linux-kernel - Re: Linux 2.6.32-rc1

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Message-ID: <20090930203818.GA24070@elte.hu>
Date:	Wed, 30 Sep 2009 22:38:18 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Linux 2.6.32-rc1


* Ingo Molnar <mingo@...e.hu> wrote:

> * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > On Wed, 30 Sep 2009, Eric Dumazet wrote:
> > > > +#define cmpxchg64(ptr, o, n)					\
> > > > +({								\
> > > > +	__typeof__(*(ptr)) __ret;				\
> > > > +	__typeof__(*(ptr)) __old = (o);				\
> > > > +	__typeof__(*(ptr)) __new = (n);				\
> > > > +	alternative_io("call cmpxchg8b_emu",			\
> > > > +			"lock; cmpxchg8b (%%esi)" ,		\
> > > > +		       X86_FEATURE_CX8,				\
> > > > +		       "=A" (__ret),				\
> > > > +		       "S" ((ptr)), "0" (__old),		\
> > > > +		       "b" ((unsigned int)__new),		\
> > > > +		       "c" ((unsigned int)(__new>>32)));	\
> > > 
> > > probably a "memory" clobber is needed, alternative_io() doesnt provide it.
> > 
> > Yeah, good catch.
> 
> Yeah - i'm testing this right now, it looks like something that could 
> explain the hang.

Yeah - that was the cause of the hang.

I've pushed out the updated patches - they should show up in this thread 
soon. I also updated the emulation implementation to your simpler 
variant. (will test that too)

	Ingo
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