linux-kernel - Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire

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Date:   Thu, 12 Jul 2018 10:45:10 +0100
From:   Will Deacon <will.deacon@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andrea Parri <andrea.parri@...rulasolutions.com>,
        Alan Stern <stern@...land.harvard.edu>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        LKMM Maintainers -- Akira Yokosawa <akiyks@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Nicholas Piggin <npiggin@...il.com>,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and
 remove it for ordinary release/acquire

On Thu, Jul 12, 2018 at 11:34:32AM +0200, Peter Zijlstra wrote:
> On Thu, Jul 12, 2018 at 09:40:40AM +0200, Peter Zijlstra wrote:
> > And I think if we raise atomic*_acquire() to require TSO (but ideally
> > raise it to RCsc) we're there.
> 
> To clarify, just the RmW-acquire. Things like atomic_read_acquire() can
> stay smp_load_acquire() and be RCpc.

I don't have strong opinions about strengthening RmW atomics to TSO, so
if it helps to unblock Alan's patch (which doesn't go near this!) then I'll
go with it. The important part is that we continue to allow roach motel
into the RmW for other accesses in the non-fully-ordered cases.

Daniel -- your AMO instructions are cool with this, right? It's just the
fence-based implementations that will need help?

Will