linux-kernel - Re: lockdep and debug objects together are broken?

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Message-ID: <20090121115451.GA20696@elte.hu>
Date:	Wed, 21 Jan 2009 12:54:51 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Nick Piggin <npiggin@...e.de>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: lockdep and debug objects together are broken?


* Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> On Wed, 2009-01-21 at 12:42 +0100, Ingo Molnar wrote:
> 
> > So by the time you'd rearm, there's a lot of tasks with no proper 
> > locking state built up. We might be able to re-arm via 
> > stop_machine_run perhaps.
> 
> Won't work either, kstopmachine only preempts everybody. We'd require 
> something stronger.

indeed - mutexes wont be covered.

> What we need is a point where there's guaranteed no locks held, for 
> regular tasks that would be a trip to userspace and back, but for kernel 
> tasks that's a bit harder -- does the freezer stuff guarantee this?

yes, that might be doable.

Sounds very fragile though.

	Ingo
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