linux-kernel - Re: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages

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Date:	Mon, 6 Jun 2011 17:08:08 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Arne Jansen <lists@...-jansens.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	efault@....de, npiggin@...nel.dk, akpm@...ux-foundation.org,
	frank.rowand@...sony.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [debug patch] printk: Add a printk killswitch to robustify NMI
 watchdog messages


* Ingo Molnar <mingo@...e.hu> wrote:

> The real fix might be to remove the lockdep_off()/on() call from 
> printk(), that looks actively evil ... we had to hack through 
> several layers of side-effects before we found the real bug - so 
> it's not like the off()/on() made things more robust!

The other obvious fix would be to *remove* the blasted wakeup from 
printk(). It's a serious debugging robustness violation and it's not 
like the wakeup is super important latency-wise.

We *already* have a timer tick driven klogd wakeup poll routine. So i 
doubt we'd have many problems from not doing wakeups from printk(). 
Opinions?

Thanks,

	Ingo
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