On Wed, 2014-06-18 at 19:05 +0300, Janne Kanniainen wrote:

This driver adds support for USB controlled led panels that exists in
MSI GT683R laptop

+static int gt683r_led_probe(struct hid_device *hdev,
+			const struct hid_device_id *id)
+{
+	int i;
+	int ret;
+	int name_sz;
+	char *name;
+	struct gt683r_led *led;
+
+	led = devm_kzalloc(&hdev->dev, sizeof(*led), GFP_KERNEL);
+	if (!led)
+		return -ENOMEM;
+
+	led->mode = GT683R_LED_NORMAL;
+	led->hdev = hdev;
+	hid_set_drvdata(hdev, led);
+
+	ret = hid_parse(hdev);
+	if (ret) {
+		hid_err(hdev, "hid parsing failed\n");
+		return ret;
+	}
+
+	ret = hid_hw_start(hdev, HID_CONNECT_HIDRAW);
+	if (ret) {
+		hid_err(hdev, "hw start failed\n");
+		return ret;
+	}
+
+	for (i = 0; i < GT683R_LED_COUNT; i++) {
+		name_sz = strlen(dev_name(&hdev->dev)) +
+				strlen(gt683r_panel_names[i]) + 3;
+
+		name = devm_kzalloc(&hdev->dev, name_sz, GFP_KERNEL);
+		if (!name) {
+			ret = -ENOMEM;
+			goto fail;
+		}
+
+		snprintf(name, name_sz, "%s::%s",
+				dev_name(&hdev->dev), gt683r_panel_names[i]);
+		led->led_devs[i].name = name;
+		led->led_devs[i].max_brightness = 1;
+		led->led_devs[i].brightness_set = gt683r_brightness_set;
+		ret = led_classdev_register(&hdev->dev, &led->led_devs[i]);
+		if (ret) {
+			hid_err(hdev, "could not register led device\n");
+			goto fail;
+		}
+	}
+
+	ret = device_create_file(&led->hdev->dev, &dev_attr_leds_mode);
+	if (ret) {
+		hid_err(hdev, "could not make mode attribute file\n");
+		goto fail;
+	}
+

This is the window.

+	mutex_init(&led->lock);
+	INIT_WORK(&led->work, gt683r_led_work);
+

And here we have a problem. This is a race condition.
At this time you've already created the sysfs files. So
their methods can be called. They will lock a mutex and/or
schedule work that hasn't been initialized.
The initialization must be done before anything in sysfs
is created. 

+	return 0;
+
+fail:
+	for (i = i - 1; i >= 0; i--)
+		led_classdev_unregister(&led->led_devs[i]);
+	hid_hw_stop(hdev);
+	return ret;
+}
+

Sorry for noticing this thread late.

	Regards
		Oliver