On 16/06/2024 14:43, Javier Martinez Canillas wrote:
Jocelyn Falempe <jfalempe@xxxxxxxxxx> writes:
Hello Jocelyn,
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.
In other words, my understanding from the discussion with Sima was that
this should be instead:
+ depends on DRM && !VT_CONSOLE
I've tested that and at least I see that a framebuffer console is present
and `echo c > /proc/sysrq-trigger` triggers the DRM panic handler message
(but don't know if the race exists and is just that I was not hitting it).
If my understanding is correct and should only be a depends on !VT_CONSOLE
then feel free to add my:
Tested-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
Best regards,
--
Jocelyn
