Machine livelock with latest (4.99.48) kernel on sparc64

[Rafal Boni <rafal%pobox.com@localhost>]

I just rebooted my trusty Netra T1 with a shiny new 4.99.48 kernel and
thought I'd kick off a userland build.  Things seemed to go swimmingly
for a few minutes, then the machine ground to an un-usable state --
userland seems to be mostly non-responsive, though the machine is
pingable, answers a ^T at a tty (well, it seems to be wedged harder
now.. it did for a while after the apparent lockup), and the disk sounds
like progress is being made on the build.

But, I can't get any echo from a tty anymore, and god forbid I should
want to log in ;)

Anyone seeing anything similar?  Should I go back to the last-known-good
kernel for a while? ;)

Machine is a Netra T1 200 -- UltraSPARC-IIe @ 500 MHz with 512MB RAM.

Thanks,
--rafal