kern/37965: umounting a union fs gives "device busy"

[ks%ub.uni-mainz.de@localhost]

>Number:         37965
>Category:       kern
>Synopsis:       umounting a union fs gives "device busy"
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Feb 05 19:50:00 +0000 2008
>Originator:     Kurt Schreiner
>Release:        -current from 08-01-30
>Organization:
Uni Mainz
>Environment:
NetBSD isunopti 4.99.52 NetBSD 4.99.52 (W2100Z) #65: Wed Jan 30 16:31:53 MET 
2008  ks@isunopti:/u/NetBSD/arch/amd64/obj/sys/arch/amd64/compile/W2100Z amd64

>Description:
since some days (not shure when this showed up the first time)
I see the following:

>-643: df
Filesystem                1K-blocks       Used      Avail %Cap Mounted on
/dev/sd0a                    128031      56856      64774  46% /
/dev/sd0i                   4066378      34250    3828810   0% /var
/dev/sd0h                    509527     402646      81405  83% /usr
/dev/sd0j                   8132773    2055146    5670989  26% /opt
/dev/sd0k                  20051105   14511984    4536566  76% /home
/dev/sd1h                  71241258   55315232   12363964  81% /u
tmpfs                       8828252         20    8828232   0% /tmp
kernfs                            1          1          0 100% /kern
procfs                            4          4          0 100% /proc
<above>:/u/NetBSD/lpkgsrc 126556490  110630464   12363964  89% /u/NetBSD/pkgsrc

>-644: fstat /u/NetBSD/pkgsrc
USER     CMD          PID   FD MOUNT       INUM MODE         SZ|DV R/W NAME

>-645: fstat /usr/pkgsrc
USER     CMD          PID   FD MOUNT       INUM MODE         SZ|DV R/W NAME

>-646: umount /usr/pkgsrc
umount: /u/NetBSD/pkgsrc: Device busy

>-647: egrep pkgsrc /etc/fstab
/u/NetBSD/lpkgsrc    /usr/pkgsrc     union   rw,noauto,nodev,nosuid  0 0


This happens after having done some IO. If I mount /usr/pkgsrc, cd to it, do 
"ls" in the top level directory - no problem w/ umount. The problem seems to 
show up when files/directories are accessed which have no counterpart in 
/u/NetBSD/lpkgsrc yet, ie. when inodes are created.

umount -f /usr/pkgsrc works and seems to have no bad effects...

>How-To-Repeat:
Use union mount, do something in the mounted fs, try to umount - et voila:
you see "device busy".
>Fix:
None known, yet.