tty: Move tty hung up check from port->lock critical section

The port->lock does not protect the filp->f_op field; move
the tty_hung_up_p() test outside the port->lock critical section
in tty_port_close_start().
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_port.c

@@ -473,12 +473,10 @@ int tty_port_close_start(struct tty_port *port,
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&port->lock, flags);
-	if (tty_hung_up_p(filp)) {
-		spin_unlock_irqrestore(&port->lock, flags);
+	if (tty_hung_up_p(filp))
 		return 0;
-	}
 
+	spin_lock_irqsave(&port->lock, flags);
 	if (tty->count == 1 && port->count != 1) {
 		printk(KERN_WARNING
 		    "tty_port_close_start: tty->count = 1 port count = %d.\n",