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smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=tbIQzedN; 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="tbIQzedN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 93DBAC4CEF5; Wed, 10 Sep 2025 08:56:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1757494619; bh=1kvJyLRA3qorOtEizalZAbRK41ujlJ31rNQpgw/YD5c=; h=Date:Subject:To:References:From:In-Reply-To:From; b=tbIQzedNhO/k//lwI6v4+36HJJIBwpYS1Wd6lLIIuqj2s/wkznvcAF7sduKvWkPJ2 2bGq5oL0hpODMChkjAH90aQTYH36QQwyOteRLA96hEOyXrI2lop6CLFACdudZBRe4v W/Y5spocNKRGu0pPZL2Z9S3Q7qQaxJrxidv3BNAG8KdxqH0VqXcER3e/FdBtFiwTjt s8sJ3gv/0DIY9yfWhbvV9Oiv8pWXQwuuicaDBVdrHCj1s+dtjLqMv/3abkG52vrer+ 6SEziOrFHEOIvCDlZZoI1Od1LrX1JMYTrsRdMBFlvt+/8zeZqQty7RLTmiahZYN5sk BZIOaGQlqD7hg== Message-ID: Date: Wed, 10 Sep 2025 10:56:58 +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 mptcp-net v2 1/5] mptcp: propagate shutdown to subflows when possible Content-Language: en-GB, fr-BE To: Geliang Tang , mptcp@lists.linux.dev References: <20250905-sft-mptcp-disc-err-v2-0-dfb3b6b4a877@kernel.org> <20250905-sft-mptcp-disc-err-v2-1-dfb3b6b4a877@kernel.org> <9f2a05ac6034fb33f579302a0ede2ec13eb6c915.camel@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Geliang, On 10/09/2025 05:24, Geliang Tang wrote: > Hi Matt, > > On Sat, 2025-09-06 at 15:42 +0200, Matthieu Baerts wrote: >> Hi Geliang, >> >> On 06/09/2025 02:45, Geliang Tang wrote: >>> On Fri, 2025-09-05 at 20:18 +0200, Matthieu Baerts (NGI0) wrote: >>>> When the MPTCP DATA FIN have been ACKed, there is no more MPTCP >>>> related >>>> metadata to exchange, and all subflows can be safely shutdown. >>>> >>>> Before this patch, the subflows were actually terminated at >>>> 'close()' >>>> time. That's certainly fine most of the time, but not when the >>>> userspace >>>> 'shutdown()' a connection, without close()ing it. When doing so, >>>> the >>>> subflows were staying in LAST_ACK state on one side -- and >>>> consequently >>>> in FIN_WAIT2 on the other side -- until the 'close()' of the >>>> MPTCP >>>> socket. >>>> >>>> Now, when the DATA FIN have been ACKed, all subflows are >>>> shutdown. A >>>> consequence of this is that the TCP 'FIN' flag can be set earlier >>>> now, >>>> but the end result is the same. This affects the packetdrill >>>> tests >>>> looking at the end of the MPTCP connections, but for a good >>>> reason. >>>> >>>> Fixes: 3721b9b64676 ("mptcp: Track received DATA_FIN sequence >>>> number >>>> and add related helpers") >>>> Fixes: 16a9a9da1723 ("mptcp: Add helper to process acks of >>>> DATA_FIN") >>>> Signed-off-by: Matthieu Baerts (NGI0) >>>> --- >>>>  net/mptcp/protocol.c | 16 ++++++++++++++++ >>>>  1 file changed, 16 insertions(+) >>>> >>>> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c >>>> index >>>> 1c26acf6c4145896ecbb5c7f7004121c66a20649..9feb9f437c2bdfff392249e >>>> 7ad0 >>>> 0edd09ba67ac3 100644 >>>> --- a/net/mptcp/protocol.c >>>> +++ b/net/mptcp/protocol.c >>>> @@ -372,6 +372,20 @@ static void mptcp_close_wake_up(struct sock >>>> *sk) >>>>   sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN); >>>>  } >>>>   >>>> +static void mptcp_shutdown_subflows(struct mptcp_sock *msk) >>>> +{ >>>> + struct mptcp_subflow_context *subflow; >>>> + >>>> + mptcp_for_each_subflow(msk, subflow) { >>>> + struct sock *ssk = >>>> mptcp_subflow_tcp_sock(subflow); >>>> + bool slow; >>>> + >>>> + slow = lock_sock_fast(ssk); >>>> + tcp_shutdown(ssk, SEND_SHUTDOWN); >>>> + unlock_sock_fast(ssk, slow); >>>> + } >>>> +} >>>> + >>>>  /* called under the msk socket lock */ >>>>  static bool mptcp_pending_data_fin_ack(struct sock *sk) >>>>  { >>>> @@ -396,6 +410,7 @@ static void mptcp_check_data_fin_ack(struct >>>> sock >>>> *sk) >>>>   break; >>>>   case TCP_CLOSING: >>>>   case TCP_LAST_ACK: >>>> + mptcp_shutdown_subflows(msk); >>>>   mptcp_set_state(sk, TCP_CLOSE); >>>>   break; >>>>   } >>>> @@ -564,6 +579,7 @@ static bool mptcp_check_data_fin(struct sock >>>> *sk) >>>>   mptcp_set_state(sk, TCP_CLOSING); >>>>   break; >>>>   case TCP_FIN_WAIT2: >>>> + mptcp_shutdown_subflows(msk); >>> >>> I think we should not directly call mptcp_shutdown_subflows() >>> within >>> mptcp_check_data_fin() and mptcp_check_data_fin_ack(), but should >>> instead call it after these functions return and the sk state is >>> TCP_CLOSE. This ensures that the original purpose of these two >>> functions remains unchanged. >> >> Thank you for the review. I'm not sure to understand what you mean >> about >> the "original purpose": they both set the appropriated actions when >> DATA_FIN have been received. Here, I do want to shut the subflows >> down >> when the DATA_FIN ACK are received, so that's the good spot, no? >> >> Note that commit 3721b9b64676 ("mptcp: Track received DATA_FIN >> sequence >> number and add related helpers") already had a hint of what should >> have >> been done: see the "Close subflows now?" comment, later removed in >> commit e16163b6e2b7 ("mptcp: refactor shutdown and close"). >> >> Or maybe do you mean their original name "check_data_fin(_ack)" is >> confusing? The "check" here is not just to check if the DATA_FIN >> (ACK) >> was set, but to check actions related to them. > > I mean not to modify mptcp_check_data_fin and mptcp_check_data_fin_ack, > but to check TCP_CLOSE in mptcp_worker(), something like: > > @@ -2749,6 +2749,9 @@ static void mptcp_worker(struct work_struct > *work) > mptcp_check_data_fin_ack(sk); > mptcp_check_data_fin(sk); > > + if (sk->sk_state == TCP_CLOSE) > + mptcp_shutdown_subflows(msk); > + > if (test_and_clear_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags)) > __mptcp_close_subflow(sk); No, we should only do that when receiving the DATA_FIN ACK, when transitioning from FIN_WAIT_2/LAST_ACK to CLOSE. I do think these data_fin functions are the best place, in the operations linked to the state machine, not here in the worker. > Another option is to call mptcp_shutdown_subflows in > mptcp_close_wake_up, which one do you think is better? No, that's not linked to 'waking up the userspace'. Cheers, Matt -- Sponsored by the NGI0 Core fund.