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Date: Thu, 15 Mar 2007 18:52:45 +0300
From: Sergei Shtylyov <sshtylyov@ru.mvista.com>
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To: Charles Krinke <ckrinke@istor.com>
Subject: Re: Exception in kernel mode
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Cc: Chris Carlson <ccarlson@istor.com>, Kevin Smith <ksmith@istor.com>,
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Hello.

Charles Krinke wrote:

> I have a PPC8241 which does an 

> Oops: Exception in kernel mode, sig: 4 [#1]
> PREEMPT
> NIP: 00000900 LR: C00E579C CTR: 00003A55

> When doing a 'tar -xvzf'. The NIP is pointing at the decrementer
> interrupt, I believe.

> As I understand the decrementer, this is basically the timer tick in the
> ppc and goes off every n ms continuously. 

> A tar is going to be concerned with date/time stamps on files, so it has
> some interaction with the clock algorithms.

> It seems to me that the decrementer should be able to go off at any time
> during kernel operation, so maybe the "Exception in kernel mode" is
> pointing us in an unusual direction.

    Obviously, you've got an exception in the decrementer exception handler 
itself -- and this was something like program check exception, judging on the 
signal you've got (SIGILL).

> So, with that said:

> "What might be the causes of such an exception from the decrementer in a
> 2.6.17.11 ppc8241 kernel?"

> "Where should one concentrate ones efforts in figuring this out?"

    Hrm, looks like some CPU errata maybe...

WBR, Sergei