Re: umounting a union fs gives "device busy"

[Andrew Doran <ad%netbsd.org@localhost>]

Hi,

On Mon, Feb 04, 2008 at 09:50:41AM +0100, Kurt Schreiner wrote:

> 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...
> 
> 
> Any idea anyone what's up there? What can I do to help debug this?

Can you file a PR please? I'm looking into unionfs problems at the moment.
Note that running unionfs on a multicpu machine is a bad idea at the moment.
If you need to use if, offline all but the boot cpu using cpuctl.

Thanks,
Andrew