Re: [PATCH] drm/i915/selftests: Fix unlocked mm.stolen in reset selftest

[Sebastian Brzezinka <sebastian.brzezinka@intel.com>]

Hi Andi,

On Fri Aug 28, 2026 at 1:17 AM CEST, Andi Shyti wrote:
> Hi Sebastian,
>
>> On Wed Aug 26, 2026 at 7:31 PM CEST, Andi Shyti wrote:
>> > Have you checked sashiko's reviews? They look valid to me.
>> >
>> I checked, and there are already existing issues, probably wrth fixing,
>> but they're outside the scope of this patch.
>
> actually you are in the middle of those issues :-)
>
>> > ...
>> >
>> >> @@ -95,9 +96,12 @@ __igt_reset_stolen(struct intel_gt *gt,
>> >>  				      ggtt->error_capture.start,
>> >>  				      PAGE_SIZE);
>> >>  
>> >> -		if (!__drm_mm_interval_first(&gt->i915->mm.stolen,
>> >> -					     page << PAGE_SHIFT,
>> >> -					     ((page + 1) << PAGE_SHIFT) - 1))
>> >> +		mutex_lock(&gt->i915->mm.stolen_lock);
>> >> +		unused = !__drm_mm_interval_first(&gt->i915->mm.stolen,
>> >> +						  page << PAGE_SHIFT,
>> >> +						  ((page + 1) << PAGE_SHIFT) - 1);
>> >> +		mutex_unlock(&gt->i915->mm.stolen_lock);
>> >> +		if (unused)
>> >
>> > this is always false.
>> Nothing really changes here, even if the if statement is always false,
>> we still need to guarantee safe access.
>
> I'm not getting your point. Do you mean that if nothing changes I
> can add things like "if (0) do_whatever_you_want;"?
I try not to change any logic, so it's now essentially if(0), just as
it was before, but now with a safe lock. I could dig deeper, but I think
it's good to fix the unrestricted access first.

-- 
Best regards,
Sebastian