[Bugfix] Don't attempt to use triton if no driver is active (#19561)

vllm/triton_utils/importing.py

@@ -12,6 +12,36 @@ HAS_TRITON = (
     find_spec("triton") is not None
     or find_spec("pytorch-triton-xpu") is not None  # Not compatible
 )
+if HAS_TRITON:
+    try:
+        from triton.backends import backends
+
+        # It's generally expected that x.driver exists and has
+        # an is_active method.
+        # The `x.driver and` check adds a small layer of safety.
+        active_drivers = [
+            x.driver for x in backends.values()
+            if x.driver and x.driver.is_active()
+        ]
+        if len(active_drivers) != 1:
+            logger.info(
+                "Triton is installed but %d active driver(s) found "
+                "(expected 1). Disabling Triton to prevent runtime errors.",
+                len(active_drivers))
+            HAS_TRITON = False
+    except ImportError:
+        # This can occur if Triton is partially installed or triton.backends
+        # is missing.
+        logger.warning(
+            "Triton is installed, but `triton.backends` could not be imported. "
+            "Disabling Triton.")
+        HAS_TRITON = False
+    except Exception as e:
+        # Catch any other unexpected errors during the check.
+        logger.warning(
+            "An unexpected error occurred while checking Triton active drivers:"
+            " %s. Disabling Triton.", e)
+        HAS_TRITON = False
 
 if not HAS_TRITON:
     logger.info("Triton not installed or not compatible; certain GPU-related"