From mboxrd@z Thu Jan  1 00:00:00 1970
From: a.p.zijlstra@chello.nl (Peter Zijlstra)
Date: Mon, 13 Aug 2012 10:15:04 +0200
Subject: RFC: mutex: hung tasks on SMP platforms with
 asm-generic/mutex-xchg.h
In-Reply-To: <alpine.LFD.2.02.1208091243080.5231@xanadu.home>
References: <20120807115647.GA12828@mudshark.cambridge.arm.com>
 <alpine.LFD.2.02.1208090029460.5231@xanadu.home>
 <20120809144953.GC18486@mudshark.cambridge.arm.com>
 <alpine.LFD.2.02.1208091201380.5231@xanadu.home>
 <alpine.LFD.2.02.1208091243080.5231@xanadu.home>
Message-ID: <1344845704.31459.11.camel@twins>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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?