From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 CBF8A38F24D; Thu, 26 Feb 2026 08:12:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772093536; cv=none; b=rDQ2dmBKm8IiqXCubu9QF/EeoDhBsqyLV8S4hjg3A2CgwE7fsLjTzUW9qnrupG/nYlENCixnwsmxBxBMjIXXF80dHGzXjvJ/pBHk/d8eCgY/Mxc/99OXYqpuQjjUMgRc9XGe7n5PYJWHzCAVWiJyHsyuMHWcMjAOL9cGHdt+GxY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772093536; c=relaxed/simple; bh=mDmhw3ldZky/Cf38m5XPHOlcO7PKFL9nTgju4Z3kRX0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GO7s12O4wKAzylXKsa2cegVF7YONa7W4hIblCscTaMFUNXhnMQcYLVVztaangIUxOjKWXJbB8d+ml0Vsx4CdOFyiuep6ga5dg/DvQirR6bZ5EfE4AMue1ze0lXksOi9U2/4/7sj0MipOnmFhSPDWccKoqt2YH07DtOEL/XBK3ZM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CoBPMtYP; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="CoBPMtYP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 19FA2C19422; Thu, 26 Feb 2026 08:12:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772093536; bh=mDmhw3ldZky/Cf38m5XPHOlcO7PKFL9nTgju4Z3kRX0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=CoBPMtYPMDLeSpzO1GzHg2zbsq3T/bq+RI4BKe48Pk+3BudWbY0fieKsdyHhqbjuG uN44fuYW04UdMimD4oIRW1Xb7xXjDArhZov9M/Qs+bNB3f4utERcyKxiRSvuQxYFYA RICr37i6ULSE4ut6HwlfD00PH4/Aj90KsZ8xmdk7MjBeAX0enNv1yL3mFW5qrad6rv j2J0byqRg0l77igQMA/ooIZDoBv5K6ziRaUY00Q/pL34V9DxrEwKcFeG2e/btogu7D L2eqYLJw9Ng2Bx4V7RpA8VfOf23sdwjbEMVBNNrnK0lDNay9B87r6WFoFOCGja5VvY W3eY+7c++21gg== Message-ID: Date: Thu, 26 Feb 2026 09:12:07 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC net-next v2 0/5] tcp: RFC 7323-compliant window retraction handling Content-Language: en-GB, fr-BE To: gmbnomis@gmail.com, Eric Dumazet , Neal Cardwell , Kuniyuki Iwashima , "David S. Miller" , Jakub Kicinski , Paolo Abeni , Simon Horman , Jonathan Corbet , Shuah Khan , David Ahern , Stefano Brivio , Jon Maloy , Jason Xing , mfreemon@cloudflare.com, Shuah Khan Cc: Christian Ebner , netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20260226-tcp_rfc7323_retract_wnd_rfc-v2-0-aa3f8f9cc639@gmail.com> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; keydata= xsFNBFXj+ekBEADxVr99p2guPcqHFeI/JcFxls6KibzyZD5TQTyfuYlzEp7C7A9swoK5iCvf YBNdx5Xl74NLSgx6y/1NiMQGuKeu+2BmtnkiGxBNanfXcnl4L4Lzz+iXBvvbtCbynnnqDDqU c7SPFMpMesgpcu1xFt0F6bcxE+0ojRtSCZ5HDElKlHJNYtD1uwY4UYVGWUGCF/+cY1YLmtfb WdNb/SFo+Mp0HItfBC12qtDIXYvbfNUGVnA5jXeWMEyYhSNktLnpDL2gBUCsdbkov5VjiOX7 CRTkX0UgNWRjyFZwThaZADEvAOo12M5uSBk7h07yJ97gqvBtcx45IsJwfUJE4hy8qZqsA62A nTRflBvp647IXAiCcwWsEgE5AXKwA3aL6dcpVR17JXJ6nwHHnslVi8WesiqzUI9sbO/hXeXw TDSB+YhErbNOxvHqCzZEnGAAFf6ges26fRVyuU119AzO40sjdLV0l6LE7GshddyazWZf0iac nEhX9NKxGnuhMu5SXmo2poIQttJuYAvTVUNwQVEx/0yY5xmiuyqvXa+XT7NKJkOZSiAPlNt6 VffjgOP62S7M9wDShUghN3F7CPOrrRsOHWO/l6I/qJdUMW+MHSFYPfYiFXoLUZyPvNVCYSgs 3oQaFhHapq1f345XBtfG3fOYp1K2wTXd4ThFraTLl8PHxCn4ywARAQABzSRNYXR0aGlldSBC YWVydHMgPG1hdHR0YmVAa2VybmVsLm9yZz7CwZEEEwEIADsCGwMFCwkIBwIGFQoJCAsCBBYC AwECHgECF4AWIQToy4X3aHcFem4n93r2t4JPQmmgcwUCZUDpDAIZAQAKCRD2t4JPQmmgcz33 EACjROM3nj9FGclR5AlyPUbAq/txEX7E0EFQCDtdLPrjBcLAoaYJIQUV8IDCcPjZMJy2ADp7 /zSwYba2rE2C9vRgjXZJNt21mySvKnnkPbNQGkNRl3TZAinO1Ddq3fp2c/GmYaW1NWFSfOmw MvB5CJaN0UK5l0/drnaA6Hxsu62V5UnpvxWgexqDuo0wfpEeP1PEqMNzyiVPvJ8bJxgM8qoC cpXLp1Rq/jq7pbUycY8GeYw2j+FVZJHlhL0w0Zm9CFHThHxRAm1tsIPc+oTorx7haXP+nN0J iqBXVAxLK2KxrHtMygim50xk2QpUotWYfZpRRv8dMygEPIB3f1Vi5JMwP4M47NZNdpqVkHrm jvcNuLfDgf/vqUvuXs2eA2/BkIHcOuAAbsvreX1WX1rTHmx5ud3OhsWQQRVL2rt+0p1DpROI 3Ob8F78W5rKr4HYvjX2Inpy3WahAm7FzUY184OyfPO/2zadKCqg8n01mWA9PXxs84bFEV2mP VzC5j6K8U3RNA6cb9bpE5bzXut6T2gxj6j+7TsgMQFhbyH/tZgpDjWvAiPZHb3sV29t8XaOF BwzqiI2AEkiWMySiHwCCMsIH9WUH7r7vpwROko89Tk+InpEbiphPjd7qAkyJ+tNIEWd1+MlX ZPtOaFLVHhLQ3PLFLkrU3+Yi3tXqpvLE3gO3LM7BTQRV4/npARAA5+u/Sx1n9anIqcgHpA7l 5SUCP1e/qF7n5DK8LiM10gYglgY0XHOBi0S7vHppH8hrtpizx+7t5DBdPJgVtR6SilyK0/mp 9nWHDhc9rwU3KmHYgFFsnX58eEmZxz2qsIY8juFor5r7kpcM5dRR9aB+HjlOOJJgyDxcJTwM 1ey4L/79P72wuXRhMibN14SX6TZzf+/XIOrM6TsULVJEIv1+NdczQbs6pBTpEK/G2apME7vf mjTsZU26Ezn+LDMX16lHTmIJi7Hlh7eifCGGM+g/AlDV6aWKFS+sBbwy+YoS0Zc3Yz8zrdbi Kzn3kbKd+99//mysSVsHaekQYyVvO0KD2KPKBs1S/ImrBb6XecqxGy/y/3HWHdngGEY2v2IP Qox7mAPznyKyXEfG+0rrVseZSEssKmY01IsgwwbmN9ZcqUKYNhjv67WMX7tNwiVbSrGLZoqf Xlgw4aAdnIMQyTW8nE6hH/Iwqay4S2str4HZtWwyWLitk7N+e+vxuK5qto4AxtB7VdimvKUs x6kQO5F3YWcC3vCXCgPwyV8133+fIR2L81R1L1q3swaEuh95vWj6iskxeNWSTyFAVKYYVskG V+OTtB71P1XCnb6AJCW9cKpC25+zxQqD2Zy0dK3u2RuKErajKBa/YWzuSaKAOkneFxG3LJIv Hl7iqPF+JDCjB5sAEQEAAcLBXwQYAQIACQUCVeP56QIbDAAKCRD2t4JPQmmgc5VnD/9YgbCr HR1FbMbm7td54UrYvZV/i7m3dIQNXK2e+Cbv5PXf19ce3XluaE+wA8D+vnIW5mbAAiojt3Mb 6p0WJS3QzbObzHNgAp3zy/L4lXwc6WW5vnpWAzqXFHP8D9PTpqvBALbXqL06smP47JqbyQxj Xf7D2rrPeIqbYmVY9da1KzMOVf3gReazYa89zZSdVkMojfWsbq05zwYU+SCWS3NiyF6QghbW voxbFwX1i/0xRwJiX9NNbRj1huVKQuS4W7rbWA87TrVQPXUAdkyd7FRYICNW+0gddysIwPoa KrLfx3Ba6Rpx0JznbrVOtXlihjl4KV8mtOPjYDY9u+8x412xXnlGl6AC4HLu2F3ECkamY4G6 UxejX+E6vW6Xe4n7H+rEX5UFgPRdYkS1TA/X3nMen9bouxNsvIJv7C6adZmMHqu/2azX7S7I vrxxySzOw9GxjoVTuzWMKWpDGP8n71IFeOot8JuPZtJ8omz+DZel+WCNZMVdVNLPOd5frqOv mpz0VhFAlNTjU1Vy0CnuxX3AM51J8dpdNyG0S8rADh6C8AKCDOfUstpq28/6oTaQv7QZdge0 JY6dglzGKnCi/zsmp2+1w559frz4+IC7j/igvJGX4KDDKUs0mlld8J2u2sBXv7CGxdzQoHaz lzVbFe7fduHbABmYz9cefQpO7wDE/Q== Organization: NGI0 Core In-Reply-To: <20260226-tcp_rfc7323_retract_wnd_rfc-v2-0-aa3f8f9cc639@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Simon, On 26/02/2026 01:49, Simon Baatz via B4 Relay wrote: > this series implements the receiver-side requirements for TCP window > retraction as specified in RFC 7323 and adds packetdrill tests to > cover the new behavior. Thank you for looking at that. > It addresses a regression with somewhat complex causes; see my message > "Re: [regression] [PATCH net-next 7/8] tcp: stronger sk_rcvbuf checks" > (https://lkml.kernel.org/netdev/aXaHEk_eRJyhYfyM@gandalf.schnuecks.de/). > > Please see the first patch for background and implementation details. > > This is an RFC because a few open questions remain: (...) > - MPTCP seems to modify tp->rcv_wnd of subflows. And the modifications > look odd: > > 1. It is updated in the RX path. Since we never advertised that > value, we shouldn't need to update rcv_mwnd_seq. FYI, with MPTCP the received windows are shared between subflows. This might be surprising, but maintaining per-subflow receive windows could end up stalling some subflows while others would not use up their window. For more details, please check this section of the RFC: https://datatracker.ietf.org/doc/html/rfc8684#sec_rwin > 2. In the TX path, there is: > > tp->rcv_wnd = min_t(u64, win, U32_MAX); > > To me, that looks very wrong and that code might need to be fixed > first. The capping is explained because the MPTCP-level ack seq is on 64-bit, while the TCP level receive window is on 32-bit. I hope this helps better understanding these modifications, and hopefully not introducing regressions on the MPTCP side :) Cheers, Matt -- Sponsored by the NGI0 Core fund.