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 4CD55286A4 for ; Thu, 13 Nov 2025 09:08:37 +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=1763024917; cv=none; b=M4jVi3JLekMQfxq9WIXoeDRkRUMOa3bbBAlu/U+XS/fI35KcxNG4Ulys9zUlOF+B3b1oMYwGrItUuoK9vXf8YP3aGd7iRWnfe2hTyoepBP9MsCJ7HMI/GehmgD7ihjUsDZm2GCe1PVBySUJYyI5pCHqFhq7BXaHfRxzt0xXJaKM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763024917; c=relaxed/simple; bh=IHW8ECmZ3UrmfPd4BtYK5OvJOmpKw9VjSnByfX6f5gY=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=gb7N1eRlJPBLy8yqFwv5Z6oThHD7jxRWIrSswsuUO7/WugVGzQm7unA3VrcfDr6MqZNbsck2DfieQDKPka90eds7jcTswOeONGaykGd+Hgfek4D1pbbTQa7ow944FTPceJ4RTX3+50flnaFHijWVHTXnP8jWDENpmLbiFT5wkUE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=F0ZhwTkk; 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="F0ZhwTkk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 60753C4CEF8; Thu, 13 Nov 2025 09:08:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763024916; bh=IHW8ECmZ3UrmfPd4BtYK5OvJOmpKw9VjSnByfX6f5gY=; h=Date:Subject:To:References:From:In-Reply-To:From; b=F0ZhwTkkZDVCGMaMd1Mg9ZwaCeOkPZgIZR39JBs3m+5vfr+RFOwu+klHEpEV8CrB1 l7NbsoSuYtEXfflpFWMqmNPZaeTTEijaxpQF9GoDUYoSIkmFaMXmxepE8CdjMvqOZ1 MpxqXFZOYQcyhNyEJAZQ300Ftx7PT//vFwmDAnh1BG1QgHJDV8PQH3X2t0NCeEZ1Yt Gyh2FIXCUhTiCDfSxvBLi5RxGC3esCaaVe+JUtkaTmEfio+5RVPXMVl+dwrlw7UMlz mDRXzvxrHTwUBk+bbBU77ikQOnluyj0FsZiaBeeFjvJPx7HV5I6NpyqYVxaGynDy+5 e+nyeWf5qJwyQ== Message-ID: <3990718e-e4a8-4eb2-965e-02847bb339c0@kernel.org> Date: Thu, 13 Nov 2025 10:08:34 +0100 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 v2 mptcp-net 1/2] mptcp: do not fallback when OoO is present Content-Language: en-GB, fr-BE To: Paolo Abeni , mptcp@lists.linux.dev References: <1929f39e-b3e5-437d-b8da-71e3c7e6f36b@kernel.org> <686e7b33-00c5-47dd-af4a-8ac3014869b4@redhat.com> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Paolo, On 13/11/2025 01:02, Paolo Abeni wrote: > On 11/11/25 6:50 PM, Matthieu Baerts wrote: >> On 11/11/2025 08:24, Paolo Abeni wrote: >>> In case of DSS corruption, the MPTCP protocol tries to avoid the >>> subflow reset if fallback is possible. Such corruptions happen in >>> the receive path; to ensure fallback is possible the stack additionally >>> need to check for OoO data, otherwise the fallback will break the data >>> stream. >> >> Thank you for the fix! >>> Fixes: e32d262c89e2 ("mptcp: handle consistently DSS corruption") >>> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/598 >>> Signed-off-by: Paolo Abeni >>> --- >>> Note: this does not avoid the WARN(), but fixes the inconsistend >>> read() behavior; the ingress data is OoO, we should not ack it >>> --- >>> net/mptcp/protocol.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c >>> index d6b08e1de358..7b966f105f89 100644 >>> --- a/net/mptcp/protocol.c >>> +++ b/net/mptcp/protocol.c >>> @@ -646,7 +646,8 @@ static void mptcp_check_data_fin(struct sock *sk) >>> >>> static void mptcp_dss_corruption(struct mptcp_sock *msk, struct sock *ssk) >>> { >>> - if (!mptcp_try_fallback(ssk, MPTCP_MIB_DSSCORRUPTIONFALLBACK)) { >>> + if (!RB_EMPTY_ROOT(&msk->out_of_order_queue) || >>> + !mptcp_try_fallback(ssk, MPTCP_MIB_DSSCORRUPTIONFALLBACK)) { >> >> Does it mean we should check the OoO queue each time mptcp_try_fallback >> is called? >> >> Should we not eventually set msk->allow_infinite_fallback to false in >> mptcp_data_queue_ofo()? > > Good question. According to the RFC here we should unconditionally reset > the subflow. "historically" we try hard to fallback - even because in > early releases fallback was a bit to easy to obtain. > > Setting msk->allow_infinite_fallback = false in mptcp_data_queue_ofo() > could possibly hit performances. queue_ofo is basically fastpath with > multiple streams and we will likely need to acquire the fallback lock to > to the thing race free. > > I'm tempted to just do a plain reset here. WDYT? Can mptcp_dss_corruption() not be called before being in fully established mode? In this case, should we not fallback instead? e.g. if a middlebox start to alter MPTCP options after the 3WHS? Or maybe moving this RB_EMPTY_ROOT(&msk->out_of_order_queue) check to mptcp_try_fallback()? (mmh, we don't have the msk) Or maybe just a plain reset is OK here? Cheers, Matt -- Sponsored by the NGI0 Core fund.