From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D24EC4363A for ; Thu, 29 Oct 2020 14:09:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1656F20825 for ; Thu, 29 Oct 2020 14:09:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603980588; bh=TtwUVFFMG65oBFG7U1vALVcKONIwt0CrlaLqNEzbKoE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=mSTTTI561IKflXEARn8AjNvULZcSEB7f+64FlFiqS28qEtBqfgT0GKi89rgdXkRp1 n/+6hmKs0pManVY/t4q4RMh14mfFY4t7uTKIqAhYezRaaw5HujfUVL01VGa+YDK06+ qBuBoCVczY7gS8mCDjmKWNJrteEYCznZprMdVJP4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726740AbgJ2OJr (ORCPT ); Thu, 29 Oct 2020 10:09:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:44604 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726291AbgJ2OJq (ORCPT ); Thu, 29 Oct 2020 10:09:46 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BF82F2076B; Thu, 29 Oct 2020 14:09:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603980585; bh=TtwUVFFMG65oBFG7U1vALVcKONIwt0CrlaLqNEzbKoE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=iJ1u9s0abfgaRCyv9SyeMUvmqdIxY7ECdRh5+mF8LW2zNX5SL5jW3tM2tUBrvU01M lIQNNCDAjm1o/WVXseCu+QwqP3AaGdcN1oi5K7dyUjmO/9oy9VQoIqk/yRBM9zwwYs axPwxcQ6hh2h9qvnX7jtSfFXMJcPqGHt969QyoxU= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 5ADA23522778; Thu, 29 Oct 2020 07:09:45 -0700 (PDT) Date: Thu, 29 Oct 2020 07:09:45 -0700 From: "Paul E. McKenney" To: Will Deacon Cc: Qian Cai , Peter Zijlstra , Catalin Marinas , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64/smp: Move rcu_cpu_starting() earlier Message-ID: <20201029140945.GK3249@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201028182614.13655-1-cai@redhat.com> <20201029091045.GA29890@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201029091045.GA29890@willie-the-truck> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 29, 2020 at 09:10:45AM +0000, Will Deacon wrote: > On Wed, Oct 28, 2020 at 02:26:14PM -0400, Qian Cai wrote: > > The call to rcu_cpu_starting() in secondary_start_kernel() is not early > > enough in the CPU-hotplug onlining process, which results in lockdep > > splats as follows: > > > > WARNING: suspicious RCU usage > > ----------------------------- > > kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!! > > > > other info that might help us debug this: > > > > RCU used illegally from offline CPU! > > rcu_scheduler_active = 1, debug_locks = 1 > > no locks held by swapper/1/0. > > > > Call trace: > > dump_backtrace+0x0/0x3c8 > > show_stack+0x14/0x60 > > dump_stack+0x14c/0x1c4 > > lockdep_rcu_suspicious+0x134/0x14c > > __lock_acquire+0x1c30/0x2600 > > lock_acquire+0x274/0xc48 > > _raw_spin_lock+0xc8/0x140 > > vprintk_emit+0x90/0x3d0 > > vprintk_default+0x34/0x40 > > vprintk_func+0x378/0x590 > > printk+0xa8/0xd4 > > __cpuinfo_store_cpu+0x71c/0x868 > > cpuinfo_store_cpu+0x2c/0xc8 > > secondary_start_kernel+0x244/0x318 > > > > This is avoided by moving the call to rcu_cpu_starting up near the > > beginning of the secondary_start_kernel() function. > > Hmm, it's not really a move though -- we'll end up calling this thing twice > afaict. It would be better to make sure we've called notify_cpu_starting() > early enough. Can we do that instead? It uses a per-CPU variable so that RCU pays attention only to the first call to rcu_cpu_starting() if there is more than one of them. This is even intentional, due to there being a generic arch-independent call to rcu_cpu_starting() in notify_cpu_starting(). So multiple calls to rcu_cpu_starting() are fine by design. Thanx, Paul