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

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Message-ID: <20120813091349.GA19113@mudshark.cambridge.arm.com>
Date:	Mon, 13 Aug 2012 10:13:49 +0100
From:	Will Deacon <will.deacon@....com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Nicolas Pitre <nico@...xnic.net>,
	"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

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
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