Re: [PATCH] drm: Disable dynamic debug as broken

[Jani Nikula <jani.nikula@intel.com>]

On Tue, 07 Feb 2023, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> On Tue, Feb 07, 2023 at 04:33:37PM +0200, Jani Nikula wrote:
>> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> 
>> CONFIG_DRM_USE_DYNAMIC_DEBUG breaks debug prints for (at least modular)
>> drm drivers. The debug prints can be reinstated by manually frobbing
>> /sys/module/drm/parameters/debug after the fact, but at that point the
>> damage is done and all debugs from driver probe are lost. This makes
>> drivers totally undebuggable.
>> 
>> There's a more complete fix in progress [1], with further details, but
>> we need this fixed in stable kernels. Mark the feature as broken and
>> disable it by default, with hopes distros follow suit and disable it as
>> well.
>> 
>> [1] https://lore.kernel.org/r/20230125203743.564009-1-jim.cromie@gmail.com
>> 
>> Fixes: 84ec67288c10 ("drm_print: wrap drm_*_dbg in dyndbg descriptor factory macro")
>> Cc: Jim Cromie <jim.cromie@gmail.com>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> Cc: Maxime Ripard <mripard@kernel.org>
>> Cc: Thomas Zimmermann <tzimmermann@suse.de>
>> Cc: David Airlie <airlied@gmail.com>
>> Cc: Daniel Vetter <daniel@ffwll.ch>
>> Cc: dri-devel@lists.freedesktop.org
>> Cc: <stable@vger.kernel.org> # v6.1+
>> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> ---
>>  drivers/gpu/drm/Kconfig | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
>> index f42d4c6a19f2..dc0f94f02a82 100644
>> --- a/drivers/gpu/drm/Kconfig
>> +++ b/drivers/gpu/drm/Kconfig
>> @@ -52,7 +52,8 @@ config DRM_DEBUG_MM
>>  
>>  config DRM_USE_DYNAMIC_DEBUG
>>  	bool "use dynamic debug to implement drm.debug"
>> -	default y
>> +	default n
>> +	depends on BROKEN
>>  	depends on DRM
>>  	depends on DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE
>>  	depends on JUMP_LABEL
>
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Thanks Greg, any more acks from anyone?

Maxime, since there's going to be an -rc8, I suggest taking this via
drm-misc-fixes. Is that okay with you? (You're doing drm-misc-fixes this
round, right?)

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center