Duplicated code in hiddev_open()

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

Oliver and Jiri:

Why is there duplicated code in
drivers/hid/usbhid/hiddev.c:hiddev_open()?

Line 267:
	/*
	 * no need for locking because the USB major number
	 * is shared which usbcore guards against disconnect
	 */
	if (list->hiddev->exist) {
		if (!list->hiddev->open++) {
			res = hid_hw_open(hiddev->hid);
			if (res < 0)
				goto bail;
		}
	} else {
		res = -ENODEV;
		goto bail;
	}

Line 286:
	mutex_lock(&hiddev->existancelock);
	if (!list->hiddev->open++)
		if (list->hiddev->exist) {
			struct hid_device *hid = hiddev->hid;
			res = hid_hw_power(hid, PM_HINT_FULLON);
			if (res < 0)
				goto bail_unlock;
			res = hid_hw_open(hid);
			if (res < 0)
				goto bail_normal_power;
		}
	mutex_unlock(&hiddev->existancelock);

The second part can never execute, because the first part ensures that 
list->hiddev->open > 0 by the time the second part runs.

Even more disturbing, why is one of these code sections protected by a 
mutex and the other not?

Note: The second section was added in commit 0361a28d3f9a ("HID: 
autosuspend support for USB HID") over ten years ago!

Alan Stern