problem updating 10-STABLE

[Yoshiaki Kasahara]

Hi,

Today I tried to update my 10-STABLE machine (full ZFS including root)
from r268480 (built on Jul 10) to r268734 (built today), but after
make installkernel and reboot into single user mode (to do make
installworld and mergemaster), I couldn't proceed further because "zfs
mount -a" crashed immediately with segfault.  Because only read-only
root fs was available, I couldn't do any debugging (/usr resides in a
separate fs).  Actually any zfs or zpool commands seemed to crash
immediately.

There were several ZFS related commits between two builds, but I
believe old userland should be usable with a newer kernel (or I cannot
follow the standard install procedure).

% uname -a
FreeBSD elvenbow.cc.kyushu-u.ac.jp 10.0-STABLE FreeBSD 10.0-STABLE #0 r268480: Thu Jul 10 15:25:15 JST 2014     root at elvenbow.cc.kyushu-u.ac.jp:/usr/obj/usr/src/sys/ELVENBOW  amd64
% what /boot/kernel.new/kernel
/boot/kernel.new/kernel:
        FreeBSD 10.0-STABLE #0 r268734: Wed Jul 16 12:36:48 JST 2014

Any suggestions?  I don't want to do make installworld during multi
user mode because I cannot ensure new zfs userland will work with new
kernel (if not, my system will become unusable).  Maybe try installing
new /rescue only and try it with the new kernel?

I'm considering to set up BE to avoid this kind of problem, but I need
some exercise...

Regards,
-- 
Yoshiaki Kasahara
Research Institute for Information Technology, Kyushu University
kasahara at nc.kyushu-u.ac.jp