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

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Message-ID: <CAKohponAkh4ZHSp_NwCSK8B0bS_sh3ttUugDQwboo98p6unWnw@mail.gmail.com>
Date:	Mon, 20 May 2013 15:54:35 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Michael Wang <wangyun@...ux.vnet.ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jiri Kosina <jkosina@...e.cz>, Tony Luck <tony.luck@...el.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux PM mailing list <linux-pm@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule,
 round 2

On 20 May 2013 15:10, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 20 May 2013 15:01, Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com> wrote:
>> And Viresh, in the regular hotplug paths, the call to gov_cancel_work() is
>> supposed to kill any pending workqueue functions pertaining to offline CPUs
>> right?
>
> Yes.. It will cancel work for all cpus first and will start again for
> online cpus again.
>
>> Could there be a synchronization bug somewhere due to which this
>> might not be happening properly?
>
> Not sure.. I have seen mutex's are used well in cpufreq_governor.. don't know
> if I missed something.

Borislav,

Can you try below change to see if the issue is still present? (Untested)

diff --git a/drivers/cpufreq/cpufreq_governor.c
b/drivers/cpufreq/cpufreq_governor.c
index 7532570..b9ae5f6 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -359,7 +359,9 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                if (dbs_data->cdata->governor == GOV_CONSERVATIVE)
                        cs_dbs_info->enable = 0;

+               mutex_lock(&cpu_cdbs->timer_mutex);
                gov_cancel_work(dbs_data, policy);
+               mutex_unlock(&cpu_cdbs->timer_mutex);

                mutex_lock(&dbs_data->mutex);
                mutex_destroy(&cpu_cdbs->timer_mutex);
--
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