pty: Ignore slave open count for master pty open

Multiple slave pty opens may be performed in parallel with the
master open. Of course, all the slave opens will fail because the
master pty is still locked but during this time the slave pty
count will be artificially greater than 1. This is should not
cause the master pty open to fail.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/pty.c

@@ -256,7 +256,7 @@ static int pty_open(struct tty_struct *tty, struct file *filp)
 		goto out;
 	if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
 		goto out;
-	if (tty->link->count != 1)
+	if (tty->driver->subtype == PTY_TYPE_SLAVE && tty->link->count != 1)
 		goto out;
 
 	clear_bit(TTY_IO_ERROR, &tty->flags);