From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751389AbbCEEUO (ORCPT ); Wed, 4 Mar 2015 23:20:14 -0500 Received: from e8.ny.us.ibm.com ([32.97.182.138]:43620 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750817AbbCEEUM (ORCPT ); Wed, 4 Mar 2015 23:20:12 -0500 Message-ID: <54F7D974.8030208@linux.vnet.ibm.com> Date: Thu, 05 Mar 2015 09:50:04 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Peter Zijlstra CC: Nicolas Pitre , tglx@linutronix.de, linux-kernel@vger.kernel.org, mingo@kernel.org, rjw@rjwysocki.net, Michael Ellerman Subject: Re: [PATCH 32/35] clockevents: Fix cpu down race for hrtimer based broadcasting References: <20150216121435.203983131@infradead.org> <20150216122413.880378334@infradead.org> <20150221124659.GG23367@worktop.ger.corp.intel.com> <20150223161457.GA5029@twins.programming.kicks-ass.net> <54EEAFCF.4080208@linux.vnet.ibm.com> <54F02F81.10901@linux.vnet.ibm.com> <20150302145635.GN21418@twins.programming.kicks-ass.net> In-Reply-To: <20150302145635.GN21418@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15030504-0029-0000-0000-0000022AAEB1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/02/2015 08:26 PM, Peter Zijlstra wrote: > On Fri, Feb 27, 2015 at 02:19:05PM +0530, Preeti U Murthy wrote: >> The problem reported in the changelog of this patch is causing severe >> regressions very frequently on our machines for certain usecases. It would >> help to put in a fix in place first and then follow that up with these >> cleanups. A fix on the below lines : > > Regression how? Neither Thomas' Changelog, nor yours mention its a > regression. > > If its a (recent) Regression you need to have a Fixes tag at the very > least. So when was this broken and by which patch? > It was found recently when doing a hotplug stress test on POWER, that the machine hits lockups spewing NMI watchdog: BUG: soft lockup - CPU#20 stuck for 23s! [swapper/20:0] or INFO: rcu_sched detected stalls on CPUs/tasks: { 2 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 2 4 25 26 27 28 29 30 31} (detected by 6, t=2102 jiffies, g=1617, c=1616, q=1441) and many other messages about lockups. This issue was reported here: http://linuxppc.10917.n7.nabble.com/offlining-cpus-breakage-td88619.html and was traced to commit 7cba160ad789a powernv/cpuidle: Redesign idle states management, which exposed the loophole in commit 5d1638acb9f6(tick: Introduce hrtimer based broadcast) and is reported in the changelog of the patch. Regards Preeti U Murthy