linux-kernel - Re: [PATCH] Make WARN_ON/WARN_ON_ONCE no-ops when CONFIG

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Message-ID: <20071215041659.GB25324@gondor.apana.org.au>
Date:	Sat, 15 Dec 2007 12:16:59 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Make WARN_ON/WARN_ON_ONCE no-ops when CONFIG_BUG is off

On Fri, Dec 14, 2007 at 12:02:46PM -0600, Matt Mackall wrote:
>
> I added CONFIG_BUG, and I think the current behavior is correct. As
> you've noticed, we have to evaluate condition, it may have
> side-effects. And if code does:
> 
> 	/* this indicates a driver bug, report and fail gracefully */
> 	if (WARN_ON(val == NULL))
> 		return -EFAULT;

That's exactly the sort of use I had in mind :) I'm actually the
one who added the ability to use WARN_ON inside an if clause.

Just as the case of a BUG_ON, a WARN_ON should never occur in
practice, unless there is a bug which the code is not aware of.
As such we want it to go away completely if CONFIG_BUG is off.

> ..we surely want it to continue returning -EFAULT, regardless of
> whether we log it, no? What use case did you have in mind?

If you're using it for a scenario which is known to actually
occur, then some other mechanism should be chosen in place of
WARN_ON.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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