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 28E1B328B57 for ; Thu, 13 Nov 2025 17:44:56 +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=1763055897; cv=none; b=IWmm4QwSE26pn3LxIc1gbiMCdyor4cQhzTH2F42igqTlbkFo/AbqrOAEk4bcMzmkd7Q5hCqftpIdUKJ6ckxiD0I5h/ajXBf5VyAftzqxz0hVJRYw/p561vKBC//eE44kndSKVS8NpWchI+6VWyqwUmyeqAnMEJ1v/Cf6pY0/lv8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763055897; c=relaxed/simple; bh=fMBKMUoixRMOIy4QVzBkJa2d/k4ZcJCtnwziDJgR9nQ=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=A0AshGURHgEOZHug5YohkVV6OJ75/SQy2W2PPH4fvnyfW/q1GAyWdZBDvPViyK56RKze6kLoYTZR8jNj6Yuup1+r4rBzaT80UI/MBINDpuFwCw9uoPdikR95x4Y5LN/PLeYypiEQyCiFi2J+7kK5tojoWbocyEEvXqDNWy3LKCY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cKMmgWLR; 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="cKMmgWLR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3E2E0C4CEF7; Thu, 13 Nov 2025 17:44:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763055896; bh=fMBKMUoixRMOIy4QVzBkJa2d/k4ZcJCtnwziDJgR9nQ=; h=Date:Subject:To:References:From:In-Reply-To:From; b=cKMmgWLRlUtY3LI1fl7IpPKXQDGydPlfq6kN7OwnI3zowf+Uii71MB1ru6ai2vXoI OKOc0W+b8EZoKocs/yUmHggJ893Wz52xEcqjx2TBachMvFYwRLAKi+bsjPlaFu3Pdw Gne1HRpqIXhLRvhquTE//uMh1SuCi1bpXwyL09c6jvYKAQIamapn/J2bPBC9eC3U+A filQYRHM1fuii2BnZbU/7odx752AvEj+GeEiR9akp46kKVLS4IxCJAzLxL0vlSEpe/ 3+xXlKNjKJcOdhFh5oODKZeCxB4eYIEoteWUM2vgyrRmSCHPtl9VYL/hPjcrRbwQas BQb37pt+Ltm+Q== Message-ID: <6d5b889c-47c2-421e-bb3d-0dcc7da21650@kernel.org> Date: Thu, 13 Nov 2025 18:44:54 +0100 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird 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> <3990718e-e4a8-4eb2-965e-02847bb339c0@kernel.org> <6e8bb6a1-0c96-4fa5-b8bf-cd0253e4450e@redhat.com> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 13/11/2025 18:32, Paolo Abeni wrote: > On 11/13/25 10:08 AM, Matthieu Baerts wrote: >> 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? > > Even if we would be before reaching fully established status, the DSS > corruption caused by the pktdrill test causes MPTCP-level OoO with data > already acked at the TCP level. We can't drop it nor we can safely > fallback, we have do reset (if ofo queue) is not empty. Yes, OK to reset in this case. >> 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? > > I think the main question is if constraining such resets to OoO cases > (in the attempt to do fallback in other scenarios) or always reset here. > > I propose to keep it simple, minimize the difference from current status > and always check OoO. Just to be sure I understand this correctly: your prefer keeping the patch as it is, and there is no need to move the OoO check to the __mptcp_try_fallback() help to check it in other cases? Cheers, Matt -- Sponsored by the NGI0 Core fund.