linux-kernel - Re: [PATCH v1] cpuidle: Fail cpuidle device registration if there is one already

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Message-ID: <20250919050928.6sprmdpz2pwgydcc@lcpd911>
Date: Fri, 19 Sep 2025 10:39:28 +0530
From: Dhruva Gole <d-gole@...com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
CC: Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v1] cpuidle: Fail cpuidle device registration if there is
 one already

Hi Rafael,

On Sep 18, 2025 at 23:19:20 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Refuse to register a cpuidle device if the given CPU has a cpuidle
> device already and print a message regarding it.
> 
> Without this, an attempt to register a new cpuidle device without
> unregistering the existing one leads to the removal of the existing
> cpuidle device without removing its sysfs interface.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/cpuidle/cpuidle.c |    8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -635,11 +635,17 @@ static void __cpuidle_device_init(struct
>  static int __cpuidle_register_device(struct cpuidle_device *dev)
>  {
>  	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
> +	unsigned int cpu = dev->cpu;
>  	int i, ret;
>  
>  	if (!try_module_get(drv->owner))
>  		return -EINVAL;
>  
> +	if (per_cpu(cpuidle_devices, cpu)) {
> +		pr_info("CPU%d: cpuidle device already registered\n", cpu);
> +		return -EEXIST;

Here we return prematurely after a try_module_get right?
Do we need a module_put() similar to how you do it later by calling
unregister_device function by checking ret = cpuidle_coupled_register_device ?

> +	}
> +
>  	for (i = 0; i < drv->state_count; i++) {
>  		if (drv->states[i].flags & CPUIDLE_FLAG_UNUSABLE)
>  			dev->states_usage[i].disable |= CPUIDLE_STATE_DISABLED_BY_DRIVER;
> @@ -648,7 +654,7 @@ static int __cpuidle_register_device(str
>  			dev->states_usage[i].disable |= CPUIDLE_STATE_DISABLED_BY_USER;
>  	}
>  
> -	per_cpu(cpuidle_devices, dev->cpu) = dev;
> +	per_cpu(cpuidle_devices, cpu) = dev;
>  	list_add(&dev->device_list, &cpuidle_detected_devices);
>  
>  	ret = cpuidle_coupled_register_device(dev);
> 
> 
> 
> 

-- 
Best regards,
Dhruva Gole
Texas Instruments Incorporated