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 240693730C6 for ; Tue, 11 Nov 2025 17:14:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762881278; cv=none; b=mB/KdTWxXzrvzkDv1HCLJDXffWxlOK0smr3PJAOzW50ZLvdfRkrtgHghWlT5Bw76BfDnBmszFHopXbKODQyCsmbxRXQxleKuxXEPogmE1kSZzh6h/NMD6UP+i4qtS70w9kNu0zfFicSOxbzps0dS1AJo8+0ly/pFeTmfhx/dpvM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762881278; c=relaxed/simple; bh=abCZ/XLB3l6pzgVHFU83kc7KysTtS2brjEOH09VTO1c=; h=Message-ID:Date:MIME-Version:Subject:To:References:From:Cc: In-Reply-To:Content-Type; b=SMJPyH6so+VK2FLxkihrB2gEDAyFyYfP4Qdz61yTDXEKoMiUYwrnnLo7C96HsFEIcXqB5PcW1e/DEmTFh8xRypoT5sK2iXgMnzs4M/50sUwLb4z5PY4dzEoIE3IHZPQanvIjfDMjuyBsc18TtxZYtungyi/v5iEM1tC08veffOE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=L1+cucAq; 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="L1+cucAq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C5DD9C16AAE; Tue, 11 Nov 2025 17:14:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762881277; bh=abCZ/XLB3l6pzgVHFU83kc7KysTtS2brjEOH09VTO1c=; h=Date:Subject:To:References:From:Cc:In-Reply-To:From; b=L1+cucAqww9uUtdPYxDQUt//ThgCecgTDXB8bU3+p1oYmrSBzC/Jis3O2qDyjFLB2 PsCmZxOoOarcMzh0LlpjF+8pd+qNg4hn+S520DOOkGMBr+Ra1yIMmpnMXbNQGC116F vr4EewaGzowuntZj4UXBMcuS18uky8yitMhCUktG5oDP3Vga3FHG/0AFQZw72/CVQt i+Hp9csAw7U4hqBr8Q2BsSMuCcdWI49PeLyuoXz2mTRj/UV/z01eFCVj5P/5NVO2Rl 4h0NNx7u8898LuWwHDtNS2nV+4hvG6zttReXUrIg57e9gRip75coTVRNftx5u/PVkl CsgLSw+LF2gzw== Message-ID: <8e2ae2b2-13b4-4615-be82-eb3710ec566f@kernel.org> Date: Tue, 11 Nov 2025 18:14:34 +0100 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 v2 mptcp-next] Squash-to: "mptcp: leverage the backlog for RX packet processing" Content-Language: en-GB, fr-BE To: Geliang Tang References: <2f6f0b1e22690e962d4fff02838d23d4b8a65f07.camel@kernel.org> From: Matthieu Baerts Cc: Paolo Abeni , mptcp@lists.linux.dev Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Geliang, On 11/11/2025 08:21, Geliang Tang wrote: > Hi Paolo, > > Thanks for this fix. > > On Sun, 2025-11-09 at 14:53 +0100, Paolo Abeni wrote: >> If a subflow receives data before gaining the memcg while the msk >> socket lock is held at accept time, or the PM locks the msk socket >> while still unaccepted and subflows push data to it at the same time, >> the mptcp_graph_subflows() can complete with a non empty backlog. >> >> The msk will try to borrow such memory, but (some) of the skbs there >> where not memcg charged. When the msk finally will return such >> accounted >> memory, we should hit the same splat of #597. >> [even if so far I was unable to replicate this scenario] >> >> This patch tries to address such potential issue by: >> - preventing the subflow from queuing data into the backlog after >>   gaining the memcg. This ensure that at the end of the look all the >>   skbs in the backlog (if any) are _not_ memory accounted. >> - mem charge the backlog to msk >> - 'restart' the subflow and spool any data waiting there. >> >> Signed-off-by: Paolo Abeni >> --- >>  net/mptcp/protocol.c | 46 >> ++++++++++++++++++++++++++++++++++++++++++-- >>  1 file changed, 44 insertions(+), 2 deletions(-) >> >> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c >> index 5e9325c7ea9c..d6b08e1de358 100644 >> --- a/net/mptcp/protocol.c >> +++ b/net/mptcp/protocol.c >> @@ -4082,10 +4082,12 @@ static void mptcp_graph_subflows(struct sock >> *sk) >>  { >>   struct mptcp_subflow_context *subflow; >>   struct mptcp_sock *msk = mptcp_sk(sk); >> + struct sock *ssk; >> + int old_amt, amt; >> + bool slow; >>   >>   mptcp_for_each_subflow(msk, subflow) { >> - struct sock *ssk = mptcp_subflow_tcp_sock(subflow); >> - bool slow; >> + ssk = mptcp_subflow_tcp_sock(subflow); >>   >>   slow = lock_sock_fast(ssk); >>   >> @@ -4095,8 +4097,48 @@ static void mptcp_graph_subflows(struct sock >> *sk) >>   if (!ssk->sk_socket) >>   mptcp_sock_graft(ssk, sk->sk_socket); >>   >> + if (!mem_cgroup_from_sk(sk)) >> + goto unlock; > > I think it's better to use "continue" here, just like in v1, so that > other subflows also have a chance to call mptcp_sock_graft(), but we > need to call unlock_sock_fast() before "continue". Mmh, that's what this code is doing: unlock and continue, no? > Besides, wouldn't it be more appropriate to squash these lines into > "mptcp: fix memcg accounting for passive sockets"? >From what I understood, that's not strickly needed: such check are done in the helpers below: here it is just to avoid doing the same check yet another time for 'subflow->closing = 1'. > >> + >>   __mptcp_inherit_cgrp_data(sk, ssk); >>   __mptcp_inherit_memcg(sk, ssk, GFP_KERNEL); >> + >> + /* Prevent subflows from queueing data into the >> backlog >> + * as soon as cg is set; note that we can't race >> + * with __mptcp_close_ssk setting this bit for a >> really >> + * closing socket, because we hold the msk socket >> lock here. >> + */ >> + subflow->closing = 1; >> + >> +unlock: >> + unlock_sock_fast(ssk, slow); >> + } >> + >> + if (!mem_cgroup_from_sk(sk)) >> + return; >> + >> + /* Charge the bl memory, note that __sk_charge accounted for >> + * fwd memory and rmem only >> + */ >> + mptcp_data_lock(sk); >> + old_amt = sk_mem_pages(sk->sk_forward_alloc + >> +        atomic_read(&sk->sk_rmem_alloc)); >> + amt = sk_mem_pages(msk->backlog_len + sk->sk_forward_alloc + >> +      atomic_read(&sk->sk_rmem_alloc)); > > The code here is not aligned properly. > >> + amt -= old_amt; >> + if (amt) >> + mem_cgroup_sk_charge(sk, amt, GFP_ATOMIC | >> __GFP_NOFAIL); > > I'm not sure if we need to call kmem_cache_charge() here, just like in > __sk_charge(). > > WDYT? > > Thanks, > -Geliang > >> + mptcp_data_unlock(sk); >> + >> + /* Finally let the subflow restart queuing data. */ >> + mptcp_for_each_subflow(msk, subflow) { >> + ssk = mptcp_subflow_tcp_sock(subflow); >> + >> + slow = lock_sock_fast(ssk); >> + subflow->closing = 0; >> + >> + if (mptcp_subflow_data_available(ssk)) >> + mptcp_data_ready(sk, ssk); >>   unlock_sock_fast(ssk, slow); >>   } >>  } > > Cheers, Matt -- Sponsored by the NGI0 Core fund.