Re: [PATCH], issue EOI to APIC prior to calling crash_kexec in die_nmi path

Neil Horman
2008-02-12T21:11:20Z

>
> Neil, is it possible to do some serial console debugging to find out
> where exactly we are hanging? Beats me, what's that operation which can
> not be executed while being in NMI handler and makes system to hang. I am
> also curious to know if it is nested NMI case.
>
> Thanks
> Vivek
>

Hey-
Some intermediate results:

I've instrumented head.S in the kernel with the following code:
#define SEROUT(z) \
mov $0x3F8,%dx;\
movb z,%al;\
outb %dx

And peppered different ascii characters throughout the startup code from
startup_32 to right before the jump to start_kernel. When I panic the system
via an:
echo c > /proc/sysrq_trigger
I see an appropriate sequence of characters on the serial console

When I panic the box by forcing an NMI watchdog timeout however, I see nothing.
The machine will either hang, or reset into the bios. I think this is
reasonably conclusive in its indication that we're not getting into the second
kernel when this problem occurs. Next I'll instrument the purgatory code in a
simmilar way.

Regards
Neil

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--
/****************************************************
* Neil Horman <nhorman@tuxdriver.com>
* Software Engineer, Red Hat
****************************************************/