linux-kernel - Re: [PATCH] vt: remove redundant condition from redraw

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Message-ID: <srp75229-623q-q31s-79op-076nqs4so36q@onlyvoer.pbz>
Date: Fri, 23 May 2025 14:22:40 -0400 (EDT)
From: Nicolas Pitre <npitre@...libre.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Jiri Slaby <jirislaby@...nel.org>
cc: linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vt: remove redundant condition from redraw_screen()

On Fri, 23 May 2025, Nicolas Pitre wrote:

> Given !con_is_visible(vc) is the equivalent of *vc->vc_display_fg != vc
> we have:
> 
> 	struct vc_data *old_vc = vc_cons[fg_console].d;
> 	if (old_vc == vc)
> 		return;
> 	*vc->vc_display_fg = vc;
> 	if (*vc->vc_display_fg != old_vc) /* !con_is_visible(old_vc) */
> 		...

Please disregard this patch. Obviously the last if substitution should
rather be:

        if (*old_vcvc->vc_display_fg != old_vc)

and there is no guarantee that vc->vc_display_fg and
old_vc->vc_display_fg have the same value.


Nicolas