linux-kernel - Re: [PATCH] locking: remove three unused Kconfig symbols

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Date:	Mon, 8 Apr 2013 17:36:14 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Paul Bolle <pebolle@...cali.nl>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux390@...ibm.com,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] locking: remove three unused Kconfig symbols


* Paul Bolle <pebolle@...cali.nl> wrote:

> On Mon, 2013-04-08 at 17:16 +0200, Ingo Molnar wrote:
> > * Paul Bolle <pebolle@...cali.nl> wrote:
> > > The Kconfig symbols ARCH_INLINE_READ_UNLOCK_IRQ,
> > > ARCH_INLINE_SPIN_UNLOCK_IRQ, and ARCH_INLINE_WRITE_UNLOCK_IRQ were added
> > > in v2.6.33, but have never actually been used. It is safe to remove
> > > these.
> > > 
> > Erm, if you look at the code in question you'll see that they are unused I think 
> > due to a bug:
> > 
> >  config INLINE_READ_UNLOCK_IRQ
> >         def_bool y
> >         depends on !PREEMPT || ARCH_INLINE_READ_UNLOCK_BH
> > 
> > Shouldn't that depend on ARCH_INLINE_READ_UNLOCK_IRQ?
> > 
> > Similarly for the others.
> 
> Yes, that seems correct. I must admit that I didn't spot that
> possibility, but then again this Kconfig file is near unreadable (too
> much repetition for human readers).

Yeah, Kconfig isn't a very sophisticated language - it's the COBOL of config 
languages.

> Would you have any idea why this problem wasn't noticed in 16 (!) releases? 
> Fedora 17, which I did this patch on, has Kconfig symbolk PREEMPT not set. Is it 
> perhaps commit to not enable that option?

AFAICS it's a latent bug: it can only be noticed if these switches are set to 
different values by an arch - but the defaults and s390 (the two main cases) never 
do that.

So it's not causing any runtime problems today - but should be fixed nevertheless, 
now that you noticed it! :-)

Thanks,

	Ingo
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