linux-kernel - Re: PATCH] debug: add notifier chain debugging

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Date:	Wed, 27 Aug 2008 03:55:01 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: PATCH] debug: add notifier chain debugging

On Wed, 27 Aug 2008 08:39:15 +0200
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Arjan van de Ven <arjan@...radead.org> wrote:
> 
> > The patch below fixes this;
> > Ingo, please replace the patch with this one.
> 
> well, this one is now less than cheap on x86:

really it isn't; dereference_function_descriptor is a fall through and
basically free.

> 
> as it's rather large. So i kept the config option, and it defaults to 
> off.

huh? the consensus was that the config needed to go ... nothing changed
on that front. I agree absolutely with not introducing config options
for things that don't need it; we have too many already anyway.


> 
> > +		if (!func_ptr_is_kernel_text(nb->notifier_call)) {
> > +			WARN(1, "Invalid notifier called!");
> > +			nb = next_nb;
> > +			continue;
> > +		}
> 
> and that should be an unlikely() too i guess.

please do not add new unlikely()'s to the kernel.. not on non-hotpaths
at least

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