linux-kernel - Re: [PATCH 5/7] cpufreq: balance out cpufreq_cpu_{get,put} for scaling drivers using setpolicy

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Date:	Wed, 06 Feb 2013 08:11:03 -0800
From:	Dirk Brandewie <dirk.brandewie@...il.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	Dirk Brandewie <dirk.brandewie@...il.com>,
	linux-kernel@...r.kernel.org, cpufreq@...r.kernel.org,
	Dirk Brandewie <dirk.j.brandewie@...el.com>
Subject: Re: [PATCH 5/7] cpufreq: balance out cpufreq_cpu_{get,put} for scaling
 drivers using setpolicy

On 02/05/2013 06:45 PM, Viresh Kumar wrote:
> On 6 February 2013 07:38, Dirk Brandewie <dirk.brandewie@...il.com> wrote:
>> On 02/05/2013 05:58 PM, Viresh Kumar wrote:
>>>
>>> On Tue, Feb 5, 2013 at 11:54 PM,  <dirk.brandewie@...il.com> wrote:
>>>>
>>>> From: Dirk Brandewie <dirk.brandewie@...il.com>
>>>>
>>>> There is an additional reference added to the driver in
>>>> cpufreq_add_dev()  that is removed in__cpufreq_governor() if the
>>>>
>>>> driver implements target().  Remove the last reference when the
>>>> driver implements setpolicy()
>>>>
>>>> Signed-off-by: Dirk Brandewie <dirk.j.brandewie@...el.com>
>>>>
>>>> ---
>>>>    drivers/cpufreq/cpufreq.c |    3 +++
>>>>    1 files changed, 3 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>>>> index 622e282..d17477b 100644
>>>> --- a/drivers/cpufreq/cpufreq.c
>>>> +++ b/drivers/cpufreq/cpufreq.c
>>>> @@ -1049,6 +1049,9 @@ static int __cpufreq_remove_dev(struct device *dev,
>>>> struct subsys_interface *sif
>>>>
>>>>           if (cpufreq_driver->target)
>>>>                   __cpufreq_governor(data, CPUFREQ_GOV_STOP);
>>>>
>>>> +       if (cpufreq_driver->setpolicy)
>>>> +               cpufreq_cpu_put(data);
>>>
>>>
>>> I don't understand this patch at all.. I grepped both cpufreq_cpu_get() &
>>> put()
>>> in bleeding-edge and found everything to be correct.
>>>
>>> Can you please point me to the exact line numbers ?
>>>
>>
>> Line 878 in cpufreq_add_dev()
>
> Following is line 878:
>
> 	for_each_online_cpu(sibling) {
> 		struct cpufreq_policy *cp = per_cpu(cpufreq_cpu_data, sibling);
> 		if (cp && cpumask_test_cpu(cpu, cp->related_cpus))
> 			return cpufreq_add_policy_cpu(cpu, sibling, dev);
> 	}
>
> How is this related to your patch?
>
our files are clearly out of sync :-)  The code in cpufreq_add_dev() is
#ifdef CONFIG_SMP
	/* check whether a different CPU already registered this
	 * CPU because it is in the same boat. */
	policy = cpufreq_cpu_get(cpu);
	if (unlikely(policy)) {
		cpufreq_cpu_put(policy);
		return 0;
	}

The reference added by this cpufreq_cpu_get() is finally dropped in 
__cpufreq_remove_dev() with the call to __cpufreq_governor()

	if (driver->target)
		__cpufreq_governor(data, CPUFREQ_GOV_STOP);

Without this change I hang at:
		pr_debug("waiting for dropping of refcount\n");
		wait_for_completion(cmp);

--Dirk
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