linux-kernel - Re: Kernel panic - not syncing: Attempted to kill the idle task!

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Message-ID: <1339499306.31548.75.camel@twins>
Date:	Tue, 12 Jun 2012 13:08:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	hi3766691@...il.com, Hillf Danton <dhillf@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Zhouping Liu <zliu@...hat.com>
Subject: Re: Kernel panic - not syncing: Attempted to kill the idle task!

On Tue, 2012-06-12 at 12:27 +0200, Peter Zijlstra wrote:
> On Tue, 2012-06-12 at 13:20 +0300, Linus Torvalds wrote:
> > Peter, you are very fundamentally wrong if you think the distance
> > array has to be symmetric. That is fundamentally not true for many
> > typologies.
> > 
> > The trivial example of a non symmetric case is just a simple
> > unidirectional ring. The distance from n to n+1 is just one, but the
> > distance from n+1 to n is n-1 hops.
> > 
> > So don't try to say that distances have to be symmetric. That's just
> > garbage. 
> 
> Sure, I realize this, but the 17,18 thing isn't a ring. It looks like
> something that should be symmetric but isn't.

Not a unidirectional one that is.. I played around a bit more and found
a shape that isn't too odd:


                  2
                /   \
              0       5
             /      /  \
            1 --- / --- 3
             \  /      /
              4       6
                \   /
                  7 


I would've crossed 0<->6 instead of 1<->3 so the 2/3 connected nodes are
spread better, but what do I know.

The only really odd thing is the numbering, which is what threw me.

But yeah, the possibility of uni-directional rings makes detecting
obvious crack tables harder, which is why I haven't got it -- yet.
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