Re: Hang on boot Was: [XenPPC] [xenppc-unstable] [POWERPC][XEN] Detect bad spurious interrupt condition and panic instead of hang

[Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>]

> Sometimes when Xen is booted and we let Linux init the MPIC for  
> "the second time" Xen could end up in a loop where the CPU is  
> constantly being interrupted by the MPIC.
> Because of console buffering, the last message you see is some  
> message from early kernel boot.
> Anyway.. we detect this now and you see a panic.
There seems to be a problem with the U3/U4 MPIC, where edge-
triggered interrupts are delivered to more than one CPU.  Every
CPU other than the one that ACKed it first, will get the spurious
vector (so functionally, the impact of this bug isn't that bad;
performance-wise it might be different).

The UART IRQ [on JS2x and Maple] is an edge IRQ; if you produce
console output for every spurious interrupt, you'll get a nice
little storm.  Is that what's happening?

> Yes, I believe, it has something to do with temperature.
Interesting observation, never thought of investigating that --
it's in line with my suspicion that something in the MPIC is
metastable though.


Segher


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