[Bug fixed] fixed the crash when enable the dp-attention on the single card (#3958)

python/sglang/srt/models/deepseek_v2.py

@@ -848,12 +848,12 @@ class DeepseekV2AttentionMLA(nn.Module):
 def all_gather(
     input_tensor: torch.Tensor, forward_batch: ForwardBatch, rank, world_size, group
 ):
-    if world_size == 1:
-        return input_tensor
-
     all_lens = forward_batch.global_num_tokens_cpu
     max_len = max(forward_batch.global_num_tokens_cpu)
 
+    if world_size == 1:
+        return input_tensor, 0, all_lens[0]
+
     padded_tensor = torch.nn.functional.pad(
         input_tensor, (0, 0, 0, max_len - input_tensor.shape[0])
     )