Good morning/afternoon/evening/night, 

I see that there was some debug code added to io_apic.c in kernel 2.4.6, 
that's compiled by default. 

It looks to me like there's a typo in the APIC_LOCKUP_DEBUG code that 
results in certain hardware setups potentially triggering an infinite loop, 
while holding the ioapic spinlock: namely when the irq_2_pin list contains 
more than one list member: the loop pointer gets reinitialized each time at 
the top of the loop - kablooey. 

After upgrading from 2.4.3 to 2.4.7, my 440GX motherboard (with a couple of 
PCI devices) keels over fast enough that even the NMI watchdog doesn't help, 
and the following patch fixes it. 

-- 
Sam