drm/amdgpu: Reserve fences for VM update

In amdgpu_dma_buf_move_notify reserve fences for the page table updates
in amdgpu_vm_clear_freed and amdgpu_vm_handle_moved. This fixes a BUG_ON
in dma_resv_add_fence when using SDMA for page table updates.
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c

@@ -403,7 +403,10 @@ amdgpu_dma_buf_move_notify(struct dma_buf_attachment *attach)
 				continue;
 		}
 
-		r = amdgpu_vm_clear_freed(adev, vm, NULL);
+		/* Reserve fences for two SDMA page table updates */
+		r = dma_resv_reserve_fences(resv, 2);
+		if (!r)
+			r = amdgpu_vm_clear_freed(adev, vm, NULL);
 		if (!r)
 			r = amdgpu_vm_handle_moved(adev, vm);