To recreate this bug you may do the following:
o Mount a CD-ROM
o Share the CD-ROM mount point to the network
o NFS mount the shared CD-ROM on a remote client
o On the remote client umount the NFS share
At this point you will not be able umount the CD-ROM on the nfs server
until you shutdown the nfs daemons. The process that I have outlined
worked on all Red Hat releases up until 5.2. Since 6.0 you have to
shutdown the nfs server to umount the CD-ROM. I have recreated this
behavior on i386, Sparc, and Sparc64 platforms.
This is a difference between 2.2.x + knfsd and 2.0.x + user-space nfsd, and is
the expected behavior. Cross-reference this message on linux-kernel,
Same here on stock 6.1, very annoying...
Verified here. knfsd seems to be hanging on to handles to mount
points. It may be a feature but its not a nice one
assigned to johnsonm
Bug 8838 has been closed because it seems fixed with the NFS in 7.2/7.3/8.0
releases. The additional step that you have to do is to stop nfs from exporting
/mnt/cdrom and then you can unmount /mnt/cdrom safely.