linux-kernel - Re: [PATCH 7/8] cpufreq: Preserve policy structure across suspend/resume

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Date:	Mon, 15 Jul 2013 17:23:43 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Viresh Kumar <viresh.kumar@...aro.org>, toralf.foerster@....de,
	robert.jarzmik@...el.com, durgadoss.r@...el.com,
	tianyu.lan@...el.com, lantianyu1986@...il.com,
	dirk.brandewie@...il.com, stern@...land.harvard.edu,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/8] cpufreq: Preserve policy structure across suspend/resume

On 07/15/2013 05:05 PM, Rafael J. Wysocki wrote:
> On Monday, July 15, 2013 03:35:04 PM Srivatsa S. Bhat wrote:
>> On 07/15/2013 03:25 PM, Viresh Kumar wrote:
>>> Hi Srivatsa,
>>>
>>> I may be wrong but it looks something is wrong in this patch.
>>>
>>> On 12 July 2013 03:47, Srivatsa S. Bhat
>>> <srivatsa.bhat@...ux.vnet.ibm.com> wrote:
>>>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>>>
>>>> @@ -1239,29 +1263,40 @@ static int __cpufreq_remove_dev(struct device *dev,
>>>>         if ((cpus == 1) && (cpufreq_driver->target))
>>>>                 __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT);
>>>>
>>>> -       pr_debug("%s: removing link, cpu: %d\n", __func__, cpu);
>>>> -       cpufreq_cpu_put(data);
>>>> +       if (!frozen) {
>>>> +               pr_debug("%s: removing link, cpu: %d\n", __func__, cpu);
>>>> +               cpufreq_cpu_put(data);
>>>
>>> So, we don't decrement usage count here. But we are still increasing
>>> counts on cpufreq_add_dev after resume, isn't it?
>>>
>>> So, we wouldn't be able to free policy struct once all the cpus of a
>>> policy are removed after suspend/resume has happened once.
>>>
>>
>> Actually even I was wondering about this while writing the patch and
>> I even tested shutdown after multiple suspend/resume cycles, to verify that
>> the refcount is messed up. But surprisingly, things worked just fine.
>>
>> Logically there should've been a refcount mismatch and things should have
>> failed, but everything worked fine during my tests. Apart from suspend/resume
>> and shutdown tests, I even tried mixing a few regular CPU hotplug operations
>> (echo 0/1 to sysfs online files), but nothing stood out.
>>
>> Sorry, I forgot to document this in the patch. Either the patch is wrong
>> or something else is silently fixing this up. Not sure what is the exact
>> situation.
> 
> OK, so I'm not going to queue [2-8/8] up until we find out what's going on
> here (and until Toralf tells me that it doesn't break his system any more).
> 

Ok, that sounds good.

> I've queued up [1/8] for 3.11 already.
> 

Thank you!
 
Regards,
Srivatsa S. Bhat

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