zpool export: umount fails, device inexplicably busy (lsof finds nothing)

[Gary Palmer]

On Thu, Nov 26, 2020 at 04:55:46PM +0000, Graham Perrin wrote:
> On 25/11/2020 17:35, Graham Perrin wrote:
> > ???
> > > root at momh167-gjp4-8570p:~ # zpool export Transcend
> > > cannot unmount '/Volumes/t500': umount failed
> > > root at momh167-gjp4-8570p:~ # umount /Volumes/t500
> > > umount: unmount of /Volumes/t500 failed: Device busy
> > > root at momh167-gjp4-8570p:~ # lsof /Volumes/t500/
> > > root at momh167-gjp4-8570p:~ #
> > > 
> > > ----
> > > 
> > > When this last occurred, I could export the pool after signing out
> > > from KDE.
> > > 
> > The problem seemed to be consistently reproducible but (fingers crossed)
> > no problem yesterday or today.
> > 
> > Previously: most often using OpenZFS in base.
> > 
> > Now using OpenZFS from ports, with r367936.
> > 
> > If the problem recurs: is it _ever_ sane to get nothing listed by lsof
> > for a volume that can not be unmounted?
> 
> I spoke too soon, the problem recurred this afternoon:
> 
> root at mowa219-gjp4-8570p:~ # zpool export Transcend
> cannot unmount '/Volumes/t500/VirtualBox': umount failed
> root at mowa219-gjp4-8570p:~ # lsof /Volumes/t500/VirtualBox
> lsof: WARNING: device cache mismatch: /dev/drm/121
> lsof: WARNING: /root/.lsof_mowa219-gjp4-8570p was updated.
> root at mowa219-gjp4-8570p:~ # lsof /Volumes/t500/VirtualBox
> root at mowa219-gjp4-8570p:~ # zpool export Transcend
> cannot unmount '/Volumes/t500/VirtualBox': umount failed
> root at mowa219-gjp4-8570p:~ # uname -v
> FreeBSD 13.0-CURRENT #72 r367936: Sun Nov 22 21:46:00 GMT 2020
> root at mowa219-gjp4-8570p:/usr/obj/usr/src/amd64.amd64/sys/GENERIC-NODEBUG
> root at mowa219-gjp4-8570p:~ # zfs --version
> zfs-0.8.0-1
> zfs-kmod-v2020110200-zfs_8583540c6
> root at mowa219-gjp4-8570p:~ #

does "fuser -c" show anything?

the -m option may also be interesting (Search through mmapped files too)

Regards,

Gary