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 28F30199BB for ; Tue, 10 Oct 2023 12:28:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="C31Ha2c4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 626AEC433C7; Tue, 10 Oct 2023 12:28:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1696940898; bh=8/7/MDrHlV/FW0bghA3h/lPCmGh1Zc1qSklo5IMvUDw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=C31Ha2c4MSP+E0kQ1VMqaVsi6nSvfXQin8Vdjw3kq3KQaen9i57wj7szYs2Zsnei/ WKLOeXCAa9S3f2RWlLSTj0LkFs40Tde7ECZS0pi7ID3WdFaghVg1RuZ6U6fhVXCgge qCYcLCCo99cEF1qAtJ0RgYQ/6oOVMECpRQdS3JeSJXCA3xWaUDboLuYJ0WFOiyekqG WfjeO1SVKS9wbfdjeM/zp8Q3IRPFPNuO3XX0p1g96dnZB++owehLYmt0amyyqWs7P+ 9pCbWc45IETkQLXYEULGC5/Gp2ZNdmhssBysZsvNMmoUnWy22n7ADYG1AS+0QVrsPE cLxsRSfUg0QVg== Message-ID: <3b95c712-82f1-4d97-97cd-4015f23ae931@kernel.org> Date: Tue, 10 Oct 2023 14:28:15 +0200 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 mptcp-next v11 1/4] mptcp: set next subflow to msk->first Content-Language: en-GB, fr-BE To: Geliang Tang Cc: mptcp@lists.linux.dev References: <6a31565e01d3474be56bdf62c54d0c20c065c65c.1696760702.git.geliang.tang@suse.com> <6c266459-dbba-4bda-b868-b5bcdaf351b0@kernel.org> <20231008123313.GA8315@localhost> <20231010060403.GA6593@localhost.localdomain> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Geliang, On 10/10/2023 08:04, Geliang Tang wrote: > On Sun, Oct 08, 2023 at 04:05:10PM +0200, Matthieu Baerts wrote: >> Hi Geliang, >> >> On 08/10/2023 14:33, Geliang Tang wrote: >>> On Sun, Oct 08, 2023 at 01:11:32PM +0200, Matthieu Baerts wrote: >>>> Hi Geliang, >>>> >>>> +cc Paolo >>>> >>>> On 08/10/2023 12:27, Geliang Tang wrote: >>>>> When closing the msk->first socket in __mptcp_close_ssk(), the original >>>>> behaviour is to reset this socket. But if there's another subflow available >>>>> in this case, it's better to set the first available subflow to msk->first, >>>>> instead of resetting the msk->first. >>>> >>>> I don't think we want to do that. If I remember well, we want to keep >>>> having 'msk->first' pointing to the initial subflow for various reasons >>>> (I don't remember exactly). >>>> >>>> I think what we want to do is not to reset the initial subflow if there >>>> are other subflows still available and we don't want to set it to 'NULL' >>>> in such case. >>> >>> Is it like this: >>> >>> if (ssk == msk->first && !msk->pm.subflows) >>> WRITE_ONCE(msk->first, NULL); > > The code: > > if (ssk == msk->first && list_is_singular(&msk->conn_list)) > WRITE_ONCE(msk->first, NULL); > > works, no NULL pointer crash with this now. I update it into v12. If I'm not mistaken, we can only set 'msk->first' back to NULL when closing the MPTCP connection. We cannot do that if there are other subflows still alive. >> No, we cannot set it to NULL nor release it but we should avoid the >> "reset" being sent. >> >> I don't have access to the code for the moment but by looking at your >> patch, I would say you should not modify 'dispose_it' nor 'msk->first' >> but maybe check if you can avoid calling 'mptcp_subflow_ctx_reset()' if >> '!dispose_it', maybe by checking something like >> 'list_is_singular(&msk->conn_list)'? (I think you should avoid looking >> at the PM structure here). > > Something like this, right: > > * disconnect should never fail > */ > WARN_ON_ONCE(tcp_disconnect(ssk, 0)); > - mptcp_subflow_ctx_reset(subflow); > + list_is_singular(&msk->conn_list) > + mptcp_subflow_ctx_reset(subflow); > release_sock(ssk); > > goto out; > > This doesn't work, if we only avoid calling mptcp_subflow_ctx_reset, > tcp_disconnect will send a RST too. Sorry, yes I meant to say if we should skip both, tcp_disconnect() included. We should only close the connection but not release it. (or we need to close, then call disconnect? I didn't check that) Cheers, Matt -- Tessares | Belgium | Hybrid Access Solutions www.tessares.net