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 46E703EE1F7 for ; Thu, 19 Mar 2026 16:48:20 +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=1773938901; cv=none; b=mkT3Z93GAhqxxQBZZg+TEt4l+zhRBbCUSqz3d7co+fLrJ3kribTaMsVDYQUQDXAKKv2xl1EeaIBECRJTBmsiDPeUsvC61JHuKBS9T93a6bfdJ5SigsafXg74vY+xnrc8FZHT6/zXHr2ingvcsakyHewPaP/MaBiMT84LVJhBrRk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773938901; c=relaxed/simple; bh=BW+s1tfvjSzvorY/ZLwBEykUFgF+GdVyXuLp1ysnz7k=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ih2ibI61/NTg8AcfZOicuPh3WtjAO9YaYU2cmIpcaymoxzeW7wk10pSoW1a5lSbHOuSMHMjunVykROtnwgT//0Y0IbZLj6Ap+aqB+f7yxl+aJlijTkvIi5zFT+7nlRVHzK5GlKe3iQmj5qZIkhzSeheZ13dGre+wtusCfwAAHBE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AU4z0T0l; 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="AU4z0T0l" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6468BC4AF0B; Thu, 19 Mar 2026 16:48:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773938900; bh=BW+s1tfvjSzvorY/ZLwBEykUFgF+GdVyXuLp1ysnz7k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=AU4z0T0ly3DCHb/hQwHCEWHIPXFk7kOJvVELPtGaFh+sliuK9/Rv2s80VtauVUTfg 1IDkgg26BBUwNnxsPRJWl3YZGD50OMKxvoIX83bP5lk9CVenO5jeAGcUrTwxR3oV8D 8OBgwJqWH4Fo5rCZJbGeH1LeYMdQ8O8ZfN2/9GLfTIAKHLbenKZQ+DqwrUWayCsj9p bbXNYZTr9KTJ46kv4dGTqAFaAQDp1G7bLYpaO/SnRZojWcr3oIJuFpf2zm+cl0XLh6 yxy286MPKQ7cy5JMOHGI7SKO/MNa4Tv1wJdaiiK7WnPhGjOsU8LCpCNi0Wbjad1yjN 5i2cidYoSEpzA== Received: from phl-compute-12.internal (phl-compute-12.internal [10.202.2.52]) by mailfauth.phl.internal (Postfix) with ESMTP id 1C889F40073; Thu, 19 Mar 2026 12:48:18 -0400 (EDT) Received: from phl-frontend-04 ([10.202.2.163]) by phl-compute-12.internal (MEProxy); Thu, 19 Mar 2026 12:48:18 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefgedrtddtgdeftdejheefucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfurfetoffkrfgpnffqhgenuceu rghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujf gurhepfffhvfevuffkfhggtggujgesthdtredttddtvdenucfhrhhomhepuehoqhhunhcu hfgvnhhguceosghoqhhunheskhgvrhhnvghlrdhorhhgqeenucggtffrrghtthgvrhhnpe ekgffhhfeuheelhfekteeuffejveetjeefffettedtteegfefftdduteduudfgleenucev lhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpegsohhquhhnod hmvghsmhhtphgruhhthhhpvghrshhonhgrlhhithihqdduieejtdelkeegjeduqddujeej keehheehvddqsghoqhhunheppehkvghrnhgvlhdrohhrghesfhhigihmvgdrnhgrmhgvpd hnsggprhgtphhtthhopeduhedpmhhouggvpehsmhhtphhouhhtpdhrtghpthhtohepsghi ghgvrghshieslhhinhhuthhrohhnihigrdguvgdprhgtphhtthhopehjohgvlhgrghhnvg hlfhesnhhvihguihgrrdgtohhmpdhrtghpthhtohepphgruhhlmhgtkheskhgvrhhnvghl rdhorhhgpdhrtghpthhtohepfhhrvgguvghrihgtsehkvghrnhgvlhdrohhrghdprhgtph htthhopehnvggvrhgrjhdrihhithhruddtsehgmhgrihhlrdgtohhmpdhrtghpthhtohep uhhrvgiikhhisehgmhgrihhlrdgtohhmpdhrtghpthhtohepsghoqhhunhdrfhgvnhhgse hgmhgrihhlrdgtohhmpdhrtghpthhtoheprhgtuhesvhhgvghrrdhkvghrnhgvlhdrohhr ghdprhgtphhtthhopehmvghmgihorhesghhmrghilhdrtghomh X-ME-Proxy: Feedback-ID: i8dbe485b:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 19 Mar 2026 12:48:17 -0400 (EDT) Date: Thu, 19 Mar 2026 09:48:16 -0700 From: Boqun Feng To: Sebastian Andrzej Siewior Cc: Joel Fernandes , paulmck@kernel.org, frederic@kernel.org, neeraj.iitr10@gmail.com, urezki@gmail.com, boqun.feng@gmail.com, rcu@vger.kernel.org, Kumar Kartikeya Dwivedi , Tejun Heo , bpf@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , John Fastabend Subject: Re: Next-level bug in SRCU implementation of RCU Tasks Trace + PREEMPT_RT Message-ID: References: <3c4c5a29-24ea-492d-aeee-e0d9605b4183@nvidia.com> <20260319090315.Ec_eXAg4@linutronix.de> <20260319163350.c7WuYOM9@linutronix.de> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260319163350.c7WuYOM9@linutronix.de> On Thu, Mar 19, 2026 at 05:33:50PM +0100, Sebastian Andrzej Siewior wrote: > On 2026-03-19 09:27:59 [-0700], Boqun Feng wrote: > > On Thu, Mar 19, 2026 at 10:03:15AM +0100, Sebastian Andrzej Siewior wrote: > > > Please just use the queue_delayed_work() with a delay >0. > > > > > > > That doesn't work since queue_delayed_work() with a positive delay will > > still acquire timer base lock, and we can have BPF instrument with timer > > base lock held i.e. calling call_srcu() with timer base lock. > > > > irq_work on the other hand doesn't use any locking. > > Could we please restrict BPF somehow so it does roam free? It is > absolutely awful to have irq_work() in call_srcu() just because it > might acquire locks. > I agree it's not RCU's fault ;-) I guess it'll be difficult to restrict BPF, however maybe BPF can call call_srcu() in irq_work instead? Or a more systematic defer mechanism that allows BPF to defer any lock holding functions to a different context. (We have a similar issue that BPF cannot call kfree_rcu() in some cases IIRC). But we need to fix this in v7.0, so this short-term fix is still needed. Regars, Boqun > > Regards, > > Boqun > > > Sebastian