linux-kernel - Re: um: WARNING: at kernel/futex.c:786 __unqueue

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Message-ID: <1300387417.16880.399.camel@gandalf.stny.rr.com>
Date:	Thu, 17 Mar 2011 14:43:37 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	laijs@...fujitsu.com, LKML <linux-kernel@...r.kernel.org>,
	user-mode-linux-devel@...ts.sourceforge.net, dvhart@...ux.intel.com
Subject: Re: um: WARNING: at kernel/futex.c:786 __unqueue_futex

On Thu, 2011-03-17 at 19:38 +0100, Eric Dumazet wrote:
>  
> 
> My point was that WARN_ON(X) always evaluates X once
> 
> And apparently, WARN_ON_SMP(X) doesnt evaluates X iF !SMP
> 
> This should be documented, or fixed ;)

My new patch has it documented. I even explain when to use the _SMP()
version, which is mainly for !spin_is_locked() as spin_is_locked()
always returns false, and !0 will trigger the warning.

It can also be used to test values that only exist in SMP.

struct foo {
	[...]
#ifdef CONFIG_SMP
	int bar;
#endif
};


	WARN_ON_SMP(zoo->bar);

We don't want that zoo->bar even evaluated for that case.

-- Steve



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