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SubjectRe: Regression on cpufreq in v3.12-rc1
On 09/20/2013 03:05 PM, Viresh Kumar wrote:
> On 20 September 2013 14:19, Viresh Kumar <viresh.kumar@linaro.org> wrote:
>> Hmm... Remember I told you last time that I have another way of fixing
>> it up, probably we need that now..
>>
>> I wanted to add another variable to reflect if a cpufreq_driver is registered
>> or not, and if not then return early from these routines..
>>
>> I will get that in now, please see if you can give it a try..
>>
>> But I am still surprised how are we reaching this place before your cpufreq
>> driver gets registered..
>
> Once we know what's going on in your system, please test attached patch
> (Will send it separately once you have tested it):
>
> commit 389fbc3c8ad7c339cd2d9572d73c355b7b967823
> Author: Viresh Kumar <viresh.kumar@linaro.org>
> Date: Fri Sep 20 14:55:31 2013 +0530
>
> cpufreq: check cpufreq driver is valid and cpufreq isn't disabled
> in cpufreq_get()
>
> cpufreq_get() can be called from external drivers which might not
> be aware if
> cpufreq driver is registered or not. And so we should actually
> check if cpufreq
> driver is registered or not and also if cpufreq is active or
> disabled, at the
> beginning of cpufreq_get().
>
> Otherwise call to lock_policy_rwsem_read() might hit BUG_ON(!policy).
>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

The patch looks reasonable to me. Earlier cpufreq_cpu_get() used to do the
necessary checks, but commit 6eed9404 removed the call to that function in
cpufreq_get(). So adding those checks back seem like the right fix to me.
Also, looking at commit 6eed9404, I think show() and store() also suffer
from a similar fate. So do you think we need to add these checks there as well?
I'm not sure, since I can't think of a situation in which show() or store()
can be invoked before the cpufreq-driver is registered.. or, is such a
situation possible with cpufreq_disabled()?

Regards,
Srivatsa S. Bhat

> ---
> drivers/cpufreq/cpufreq.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 82ecbe3..db004a8 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1460,6 +1460,9 @@ unsigned int cpufreq_get(unsigned int cpu)
> {
> unsigned int ret_freq = 0;
>
> + if (cpufreq_disabled() || !cpufreq_driver)
> + return -ENOENT;
> +
> if (!down_read_trylock(&cpufreq_rwsem))
> return 0;
>



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