Re: [PATCH v2] gpu: Fix uninitialized buddy for built-in drivers

["Danilo Krummrich" <dakr@kernel.org>]

On Thu Feb 19, 2026 at 11:38 AM CET, Matthew Auld wrote:
> On 19/02/2026 10:16, Danilo Krummrich wrote:
>> On Mon Feb 16, 2026 at 12:19 PM CET, Koen Koning wrote:
>>> Use subsys_initcall instead of module_init for the GPU buddy allocator,
>>> so its initialization code runs before any gpu drivers.
>>> Otherwise, a built-in driver that tries to use the buddy allocator will
>>> run into a kernel NULL pointer dereference because slab_blocks is
>>> uninitialized.
>>>
>>> Specifically, this fixes drm/xe (as built-in) running into a kernel
>>> panic during boot, because it uses buddy during device probe.
>> 
>> I just noticed that this patch was sent twice, and I posted my feedback on [1]
>> -- pasting it here as well.
>> 
>>> Fixes: ba110db8e1bc ("gpu: Move DRM buddy allocator one level up (part two)")
>> 
>> This Fixes: tag seems wrong. How is this code move related to this problem?
>
> This popped up as a very recent regression for us internally. It looks 
> like it worked before since link order ensured drm_buddy came before all 
> the driver code. With above commit the link order changed and became 
> drm/ and then buddy. See [1] also, which is maybe clearer to see this.

I see, I think this would be a good hint for the commit message. :)

However, I think it was never meant to rely on a build system implementation
detail, nor would this be correct. So, I think this should add both Fixes: tags.

Whether it should be backported is a different question though, as it seems to
work by accident in previous versions, i.e. it is only a "potential bug".

My personal opinion is that it should be backported either way, however that's
ultimately up to the stable team.

- Danilo

>
> [1] 
> https://lore.kernel.org/intel-xe/20260213152047.179628-1-koen.koning@linux.intel.com/
>
>> 
>> This should rather be:
>> 
>> Fixes: 6387a3c4b0c4 ("drm: move the buddy allocator from i915 into common drm")
>> 
>> Also, please add:
>> 
>> Cc: stable@vger.kernel.org
>> 
>>> Cc: Joel Fernandes <joelagnelf@nvidia.com>
>>> Cc: Dave Airlie <airlied@redhat.com>
>>> Cc: intel-xe@lists.freedesktop.org
>>> Cc: Peter Senna Tschudin <peter.senna@linux.intel.com>
>>> Cc: Matthew Auld <matthew.auld@intel.com>
>>> Signed-off-by: Koen Koning <koen.koning@linux.intel.com>
>> 
>> [1] https://lore.kernel.org/all/DGIUUFLC31D5.2OZBF5FWQJWMZ@kernel.org/