Description of problem:
A similar issue was reported upstream: https://bugs.launchpad.net/neutron/+bug/1885898

Please take a look at the logs pasted here: http://pastebin.test.redhat.com/887526

All controller logs can be found here: http://file.mad.redhat.com/eolivare/ovn-race-bug-16.1/

This is the test failing due to this bug: https://rhos-qe-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/job/DFG-network-networking-ovn-16.1_director-rhel-virthost-3cont_2comp-ipv4-geneve/93/testReport/junit/neutron_tempest_plugin.scenario.test_connectivity/NetworkConnectivityTest/test_connectivity_through_2_routers_id_8944b90d_1766_4669_bd8a_672b5d106bb7_/


The test fails when trying to connect via ssh to a VM instance with a FIP. What happens, according to the logs, is that a port was not added correctly to the router and due to that, the FIP is not reachable. The transaction was answered with a 200 OK by the neutron API, which is wrong too.

Apparently, there were two transactions on that port happening simultaneously: first one from controller-1 and second one from controller-2.
This is from controller-2: 
2020-07-24 09:03:23.416 26 INFO networking_ovn.db.revision [req-9a7f0860-874b-400c-8da1-8e9dd7bc0225 - - - - -] Successfully bumped revision number for resource 506b38c9-9c96-4ea3-ad73-1df17fcb5d39 (type: ports) to 5
Meanwhile, controller-1:
2020-07-24 09:03:23.792 30 INFO networking_ovn.db.revision [req-f075e29f-18fb-4847-a8ca-a75f18691a4d 16fba420c546457da720cb2460389130 f748c640989141599d3d9a416fdfd1ee - default default] Successfully bumped revision number for resource 506b38c9-9c96-4ea3-ad73-1df17fcb5d39 (type: router_ports) to 4

And finally, the transaction crashes on controller-1:
2020-07-24 09:03:23.972 30 ERROR ovsdbapp.backend.ovs_idl.transaction [req-f075e29f-18fb-4847-a8ca-a75f18691a4d 16fba420c546457da720cb2460389130 f748c640989141599d3d9a416fdfd1ee - default default] Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/ovsdbapp/backend/ovs_idl/connection.py", line 122, in run
    txn.results.put(txn.do_commit())                                            
  File "/usr/lib/python3.6/site-packages/ovsdbapp/backend/ovs_idl/transaction.py", line 86, in do_commit
    command.run_idl(txn)                                                        
  File "/usr/lib/python3.6/site-packages/networking_ovn/ovsdb/commands.py", line 1021, in run_idl
    resource_id=self.name, resource_type=self.resource_type)                    
networking_ovn.common.exceptions.RevisionConflict: OVN revision number for 506b38c9-9c96-4ea3-ad73-1df17fcb5d39 (type: ports) is equal or higher than the given resource. Skipping update





Version-Release number of selected component (if applicable):
RHOS-16.1-RHEL-8-20200723.n.0
ovn2.13-host-2.13.0-37.el8fdp.x86_64
python3-networking-ovn-7.2.1-0.20200611111150.18fabca.el8ost.noarch

The test did not fail with RHOS-16.1-RHEL-8-20200714.n.0, which has same OVN versions. This is normal because the issue is due to a race condition


How reproducible:
Not often, it is due to a race condition


Steps to Reproduce:
1. it was reproduced by tempest test neutron_tempest_plugin.scenario.test_connectivity.NetworkConnectivityTest.test_connectivity_through_2_routers
2.
3.