diff mbox series

[1/7] drm: mark drm.debug-on-dyndbg as BROKEN for now

Message ID 20221111221715.563020-2-jim.cromie@gmail.com
State New
Headers
Series DYNAMIC_DEBUG fixups for rc |

Commit Message

Jim Cromie Nov. 11, 2022, 10:17 p.m. UTC 
  drm.debug-on-dyndbg has a regression, due to a chicken-egg
initialization problem:

1- modprobe i915
   i915 needs drm.ko, which is loaded 1st

2- "modprobe drm drm.debug=0x1ff" (virtual/implied)
   drm.debug is set post-initialization, from boot-args etc

3- `modprobe i915` finishes

W/O drm.debug-on-dyndbg that just works, because all drm_dbg*
callsites use drm_debug_enabled() to check __drm_debug & DEM_UT_<CAT>
before printing.

But the whole point of drm.debug-on-dyndbg is to avoid that runtime
test, by enabling (at post-modinit) a static-key at each callsite in
the just-loaded module.

And since drm.ko is loaded before all dependent modules, none are
"just-loaded", and no drm.debug callsites are present yet, except
those in drm.ko itself.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 drivers/gpu/drm/Kconfig | 1 +
 1 file changed, 1 insertion(+)

Comments

Ville Syrjälä Nov. 14, 2022, 12:20 p.m. UTC | #1 
On Fri, Nov 11, 2022 at 03:17:09PM -0700, Jim Cromie wrote:
> drm.debug-on-dyndbg has a regression, due to a chicken-egg
> initialization problem:
> 
> 1- modprobe i915
>    i915 needs drm.ko, which is loaded 1st
> 
> 2- "modprobe drm drm.debug=0x1ff" (virtual/implied)
>    drm.debug is set post-initialization, from boot-args etc
> 
> 3- `modprobe i915` finishes
> 
> W/O drm.debug-on-dyndbg that just works, because all drm_dbg*
> callsites use drm_debug_enabled() to check __drm_debug & DEM_UT_<CAT>
> before printing.
> 
> But the whole point of drm.debug-on-dyndbg is to avoid that runtime
> test, by enabling (at post-modinit) a static-key at each callsite in
> the just-loaded module.
> 
> And since drm.ko is loaded before all dependent modules, none are
> "just-loaded", and no drm.debug callsites are present yet, except
> those in drm.ko itself.
> 
> Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
> ---
>  drivers/gpu/drm/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 34f5a092c99e..0d1e59e6bb7e 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -54,6 +54,7 @@ config DRM_DEBUG_MM
>  config DRM_USE_DYNAMIC_DEBUG
>  	bool "use dynamic debug to implement drm.debug"
>  	default y

Could you switch to 'default n' as well? i915 CI actually enables
BROKEN so that we can test some more experimental stuff which is
hidden behind BROKEN for normal users.

> +	depends on BROKEN	# chicken-egg initial enable problem
>  	depends on DRM
>  	depends on DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE
>  	depends on JUMP_LABEL
> -- 
> 2.38.1
Greg KH Nov. 17, 2022, 6:29 a.m. UTC | #2 
On Fri, Nov 11, 2022 at 03:17:09PM -0700, Jim Cromie wrote:
> drm.debug-on-dyndbg has a regression, due to a chicken-egg
> initialization problem:
> 
> 1- modprobe i915
>    i915 needs drm.ko, which is loaded 1st
> 
> 2- "modprobe drm drm.debug=0x1ff" (virtual/implied)
>    drm.debug is set post-initialization, from boot-args etc
> 
> 3- `modprobe i915` finishes
> 
> W/O drm.debug-on-dyndbg that just works, because all drm_dbg*
> callsites use drm_debug_enabled() to check __drm_debug & DEM_UT_<CAT>
> before printing.
> 
> But the whole point of drm.debug-on-dyndbg is to avoid that runtime
> test, by enabling (at post-modinit) a static-key at each callsite in
> the just-loaded module.
> 
> And since drm.ko is loaded before all dependent modules, none are
> "just-loaded", and no drm.debug callsites are present yet, except
> those in drm.ko itself.
> 
> Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
> ---
>  drivers/gpu/drm/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 34f5a092c99e..0d1e59e6bb7e 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -54,6 +54,7 @@ config DRM_DEBUG_MM
>  config DRM_USE_DYNAMIC_DEBUG
>  	bool "use dynamic debug to implement drm.debug"
>  	default y
> +	depends on BROKEN	# chicken-egg initial enable problem
>  	depends on DRM
>  	depends on DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE
>  	depends on JUMP_LABEL
> -- 
> 2.38.1

This should go through the drm tree now.  The rest probably should also
go that way and not through my tree as well.

thanks,

greg k-h
diff mbox series

Patch

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 34f5a092c99e..0d1e59e6bb7e 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -54,6 +54,7 @@  config DRM_DEBUG_MM
 config DRM_USE_DYNAMIC_DEBUG
 	bool "use dynamic debug to implement drm.debug"
 	default y
+	depends on BROKEN	# chicken-egg initial enable problem
 	depends on DRM
 	depends on DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE
 	depends on JUMP_LABEL