pty: Hold ctrl_lock for packet mode updates

Updates to the packet mode enable require holding the ctrl_lock;
the serialization prevents corruption of adjacent fields.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Reviewed-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/pty.c

@@ -47,7 +47,9 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 	set_bit(TTY_IO_ERROR, &tty->flags);
 	wake_up_interruptible(&tty->read_wait);
 	wake_up_interruptible(&tty->write_wait);
+	spin_lock_irq(&tty->ctrl_lock);
 	tty->packet = 0;
+	spin_unlock_irq(&tty->ctrl_lock);
 	/* Review - krefs on tty_link ?? */
 	if (!tty->link)
 		return;