[PATCH v3] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount
viresh.kumar at linaro.org
Sun Jan 19 21:32:50 PST 2020
On 19-01-20, 15:09, 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.
> For fixing this bug, cpufreq_get_policy() is referenced to do a proper
> cpufreq_cpu_get()/cpufreq_cpu_put() and fill a policy copy for the user.
> If the policy return NULL, we just return 0 to hit the code path of
> Signed-off-by: chenqiwu <chenqiwu at xiaomi.com>
> drivers/cpufreq/brcmstb-avs-cpufreq.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
> diff --git a/drivers/cpufreq/brcmstb-avs-cpufreq.c b/drivers/cpufreq/brcmstb-avs-cpufreq.c
> index 77b0e5d..ee0d404 100644
> --- a/drivers/cpufreq/brcmstb-avs-cpufreq.c
> +++ b/drivers/cpufreq/brcmstb-avs-cpufreq.c
> @@ -452,8 +452,16 @@ 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);
Why can't we just add a corresponding cpufreq_cpu_put() instead of all this ?
> - struct private_data *priv = policy->driver_data;
> + struct cpufreq_policy policy;
> + struct private_data *priv;
> + /*
> + * In case cpufreq policy has been released, just return 0.
> + */
> + if (cpufreq_get_policy(&policy, cpu))
> + return 0;
Why did you move away from the previous implementation of cpufreq_cpu_get() ?
> + priv = policy.driver_data;
> return brcm_avs_get_frequency(priv->base);
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