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 15:06:01 +0800 Message-ID: <5199CB59.1020309@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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5199C990.3020602@linux.vnet.ibm.com> Sender: cpufreq-owner@vger.kernel.org To: Borislav Petkov Cc: Tejun Heo , "Paul E. McKenney" , Jiri Kosina , Frederic Weisbecker , Tony Luck , linux-kernel@vger.kernel.org, x86@kernel.org, Thomas Gleixner , rjw@sisk.pl, Viresh Kumar , cpufreq@vger.kernel.org, linux-pm@vger.kernel.org List-Id: linux-pm@vger.kernel.org On 05/20/2013 02:58 PM, Michael Wang wrote: > On 05/20/2013 02:47 PM, Borislav Petkov wrote: >> On Mon, May 20, 2013 at 02:23:37PM +0800, Michael Wang wrote: >>> On 05/20/2013 12:50 PM, Borislav Petkov wrote: >>>> On Mon, May 20, 2013 at 11:16:33AM +0800, Michael Wang wrote: >>>>> I suppose the reason is that the cpu we passed to >>>>> mod_delayed_work_on() has a chance to become offline before we >>>>> disabled irq, what about check it before send resched ipi? like: >>>> >>>> I think this is only addressing the symptoms - what we should be doing >>>> instead is asking ourselves why are we even scheduling work on a cpu if >>>> the machine goes offline? >>>> >>>> I don't know though who should be responsible for killing all that >>>> work - the workqueue itself or the guy who created it, i.e. cpufreq >>>> governor... >>> >>> So there are two questions here: >>> 1. Is gov_queue_work() want to queue the work on offline cpu? >>> 2. Is mod_delayed_work_on() allow offline cpu? >>> >>> I guess both should be false? >> >> Well, if we don't allow queueing work on a cpu which goes offline, i.e. >> #2, the problem should be solved. > > I've take a look at the usage of queue_delayed_work_on() and > mod_delayed_work_on(), mostly passed this_cpu, or those in online mask, > I think offline cpu is not by designed. > > Besides, the cpu gov_queue_work() is using 'policy->cpus' which seems to > be updated during UP DOWN notify, I think they are supposed to be online. > > But we need expert in cpufreq to confirm all these... And I guess this may help to reduce the chance to trigger WARN: diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c index 443442d..0f96013 100644 --- a/drivers/cpufreq/cpufreq_governor.c +++ b/drivers/cpufreq/cpufreq_governor.c @@ -180,7 +180,7 @@ 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 { - for_each_cpu(i, policy->cpus) + for_each_cpu_and(i, policy->cpus, cpu_online_mask) __gov_queue_work(i, dbs_data, delay); } } Well, disable irq will be better, anyway...still need folks who own that driver to make the decision, so let's CC them :) Regards, Michael Wang > > Regards, > Michael Wang > >> >> Tejun? >> >> Here are the splats: http://marc.info/?l=linux-kernel&m=136879901425951 >> > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >