vt: invoke notifier on screen size change

BugLink: https://bugs.launchpad.net/bugs/1818803

commit 0c9b1965 upstream.

User space using poll() on /dev/vcs devices are not awaken when a
screen size change occurs. Let's fix that.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/tty/vt/vt.c

@@ -969,6 +969,7 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
 	if (CON_IS_VISIBLE(vc))
 		update_screen(vc);
 	vt_event_post(VT_EVENT_RESIZE, vc->vc_num, vc->vc_num);
+	notify_update(vc);
 	return err;
 }