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 8410CC2D0A3 for ; Thu, 29 Oct 2020 09:10:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 312762076B for ; Thu, 29 Oct 2020 09:10:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603962652; bh=LtTLUdpxG7bjGsCM6IUA5h7OYDjxp2VftjxTgl41aaQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=FkL3M+jZfR5FcC0cMbqqpEL770qEGGPXKBy0JjwL/N3M+xVKyNmO/ZqmkRqila5yO Ks+V1xmFJgKELGsBtWFTmukO5XwHyhdbw3LI0OOAjvw07KM6EIipykersNh6ELssdy xVDi1CWyQqvC+Y4bwP6hgFDMTRJtTVHOiTWuy5YI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725933AbgJ2JKv (ORCPT ); Thu, 29 Oct 2020 05:10:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:53556 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725613AbgJ2JKv (ORCPT ); Thu, 29 Oct 2020 05:10:51 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (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 51EBB206D9; Thu, 29 Oct 2020 09:10:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603962650; bh=LtTLUdpxG7bjGsCM6IUA5h7OYDjxp2VftjxTgl41aaQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=pTmTYwKfEOQppT2Du0O08zinNJTX6DnnIgxTAYMTG7gNuvzUOjxPWM8E0Ln9sYVMw VQb2ZQ3W9T8IL2IMgZlQ6K5aQ/9f6MNW/8p6TbLqQbX8BZA6gZTbUt9aDhId2iP3IR 3+I9ioMnRY4TUpvTHPP2MFHc2N+K/XJtuEDEq/lM= Date: Thu, 29 Oct 2020 09:10:45 +0000 From: Will Deacon To: Qian Cai Cc: "Paul E. McKenney" , 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: <20201029091045.GA29890@willie-the-truck> References: <20201028182614.13655-1-cai@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201028182614.13655-1-cai@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Will