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Date: Fri, 13 Aug 2004 18:29:42 -0400 (EDT)
From: Robert Watson <rwatson@FreeBSD.org>
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To: Lukas Ertl <le@FreeBSD.org>
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cc: Martin Blapp <mb@imp.ch>
Subject: Re: Deadlocks with recent SMP current
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On Fri, 13 Aug 2004, Lukas Ertl wrote:

> On Fri, 13 Aug 2004, Robert Watson wrote:
> 
> > will eventually get a solid hang.  I tried it on a new SMP box with an NMI
> > button I received yesterday but was unable to get into the debugger.  I'm
> > in the process of de-obfuscating the NMI path to increase the chances of
> > successfully getting into the debugger and then I'll try again to see what
> > I can figure out.
> 
> I have an NMI-enabled SMP box too, and the only message I got when
> sending an NMI to the deadlocked system was 'kernel trap 12 with
> interrupts disabled', but nothing more. 
> 
> If you want me to test something, feel free to shout out. 

I'm having trouble making headway with this box, as the NMI doesn't seem
to be delivering in this hang (er, ouch).  You might want to try putting a
kdb_enter() just after the T_NMI in both switch statements in trap() in
i386/i386/trap.c.  This will cause the kernel to enter the debugger before
digging into the more general NMI code, which generates log messages, etc,
that may increase the chances of a problem.

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Principal Research Scientist, McAfee Research