tty: remove tty_lock_nested

This changes all remaining users of tty_lock_nested
to be non-recursive, which lets us kill this function.
As a consequence, we won't need to keep the lock count
any more, which allows more simplifications later.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/char/selection.c b/drivers/char/selection.c
index 75889cd..ebae344 100644
--- a/drivers/char/selection.c
+++ b/drivers/char/selection.c
@@ -313,7 +313,8 @@
 	struct  tty_ldisc *ld;
 	DECLARE_WAITQUEUE(wait, current);
 
-	tty_lock_nested(); /* always called with BTM from vt_ioctl */
+	/* always called with BTM from vt_ioctl */
+	WARN_ON(!tty_locked());
 
 	acquire_console_sem();
 	poke_blanked_console();
@@ -343,6 +344,5 @@
 	__set_current_state(TASK_RUNNING);
 
 	tty_ldisc_deref(ld);
-	tty_unlock();
 	return 0;
 }