Unmounting a GFS2 filesystem appears to hang on RHEL 6

Environment

• Red Hat Enterprise Linux Server 6, 7 (with the High Availability and Resilient Storage Add Ons)
• A Global Filesystem 2(GFS2)

Issue

• Unmounting a GFS2 filesystem appears to hang.

Resolution

• This issue has been resolved with the errata RHSA-2016-0855 for the package(s) kernel-2.6.32-642.el6 or later for the channel(s) RHEL Desktop (v.6), RHEL HPC Node (v.6), RHEL Server (v.6), RHEL Workstation (v.6).
• This issue has been resolved with the errata RHSA-2016-2574 for the package(s) kernel-3.10.0-514.el7, kernel-tools-3.10.0-514.el7, kernel-tools-libs-3.10.0-514.el7 or later for the channel(s) RHEL Desktop (v.7), RHEL HPC Node (v.7), RHEL Server (v.7), RHEL Workstation (v.7).

Workaround:
Reboot the host that has the umount process that appears to be hung unmounting a GFS2 filesystem.

Root Cause

The umount is related to reference counting which was discovered when investigating another issue. In addition, it was discovered that the umount operation would not timeout and print to /var/log/dmesg the glocks that could not be cleared.

Diagnostic Steps

• Review the /var/log/messages file for any log events that showed a umount process that blocked for more than 120 seconds. This message is not guaranteed to be there when this issue occurs.
• Dump the process threads with sysrq -t so that GFS2 related processes can be reviewed.

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