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 81A6A23F397 for ; Mon, 17 Mar 2025 13:57:25 +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=1742219845; cv=none; b=A8S5/sWISTU7Iz/lBKd0awLsaL9DbBAl+B4PlnpLVId4X6zutOs4bGyNq1n/rhN3j+h14yw9ae3KzZZmGLG/XNpIquHgjfT86z80ZmypF5m6rmR3a0ONPcbRBSfNEICKb9wY0yM8yS9VeT+dWoHukhxW/Bxa990p58JatHYueLc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742219845; c=relaxed/simple; bh=bNAAkrfg4wow3GDy11flt+3iMQJukTUQceLM3KmFIOw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=u4fmwmXQH23rfGFGBVsz6uGd4SKoBKCZiKViiBQfgBl/kNYLxAcC20D/fYbvvg98Fo5r6hgd7Hrzl/ZwypdpFJj2DNsbEHW+ts3EIZDZuVvZit7qw4QQ3byb81MhJY9WU4/AqAKhtPRn3AYTF7O8W5ZZNkK2FSYvOU27bVjCV3s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KzlckITA; 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="KzlckITA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 16060C4CEE3; Mon, 17 Mar 2025 13:57:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1742219845; bh=bNAAkrfg4wow3GDy11flt+3iMQJukTUQceLM3KmFIOw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=KzlckITAKcFsYaVmhtCwV8QV0zPr+O02zs6P1tBErsT7TGtBp7Kty6cX9Mgmefrfv 13QSv5GOuurtF51QW/IQ6poTxNlwSgq3xfvjmGq4LmbJTikhCs6FbzMCg29ajUsH71 01Jvg3XXDcET+mHLJ5eByLZQ2cLSPSmUsED/jdxGkr9f2Bx36iMpP1HG5eQAByrzj7 kP1izrNCvXWoMaZqXrfvOJV5UKkhwNptAv1gUl0kHYE4wV842Cqr9lK0RHUWL+j95J Fpzt1+LIGY/DKk5defhbJNgUfbxMFtddWKRPnnfV4Bq3MS2SfPRgaVOVRnR3R7+6HO NqZya4M94qCwQ== Message-ID: <459fd93c-d99d-4733-9194-3f62467854c6@kernel.org> Date: Mon, 17 Mar 2025 14:57:21 +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 mptcp-next v3 1/2] mptcp: add bpf_iter_task for mptcp_sock Content-Language: en-GB To: Geliang Tang , Mat Martineau Cc: Geliang Tang , mptcp@lists.linux.dev References: <2b680d20eb5873f14f35d9d23aa78b2f5a9d5bfd.camel@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Geliang, On 17/03/2025 11:59, Geliang Tang wrote: > Hi Matt, > > On Mon, 2025-03-17 at 11:29 +0100, Matthieu Baerts wrote: >> Hi Geliang, Mat, >> >> On 17/03/2025 10:41, Geliang Tang wrote: >>> On Mon, 2025-03-10 at 11:30 +0800, Geliang Tang wrote: >>>> From: Geliang Tang >>>> >>>> To make sure the mptcp_subflow bpf_iter is running in the >>>> MPTCP context. This patch adds a simplified version of tracking >>>> for it: >>>> >>>> 1. Add a 'struct task_struct *bpf_iter_task' field to struct >>>> mptcp_sock. >>>> >>>> 2. Do a WRITE_ONCE(msk->bpf_iter_task, current) before calling >>>> a MPTCP BPF hook, and WRITE_ONCE(msk->bpf_iter_task, NULL) after >>>> the hook returns. >>>> >>>> 3. In bpf_iter_mptcp_subflow_new(), check >>>> >>>> "READ_ONCE(msk->bpf_scheduler_task) == current" >>>> >>>> to confirm the correct task, return -EINVAL if it doesn't match. >>>> >>>> Also creates helpers for setting, clearing and checking that >>>> value. (...) >>>> +static inline bool mptcp_check_bpf_iter_task(struct mptcp_sock >>>> *msk) >>>> +{ >>>> + struct task_struct *task = READ_ONCE(msk- >>>>> bpf_iter_task); >>>> + >>>> + if (task && task == current) >>>> + return true; >>>> + return false; >>>> +} >>> >>> This v3 has a bug. When I was testing MPTCP BPF selftests in a >>> loop, I >>> found that the test would break in some cases. After debugging, I >>> found >>> that "task" and "current" were not equal: >>> >>> [  520.209749][T11984] MPTCP: bpf_iter_mptcp_subflow_new >>> msk=00000000fc8f7370 in_interrupt=0 task=00000000ef28139f >>> current=0000000024db2987 >>> >>> I will try to fix it, but haven't found a solution yet. >> >> (sorry for the delay, I need a bit of time to catch up) >> >> I talked a bit to Alexei Starovoitov last week. He told me that with >> the >> BPF struct_ops, it is possible to tell the verifier that some locks >> are >> taken either by some struct_ops types, or even per callbacks of some >> specific struct_ops (WIP on sched_ext side). It is also possible to >> get >> some locks automatically (polymorphism), and there are examples on >> VFS side. > > Thanks for your reminder, I will look at these BPF codes. Our goal is > to make mptcp_subflow bpf_iter only used by struct_ops defined by MPTCP > BPF (bpf_mptcp_sched_ops and bpf_mptcp_pm_ops), right? Other struct_ops > are not allowed to use mptcp_subflow bpf_iter. Yes, that's correct. I didn't check, but **maybe** some mptcp_sched_ops and mptcp_pm_ops callback might not be allowed to use bpf_iter. In this case, it might be needed to allow only some of them to use bpf_iter. Note that it sounds like all mptcp_{pm,sched}_ops callbacks should be done while holding the msk lock, e.g. being called from the worker and not from a subflow event, etc. but maybe there are some exceptions needed. >> In other words, it means we don't need to add this "bpf_iter_task", >> there are other techniques, but I don't have more details, and I >> didn't >> check in the code. If it is not clear for you and you don't find  >> other >> examples elsewhere (sched_ext? check WIP patches maybe?), then Alexei >> said we should not hesitate to ask questions on the BPF mailing list. > > We can send "Add mptcp_subflow bpf_iter support" v3 to the BPF mailing > list and ask questions during the reviewing process. Indeed. I hope to be able to find a bit of time this week to send the v3. Cheers, Matt -- Sponsored by the NGI0 Core fund.