From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=74.125.82.170 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794149948; b=E8M0SWJ7HE8hOS5YzDKQVKmzc7KiDPdKPL0DQJUO6165X+AQf4WYkuf7+qwwPKb8DM1a WZMS0dm1rVJ6eECMQhuenihZyD4RRzWJc08xGcKReLiCJWUrUJR3vYWtWJzZUZvtv9EVg cA32CDyoCqCrip5bXFAntDTZiHK0nfQEYyDEq4Uz/czBpuuHWso9rx35wWXdYwOnxmwwe Ms9PriP2tAgdhvFHn20Uk/Q1Lj8k+i62PTYTddOaYce0/iXkWBFWK0mK1VH1AirfS2fbx gDa5HsIkCDX+QSzskz1/FJfFgJPHD2c9XH/BzzgeN114n2r7paHi/kh8KtxffXhFUXA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794149948; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: Content-Type:Mime-Version:Subject:From:In-Reply-To:Date:Cc: Content-Transfer-Encoding:Message-Id:References:To:X-Mailer; bh=46GXHeUALtpO4O3TOALhIC4HG0bGJ4xyjvuRvhuOfq0=; b=T+Vb/iVb/gzn5f/JhKQ2VzA7cg0oMWLDR12E9xmeDmi+TaHwRsvvrKFqwtLlhR3bHiMV cgiZm+2XCOsYNw/sU6YusGF2WOMOwQ+ZVVPinPCc0PIEDAn2UmIBmGlQ1WKWLlxo5pTZG 8zZIpmtn7vnFc4ZYd/XGRkbi11l0dRI8HzebFBzMdAAltcPS0SuiN1uVwA6ytzF6iybEZ ySwIwkDLZWYOG5pPZjeRxhqH8nbmDAfEWeQNm4BW0MGxEj7LW4VxAyEl93GXeawgGUwPY xAYWFJm6/SjM1aIIBYpiwkgLwtWP1wU9PK3aS0yJeY7WzB6mbjjHwKKd0RkDIwdy+iA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=I+mgnbqn; arc=none smtp.remote-ip=74.125.82.170 Received: from mail-dy1-f170.google.com (mail-dy1-f170.google.com [74.125.82.170]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 47865606A321 for ; Sun, 8 Nov 2026 14:59:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 47865606A321 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=I+mgnbqn Received: by mail-dy1-f170.google.com with SMTP id 5a478bee46e88-3645f0f3fcdso247191eec.0 for ; Sun, 08 Nov 2026 06:59:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20260707; t=1794149947; x=1794754747; darn=vger.kernel.org; h=to:references:message-id:content-transfer-encoding:cc:date :in-reply-to:from:subject:mime-version:content-type:from:to:cc :subject:date:message-id:reply-to:content-type; bh=46GXHeUALtpO4O3TOALhIC4HG0bGJ4xyjvuRvhuOfq0=; b=I+mgnbqnq8NSHuqYlXQCBRsCwEE4OSEQinRr8N0VZR0arR5lJW+qfCv8UvBUUbAt1A iuNEdhaiHT5wbCtr0NgDNbh48EXeKcpGcaJZszJnqmKYY6z5U3E7veLLoAjgfQmxcYbI JmwYZwMdrk6PAc5Yq2opy2NeE8Ns4p9GNTn5qsxTBDmYfYaVZgbenDQNJpseaGv71hEL IzcqwNqVhVdURUQvExrPOvJSU09getdEEbZeaHkZ//MDYaHZJZh758RQ4kLPXtqv0tlB c0JPbzbwIdq925YL/RhIsc1eAj6H9AHwfkKLa/2RLe2lI/PDG6FNJGBWO2PgUC01qL0i lWMw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1794149947; x=1794754747; h=to:references:message-id:content-transfer-encoding:cc:date :in-reply-to:from:subject:mime-version:content-type:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=46GXHeUALtpO4O3TOALhIC4HG0bGJ4xyjvuRvhuOfq0=; b=N93213ZBNtxXBKDqnnWKCxREpqFDOENE0EFH+D2Bj3FKyd0t1w6z5eipy93IEZ3Kr1 B0w12DlqvliZfnJwaA8LJkwbgceXkYF9Yz8q3M5vH81vPD6CkGnv+MSZfR2RH/MdVSAr TZ06TSkSHTLAp/bPJT/iekzQQP7F+YXQ6x8rUTHKJE1BibpUYdM1QsBKxF7w4x9ELYUF P5odhqX8qiLj73EdCJl7+k5rMBPopj6PHwWPADerO/wuEXsn7rQxZJ9zq+Uu+mYbJ4hy Bu2PC8nvT3cGgzQwvhahNf0FI9SmMoJQsyVNvuhD+B7S1RFVGNikLAzFKOKAULHII438 I3Ig== X-Forwarded-Encrypted: i=1; AL+hErEfKFqFIyiUhdN/LhMXZkNOAYG+2CK7e037iV83Qbi3p6pm9ww7EIYmbQH+2YDRf7TqW4kN3yeRsGTVwLM=@vger.kernel.org X-Gm-Message-State: APuU4Z8pLDEBxJ23UMpKOedHd7pt6zWeAz63U88qBxDPYc7YzV21z/1Z 1cOU8lYQPS11RiQvN4OEY6xFa2k3OKgIthV0MQIYNKdh9OQrxHyluevk X-Gm-Gg: AYBFou1nTwOhm2SjUBqcd5tARE/1VrZZOktgfeDQCTut/jIT6kp5j4yxoLUKTGFg3P9 eu70+e4NyewVfc2jiZrRhd/EDJfBA6zFZ5w6dIPYyfADbC4ome3Pw1Qw3UUSkGHOPwXml1sag/S 7F946UiTRtY72bAXvERLAWxKpiDydvW3opnRgR/Chq0NRvPaaU1bf0dKC9DtWmepc96qFiiN2kd lDX4/Sb7QzBqqG2+29Tn76u00yEmtELyNtpgg1WfDgn7W3keCRhQOzymEyOLdcNc4EdzSCjTrfp J4jpCkFNWr4i2p85FxDoySdc0klR5Wcw8ylWA7TydnN0AieR6PViTpsiTVGYYsM+035VnH8/aoy 7+7TpG59ZpYgt5PXeJfHmVs2YMFnDWHvMFi3WoeUMKiVbSeTqTrSQF5bX9ejX9/F9G7gZn+FM// NZ8Ad/pmfikZM4sMs4bq6WUu4BPodVJ+ilMyPmwJ45/r6AX+VIV/g72s5jDVqv4wVXQuMY7jLKX RLwbvLmyjEV50BYbP2kyfekv+iBIkY9MXAS8GixcgvS5l43DAuIHStVS9ccVPOaxacdzU9ZVRkW 8xF85tgiyDqi+n+FsDp/XbswmYFi3ilWOvS8O5coS+hWJm4q/mI9kJO1rMJzXQtbJw== X-Received: by 2002:a05:7300:680e:b0:36b:d3dd:2e85 with SMTP id 5a478bee46e88-372575c63fcmr3296545eec.36.1794149947219; Sun, 08 Nov 2026 06:59:07 -0800 (PST) Received: from smtpclient.apple (v133-18-180-162.vir.kagoya.net. [133.18.180.162]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-37265c06c61sm5679879eec.14.2026.11.08.06.59.02 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sun, 08 Nov 2026 06:59:06 -0800 (PST) Content-Type: text/plain; charset=us-ascii X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3901.100.1.1.12\)) Subject: Re: [PATCH net-next v2 0/4] tcp: fix tcp_base_mss on passive connections and test MTU probing From: Esko Mobius In-Reply-To: <179414895487.488859.839196891969031483@kernel.org> Date: Sun, 8 Nov 2026 22:58:50 +0800 Cc: davem@davemloft.net, pabeni@redhat.com, ncardwell@google.com, horms@kernel.org, kuba@kernel.org, kuniyu@google.com, shuah@kernel.org, edumazet@kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, panweiping3@gmail.com, netdev@vger.kernel.org Content-Transfer-Encoding: 7bit Message-Id: <6A5F2D50-D257-4F6B-A1B6-BE08489591F6@gmail.com> References: <20261108-mtu-probing-series-v2-0-355d6490c3db@gmail.com> <179414895487.488859.839196891969031483@kernel.org> To: netdev-bot+sinfo@kernel.org X-Mailer: Apple Mail (2.3901.100.1.1.12) > How the issue was discovered Hi, This came up while adding packetdrill coverage for tcp_mtu_probing=2. The test work involved comparing the initial send MSS and what happened after the first probe was acknowledged on active and passive IPv4 connections. With tcp_base_mss=1024, the active connection started at 1024 as expected. The passive connection started at 1460, and its send MSS dropped to 1242 after the first probe was acknowledged. That led to checking the passive setup path, where tcp_v4_syn_recv_sock() called tcp_sync_mss() before tcp_init_transfer() enabled MTU probing. Thanks, Yongjian