Fix pci_tracker.save to delete all removed devs

The bug is that the save code modifies the self.pci_devs.object list
while iterating it. This resulted in only half of the removed devs was
deleted at each save() run. Iterating on a shallow copy of that list
fixes it.

Closes-Bug: #2115729
Change-Id: I2711be9605618c1b93104d1dbddd8c7ee73b577e
Signed-off-by: Balazs Gibizer <gibi@redhat.com>

nova/pci/manager.py

@@ -15,6 +15,7 @@
 #    under the License.
 
 import collections
+import copy
 import typing as ty
 
 from oslo_config import cfg
@@ -97,7 +98,8 @@ class PciDevTracker(object):
                 self.stats.add_device(dev)
 
     def save(self, context: ctx.RequestContext) -> None:
-        for dev in self.pci_devs:
+        devs = copy.copy(self.pci_devs.objects)
+        for dev in devs:
             if dev.obj_what_changed():
                 with dev.obj_alternate_context(context):
                     dev.save()

nova/tests/unit/pci/test_manager.py

@@ -885,18 +885,8 @@ class PciDevTrackerTestCase(test.NoDBTestCase):
         dev2.remove()
         self.tracker.save(self.fake_context)
 
-        # This is https://bugs.launchpad.net/nova/+bug/2115729 as
-        # only one half of the removed devices are destroyed.
-        self.assertEqual(len(self.tracker.pci_devs), 2)
-        self.assertEqual(self.destroy_called, 1)
-        # a subsequent save will destroy half of the remaining removed devices
-        self.tracker.save(self.fake_context)
         self.assertEqual(len(self.tracker.pci_devs), 1)
         self.assertEqual(self.destroy_called, 2)
-        # after the fix we should see that a single save causes all the
-        # removed devices destroyed
-        # self.assertEqual(len(self.tracker.pci_devs), 1)
-        # self.assertEqual(self.destroy_called, 2)
 
     def test_clean_usage(self):
         inst_2 = copy.copy(self.inst)