ZFS hang during reboot after updating / to rw

[Bruce Cran]

Hi,

I don't know if I'm doing something wrong, but I've found a way to
reliably hang the system during reboot - I'm running the latest HEAD
amd64 with ZFS on all the filesystems. After booting into single-user
mode I wanted to mount all the filesystems rw so I did:

# mount -a
(realised I needed to use "zfs mount -a" instead)
# zfs mount -a
(/ is still ro, so update it to rw)
# mount -u -o rw /

Then, when rebooting the reboot task got stuck with the following backtrace:

sched_switch()
mi_switch()
sleepq_switch()
sleepq_wait()
_sleep()
zfsvfs_teardown()
zfs_unmount()
dounmount()
vfs_unmountall()
kern_reboot()
reboot()
syscallenter()
syscall()
Xfast_syscall()

-- 
Bruce Cran