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 35853132139; Fri, 2 Aug 2024 08:48:31 +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=1722588512; cv=none; b=KdVS6QDetsbtNhaaZmoO82k2rDk+dE1whw5NS0dKg+ZuQDqoyl4shCUrk/N6heY7ehIwLLfOhvdE51eoAjF543JizgkmdGeak7YIjOjrfPH9qKkVTmY/vy7aZbqXgGwt92rVzN8mkgU/USiPRDxL/agRzcIAnqmy/LY2w3jTdg4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722588512; c=relaxed/simple; bh=cQwlhsKmJKAFEKRQ/MzNl2oigPWjtiwSf5Pvm1J5Iuo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=CfjiHD4Egc67eRzD24+1Mm6Lhg+fAsSexBd9K9InweWa4mQjEEbKZ7YWUXV7S6LxyumKroLgZ+CPo+DGeMxIDg8rl42Q6peAJ5M/PYJDQZHl4tUzbeom+2qV/6z7pJNXH3JAer753MciZbvMVDEPDGI3q7nATjHt5T6nZIMb7N4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Aw1vfFK9; 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="Aw1vfFK9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A5A5DC32782; Fri, 2 Aug 2024 08:48:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1722588511; bh=cQwlhsKmJKAFEKRQ/MzNl2oigPWjtiwSf5Pvm1J5Iuo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Aw1vfFK9apg27Eh/1gmfHYfcrIr/w87XQZpiYjP8gCQ5ZEcbXaFOI1HcqQs26h5kw WIuXOdlbri6X9DdHtr4qUDDSEnXi6u6+Oc6JPO1PsY0gVwOmihazc0RSahOKFZioBJ Pmko/jMn6kt69UramvxjvdofOhgenLTw9Z8pzGvWc4pxjnodxDyBhxJQwUv7+xKWJD K5a/Z4C53jwoiD/1naccN5Q3IkuDF3sgzqJ5Du0wr5Twi0RYG+Upq1N5x31zsqKZFo khQtfpoXhLTd5Kdf0mlNZEdlywEPTxbZvp9p8ZzNAz0M67v1EItO/cN56OcTnHw7E+ /v4bxQPRJdFnw== Message-ID: <79e327c5-f87f-4295-b461-81c09a699af6@kernel.org> Date: Fri, 2 Aug 2024 10:48:26 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH net-next] tcp: limit wake-up for crossed SYN cases with SYN-ACK Content-Language: en-GB To: Eric Dumazet Cc: mptcp@lists.linux.dev, "David S. Miller" , David Ahern , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Kuniyuki Iwashima References: <20240801-upstream-net-next-20240801-tcp-limit-wake-up-x-syn-v1-1-3a87f977ad5f@kernel.org> 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 01/08/2024 19:52, Eric Dumazet wrote: > On Thu, Aug 1, 2024 at 6:39 PM Matthieu Baerts (NGI0) > wrote: >> >> In TCP_SYN_RECV states, sk->sk_socket will be assigned in case of >> marginal crossed SYN, but also in other cases, e.g. >> >> - With TCP Fast Open, if the connection got accept()'ed before >> receiving the 3rd ACK ; >> >> - With MPTCP, when accepting additional subflows to an existing MPTCP >> connection. >> >> In these cases, the switch to TCP_ESTABLISHED is done when receiving the >> 3rd ACK, without the SYN flag then. >> >> To properly restrict the wake-up to crossed SYN cases as expected there, >> it is then required to also limit the check to packets containing the >> SYN-ACK flags. >> >> Without this modification, it looks like the wake-up was not causing any >> visible issue with TFO and MPTCP, apart from not being needed. That's >> why this patch doesn't contain a Cc to stable, and a Fixes tag. >> >> While at it, the attached comment has also been updated: sk->sk_sleep >> has been removed in 2010, and replaced by sk->sk_wq in commit >> 43815482370c ("net: sock_def_readable() and friends RCU conversion"). >> >> Suggested-by: Kuniyuki Iwashima >> Signed-off-by: Matthieu Baerts (NGI0) >> --- >> Notes: >> - This is the same patch as the one suggested earlier in -net as part >> of another series, but targeting net-next (Eric), and with an >> updated commit message. The previous version was visible there: >> https://lore.kernel.org/20240718-upstream-net-next-20240716-tcp-3rd-ack-consume-sk_socket-v2-2-d653f85639f6@kernel.org/ >> --- > > Note: I am not aware of any tests using FASYNC > > sock_wake_async() / kill_fasync() are sending signals, not traditional wakeups. Thank you for the review and the explanation! > Do we really want to potentially break some applications still using > pre-multi-thread era async io ? They are potentially already broken if we don't test them :-D > Not that I really care, but I wonder why you care :) More seriously, I sent this patch, because in previous discussions about the crossed SYN case, Kuniyuki mentioned that he used the same condition as the one I modified here. I didn't see why it is needed to send such signal there for TFO and MPTCP cases, so I sent this patch. On the other hand, I suppose such old apps relying on FASYNC will not natively use TFO or MPTCP (except if they are forced externally). In other words, I'm not fixing a problem I saw here, I'm only restricting the condition to crossed SYN case, as mentioned in the linked comment, then excluding TFO and MPTCP cases that don't seem to require this signal at that moment. But then it's fine for me to drop this patch if you think it is not needed :) Cheers, Matt -- Sponsored by the NGI0 Core fund.