From mboxrd@z Thu Jan  1 00:00:00 1970
From: will.deacon@arm.com (Will Deacon)
Date: Mon, 13 Aug 2012 10:13:49 +0100
Subject: RFC: mutex: hung tasks on SMP platforms with
 asm-generic/mutex-xchg.h
In-Reply-To: <1344845704.31459.11.camel@twins>
References: <20120807115647.GA12828@mudshark.cambridge.arm.com>
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 <20120809144953.GC18486@mudshark.cambridge.arm.com>
 <alpine.LFD.2.02.1208091201380.5231@xanadu.home>
 <alpine.LFD.2.02.1208091243080.5231@xanadu.home>
 <1344845704.31459.11.camel@twins>
Message-ID: <20120813091349.GA19113@mudshark.cambridge.arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Hi Peter,

On Mon, Aug 13, 2012 at 09:15:04AM +0100, Peter Zijlstra wrote:
> On Thu, 2012-08-09 at 12:57 -0400, Nicolas Pitre wrote:
> > 
> > In other words, I think this should look like this:
> > 
> > diff --git a/include/asm-generic/mutex-xchg.h b/include/asm-generic/mutex-xchg.h
> > index 580a6d35c7..44a66c99c8 100644
> > --- a/include/asm-generic/mutex-xchg.h
> > +++ b/include/asm-generic/mutex-xchg.h
> > @@ -25,8 +25,11 @@
> >  static inline void
> >  __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
> >  {
> > -       if (unlikely(atomic_xchg(count, 0) != 1))
> > -               fail_fn(count);
> > +       if (unlikely(atomic_xchg(count, 0) != 1)) {
> > +               /* Mark lock contention explicitly */
> > +               if (likely(atomic_xchg(count, -1) != 1))
> > +                       fail_fn(count);
> > +       }
> >  } 
> 
> OK, I like this.. Thanks guys! Will will you send a final and complete
> patch?

I sent one out on Friday but somehow managed to drop you from CC -- sorry
about that:

  http://thread.gmane.org/gmane.linux.kernel/1341305

Cheers,

Will