Only involve tensor device in CUDA -> CPU copy, not current device. (#11592)

Summary:
This also unifies the device usage between the async and sync case.

Fixes https://github.com/pytorch/pytorch/issues/10832.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/11592

Differential Revision: D9797355

Pulled By: gchanan

fbshipit-source-id: e496cd371111cfaf9a6c664167967b395e3d72e9

test/test_cuda_primary_ctx.py

@@ -0,0 +1,58 @@
+import ctypes
+import torch
+from common import TestCase, run_tests, skipIfRocm
+import unittest
+
+# NOTE: this needs to be run in a brand new process
+
+# We cannot import TEST_CUDA and TEST_MULTIGPU from common_cuda here,
+# because if we do that, the TEST_CUDNN line from common_cuda will be executed
+# multiple times as well during the execution of this test suite, and it will
+# cause CUDA OOM error on Windows.
+TEST_CUDA = torch.cuda.is_available()
+TEST_MULTIGPU = TEST_CUDA and torch.cuda.device_count() >= 2
+
+if not TEST_CUDA:
+    print('CUDA not available, skipping tests')
+    TestCase = object  # noqa: F811
+
+
+def get_is_primary_context_created(device):
+    flags = ctypes.cast((ctypes.c_uint * 1)(), ctypes.POINTER(ctypes.c_uint))
+    active = ctypes.cast((ctypes.c_int * 1)(), ctypes.POINTER(ctypes.c_int))
+    result = torch.cuda.cudart().cuDevicePrimaryCtxGetState(ctypes.c_int(device), flags, active)
+    assert result == 0, 'cuDevicePrimaryCtxGetState failed'
+    return bool(active[0])
+
+
+class TestCudaPrimaryCtx(TestCase):
+    @unittest.skipIf(not TEST_MULTIGPU, "only one GPU detected")
+    @skipIfRocm
+    def test_cuda_primary_ctx(self):
+        # Ensure context has not been created beforehand
+        self.assertFalse(get_is_primary_context_created(0))
+        self.assertFalse(get_is_primary_context_created(1))
+
+        x = torch.randn(1, device='cuda:1')
+
+        # We should have only created context on 'cuda:1'
+        self.assertFalse(get_is_primary_context_created(0))
+        self.assertTrue(get_is_primary_context_created(1))
+
+        print(x)
+
+        # We should still have only created context on 'cuda:1'
+        self.assertFalse(get_is_primary_context_created(0))
+        self.assertTrue(get_is_primary_context_created(1))
+
+        y = torch.randn(1, device='cpu')
+        y.copy_(x)
+
+        # We should still have only created context on 'cuda:1'
+        self.assertFalse(get_is_primary_context_created(0))
+        self.assertTrue(get_is_primary_context_created(1))
+
+    # DO NOT ADD ANY OTHER TESTS HERE!  ABOVE TEST REQUIRES FRESH PROCESS
+
+if __name__ == '__main__':
+    run_tests()