vt: Fix secure clear screen

\E[3J console code (secure clear screen) needs to update_screen(vc)
in order to write-through blanks into off-screen video memory.

This has been removed accidentally in 3.6 by:

commit 81732c3b2fede049a692e58a7ceabb6d18ffb18c
Author: Jean-François Moine <moinejf@free.fr>
Date:   Thu Sep 6 19:24:13 2012 +0200

    tty vt: Fix line garbage in virtual console on command line edition

Signed-off-by: Petr Písař <petr.pisar@atlas.cz>
Cc: stable <stable@vger.kernel.org> # 3.6
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 61b1137d7e56..23b5d32954bf 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1164,6 +1164,8 @@ static void csi_J(struct vc_data *vc, int vpar)
                         scr_memsetw(vc->vc_screenbuf, vc->vc_video_erase_char,
                                     vc->vc_screenbuf_size >> 1);
                         set_origin(vc);
+                        if (CON_IS_VISIBLE(vc))
+                                update_screen(vc);
                         /* fall through */
                 case 2: /* erase whole display */
                         count = vc->vc_cols * vc->vc_rows;