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
