[Gllug] Remounting readonly fails

[Tet]

I keep /usr mounted readonly. Whenever I need to install or upgrade
something, the sequence goes something like this:

mrburns:~# mount -oremount,rw /usr
mrburns:~# yum update
mrburns:~# mount -oremount,ro /usr

However, occasionally, the third step fails:

mrburns:~# mount -o remount,ro /usr
mount: /usr is busy
mrburns:~# fuser -mv /usr

                     USER        PID ACCESS COMMAND
/usr                 root       2553 ....m  prefdm
                     root       2649 ...e.  xdm
                     root       2789 ...e.  X
                     root      19931 ...e.  sshd
                     root      22501 ...e.  xdm
                     tet       22513 ....m  fvwm
                     root      22563 ...e.  ssh-agent
                     root      22566 ...e.  ssh-agent
                     tet       22571 ....m  FvwmPager
                     tet       22572 ....m  FvwmEvent
                     root      32016 ...e.  xfs
                     tet       32041 ...e.  xterm
                     tet       32043 ....m  bash
                     root      32065 ....m  su
                     root      32068 ....m  bash
                     root      32206 ....m  fuser

fuser doesn't show anything obvious that's preventing the filesystem
from being remounted ro. Similarly, lsof doesn't show anything that
looks out of place. Any ideas? The kernel source shows that this error
is generated if there's an open file on that filesystem. But I can't
see one. Nor is there a lookback mount present (which has caught me
out in the past).

How can I find out what's marking the filesystem as busy?

Tet
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