Fix a bug in cuda graph runner (#1094)

python/sglang/srt/model_executor/cuda_graph_runner.py

@@ -98,8 +98,8 @@ class CudaGraphRunner:
         self.req_pool_indices = torch.zeros(
             (self.max_bs,), dtype=torch.int32, device="cuda"
         )
-        self.seq_lens = torch.ones((self.max_bs,), dtype=torch.int32, device="cuda")
-        self.position_ids_offsets = torch.zeros(
+        self.seq_lens = torch.zeros((self.max_bs,), dtype=torch.int32, device="cuda")
+        self.position_ids_offsets = torch.ones(
             (self.max_bs,), dtype=torch.int32, device="cuda"
         )
         self.out_cache_loc = torch.zeros(
@@ -201,7 +201,7 @@ class CudaGraphRunner:
                 out_cache_loc=out_cache_loc,
                 return_logprob=False,
                 top_logprobs_nums=0,
-                positions=(seq_lens - 1).to(torch.int64),
+                positions=(seq_lens - 1 + position_ids_offsets).to(torch.int64),
                 flashinfer_decode_wrapper=flashinfer_decode_wrapper,
             )
 
@@ -225,8 +225,8 @@ class CudaGraphRunner:
         index = bisect.bisect_left(self.batch_size_list, raw_bs)
         bs = self.batch_size_list[index]
         if bs != raw_bs:
-            self.seq_lens.fill_(1)
-            self.position_ids_offsets.zero_()
+            self.seq_lens.zero_()
+            self.position_ids_offsets.fill_(1)
             self.out_cache_loc.zero_()
 
         # Common inputs