linux-kernel - Re: [PATCH] tools/memory-model: remove rb-dep, smp_read_barrier_depends, and lockless

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Message-ID: <20180219174413.GV25201@hirez.programming.kicks-ass.net>
Date:   Mon, 19 Feb 2018 18:44:13 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Andrea Parri <parri.andrea@...il.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Akira Yokosawa <akiyks@...il.com>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        mingo@...nel.org, Will Deacon <will.deacon@....com>,
        boqun.feng@...il.com, npiggin@...il.com, dhowells@...hat.com,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH] tools/memory-model: remove rb-dep,
 smp_read_barrier_depends, and lockless_dereference

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.