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

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

symbol_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/symbolserial.c

@@ -179,20 +179,24 @@ static void symbol_unthrottle(struct tty_struct *tty)
 	struct symbol_private *priv = usb_get_serial_data(port->serial);
 	unsigned long flags;
 	int result;
+	bool was_throttled;
 
 	dbg("%s - port %d", __func__, port->number);
 
 	spin_lock_irqsave(&priv->lock, flags);
 	priv->throttled = false;
+	was_throttled = priv->actually_throttled;
 	priv->actually_throttled = false;
 	spin_unlock_irqrestore(&priv->lock, flags);
 
 	priv->int_urb->dev = port->serial->dev;
-	result = usb_submit_urb(priv->int_urb, GFP_ATOMIC);
-	if (result)
-		dev_err(&port->dev,
-			"%s - failed submitting read urb, error %d\n",
+	if (was_throttled) {
+		result = usb_submit_urb(priv->int_urb, GFP_ATOMIC);
+		if (result)
+			dev_err(&port->dev,
+				"%s - failed submitting read urb, error %d\n",
 							__func__, result);
+	}
 }
 
 static int symbol_startup(struct usb_serial *serial)