Add functional regression recreate test for bug 1790204

Since Pike, the FilterScheduler "claims" resources in
placement via allocations based on the flavor during
scheduling. For a same-host resize, the old and new flavor
are summed to get the overall allocation against the single
compute node resource provider, which can cause NoValidHost
failures during scheduling because the sum is over capacity
for the resource provider even though the new flavor alone
may be OK.

This adds a functional regression test to recreate the bug.

Change-Id: I036a5ceabe88dcc1fd85c09472481de7d02edf5f
Related-Bug: #1790204

nova/tests/functional/regressions/test_bug_1790204.py

@@ -0,0 +1,77 @@
+# Licensed 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.
+
+from oslo_utils.fixture import uuidsentinel as uuids
+import six
+
+from nova.tests.functional.api import client as api_client
+from nova.tests.functional import integrated_helpers
+
+
+class ResizeSameHostDoubledAllocations(
+        integrated_helpers.ProviderUsageBaseTestCase):
+    """Regression test for bug 1790204 introduced in Pike.
+
+    Since Pike, the FilterScheduler uses Placement to "claim" resources
+    via allocations during scheduling. During a move operation, the
+    scheduler will claim resources on the selected destination resource
+    provider (compute node). For a same-host resize, this means claiming
+    resources from the *new_flavor* on the destination while holding
+    allocations for the *old_flavor* on the source, which is the same
+    provider. This can lead to NoValidHost failures during scheduling a
+    resize to the same host since the allocations are "doubled up" on the
+    same provider even though the *new_flavor* allocations could fit.
+
+    This test reproduces the regression.
+    """
+
+    # Use the SmallFakeDriver which has little inventory:
+    # vcpus = 2, memory_mb = 8192, local_gb = 1028
+    compute_driver = 'fake.SmallFakeDriver'
+
+    def setUp(self):
+        super(ResizeSameHostDoubledAllocations, self).setUp()
+        self._start_compute(uuids.host)
+
+    def test_resize_same_host_full_allocations(self):
+        self.flags(allow_resize_to_same_host=True)
+        # Create two flavors so we can control what the test uses.
+        flavor = {
+            'flavor': {
+                'name': 'v1r2d1', 'ram': 2048, 'vcpus': 1, 'disk': 1028,
+            }
+        }
+        flavor1 = self.admin_api.post_flavor(flavor)
+        # Tweak the flavor to increase the number of VCPUs.
+        flavor['flavor'].update({'name': 'v2r2d1', 'vcpus': 2})
+        flavor2 = self.admin_api.post_flavor(flavor)
+
+        # Create a server from flavor1.
+        server = self._boot_and_check_allocations(flavor1, uuids.host)
+
+        # Now try to resize to flavor2.
+        resize_req = {
+            'resize': {
+                'flavorRef': flavor2['id'],
+            }
+        }
+        # FIXME(mriedem): This is bug 1790204 where scheduling fails with
+        # NoValidHost because the scheduler fails to claim "doubled up"
+        # allocations on the same compute node resource provider. Scheduling
+        # fails because DISK_GB inventory allocation ratio is 1.0 and when
+        # resizing to the same host we'll be trying to claim 2048 but the
+        # provider only has a total of 1024.
+        ex = self.assertRaises(api_client.OpenStackApiException,
+                               self.api.post_server_action,
+                               server['id'], resize_req)
+        self.assertEqual(400, ex.response.status_code)
+        self.assertIn('No valid host was found', six.text_type(ex))