linux-kernel - Re: [PATCH] cpufreq: Avoid using inactive policies

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Message-ID: <20161118031750.GD3110@vireshk-i7>
Date:   Fri, 18 Nov 2016 08:47:50 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM list <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH] cpufreq: Avoid using inactive policies

On 17-11-16, 16:08, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> There are two places in the cpufreq core in which low-level driver
> callbacks may be invoked for an inactive cpufreq policy, which isn't
> guaranteed to work in general.  Both are due to possible races with
> CPU offline.
> 
> First, in cpufreq_get(), the policy may become inactive after
> the check against policy->cpus in cpufreq_cpu_get() and before
> policy->rwsem is acquired, in which case using the policy going
> forward may not be correct.
> 
> Second, an analogous situation is possible in cpufreq_update_policy().
> 
> Avoid using inactive policies by adding policy_is_inactive() checks
> to the code in the above places.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/cpufreq/cpufreq.c |    8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> Index: linux-pm/drivers/cpufreq/cpufreq.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/cpufreq.c
> +++ linux-pm/drivers/cpufreq/cpufreq.c
> @@ -1526,7 +1526,10 @@ unsigned int cpufreq_get(unsigned int cp
>  
>  	if (policy) {
>  		down_read(&policy->rwsem);
> -		ret_freq = __cpufreq_get(policy);
> +
> +		if (!policy_is_inactive(policy))
> +			ret_freq = __cpufreq_get(policy);
> +
>  		up_read(&policy->rwsem);
>  
>  		cpufreq_cpu_put(policy);
> @@ -2265,6 +2268,9 @@ int cpufreq_update_policy(unsigned int c
>  
>  	down_write(&policy->rwsem);
>  
> +	if (policy_is_inactive(policy))

You also need to set some value to 'ret' as it is uninitialized right now.

> +		goto unlock;
> +
>  	pr_debug("updating policy for CPU %u\n", cpu);
>  	memcpy(&new_policy, policy, sizeof(*policy));
>  	new_policy.min = policy->user_policy.min;

-- 
viresh