[hardware][rocm] allow rocm to override default env var (#7926)

vllm/core/scheduler.py

@@ -1088,7 +1088,8 @@ class Scheduler:
         )
 
     def _allow_async_output_proc(self, seq_group: SequenceGroup) -> bool:
-        no_beam_search = (seq_group.sampling_params.best_of == 1
+        no_beam_search = seq_group.sampling_params is None or (
+            seq_group.sampling_params.best_of == 1
             and not seq_group.sampling_params.use_beam_search)
 
         return no_beam_search

vllm/platforms/rocm.py

@@ -1,10 +1,21 @@
+import os
 from functools import lru_cache
 from typing import Tuple
 
 import torch
 
+from vllm.logger import init_logger
+
 from .interface import Platform, PlatformEnum
 
+logger = init_logger(__name__)
+
+if os.environ.get("VLLM_WORKER_MULTIPROC_METHOD", None) in ["fork", None]:
+    logger.warning("`fork` method is not supported by ROCm. "
+                   "VLLM_WORKER_MULTIPROC_METHOD is overridden to"
+                   " `spawn` instead.")
+    os.environ["VLLM_WORKER_MULTIPROC_METHOD"] = "spawn"
+
 
 class RocmPlatform(Platform):
     _enum = PlatformEnum.ROCM