From c74a4037fb0fb7afc6384c7b70b1f9773119548f Mon Sep 17 00:00:00 2001
From: "minke.yu" <minke.yu@ucloud.cn>
Date: Mon, 21 Sep 2026 12:46:25 +0800
Subject: [PATCH] mooncake: probe pointers via cuda.bindings instead of ctypes
 libcudart

The ctypes-based probing loaded a second libcudart copy into the process,
which corrupted CUDA/runtime state and segfaulted the scheduler processes
shortly after registration (reproducible on prefill ranks, intermittent on
decode). cuda.bindings.runtime.cudaPointerGetAttributes is a properly
typed binding and boots cleanly on both roles.
---
 .../srt/disaggregation/mooncake/conn.py       | 65 ++++++-------------
 1 file changed, 21 insertions(+), 44 deletions(-)

diff --git a/python/sglang/srt/disaggregation/mooncake/conn.py b/python/sglang/srt/disaggregation/mooncake/conn.py
index 7dbc59e65..69b0b76c4 100644
--- a/python/sglang/srt/disaggregation/mooncake/conn.py
+++ b/python/sglang/srt/disaggregation/mooncake/conn.py
@@ -101,32 +101,12 @@ FAILED_SESSION_RECOVERIES = Counter(
 
 import ctypes as _ctypes
 
-
-class _CudaPointerAttributes(_ctypes.Structure):
-    _fields_ = [
-        ("type", _ctypes.c_int),
-        ("device", _ctypes.c_int),
-        ("devicePointer", _ctypes.c_void_p),
-        ("hostPointer", _ctypes.c_void_p),
-    ]
-
-
 _CUDA_MEMORY_TYPE_DEVICE = 2
-_CUDART = None
 
-
-def _get_cudart():
-    global _CUDART
-    if _CUDART is None:
-        for name in ("libcudart.so", "libcudart.so.13", "libcudart.so.12"):
-            try:
-                _CUDART = _ctypes.CDLL(name)
-                break
-            except OSError:
-                continue
-        else:
-            _CUDART = False
-    return _CUDART or None
+try:
+    from cuda.bindings import runtime as _cudart
+except ImportError:  # pragma: no cover - cuda-python is always present in images
+    _cudart = None
 
 
 def _is_device_pointer(ptr: int) -> bool:
@@ -136,34 +116,32 @@ def _is_device_pointer(ptr: int) -> bool:
     segment addresses). Returns False on any error so the caller falls back
     to the safe host path.
     """
-    cudart = _get_cudart()
-    if cudart is None:
+    if _cudart is None:
         # Cannot tell; assume device so behavior stays unchanged.
         return True
-    attr = _CudaPointerAttributes()
-    ret = cudart.cudaPointerGetAttributes(
-        _ctypes.byref(attr), _ctypes.c_void_p(int(ptr))
-    )
-    if ret != 0:
+    err, attr = _cudart.cudaPointerGetAttributes(int(ptr))
+    if int(err) != 0:
         # Clear the error so subsequent CUDA calls are not poisoned.
-        cudart.cudaGetLastError()
+        _cudart.cudaGetLastError()
         return False
-    return attr.type == _CUDA_MEMORY_TYPE_DEVICE
+    return int(attr.type) == _CUDA_MEMORY_TYPE_DEVICE
 
 
 def _read_bytes_from_address(addr: int, length: int) -> Optional[bytes]:
     if length <= 0:
         return b""
     if _is_device_pointer(addr):
-        cudart = _get_cudart()
-        buf = (_ctypes.c_char * length)()
+        buf = bytearray(length)
         # cudaMemcpyDeviceToHost = 2; synchronous default-stream copy.
-        ret = cudart.cudaMemcpy(
-            buf, _ctypes.c_void_p(int(addr)), _ctypes.c_size_t(length), 2
+        err, = _cudart.cudaMemcpy(
+            _ctypes.addressof((_ctypes.c_char * length).from_buffer(buf)),
+            int(addr),
+            length,
+            2,
         )
-        if ret != 0:
+        if int(err) != 0:
             logger.error(
-                f"cudaMemcpy D2H failed (ret={ret}) for addr {hex(addr)} len {length}"
+                f"cudaMemcpy D2H failed (err={err}) for addr {hex(addr)} len {length}"
             )
             return None
         return bytes(buf)
@@ -174,15 +152,14 @@ def _write_bytes_to_address(addr: int, data: bytes) -> bool:
     if not data:
         return True
     if _is_device_pointer(addr):
-        cudart = _get_cudart()
         buf = _ctypes.create_string_buffer(data, len(data))
         # cudaMemcpyHostToDevice = 1; synchronous default-stream copy.
-        ret = cudart.cudaMemcpy(
-            _ctypes.c_void_p(int(addr)), buf, _ctypes.c_size_t(len(data)), 1
+        err, = _cudart.cudaMemcpy(
+            int(addr), _ctypes.addressof(buf), len(data), 1
         )
-        if ret != 0:
+        if int(err) != 0:
             logger.error(
-                f"cudaMemcpy H2D failed (ret={ret}) for addr {hex(addr)} "
+                f"cudaMemcpy H2D failed (err={err}) for addr {hex(addr)} "
                 f"len {len(data)}"
             )
             return False