From: Nicolas Pitre nico@fluxnic.net
commit 3f4ef485be9d54040b695f32ec76d0f1ea50bbf3 upstream.
Commit a6dbe4427559 ("vt: perform safe console erase in the right order") provided fixes to an earlier commit by gathering all console scrollback flushing operations in a function of its own. This includes the invocation of vc_sw->con_switch() as previously done through a update_screen() call. That commit failed to carry over the con_is_visible() conditional though, as well as cursor handling, which caused problems when "\e[3J" was written to a background console.
One could argue for preserving the call to update_screen(). However this does far more than we need, and it is best to remove scrollback assumptions from it. Instead let's gather the minimum needed to actually perform scrollback flushing properly in that one place.
While at it, let's document the vc_sw->con_switch() side effect being relied upon.
Signed-off-by: Nicolas Pitre nico@fluxnic.net Reported-and-tested-by: Lukas Wunner lukas@wunner.de Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/nycvar.YSQ.7.76.2001281205560.1655@knanqh.ubzr Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/tty/vt/vt.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-)
--- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -936,10 +936,21 @@ static void flush_scrollback(struct vc_d WARN_CONSOLE_UNLOCKED();
set_origin(vc); - if (vc->vc_sw->con_flush_scrollback) + if (vc->vc_sw->con_flush_scrollback) { vc->vc_sw->con_flush_scrollback(vc); - else + } else if (con_is_visible(vc)) { + /* + * When no con_flush_scrollback method is provided then the + * legacy way for flushing the scrollback buffer is to use + * a side effect of the con_switch method. We do it only on + * the foreground console as background consoles have no + * scrollback buffers in that case and we obviously don't + * want to switch to them. + */ + hide_cursor(vc); vc->vc_sw->con_switch(vc); + set_cursor(vc); + } }
/*