From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 2/2] [RESEND] console: implement lockdep support for
 console_lock
Date: Mon, 24 Sep 2012 14:17:07 +0200
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To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: LKML <linux-kernel@vger.kernel.org>, Intel Graphics Development <intel-gfx@lists.freedesktop.org>, DRI Development <dri-devel@lists.freedesktop.org>, Dave Airlie <airlied@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, Alan Cox <alan@lxorguk.ukuu.org.uk>
List-Id: intel-gfx@lists.freedesktop.org

On Tue, 2012-09-18 at 01:03 +0200, Daniel Vetter wrote:
> - In the printk code there's a special trylock, only used to kick off
>   the logbuffer printk'ing in console_unlock. But all that happens
>   while lockdep is disable (since printk does a few other evil
>   tricks). So no issue there, either. 

Not particularly evil, just plain broken.

See this series:

  http://marc.info/?l=linux-kernel&m=132446644123326&w=2

In particular see patches 1-4. The problem with lockdep is that lockdep
uses printk and printk's recursion stuff is utterly broken.

Console drivers being on crack simply doesn't help :-) Note that I would
never recommend drm/ksm to anybody who really cares about their console
output.