Re: [RFC PATCH 11/19] cpufreq: assert policy->rwsem is held in __cpufreq_governor

[Saravana Kannan]

On 02/02/2016 06:13 PM, Viresh Kumar wrote:
> On 02-02-16, 13:37, Saravana Kannan wrote:
> > On 02/01/2016 10:34 PM, Viresh Kumar wrote:
> > > What will that solve? It will stay exactly same then as well, as we
> > > would be adding/removing these attributes from within the same
> > > policy->rwsem ..
> >
> > The problem isn't that you are holding the policy rwsem. The problem is that
> > we are trying to grab the same locks in different order. This is trying to
> > fix that.
>
> That's exactly what I was trying to say, sorry for not being very
> clear.
>
> Even if you would move the sysfs file creation thing into the cpufreq
> core, instead of governor, we will have locks this way:
>
> CPU0                            CPU1
> (sysfs read)                    (sysfs dir remove)
> s_active lock                   policy->rwsem
> policy->rwsem
>                                  s_active lock (hang)
>
>
> And so I said, nothing will change.

What's the s_active lock in CPU1 coming from? The only reason it's there 
today is because of the sysfs dir remove. If you move it before the 
policy->rwsem, you won't have it after the policy->rwsem too. So, I 
think it will fix the issue.

-Saravana

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