should be after logSync, as we do in other FSN places (rename, delete, write with overwrite), the reason is discussed in
HDFS-2815 and https://issues.apache.org/jira/browse/HDFS-6871?focusedCommentId=14110068&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14110068
We'd better to use dir.getAuditFileInfo, since it's only for audit log. If audit log is not on, we don't need to get the file info.
is not necessary.