linux-kernel - Re: [PATCH 2/2] tools/memory-model: Add write ordering by release-acquire and by locks

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Message-ID: <20180625073229.GR2494@hirez.programming.kicks-ass.net>
Date:   Mon, 25 Jun 2018 09:32:29 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Will Deacon <will.deacon@....com>,
        LKMM Maintainers -- Akira Yokosawa <akiyks@...il.com>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Boqun Feng <boqun.feng@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Nicholas Piggin <npiggin@...il.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] tools/memory-model: Add write ordering by
 release-acquire and by locks


I have yet to digest the rest of the discussion, however:

On Fri, Jun 22, 2018 at 02:09:04PM -0400, Alan Stern wrote:
> The LKMM uses the same CAT code for acquire/release and lock/unlock.
> (In essence, it considers a lock to be an acquire and an unlock to be a
> release; everything else follows from that.)  Treating one differently
> from the other in these tests would require some significant changes.
> It wouldn't be easy.

That is problematic, acquire+release are very much simpler operations
than lock+unlock.

At the very least, lock includes a control-dependency, where acquire
does not.