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Date:   Wed, 25 May 2022 12:17:59 +0200
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Subject: Re: [PATCH 5.17 114/158] mptcp: strict local address ID selection
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To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Mat Martineau <mathew.j.martineau@linux.intel.com>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Paolo Abeni <pabeni@redhat.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Sasha Levin <sashal@kernel.org>
References: <20220523165830.581652127@linuxfoundation.org>
 <20220523165849.851212488@linuxfoundation.org>
 <fa953ec-288f-7715-c6fb-47a222e85270@linux.intel.com>
 <Yo3gAprjnapHfKar@kroah.com>
From:   Matthieu Baerts <matthieu.baerts@tessares.net>
In-Reply-To: <Yo3gAprjnapHfKar@kroah.com>
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Hi Greg, Mat,

On 25/05/2022 09:51, Greg Kroah-Hartman wrote:
> On Mon, May 23, 2022 at 08:51:52PM -0700, Mat Martineau wrote:
>> On Mon, 23 May 2022, Greg Kroah-Hartman wrote:
>>
>>> From: Paolo Abeni <pabeni@redhat.com>
>>>
>>> [ Upstream commit 4cf86ae84c718333928fd2d43168a1e359a28329 ]
>>>
>>> The address ID selection for MPJ subflows created in response
>>> to incoming ADD_ADDR option is currently unreliable: it happens
>>> at MPJ socket creation time, when the local address could be
>>> unknown.
>>>
>>> Additionally, if the no local endpoint is available for the local
>>> address, a new dummy endpoint is created, confusing the user-land.
>>>
>>> This change refactor the code to move the address ID selection inside
>>> the rebuild_header() helper, when the local address eventually
>>> selected by the route lookup is finally known. If the address used
>>> is not mapped by any endpoint - and thus can't be advertised/removed
>>> pick the id 0 instead of allocate a new endpoint.
>>>
>>> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
>>> Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
>>> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
>>> Signed-off-by: Sasha Levin <sashal@kernel.org>
>>> ---
>>> net/mptcp/pm_netlink.c | 13 --------
>>> net/mptcp/protocol.c   |  3 ++
>>> net/mptcp/protocol.h   |  3 +-
>>> net/mptcp/subflow.c    | 67 ++++++++++++++++++++++++++++++++++++------
>>> 4 files changed, 63 insertions(+), 23 deletions(-)
>>>
>>
>> Greg, Sasha -
>>
>> Is it possible to drop this one patch? It makes one of the mptcp selftests
>> fail (mptcp_join.sh, "single address, backup").
> 
> Does that mean the backport is incorrect, or that the selftest is wrong?

The backport is correct but the commit that is backported here was part
of a series that was changing the behaviour. This modification is
visible in the selftests.

If I'm not mistaken, we would need these two commits to fix the
regression in the selftests:

  69c6ce7b6eca selftests: mptcp: add implicit endpoint test case

  d045b9eb95a9 mptcp: introduce implicit endpoints


But we don't want to change the behaviour in stable and it is better to
drop this patch ("mptcp: strict local address ID selection"), it is not
needed for stable from what I see.

Cheers,
Matt
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