Subject: Re: [tip:core/urgent] WARN_ON_SMP(): Allow use in if() statements
 on UP
From: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org,
        dvhart@linux.intel.com, peterz@infradead.org,
        akpm@linux-foundation.org, srostedt@redhat.com, tglx@linutronix.de,
        laijs@cn.fujitsu.com, mingo@elte.hu, linux-tip-commits@vger.kernel.org
In-Reply-To: <AANLkTikfq9bz_cKdvq9ab+KS218Q7uVvoNdJeMe_-RUg@mail.gmail.com>
References: <20110317192208.444147791@goodmis.org>
	 <tip-2092e6be82ec71ecbf5a8ceeef004bbcbdb78812@git.kernel.org>
	 <AANLkTikfq9bz_cKdvq9ab+KS218Q7uVvoNdJeMe_-RUg@mail.gmail.com>
Content-Type: text/plain; charset="ISO-8859-15"
Date: Fri, 25 Mar 2011 14:16:21 -0400
Message-ID: <1301076981.14261.197.camel@gandalf.stny.rr.com>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 941
Lines: 34

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@redhat.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


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/