USB: ldusb should signal an error in poll if the device is disconnected

poll() should test for a disconnection of the device.
Signed-off-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/misc/ldusb.c

@@ -412,6 +412,9 @@ static unsigned int ld_usb_poll(struct file *file, poll_table *wait)
 
 	dev = file->private_data;
 
+	if (!dev->intf)
+		return POLLERR | POLLHUP;
+
 	poll_wait(file, &dev->read_wait, wait);
 	poll_wait(file, &dev->write_wait, wait);
 
@@ -767,6 +770,9 @@ static void ld_usb_disconnect(struct usb_interface *intf)
 		ld_usb_delete(dev);
 	} else {
 		dev->intf = NULL;
+		/* wake up pollers */
+		wake_up_interruptible_all(&dev->read_wait);
+		wake_up_interruptible_all(&dev->write_wait);
 		mutex_unlock(&dev->mutex);
 	}