Re: [PATCH v3 5/5] platform/x86: hp-wmi: add locking for concurrent hwmon access

[Ilpo Järvinen]

On Sun, 5 Apr 2026, Emre Cecanpunar wrote:

> hp_wmi_hwmon_priv.mode and .pwm are written by hp_wmi_hwmon_write() in
> sysfs context and read by hp_wmi_hwmon_keep_alive_handler() in a
> workqueue. A concurrent write and keep-alive expiry can observe an
> inconsistent mode/pwm pair (e.g. mode=MANUAL with a stale pwm).
> 
> Add a mutex to hp_wmi_hwmon_priv protecting mode and pwm. Hold it in
> hp_wmi_hwmon_write() across the field update and apply call, and in
> hp_wmi_hwmon_keep_alive_handler() before calling apply.
> 
> In hp_wmi_hwmon_read(), only the pwm_enable path reads priv->mode; use
> scoped_guard() there to avoid holding the lock across unrelated WMI
> calls.
> 
> Fixes: c203c59fb5de ("platform/x86: hp-wmi: implement fan keep-alive")
> Signed-off-by: Emre Cecanpunar <emreleno@xxxxxxxxx>
> ---
>  drivers/platform/x86/hp/hp-wmi.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/platform/x86/hp/hp-wmi.c b/drivers/platform/x86/hp/hp-wmi.c
> index db72ad9da0a5..1096fb46cbcd 100644
> --- a/drivers/platform/x86/hp/hp-wmi.c
> +++ b/drivers/platform/x86/hp/hp-wmi.c
> @@ -453,6 +453,7 @@ enum pwm_modes {
>  };
>  
>  struct hp_wmi_hwmon_priv {
> +	struct mutex lock;	/* protects mode, pwm */
>  	u8 min_rpm;
>  	u8 max_rpm;
>  	int gpu_delta;
> @@ -2422,6 +2423,7 @@ static int hp_wmi_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
>  {
>  	struct hp_wmi_hwmon_priv *priv;
>  	int rpm, ret;
> +	u8 mode;
>  
>  	priv = dev_get_drvdata(dev);
>  	switch (type) {
> @@ -2445,11 +2447,13 @@ static int hp_wmi_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
>  			*val = rpm_to_pwm(rpm / 100, priv);
>  			return 0;
>  		}
> -		switch (priv->mode) {
> +		scoped_guard(mutex, &priv->lock)
> +			mode = priv->mode;
> +		switch (mode) {
>  		case PWM_MODE_MAX:
>  		case PWM_MODE_MANUAL:
>  		case PWM_MODE_AUTO:
> -			*val = priv->mode;
> +			*val = mode;
>  			return 0;
>  		default:
>  			/* shouldn't happen */
> @@ -2467,6 +2471,7 @@ static int hp_wmi_hwmon_write(struct device *dev, enum hwmon_sensor_types type,
>  	int rpm;
>  
>  	priv = dev_get_drvdata(dev);
> +	guard(mutex)(&priv->lock);
>  	switch (type) {
>  	case hwmon_pwm:
>  		if (attr == hwmon_pwm_input) {
> @@ -2535,6 +2540,8 @@ static void hp_wmi_hwmon_keep_alive_handler(struct work_struct *work)
>  
>  	dwork = to_delayed_work(work);
>  	priv = container_of(dwork, struct hp_wmi_hwmon_priv, keep_alive_dwork);
> +
> +	guard(mutex)(&priv->lock);
>  	/*
>  	 * Re-apply the current hwmon context settings.
>  	 * NOTE: hp_wmi_apply_fan_settings will handle the re-scheduling.
> @@ -2592,6 +2599,8 @@ static int hp_wmi_hwmon_init(void)
>  	if (!priv)
>  		return -ENOMEM;
>  
> +	mutex_init(&priv->lock);

Please use devm_mutex_init() so you don't need to deinit it manually with 
mutex_destroy(). While changing that, don't forget that devm_*() can fail 
so remember to handle the error.

-- 
 i.