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

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Date:	Mon, 15 Jul 2013 13:35:56 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
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 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).

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

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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