cherry-pick #20424 (#20661)

test=release/1.6, test=develop

python/paddle/fluid/framework.py

@@ -373,8 +373,8 @@ def cuda_pinned_places(device_count=None):
     assert core.is_compiled_with_cuda(), \
         "Not compiled with CUDA"
     if device_count is None:
-        device_count = _cpu_num()
-    return [core.cuda_pinned_places()] * device_count
+        device_count = len(_cuda_ids())
+    return [core.CUDAPinnedPlace()] * device_count
 
 
 class NameScope(object):

python/paddle/fluid/tests/unittests/test_tensor.py

@@ -275,6 +275,10 @@ class TestTensor(unittest.TestCase):
             self.assertTrue(
                 isinstance(
                     tensor._mutable_data(place, dtype), numbers.Integral))
+            places = fluid.cuda_pinned_places()
+            self.assertTrue(
+                isinstance(
+                    tensor._mutable_data(places[0], dtype), numbers.Integral))
 
 
 if __name__ == '__main__':