linux-kernel - Re: [PATCH] doc: Update wake_up() & co. memory-barrier guarantees

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Message-ID: <20180625122850.GA14561@andrea>
Date:   Mon, 25 Jun 2018 14:28:50 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>,
        Will Deacon <will.deacon@....com>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH] doc: Update wake_up() & co. memory-barrier guarantees

On Mon, Jun 25, 2018 at 01:12:45PM +0100, David Howells wrote:
> Peter Zijlstra <peterz@...radead.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.

RELEASE and ACQUIRE are not enough in SB.  Can you elaborate?

  Andrea


> 
> David