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smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kr5CFOu0; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kr5CFOu0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8186D1F000E9; Wed, 27 May 2026 00:59:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779843588; bh=k0LWpQXG3BKTJgYAJyuqgLaGYD6/oMecJAFUQdoQets=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=kr5CFOu0+0o663ogb4gJyPJ7sfA0PfDnKyVcUrigzgy1xNeCb2UprLTxwC7YvXuMy mGtHiHa88ra3jWpb0/z226d4T/Hg/YdTU58GEuRDqKw1aNtlen5EMwwPZ0Kgh36eGl HDPp3hmXOqPZa9H/EtwJSp76LxrXZKNktyP18M1ZEYMlhFHkrj7gDM0IzRfIFaOglY 85SiQTVxpvcSJJTNJ83sKJ7oZk+TtpJtNGzZ43f+IPnsEqqhKai/v5gIhG0V4dQWgH tabddLsYthZVYcz66YBk1TORK5tic0GTwsYCqYBZR075Llel43RUoJD1u+rKCCmSl5 Yskcrjr/2OJig== Message-ID: <6dd054c7-63c6-4d50-8f03-52684a0d9e67@kernel.org> Date: Wed, 27 May 2026 10:59:42 +1000 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 net] mptcp: pm: don't WARN on re-announced addr in kernel PM Content-Language: fr To: Kalpan Jani Cc: mptcp , martineau , pabeni , janak , "shardul.b" , kalpanjani009 , shardulsb08 References: <20260525121911.2410171-1-kalpan.jani@mpiricsoftware.com> <07bf06c0-20dd-4e31-960a-b79f6fffcecc@kernel.org> <19e63fedc1e.19d76b97534353.4482082124048801251@mpiricsoftware.com> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Kalpan, On 26/05/2026 21:15, Kalpan Jani wrote: > Hi Matt, > > Thank you for the review. > > On 26/05/2026 ..:.., Matthieu Baerts wrote: >>> The WARN assumes the kernel PM can never reselect an address that is >>> still in msk->pm.anno_list. That is not true: [...] >> >> From what I understand, it means that if a "signal" MPTCP endpoint is >> removed the echo got received, the in-kernel PM will continue >> retransmitting the ADD_ADDR. That doesn't seem correct. I didn't check >> in the code, but I thought that the retransmit timer was at least >> stopped, but maybe the entry was not removed from the list? > > You are right to expect the teardown. I checked the code, and it is not > uniform across the two removal paths: > > - For a non-zero id endpoint, mptcp_nl_remove_subflow_and_signal_addr() > -> mptcp_pm_remove_anno_addr() -> mptcp_remove_anno_list_by_saddr() > -> mptcp_pm_del_add_timer(.., false): the timer is stopped and the > anno_list entry is unlinked and freed. This path is fine. > > - For the id 0 endpoint, mptcp_nl_remove_id_zero_address() does NOT > call that teardown. It only queues a RM_ADDR and marks the id as > available again; the pending anno_list entry and its armed timer are > left alive. > > So a stale entry can only survive on the id 0 removal path. When that > endpoint is re-added, the kernel PM reselects id 0, reaches > mptcp_pm_alloc_anno_list() a second time, finds the stale entry and > hits the WARN. That is the actual bug here. I guess there were some confusions at some points that the ID 0 wouldn't be sent as an ADD_ADDR. But that can be the case when the linked address is removed, then re-added. Then, I guess to have the bug, you need to create a connection, with an extra subflow, then remove and re-add the endpoint linked to the initial subflow, and repeat this once more to hit the bug, no? >> Does it also mean that if an ADD_ADDR echo is never received, the entry >> is never removed, even after having reached the max retransmissions? > > Yes. In mptcp_pm_add_timer(), once retrans_times reaches > ADD_ADDR_RETRANS_MAX the timer stops re-arming (timeout = 0), but the > anno_list entry itself is not freed there; it stays on the list until > the endpoint is removed. Only for the ID0, when re-added then. >>> This is a benign transient state, so drop the WARN. [...] >> >> If I understand correctly, the transient state is not benign, and the >> WARN should not be dropped. > > Agreed. I will drop this patch. The WARN is a valid assertion; the fix > should keep it and instead make the id 0 removal path tear down the > pending ADD_ADDR, mirroring the non-zero id path (drop the anno_list > entry, stop its timer, and decrement add_addr_signaled if it had been > announced). I will send that as v2. Thanks! >> Also, it would be nice to add a new test to validate that. Here, it >> might be easier with a packetdrill test [1] [...] > > Will do. I will add a packetdrill test that sends an ADD_ADDR, withholds > the echo, and then removes and re-adds the endpoint, based on > add_addr4_server.pkt. See above: you might need an extra subflow (see the tests in mp_join), and re-add the endpoint twice, because once is enough to trigger the fact the entry is not removed, but not enough to hit the WARN if I understood correctly. Cheers, Matt -- Sponsored by the NGI0 Core fund.