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

Open Source and information security mailing list archives

Date:	Tue, 12 Feb 2008 16:08:16 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, "Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	tglx@...utronix.de
Subject: Re: [PATCH], issue EOI to APIC prior to calling crash_kexec in
	die_nmi path

> 
> 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

> _______________________________________________
> kexec mailing list
> kexec@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec

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