Re: [PATCH] cpufreq: Make cpufreq_quick_get() safe to call.

[Rafael J. Wysocki]

On Thursday, March 10, 2016 04:10:36 PM Richard Cochran wrote:
> The function, cpufreq_quick_get, accesses the global 'cpufreq_driver' and
> its fields without taking the associated lock, cpufreq_driver_lock.
> 
> Without the locking, nothing guarantees that 'cpufreq_driver' remains
> consistent during the call.  This patch fixes the issue by taking the lock
> before accessing the data structure.
> 
> Cc: Dirk Brandewie <dirk.brande...@gmail.com>
> Cc: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
> Cc: Viresh Kumar <viresh.ku...@linaro.org>
> Signed-off-by: Richard Cochran <rcoch...@linutronix.de>

Can you please CC PM-related patches to linux...@vger.kernel.org?  They
are much easier to handle for me then.

> ---
>  drivers/cpufreq/cpufreq.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index e979ec7..ce02b2b 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1457,9 +1457,17 @@ unsigned int cpufreq_quick_get(unsigned int cpu)
>  {
>       struct cpufreq_policy *policy;
>       unsigned int ret_freq = 0;
> +     unsigned long flags;
> +
> +     read_lock_irqsave(&cpufreq_driver_lock, flags);
>  
>       if (cpufreq_driver && cpufreq_driver->setpolicy && cpufreq_driver->get)
> -             return cpufreq_driver->get(cpu);
> +             ret_freq = cpufreq_driver->get(cpu);
> +
> +     read_unlock_irqrestore(&cpufreq_driver_lock, flags);
> +
> +     if (ret_freq)
> +             return ret_freq;
>  
>       policy = cpufreq_cpu_get(cpu);
>       if (policy) {
> 

I would prefer something like this:

        read_lock_irqsave(&cpufreq_driver_lock, flags);

        if (cpufreq_driver && cpufreq_driver->setpolicy && cpufreq_driver->get) 
{
                unsigned int ret_freq = cpufreq_driver->get(cpu);

                read_unlock_irqrestore(&cpufreq_driver_lock, flags);
                return ret_freq;
        }

        read_unlock_irqrestore(&cpufreq_driver_lock, flags);

Thanks,
Rafael