drm/ttm: use RCU in ttm_bo_flush_all_fences

This allows it to call the function without the lock held.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: xinhui pan <xinhui.pan@amd.com>
Link: https://patchwork.freedesktop.org/patch/352742/

drivers/gpu/drm/ttm/ttm_bo.c

@@ -429,22 +429,24 @@ static int ttm_bo_individualize_resv(struct ttm_buffer_object *bo)
 
 static void ttm_bo_flush_all_fences(struct ttm_buffer_object *bo)
 {
+	struct dma_resv *resv = &bo->base._resv;
 	struct dma_resv_list *fobj;
 	struct dma_fence *fence;
 	int i;
 
-	fobj = dma_resv_get_list(&bo->base._resv);
-	fence = dma_resv_get_excl(&bo->base._resv);
+	rcu_read_lock();
+	fobj = rcu_dereference(resv->fence);
+	fence = rcu_dereference(resv->fence_excl);
 	if (fence && !fence->ops->signaled)
 		dma_fence_enable_sw_signaling(fence);
 
 	for (i = 0; fobj && i < fobj->shared_count; ++i) {
-		fence = rcu_dereference_protected(fobj->shared[i],
-					dma_resv_held(bo->base.resv));
+		fence = rcu_dereference(fobj->shared[i]);
 
 		if (!fence->ops->signaled)
 			dma_fence_enable_sw_signaling(fence);
 	}
+	rcu_read_unlock();
 }
 
 static void ttm_bo_cleanup_refs_or_queue(struct ttm_buffer_object *bo)