Re: [PATCH 2/4] platform/x86: xiaomi-wmi: Fix race condition when reporting key events

[Kuppuswamy Sathyanarayanan]

On 3/27/24 6:23 PM, Armin Wolf wrote:
> Multiple WMI events can be received concurrently, so multiple instances
> of xiaomi_wmi_notify() can be active at the same time. Since the input
> device is shared between those handlers, the key input sequence can be
> disturbed.

Since locking is needed for all notify related calls in all WMI drivers,
is there a generic way to add this support in WMI core driver? Like
defining some common function which will hold the lock and call
driver specific notify handler? I am just thinking aloud.. If it is not
feasible, then it is fine.

> Fix this by protecting the key input sequence with a mutex.
>
> Compile-tested only.
>
> Fixes: edb73f4f0247 ("platform/x86: wmi: add Xiaomi WMI key driver")
> Signed-off-by: Armin Wolf <W_Armin@xxxxxx>
> ---
>  drivers/platform/x86/xiaomi-wmi.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/drivers/platform/x86/xiaomi-wmi.c b/drivers/platform/x86/xiaomi-wmi.c
> index 1f5f108d87c0..7efbdc111803 100644
> --- a/drivers/platform/x86/xiaomi-wmi.c
> +++ b/drivers/platform/x86/xiaomi-wmi.c
> @@ -2,8 +2,10 @@
>  /* WMI driver for Xiaomi Laptops */
>
>  #include <linux/acpi.h>
> +#include <linux/device.h>
>  #include <linux/input.h>
>  #include <linux/module.h>
> +#include <linux/mutex.h>
>  #include <linux/wmi.h>
>
>  #include <uapi/linux/input-event-codes.h>
> @@ -20,12 +22,21 @@
>
>  struct xiaomi_wmi {
>  	struct input_dev *input_dev;
> +	struct mutex key_lock;	/* Protects the key event sequence */
>  	unsigned int key_code;
>  };
>
> +static void xiaomi_mutex_destroy(void *data)
> +{
> +	struct mutex *lock = data;
> +
> +	mutex_destroy(lock);
> +}
> +
>  static int xiaomi_wmi_probe(struct wmi_device *wdev, const void *context)
>  {
>  	struct xiaomi_wmi *data;
> +	int ret;
>
>  	if (wdev == NULL || context == NULL)
>  		return -EINVAL;
> @@ -35,6 +46,11 @@ static int xiaomi_wmi_probe(struct wmi_device *wdev, const void *context)
>  		return -ENOMEM;
>  	dev_set_drvdata(&wdev->dev, data);
>
> +	mutex_init(&data->key_lock);
> +	ret = devm_add_action_or_reset(&wdev->dev, xiaomi_mutex_destroy, &data->key_lock);
> +	if (ret < 0)
> +		return ret;
> +
>  	data->input_dev = devm_input_allocate_device(&wdev->dev);
>  	if (data->input_dev == NULL)
>  		return -ENOMEM;
> @@ -59,10 +75,12 @@ static void xiaomi_wmi_notify(struct wmi_device *wdev, union acpi_object *dummy)
>  	if (data == NULL)
>  		return;
>
> +	mutex_lock(&data->key_lock);
>  	input_report_key(data->input_dev, data->key_code, 1);
>  	input_sync(data->input_dev);
>  	input_report_key(data->input_dev, data->key_code, 0);
>  	input_sync(data->input_dev);
> +	mutex_unlock(&data->key_lock);
>  }
>
>  static const struct wmi_device_id xiaomi_wmi_id_table[] = {
> --
> 2.39.2
>
>
-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer