Re: [PATCH] cpufreq: initialize policy rwsem before sysfs publication

[Zhongqiu Han]

On 8/30/2026 11:53 PM, Runyu Xiao wrote:
> cpufreq_policy_alloc() initializes policy->rwsem after
> kobject_init_and_add() has created the policy sysfs directory and its
> default attributes. A sysfs access can therefore reach a policy callback
> before the semaphore has been initialized.
>
> Initialize policy->rwsem before publishing the policy kobject so sysfs
> callbacks always see an initialized semaphore.
>
> Fixes: ad7722dab729 ("cpufreq: create per policy rwsem instead of per CPU cpu_policy_rwsem")

The tag should be 2fc3384dc75b ("cpufreq: Initialize policy->kobj while
allocating policy").

> Cc: stable@xxxxxxxxxxxxxxx
> Assisted-by: Codex:GPT-5
> Signed-off-by: Runyu Xiao <runyu.xiao@xxxxxxxxxx>
> ---
>   drivers/cpufreq/cpufreq.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 0d0df986f..9efbf5b17 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1258,6 +1258,8 @@ static struct cpufreq_policy *cpufreq_policy_alloc(unsigned int cpu)
>   	if (!zalloc_cpumask_var(&policy->real_cpus, GFP_KERNEL))
>   		goto err_free_rcpumask;
>   
> +	init_rwsem(&policy->rwsem);
> +
>   	init_completion(&policy->kobj_unregister);
>   	ret = kobject_init_and_add(&policy->kobj, &ktype_cpufreq,
>   				   cpufreq_global_kobject, "policy%u", cpu);
> @@ -1272,8 +1274,6 @@ static struct cpufreq_policy *cpufreq_policy_alloc(unsigned int cpu)
>   		goto err_free_real_cpus;
>   	}
>   
> -	init_rwsem(&policy->rwsem);
> -
>   	freq_constraints_init(&policy->constraints);
>   
>   	policy->nb_min.notifier_call = cpufreq_notifier_min;


A separate issue: policy->cpus is allocated with alloc_cpumask_var() (no
__GFP_ZERO), so once the kobject is published policy_is_inactive() can
read a garbage mask and let show()/store() reach the attribute callbacks
on a half-initialized policy. I'll send a separate fix for this.


--
Thx and BRs,
Zhongqiu Han