linux-kernel - Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send

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Date:	Mon, 20 May 2013 16:56:45 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Viresh Kumar <viresh.kumar@...aro.org>, Tejun Heo <tj@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>, rjw@...k.pl,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule,
 round 2

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?

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 <linux/tick.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
+#include <linux/cpu.h>

 #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 :)

Regards,
Michael Wang

> 
> Regards,
> Michael Wang
> 
> 
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