Fail fast on extra_buffer for a non-mamba arch

python/sglang/srt/arg_groups/model_hook.py

@@ -921,6 +921,13 @@ def handle_mamba_radix_cache(server_args: Any, model_arch: str):
     run_post_process_pass(server_args, _mamba_radix_cache_resolution)
     view = resolved_view(server_args)
     if not view.uses_mamba_radix_cache:
+        # extra_buffer arms mamba-only ping-pong buffers that crash on a None
+        # buffer at decode. auto/no_buffer stay inert on a non-mamba arch.
+        if view.mamba_radix_cache_strategy in ("extra_buffer", "extra_buffer_lazy"):
+            raise ValueError(
+                f"--mamba-radix-cache-strategy={view.mamba_radix_cache_strategy} needs a model "
+                f"with mamba state, but {model_arch} has none. Use 'auto' (default) or 'no_buffer'."
+            )
         return
 
     if mamba_extra_buffer_of(view):

test/registered/unit/server_args/test_mamba_extra_buffer_arch_guard.py

@@ -0,0 +1,44 @@
+"""A mamba-only extra_buffer strategy on a non-mamba arch must fail fast at
+resolution, not arm the ping-pong track buffers and crash on a None buffer at
+decode. auto/no_buffer stay inert on such an arch.
+"""
+
+import unittest
+from types import SimpleNamespace
+
+from sglang.srt.arg_groups.model_hook import handle_mamba_radix_cache
+from sglang.srt.server_args import ServerArgs
+from sglang.test.ci.ci_register import register_cpu_ci
+from sglang.test.test_utils import CustomTestCase
+
+register_cpu_ci(est_time=1, suite="base-a-test-cpu")
+
+_NON_MAMBA_ARCH = "Qwen2ForCausalLM"
+
+
+class TestMambaExtraBufferArchGuard(CustomTestCase):
+    def _server_args(self, strategy):
+        sa = ServerArgs(model_path="dummy", mamba_radix_cache_strategy=strategy)
+        sa._model_config = SimpleNamespace(
+            hf_config=SimpleNamespace(architectures=[_NON_MAMBA_ARCH])
+        )
+        return sa
+
+    def test_extra_buffer_on_non_mamba_arch_raises(self):
+        for strategy in ("extra_buffer", "extra_buffer_lazy"):
+            with self.subTest(strategy=strategy):
+                with self.assertRaisesRegex(
+                    ValueError, "needs a model with mamba state"
+                ):
+                    handle_mamba_radix_cache(
+                        self._server_args(strategy), _NON_MAMBA_ARCH
+                    )
+
+    def test_inert_strategy_on_non_mamba_arch_is_accepted(self):
+        for strategy in ("auto", "no_buffer"):
+            with self.subTest(strategy=strategy):
+                handle_mamba_radix_cache(self._server_args(strategy), _NON_MAMBA_ARCH)
+
+
+if __name__ == "__main__":
+    unittest.main()