linux-kernel - Re: [PATCH v2] cpufreq: fix locking order in store_local

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Message-ID: <20250429052444.zfmfzjirkcaq3edh@vireshk-i7>
Date: Tue, 29 Apr 2025 10:54:44 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Seyediman Seyedarab <imandevel@...il.com>
Cc: rafael@...nel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev
Subject: Re: [PATCH v2] cpufreq: fix locking order in store_local_boost to
 prevent deadlock

On 28-04-25, 13:19, Seyediman Seyedarab wrote:
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index acf19b004..5464c8487 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -653,10 +653,7 @@ static ssize_t store_local_boost(struct cpufreq_policy *policy,
>  
>  	policy->boost_enabled = enable;
>  
> -	cpus_read_lock();
>  	ret = cpufreq_driver->set_boost(policy, enable);
> -	cpus_read_unlock();
> -
>  	if (ret) {
>  		policy->boost_enabled = !policy->boost_enabled;
>  		return ret;
> @@ -1045,11 +1042,17 @@ static ssize_t store(struct kobject *kobj, struct attribute *attr,
>  	if (!fattr->store)
>  		return -EIO;
>  
> +	if (fattr == &local_boost)
> +		cpus_read_lock();
> +

Please add a comment as well to explain why this is required here.

>  	down_write(&policy->rwsem);

And please rebase over PM tree's linux-next branch, your patch won't
apply anymore due to recent changes.

>  	if (likely(!policy_is_inactive(policy)))
>  		ret = fattr->store(policy, buf, count);
>  	up_write(&policy->rwsem);
>  
> +	if (fattr == &local_boost)
> +		cpus_read_unlock();
> +
>  	return ret;
>  }

-- 
viresh