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

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Message-Id: <1232538602.4847.158.camel@laptop>
Date:	Wed, 21 Jan 2009 12:50:02 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
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?

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.

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?

Supposing we have such a point for all tasks, what you then do is wipe
all lock state and rig a trigger to start tracking lock state once you
passed through the point.

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