From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: CpuFreq Laptop Scaling broken?
Date: Sat, 6 Sep 2014 00:47:35 +0200 (CEST)
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Cc: Harry van Haaren <harryhaaren@gmail.com>,
	"linux-rt-users@vger.kernel.org" <linux-rt-users@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Carsten Emde <cbe@osadl.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
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On Fri, 5 Sep 2014, Viresh Kumar wrote:

> On 5 September 2014 17:36, Harry van Haaren <harryhaaren@gmail.com> wrote:
> > The down_read_trylock() fails, the other checks are fine.
> 
> So my initial guess was correct :)
> 
> > If i'm understanding correctly, the cpufreq_rwsem locks the module
> > from being unloaded during critical sections while writing to CPU
> > speed etc?
> 
> Its not about changing speed, but its more of a lock for critical sections
> only.. So, yes its required..
> 
> > Would that mean that an un-matched pair of down_read() up_write()
> > could cause the failure of changing CPU speed?
> 
> Probably yes, but why doesn't that happen without rt?

I think Carsten had looked into this.