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

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Date:	Mon, 02 Feb 2015 11:56:36 +0800
From:	ethan zhao <ethan.zhao@...cle.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
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 2015/2/2 11:43, Viresh Kumar wrote:
> 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().
  How to prevent the policy to be freed between

cpufreq_cpu_get()  and cpufreq_cpu_put() ?

>>>>              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.
You are maxing up the water with sand ?

Thanks,
Ethan

>
> --
> viresh

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