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

ethan zhao
2015-02-02T03:56:58Z

On 2015/2/2 11:43, Viresh Kumar wrote:
> 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().
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