[LU-14663] race in mdc changelog polling code

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.15.0
• Severity: 3
• Assignee: Alex Zhuravlev
• Reporter: Alex Zhuravlev

Description

userspace changelog consumers set CHANGELOG_FLAG_FOLLOW so that MDC'c changelog thread re-open/re-process the changelog once the end is reached.
the thread processing the changelog starts at open and can get to the end before that flag is set. so a consumer will miss all new records.