Re: troubleshooting/debugging hard locks

[Lee Howard]

Zan Lynx wrote:
> On Wed, 2008-05-14 at 15:43 -0700, Ray Lee wrote:
>   
> > On Wed, May 14, 2008 at 12:27 PM, Lee Howard <faxguy@xxxxxxxxxxxxxxxx> wrote:
> >     
>
>   
> > >  But, without kernel messages indicating where to look to debug... what is
> > > the best approach to start troubleshooting and debugging this condition?  Is
> > > there some general debug feature that can be enabled in the kernel that
> > > would help hone in on the culprit?
> > >       
> > There's something called the NMI watchdog, that will print debugging
> > messages out if it finds the system has hard locked. The short version
> > is that you should add "nmi_watchdog=1" (no quotes) to the line in
> > GRUB that has the kernel options. That assumes you have an APIC on the
> > system. If that's not the case (you're on Uniprocessor, and no APIC)
> > then you can try nmi_watchdog=2 instead. That'll only work on some
> > systems, though.
> >
> > Better docs (than my cheesy writeup) are in
> > Documentation/nmi_watchdog.txt in the kernel source distribution.
> >     
>
> I was once told to add these to the kernel command line as well when
> using NMI watchdog and they do seem to help it trigger more reliably: 
>
> "idle=poll nohz=off"

Thank you to both Ray and Zan.  This was very helpful, and I think that 
it has gotten me what I needed.

"serial8250: too much work for irq16"

Interestingly, now CTRL-SysRq-H will wake it back up... things get 
running normally afterwards - the hard lock never occurs.

Thanks,

Lee.
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