On Thu Feb 19, 2026 at 1:44 PM CET, Matthew Auld wrote:
> On 19/02/2026 11:14, Danilo Krummrich wrote:
>> 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.
>
> Yeah, I'm really not sure tbh. From a quick grep there do seem to be
> other users relying on this:
>
> drm/drm_drv.c:1274:module_init(drm_core_init);
> drm/scheduler/sched_fence.c:238:module_init(drm_sched_fence_slab_init);
>
> The sched one looks identical with the slab thing. Do these need to be
> fixed also?
Yes, those should be fixed as well.
Also note that module_init() compiles down to device_initcall() when built-in,
i.e. the initcall stage that is mainly for drivers, not for subsystem code.
Do you want to send a fix for thise as well?
>>
>> 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/[email protected]/
>>>
>>>>
>>>> This should rather be:
>>>>
>>>> Fixes: 6387a3c4b0c4 ("drm: move the buddy allocator from i915 into common
>>>> drm")
>>>>
>>>> Also, please add:
>>>>
>>>> Cc: [email protected]
>>>>
>>>>> Cc: Joel Fernandes <[email protected]>
>>>>> Cc: Dave Airlie <[email protected]>
>>>>> Cc: [email protected]
>>>>> Cc: Peter Senna Tschudin <[email protected]>
>>>>> Cc: Matthew Auld <[email protected]>
>>>>> Signed-off-by: Koen Koning <[email protected]>
>>>>
>>>> [1] https://lore.kernel.org/all/[email protected]/
>>
