[Bugfix] CudaDeviceAPI::GetAttr may check kExist when GPUs absent (#1…

…6903)

This commit resolves a bug that was introduced in
#16377.  If no CUDA-capable GPUs are
present, the call to `cudaGetDeviceCount` will return an error, which will
be raised as an exception by the `CUDA_CALL` macro.  However, checking
the `kExist` flag is valid even if no GPUs are present.

This commit removes the use of `CUDA_CALL`, and instead returns false
in this case.

src/runtime/cuda/cuda_device_api.cc

@@ -41,11 +41,12 @@ class CUDADeviceAPI final : public DeviceAPI {
   void GetAttr(Device dev, DeviceAttrKind kind, TVMRetValue* rv) final {
     int value = 0;
     switch (kind) {
-      case kExist:
+      case kExist: {
         int count;
-        CUDA_CALL(cudaGetDeviceCount(&count));
-        value = static_cast<int>(dev.device_id < count);
+        auto err = cudaGetDeviceCount(&count);
+        value = (err == cudaSuccess && static_cast<int>(dev.device_id < count));
         break;
+      }
       case kMaxThreadsPerBlock: {
         CUDA_CALL(cudaDeviceGetAttribute(&value, cudaDevAttrMaxThreadsPerBlock, dev.device_id));
         break;

tests/python/runtime/test_runtime_device_api.py

@@ -0,0 +1,52 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+import os
+import subprocess
+import sys
+
+import tvm
+import tvm.testing
+
+
+def test_check_if_device_exists():
+    """kExist can be checked when no devices are present
+
+    This test uses `CUDA_VISIBLE_DEVICES` to disable any CUDA-capable
+    GPUs from being accessed by the subprocess.  Within the
+    subprocess, the CUDA driver cannot be initialized.  While most
+    functionality of CUDADeviceAPI would raise an exception, the
+    `kExist` property can still be checked.
+
+    """
+
+    cmd = [
+        sys.executable,
+        "-c",
+        "import tvm; tvm.device('cuda').exist",
+    ]
+    subprocess.check_call(
+        cmd,
+        env={
+            **os.environ,
+            "CUDA_VISIBLE_DEVICES": "",
+        },
+    )
+
+
+if __name__ == "__main__":
+    tvm.testing.main()