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

[Lang Yu]

Using cpu to update page tables is sychronous, no need to wait fence
and it is NULL in such a case.

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);
-- 
2.25.1