Comment 98 for bug 769927

Same issue here.
Once the last open file under the mountpoint is closed, umount causes kernel ooops. It looks to me like something has been freed when it shouldn't have been. Note the fact that umount reports "/cluster/gslap01: not mounted", when it most certainly was mounted:

[root@gslap02 ~]# killall -TERM lock_cleaner
[root@gslap02 ~]# lsof | grep /cluster/gslap01
lock_clea 7592 survey1 txt REG 0,23 1332384 95191157 /cluster/gslap01/gs/bin/a.1.1.0/lock_cleaner
lock_clea 7592 survey1 1w REG 0,23 3886 95191163 /cluster/gslap01/gs/bin/a.1.1.0/lock_cleaner.errors
lock_clea 7592 survey1 2w REG 0,23 3886 95191163 /cluster/gslap01/gs/bin/a.1.1.0/lock_cleaner.errors
lock_clea 7592 survey1 3u REG 0,23 16018 94405062 /cluster/gslap01/gs/database/11_7med/mission_plan/db_lock_table.dat
lock_clea 7592 survey1 4u REG 0,23 260 95191135 /cluster/gslap01/gs/bin/a.1.1.0/common_lock_table.dat
[root@gslap02 ~]#
[root@gslap02 ~]# lsof | grep /cluster/gslap01
[root@gslap02 ~]# umount /cluster/gslap01
umount: /cluster/gslap01: not mounted
[root@gslap02 ~]#
Message from syslogd@ at Mon Sep 5 10:54:52 2011 ...
gslap02 kernel: ------------[ cut here ]------------

Message from syslogd@ at Mon Sep 5 10:54:52 2011 ...
gslap02 kernel: invalid opcode: 0000 [#1] PREEMPT SMP

Message from syslogd@ at Mon Sep 5 10:54:52 2011 ...
gslap02 kernel: last sysfs file: /sys/devices/pci0000:00/0000:00:1c.5/0000:09:00.0/net/eth0/statistics/collisions

Message from syslogd@ at Mon Sep 5 10:54:52 2011 ...
gslap02 kernel: Process umount.nfs4 (pid: 8895, ti=e0834000 task=e08b7540 task.ti=e0834000)

Message from syslogd@ at Mon Sep 5 10:54:52 2011 ...
gslap02 kernel: Stack:

Message from syslogd@ at Mon Sep 5 10:54:52 2011 ...
gslap02 kernel: Call Trace:

Message from syslogd@ at Mon Sep 5 10:54:52 2011 ...
gslap02 kernel: Code: 46 20 c7 45 ec 00 00 00 00 85 c0 74 06 8b 40 60 89 45 ec 8d 82 5c 01 00 00 50 51 53 57 ff 75 ec 56 68 18 26 7f c0 e8 fe d2 f3 ff <0f> 0b 83 c4 1c eb fe 8b 7e 10 8d 46 68 89 45 e4 39 fe 75 1f 8b

Message from syslogd@ at Mon Sep 5 10:54:52 2011 ...
gslap02 kernel: EIP: [<c050360a>] shrink_dcache_for_umount_subtree+0xd5/0x1a0 SS:ESP 0068:e0835e8c