linux-kernel - Re: [tip:core/urgent] WARN_ON_SMP(): Allow use in if() statements on UP

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Message-ID: <1301076981.14261.197.camel@gandalf.stny.rr.com>
Date:	Fri, 25 Mar 2011 14:16:21 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	dvhart@...ux.intel.com, peterz@...radead.org,
	akpm@...ux-foundation.org, srostedt@...hat.com, tglx@...utronix.de,
	laijs@...fujitsu.com, mingo@...e.hu,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/urgent] WARN_ON_SMP(): Allow use in if() statements
 on UP

On Fri, 2011-03-25 at 09:45 -0700, Linus Torvalds wrote:
> On Fri, Mar 25, 2011 at 3:48 AM, tip-bot for Steven Rostedt
> <srostedt@...hat.com> wrote:
> > -# define WARN_ON_SMP(x)                        do { } while (0)
> > +# define WARN_ON_SMP(x)                        ({0;})
> 
> That's a VERY odd way of writing "0".
> 
> Am I missing something subtle?

I thought about using "0", but when WARN_ON_SMP() is used outside of an
if statement, it turns into:

	0;

Which seems strange to me. Thus the ({0;}) was basically a way to state
that this is also a function and not just a 0 value.

Also, a quick test shows that

	0;

gives the warning:

	"warning: statement with no effect"

-- Steve


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