FreeBSD ZFS v13 MFC — force unmount is experimental

As mentioned in previous blog post, ZFS version 13 has been MFC’d to RELENG_7. Things looked great even after upgrading zpool and zfs metadata… until I shut down the machine (e.g. reboot, shutdown -p now, etc.). A message in similar format is being spit out on VGA/serial console, once per ZFS pool/filesystem listed:

Force unmount is experimental - report any problems.

The code responsible for the message is here:

Further investigative efforts turn up this, which indicate this is may be “by design”…

…but I’d like to know why FreeBSD is setting MS_FORCE in fflag when calling zfs_umount(), especially when the machine is being shut down.

Someone did report this problem back in November 2008 (when the code was slightly different), but no one responded. However please note that the message in question is output once per ZFS pool/filesystem listed, and has nothing to do with ZFS as a root filesystem or not:

I’ve mailed Kip about this, so we’ll see what transpires…