TTY: ldisc, fix open flag handling

commit 7f90cfc5 upstream.

When a concrete ldisc open fails in tty_ldisc_open, we forget to clear
TTY_LDISC_OPEN. This causes a false warning on the next ldisc open:
WARNING: at drivers/char/tty_ldisc.c:445 tty_ldisc_open+0x26/0x38()
Hardware name: System Product Name
Modules linked in: ...
Pid: 5251, comm: a.out Tainted: G        W  2.6.32-5-686 #1
Call Trace:
 [<c1030321>] ? warn_slowpath_common+0x5e/0x8a
 [<c1030357>] ? warn_slowpath_null+0xa/0xc
 [<c119311c>] ? tty_ldisc_open+0x26/0x38
 [<c11936c5>] ? tty_set_ldisc+0x218/0x304
...

So clear the bit when failing...

Introduced in c65c9bc3 (tty: rewrite the ldisc locking) back in
2.6.31-rc1.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Reported-by: Sergey Lapin <slapin@ossfans.org>
Tested-by: Sergey Lapin <slapin@ossfans.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/char/tty_ldisc.c

@@ -444,9 +444,14 @@ static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
 
 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
 {
+	int ret;
+
 	WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
-	if (ld->ops->open)
-		return ld->ops->open(tty);
+	if (ld->ops->open) {
+		ret = ld->ops->open(tty);
+		if (ret)
+			clear_bit(TTY_LDISC_OPEN, &tty->flags);
+	}
 	return 0;
 }