Re: [Xen-devel] Xen-unstable: Regression (on AMD) host boot stuck on (XEN) testing the IO APIC.......................

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.08.14 at 20:25, <linux@xxxxxxxxxxxxxx> wrote:
> Monday, August 25, 2014, 7:54:05 PM, you wrote:
>> Hmm - Does reverting e13b3203990706db1313ec2aadd9a30b249ee793 fix the issue?
> 
> Hmm i completely overlooked that commit (it's quite evident when you look at 
> the 
> commitdiff :-) )
> 
> Just tested reverting that single commit and that indeed lets the machine 
> boot again.

Considering how early this is, the only theory I have is that
rcu_pending() may end up constantly returning true, thus always
causing RCU_SOFTIRQ to get raised, not allowing the loop in
__do_softirq() to ever exit. If that's the case, we seem to have
two options:
- pass into __print_IO_APIC() whether it's being called from a key
  handler
- only call process_pending_softirqs() when system_state >=
  SYS_STATE_smp_boot

Personally I'd prefer the former option.

But Sander, a fundamental question: Why would you _always_
boot your system with "apic=debug" and those various other
debugging options? They are, as you may guess, for debugging,
not for day to day use. (That said I'm glad you have this in place
for this particular case, as it allowed spotting a regression early.)

Jan


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