linux-kernel - Re: [PATCH Resend] cpufreq: Set cpufreq_cpu

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Date:	Mon, 2 Feb 2015 09:13:04 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	ethan zhao <ethan.zhao@...cle.com>
Cc:	Rafael Wysocki <rjw@...ysocki.net>,
	santosh shilimkar <santosh.shilimkar@...cle.com>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH Resend] cpufreq: Set cpufreq_cpu_data to NULL before
 putting kobject

On 2 February 2015 at 09:08, ethan zhao <ethan.zhao@...cle.com> wrote:
>> We take cpufreq_driver_lock() here, and so this will
>> block thread B.
>
>  No, there is no  cpufreq_driver_lock acquired between
>
>  cpufreq_cpu_get()  and cpufreq_cpu_put()

I am not saying that the lock is taken between them. But within
cpufreq_cpu_get() to make sure policy doesn't get freed while we
are doing kobject_get().

>>>             beginning the deference of policy        Thread B:
>>>             ... ... __cpufreq_remove_dev_finish()
>>> cpufreq_policy_free(policy);
>>>
>>>
>>> Perhaps move policy->rwsem out side the policy structure is a way to
>>> avoid
>>> it completely.
>>> and you could stopping the PPC thread stepping forward as my patch as
>>> temporary workaround.
>>
>> I couldn't understand your problem completely. Apart from giving a
>> detailed
>> look of what's going on both threads, always specify where the BUG
>> actually
>> is..
>
> The problem is you are using a rwsem inside policy structure to protect its
> assessment, that is bad design.

What is the current bug you are facing right now, I haven't understood it well.
Also a lock within the structure isn't new. Its all over the kernel. I
don't understand
why you say its a bad design.

--
viresh
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