Subject: Re: [debug patch] printk: Add a printk killswitch to robustify NMI
 watchdog messages
From: Mike Galbraith <efault@gmx.de>
To: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>, Arne Jansen <lists@die-jansens.de>,
        Linus Torvalds <torvalds@linux-foundation.org>, mingo@redhat.com,
        hpa@zytor.com, linux-kernel@vger.kernel.org, npiggin@kernel.dk,
        akpm@linux-foundation.org, frank.rowand@am.sony.com,
        tglx@linutronix.de, linux-tip-commits@vger.kernel.org
In-Reply-To: <20110606150808.GF30348@elte.hu>
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Date: Mon, 06 Jun 2011 19:44:00 +0200
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On Mon, 2011-06-06 at 17:08 +0200, Ingo Molnar wrote:
> * Ingo Molnar <mingo@elte.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?

Seconded!  I routinely whack that damn thing.

	-Mike

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