[BugFix] Avoid initializing CUDA too early (#3487)

vllm/config.py

@@ -577,12 +577,12 @@ class DeviceConfig:
     def __init__(self, device: str = "auto") -> None:
         if device == "auto":
             # Automated device type detection
-            if torch.cuda.is_available():
-                self.device_type = "cuda"
-            elif is_neuron():
+            if is_neuron():
                 self.device_type = "neuron"
             else:
-                raise RuntimeError("No supported device detected.")
+                # We don't call torch.cuda.is_available() here to
+                # avoid initializing CUDA before workers are forked
+                self.device_type = "cuda"
         else:
             # Device type is assigned explicitly
             self.device_type = device