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