[MRV2] Fix hanging issue with DeepSeek V3.2 by setting `skip_attn=False` (#39098)

Signed-off-by: WoosukKwon <woosuk.kwon@berkeley.edu>
Signed-off-by: Woosuk Kwon <woosuk@inferact.ai>

vllm/v1/worker/gpu/model_runner.py

@@ -391,12 +391,17 @@ class GPUModelRunner(LoRAModelRunnerMixin):
         self,
         num_tokens: int,
         *args,
-        skip_attn: bool = True,
+        skip_attn: bool = False,
         uniform_decode: bool = False,
         skip_eplb: bool = False,
         is_profile: bool = False,
         **kwargs,
     ) -> tuple[torch.Tensor | None, torch.Tensor | None]:
+        if skip_attn and not is_profile:
+            raise ValueError(
+                "skip_attn must only be True for initial memory profiling."
+            )
+
         # Create a dummy scheduler output.
         num_reqs = min(num_tokens, self.max_num_reqs)
         if uniform_decode:
@@ -988,6 +993,10 @@ class GPUModelRunner(LoRAModelRunnerMixin):
             if not skip_attn_for_dummy_run:
                 block_tables, slot_mappings = self.prepare_dummy_attn(input_batch)
             else:
+                assert batch_desc.cg_mode != CUDAGraphMode.FULL, (
+                    "Attention metadata must be prepared for dummy runs when using "
+                    "FULL cudagraph mode."
+                )
                 block_tables = None
                 slot_mappings = None
             # FIXME(woosuk): Fix warmup for LoRA.