linux-kernel - Re: [tip:core/ipi] generic-ipi: eliminate spurious pointlessWARN

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Date:	Fri, 13 Mar 2009 10:43:43 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jan Beulich <jbeulich@...ell.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [tip:core/ipi] generic-ipi: eliminate spurious
 pointlessWARN_ON()s

On Fri, 2009-03-13 at 09:21 +0000, Jan Beulich wrote:
> >>> Peter Zijlstra <peterz@...radead.org> 13.03.09 09:54 >>>
> >Wouldn't leaving them in place but changing them to:
> >
> >WARN_ON(irqs_disabled() && system_state == SYSTEM_RUNNING);
> >
> >be clearer?
> 
> I don't think that would be precise: system_state gets set to
> SYSTEM_RUNNING much later than APs get brought up (i.e. there are
> cases where the WARN_ON()s could validly trigger with SYSTEM_BOOTING),
> and also doesn't cover states > SYSTEM_RUNNING (where, again, after
> perhaps having brought down all APs the warnings could become pointless,
> but the warnings could be meaningful as long as there are still some APs
> online).
> 
> While from an abstract code reading perspective your suggestion might
> seem reasonable, the changed placement really reflects what the warning
> is trying to warn about - a potential deadlock which cannot occur under
> the conditions filtered out by conditionals the warnings were moved
> beyond.

How about?

WARN_ON_ONCE(irqs_disabled() && !oops_in_progress)


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