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From:   David Howells <dhowells@redhat.com>
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To:     Peter Zijlstra <peterz@infradead.org>
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Subject: Re: [PATCH] doc: Update wake_up() & co. memory-barrier guarantees
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Date:   Mon, 25 Jun 2018 13:12:45 +0100
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Peter Zijlstra <peterz@infradead.org> wrote:

> So yes, I suppose we're entirely suck with the full memory barrier
> semantics like that. But I still find it easier to think of it like a
> RELEASE that pairs with the ACQUIRE of waking up, such that the task
> is guaranteed to observe it's own wake condition.
> 
> And maybe that is the thing I'm missing here. These comments only state
> that it does in fact imply a full memory barrier, but do not explain
> why, should it?

I think because RELEASE and ACQUIRE concepts didn't really exist in Linux at
the time I wrote the doc, so the choices were read/readdep, write or full.

Since this document defines the *minimum* you can expect rather than what the
kernel actually gives you, I think it probably makes sense to switch to
RELEASE and ACQUIRE here.

David