp_sk(sk);
@@ -446,18 +446,18 @@ static void tcp_ecn_openreq_child(struct sock *sk,
 	// 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.
 	if (treq->accecn_ok) {
-	    const struct tcphdr *th = (const struct tcphdr *)skb->data;
-	    tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
-	    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;
-	    tp->prev_ecnfield = treq->syn_ect_rcv;
-	    tp->accecn_opt_demand = 1;
-	    tcp_ecn_received_counters(sk, skb, skb->len - th->doff * 4);
+		const struct tcphdr *th = (const struct tcphdr *)skb->data;
+		tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
+		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;
+		tp->prev_ecnfield = treq->syn_ect_rcv;
+		tp->accecn_opt_demand = 1;
+		tcp_ecn_received_counters(sk, skb, skb->len - th->doff * 4);
 	} else {
-	    tcp_ecn_mode_set(tp, inet_rsk(req)->ecn_ok && !tcp_ca_no_fallback_rfc3168(sk) ?
-	    		     TCP_ECN_MODE_RFC3168 :
-	    		     TCP_ECN_DISABLED);
+		tcp_ecn_mode_set(tp, inet_rsk(req)->ecn_ok && !tcp_ca_no_fallback_rfc3168(sk) ?
+				     TCP_ECN_MODE_RFC3168 :
+				     TCP_ECN_DISABLED);
 	}
 }
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 04313da0783d..e0987c3e7ed4 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -378,7 +378,7 @@ static void tcp_accecn_echo_syn_ect(struct tcphdr *th, u8 ect)
 }
 
 static void
-tcp_ecn_make_synack(struct sock *sk, struct request_sock *req, struct tcphdr *th)
+tcp_ecn_make_synack(struct sock *sk, const struct request_sock *req, struct tcphdr *th)
 {
 	if (req->num_timeout < 2) {
 		if (tcp_rsk(req)->accecn_ok)

From 24da58c05a036e69f364fd84e7ed65c0b699f947 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Sun, 21 Jan 2024 11:44:16 +0100
Subject: [PATCH 10/24] Fix typo in tcp.c

---
 net/ipv4/tcp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index a9ccb83a8548..a2058babe9d8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3033,7 +3033,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tp->delivered_ce = 0;
 	tp->saw_accecn_opt = 0;
 	tp->ecn_fail = 0;
-	tp->accecn_no_preocess = 0;
+	tp->accecn_no_process = 0;
 	tcp_accecn_init_counters(tp);
 	tp->prev_ecnfield = 0;
 	tp->accecn_opt_tstamp = 0;

From 7a6a4eeac615f43353f9bd58958d201d8cb4d15c Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Sun, 21 Jan 2024 17:40:49 +0100
Subject: [PATCH 11/24] Update retx counter for synack

---
 net/ipv4/tcp_timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index e873a768f9e8..46d40b967a68 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -428,8 +428,8 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
 	 * regular retransmit because if the child socket has been accepted
 	 * it's not good to give up too easily.
 	 */
-	inet_rtx_syn_ack(sk, req);
 	req->num_timeout++;
+	inet_rtx_syn_ack(sk, req);
 	icsk->icsk_retransmits++;
 	if (!tp->retrans_stamp)
 		tp->retrans_stamp = tcp_time_stamp(tp);

From 3941f6d878415bc54058720aa733bfbb5ae3c6ca Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Sun, 21 Jan 2024 23:47:45 +0100
Subject: [PATCH 12/24] Add is_rtx flag

---
 include/net/request_sock.h      | 4 +++-
 net/ipv4/inet_connection_sock.c | 1 +
 net/ipv4/tcp_output.c           | 4 ++--
 net/ipv4/tcp_timer.c            | 2 +-
 4 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index 29e41ff3ec93..d382e540f329 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -62,7 +62,8 @@ struct request_sock {
 	u16				mss;
 	u8				num_retrans; /* number of retransmits */
 	u8				syncookie:1; /* syncookie: encode tcpopts in timestamp */
-	u8				num_timeout:7; /* number of timeouts */
+	u8				num_timeout:7,
+					is_rtx:1; /* number of timeouts */
 	u32				ts_recent;
 	struct timer_list		rsk_timer;
 	const struct request_sock_ops	*rsk_ops;
@@ -105,6 +106,7 @@ reqsk_alloc(const struct request_sock_ops *ops, struct sock *sk_listener,
 	sk_tx_queue_clear(req_to_sk(req));
 	req->saved_syn = NULL;
 	req->num_timeout = 0;
+	req->is_rtx = 0;
 	req->num_retrans = 0;
 	req->sk = NULL;
 	refcount_set(&req->rsk_refcnt, 0);
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index a53f9bf7886f..9d20f2456cf2 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -688,6 +688,7 @@ static void syn_ack_recalc(struct request_sock *req,
 
 int inet_rtx_syn_ack(const struct sock *parent, struct request_sock *req)
 {
+	req->is_rtx = 1;
 	int err = req->rsk_ops->rtx_syn_ack(parent, req);
 
 	if (!err)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index e0987c3e7ed4..6f2a4ff81a58 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -380,7 +380,7 @@ static void tcp_accecn_echo_syn_ect(struct tcphdr *th, u8 ect)
 static void
 tcp_ecn_make_synack(struct sock *sk, const struct request_sock *req, struct tcphdr *th)
 {
-	if (req->num_timeout < 2) {
+	if (!req->is_rtx || req->num_timeout < 1) {
 		if (tcp_rsk(req)->accecn_ok)
 		    tcp_accecn_echo_syn_ect(th, tcp_rsk(req)->syn_ect_rcv);
 		else if (inet_rsk(req)->ecn_ok)
@@ -1107,7 +1107,7 @@ static unsigned int tcp_synack_options(const struct sock *sk,
 	// [CY] 3.2.3.2.2. Testing for Loss of Packets Carrying the AccECN Option - TCP Server SHOULD retransmit the 
 	// SYN/ACK, but with no AccECN Option
 	if (treq->accecn_ok && sock_net(sk)->ipv4.sysctl_tcp_ecn_option &&
-	    req->num_timeout < 1 && (remaining >= TCPOLEN_ACCECN_BASE)) {
+	    !req->is_rtx && (remaining >= TCPOLEN_ACCECN_BASE)) {
 		opts->ecn_bytes = synack_ecn_bytes;
 		remaining -= tcp_options_fit_accecn(opts, 0, remaining,
 						    tcp_synack_options_combine_saving(opts));
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 46d40b967a68..e873a768f9e8 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -428,8 +428,8 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
 	 * regular retransmit because if the child socket has been accepted
 	 * it's not good to give up too easily.
 	 */
-	req->num_timeout++;
 	inet_rtx_syn_ack(sk, req);
+	req->num_timeout++;
 	icsk->icsk_retransmits++;
 	if (!tp->retrans_stamp)
 		tp->retrans_stamp = tcp_time_stamp(tp);

From 3ff07b9511a5e49eb428f160455535f849e81309 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Mon, 22 Jan 2024 10:40:59 +0100
Subject: [PATCH 13/24] Fix missing SYN retx in AccECN draft

---
 net/ipv4/tcp_output.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 6f2a4ff81a58..695b437ff06d 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3451,12 +3451,20 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
 			tcp_retrans_try_collapse(sk, skb, avail_wnd);
 	}
 
-	/* RFC3168, section 6.1.1.1. ECN fallback
-	 * As AccECN uses the same SYN flags (+ AE), this check covers both
-	 * cases.
+	/* [CY] 3.1.4.1. Retransmitted SYNs - If the sender of an AccECN SYN (the TCP Client) times out before receiving the SYN/ACK,
+	 * it SHOULD attempt to negotiate the use of AccECN at least one more time by continuing to set all three TCP ECN flags
+	 * (AE,CWR,ECE) = (1,1,1) on the first retransmitted SYN (using the usual retransmission time-outs). If this first
+	 * retransmission also fails to be acknowledged, in deployment scenarios where AccECN path traversal might be problematic, the
+	 * TCP Client SHOULD send subsequent retransmissions of the SYN with the three TCP-ECN flags cleared (AE,CWR,ECE) = (0,0,0).
 	 */
-	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
-		tcp_ecn_clear_syn(sk, skb);
+	if (!tcp_ecn_mode_pending(tp) || icsk->icsk_retransmits > 1) {
+		/* RFC3168, section 6.1.1.1. ECN fallback
+		 * As AccECN uses the same SYN flags (+ AE), this check covers both
+		 * cases.
+		 */
+		if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
+			tcp_ecn_clear_syn(sk, skb);
+	}
 
 	/* Update global and local TCP statistics. */
 	segs = tcp_skb_pcount(skb);

From 15a3b7ce1ab461d76c7d2bf58ae4bdd8932e18a7 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Mon, 22 Jan 2024 16:44:19 +0100
Subject: [PATCH 14/24] Update syn_ack_rcv for challenge ack

---
 net/ipv4/tcp_input.c     | 5 +++++
 net/ipv4/tcp_minisocks.c | 6 ------
 net/ipv4/tcp_output.c    | 1 -
 3 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 56d2a9a454fd..bfa026e76638 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6235,6 +6235,11 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 	if (th->syn) {
 		if (tcp_ecn_mode_accecn(tp)) {
 			send_accecn_reflector = true;
+			/* [CY] 3.1.5. Implications of AccECN Mode - 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.”
+			 */
+			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) {
 				tp->saw_accecn_opt = tcp_accecn_option_init(skb,
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 95a4bfdb189e..acf58f2c224b 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -411,11 +411,6 @@ void tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
 		// feedback. Nonetheless, as a Data Receiver it MUST NOT disable AccECN feedback.
 		tp->ecn_fail = 1;
 		tp->accecn_no_process = 1;
-		//INET_ECN_dontxmit(sk);
-		//if (!TCP_SKB_CB(skb)->sacked) {
-		//    tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
-		//    verify_ace = false;
-		//}
 		break;
 	case 0x7:
 	case 0x5:
@@ -720,7 +715,6 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 			// 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
 			    tcp_sk(sk)->ecn_fail = 1;
-			    //INET_ECN_dontxmit(sk);
 			}
 		    }
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 695b437ff06d..ddc5f1c4d06c 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -396,7 +396,6 @@ tcp_ecn_make_synack(struct sock *sk, const struct request_sock *req, struct tcph
 	// 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.
 		tcp_sk(sk)->ecn_fail = 1;
-		//INET_ECN_dontxmit(sk);
 	}
 }
 

From 08367ec3369f82259117c01b26eb17fe351f5b85 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Tue, 23 Jan 2024 01:40:28 +0100
Subject: [PATCH 15/24] Update syn_ect_rcv for retx SYN

---
 net/ipv4/tcp_minisocks.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index acf58f2c224b..4054fcbf12da 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -709,7 +709,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 			// [CY] 3.1.5. Implications of AccECN Mode - A TCP Server already in AccECN mode: SHOULD 
 			// acknowledge a valid SYN arriving with (AE,CWR,ECE) =(0,0,0) by emitting an AccECN SYN/ACK (with
 			// the appropriate combination of TCP-ECN flags to feed back the IP-ECN field of this latest SYN)
-			    tcp_sk(sk)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
+			    tcp_rsk(req)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
 
 			// [CY] 3.1.5. Implications of AccECN Mode - 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 

From b9fd5d0bfa39704b371927b79fc16ecac406020c Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Tue, 23 Jan 2024 11:18:27 +0100
Subject: [PATCH 16/24] Modification for ACCECN draft

---
 net/ipv4/tcp_minisocks.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 4054fcbf12da..5d661a5c3180 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -705,15 +705,16 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 					  &tcp_rsk(req)->last_oow_ack_time)) {
 
 		    if (tcp_rsk(req)->accecn_ok) {
+			/* [CY] 3.1.5 Implications of AccECN Mode - 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.
+			 */ 
+			tcp_rsk(req)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
 			if (tcp_accecn_ace(tcp_hdr(skb)) == 0x0) {
-			// [CY] 3.1.5. Implications of AccECN Mode - A TCP Server already in AccECN mode: SHOULD 
-			// acknowledge a valid SYN arriving with (AE,CWR,ECE) =(0,0,0) by emitting an AccECN SYN/ACK (with
-			// the appropriate combination of TCP-ECN flags to feed back the IP-ECN field of this latest SYN)
-			    tcp_rsk(req)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
-
-			// [CY] 3.1.5. Implications of AccECN Mode - 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
+			/* [CY] 3.1.5. Implications of AccECN Mode - 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
+			 */
 			    tcp_sk(sk)->ecn_fail = 1;
 			}
 		    }

From 8780b899edb517ce6dbea01514368f953603e5e1 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Thu, 25 Jan 2024 16:00:58 +0100
Subject: [PATCH 17/24] Include the case of 3.2.3.2.2. for packet loss carrying
 AccECN option

---
 include/linux/tcp.h      |  3 ++-
 net/ipv4/tcp.c           |  1 +
 net/ipv4/tcp_input.c     | 29 ++++++++++++++++++++---------
 net/ipv4/tcp_minisocks.c | 16 ++++++++--------
 net/ipv4/tcp_output.c    | 21 ++++++++++++---------
 5 files changed, 43 insertions(+), 27 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 50f036db09bf..cc1013374a96 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -233,7 +233,8 @@ struct tcp_sock {
 		syn_ect_snt:2,	/* AccECN ECT memory, only */
 		syn_ect_rcv:2,	/* ... needed durign 3WHS + first seqno */
 		ecn_fail:1;	/* ECN reflector detected path mangling */
-	u8	accecn_no_process:1; /* AccECN no response on feedback */
+	u8	accecn_no_process:1, /* AccECN no response on feedback */
+		accecn_no_options:1;
 	u8	saw_accecn_opt:2,    /* An AccECN option was seen */
 		fast_ack_mode:2, /* which fast ack mode ? */
 		unused:4;
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index a2058babe9d8..8b4fce6fef4c 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3034,6 +3034,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tp->saw_accecn_opt = 0;
 	tp->ecn_fail = 0;
 	tp->accecn_no_process = 0;
+	tp->accecn_no_options = 0;
 	tcp_accecn_init_counters(tp);
 	tp->prev_ecnfield = 0;
 	tp->accecn_opt_tstamp = 0;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index bfa026e76638..94aed08fd16e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -449,11 +449,11 @@ static void tcp_ecn_rcv_synack(struct sock *sk, const struct sk_buff *skb,
 		else
 		    tcp_ecn_mode_set(tp, TCP_ECN_MODE_RFC3168);
 		break;
-	// [CY] 3.1.2. Backward Compatibility - If a TCP Client has sent a SYN requesting AccECN feedback with 
-	// (AE,CWR,ECE) = (1,1,1) then receives a SYN/ACK with the currently reserved combination (AE,CWR,ECE) 
-	// = (1,0,1) but it does not have logic specific to such a combination, the Client MUST enable AccECN 
-	// mode as if the SYN/ACK confirmed that the Server supported AccECN and as if it fed back that the 
-	// IP-ECN field on the SYN had arrived unchanged.
+	/* [CY] 3.1.2. Backward Compatibility - If a TCP Client has sent a SYN requesting AccECN feedback with (AE,CWR,ECE) =
+	 * (1,1,1) then receives a SYN/ACK with the currently reserved combination (AE,CWR,ECE) = (1,0,1) but it does not
+	 * have logic specific to such a combination, the Client MUST enable AccECN mode as if the SYN/ACK confirmed that the
+	 * Server supported AccECN and as if it fed back that the IP-ECN field on the SYN had arrived unchanged.
+	 */
 	case 0x5:
 		if (tcp_ecn_mode_pending(tp)) {
 		    tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
@@ -595,7 +595,7 @@ static bool tcp_accecn_process_option(struct tcp_sock *tp,
 	bool order1, res;
 	unsigned int i;
 
-	if (tp->saw_accecn_opt == TCP_ACCECN_OPT_FAIL || tp->accecn_no_process)
+	if (tp->saw_accecn_opt == TCP_ACCECN_OPT_FAIL || tp->accecn_no_response)
 		return false;
 
 	if (!(flag & FLAG_SLOWPATH) || !tp->rx_opt.accecn) {
@@ -4893,8 +4893,19 @@ static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
 	 * DSACK state and change the txhash to re-route speculatively.
 	 */
 	if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq &&
-	    sk_rethink_txhash(sk))
+	    sk_rethink_txhash(sk)) {
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);
+		/* [CY] 3.2.3.2.2. Testing for Loss of Packets Carrying the AccECN Option - If a middlebox is dropping
+		 * packets with options it does not recognize, a host that is sending little or no data but mostly pure
+		 * ACKs will not inherently detect such losses. Such a host MAY detect loss of ACKs carrying the AccECN
+		 * Option by detecting whether the acknowledged data always reappears as a retransmission. In such cases,
+		 * the host SHOULD disable the sending of the AccECN Option for this half-connection.
+		 */
+			if (tcp_ecn_mode_accecn(tp))
+				tcp_sock(sk)->accecn_no_options = 1;
+		}
+
+	}
 }
 
 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
@@ -6235,8 +6246,8 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 	if (th->syn) {
 		if (tcp_ecn_mode_accecn(tp)) {
 			send_accecn_reflector = true;
-			/* [CY] 3.1.5. Implications of AccECN Mode - 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 
+			/* [CY] 3.1.5. Implications of AccECN Mode - 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.”
 			 */
 			tp->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 5d661a5c3180..2066097415f2 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -405,12 +405,12 @@ void tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
 
 	switch (ace) {
 	case 0x0:
-		// [CY] 3.2.2.1. ACE Field on the ACK of the SYN/ACK - If the Server is in AccECN mode and in SYN-RCVD 
+		// [CY] 3.2.2.1. ACE Field on the ACK of the SYN/ACK - If the Server is in AccECN mode and in SYN-RCVD
 		// state, and if it receives a value of zero on a pure ACK with SYN=0 and no SACK blocks, for the rest
-		// of the connection the Server MUST NOT set ECT on outgoing packets and MUST NOT respond to AccECN 
+		// of the connection the Server MUST NOT set ECT on outgoing packets and MUST NOT respond to AccECN
 		// feedback. Nonetheless, as a Data Receiver it MUST NOT disable AccECN feedback.
 		tp->ecn_fail = 1;
-		tp->accecn_no_process = 1;
+		tp->accecn_no_response = 1;
 		break;
 	case 0x7:
 	case 0x5:
@@ -437,8 +437,8 @@ static void tcp_ecn_openreq_child(struct sock *sk,
 	const struct tcp_request_sock *treq = tcp_rsk(req);
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	// [CY] 3.1.5. Implications of AccECN Mode - 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 
+	// [CY] 3.1.5. Implications of AccECN Mode - 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.
 	if (treq->accecn_ok) {
 		const struct tcphdr *th = (const struct tcphdr *)skb->data;
@@ -706,13 +706,13 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 
 		    if (tcp_rsk(req)->accecn_ok) {
 			/* [CY] 3.1.5 Implications of AccECN Mode - 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 
+			 * 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.
 			 */ 
 			tcp_rsk(req)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
 			if (tcp_accecn_ace(tcp_hdr(skb)) == 0x0) {
-			/* [CY] 3.1.5. Implications of AccECN Mode - 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 
+			/* [CY] 3.1.5. Implications of AccECN Mode - 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
 			 */
 			    tcp_sk(sk)->ecn_fail = 1;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ddc5f1c4d06c..4806686bcb49 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -386,15 +386,17 @@ tcp_ecn_make_synack(struct sock *sk, const struct request_sock *req, struct tcph
 		else if (inet_rsk(req)->ecn_ok)
 		    th->ece = 1;
 	} else if (tcp_rsk(req)->accecn_ok) {
-	// [CY] 3.2.3.2.2. Testing for Loss of Packets Carrying the AccECN Option - If this retransmission times out, 
-	// to expedite connection setup, the TCP Server SHOULD retransmit the SYN/ACK with (AE,CWR,ECE) = (0,0,0) and 
-	// no AccECN Option, but it remains in AccECN feedback mode
+	/* [CY] 3.2.3.2.2. Testing for Loss of Packets Carrying the AccECN Option - If this retransmission times out,
+	 * to expedite connection setup, the TCP Server SHOULD retransmit the SYN/ACK with (AE,CWR,ECE) = (0,0,0) and
+	 * no AccECN Option, but it remains in AccECN feedback mode
+	 */
 		th->ae  = 0;
 		th->cwr = 0;
 		th->ece = 0;
-	// [CY] 3.1.5. Implications of AccECN Mode - 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.
+	/* [CY] 3.1.5. Implications of AccECN Mode - 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.
+	 */
 		tcp_sk(sk)->ecn_fail = 1;
 	}
 }
@@ -1103,8 +1105,9 @@ static unsigned int tcp_synack_options(const struct sock *sk,
 
 	smc_set_option_cond(tcp_sk(sk), ireq, opts, &remaining);
 
-	// [CY] 3.2.3.2.2. Testing for Loss of Packets Carrying the AccECN Option - TCP Server SHOULD retransmit the 
-	// SYN/ACK, but with no AccECN Option
+	/* [CY] 3.2.3.2.2. Testing for Loss of Packets Carrying the AccECN Option - TCP Server SHOULD retransmit the
+	 * SYN/ACK, but with no AccECN Option
+	 */
 	if (treq->accecn_ok && sock_net(sk)->ipv4.sysctl_tcp_ecn_option &&
 	    !req->is_rtx && (remaining >= TCPOLEN_ACCECN_BASE)) {
 		opts->ecn_bytes = synack_ecn_bytes;
@@ -1186,7 +1189,7 @@ static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb
 
 	if (tcp_ecn_mode_accecn(tp) &&
 	    sock_net(sk)->ipv4.sysctl_tcp_ecn_option &&
-	    (tp->saw_accecn_opt && tp->saw_accecn_opt != TCP_ACCECN_OPT_FAIL)) {
+	    (tp->saw_accecn_opt && tp->saw_accecn_opt != TCP_ACCECN_OPT_FAIL && !tp->accecn_no_options)) {
 		if (sock_net(sk)->ipv4.sysctl_tcp_ecn_option >= 2 ||
 		    tp->accecn_opt_demand ||
 		    tcp_accecn_option_beacon_check(sk)) {

From 821d92cc77deac49a46cd514676266a122ef799e Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Thu, 25 Jan 2024 17:28:55 +0100
Subject: [PATCH 18/24] Fix typo

---
 include/linux/tcp.h      | 4 ++--
 net/ipv4/tcp.c           | 2 +-
 net/ipv4/tcp_input.c     | 2 +-
 net/ipv4/tcp_minisocks.c | 2 +-
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index cc1013374a96..ee11ba9a1f1d 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -233,8 +233,8 @@ struct tcp_sock {
 		syn_ect_snt:2,	/* AccECN ECT memory, only */
 		syn_ect_rcv:2,	/* ... needed durign 3WHS + first seqno */
 		ecn_fail:1;	/* ECN reflector detected path mangling */
-	u8	accecn_no_process:1, /* AccECN no response on feedback */
-		accecn_no_options:1;
+	u8	accecn_no_respond:1, /* AccECN no response on feedback */
+		accecn_no_options:1; /* AccECN no options send out */
 	u8	saw_accecn_opt:2,    /* An AccECN option was seen */
 		fast_ack_mode:2, /* which fast ack mode ? */
 		unused:4;
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 8b4fce6fef4c..ad66e0cd8c01 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3033,7 +3033,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tp->delivered_ce = 0;
 	tp->saw_accecn_opt = 0;
 	tp->ecn_fail = 0;
-	tp->accecn_no_process = 0;
+	tp->accecn_no_respond = 0;
 	tp->accecn_no_options = 0;
 	tcp_accecn_init_counters(tp);
 	tp->prev_ecnfield = 0;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 94aed08fd16e..3e019e324c46 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -595,7 +595,7 @@ static bool tcp_accecn_process_option(struct tcp_sock *tp,
 	bool order1, res;
 	unsigned int i;
 
-	if (tp->saw_accecn_opt == TCP_ACCECN_OPT_FAIL || tp->accecn_no_response)
+	if (tp->saw_accecn_opt == TCP_ACCECN_OPT_FAIL || tp->accecn_no_respond)
 		return false;
 
 	if (!(flag & FLAG_SLOWPATH) || !tp->rx_opt.accecn) {
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 2066097415f2..7318de84a6c8 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -410,7 +410,7 @@ void tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
 		// of the connection the Server MUST NOT set ECT on outgoing packets and MUST NOT respond to AccECN
 		// feedback. Nonetheless, as a Data Receiver it MUST NOT disable AccECN feedback.
 		tp->ecn_fail = 1;
-		tp->accecn_no_response = 1;
+		tp->accecn_no_respond = 1;
 		break;
 	case 0x7:
 	case 0x5:

From 08b1f990ee1f55e95fc2ad4ea6979bdcd2db4f0d Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Tue, 30 Jan 2024 17:20:30 +0100
Subject: [PATCH 19/24] Fix typo and comments

---
 net/ipv4/tcp_input.c     |  1 -
 net/ipv4/tcp_minisocks.c | 16 +++++++++-------
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 3e019e324c46..760e69e593c6 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4903,7 +4903,6 @@ static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
 		 */
 			if (tcp_ecn_mode_accecn(tp))
 				tcp_sock(sk)->accecn_no_options = 1;
-		}
 
 	}
 }
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 7318de84a6c8..8aeeca7423dc 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -405,10 +405,11 @@ void tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
 
 	switch (ace) {
 	case 0x0:
-		// [CY] 3.2.2.1. ACE Field on the ACK of the SYN/ACK - If the Server is in AccECN mode and in SYN-RCVD
-		// state, and if it receives a value of zero on a pure ACK with SYN=0 and no SACK blocks, for the rest
-		// of the connection the Server MUST NOT set ECT on outgoing packets and MUST NOT respond to AccECN
-		// feedback. Nonetheless, as a Data Receiver it MUST NOT disable AccECN feedback.
+		/* [CY] 3.2.2.1. ACE Field on the ACK of the SYN/ACK - If the Server is in AccECN mode and in SYN-RCVD
+		 * state, and if it receives a value of zero on a pure ACK with SYN=0 and no SACK blocks, for the rest
+		 * of the connection the Server MUST NOT set ECT on outgoing packets and MUST NOT respond to AccECN
+		 * feedback. Nonetheless, as a Data Receiver it MUST NOT disable AccECN feedback.
+		 */
 		tp->ecn_fail = 1;
 		tp->accecn_no_respond = 1;
 		break;
@@ -437,9 +438,10 @@ static void tcp_ecn_openreq_child(struct sock *sk,
 	const struct tcp_request_sock *treq = tcp_rsk(req);
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	// [CY] 3.1.5. Implications of AccECN Mode - 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.
+	/* [CY] 3.1.5. Implications of AccECN Mode - A TCP Server in AccECN mode: MUST NOT set ECT oni
+	 * 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.
+	 */
 	if (treq->accecn_ok) {
 		const struct tcphdr *th = (const struct tcphdr *)skb->data;
 		tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);

From 4538174db72a276736f9c5e517b43926be79cc67 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Tue, 30 Jan 2024 18:21:17 +0100
Subject: [PATCH 20/24] Fix typo

---
 net/ipv4/tcp_input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 760e69e593c6..4eeba5e3bfe0 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4901,7 +4901,7 @@ static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
 		 * Option by detecting whether the acknowledged data always reappears as a retransmission. In such cases,
 		 * the host SHOULD disable the sending of the AccECN Option for this half-connection.
 		 */
-			if (tcp_ecn_mode_accecn(tp))
+			if (tcp_ecn_mode_accecn(tcp_sock(sk)))
 				tcp_sock(sk)->accecn_no_options = 1;
 
 	}

From bde09fefe1e049e25a745b6860d2b5e99c034ac7 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Tue, 30 Jan 2024 19:23:54 +0100
Subject: [PATCH 21/24] Fix typo

---
 net/ipv4/tcp_input.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 4eeba5e3bfe0..68835c3010a4 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4901,8 +4901,8 @@ static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
 		 * Option by detecting whether the acknowledged data always reappears as a retransmission. In such cases,
 		 * the host SHOULD disable the sending of the AccECN Option for this half-connection.
 		 */
-			if (tcp_ecn_mode_accecn(tcp_sock(sk)))
-				tcp_sock(sk)->accecn_no_options = 1;
+			if (tcp_ecn_mode_accecn(tcp_sk(sk)))
+				tcp_sk(sk)->accecn_no_options = 1;
 
 	}
 }

From 5d809aaa59df0fc2f484a3d614f6c8ce798d3812 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Sat, 3 Feb 2024 15:33:06 +0100
Subject: [PATCH 22/24] Add ACE check on first data ACK

---
 include/linux/tcp.h      |  3 ++-
 net/ipv4/tcp.c           |  1 +
 net/ipv4/tcp_input.c     | 15 +++++++++++++++
 net/ipv4/tcp_minisocks.c |  2 +-
 4 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index ee11ba9a1f1d..73ab3e9c7942 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -234,7 +234,8 @@ struct tcp_sock {
 		syn_ect_rcv:2,	/* ... needed durign 3WHS + first seqno */
 		ecn_fail:1;	/* ECN reflector detected path mangling */
 	u8	accecn_no_respond:1, /* AccECN no response on feedback */
-		accecn_no_options:1; /* AccECN no options send out */
+		accecn_no_options:1, /* AccECN no options send out */
+		first_data_ack:1;    /* Check for first data ack */
 	u8	saw_accecn_opt:2,    /* An AccECN option was seen */
 		fast_ack_mode:2, /* which fast ack mode ? */
 		unused:4;
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index ad66e0cd8c01..3f7a83eb6fae 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3035,6 +3035,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tp->ecn_fail = 0;
 	tp->accecn_no_respond = 0;
 	tp->accecn_no_options = 0;
+	tp->first_data_ack = 0;
 	tcp_accecn_init_counters(tp);
 	tp->prev_ecnfield = 0;
 	tp->accecn_opt_tstamp = 0;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 68835c3010a4..dee1e31d9b8a 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -703,6 +703,21 @@ static u32 __tcp_accecn_process(struct sock *sk, const struct sk_buff *skb,
 	if (flag & FLAG_SYN_ACKED)
 		return 0;
 
+	/* [CY] 3.2.2.4. Testing for Zeroing of the ACE Field - If AccECN has been successfully negotiated, the Data Sender
+	 * MAY check the value of the ACE counter in the first feedback packet (with or without data) that arrives after the
+	 * 3-way handshake.  If the value of this ACE field is found to be zero (0b000), for the remainder of the half-
+	 * connection the Data Sender ought to send non-ECN-capable packets and it is advised not to respond to any feedback
+	 * of CE markings.
+	 */
+	if (!tp->first_data_ack) {
+		tp->first_data_ack = 1;
+		if (!tcp_accecn_ace(tcp_hdr(skb))) {
+			tp->ecn_fail = 1;
+			tp->accecn_no_respond = 1;
+			return 0;
+		}
+	}
+
 	if (tp->received_ce_pending >= TCP_ACCECN_ACE_MAX_DELTA)
 		inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
 
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 8aeeca7423dc..ba104fb82c7d 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -438,7 +438,7 @@ static void tcp_ecn_openreq_child(struct sock *sk,
 	const struct tcp_request_sock *treq = tcp_rsk(req);
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	/* [CY] 3.1.5. Implications of AccECN Mode - A TCP Server in AccECN mode: MUST NOT set ECT oni
+	/* [CY] 3.1.5. Implications of AccECN Mode - 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.
 	 */

From ebae93fe595af2c517daa156df765b7c4ba97c83 Mon Sep 17 00:00:00 2001
From: Chia-Yu <chia-yu.chang@nokia-bell-labs.com>
Date: Mon, 5 Feb 2024 22:11:12 +0100
Subject: [PATCH 23/24] Add ACE check on first data ACK

---
 net/ipv4/tcp_input.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index dee1e31d9b8a..c2c72a2688ef 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -711,8 +711,9 @@ static u32 __tcp_accecn_process(struct sock *sk, const struct sk_buff *skb,
 	 */
 	if (!tp->first_data_ack) {
 		tp->first_data_ack = 1;
-		if (!tcp_accecn_ace(tcp_hdr(skb))) {
+		if (tcp_accecn_ace(tcp_hdr(skb)) == 0x0) {
 			tp->ecn_fail = 1;
+			INET_ECN_dontxmit(sk);
 			tp->accecn_no_respond = 1;
 			return 0;
 		}

From 623cd470dd64fcf2522b7246fdf5a4bafbe45495 Mon Sep 17 00:00:00 2001
From: Chia-Yu Chang <125277758+minuscat@users.noreply.github.com>
Date: Wed, 7 Feb 2024 13:07:17 +0100
Subject: [PATCH 24/24] Update kernel.yml

---
 .github/workflows/kernel.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/kernel.yml b/.github/workflows/kernel.yml
index 4c81b75c797e..1c6d3320a606 100644
--- a/.github/workflows/kernel.yml
+++ b/.github/workflows/kernel.yml
@@ -63,7 +63,7 @@ jobs:
     runs-on: ubuntu-20.04
     needs: build
     permissions: write-all
-    if: ${{ github.ref == 'refs/heads/testing' || github.ref == 'refs/heads/ratebase' || github.ref == 'refs/heads/AccECN-2023' || github.ref == 'refs/heads/AccECN-2024'}}
+    if: ${{ github.ref == 'refs/heads/testing' || github.ref == 'refs/heads/ratebase' || github.ref == 'refs/heads/AccECN-2023'}}
     steps:
     - name: Get artifact
       uses: actions/download-artifact@v3