[PATCH] drm/amdgpu: avoid null dereference of fence when using cpu to update page tables

[Christian König]

Am 05.05.23 um 11:10 schrieb Lang Yu:
> Using cpu to update page tables is sychronous, no need to wait fence
> and it is NULL in such a case.

Good catch, be we usually install the stub into fence pointers when they 
are unused. See dma_fence_get_stub().

Christian.

>
> Signed-off-by: Lang Yu <Lang.Yu at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c
> index f0f00466b59f..197981c4ac7d 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c
> @@ -1043,8 +1043,11 @@ int amdgpu_mes_add_ring(struct amdgpu_device *adev, int gang_id,
>   
>   	amdgpu_mes_ring_to_queue_props(adev, ring, &qprops);
>   
> -	dma_fence_wait(gang->process->vm->last_update, false);
> -	dma_fence_wait(ctx_data->meta_data_va->last_pt_update, false);
> +	if (gang->process->vm->last_update)
> +		dma_fence_wait(gang->process->vm->last_update, false);
> +	if (ctx_data->meta_data_va->last_pt_update)
> +		dma_fence_wait(ctx_data->meta_data_va->last_pt_update, false);
> +
>   	amdgpu_mes_unlock(&adev->mes);
>   
>   	r = amdgpu_mes_add_hw_queue(adev, gang_id, &qprops, &queue_id);