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=-8.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS 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 251E9C388F7 for ; Thu, 5 Nov 2020 23:02:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A073920A8B for ; Thu, 5 Nov 2020 23:02:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Yh0a9Cgk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732488AbgKEXC5 (ORCPT ); Thu, 5 Nov 2020 18:02:57 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:20300 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731899AbgKEXC5 (ORCPT ); Thu, 5 Nov 2020 18:02:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604617376; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=JnHZYUF/teL6IX1yin+oJWg9fIjSJKlhuSAPesf84sw=; b=Yh0a9Cgk7GeqyaoauE9JBGwjf588Nr4lkRlr/t/pEymITO7ed0nEz2RueY3vd6vhmsmcTC 0u/cT95zTjJP6CPR4EThR8sl2frt+NSk0gukkiwrq0YOmY9XGD3RgHxmCNTbUIkkLiY56R o3Gwm0eLc6HvF8NFfBpjv0dNX+R4UIc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-592-IDS3vivjNVanTsHcHtjzIg-1; Thu, 05 Nov 2020 18:02:52 -0500 X-MC-Unique: IDS3vivjNVanTsHcHtjzIg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 09DFD6D242; Thu, 5 Nov 2020 23:02:51 +0000 (UTC) Received: from ovpn-114-171.rdu2.redhat.com (ovpn-114-171.rdu2.redhat.com [10.10.114.171]) by smtp.corp.redhat.com (Postfix) with ESMTP id 46A0C6198D; Thu, 5 Nov 2020 23:02:50 +0000 (UTC) Message-ID: <3b4c324abdabd12d7bd5346c18411e667afe6a55.camel@redhat.com> Subject: Re: [PATCH] arm64/smp: Move rcu_cpu_starting() earlier From: Qian Cai To: Will Deacon , "Paul E. McKenney" Cc: catalin.marinas@arm.com, kernel-team@android.com, Peter Zijlstra , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Date: Thu, 05 Nov 2020 18:02:49 -0500 In-Reply-To: <20201105222242.GA8842@willie-the-truck> References: <20201028182614.13655-1-cai@redhat.com> <160404559895.1777248.8248643695413627642.b4-ty@kernel.org> <20201105222242.GA8842@willie-the-truck> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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?