[config reload][202012] race condition introduced by `cli.run_command`

[zjswhhh]

[config reload][202012] race condition introduced by `cli.run_command`

[zjswhhh]

The cause is config reload calls db_migrator with return_cmd=False.

Before STATE_DB is "migrated", services are started.

sonic-utilities/config/main.py

Lines 1666 to 1683 in 6f84aae

	# Migrate DB contents to latest version
	db_migrator='/usr/local/bin/db_migrator.py'
	if os.path.isfile(db_migrator) and os.access(db_migrator, os.X_OK):
	if namespace is None:
	command = "{} -o migrate".format(db_migrator)
	else:
	command = "{} -o migrate -n {}".format(db_migrator, namespace)
	clicommon.run_command(command, display_cmd=True)
	# Re-generate the environment variable in case config_db.json was edited
	update_sonic_environment()
	# We first run "systemctl reset-failed" to remove the "failed"
	# status from all services before we attempt to restart them
	if not no_service_restart:
	_reset_failed_services()
	log.log_notice("'reload' restarting services...")
	_restart_services()

[zjswhhh]

Discussed with Vaibhav offline, seems like db_migrator is not the cause as it only explicitly retore certain list of tables.