Re: [Intel-gfx] [PATCH 1/4] drm/i915/gt: GEM_BUG_ON unexpected NULL at scatterlist walking

["Hellstrom, Thomas" <thomas.hellstrom@intel.com>]

On Thu, 2022-04-21 at 17:08 +0530, Ramalingam C wrote:
> While locating the start of ccs scatterlist in smem scatterlist, that
> has
> to be the size of lmem obj size + corresponding ccs data size. Report
> bug
> if scatterlist terminate before that length.
> 
> Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_migrate.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_migrate.c
> b/drivers/gpu/drm/i915/gt/intel_migrate.c
> index 9d552f30b627..29d761da02c4 100644
> --- a/drivers/gpu/drm/i915/gt/intel_migrate.c
> +++ b/drivers/gpu/drm/i915/gt/intel_migrate.c
> @@ -687,6 +687,12 @@ static void get_ccs_sg_sgt(struct sgt_dma *it,
> u32 bytes_to_cpy)
>                 bytes_to_cpy -= len;
>  


>                 it->sg = __sg_next(it->sg);

If bytes_to_cpy == 0 here, couldn't it->sg be NULL then?

> +
> +               /*
> +                * scatterlist supposed to be the size of
> +                * bytes_to_cpy + GET_CCS_BYTES(bytes_to_copy).
> +                */
> +               GEM_BUG_ON(!it->sg);
>                 it->dma = sg_dma_address(it->sg);
>                 it->max = it->dma + sg_dma_len(it->sg);
>         } while (bytes_to_cpy);

/Thomas