Re: [Intel-gfx] [PATCH] drm/i915: Accomodate for nested dma_resv fence addition

["Das, Nirmoy" <nirmoy.das@intel.com>]

This needs better explanation and probably CC to stable.

Please ignore this, I will resend.


Nirmoy

On 12/19/2022 1:36 PM, Nirmoy Das wrote:
> We have below nested fence slot reservation and then fence addition
> to that dma_resv.
> 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()
>
> A nested dma_resv_reserve_fences will not reserve extra slots and if the
> BO comes with lots of fences in its dma_resv, we might see:
>
> BUG_ON(fobj->num_fences >= fobj->max_fences);
>
> Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
> ---
>   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;
>