Hard hang in hypervisor!?

[linas@austin.ibm.com (Linas Vepstas)]

I was futzing with linux-2.6.23-rc8-mm1 in a power6 lpar when,
for whatever reason, a spinlock locked up. The bizarre thing 
was that the rest of system locked up as well: an ssh terminal,
and also an hvc console.

Breaking into the debugger showed 4 cpus, 1 of which was 
deadlocked in the spinlock, and the other 3 in 
.pseries_dedicated_idle_sleep

This was, ahhh, unexpected.  What's up with that? Can
anyone provide any insight?

I should mention:
-- prior to the complete hard lockp, I did see 
 BUG: soft lockup - CPU#0 stuck for 11s! [ip:4473]
go off, and I did manage to sneak in a few commands
into the console and the ssh session. Then it locked
up hard -- but still not completely -- exactly 
360 seconds later, a kernel thread ran for a while, 
producing some console output, even though the 
keyboard and console were locked up.

--linas