pty: Ignore slave pty close() if never successfully opened

If the master and slave ptys are opened in parallel, the slave open
fails because the pty is still locked. This is as designed.
However, pty_close() is still called for the slave pty which sets
TTY_OTHER_CLOSED in the master pty. This can cause the master open
to fail as well.

Use a common pattern in other tty drivers by setting TTY_IO_ERROR
until the open is successful and only closing the pty if not set.

Note: the master pty always closes regardless of whether the open
was successful, so that proper cleanup can occur.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/pty.c

@@ -38,9 +38,12 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 	if (tty->driver->subtype == PTY_TYPE_MASTER)
 		WARN_ON(tty->count > 1);
 	else {
+		if (test_bit(TTY_IO_ERROR, &tty->flags))
+			return;
 		if (tty->count > 2)
 			return;
 	}
+	set_bit(TTY_IO_ERROR, &tty->flags);
 	wake_up_interruptible(&tty->read_wait);
 	wake_up_interruptible(&tty->write_wait);
 	tty->packet = 0;
@@ -246,6 +249,8 @@ static int pty_open(struct tty_struct *tty, struct file *filp)
 	if (!tty || !tty->link)
 		goto out;
 
+	set_bit(TTY_IO_ERROR, &tty->flags);
+
 	retval = -EIO;
 	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 		goto out;
@@ -254,6 +259,7 @@ static int pty_open(struct tty_struct *tty, struct file *filp)
 	if (tty->link->count != 1)
 		goto out;
 
+	clear_bit(TTY_IO_ERROR, &tty->flags);
 	clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
 	set_bit(TTY_THROTTLED, &tty->flags);
 	retval = 0;