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Date: Wed, 1 Dec 2010 00:54:37 +0000
From: Bruce Cran <bruce@cran.org.uk>
To: freebsd-fs@freebsd.org
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Subject: ZFS hang during reboot after updating / to rw
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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