Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2]

[skannan@codeaurora.org]

Viresh Kumar wrote:
> On 5 August 2014 01:46, Saravana Kannan <skannan@codeaurora.org> wrote:
>> The problem is when between one thread trying to cat a governor's file
>> (say,
>> sampling_rate) vs the governor getting a POLICY_EXIT.
>
> I don't see two threads racing against each other here. Simply changing
> the governor from conservative->ondemand creates this.
>
> Or is it that the kernel is detecting two different orders of taking lock?
>
> But during governor change, isn't the sysfs lock taken first as we are
> storing a value to "scaling_governor"? So, isn't this a sysfs lock first
> in all cases?
>
> In short, I am still unclear about the *exact* problem here.
>
>> Could you please look at my policy free/remove patches? If you can do
>> that,
>> I can work on a fix for this. It might also be simpler to fix after my
>> patch
>> series (not sure, might be).
>
> I had an overall look of those on the day you posted them, but haven't
> commented yet as was going away..
>
> There is no way those can land in 3.17-rc1 atleast and so we still have
> some time to get them pushed..
>
> Anyway, they are my number two priority and the number one is this bug,
> which we have to fix in stable kernels as well. So, a dependency on your
> series wouldn't work..

Sigh... ok. I too will try to fix this one. I already have something in
mind for this.

Looks like Srivatsa has gone off the grid too. I'm hoping at least one of
you can do a review of my series. Come on guys, not everyone has to work
on the same patch/issue. :-(

-Saravana

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