[PATCH v4] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount
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:
index 77b0e5d0fb13..4f86ce2db34f 100644
@@ -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;
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