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=-8.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 A6DDCC55179 for ; Fri, 6 Nov 2020 10:39:14 +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 2A4AA20702 for ; Fri, 6 Nov 2020 10:39:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="eNam0eQy"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="Wyh+J6ql" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2A4AA20702 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=4Bnzagklf6YeRmVzAffVqRbzPfaKh/m046CnDKBs+Eg=; b=eNam0eQy019/ZgG95T46F76M9 x0xg4BEocs3Y6+DNe47jmNRFYXR9liqnO691YmPku19gwrUlR8NoSTSeHRE7M2uLJLr3L5M65Ee/c 4CPju43RZfgBpxHyZ38Jkw3SjIGuS1FZE2sh5RAHPV2gdEp9DKRLnyE/Ay1bRYkGRnPaXzJ8cURIJ pmC+nEZpmLVdPQYyHo034c4JA0MY28cUwHr+HTyDFULGVBCxvkyIjxxcmy58H63ARyKJQJqckZHU8 R9rDz51ClhtTnPm+Brq4OhyXCSf3ecNIpAhTkW06NsU7aNqn824z23RUjXBUwST/ERPzgG8SOunWi BQ9HVId9A==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kaz8C-00054H-Fr; Fri, 06 Nov 2020 10:38:08 +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 1kaz87-000528-0V for linux-arm-kernel@lists.infradead.org; Fri, 06 Nov 2020 10:38:05 +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 73ECD20702; Fri, 6 Nov 2020 10:38:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604659082; bh=96sVWS8VO/ONFzQ6FJE2fVYD3WeXWxXGoalF8Bg6h0w=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Wyh+J6qlrauKrR/bERnNw4Y+vAInAXAPR/KcIYirYfG3g+VypK3ZSInJI+i2fM8cT qhlM59AfksNVPWlt3cZDeYImQWV8NDsVnFm/YK7XtWNar0toedXmM9YVi1rZok7Alq Gz4XqBMmVMAI4ilfaN8TJfxKsASoHHU6RhepPiVE= Date: Fri, 6 Nov 2020 10:37:56 +0000 From: Will Deacon To: Qian Cai Subject: Re: [PATCH] arm64/smp: Move rcu_cpu_starting() earlier Message-ID: <20201106103755.GA9729@willie-the-truck> References: <20201028182614.13655-1-cai@redhat.com> <160404559895.1777248.8248643695413627642.b4-ty@kernel.org> <20201105222242.GA8842@willie-the-truck> <3b4c324abdabd12d7bd5346c18411e667afe6a55.camel@redhat.com> <20201105232813.GR3249@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: 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-20201106_053803_322702_02F7905F X-CRM114-Status: GOOD ( 30.64 ) 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: paulmck@kernel.org, Peter Zijlstra , catalin.marinas@arm.com, linux-kernel@vger.kernel.org, kernel-team@android.com, linux-arm-kernel@lists.infradead.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, Nov 05, 2020 at 09:15:24PM -0500, Qian Cai wrote: > On Thu, 2020-11-05 at 15:28 -0800, Paul E. McKenney wrote: > > 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: > > > > 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? > I don't think that is an issue here. cpu_die_early() set CPU_STUCK_IN_KERNEL, > and then __cpu_up() will see a timeout waiting for the AP online and then deal > with CPU_STUCK_IN_KERNEL according. Thus, something like this? I don't see > anything in rcu_report_dead() depends on CONFIG_HOTPLUG_CPU=y. Cheers both for suggesting rcu_report_dead(). > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c > index 09c96f57818c..10729d2d6084 100644 > --- a/arch/arm64/kernel/smp.c > +++ b/arch/arm64/kernel/smp.c > @@ -421,6 +421,8 @@ void cpu_die_early(void) > > update_cpu_boot_status(CPU_STUCK_IN_KERNEL); > > + rcu_report_dead(cpu); I think this is in the wrong place, see: https://lore.kernel.org/r/20201106103602.9849-1-will@kernel.org which seems to fix the problem for me. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel