linux-kernel - Re: [PATCH 2/2] [RESEND] console: implement lockdep support for console

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Message-ID: <1348489478.11847.55.camel@twins>
Date:	Mon, 24 Sep 2012 14:24:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	DRI Development <dri-devel@...ts.freedesktop.org>,
	Dave Airlie <airlied@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH 2/2] [RESEND] console: implement lockdep support for
 console_lock

On Mon, 2012-09-24 at 14:17 +0200, Peter Zijlstra wrote:
> 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.

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