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=-10.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 3A46FC388F7 for ; Thu, 5 Nov 2020 23:28:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D339A20715 for ; Thu, 5 Nov 2020 23:28:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604618895; bh=uW+s9tk8sFCHpIi1ccM7lmNw5WWhWb4a2EYXNp87zEM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=xojyUUlUqXhNsfnrFsGbkE312mY71Gq/w4qRFI8IkoCjBaxdqb4kQJPm8y/X+LXEE rS3lObOQAMhjFay2tjxZigQylrgCFCYQKIBXNaDI3lFBI4YEBO5JTbKe7pVDkDoudv amVp2uhfTY4G9hRIc26fKoucR1QBGgXoACYgxMyw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732200AbgKEX2O (ORCPT ); Thu, 5 Nov 2020 18:28:14 -0500 Received: from mail.kernel.org ([198.145.29.99]:41476 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729784AbgKEX2O (ORCPT ); Thu, 5 Nov 2020 18:28:14 -0500 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 8B2FD20704; Thu, 5 Nov 2020 23:28:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604618893; bh=uW+s9tk8sFCHpIi1ccM7lmNw5WWhWb4a2EYXNp87zEM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=rA6UeTi7wirfhxjAkj1CmQNLIOBtEWWKe2kidYVtIWNkUdVfmQzDMsM14sljW8/cz JvyABj0PmLNKek5rqbJRUUuIrSOFFxzYlvyn+4fb1fDLGsJJxHx5I1SqOzz7v5Bn4g m6RLj6ykMVGcvKrtmWUMbK0nHRZRmnInrGHF7hoY= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 4D0AD3522A76; Thu, 5 Nov 2020 15:28:13 -0800 (PST) Date: Thu, 5 Nov 2020 15:28:13 -0800 From: "Paul E. McKenney" To: Qian Cai Cc: Will Deacon , catalin.marinas@arm.com, kernel-team@android.com, Peter Zijlstra , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] arm64/smp: Move rcu_cpu_starting() earlier Message-ID: <20201105232813.GR3249@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201028182614.13655-1-cai@redhat.com> <160404559895.1777248.8248643695413627642.b4-ty@kernel.org> <20201105222242.GA8842@willie-the-truck> <3b4c324abdabd12d7bd5346c18411e667afe6a55.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3b4c324abdabd12d7bd5346c18411e667afe6a55.camel@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 05, 2020 at 06:02:49PM -0500, Qian Cai wrote: > On Thu, 2020-11-05 at 22:22 +0000, Will Deacon wrote: > > On Fri, Oct 30, 2020 at 04:33:25PM +0000, Will Deacon wrote: > > > On Wed, 28 Oct 2020 14:26:14 -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!! > > > > > > > > [...] > > > > > > Applied to arm64 (for-next/fixes), thanks! > > > > > > [1/1] arm64/smp: Move rcu_cpu_starting() earlier > > > https://git.kernel.org/arm64/c/ce3d31ad3cac > > > > Hmm, this patch has caused a regression in the case that we fail to > > online a CPU because it has incompatible CPU features and so we park it > > in cpu_die_early(). We now get an endless spew of RCU stalls because the > > core will never come online, but is being tracked by RCU. So I'm tempted > > to revert this and live with the lockdep warning while we figure out a > > proper fix. > > > > What's the correct say to undo rcu_cpu_starting(), given that we cannot > > invoke the full hotplug machinery here? Is it correct to call > > rcutree_dying_cpu() on the bad CPU and then rcutree_dead_cpu() from the > > CPU doing cpu_up(), or should we do something else? > It looks to me that rcu_report_dead() does the opposite of rcu_cpu_starting(), > so lift rcu_report_dead() out of CONFIG_HOTPLUG_CPU and use it there to rewind, > Paul? Yes, rcu_report_dead() should do the trick. Presumably the earlier online-time CPU-hotplug notifiers are also unwound? Thanx, Paul