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=-5.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 8E796C55178 for ; Fri, 30 Oct 2020 08:15:45 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1950C22210 for ; Fri, 30 Oct 2020 08:15:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="3gqj6r2S"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="puxtbR9u" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1950C22210 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=+8ghypYX5lqswlC4kg5iIUUgqyDMXFtIi2BQjEobxEs=; b=3gqj6r2SP4Q6vKuKKGSVoQ2UJ /PmUIw6jPmrNu3c87US5ryeTLpYTD9rnv8SQarbwcLY8HqEOd0qbWi+Khz2sYsfOe7xwZMrWQ5hnk 2dITkDi4iy4mPeLAqmYK1mktA2ff36vRYKYz8XWta/HBEi2MPZlv8vs0rAS2lR2Ed8s+nfLpX4+uS wMZ/ruy0yADgHCYVHHUYt+o9s1ewh2cny7bKh8iGOrdGxiAXrRvKBgPQGtQ1BUiZLQCt3HUma0qVn jf8WUPWGqyYh4iSbA71NJhfWtXDIpYobvdMLWTWuTGXNMyhwTeyaW92GXyPico46kdD7tj4edx11n C1s4rkDZQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kYPZ4-0002WF-Bj; Fri, 30 Oct 2020 08:15:14 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kYPZ1-0002VT-QD for linux-arm-kernel@lists.infradead.org; Fri, 30 Oct 2020 08:15:12 +0000 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 2AD2E22210; Fri, 30 Oct 2020 08:15:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604045710; bh=cL84aTK/24ewPnTFSjlH1fNL1pJ9MsG620CFfJNX3hk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=puxtbR9uUjZdyiWmr+4ZjxFAl5O73WsfJab2/kLDNZ+sfSxEzyodJct4Nl5f3Lgki jdSjgsmj/W02Zmw9YROYXNke9y2R3lRYKmV6/Mnvg3p0PVRAypCt2PxkNY/eQ3zm3Z bX886FXedwZ3u007WJI2ZQKvsQQlQ+39Po1kXIik= Date: Fri, 30 Oct 2020 08:15:05 +0000 From: Will Deacon To: Qian Cai Subject: Re: [PATCH] arm64/smp: Move rcu_cpu_starting() earlier Message-ID: <20201030081505.GA32066@willie-the-truck> References: <20201028182614.13655-1-cai@redhat.com> <20201029091045.GA29890@willie-the-truck> <4375b3c87d91af36509291ec18e98ed41420ec41.camel@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4375b3c87d91af36509291ec18e98ed41420ec41.camel@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201030_041511_993225_087806CF X-CRM114-Status: GOOD ( 25.13 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Zijlstra , Catalin Marinas , linux-arm-kernel@lists.infradead.org, "Paul E. McKenney" , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 29, 2020 at 09:17:35AM -0400, Qian Cai wrote: > On Thu, 2020-10-29 at 09:10 +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? > > Paul mentioned that it is fine to call rcu_cpu_starting() multiple times, and > Peter mentioned that CPU bringup is complicated. Thus, I thought about doing > something safe here. > > I tested a bit of patch below which seems fine, but I can't tell for sure if it > is safe. Any suggestion? No, you're right -- this does look dodgy as I think we'll end up kicking the CPU notifiers before things like CPU errata have been figured out. So I'll pick up your original patch with Paul's ack. Thanks! Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel