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Date: Wed, 21 Jan 2009 12:54:51 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nick Piggin <npiggin@suse.de>, Vegard Nossum <vegard.nossum@gmail.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: lockdep and debug objects together are broken?
Message-ID: <20090121115451.GA20696@elte.hu>
References: <20090120085559.GB19505@wotan.suse.de> <19f34abd0901201311t2425056dia6182812f7270297@mail.gmail.com> <20090121071950.GM24891@wotan.suse.de> <20090121114229.GA10606@elte.hu> <1232538602.4847.158.camel@laptop>
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* Peter Zijlstra <a.p.zijlstra@chello.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