[v4] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount
diff mbox series

Message ID 1579506088-6736-1-git-send-email-qiwuchen55@gmail.com
State New
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Series
  • [v4] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount
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Commit Message

chenqiwu Jan. 20, 2020, 7:41 a.m. UTC
From: chenqiwu <chenqiwu@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@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(-)

Comments

Viresh Kumar Jan. 20, 2020, 7:54 a.m. UTC | #1
On 20-01-20, 15:41, qiwuchen55@gmail.com wrote:
> From: chenqiwu <chenqiwu@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@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);
 }

Patch
diff mbox series

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