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

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Date:	Mon, 24 Sep 2012 14:54:47 +0200
From:	Daniel Vetter <daniel.vetter@...ll.ch>
To:	Peter Zijlstra <peterz@...radead.org>
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, Sep 24, 2012 at 2:24 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 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.

I've read through the patches and I'm hoping you don't volunteer me to
pick these up ... ;-) But there doesn't seem to be anything that would
get worse through this lockdep annotation patch, right?

> Also, don't cross-post with a subscribe only list.

Sorry, forgot about this, I'll try to fix this - we really need an
intel-gfx that's open to people not subscribed to it.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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