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Date:   Mon, 19 Feb 2018 18:44:13 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     Andrea Parri <parri.andrea@gmail.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Akira Yokosawa <akiyks@gmail.com>,
        Kernel development list <linux-kernel@vger.kernel.org>,
        mingo@kernel.org, Will Deacon <will.deacon@arm.com>,
        boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Luc Maranget <luc.maranget@inria.fr>,
        Patrick Bellasi <patrick.bellasi@arm.com>
Subject: Re: [PATCH] tools/memory-model: remove rb-dep,
 smp_read_barrier_depends, and lockless_dereference
Message-ID: <20180219174413.GV25201@hirez.programming.kicks-ass.net>
References: <20180217151413.GA3785@andrea>
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On Mon, Feb 19, 2018 at 12:14:45PM -0500, Alan Stern wrote:
> Note that operations like atomic_add_unless() already include memory 
> barriers.

It is valid for atomic_add_unless() to not imply any barriers when the
addition doesn't happen.