Revert "TTY: get rid of BTM around devpts_*"

This reverts commit d3bda5298aad98c7a27678bdd0dd9d008ab9e685.

Sasha reported that this causes problems, so revert it.

Cc: Sasha Levin <levinsasha928@gmail.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/pty.c

@@ -54,8 +54,8 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 	wake_up_interruptible(&tty->link->write_wait);
 	if (tty->driver->subtype == PTY_TYPE_MASTER) {
 		set_bit(TTY_OTHER_CLOSED, &tty->flags);
-		tty_unlock();
 		devpts_pty_kill(tty->link);
+		tty_unlock();
 		tty_vhangup(tty->link);
 		tty_lock();
 	}
@@ -613,7 +613,9 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 		return retval;
 
 	/* find a device that is not in use. */
+	tty_lock();
 	index = devpts_new_index(inode);
+	tty_unlock();
 	if (index < 0) {
 		retval = index;
 		goto err_file;
@@ -648,8 +650,8 @@ err_release:
 	tty_release(inode, filp);
 	return retval;
 out:
-	tty_unlock();
 	devpts_kill_index(inode, index);
+	tty_unlock();
 err_file:
 	tty_free_file(filp);
 	return retval;

drivers/tty/tty_io.c

@@ -1789,11 +1789,11 @@ int tty_release(struct inode *inode, struct file *filp)
 	 * the slots and preserving the termios structure.
 	 */
 	release_tty(tty, idx);
-	tty_unlock();
 
 	/* Make this pty number available for reallocation */
 	if (devpts)
 		devpts_kill_index(inode, idx);
+	tty_unlock();
 	return 0;
 }