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 EE4C336C587 for ; Tue, 11 Nov 2025 16:21:24 +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=1762878085; cv=none; b=OUx35Cm2l6N5F3ve2WCwvrjG+zwxf2YqvnAFGvNMLDY+Qw+hD1EseMHGqrJWC94eAtxusGD/T+ExhfO9Rz3PZ/DyYrlxCKemD6zp++uYhjRGQfeTPQ+Xs+45XDrxSoSkMDH0sDN/LrmEGO3TBS+cEywVmFR6zzYPdkdG6LKA3hc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762878085; c=relaxed/simple; bh=u26maQ0nwiVW/Xk5u9yHntcgSsE6XMdO2olI060Cgso=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=ixRQXK9eP4qsChEnVqKGJONhBo7RN2tqPQd9+JMjiqvmqey7bj89nShqKE4WXxuK/9okbFf4Yewf3/sjXsP0GjAmYDOTScIdwwk7HT5MCkRODr1fRFgGo6WYiIBS6/SmpKkfT13wrJclkTYg9itULlHi55TBcosUy38KzB0DCp4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GOE9waaS; 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="GOE9waaS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34ECEC4CEF5; Tue, 11 Nov 2025 16:21:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762878084; bh=u26maQ0nwiVW/Xk5u9yHntcgSsE6XMdO2olI060Cgso=; h=Date:Subject:To:References:From:In-Reply-To:From; b=GOE9waaSogD4b/ZAscbZo/LkAqLi+5Sdls1C2XA6K/EAEMS0j0fVR7MyiSoC9LLSD iEWL3A1PzEf5IZhkZFLoXe4mHXAEP2x6VPbOYxTb1sVscmfp6z52MvPR83qVuxp3/A NtjpfmmTAlzMhWJSB1/95BGVZYnGtvyr4HcQbKcvQEdVGPYwP/HsgZVCXOe6ogd/FU 2p841dL6ktCZYce334ZIBRs86sFq9qqvUl4R8dpNWZEXgevSq965Urr+VXJhqzs6fP gehJR4jmvUzvWUP8No8TAUvXzyW0+kZvjimk37i7x9s+dD4t0jwWxJz3me3I54zBs1 I+Hrt9rb/i4vg== Message-ID: <704b4358-30b2-4065-abbb-752f4f9a3c79@kernel.org> Date: Tue, 11 Nov 2025 17:21:22 +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: Paolo Abeni , mptcp@lists.linux.dev References: From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Paolo, On 09/11/2025 14:53, 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)) Should we not call mem_cgroup_sk_enabled() instead? It does this: return mem_cgroup_sockets_enabled && mem_cgroup_from_sk(sk); That's what is done in net/core/sock.c and net/ipv4/tcp_output.c. Not in __inet_accept(), because mem_cgroup_sockets_enabled() is checked before. Maybe we should do the same here? (Note that it is not clear to me if mem_cgroup can be enabled later on, and if yes, what should be done with existing connections.) > + goto unlock; > + > __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)) Same here? > + 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)); (Same as Geliang for the alignment here, and eventually calling kmem_cache_charge() like in __inet_accept()) > + amt -= old_amt; > + if (amt) > + mem_cgroup_sk_charge(sk, amt, GFP_ATOMIC | __GFP_NOFAIL); Just to be sure: no need to check if there was an error? It is not done in __inet_accept() either, so I guess no? > + 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.