From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Wang Subject: Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2 Date: Mon, 20 May 2013 17:24:05 +0800 Message-ID: <5199EBB5.7060209@linux.vnet.ibm.com> References: <20130509125040.GF27333@pd.tnic> <20130509125859.GG27333@pd.tnic> <20130515184528.GO4442@linux.vnet.ibm.com> <20130515224358.GF11783@pd.tnic> <20130515235512.GT4442@linux.vnet.ibm.com> <20130517135641.GF23035@pd.tnic> <51999591.8030401@linux.vnet.ibm.com> <20130520045023.GA12690@pd.tnic> <5199C169.7060504@linux.vnet.ibm.com> <20130520064727.GD12690@pd.tnic> <5199C990.3020602@linux.vnet.ibm.com> <5199CB59.1020309@linux.vnet.ibm.com> <5199CFD0.9030101@linux.vnet.ibm.com> <5199E54D.7030407@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from e28smtp05.in.ibm.com ([122.248.162.5]:56871 "EHLO e28smtp05.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752097Ab3ETJYT (ORCPT ); Mon, 20 May 2013 05:24:19 -0400 Received: from /spool/local by e28smtp05.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 20 May 2013 14:50:06 +0530 In-Reply-To: Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Viresh Kumar Cc: Borislav Petkov , Tejun Heo , "Paul E. McKenney" , Jiri Kosina , Frederic Weisbecker , Tony Luck , linux-kernel@vger.kernel.org, x86@kernel.org, Thomas Gleixner , rjw@sisk.pl, cpufreq@vger.kernel.org, linux-pm@vger.kernel.org On 05/20/2013 05:09 PM, Viresh Kumar wrote: > On 20 May 2013 14:26, Michael Wang wrote: >> On 05/20/2013 03:25 PM, Michael Wang wrote: >>> Yeah, that's right, I guess the issue is, although the policy->cpus is >>> correct at a given time, after get cpu from it, it's possible to be >>> changed, unless we disabled preempt or irq, or hotplug before we use it... >>> >>> Like such issue cases: >>> get x from policy->cpus >>> DOWN notifier >>> change policy->cpus >>> do offline x >>> send ipi to x >>> >>> Will that happen? > > Sorry I am not sure. :( > > I can see mutex being used in cpufreq_governor.c which should take care > of race conditions... > >> May be we could do some test to confirm it? >> >> diff --git a/drivers/cpufreq/cpufreq_governor.c >> b/drivers/cpufreq/cpufreq_governor.c >> index 443442d..449be88 100644 >> --- a/drivers/cpufreq/cpufreq_governor.c >> +++ b/drivers/cpufreq/cpufreq_governor.c >> @@ -26,6 +26,7 @@ >> #include >> #include >> #include >> +#include >> >> #include "cpufreq_governor.h" >> >> @@ -180,8 +181,10 @@ void gov_queue_work(struct dbs_data *dbs_data, >> struct cpufreq_policy *policy, >> if (!all_cpus) { >> __gov_queue_work(smp_processor_id(), dbs_data, delay); >> } else { >> + get_online_cpus(); >> for_each_cpu(i, policy->cpus) >> __gov_queue_work(i, dbs_data, delay); >> + put_online_cpus(); >> } >> } >> EXPORT_SYMBOL_GPL(gov_queue_work); >> >> This is supposed to make WARN disappear, if it works, then BINGO :) > > Let people test it and then we can talk :) Agree :) Borislav, would you like to take a try? If this fix cause other troubles, you could try get_cpu() or disable irq also. Regards, Michael Wang >