platform/x86: xiaomi-wmi: Fix race condition when reporting key events

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.

Fix this by protecting the key input sequence with a mutex.

Compile-tested only.

Fixes: edb73f4 ("platform/x86: wmi: add Xiaomi WMI key driver")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20240402143059.8456-2-W_Armin@gmx.de
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

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[] = {