[PATCH] tty_io.c balance tty_ldisc_ref()

tty_ldisc_deref() should only be called when tty_ldisc_ref() succeeds
otherwise it triggers a BUG().  There's already a function
tty_ldisc_flush() that flushes properly.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/char/tty_io.c

@@ -3335,18 +3335,13 @@ static void __do_SAK(struct work_struct *work)
 	int session;
 	int		i;
 	struct file	*filp;
-	struct tty_ldisc *disc;
 	struct fdtable *fdt;
 
 	if (!tty)
 		return;
 	session = tty->session;
 
-	/* We don't want an ldisc switch during this */
-	disc = tty_ldisc_ref(tty);
-	if (disc && disc->flush_buffer)
-		disc->flush_buffer(tty);
-	tty_ldisc_deref(disc);
+	tty_ldisc_flush(tty);
 
 	if (tty->driver->flush_buffer)
 		tty->driver->flush_buffer(tty);