linux-kernel - Re: troubleshooting/debugging hard locks

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Date:	Wed, 14 May 2008 20:43:13 -0700
From:	Lee Howard <faxguy@...ardsilvan.com>
To:	Zan Lynx <zlynx@....org>
CC:	Ray Lee <ray-lk@...rabbit.org>, linux-kernel@...r.kernel.org
Subject: Re: troubleshooting/debugging hard locks

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@...ardsilvan.com> 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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