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Date:	Tue, 12 Aug 2014 10:26:35 +0300
From:	Oleksandr Natalenko <oleksandr@...alenko.name>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [BUG] oops in cpufreq driver with AMD Kaveri CPU

Got that and will try to investigate ASAP.

Just to note: I tried to use powersave governor and got the same result. I believe notifiers are used with powersave governor as well. Am I wrong?

On August 12, 2014 9:16:21 AM EEST, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>On Tue, Aug 12, 2014 at 11:25 AM, Oleksandr Natalenko
><oleksandr@...alenko.name> wrote:
>> What should I do to debug it? Is that necessary to recompile kernel
>with full
>> debug?
>
>Yeah, you need to recompile the kernel for sure but not necessarily
>with debug
>support..
>
>Some background:
>
>In cpufreq framework, we manage a CPUs frequency based on the load
>on CPU. You are using ondemand governor which tries to
>increase/decrease frequency
>continuously at fixed intervals.
>
>Now, when we change the frequency we *may* need to communicate this to
>few
>drivers which *may* depend on CPUs frequency for their functioning.
>
>This is handled via notifications.
>
>Other drivers are required to do this:
>cpufreq_register_notifier(&<some-local-struct>,
>CPUFREQ_TRANSITION_NOTIFIER);
>
>to register themselves for frequency-change and them a routine of
>theirs would
>be called from cpufreq-core..
>
>This is exactly where it is crashing for you. i.e. while calling the
>notifier list.
>
>So, you need to check which all notifiers are registered and out of
>those which
>one is crashing..
>
>The first parameter of the above register-call should be declared this
>way:
>
>static struct notifier_block xyz_notifier_block = {
>    .notifier_call = xyz_freq_notifier,
>};
>
>I would have done it this way:
>
>- Add a print in cpufreq_register_notifier() to print the address of
>routine
>present in .notifier_call for case: CPUFREQ_TRANSITION_NOTIFIER
>
>- Then add prints to all the notifiers added for your configuration,
>shouldn't
>be much only 4-5 I believe. i.e. you can add print messages to the
>notifier
>callbacks..
>
>- Then see the sequence/order in which they are called normally, when
>we
>don't crash.. and check that when it crashes..
>
>- You will be able to make out which notifier is crashing. And then we
>can
>see why?
>
>- You can add something like this to notifier routines:
>pr_info("%s\n", __func__);
>
>This will print function name.
>
>>> Which patch are you talking about here?
>>
>> I thought about this one [1], but I guess that's not my case.
>>
>> [1] https://lkml.org/lkml/2014/7/16/815
>
>I guessed so and I don't think it will help as the crashes reported in
>this
>bug-log is something different.

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-- 
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