umount -f broken again [with devfs/NFS]

[Garrett Cooper]

On Wed, Dec 19, 2012 at 6:23 PM, Garrett Cooper <yanegomi at gmail.com> wrote:
>     Ran into this with a build of CURRENT 2 week or so old version of
> CURRENT (gjb's livecd) and while unmounting devfs with a week old
> build:
>
> # umount -f /ifs
> umount: unmount of /ifs failed: Device busy
> # uname -a
> FreeBSD wf158.west.isilon.com 10.0-CURRENT FreeBSD 10.0-CURRENT #3
> r+5a05236: Wed Dec 12 17:35:14 PST 2012
> root at wf158.west.isilon.com:/usr/obj/usr/src/sys/ISI-GENERIC  amd64
>
>     My gut reaction is that some recently changes to VFS probably
> broke this (a couple week old 9-STABLE build just hangs on an NFS
> mountpoint that's gone out to lunch).

    Interesting. Killed a "rogue mergemaster" instance and I noticed
that the umount -f command I had going on the 9-STABLE box is still
hung in newnfs state BUT the mountpoint is gone:

load: 0.11  cmd: umount 91115 [newnfs] 521.60r 0.00u 0.09s 0% 1440k
load: 0.11  cmd: umount 91115 [newnfs] 521.64r 0.00u 0.09s 0% 1440k
load: 0.11  cmd: umount 91115 [newnfs] 521.68r 0.00u 0.09s 0% 1440k
load: 0.11  cmd: umount 91115 [newnfs] 521.72r 0.00u 0.09s 0% 1440k

$ mount | grep /mnt/temp || echo "not found"
not found
$ ps auxww | grep umount | grep -v grep
root    91114    0.0  0.0   40152   2512 11  I+    6:15PM      0:00.03
sudo umount -f /mnt/temp
root    91115    0.0  0.0    9872   1456 11  D+    6:15PM      0:00.10
umount -f /mnt/temp
$ uname -a
FreeBSD forza.west.isilon.com 9.1-PRERELEASE FreeBSD 9.1-PRERELEASE #0
r+2fd0a57: Mon Dec  3 12:02:18 PST 2012
gcooper at forza.west.isilon.com:/usr/obj/usr/src/sys/FORZA  amd64

    I'm going to restart the box in a minute (have to swap out some
hardware), but I thought this was kind of strange.
Thanks,
-Garrett