linux-kernel - Re: RFC: mutex: hung tasks on SMP platforms with asm-generic/mutex-xchg.h

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Message-ID: <1344845704.31459.11.camel@twins>
Date:	Mon, 13 Aug 2012 10:15:04 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Nicolas Pitre <nico@...xnic.net>
Cc:	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Chris Mason <chris.mason@...ionio.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: RFC: mutex: hung tasks on SMP platforms with
 asm-generic/mutex-xchg.h

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?
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