vt: Perform safe console erase only once

Commit f8df13e0a9 ("tty: Clean console safely") added code to clear
both the scrollback buffer and the screen with "\e[3J", then execution
falls through into the code to simply clear the screen. This means
scr_memsetw() and the console driver update callback are called twice
on the whole screen buffer. Let's reorganize the code so the same work
is not performed twice needlessly.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 9 deletions

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index f97251f39c26..1eb1a376a041 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1178,15 +1178,8 @@ static void csi_J(struct vc_data *vc, int vpar)
                         count = ((vc->vc_pos - vc->vc_origin) >> 1) + 1;
                         start = (unsigned short *)vc->vc_origin;
                         break;
-                case 3: /* erase scroll-back buffer (and whole display) */
-                        scr_memsetw(vc->vc_screenbuf, vc->vc_video_erase_char,
-                                    vc->vc_screenbuf_size);
-                        flush_scrollback(vc);
-                        set_origin(vc);
-                        if (con_is_visible(vc))
-                                update_screen(vc);
-                        /* fall through */
                 case 2: /* erase whole display */
+                case 3: /* (and scrollback buffer later) */
                         count = vc->vc_cols * vc->vc_rows;
                         start = (unsigned short *)vc->vc_origin;
                         break;
@@ -1194,7 +1187,12 @@ static void csi_J(struct vc_data *vc, int vpar)
                         return;
         }
         scr_memsetw(start, vc->vc_video_erase_char, 2 * count);
-        if (con_should_update(vc))
+        if (vpar == 3) {
+                set_origin(vc);
+                flush_scrollback(vc);
+                if (con_is_visible(vc))
+                        update_screen(vc);
+        } else if (con_should_update(vc))
                 do_update_region(vc, (unsigned long) start, count);
         vc->vc_need_wrap = 0;
 }