From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 4F03D37F72C for ; Tue, 7 Jul 2026 11:27:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783423632; cv=none; b=aB8EvUiyPQQqzZdmqj0vI8hcPgbsI+LTHhldL0zOOK/lCvKg9KmNZplMEKUfrlRdrKj4H5srYm7YB2i8avNYEdmWML2sHrvZM8bccr0p2VjESDpxaPzPBSFJEQoYW0WabeWh22ZLcetWivVxnNLBsQtaPu8i7XcCDD6yyVBBjpg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783423632; c=relaxed/simple; bh=T/XYgpu/ULYAhsUBnIj7SIPozNjBSefcJL8IkP40638=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XwBaNs9Eb9WMJ/xpCrYXba6OjSyPHyJVI9V0uuIDkdvTLAA2fBclnZT9MJ5ah7rodM0PG9Nqgn6J0DAnrVAL8rV6W6mvmcbNGlT48OdCskIxaRHS5AGxLGjJ2pKtLkxiWSzrfxjeiKo7pjK2fPryPxN9wzqD6/4/Gx9Ew4OUPWI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MivkY43x; 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="MivkY43x" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5AD391F000E9; Tue, 7 Jul 2026 11:27:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783423631; bh=GgdS985dVOgDkV/zaZ7aBTarS2xFoS9ffuM52S+qljg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=MivkY43xrBLdgBTzrXpBN68lLw9GVL5MXh8x7FxN8F/lKyIFbg6RwUQOcHAzSqyw/ Gkdh9G/MyI6QwTKS20f8MGFMq6HIV0y5qCD26n2KltiKR3HJTTb2H47aunvBdzqRLy VSA97JHMqRsVnC7t/6eJjA38DuFesALtTVRLiuxJADo9MJSK2NrXzetSIceZCJodvT iDm3u9g+qfbbqLP7h/1SsJg8eYEbWVtYPZcP56JQbpsacDk//wmc11z5Aj/5Cj/vxh rTMoban1xq5IjSiuy6d4axJhPt8xKrOc1ukRdcC6SSTFcLbl5QynGzPRjxNToeMxoO BLynRVwC/AHTA== Message-ID: Date: Tue, 7 Jul 2026 13:27:06 +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 net v2] mptcp: pm: drop pending ADD_ADDR when removing id 0 endpoint Content-Language: fr To: Kalpan Jani Cc: mptcp , martineau , pabeni , "shardul.b" , janak , kalpanjani009 , shardulsb08 References: <20260529064355.922763-1-kalpan.jani@mpiricsoftware.com> <0f13954f-3bfa-4630-af9f-6f1f4b138a13@kernel.org> <19e72995d6d.89137929840232.7611532549298755137@mpiricsoftware.com> <19e830d30d7.701114c6187254.5018026155515510877@mpiricsoftware.com> <6d0b954c-4028-4c1e-bf02-5bf5f43f58af@kernel.org> <19f3b374a41.2132097d1809464.3759794617307044756@mpiricsoftware.com> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Kalpan, Thank you for your reply. On 07/07/2026 08:15, Kalpan Jani wrote: > Hi Matt, > > Thank you for the clear question — here is my honest assessment. > > The blocking point for a packetdrill test of this specific bug is > that the trigger sequence requires the kernel PM worker to run > between a "del id 0" and a second signal endpoint add, and > packetdrill's shell-escape timing is coarser than what reliably > controls that window. > > More specifically, the reproducer needs: > > 1. A fully-established MPTCP connection. > 2. A second subflow via MP_JOIN (to keep the connection alive > across the id 0 removal) — this part packetdrill handles well, > as shown in mp_join_server.pkt. > 3. An ADD_ADDR for the id-0 address already in flight with the > echo withheld — also doable: just don't send the echo packet. > 4. `ip mptcp endpoint delete id 0 ` via a shell escape — > packetdrill supports this. > 5. `ip mptcp endpoint add flags signal` to force PM > reselection — also a shell escape. > > The difficulty is between steps 3 and 4: the ADD_ADDR for id 0 > only gets sent after mptcp_mpc_endpoint_setup() has accounted the > MPC endpoint and the PM worker has run. In the mptcp_join.sh > reproducer this is handled by waiting for the second join > (wait_mpj) and checking the add_addr_signal counter before > proceeding. In packetdrill, the closest control is expecting the > `> add_address address_id=0 ...` line before issuing the shell > escape — and that does work in principle. Note that if needed (but I don't think it is if I understood correctly), you can always call commands or scripts in Packetdrill, e.g. to wait for an internal state to change. > Where it gets fragile: after the del+re-add, the PM reselects id 0 > and the WARN fires inside the add_addr_doit netlink handler, which > is synchronous with the shell-escape command. Packetdrill would > then need to expect a second `> add_address address_id=0 ...` line > that a fixed kernel would *not* send (since mptcp_pm_announced_alloc > returns false silently). That asymmetry — expecting a packet that > a fixed kernel suppresses — means the test structure naturally > inverts: you'd write it to expect *no* retransmission after the > del+re-add, which is harder to express cleanly than "this packet > must appear". The mptcp_join.sh counter check (`add_addr_signal` > going from 2 to 1 after the del) is a more direct assertion. You can also check ss' status. But here, you can also simply inject another packet after a small delay, and expect an ACK without ADD_ADDR to be sent instead. > That said, I think a packetdrill test *is* achievable if it's > structured around the ADD_ADDR retransmit that fires on an unfixed > kernel after the del+re-add: on an unfixed kernel the stale entry > triggers a second `> add_address address_id=0` packet; a fixed > kernel does not send it. So the test would: > > - inject the MP_JOIN to create the second subflow; > - see `> add_address address_id=0` (the first, legitimate one); > - not send the echo; > - issue `ip mptcp endpoint delete id 0 $OPT_LOCAL_IP` as a > shell escape; > - issue `ip mptcp endpoint add $OPT_LOCAL_IP flags signal`; > - add a ~`*` line that expects *no* spurious second > add_address — which is the opposite of what unfixed kernels > produce. > > The main uncertainty is whether packetdrill's `*` (any-packet) > handling can cleanly express "this packet must NOT appear within > N ms", or whether we'd need a short timeout + close to flush the > pipe. That's the part I haven't mastered yet in packetdrill. > > If you can point me at an existing test that uses a negative > packet assertion (or a timeout to prove absence), I can turn the > mptcp_join.sh reproducer into a packetdrill test for the next > version. Otherwise I'll send the mptcp_join.sh subtest as patch 2 > of v6 (with the `addr` fix in patch 1), and follow up with a > packetdrill test separately once I understand that idiom better. I think the easiest is to inject a packet after the timeout to force the kernel to react, e.g. sending a DATA_FIN, data, an out of window packet, etc. Then see that the reaction is the expected one, not a wrong retransmission. I just noticed that's what is done in add_addr_retry_errors.pkt, lines 32-38. In general, about Packetdrill, I recommend this presentation: https://netdevconf.info/0x19/sessions/tutorial/tutorial-using-packetdrill-to-write-automated-tests-for-the-linux-networking-stack.html e.g. on page 15, there are some explanations about timing: https://netdevconf.info/0x19/docs/netdev-0x19-paper23-talk-slides/packetdrill%20-%20NetDev%202025-03-10.pdf Back to the series you sent: we could say that the mptcp_join.sh reproducer is enough, but I think it would be useful for you -- and to avoid a new "speed=slow" subtest: mptcp_join.sh's execution is already long enough -- to try a bit more with Packetdrill if that's OK. WDYT? Cheers, Matt -- Sponsored by the NGI0 Core fund.