From 5a20996405c5788855a2457283bbbe7d78140a9c Mon Sep 17 00:00:00 2001
From: Matt Riedemann <mriedem.os@gmail.com>
Date: Tue, 29 Oct 2019 12:10:08 -0400
Subject: [PATCH] Reset instance to current vm_state if rolling back in
 resize_instance

You can resize a stopped instance and if the compute driver raises
InstanceFaultRollback from migrate_disk_and_power_off, the
_error_out_instance_on_exception decorator, used in the _resize_instance
method, will by default reset the instance vm_state to ACTIVE even though
the guest is stopped. The driver could raise InstanceFaultRollback if you
try resizing the root disk down on a non-volume-backed instance.

This builds on [1] and does the same thing as prep_resize [2] for
making sure the original vm_state is reset on InstanceFaultRollback.

[1] Ie4f9177f4d54cbc7dbcf58bd107fd5f24c60d8bb
[2] I17543ecb572934ecc7d0bbc7a4ad2f537fa499bc

Change-Id: Iff1f9f28a1e4ecf00368cbcac27b7687a5eb0dcf
Closes-Bug: #1551703
---
 nova/compute/manager.py                     |  7 ++++++-
 nova/tests/unit/compute/test_compute_mgr.py | 22 +++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/nova/compute/manager.py b/nova/compute/manager.py
index 79fc3058eb9c..6584edb3abd9 100644
--- a/nova/compute/manager.py
+++ b/nova/compute/manager.py
@@ -5032,7 +5032,12 @@ class ComputeManager(manager.Manager):
     def _resize_instance(self, context, instance, image,
                          migration, instance_type, clean_shutdown,
                          request_spec):
-        with self._error_out_instance_on_exception(context, instance), \
+        # Pass instance_state=instance.vm_state because we can resize
+        # a STOPPED server and we don't want to set it back to ACTIVE
+        # in case migrate_disk_and_power_off raises InstanceFaultRollback.
+        instance_state = instance.vm_state
+        with self._error_out_instance_on_exception(
+                context, instance, instance_state=instance_state), \
              errors_out_migration_ctxt(migration):
             network_info = self.network_api.get_instance_nw_info(context,
                                                                  instance)
diff --git a/nova/tests/unit/compute/test_compute_mgr.py b/nova/tests/unit/compute/test_compute_mgr.py
index 0712767f85cb..94a9bb0d9894 100644
--- a/nova/tests/unit/compute/test_compute_mgr.py
+++ b/nova/tests/unit/compute/test_compute_mgr.py
@@ -7829,6 +7829,28 @@ class ComputeManagerMigrationTestCase(test.NoDBTestCase,
         # Assert that we set the migration to an error state
         self.assertEqual("error", self.migration.status)
 
+    def test_resize_instance_fail_rollback_stays_stopped(self):
+        """Tests that when the driver's migrate_disk_and_power_off method
+        raises InstanceFaultRollback that the instance vm_state is preserved
+        rather than reset to ACTIVE which would be wrong if resizing a STOPPED
+        server.
+        """
+        with self._mock_resize_instance() as (
+                migrate_disk_and_power_off, notify):
+            migrate_disk_and_power_off.side_effect = \
+                exception.InstanceFaultRollback(
+                    exception.ResizeError(reason='unable to resize disk down'))
+            self.instance.vm_state = vm_states.STOPPED
+            self.assertRaises(
+                exception.ResizeError, self.compute.resize_instance,
+                context=self.context, instance=self.instance, image=self.image,
+                migration=self.migration,
+                instance_type='type', clean_shutdown=True,
+                request_spec=objects.RequestSpec())
+
+        # Assert the instance vm_state was unchanged.
+        self.assertEqual(vm_states.STOPPED, self.instance.vm_state)
+
     def test_resize_instance_notify_failure(self):
         # Raise an exception sending the end notification, which is after we
         # cast the migration to the destination host