Namenode has FSN lock and FSD lock. Most of the namenode operations need to take FSN lock first and then FSD lock. The permission check is done via FSPermissionChecker at FSD layer assuming FSN lock is taken.
The FSPermissionChecker constructor invokes callerUgi.getGroups() that can take seconds sometimes. There are external cache scheme such SSSD and internal cache scheme for group lookup. However, the delay could still occur during cache refresh, which causes severe FSN lock contentions and unresponsive namenode issues.
Checking the current code, we found that getBlockLocations(..) did it right but some methods such as getFileInfo(..), getContentSummary(..) did it wrong. This ticket is open to ensure the group lookup for permission checker is outside the FSN lock.