From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 7FFE843CE6D; Mon, 17 Aug 2026 13:40:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786974058; cv=none; b=SPJ8N+7RENiohjWvx4L2js01hlZ+Zl0s9Mp4ZAFqMcQb0mL6qJT3NaqTMy9GP435YCQGxupXDAFZQh+mhcBAAN7jIfwUFrrI5A/pfKNK+qDAJh5k5BBcAcUEIKPxg98xBXLgqi0qu8D74KDw4s9gTFbftxy5EPmWkbhsBdo0cLQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786974058; c=relaxed/simple; bh=ztYt6pNjurpywTZUNWPPFEDvlws7UE0NB9+70rJQTBs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=IllBIE6NBcNDffSLlSev/kO71/ilaOtVrkrD3Pa2YA5DM71qhMsZNjzOtqYero4H1ZRgTJNIovDIASQgnSAk/3E/l3HJPWoFxo/XBztbbvUfRTjBoKFG/4kgA9SlLBm1ofQHb332SpFkem+vztrcnAmaXAql3pNq8jypgFu5cDg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=cpfEAeJF; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="cpfEAeJF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 623FD1F00A3D; Mon, 17 Aug 2026 13:40:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1786974048; bh=qOFlVL0XWQecZTc5cRB4ogtQPwPVwektPRlpdTnqj+M=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=cpfEAeJFl2zvDk9LxGmpIH/N5EiZVKCuKSh+rXFzVMezaYIdeWBKPlQdMjLBBKNgd 4pDg+yBO/MYeirNOhwjnoYaC4DBJqPfjVvVGuWFqPsrPjVz2csOKL+GSzZAiwH/5c0 DVvhKxkWxGYmRocutgyt8k24aS/3zCU6tKUX5Ogs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Nathan Gao , Jakub Kicinski , Sasha Levin Subject: [PATCH 7.1 070/271] tcp: do not change rcv_ssthresh in tcp_measure_rcv_mss() Date: Mon, 17 Aug 2026 15:29:55 +0200 Message-ID: <20260817132539.620305180@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260817132536.752504388@linuxfoundation.org> References: <20260817132536.752504388@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 7.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nathan Gao [ Upstream commit 0e125ecfe20c077625cf0be8d750d5c3abc0dce9 ] Commit f5da7c45188e ("tcp: adjust rcvq_space after updating scaling ratio") replaced the direct window_clamp update in tcp_measure_rcv_mss() with a call to tcp_set_window_clamp(), a helper that implements the TCP_WINDOW_CLAMP setsockopt. As a side effect, the helper also shrinks rcv_ssthresh via __tcp_adjust_rcv_ssthresh(). As a result, each scaling_ratio decrease detected by tcp_measure_rcv_mss() also cuts rcv_ssthresh. Elsewhere in TCP, rcv_ssthresh is usually cut under memory pressure and grows via tcp_grow_window(). Flows whose segment sizes vary keep scaling_ratio oscillating, which leads to an unstable rcv_ssthresh: a dip of rcv_ssthresh only recovers via tcp_grow_window(), keeping the advertised window at a relatively low level even after the ratio itself has recovered, and can even stall the sender. Observed on a customer's proxy gateway after upgrading from kernel 6.1 to 6.12: in the worst case, rcv_ssthresh was cut in half by a scaling_ratio dip. P99 latency jumped from <10ms on 6.1 to ~100ms on 6.12, and almost returned to the 6.1 level with this patch applied. Restore the plain WRITE_ONCE() update of window_clamp, as introduced in commit a2cbb1603943 ("tcp: Update window clamping condition"), and keep the rcvq_space.space adjustment. Now rcv_ssthresh is decoupled from scaling_ratio changes in tcp_measure_rcv_mss(). Fixes: f5da7c45188e ("tcp: adjust rcvq_space after updating scaling ratio") Signed-off-by: Nathan Gao Link: https://patch.msgid.link/20260725030806.28135-1-zcgao@amazon.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- 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 eed808c2adbb5..e2c022f02c644 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -252,7 +252,7 @@ static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb) struct tcp_sock *tp = tcp_sk(sk); val = tcp_win_from_space(sk, sk->sk_rcvbuf); - tcp_set_window_clamp(sk, val); + WRITE_ONCE(tp->window_clamp, val); if (tp->window_clamp < tp->rcvq_space.space) tp->rcvq_space.space = tp->window_clamp; -- 2.53.0