Heads-up: Possible regression between 10.0-RELEASE and 10.1-BETA1 with '/ on ZFS' setup

[Glen Barber]

During testing of the 10.1-RC1, I set up a multi-disk VirtualBox VM to
test '/ on ZFS' in various scenarios.  FreeBSD 10.1-RC1 i386, when
installed on ZFS with more than one disk (i.e., mirror, raidz-1,
raidz-2, etc.) crashes when rebooting post-install.

This does not happen with a single-drive '/ on ZFS' setup under the same
configuration.

FreeBSD 10.0-RELEASE i386 does not exhibit this behavior, however
upgrading from 10.0-RELEASE to 10.0-BETA1 or later may exhibit
a double-fault panic on boot.

A possible solution to this is to set kern.kstack_pages=4 via loader(8),
however in my tests (solely in VirtualBox), this has been ineffective.

It is unclear to me right now if this is something specific to
VirtualBox or not, though this problem was reported recently through
Bugzilla ( https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=194015 ).

I am still bisecting the stable/10 tree to try to identify when this
possible regression was introduced, in addition to scrounging up the
hardware to be able to test this on a bare-metal machine to determine if
this is a VirtualBox (or hypervisor in general) specific problem, but
this is taking longer than initially expected.

To be perfectly clear, the panic does occur in my particular testing
environment as far back as 10.1-BETA1, so this is *not* something new to
the upcoming 10.1-RC1.

If you have a multi-drive '/ on ZFS' setup (mirror, raidz-1) *without*
PAE, and have upgraded to 10.1-BETA1 or later, please speak up in case
this is a problem specific to my testing environment, which will likely
be at least another day before I can verify is the case.

Glen

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