[Intel-gfx] [PATCH] drm/i915: Reserve enough fence slot for i915_vma_unbind_async

[Das, Nirmoy]

On 1/5/2023 10:56 AM, Matthew Auld wrote:
> On Fri, 23 Dec 2022 at 09:20, Nirmoy Das <nirmoy.das at intel.com> wrote:
>> A nested dma_resv_reserve_fences(1) will not reserve slot from the
>> 2nd call onwards and folowing dma_resv_add_fence() might hit the
>> "BUG_ON(fobj->num_fences >= fobj->max_fences)" check.
>>
>> I915 hit above nested dma_resv case in ttm_bo_handle_move_mem() with
>> async unbind:
>>
>> dma_resv_reserve_fences() from --> ttm_bo_handle_move_mem()
>>          dma_resv_reserve_fences() from --> i915_vma_unbind_async()
>>          dma_resv_add_fence() from --> i915_vma_unbind_async()
>> dma_resv_add_fence() from -->ttm_bo_move_accel_cleanup()
>>
>> Resolve this by adding an extra fence in i915_vma_unbind_async().
>>
>> Suggested-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>> Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
> Reviewed-by: Matthew Auld <matthew.auld at intel.com>
>
> Does this need a fixes tag?
>
> Fixes: 2f6b90da9192 ("drm/i915: Use vma resources for async unbinding")
> Cc: <stable at vger.kernel.org> # v5.18+
>
> I can add when pushing.


Yes, please add that.


Thanks,

Nirmoy

>
>> ---
>>   drivers/gpu/drm/i915/i915_vma.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
>> index 7d044888ac33..5ac4c1c2403c 100644
>> --- a/drivers/gpu/drm/i915/i915_vma.c
>> +++ b/drivers/gpu/drm/i915/i915_vma.c
>> @@ -2149,7 +2149,7 @@ int i915_vma_unbind_async(struct i915_vma *vma, bool trylock_vm)
>>          if (!obj->mm.rsgt)
>>                  return -EBUSY;
>>
>> -       err = dma_resv_reserve_fences(obj->base.resv, 1);
>> +       err = dma_resv_reserve_fences(obj->base.resv, 2);
>>          if (err)
>>                  return -EBUSY;
>>
>> --
>> 2.38.0
>>