platform/x86: dell-ddv: Fix cache invalidation on resume

If one or both sensor buffers could not be initialized, either
due to missing hardware support or due to some error during probing,
the resume handler will encounter undefined behaviour when
attempting to lock buffers then protected by an uninitialized or
destroyed mutex.
Fix this by introducing a "active" flag which is set during probe,
and only invalidate buffers which where flaged as "active".

Tested on a Dell Inspiron 3505.

Fixes: 3b7eeff ("platform/x86: dell-ddv: Add hwmon support")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20230218115318.20662-1-W_Armin@gmx.de
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/dell/dell-wmi-ddv.c

@@ -96,6 +96,7 @@ struct combined_chip_info {
 };
 
 struct dell_wmi_ddv_sensors {
+	bool active;
 	struct mutex lock;	/* protect caching */
 	unsigned long timestamp;
 	union acpi_object *obj;
@@ -520,6 +521,9 @@ static struct hwmon_channel_info *dell_wmi_ddv_channel_create(struct device *dev
 
 static void dell_wmi_ddv_hwmon_cache_invalidate(struct dell_wmi_ddv_sensors *sensors)
 {
+	if (!sensors->active)
+		return;
+
 	mutex_lock(&sensors->lock);
 	kfree(sensors->obj);
 	sensors->obj = NULL;
@@ -530,6 +534,7 @@ static void dell_wmi_ddv_hwmon_cache_destroy(void *data)
 {
 	struct dell_wmi_ddv_sensors *sensors = data;
 
+	sensors->active = false;
 	mutex_destroy(&sensors->lock);
 	kfree(sensors->obj);
 }
@@ -549,6 +554,7 @@ static struct hwmon_channel_info *dell_wmi_ddv_channel_init(struct wmi_device *w
 		return ERR_PTR(ret);
 
 	mutex_init(&sensors->lock);
+	sensors->active = true;
 
 	ret = devm_add_action_or_reset(&wdev->dev, dell_wmi_ddv_hwmon_cache_destroy, sensors);
 	if (ret < 0)
@@ -852,7 +858,7 @@ static int dell_wmi_ddv_resume(struct device *dev)
 {
 	struct dell_wmi_ddv_data *data = dev_get_drvdata(dev);
 
-	/* Force re-reading of all sensors */
+	/* Force re-reading of all active sensors */
 	dell_wmi_ddv_hwmon_cache_invalidate(&data->fans);
 	dell_wmi_ddv_hwmon_cache_invalidate(&data->temps);