Hard hang in hypervisor!?

[Nathan Lynch]

Linas Vepstas wrote:
> 
> 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?

Sounds consistent with a task trying to double-acquire the lock, or an
interrupt handler attempting to acquire a lock that the current task
holds.  Or maybe even an uninitialized spinlock.  Do you know which
lock it was?