linux-kernel - Re: [PATCH v6 1/2] cpufreq: split the cpufreq_driver

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Message-ID: <20130402145536.GA31757@gulag1.americas.sgi.com>
Date:	Tue, 2 Apr 2013 09:55:36 -0500
From:	Nathan Zimmer <nzimmer@....com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Nathan Zimmer <nzimmer@....com>, rjw@...k.pl,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/2] cpufreq: split the cpufreq_driver_lock and use
	the rcu

On Tue, Apr 02, 2013 at 10:35:46AM +0530, Viresh Kumar wrote:
> On 2 April 2013 01:41, Nathan Zimmer <nzimmer@....com> wrote:
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> 
> > +static struct cpufreq_driver __rcu *cpufreq_driver;
> > +static DEFINE_SPINLOCK(cpufreq_driver_lock);
> 
> You really need this lock? This is only used in cpufreq_register_driver
> and unregister_driver... And it doesn't protect other routines at all. And
> because we are using rcu stuff now, probably this lock is just not required.
> 
The lock is unneeded if we expect register and unregister driver to not be
called from muliple threads at once.  I didn't make that assumption.

> > +static DEFINE_SPINLOCK(cpufreq_data_lock);
> 
> Only this one is required and it can be the rwlock which is already pushed
> by rafael.
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