Fix cuda graph mode in flashinfer attn backend (#10056)

python/sglang/srt/layers/attention/flashinfer_backend.py

@@ -501,8 +501,9 @@ class FlashInferAttnBackend(AttentionBackend):
                 sm_scale=layer.scaling,
                 window_left=layer.sliding_window_size,
                 logits_soft_cap=logits_soft_cap,
-                k_scale=layer.k_scale,
-                v_scale=layer.v_scale,
+                # Must use _float to avoid device-to-host copy that breaks cuda graph capture.
+                k_scale=layer.k_scale_float,
+                v_scale=layer.v_scale_float,
             )
         else:
             causal = True
@@ -580,8 +581,9 @@ class FlashInferAttnBackend(AttentionBackend):
             forward_batch.token_to_kv_pool.get_kv_buffer(layer.layer_id),
             sm_scale=layer.scaling,
             logits_soft_cap=layer.logit_cap,
-            k_scale=layer.k_scale,
-            v_scale=layer.v_scale,
+            # Must use _float to avoid device-to-host copy that breaks cuda graph capture.
+            k_scale=layer.k_scale_float,
+            v_scale=layer.v_scale_float,
         )
 
         return o.view(-1, layer.tp_q_head_num * layer.head_dim)