kern/38990: Unmounting a disk fails the first time

[apb%cequrux.com@localhost]

>Number:         38990
>Category:       kern
>Synopsis:       Unmounting a disk fails the first time
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Jun 19 17:35:00 +0000 2008
>Originator:     Alan Barrett
>Release:        NetBSD 4.99.63
>Organization:
Not much
>Environment:
System: NetBSD 4.99.63
Architecture: i386
Machine: i386
>Description:
        Attempting to unmount a file system that has recently been busy
        may fail.  Unmounting again after a short delay and/or sync is
        successful.

>How-To-Repeat:
        $ sudo mount -t ffs /dev/sd0e /mnt
        $ rsync /something/ /mnt/something/ # a large directory tree
        $ sudo umount /mnt
        umount: /mnt: Device busy
        $ sync ; sleep 1 ; sync ; sleep 1 ; sync
        $ sudo umount /mnt
        [ no error ]

>Fix:
        It seems to me that, if no user processes are keeping the
        device busy, then umount should succeed without an error.  It
        should internally cause buffered data to be flushed to disk if
        necessary.