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Date:	Mon, 10 Mar 2014 12:26:53 +0800
From:	Viresh Kumar <>
To:	"Rafael J. Wysocki" <>
Cc:	Aaron Plattner <>,
	"" <>,
	"" <>,
	Linux Kernel Mailing List <>
Subject: Re: [PATCH] cpufreq: use cpufreq_cpu_get to avoid cpufreq_get race conditions

On 6 March 2014 09:23, 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?
>> Fix this by using cpufreq_cpu_get(cpu) to look up the policy rather than reading
>> it out of cpufreq_cpu_data directly.  cpufreq_cpu_get takes the appropriate
>> locks to prevent this race from happening.
>> Since it's possible for policy to be NULL if the caller passes in an invalid CPU
>> number or calls the function before cpufreq is initialized, delete the
>> BUG_ON(!policy) and simply return 0.  Don't try to return -ENOENT because that's
>> negative and the function returns an unsigned integer.
>> Signed-off-by: Aaron Plattner <>
> Viresh, have you seen this?

Sorry for being late. Though I see you have already applied this one,
I will still add this for records :)

Acked-by: Viresh Kumar <>
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