From 10f0a42de162c90c701f70c9c28dc31bfada87db Mon Sep 17 00:00:00 2001
From: Stephen Finucane <stephenfin@redhat.com>
Date: Wed, 5 Aug 2020 14:11:59 +0100
Subject: [PATCH] tests: Add reproducer for bug #1879878

When one resizes a pinned instance, the instance claims host CPUs for
pinning purposes on the destination. However, the host CPUs on the
source are not immediately relinquished. Rather, they are held by the
migration record, to handle the event that the resize is reverted. It is
only when one confirms this resize that the old cores are finally
relinquished.

It appears there is a potential race between the resource tracker's
periodic task and the freeing of these resources, resulting in attempts
to unpin host cores that have already been unpinned. This test
highlights that bug pending a fix.

Change-Id: Ie092628ac71eb87c9dfa7220255a2953ada9e04d
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
Related-Bug: #1879878
---
 .../functional/libvirt/test_numa_servers.py   | 83 +++++++++++++++++++
 1 file changed, 83 insertions(+)

diff --git a/nova/tests/functional/libvirt/test_numa_servers.py b/nova/tests/functional/libvirt/test_numa_servers.py
index 840cbab48dce..48bc8c0de2cd 100644
--- a/nova/tests/functional/libvirt/test_numa_servers.py
+++ b/nova/tests/functional/libvirt/test_numa_servers.py
@@ -20,6 +20,7 @@ import testtools
 from oslo_config import cfg
 from oslo_log import log as logging
 
+import nova
 from nova.conf import neutron as neutron_conf
 from nova import context as nova_context
 from nova import objects
@@ -598,6 +599,88 @@ class NUMAServersTest(NUMAServersTestBase):
                     'usages']
             self.assertEqual(expected_usage, compute_usage)
 
+    def test_resize_bug_1879878(self):
+        """Resize a instance with a NUMA topology when confirm takes time.
+
+        Bug 1879878 describes a race between the periodic tasks of the resource
+        tracker and the libvirt virt driver. The virt driver expects to be the
+        one doing the unpinning of instances, however, the resource tracker is
+        stepping on the virt driver's toes.
+        """
+        self.flags(
+            cpu_dedicated_set='0-3', cpu_shared_set='4-7', group='compute')
+        self.flags(vcpu_pin_set=None)
+
+        orig_confirm = nova.virt.libvirt.driver.LibvirtDriver.confirm_migration
+
+        def fake_confirm_migration(*args, **kwargs):
+            # run periodics before finally running the confirm_resize routine,
+            # simulating a race between the resource tracker and the virt
+            # driver
+            self._run_periodics()
+
+            # then inspect the ComputeNode objects for our two hosts
+            src_numa_topology = objects.NUMATopology.obj_from_db_obj(
+                objects.ComputeNode.get_by_nodename(
+                    self.ctxt, src_host,
+                ).numa_topology,
+            )
+            dst_numa_topology = objects.NUMATopology.obj_from_db_obj(
+                objects.ComputeNode.get_by_nodename(
+                    self.ctxt, dst_host,
+                ).numa_topology,
+            )
+            # FIXME(stephenfin): There should still be two pinned cores here
+            self.assertEqual(0, len(src_numa_topology.cells[0].pinned_cpus))
+            self.assertEqual(2, len(dst_numa_topology.cells[0].pinned_cpus))
+
+            # before continuing with the actualy confirm process
+            return orig_confirm(*args, **kwargs)
+
+        self.stub_out(
+            'nova.virt.libvirt.driver.LibvirtDriver.confirm_migration',
+            fake_confirm_migration,
+        )
+
+        # start services
+        self.start_computes(save_rp_uuids=True)
+
+        # create server
+        flavor_a_id = self._create_flavor(
+            vcpu=2, extra_spec={'hw:cpu_policy': 'dedicated'})
+        server = self._create_server(flavor_id=flavor_a_id)
+
+        src_host = server['OS-EXT-SRV-ATTR:host']
+
+        # we don't really care what the new flavor is, so long as the old
+        # flavor is using pinning. We use a similar flavor for simplicity.
+        flavor_b_id = self._create_flavor(
+            vcpu=2, extra_spec={'hw:cpu_policy': 'dedicated'})
+
+        # TODO(stephenfin): The mock of 'migrate_disk_and_power_off' should
+        # probably be less...dumb
+        with mock.patch(
+            'nova.virt.libvirt.driver.LibvirtDriver'
+            '.migrate_disk_and_power_off', return_value='{}',
+        ):
+            # TODO(stephenfin): Replace with a helper
+            post = {'resize': {'flavorRef': flavor_b_id}}
+            self.api.post_server_action(server['id'], post)
+            server = self._wait_for_state_change(server, 'VERIFY_RESIZE')
+
+        dst_host = server['OS-EXT-SRV-ATTR:host']
+
+        # Now confirm the resize
+
+        # FIXME(stephenfin): This should be successful, but it's failing with a
+        # HTTP 500 due to bug #1879878
+        post = {'confirmResize': None}
+        exc = self.assertRaises(
+            client.OpenStackApiException,
+            self.api.post_server_action, server['id'], post)
+        self.assertEqual(500, exc.response.status_code)
+        self.assertIn('CPUUnpinningInvalid', str(exc))
+
 
 class NUMAServerTestWithCountingQuotaFromPlacement(NUMAServersTest):