RHEL6: After upgrading the kernel, umount of NFS exported filesystem returns EBUSY even after stopping NFS and fuser and lsof shows no open files
Issue
After upgrading kernel version to 2.6.32-696.16.1.el6 a umount of an NFS exported filesystem returns EBUSY even after stopping NFS and there are no open files shown with lsof or fuser. After downgrading to older kernel version 2.6.32-696.10.3.el6_86_64, this issue does not reproduce.
# service nfs status
rpc.svcgssd is stopped
rpc.mountd is stopped
nfsd is stopped
rpc.rquotad is stopped
# fuser /export
# lsof /export
# unmount /export
unmount: /export: device is busy.
# umount -f /export
umount2: Device or resource busy
umount: /export: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))
umount2: Device or resource busy
# exportfs -au
# umount -f /export
umount2: Device or resource busy
umount: /export: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))
umount2: Device or resource busy
Environment
- Red Hat Enterprise Linux 6.6, 6.7 and 6.9 (NFS server)
- Seen after applying upgrade to kernel-2.6.32-696.16.1.el6
- NFSv3
- NFS server exporting a subdirectory of a mounted ext4 filesystem
- NFS client mounting a subdirectory of the exported subdirectory with NFSv3
- Original environment details (may not be relevant)
- Seen with ext4 filesystem over DRBD volume exported via NFS
- Seen with IBM Netezza NPS tool (changes /etc/exports)
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