TTY: vt, fix paste_selection ldisc handling

There used to be a single tty_ldisc_ref_wait. But then, when a
big-tty-mutex (BTM) was introduced, it has to be tty_ldisc_ref +
tty_unlock + tty_ldisc_ref_wait + tty_lock. Later, BTM was removed
from that path and tty_ldisc_ref + tty_ldisc_ref_wait remained there.
But it makes no sense now. So leave there only tty_ldisc_ref_wait.

And when we have a reference to an ldisc, actually use it in the loop.
Otherwise it may be racy.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Acked-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/selection.c

@@ -341,15 +341,11 @@ int paste_selection(struct tty_struct *tty)
 	struct  tty_ldisc *ld;
 	DECLARE_WAITQUEUE(wait, current);
 
-
 	console_lock();
 	poke_blanked_console();
 	console_unlock();
 
-	/* FIXME: wtf is this supposed to achieve ? */
-	ld = tty_ldisc_ref(tty);
-	if (!ld)
-		ld = tty_ldisc_ref_wait(tty);
+	ld = tty_ldisc_ref_wait(tty);
 
 	/* FIXME: this is completely unsafe */
 	add_wait_queue(&vc->paste_wait, &wait);
@@ -361,8 +357,7 @@ int paste_selection(struct tty_struct *tty)
 		}
 		count = sel_buffer_lth - pasted;
 		count = min(count, tty->receive_room);
-		tty->ldisc->ops->receive_buf(tty, sel_buffer + pasted,
-								NULL, count);
+		ld->ops->receive_buf(tty, sel_buffer + pasted, NULL, count);
 		pasted += count;
 	}
 	remove_wait_queue(&vc->paste_wait, &wait);