linux-kernel - Re: [PATCH] cpufreq: use cpufreq_cpu_get to avoid cpufreq

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Date:	Thu, 06 Mar 2014 13:30:57 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Aaron Plattner <aplattner@...dia.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: use cpufreq_cpu_get to avoid cpufreq_get race conditions

On Wednesday, March 05, 2014 05:14:26 PM Aaron Plattner wrote:
> On 03/05/14 17:23, Rafael J. Wysocki wrote:
> > On Tuesday, March 04, 2014 12:42:15 PM Aaron Plattner wrote:
> >> If a module calls cpufreq_get while cpufreq is initializing, it's possible for
> >> it to be called after cpufreq_driver is set but before cpufreq_cpu_data is
> >> written during subsys_interface_register.  This happens because cpufreq_get
> >> doesn't take the cpufreq_driver_lock around its use of cpufreq_cpu_data.
> >
> > Is this a theoretical race, or can you actually reproduce it?  If so, on what
> > system/driver?  Or are there any bug reports related to this you can point me
> > to?
> 
> It reproduces on my Arch Linux system at home with the nvidia driver, 
> and there has been at least one bug report that looks like the same thing:
> 
> https://bbs.archlinux.org/viewtopic.php?id=177934
> 
> I reproduced the problem with v3.13.5, then applied this change and was 
> able to boot successfully 10/10 times.  So I guess that means you can add
> 
> Tested-by: Aaron Plattner <aplattner@...dia.com>

Tested-by is not needed if you're the author.

Everybody should test their patches, right? ;-)

I'll mark it for 3.13-stable and add the link above to the changelog.

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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