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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200120053250.igkwofqfzvmqb3c3@vireshk-i7>
Date:   Mon, 20 Jan 2020 11:02:50 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     qiwuchen55@...il.com
Cc:     mmayer@...adcom.com, rjw@...ysocki.net, f.fainelli@...il.com,
        bcm-kernel-feedback-list@...adcom.com, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        chenqiwu <chenqiwu@...omi.com>
Subject: Re: [PATCH v3] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy
 refcount

On 19-01-20, 15:09, qiwuchen55@...il.com wrote:
> From: chenqiwu <chenqiwu@...omi.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@...omi.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