From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C75C92C11CD; Wed, 25 Feb 2026 06:55:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772002557; cv=none; b=AFu0WmmpaBHD0nne7xarDQtKWdSq8fYzfrpsEuee8bKebNKJXF4iM10JfbUgywpm1YI3I/ptgzthqy9h/KrhvjdFgzIjvI/sDTQ1dM9qwKgmLUs8VpCbzEv925K67ZXeYkacbzwTIykV2JWNKBVlImkN/YZp3S4x+ruGhnC/nmE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772002557; c=relaxed/simple; bh=RAuTu3H2aF6KY5rHPf/qEOIbXQIqkl9Fo3a3wt3RfEY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=dWPezOSsPkCuKAzcxqfBZS/5mdRdDl1saY7tRj2YTOGzjeikpDf0m9X0EucKeN7cXM1VU/GJKT5/6BOovqNlJa6oYZSnZU0YKGpmyAS1IMzHunzVqyUN5Tb0XwZMe656Mw3UAo8phNBSirab/j06kf3DNMn08kyCkDbS9okJSfU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=eyKdSzKs; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="eyKdSzKs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2F1ECC116D0; Wed, 25 Feb 2026 06:55:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1772002557; bh=RAuTu3H2aF6KY5rHPf/qEOIbXQIqkl9Fo3a3wt3RfEY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=eyKdSzKs6ncoUj2U6JLM0LS+YbZFRYrJeAZI/j7odyHXx2Oskb/A1N6nAHSnAxuej Cjl5Os/WnSmh1ciDYwFOBAiHNx3IkgIUN2tm4xrD0j/Dl663m8bXtJoQT3ZzSkT3EE D263UN9GQi9+8VtAITQB24KPyCXRDEOhCcSF8bGE= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Chia-Yu Chang , Paolo Abeni , Eric Dumazet , Sasha Levin Subject: [PATCH 6.18 295/641] tcp: disable RFC3168 fallback identifier for CC modules Date: Tue, 24 Feb 2026 17:20:21 -0800 Message-ID: <20260225012355.898065396@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260225012348.915798704@linuxfoundation.org> References: <20260225012348.915798704@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Chia-Yu Chang [ Upstream commit e68c28f22f46ecfdec3656ae785dd8ccbb4d557d ] When AccECN is not successfully negociated for a TCP flow, it defaults fallback to classic ECN (RFC3168). However, L4S service will fallback to non-ECN. This patch enables congestion control module to control whether it should not fallback to classic ECN after unsuccessful AccECN negotiation. A new CA module flag (TCP_CONG_NO_FALLBACK_RFC3168) identifies this behavior expected by the CA. Signed-off-by: Chia-Yu Chang Acked-by: Paolo Abeni Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260131222515.8485-6-chia-yu.chang@nokia-bell-labs.com Signed-off-by: Paolo Abeni Stable-dep-of: c5ff6b837159 ("tcp: accecn: handle unexpected AccECN negotiation feedback") Signed-off-by: Sasha Levin --- include/net/tcp.h | 12 +++++++++++- include/net/tcp_ecn.h | 11 ++++++++--- net/ipv4/tcp_input.c | 2 +- net/ipv4/tcp_minisocks.c | 7 ++++--- 4 files changed, 24 insertions(+), 8 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index c1db8a851243d..3c84d95cdba81 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1194,8 +1194,11 @@ enum tcp_ca_ack_event_flags { #define TCP_CONG_NEEDS_ACCECN BIT(2) /* Use ECT(1) instead of ECT(0) while the CA is uninitialized */ #define TCP_CONG_ECT_1_NEGOTIATION BIT(3) +/* Cannot fallback to RFC3168 during AccECN negotiation */ +#define TCP_CONG_NO_FALLBACK_RFC3168 BIT(4) #define TCP_CONG_MASK (TCP_CONG_NON_RESTRICTED | TCP_CONG_NEEDS_ECN | \ - TCP_CONG_NEEDS_ACCECN | TCP_CONG_ECT_1_NEGOTIATION) + TCP_CONG_NEEDS_ACCECN | TCP_CONG_ECT_1_NEGOTIATION | \ + TCP_CONG_NO_FALLBACK_RFC3168) union tcp_cc_info; @@ -1341,6 +1344,13 @@ static inline bool tcp_ca_ect_1_negotiation(const struct sock *sk) return icsk->icsk_ca_ops->flags & TCP_CONG_ECT_1_NEGOTIATION; } +static inline bool tcp_ca_no_fallback_rfc3168(const struct sock *sk) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + + return icsk->icsk_ca_ops->flags & TCP_CONG_NO_FALLBACK_RFC3168; +} + static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event) { const struct inet_connection_sock *icsk = inet_csk(sk); diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h index fdde1c342b35c..2e1637edf1d3c 100644 --- a/include/net/tcp_ecn.h +++ b/include/net/tcp_ecn.h @@ -507,7 +507,9 @@ static inline void tcp_ecn_rcv_synack(struct sock *sk, const struct sk_buff *skb * | ECN | AccECN | 0 0 1 | Classic ECN | * +========+========+============+=============+ */ - if (tcp_ecn_mode_pending(tp)) + if (tcp_ca_no_fallback_rfc3168(sk)) + tcp_ecn_mode_set(tp, TCP_ECN_DISABLED); + else if (tcp_ecn_mode_pending(tp)) /* Downgrade from AccECN, or requested initially */ tcp_ecn_mode_set(tp, TCP_ECN_MODE_RFC3168); break; @@ -531,9 +533,11 @@ static inline void tcp_ecn_rcv_synack(struct sock *sk, const struct sk_buff *skb } } -static inline void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th, +static inline void tcp_ecn_rcv_syn(struct sock *sk, const struct tcphdr *th, const struct sk_buff *skb) { + struct tcp_sock *tp = tcp_sk(sk); + if (tcp_ecn_mode_pending(tp)) { if (!tcp_accecn_syn_requested(th)) { /* Downgrade to classic ECN feedback */ @@ -545,7 +549,8 @@ static inline void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th, tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN); } } - if (tcp_ecn_mode_rfc3168(tp) && (!th->ece || !th->cwr)) + if (tcp_ecn_mode_rfc3168(tp) && + (!th->ece || !th->cwr || tcp_ca_no_fallback_rfc3168(sk))) tcp_ecn_mode_set(tp, TCP_ECN_DISABLED); } diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index f920fa44c3d39..ede266463d5d1 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -6817,7 +6817,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, tp->snd_wl1 = TCP_SKB_CB(skb)->seq; tp->max_window = tp->snd_wnd; - tcp_ecn_rcv_syn(tp, th, skb); + tcp_ecn_rcv_syn(sk, th, skb); tcp_mtup_init(sk); tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index 2ec8c6f1cdccc..1fade94813c62 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -488,9 +488,10 @@ static void tcp_ecn_openreq_child(struct sock *sk, tp->accecn_opt_demand = 1; tcp_ecn_received_counters_payload(sk, skb); } else { - tcp_ecn_mode_set(tp, inet_rsk(req)->ecn_ok ? - TCP_ECN_MODE_RFC3168 : - TCP_ECN_DISABLED); + if (inet_rsk(req)->ecn_ok && !tcp_ca_no_fallback_rfc3168(sk)) + tcp_ecn_mode_set(tp, TCP_ECN_MODE_RFC3168); + else + tcp_ecn_mode_set(tp, TCP_ECN_DISABLED); } } -- 2.51.0