linux-kernel - Re: -tip: WARNING: at kernel/lockdep.c:2738

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Message-ID: <20080629174302.6d5d0797@linux360.ro>
Date:	Sun, 29 Jun 2008 17:43:02 +0300
From:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
To:	"Vegard Nossum" <vegard.nossum@...il.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Steven Rostedt" <srostedt@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: -tip: WARNING: at kernel/lockdep.c:2738

On Sun, 29 Jun 2008 15:51:33 +0200
"Vegard Nossum" <vegard.nossum@...il.com> wrote:

> Yep, thanks, that gets rid of it for me! Although I'm not sure how
> reproducible it was in the first place.
> 
> 
> Vegard
> 

lockdep's warnings are very reproducible as long as that code runs at
least once and that specific state transition occurs. AFAICS, all you
need to do is make sure cpu_clock() is called at least once with IRQs on
and at least once with IRQs off (this covers all possible cases). The
first case (IRQs on) is the important one and the one that produced the
bug, IMO.

The problem was raw_local_irq_save() does not record transitions, which
misleads lockdep. This likely wasn't a real bug.

	Eduard
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