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Date: Thu, 1 Oct 2015 14:28:02 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
 Ingo Molnar <mingo@kernel.org>,
 Benjamin Herrenschmidt <benh@kernel.crashing.org>,
 Paul Mackerras <paulus@samba.org>, Michael Ellerman <mpe@ellerman.id.au>,
 Thomas Gleixner <tglx@linutronix.de>, Will Deacon <will.deacon@arm.com>,
 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
 Waiman Long <waiman.long@hp.com>
Subject: Re: [RFC v2 6/7] powerpc: atomic: Make atomic{,64}_xchg and xchg a
 full barrier
Message-ID: <20151001122802.GR2881@worktop.programming.kicks-ass.net>
References: <1442418575-12297-1-git-send-email-boqun.feng@gmail.com>
 <1442418575-12297-7-git-send-email-boqun.feng@gmail.com>
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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?