USB: serial: fix race between unthrottle and completion handler in visor

usb:usbserial:visor: fix race between unthrottle and completion handler

visor_unthrottle() mustn't resubmit the URB unconditionally
as the URB may still be running.

the same bug as opticon.
Signed-off-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/visor.c

@@ -595,20 +595,23 @@ static void visor_unthrottle(struct tty_struct *tty)
 {
 	struct usb_serial_port *port = tty->driver_data;
 	struct visor_private *priv = usb_get_serial_port_data(port);
-	int result;
+	int result, was_throttled;
 
 	dbg("%s - port %d", __func__, port->number);
 	spin_lock_irq(&priv->lock);
 	priv->throttled = 0;
+	was_throttled = priv->actually_throttled;
 	priv->actually_throttled = 0;
 	spin_unlock_irq(&priv->lock);
 
+	if (was_throttled) {
 		port->read_urb->dev = port->serial->dev;
 		result = usb_submit_urb(port->read_urb, GFP_KERNEL);
 		if (result)
 			dev_err(&port->dev,
 				"%s - failed submitting read urb, error %d\n",
 							__func__, result);
+	}
 }
 
 static int palm_os_3_probe(struct usb_serial *serial,