On 17/06/2024 10:25, Geert Uytterhoeven wrote:
Hi Jocelyn,
On Mon, Jun 17, 2024 at 10:16 AM Jocelyn Falempe <jfalempe@xxxxxxxxxx> wrote:
On 16/06/2024 14:43, Javier Martinez Canillas wrote:
Jocelyn Falempe <jfalempe@xxxxxxxxxx> 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@xxxxxxxx>
Signed-off-by: Jocelyn Falempe <jfalempe@xxxxxxxxxx>
---
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.
Ah thanks, but I think vgacon is safe to use with drm_panic.
The problem with fbcon, is that it can also uses the fbdev emulation
from the drm driver, and in this case, drm_panic will write to the same
framebuffer as fbcon during a panic, leading to corrupted output.
This can't occur with other graphical console, so !(FRAMEBUFFER_CONSOLE
&& VT_CONSOLE) is probably good.
--
Jocelyn
Gr{oetje,eeting}s,
Geert
