[PATCH] drm/panic: depends on !VT_CONSOLE

[Geert Uytterhoeven]

Hi Jocelyn,

On Mon, Jun 17, 2024 at 10:16 AM Jocelyn Falempe <jfalempe at redhat.com> wrote:
> On 16/06/2024 14:43, Javier Martinez Canillas wrote:
> > Jocelyn Falempe <jfalempe at redhat.com> writes:
> >> The race condition between fbcon and drm_panic can only occurs if
> >> VT_CONSOLE is set. So update drm_panic dependency accordingly.
> >> This will make it easier for Linux distributions to enable drm_panic
> >> by disabling VT_CONSOLE, and keeping fbcon terminal.
> >> The only drawback is that fbcon won't display the boot kmsg, so it
> >> should rely on userspace to do that.
> >> At least plymouth already handle this case with
> >> https://gitlab.freedesktop.org/plymouth/plymouth/-/merge_requests/224
> >>
> >> Suggested-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> >> Signed-off-by: Jocelyn Falempe <jfalempe at redhat.com>
> >> ---
> >>   drivers/gpu/drm/Kconfig | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> >> index a9df94291622..f5c989aed7e9 100644
> >> --- a/drivers/gpu/drm/Kconfig
> >> +++ b/drivers/gpu/drm/Kconfig
> >> @@ -107,7 +107,7 @@ config DRM_KMS_HELPER
> >>
> >>   config DRM_PANIC
> >>      bool "Display a user-friendly message when a kernel panic occurs"
> >> -    depends on DRM && !FRAMEBUFFER_CONSOLE
> >> +    depends on DRM && !(FRAMEBUFFER_CONSOLE && VT_CONSOLE)
> >
> > I thought the idea was to only make it depend on !VT_CONSOLE, so that
> > distros could also enable fbcon / VT but prevent the race condition to
> > happen due the VT not being a system console for the kernel to print
> > messages ?
>
> Yes, but when writing the patch, I thought that if you have VT_CONSOLE=y
> and FRAMEBUFFER_CONSOLE=n, then there won't be any race condition, and
> drm_panic can be enabled safely.
> I don't know if that really matters, and if VT_CONSOLE has any usage
> apart from fbcon.

It is used for any kind of virtual terminal, so also for vgacon.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds