linux-kernel - Re: [RFC PATCH 13/19] cpufreq: fix locking of policy->rwsem in cpufreq_offline

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Date:	Tue, 12 Jan 2016 16:24:47 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Juri Lelli <juri.lelli@....com>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	peterz@...radead.org, rjw@...ysocki.net, mturquette@...libre.com,
	steve.muckle@...aro.org, vincent.guittot@...aro.org,
	morten.rasmussen@....com, dietmar.eggemann@....com
Subject: Re: [RFC PATCH 13/19] cpufreq: fix locking of policy->rwsem in
 cpufreq_offline_prepare

On 11-01-16, 17:35, Juri Lelli wrote:
> There are paths in cpufreq_offline_prepare where policy is used, but its
> rwsem is not held.
> 
> Fix it.
> 
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Juri Lelli <juri.lelli@....com>
> ---
>  drivers/cpufreq/cpufreq.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)

I know the locking in general in cpufreq core is poor. We recently
fixed lots of issues in governors ..

> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 2c7cc6c73..91158b0 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1332,13 +1332,13 @@ static void cpufreq_offline_prepare(unsigned int cpu)
>  		return;
>  	}
>  
> +	down_write(&policy->rwsem);
>  	if (has_target()) {
>  		int ret = __cpufreq_governor(policy, CPUFREQ_GOV_STOP);
>  		if (ret)
>  			pr_err("%s: Failed to stop governor\n", __func__);
>  	}
>  
> -	down_write(&policy->rwsem);
>  	cpumask_clear_cpu(cpu, policy->cpus);
>  
>  	if (policy_is_inactive(policy)) {
> @@ -1356,12 +1356,16 @@ static void cpufreq_offline_prepare(unsigned int cpu)
>  	/* Start governor again for active policy */
>  	if (!policy_is_inactive(policy)) {

Why shouldn't this be under the lock?

>  		if (has_target()) {
> -			int ret = __cpufreq_governor(policy, CPUFREQ_GOV_START);
> +			int ret;
> +
> +			down_write(&policy->rwsem);
> +			ret = __cpufreq_governor(policy, CPUFREQ_GOV_START);
>  			if (!ret)
>  				ret = __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);
>  
>  			if (ret)
>  				pr_err("%s: Failed to start governor\n", __func__);
> +			up_write(&policy->rwsem);
>  		}
>  	} else if (cpufreq_driver->stop_cpu) {
>  		cpufreq_driver->stop_cpu(policy);

And this ?

-- 
viresh