[PATCH 2/2] drm/amdkfd: Fix resource cursor initialization

[Christian König]

Am 13.03.21 um 03:43 schrieb Felix Kuehling:
> Make sure the cur->size doesn't exceed cur->remaining. Otherwise the
> first call to amdgpu_res_next will trigger the BUG_ON in that function.

Mhm the BUG_ON is correct since the function complains that we want to 
move the cursor forward by more than originally expected.

The problem is rather that somebody is using cur->size which is the size 
of the current segment as parameter for amdgpu_res_next().

Do you have a backtrace of this?

Thanks,
Christian.

>
> Fixes: 3af0a018a728 ("drm/amdgpu: new resource cursor")
> CC: Christian König <christian.koenig at amd.com>
> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_res_cursor.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_res_cursor.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_res_cursor.h
> index 1335e098510f..b49a61d07d60 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_res_cursor.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_res_cursor.h
> @@ -68,7 +68,7 @@ static inline void amdgpu_res_first(struct ttm_resource *res,
>   		start -= node++->size << PAGE_SHIFT;
>   
>   	cur->start = (node->start << PAGE_SHIFT) + start;
> -	cur->size = (node->size << PAGE_SHIFT) - start;
> +	cur->size = min((node->size << PAGE_SHIFT) - start, size);
>   	cur->remaining = size;
>   	cur->node = node;
>   }