[BugFix][MRV2] Fix cuda event reuse race (#39115)

Signed-off-by: Nick Hill <nickhill123@gmail.com>

vllm/v1/worker/gpu/async_utils.py

@@ -17,7 +17,6 @@ class AsyncOutput(AsyncModelRunnerOutput):
         num_sampled_tokens: torch.Tensor,
         main_stream: torch.cuda.Stream,
         copy_stream: torch.cuda.Stream,
-        copy_event: torch.cuda.Event,
     ):
         # NOTE(woosuk): We must retain references to the GPU tensors,
         # as the copy operations are performed on a different CUDA stream than
@@ -25,7 +24,7 @@ class AsyncOutput(AsyncModelRunnerOutput):
         self.model_runner_output = model_runner_output
         self.sampler_output = sampler_output
         self.num_sampled_tokens = num_sampled_tokens
-        self.copy_event = copy_event
+        self.copy_event = torch.cuda.Event()
 
         with stream(copy_stream, main_stream):
             copy_stream.wait_stream(main_stream)
@@ -78,12 +77,11 @@ class AsyncPoolingOutput(AsyncModelRunnerOutput):
         is_valid: torch.Tensor | None,
         main_stream: torch.cuda.Stream,
         copy_stream: torch.cuda.Stream,
-        copy_event: torch.cuda.Event,
     ):
         self.model_runner_output = model_runner_output
         self.pooler_output = pooler_output
         self.is_valid = is_valid
-        self.copy_event = copy_event
+        self.copy_event = torch.cuda.Event()
 
         with stream(copy_stream, main_stream):
             copy_stream.wait_stream(main_stream)

vllm/v1/worker/gpu/model_runner.py

@@ -130,7 +130,6 @@ class GPUModelRunner(LoRAModelRunnerMixin):
 
         self.use_async_scheduling = self.scheduler_config.async_scheduling
         self.output_copy_stream = torch.cuda.Stream(self.device)
-        self.output_copy_event = torch.cuda.Event()
 
         # Pipeline parallelism.
         self.use_pp = self.parallel_config.pipeline_parallel_size > 1
@@ -1180,7 +1179,6 @@ class GPUModelRunner(LoRAModelRunnerMixin):
             num_sampled_tokens=num_sampled,
             main_stream=self.main_stream,
             copy_stream=self.output_copy_stream,
-            copy_event=self.output_copy_event,
         )
 
         mm_inputs: tuple[list[torch.Tensor], torch.Tensor] | None = None
@@ -1270,7 +1268,6 @@ class GPUModelRunner(LoRAModelRunnerMixin):
             is_valid=is_valid,
             main_stream=self.main_stream,
             copy_stream=self.output_copy_stream,
-            copy_event=self.output_copy_event,
         )
 
         self.postprocess_pool(input_batch)