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

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Date:	Mon, 06 Jun 2011 15:31:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
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

On Mon, 2011-06-06 at 15:21 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Mon, 2011-06-06 at 15:10 +0200, Ingo Molnar wrote:
> > 
> > 
> > > diff --git a/kernel/printk.c b/kernel/printk.c
> > > index 3518539..1b9d2be 100644
> > > --- a/kernel/printk.c
> > > +++ b/kernel/printk.c
> > > @@ -859,7 +859,6 @@ asmlinkage int vprintk(const char *fmt, va_list args)
> > >  		zap_locks();
> > >  	}
> > >  
> > > -	lockdep_off();
> > 
> > At the very least you should also do: s/raw_local_irq_/local_irq/ on
> > this function.
> 
> Right, i've also removed the preempt_disable()/enable() pair - that 
> looks superfluous.

aside from the preempt thing, such a patch was just tested, I had a
module trigger a lockdep warning, and stuck a printk() in the middle of
ttwu (conditional so I could actually boot).

So go ahead, and merge this.

We still need the patch to lock_is_held() though, since there's a few
other lockdep_off() sites in the kernel, and at least the NTFS one needs
to be able to schedule.


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