Re: [PATCH Resend] cpufreq: Set cpufreq_cpu_data to NULL before putting kobject

Viresh Kumar
2015-02-02T03:43:10Z

On 2 February 2015 at 09:08, ethan zhao <ethan.zhao@oracle.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