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Sun, 8 Nov 2026 14:39:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794148795; bh=umoo2Lp9rUq60YFsX4JKM8uqEu+Er3Yh7U0wKuiM0Qk=; h=From:Subject:Date:To:Cc:Reply-To; b=hfpG0vNe+S9Jx5aSw0hBg7p88/9121tNdvVQyRvsmB7Xl6CKxH5Yuu29V8fUvlSDs n50onqQE5IfUtKngr0kLN3FModgseTU5BiDCu8ylHxM7VxyYY0kA+O4yzHBqjoo9CU bUZI0oYCjTuwbbLms/EaS0OLlclItp8qR57WVFMYh+dXuf28s/kxeaN0A8dD2UZ6uY EK2uiVWx6+FiionQYsBKE+vtIZ+mKg8LUk4BufcaHCXvX5yloqugjBvT9HriyTWvRA 5NXhgw0jpYBTD7LrUSGTM6kdbhaewo9/UtISxxbTG2jm9s517R/2bmOPmYObntq8zG yZQ781u8AZ5lQ== Received: from nexus.subspace.kernel.org (localhost [IPv6:::1]) by lkml.kernel.org (Postfix) with ESMTP id 6039B47FB7; Sun, 8 Nov 2026 14:39:53 +0000 (UTC) From: Yongjian Wang via B4 Relay Subject: [PATCH net-next v2 0/4] tcp: fix tcp_base_mss on passive connections and test MTU probing Date: Sun, 08 Nov 2026 22:39:50 +0800 Message-Id: <20261108-mtu-probing-series-v2-0-355d6490c3db@gmail.com> 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 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-B4-Tracking: v=1; b=H4sIALaJ8GoC/32NzQ6CMBCEX4Xs2TVtiQKefA/DoYUF1khL2kIwh HeXn7vHycw33wKBPFOAR7KAp4kDO7sFdUmg6rRtCbneMiih7lKKFPs44uCdYdviyaLOM5MWTW2 obmADB08Nz8fpCyxFtDRHKM8mjOZNVdw/923HITr/PfyTPIh/qkmiQK1yUVCmblrrZ9tr/lwr1 0O5rusP5Xx3w9AAAAA= X-Change-ID: 20261103-mtu-probing-series-a87b39fdbedf To: davem@davemloft.net, pabeni@redhat.com, ncardwell@google.com, horms@kernel.org, kuba@kernel.org, kuniyu@google.com, shuah@kernel.org, edumazet@kernel.org Cc: linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, panweiping3@gmail.com, netdev@vger.kernel.org, Yongjian Wang X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=ed25519-sha256; t=1794148792; l=1935; i=echoowall@gmail.com; s=20261026; h=from:subject:message-id; bh=19c4Gk3Gwmmdf6hcqazZwt4ILAXYtGIkiZQuAikm1yE=; b=lsncIAFuU5jy3vx7rFvzCCDrgzTHmMBJXO9pb8CuTOJIbro6eZmufAC0uCoBMgQMAujaU2d0m AhkcMvtSmitAqXR5SheoluhamBWjXdtlJYOE25fEXTuQJY3BI+yU6T+ X-Developer-Key: i=echoowall@gmail.com; a=ed25519; pk=9XP6JhqjjPsHCF6UZZZTeqTRnXIa4+ufggnxXtTJ+no= X-Endpoint-Received: by B4 Relay for echoowall@gmail.com/20261026 with auth_id=1323 X-Original-From: Yongjian Wang Reply-To: echoowall@gmail.com With tcp_mtu_probing=2, passive TCP connections can start at the full MSS because they sync MSS before initializing MTU probing. Patch 1 moves initialization next to the existing MSS sync in the passive paths and in the active SYN-ACK path. Patch 2 adds a regression test. Patches 3 and 4 add coverage for black hole detection and the MTU search on active connections. Tested on x86_64 KVM with all 496 packetdrill cases passing, plus targeted checks for simultaneous open and Fast Open with MTU probing enabled. The three affected TCP objects also build with W=1 under allyesconfig and allmodconfig. --- Changes in v2: - Move tcp_mtup_init() before the existing MSS sync in IPv4 and IPv6 passive opens and in the active SYN-ACK path. Remove the late initialization from tcp_init_transfer() (Kuniyuki and Neal). - Keep the three packetdrill patches unchanged. - Link to v1: https://lore.kernel.org/netdev/20261103-mtu-probing-series-v1-0-a2809e725aaa@gmail.com/ --- Yongjian Wang (4): tcp: initialize MTU probing before syncing MSS at connection setup selftests/net: packetdrill: test tcp_base_mss on passive connections selftests/net: packetdrill: add TCP black hole detection test selftests/net: packetdrill: add TCP MTU probing test net/ipv4/tcp_input.c | 2 +- net/ipv4/tcp_ipv4.c | 1 + net/ipv6/tcp_ipv6.c | 1 + .../net/packetdrill/tcp_mtu_probing_blackhole.pkt | 37 +++++++++++++++++++ .../net/packetdrill/tcp_mtu_probing_passive.pkt | 27 ++++++++++++++ .../net/packetdrill/tcp_mtu_probing_search.pkt | 43 ++++++++++++++++++++++ 6 files changed, 110 insertions(+), 1 deletion(-) --- base-commit: fa5196392691051963726787944db872420dfa75 change-id: 20261103-mtu-probing-series-a87b39fdbedf Best regards, -- Yongjian Wang