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Subject: Re: um: WARNING: at kernel/futex.c:786 __unqueue_futex
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
        richard -rw- weinberger <richard.weinberger@gmail.com>,
        laijs@cn.fujitsu.com, LKML <linux-kernel@vger.kernel.org>,
        user-mode-linux-devel@lists.sourceforge.net, dvhart@linux.intel.com
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Date: Thu, 17 Mar 2011 19:38:42 +0100
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Le jeudi 17 mars 2011 à 19:25 +0100, Geert Uytterhoeven a écrit :
> On Thu, Mar 17, 2011 at 19:16, Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Thu, 2011-03-17 at 18:02 +0100, Eric Dumazet wrote:
> >> Le jeudi 17 mars 2011 à 12:55 -0400, Steven Rostedt a écrit :
> >> > Here, test this patch. I'm in the process of committing it now.
> >> > It will be two patches, one for the WARN_ON_SMP() change, the other for
> >> > the futex change.
> >> >
> >> > -- Steve
> >> >
> >> > diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
> >> > index c2c9ba0..25f1e9e 100644
> >> > --- a/include/asm-generic/bug.h
> >> > +++ b/include/asm-generic/bug.h
> >> > @@ -168,7 +168,7 @@ extern void warn_slowpath_null(const char *file, const int line);
> >> >  #ifdef CONFIG_SMP
> >> >  # define WARN_ON_SMP(x)                    WARN_ON(x)
> >> >  #else
> >> > -# define WARN_ON_SMP(x)                    do { } while (0)
> >> > +# define WARN_ON_SMP(x)                    ({0;})
> >> >  #endif
> >> >
> >>
> >> You meant :
> >>
> >> # define WARN_ON_SMP(x)                       ({x;})
> >>
> >> or
> >>
> >> # define WARN_ON_SMP(x)         do { } while (x, 0)
> >>
> >> ?
> >>
> >
> > Does if (do { } while (x, 0)) work?
> 

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 ;)