[PATCH v4] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount

Viresh Kumar viresh.kumar at linaro.org
Sun Jan 19 23:54:38 PST 2020


On 20-01-20, 15:41, qiwuchen55 at gmail.com wrote:
> From: chenqiwu <chenqiwu at xiaomi.com>
> 
> brcm_avs_cpufreq_get() calls cpufreq_cpu_get() to get the cpufreq
> policy, meanwhile, it also increments the kobject reference count
> to mark it busy. However, a corresponding call of cpufreq_cpu_put()
> is ignored to decrement the kobject reference count back, which may
> lead to a potential stuck risk that the cpuhp thread deadly waits
> for dropping of kobject refcount when cpufreq policy free.
> 
> With this patch, the cpuhp thread can be easily exercised by
> attempting to force an unbind of the CPUfreq driver.
> 
> Signed-off-by: chenqiwu <chenqiwu at xiaomi.com>
> ---
> changes in v4:
>  - Rewrit commit message.
>  - Use cpufreq_cpu_get() and a corresponding cpufreq_cpu_put()
>    instead of cpufreq_get_policy() for promoting efficiency.
> ---
>  drivers/cpufreq/brcmstb-avs-cpufreq.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/brcmstb-avs-cpufreq.c b/drivers/cpufreq/brcmstb-avs-cpufreq.c
> index 77b0e5d..0767206 100644
> --- a/drivers/cpufreq/brcmstb-avs-cpufreq.c
> +++ b/drivers/cpufreq/brcmstb-avs-cpufreq.c
> @@ -453,7 +453,13 @@ static bool brcm_avs_is_firmware_loaded(struct private_data *priv)
>  static unsigned int brcm_avs_cpufreq_get(unsigned int cpu)
>  {
>  	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
> -	struct private_data *priv = policy->driver_data;
> +	struct private_data *priv;
> +
> +	if (!policy)
> +		return 0;
> +

As I told you earlier, this isn't required as policy can't be NULL here.

> +	priv = policy->driver_data;
> +	cpufreq_cpu_put(policy);
>  
>  	return brcm_avs_get_frequency(priv->base);
>  }

Applied the patch with following diff:

req/brcmstb-avs-cpufreq.c b/drivers/cpufreq/brcmstb-avs-cpufreq.c
index 77b0e5d0fb13..4f86ce2db34f 100644
--- a/drivers/cpufreq/brcmstb-avs-cpufreq.c
+++ b/drivers/cpufreq/brcmstb-avs-cpufreq.c
@@ -455,6 +455,8 @@ static unsigned int brcm_avs_cpufreq_get(unsigned int cpu)
        struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
        struct private_data *priv = policy->driver_data;
 
+       cpufreq_cpu_put(policy);
+
        return brcm_avs_get_frequency(priv->base);
 }
 

-- 
viresh



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