linux-kernel - Re: [PATCH] cpufreq: Call __cpufreq_governor() with correct policy->cpus mask

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Date:	Thu, 11 Apr 2013 23:34:03 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, robin.randhawa@....com,
	Steve.Bannister@....com, Liviu.Dudau@....com,
	charles.garcia-tobin@....com, arvind.chauhan@....com,
	linaro-kernel@...ts.linaro.org, patches@...aro.org
Subject: Re: [PATCH] cpufreq: Call __cpufreq_governor() with correct policy->cpus mask

On Thursday, April 11, 2013 01:34:53 PM Viresh Kumar wrote:
> __cpufreq_governor() must be called with correct policy->cpus mask. In
> __cpufreq_remove_dev() we initially clear policy->cpus with cpumask_clear_cpu()
> and then call __cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT). In case
> governor is doing some per-cpu stuff in EXIT callback, this can create uncertain
> behavior.
> 
> Generic governors in drivers/cpufreq/ doesn't do any per-cpu stuff in EXIT
> callback and so we don't face any issues currently. But its better to keep the
> code clean, so we don't face any issues in future.
> 
> Now, we call cpumask_clear_cpu() only when multiple cpus are managed by policy.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>

Applied.

Thanks,
Rafael


> ---
>  drivers/cpufreq/cpufreq.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index fd97a62..3564947 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1105,7 +1105,9 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
>  
>  	WARN_ON(lock_policy_rwsem_write(cpu));
>  	cpus = cpumask_weight(data->cpus);
> -	cpumask_clear_cpu(cpu, data->cpus);
> +
> +	if (cpus > 1)
> +		cpumask_clear_cpu(cpu, data->cpus);
>  	unlock_policy_rwsem_write(cpu);
>  
>  	if (cpu != data->cpu) {
> 
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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