linux-kernel - Re: WARN_ON() which sometimes sucks

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Message-ID: <alpine.LFD.0.999.0707312101410.3582@woody.linux-foundation.org>
Date:	Tue, 31 Jul 2007 21:05:43 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Paul Mackerras <paulus@...ba.org>
cc:	Al Viro <viro@....linux.org.uk>, Alexey Dobriyan <adobriyan@...ru>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	herbert@...dor.apana.org.au
Subject: Re: WARN_ON() which sometimes sucks

On Wed, 1 Aug 2007, Paul Mackerras wrote:
>
> It will mean more code on architectures which have a
> conditional-trap-on-nonzero instruction, such as powerpc, since the
> compiler will generate instructions to evaluate !!x.  But I don't see
> any reason why ret_warn_on couldn't be a long.

Umm. The WARN_ON() might actually get a "long long" value for all we know. 
Ie it's perfectly possible that the WARN_ON might look like

	/* Must not have high bits on */
	WARN_ON(offset & 0xffffffff00000000);

which on a 32-bit pcc would apparently do the wrong thing entirely as it 
stands now. No?

I think I'll commit the !!(x) version, and you guys can try to figure out 
what the right thing is long-term. For all I know, the proper solution is 
to just revert the whole mess, and *not* make WARN_ON() return a value at 
all, since that seems to be the fundamental mistake here.

			Linus
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