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Date: Wed, 4 Nov 2015 17:01:04 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [GIT PULL] locking changes for v4.4
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On Wed, Nov 04, 2015 at 03:51:01PM +0100, Dmitry Vyukov wrote:
> To clarify, yes, documentation and tooling was my main motivation.

Right; I don't object to having _ctrl() methods purely for documentation
purposes, I keep finding places we rely on them. Having them stand out
better might be useful.

> It is usually helpful to see acquire/release, rmb/wmb pairs, and so it
> is useful to know that something below is ordered wrt this load by
> means of a control dependency (which effectively becomes an acquire,
> and there must be a pairing release somewhere).

You need at least a trailing smp_rmb() before you cover the ACQUIRE
semantics -- or have no trailing reads at all of course.