drm/amdgpu: fix userptr lockup

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>
Reviewed-by: Monk Liu <monk.liu@amd.com>

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

@@ -142,6 +142,9 @@ static void amdgpu_mn_invalidate_range_start(struct mmu_notifier *mn,
 
 		list_for_each_entry(bo, &node->bos, mn_list) {
 
+			if (!bo->tbo.ttm || bo->tbo.ttm->state != tt_bound)
+				continue;
+
 			r = amdgpu_bo_reserve(bo, true);
 			if (r) {
 				DRM_ERROR("(%ld) failed to reserve user bo\n", r);