From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-183.mta0.migadu.com (out-183.mta0.migadu.com [91.218.175.183]) (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 6A58D24C06A for ; Fri, 28 Nov 2025 15:27:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.183 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764343659; cv=none; b=u7yvgtTzyEkn9pStV7gmuU0dFK1tbQLKetVIypA4HthmRl0N+VdMRdjDBS4Hg7zDfp4jAXjoRjOy6vz+iOzuAdHLuDCyHJj9IEpumsIzeRRvapzvPKYM34c/a54wp5GTOm7ARbTyYGGqRxF0XmUu2qvZDFc5zYPCVQpnvT77ceM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764343659; c=relaxed/simple; bh=d0UU7120GMC1pIY5MTl7O8DhaCxjBCqdmMA7uhKFgoY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=SMhbNPO00eELxd96wM/W1c46RHcpb6xp7XX2mWSZcbOoRn1kzmXD4kOAiwF01Cx9eN+JXTMAZY/2dwE4EzpgGxzHlsgilAGa/l+eCl+jiQLr9xWfz/5KQP77S2K01E3y+8lVRAZMe/wueJgfbBrZZ693cQ2P4bCyCeV5Pwldu2c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=SAZn80rl; arc=none smtp.client-ip=91.218.175.183 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="SAZn80rl" Date: Fri, 28 Nov 2025 23:27:10 +0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1764343653; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=dXu5n4/4VvQeBIc/KeE3YDcQqJx7qhaKkJlGMpgYWJM=; b=SAZn80rlXckWwFrtKQKU/Co3p8Dbkwr1YNZCeQhlu25G3NH44J46lhSfIEFb6u8D9JCg7b uPBhwACh6pUCuURkbHhoyQqOP3BgFlLrfCUd3J3DgT0cjk+k/nvCLWV9jWz5PqPDI8NMyi hzQaLuZZ4baLjJnOdU7I+dwQDkjynYY= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: GangYan To: Paolo Abeni Cc: mptcp@lists.linux.dev, Gang Yan Subject: Re: [PATCH mptcp-net] mptcp: sync the msk->sndbuf at accept() time Message-ID: References: <20251128094417.14463-1-gang.yan@linux.dev> Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT > On Fri, Nov 28, 2025 at 03:53:54PM +0100, Paolo Abeni wrote: > On 11/28/25 10:44 AM, Gang Yan wrote: > > From: Gang Yan > > Hi Paoto, So glad to receive your messages. > > After an MPTCP connection is established, the sk_sndbuf of client's msk > > can be updated through 'subflow_finish_connect'. However, the newly > > accepted msk on the server side has a small sk_sndbuf than > > msk->first->sk_sndbuf: > > > > ''' > > MPTCP: msk:00000000e55b09db, msk->sndbuf:20480, msk->first->sndbuf:2626560 > > ''' > > How do you observe the above exactly? subflow-level rcvbuf increases - I observe this through an normal test, using server to send MSG DONTWAIT messages to the client once the connection is established. In fact, we can use the 'send_recv_data'’in mptcp's bpfselftest with MSG DONTWAIT flag. > in tcp_new_space() - are propagated to the msk via: > > ssk->sk_write_space -> subflow_write_space -> mptcp_propagate_sndbuf. > Yes, but the 'tcp_sndbuf_extend' also called in 'tcp_init_buffer_space' immediately after connection enters established state. The client side is updated via: "subflow_finish_connect' -> 'mptcp propagate_state'. But the server side seems need to update msk->sk_sndbuf too. > > This means that when the server immediately sends MSG_DONTWAIT data to > > the client after the connection is established, it is more likely to > > encounter EAGAIN. > > It's unclear to me how the subflow rcvbuf can be greater than default > before sending any data. I raised an issue in multpath-tcp/mptcp-net-next, and post some information here, maybe it is helpful; https://github.com/multipath-tcp/mptcp_net-next/1ssues/602 Thanks Gang > > /P > >