more fun, upgrading from 10.3-STABLE 10.4-RELENG to 11.2-RELENG - kernel panic

[Lee Damon]

After discussion with Bob Bishop (thanks for the help!) I've tried to do 
the following to upgrade one of the old boxes I mentioned previously.

cd /usr/src
tar ... .
rm -rf .??* *
svn checkout httpg://svn.freebsd.org/base/releng/10.3 /usr/src
compile, installkernel, installworld...

Now that the host is running RELENG the next step was to update from 
10.4 to 11.2 via freebsd-update

freebsd-update
freebsd-install
freebsd-update upgrade -r 11.2-RELEASE
freebsd-update install

so far, so good. Now it all falls apart

shutdown -r now
... why isn't the host coming back? Oh look, kernel panic.

   Fatal trap 12: page fault while in kernel mode
   cpuid = 1; apci id = 01
   fault virtual address = 0x84
   fault code = supervisor read data, page not present

Google searches find references to the same panic type in VMs running 
11.1, including https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=220923

The differences are, that's 11.1 not 11.2 (I would presume the fix made 
it into 11.2 but maybe not) and most notably, that's against VMs and the 
host I'm doing this on is bare iron (Sun x4500).

Still, I gave the two entries in /boot/loader.conf a try, no joy. 
Exactly the same panic. Recording the boot with slow-mo shows the panic 
happening just after the USB devices are enumerated by the kernel. It 
never even tries to mount root.

I am able to boot to kernel.old, which appears to be my old 10.4-STABLE 
kernel. So now I'm kind of stuck. The update has already modified the 
config files as part of the first pass so rolling back may be a problem 
and moving forward seems unwise.

I have only one x4500 but I have three x4540s running 11.2-STABLE (also 
installed from source) just fine.

Anyone have any brilliant suggestions? I'm thinking of trying to compile 
11.2-RELENG in /usr/src so I can try installing that kernel but that'll 
take several hours at least (it's an old box).

nomad