linux-kernel - Re: [LOCKDEP] cpufreq: possible circular locking dependency detected

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Date:	Mon, 15 Jul 2013 10:46:53 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...en8.de>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [LOCKDEP] cpufreq: possible circular locking dependency detected

On 07/14/2013 11:56 PM, Rafael J. Wysocki wrote:
[snip]
>> +
>> +	/*
>> +	 * Since there is no lock to prvent re-queue the
>> +	 * cancelled work, some early cancelled work might
>> +	 * have been queued again by later cancelled work.
>> +	 *
>> +	 * Flush the work again with dbs_data->queue_stop
>> +	 * enabled, this time there will be no survivors.
>> +	 */
>> +	if (round)
>> +		goto redo;
> 
> Well, what about doing:
> 
> 	for (round = 2; round; round--)
> 	  	for_each_cpu(i, policy->cpus) {
> 	  		cdbs = dbs_data->cdata->get_cpu_cdbs(i);
> 	  		cancel_delayed_work_sync(&cdbs->work);
> 	  	}
> 
> instead?
> 

It could works, while I was a little dislike to use nested 'for' logical...

Anyway, seems like we have not solved the issue yet, so let's put these
down and focus on the fix firstly ;-)

Regards,
Michael Wang

>> +	dbs_data->queue_stop = 0;
>>  }
>>  
>>  /* Will return if we need to evaluate cpu load again or not */
>> diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h
>> index e16a961..9116135 100644
>> --- a/drivers/cpufreq/cpufreq_governor.h
>> +++ b/drivers/cpufreq/cpufreq_governor.h
>> @@ -213,6 +213,7 @@ struct dbs_data {
>>  	unsigned int min_sampling_rate;
>>  	int usage_count;
>>  	void *tuners;
>> +	int queue_stop;
>>  
>>  	/* dbs_mutex protects dbs_enable in governor start/stop */
>>  	struct mutex mutex;
>>
> 
> 

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