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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Matthew Whitehead <tedheadster@gmail.com>,
        Nicolas Pitre <nico@linaro.org>
Subject: [PATCH 4.19 251/280] vt: perform safe console erase in the right order
Date:   Fri, 22 Mar 2019 12:16:44 +0100
Message-Id: <20190322111341.543743624@linuxfoundation.org>
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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicolas Pitre <nicolas.pitre@linaro.org>

commit a6dbe442755999960ca54a9b8ecfd9606be0ea75 upstream.

Commit 4b4ecd9cb853 ("vt: Perform safe console erase only once") removed
what appeared to be an extra call to scr_memsetw(). This missed the fact
that set_origin() must be called before clearing the screen otherwise
old screen content gets restored on the screen when using vgacon. Let's
fix that by moving all the scrollback handling to flush_scrollback()
where it logically belongs, and invoking it before the actual screen
clearing in csi_J(), making the code simpler in the end.

Reported-by: Matthew Whitehead <tedheadster@gmail.com>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Tested-by: Matthew Whitehead <tedheadster@gmail.com>
Fixes: 4b4ecd9cb853 ("vt: Perform safe console erase only once")
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/tty/vt/vt.c |   15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -935,8 +935,11 @@ static void flush_scrollback(struct vc_d
 {
 	WARN_CONSOLE_UNLOCKED();
 
+	set_origin(vc);
 	if (vc->vc_sw->con_flush_scrollback)
 		vc->vc_sw->con_flush_scrollback(vc);
+	else
+		vc->vc_sw->con_switch(vc);
 }
 
 /*
@@ -1506,8 +1509,10 @@ static void csi_J(struct vc_data *vc, in
 			count = ((vc->vc_pos - vc->vc_origin) >> 1) + 1;
 			start = (unsigned short *)vc->vc_origin;
 			break;
+		case 3: /* include scrollback */
+			flush_scrollback(vc);
+			/* fallthrough */
 		case 2: /* erase whole display */
-		case 3: /* (and scrollback buffer later) */
 			vc_uniscr_clear_lines(vc, 0, vc->vc_rows);
 			count = vc->vc_cols * vc->vc_rows;
 			start = (unsigned short *)vc->vc_origin;
@@ -1516,13 +1521,7 @@ static void csi_J(struct vc_data *vc, in
 			return;
 	}
 	scr_memsetw(start, vc->vc_video_erase_char, 2 * count);
-	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);
+	update_region(vc, (unsigned long) start, count);
 	vc->vc_need_wrap = 0;
 }