linux-kernel - [PATCH net 2/2] tcp_metrics: use ssthresh value from dst if there is no metrics

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Message-ID: <20250613102012.724405-3-ptesarik@suse.com>
Date: Fri, 13 Jun 2025 12:20:12 +0200
From: Petr Tesarik <ptesarik@...e.com>
To: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Kuniyuki Iwashima <kuniyu@...gle.com>,
	netdev@...r.kernel.org (open list:NETWORKING [TCP])
Cc: David Ahern <dsahern@...nel.org>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	linux-kernel@...r.kernel.org (open list),
	Petr Tesarik <ptesarik@...e.com>
Subject: [PATCH net 2/2] tcp_metrics: use ssthresh value from dst if there is no metrics

If there is no cached TCP metrics entry for a connection, initialize
tp->snd_ssthresh from the corresponding dst entry. Also move the check
against tp->snd_cwnd_clamp to the common path to ensure that the ssthresh
value is never greater than maximum cwnd, regardless where it came from.

Fixes: 51c5d0c4b169 ("tcp: Maintain dynamic metrics in local cache.")
Signed-off-by: Petr Tesarik <ptesarik@...e.com>
---
 net/ipv4/tcp_metrics.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index dd8f3457bd72e..b08920abec0e6 100644
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -479,6 +479,9 @@ void tcp_init_metrics(struct sock *sk)
 
 	if (dst_metric_locked(dst, RTAX_CWND))
 		tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
+	val = dst_metric(dst, RTAX_SSTHRESH);
+	if (val)
+		tp->snd_ssthresh = val;
 
 	rcu_read_lock();
 	tm = tcp_get_metrics(sk, dst, false);
@@ -489,11 +492,8 @@ void tcp_init_metrics(struct sock *sk)
 
 	val = READ_ONCE(net->ipv4.sysctl_tcp_no_ssthresh_metrics_save) ?
 	      0 : tcp_metric_get(tm, TCP_METRIC_SSTHRESH);
-	if (val) {
+	if (val)
 		tp->snd_ssthresh = val;
-		if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
-			tp->snd_ssthresh = tp->snd_cwnd_clamp;
-	}
 	val = tcp_metric_get(tm, TCP_METRIC_REORDERING);
 	if (val && tp->reordering != val)
 		tp->reordering = val;
@@ -537,6 +537,9 @@ void tcp_init_metrics(struct sock *sk)
 
 		inet_csk(sk)->icsk_rto = TCP_TIMEOUT_FALLBACK;
 	}
+
+	if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
+		tp->snd_ssthresh = tp->snd_cwnd_clamp;
 }
 
 bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst)
-- 
2.49.0