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 69B2C237713 for ; Wed, 9 Jul 2025 10:39:13 +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=1752057554; cv=none; b=PPEtkJ/OOvEEPgggnJp0NIOu8akVqqzxmt49Fk96YmqCEBBeRyJ8ZHcQ3oZdRmD/TpfPtx4pYxsJAVWn7UfQ4m4DOycKDGH5L7tvbSlTzGIH2rODPCtkZ3oW6Rxzw9trM3AgKmiVoJ6f39k04hy308g/CaPmPpZAgqwZ+LhV06g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752057554; c=relaxed/simple; bh=mm3+pbcYIL6fIvWPoK8pCjk1LwGsCzkH2M2IP65r6Dg=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=icKSbRIAoHfQBIBRuGqrb1cnGi1szVauloW5RtMmV4n/pllRzsmwToCwMfuaqaNNGPkqBj1qlplw/pm8wWaRfKO/1IygExVoppcLNkOmdolILybSEc/XgQbQxz7ZPPuNESsyg7jPfwF7T402ixKYy1aNwhY8wc4InYiCs4z3sbc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FuS6mG2J; 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="FuS6mG2J" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 17A3AC4CEEF; Wed, 9 Jul 2025 10:39:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1752057553; bh=mm3+pbcYIL6fIvWPoK8pCjk1LwGsCzkH2M2IP65r6Dg=; h=Date:Subject:To:References:From:In-Reply-To:From; b=FuS6mG2JpjXdcMiRUfJ2xxhQRJU9XUWgAXl2IbwOwVqKCxwJE9WjgAxqU25iHGOAp 8XUYblixD6Ib7CMlDMflg3oKcjNkkd0taBGXZmhGjM1hNJg9IMjiIGgCUhAJad4a2q bH4D0+0s+QFo2g7hiaD5cTIPjuMFzqtyXMVItL7drSJsyevd8UZSHf1IFmgiINPhTR u05LrUlnT8WEwuxCV2VHYo4V+qavPF9P0zLPl5PbV8YUbOu56PgeKMt2x3QeJrPdIF lrxTu4rorAROk9p+TS1H30Qb8ezxx+mu+nf2qC+43DzMBqsgDGwOD/dkR1xOeTTjvQ tmXifQ1RjgKHw== Message-ID: Date: Wed, 9 Jul 2025 12:39:10 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH mptcp-net v2 3/5] mptcp: fix status reset on disconnect() Content-Language: en-GB, fr-BE To: Paolo Abeni , mptcp@lists.linux.dev References: <31fe0442-ab45-438c-abe6-25a9d4f08927@redhat.com> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Paolo, Thank you for your reply! On 09/07/2025 11:27, Paolo Abeni wrote: > > > On 7/8/25 5:43 PM, Matthieu Baerts wrote: >> Hi Paolo, >> >> On 05/07/2025 09:24, Paolo Abeni wrote: >>> disconnect() can still race with subflow fallback leaving the msk in >>> inconsistent status. To avoid such race, disconnect() must be blocking, >>> error out if the argument prevent such wait: the socket will linger >>> in SS_DISCONNECT state forever. >> >> Good idea! >> >> Just to be sure, this is not really a behaviour change compared to TCP, >> right? > > Actually it is, as the TCP disconnect never blocks. On the flip side the > race actually exists and I haven't find another way to plug it. > > An alternative I thought about was to create a new first subflow on > disconnect and let the old one 'detach' from the mptcp socket, but that > was problematic as the 'detached' ssk would have a NULL subflow->conn > and currently we assume that to be ~always != NULL Indeed, it doesn't sound safer :) >> No risks of breaking some cases? (io_uring, etc.?) > > Do io_uring work with mptcp? I don't know, I never tried. But I don't see why it wouldn't. (Of course, not when used with zero copy, etc.) > The disconnect failure when blocking is not > possible should really never be a problem from a functional PoV: > disconnect() can fail per documentation and the application should > handle that case. But it could set "O_NONBLOCK" and do the close later, no? Or is this correctly handled? > Blocking could cause some additional latency or slowdown in that code > path. I think it should be not problematic, but I have no real idea and > tend to be too optimistic WRT this kind of issues. > > I suggest not sending this to stable (with a note in the commit message). Maybe safer indeed. >> In which cases is this MSG_DONTWAIT flag set with disconnect()? > > Typo in the patch, should be O_NONBLOCK. The socket layer, the vfs layer > and iouring could set that. So typically what we do in the packetdrill tests. But maybe we don't check the returned value? Cheers, Matt -- Sponsored by the NGI0 Core fund.