linux-kernel - Re: [RFC v2 6/7] powerpc: atomic: Make atomic{,64}

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Message-ID: <20151002052542.GZ3816@twins.programming.kicks-ass.net>
Date:	Fri, 2 Oct 2015 07:25:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Boqun Feng <boqun.feng@...il.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Waiman Long <waiman.long@...com>,
	Ingo Molnar <mingo@...nel.org>,
	Will Deacon <will.deacon@....com>,
	Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [RFC v2 6/7] powerpc: atomic: Make atomic{,64}_xchg and xchg a
 full barrier

On Fri, Oct 02, 2015 at 07:19:04AM +0800, Boqun Feng wrote:
> Hi Peter,
> 
> Please forgive me for the format of my reply. I'm travelling,
> and replying from my phone.
> 
> 2015年10月1日 下午7:28，"Peter Zijlstra" <peterz@...radead.org>写道：
> >
> > On Wed, Sep 16, 2015 at 11:49:34PM +0800, Boqun Feng wrote:
> > > According to memory-barriers.txt, xchg and its atomic{,64}_ versions
> > > need to imply a full barrier, however they are now just RELEASE+ACQUIRE,
> > > which is not a full barrier.
> > >
> > > So remove the definition of xchg(), and let __atomic_op_fence() build
> > > the full-barrier versions of these operations.
> >
> > Do you want to do a patch for -stable fixing the current implementation?
> 
> Good idea! I didn't think of this before, and I'd love to do the patch,
> but thing is that I'm not able to use my laptop until Oct 10th.
> I will send the patch once I'm back.
> Does that work for you?

Sure, no hurry.
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