From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.227 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793108706; b=w4USpQyKWZwX9fWcjarpe1QL6pvcKyvTrfIkgzNPBPHVgl9SgPcEVzmPC0qhE7BulwkX BV6daL8NXd4of17x8l1KcugyllxNFt0g50aQnVXLxWLwlBfsGm+hI/oBWJgPCVHLvhEU6 2fMx9tAQw7nRyZL+7Rm7oDCZczkGiBOHkFLlE9alHG4Z/FgmWJpCLtFLFRTP5NdmJAED7 QMpq9gqJ26sSp62mPVy0D9nGp3oq/gE3qXUg7AD1jrpHAtS5HhT7HhovFpcLLCbsBhBuQ 82BBe6dSC4XF/WT6h8uOnauo5VTOE4FOZpvrAgNdNcvfFV9U0fZH4rW2979kNv8kKlg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793108706; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:In-Reply-To:Content-Type: Content-Transfer-Encoding; bh=+zgFas+4hJZZwgPEJMUzFoGVQwC5WpjC0swXnGqt0W0=; b=DX15YlqFybl0Mmie+ChHAMim12lhzzyOqPcZHa7Lypc99z9IgBa+ky24qp/3vWniaotV dnU3OLOgYxepaYYf26hLY2ecjsmV1BuG/PqoGUhNPIrNyyszET7RMAW7VpFGqbvnwLssk l9wKioyJFEUbbyRKFU+Edp2QGW5dpDk+DUdAp3e79fDaMJsi7rXvzT8KN5s4Daq+6MCdG aDsfd0ZOUnFbTLlH5eZA9i4Dq6aMp//hKal6OtdhSR6n91Y8x7eRQQVsKCLDR8OB0tYDe gxgPLTFLgW2i4RN04fEdMeH7kyluqB3H+WfOyU+eRC8UlP9Kr+QQsTSdcFTFMvNZbrQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=aevUmP1E; arc=none smtp.remote-ip=91.218.175.227 Received: from mta0.migadu.com (out-227.mta0.migadu.com [91.218.175.227]) (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 C09CD606A31D for ; Tue, 27 Oct 2026 13:45:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org C09CD606A31D Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=aevUmP1E X-Envelope-To: netdev@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=aWAzItW6Ln/bOAVvVXsGvaelikw5SSSjsKUtt55BHao=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793108703; v=1; x=1793713503; b=aevUmP1E+qeSYvFJ2KQi47ut7Muf9TyYC2Elimi2ZcYxGcHN97rwDzMVkkK/6EhT1rIDqSJt +apTE7aRIzMjtFhpIgm6ogDUDcqc7JoZkm3/tuPuXUcmHhbs40D2ZFeo10a0gQDPyEqQ7ZTlk49 mZmr7QL+ql4XvusL8KuMmRAA= X-Envelope-To: netdev@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 17da54f9e5b41fb1; Tue, 27 Oct 2026 13:45:03 +0000 X-Mizu-Trace-ID: 17da54f9e5b41fb1 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Tue, 27 Oct 2026 21:44:53 +0800 X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net 2/2] Revert "net: advertise TCP MSS from the configured MTU, not the learned PMTU" To: Esko Mobius , Eric Dumazet Cc: netdev@vger.kernel.org, Jakub Kicinski , Paolo Abeni , "David S. Miller" , Simon Horman , David Ahern , Ido Schimmel , Shuah Khan , Thorsten Leemhuis , regressions@lists.linux.dev, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20261026-advmss-revert-v1-0-272fa4b7ecb6@gmail.com> <20261026-advmss-revert-v1-2-272fa4b7ecb6@gmail.com> From: Jiayuan Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/27/26 9:12 PM, Esko Mobius wrote: > On 10/27/26 1:45 PM, Jiayuan Chen wrote: >> This precondition does all the work. The server only learns the PMTU >> when it sends a full-size segment itself. [...] >> >> Please re-run the 6.12.107 case without seeding the PMTU. > You are right. Without seeding, 6.12.107 stalls the same way: > > kernel PMTU seeded SYN-ACK MSS 1 MB upload > 6.12.107 no 1460 stalls > 6.12.107 yes (ping) 1416 OK > > My reproducer took a shortcut there. What it should have modelled is > our production setup, which is the masquerading relay you describe: > the clients share the relay's address, so ordinary downloads by other > clients keep the server's PMTU entry fresh. Modelling that directly, > with no artificial seeding (cliA downloads 1 MB, then cliB, behind a > firewall dropping frag-needed, uploads 1 MB through the same relay): > > kernel SYN-ACK MSS to cliB cliB upload > 6.12.107 1416 OK > 6.12.111 1460 stalls Thanks Esko for the testing, and Eric for the explanation. Agreed. > So I agree it was never a designed mechanism, it is the side effect > Eric describes. We have since added MSS clamping on our relays. > > If it helps, I can send a v2 that describes the masquerading case > instead of the seeded one in the changelog. And I am happy to test > the net-next follow-up on this setup. No need for a v2 from my side, I just wanted to confirm the actual scenario. I saw your report earlier but was swamped and could not get to it in time, sorry about that. Reviewed-by: Jiayuan Chen > > Thanks, > Esko