Re: [PATCH v3] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount

From: Viresh Kumar <viresh.kumar@linaro.org>
To: qiwuchen55@gmail.com
Cc: mmayer@broadcom.com, rjw@rjwysocki.net, f.fainelli@gmail.com,
	bcm-kernel-feedback-list@broadcom.com, linux-pm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, chenqiwu <chenqiwu@xiaomi.com>
Subject: Re: [PATCH v3] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount
Date: Mon, 20 Jan 2020 11:02:50 +0530	[thread overview]
Message-ID: <20200120053250.igkwofqfzvmqb3c3@vireshk-i7> (raw)
In-Reply-To: <1579417750-21984-1-git-send-email-qiwuchen55@gmail.com>

On 19-01-20, 15:09, 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.
> 
> 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
> cpufreq_driver->get.
> 
> Signed-off-by: chenqiwu <chenqiwu@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);
>  }
> -- 
> 1.9.1

-- 
viresh