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 8F3932F6577 for ; Tue, 11 Nov 2025 17:09:19 +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=1762880960; cv=none; b=HftklwPnKAutQHdvUmEgXT3a0NyiDyjRGV4a+PyRdRyhXHrOJel6YHqV+S4UQFw5zZ3VrvSmVUECYj97warmNF/uqC2sD/hzPiRCkub+QqBl+qRVrp9rkC4MxmDJosLXMNDwwt3Xu+LcYD/qYmDBNuY3rd3yySP0D4O+WSVB+po= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762880960; c=relaxed/simple; bh=hsV8BnXNoXMpLuJq477hMITIPi6J30lBo7E3cH2DrJI=; h=Message-ID:Date:MIME-Version:Subject:From:To:References: In-Reply-To:Content-Type; b=TlRL57eFVeUg5SqDFRkLCmvTQKpDFx1lGXqqPC/6MT1VAyKa8lAStCjNUyg5MstGRhrM/leAEn7OcxyW9DdKB7JQuzIl63poDraKjCQA8ccINanjtk4MneUXHYaBuon+KAKDK2hH/Uq1xGzVOh7BFAD88KLhobq8SPhSiT4rj84= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RJymFrqS; 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="RJymFrqS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8BC49C116D0; Tue, 11 Nov 2025 17:09:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762880959; bh=hsV8BnXNoXMpLuJq477hMITIPi6J30lBo7E3cH2DrJI=; h=Date:Subject:From:To:References:In-Reply-To:From; b=RJymFrqS2oQvoM4m5VtPxJvDTJyn8KsSk4kZcWgAqW0gRtWe/6r3mgBYj6h7isVn7 yuPCw+AmxQdI8kNBa1tFg0JcwofhDzmARtwPbYwQ09YUjSJdg2U+yYWkIwFPjmDjfs U+t7MDxahdA6197atEZwF+K9bJH22rIFteIx2Go5J3XUuWPC9z6/GNI6UdYuCwvcLR K+J5Mw/GxFMJv93oAKdFVA5vD1vWIBD1WYt3B/oUn5z//ZcQUDZ0ksSchB41ROdXKc PkS4Mk9zCvOSjDslJb5Sm4zTyf/FLXNMecCQHuQe1hiPDOYPoB8StwXpMnSLTCV9ua 9sHawMVgMrycA== Message-ID: <9558784a-bb5b-417a-b758-da9ccda80f8b@kernel.org> Date: Tue, 11 Nov 2025 18:09:16 +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 From: Matthieu Baerts To: Paolo Abeni , mptcp@lists.linux.dev References: <704b4358-30b2-4065-abbb-752f4f9a3c79@kernel.org> Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Paolo, On 11/11/2025 17:21, Matthieu Baerts wrote: > 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.) Also, do you not still need to call __mptcp_inherit_cgrp_data() even if !mem_cgroup_sockets_enabled() (or !mem_cgroup_from_sk())? I guess the two are often linked, but can they not be used independently? Cheers, Matt > >> + 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); >> } >> } -- Sponsored by the NGI0 Core fund.