zfs panic mounting fs after crash with RC2

Hi,

since I got no further reaction on this on -stable, I'm trying it here on
-current as some discussion of RC2-issues seems to go on here, too. Any
help is -of course- very much appreciated:


Begin forwarded message:

Date: Wed, 4 Nov 2009 09:29:00 +0100
From: Gerrit Kühn <gerrit_at_pmp.uni-hannover.de>
To: freebsd-stable_at_FreeBSD.ORG
Cc: 
Subject: zfs panic mounting fs after crash with RC2


Hi,

Yesterday I had the opportunity to play around with my yet-to-become new
fileserver a bit more. Originally I had installed 7.2-R, which I upgraded
to 8-0-RC2 yesterday. After that I upgraded my zpool consisting of 4 disks
in raidz1 constallation to v13.
Some time later I tried to use powerd which was obviously a bad idea: it
crashed the machine immediately. I will give a separate report on that
later as it is probably related to the hardware, which is a bit exotic (VIA
VB8001 board with 64bit Via Nano processor).
However, the worst thing for me is, that after rebooting from that crash,
one of my zfs fs cannot be mounted anymore. As soon as I try to mount it I
get a kernel panic. I can still access the properties (I made use of
"canmount=noauto" for the first time :-), but I cannot do a snapshot of
the fs (funny enough, zfs complains that the fs is busy, while in reality
it is not even mounted - so how could it be busy?).

I took a picture of the kernel panic and put it here (don't know if there
is any useful information in it):
<http://www.pmp.uni-hannover.de/test/Mitarbeiter/g_kuehn/data/zfs-panic.jpg>

The pool as such seems to be fine, all other fs in it can be mounted and
used, only trying to mount tank/sys/var triggers this panic.
Are there any suggestions what I could do to get my fs back? Please let me
know if (and how) I can provide more debugging information.


cu
  Gerrit