[LU-16536] MDS umount can get stuck due to LDLM locks

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: Lustre 2.16.0
• Severity: 3
• Assignee: Alex Zhuravlev
• Reporter: Alex Zhuravlev

Description

the scenario is the following:

• rmdir is trying to unlink a striped dir
• a set of LDLM locks (from different MDT) are held by MDT
• number of RPCs are sent to another MDTs to destroy the objects
• another MDT umounts and no reply is sent back
• this MDT starts to umount, deactivate OSP#0 (corresponding RPCs are interrupted) and waiting for LDLM lock in this namespace to release
• the lock is still held by the original MDT thread doing rmdir
• other OSPs are still active trying to reconnect to umounted MDTs
• deadlock