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:   Tue, 10 Jul 2018 17:24:04 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     "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>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....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

> >   ACQUIRE operations include LOCK operations and both smp_load_acquire()
> >   and smp_cond_acquire() operations.  [BTW, the latter was replaced by
> >   smp_cond_load_acquire() in 1f03e8d2919270 ...]
> > 
> >   RELEASE operations include UNLOCK operations and smp_store_release()
> >   operations. [...]
> > 
> >   [...] after an ACQUIRE on a given variable, all memory accesses
> >   preceding any prior RELEASE on that same variable are guaranteed
> >   to be visible.
> 
> As far as I can see, these statements remain valid.

Interesting; ;-)  What does these statement tells you ;-)  when applied
to a: and b: below?

  a: WRITE_ONCE(x, 1); // "preceding any prior RELEASE..."
  smp_store_release(&s, 1);
  smp_load_acquire(&s);
  b: WRITE_ONCE(y, 1); // "after an ACQUIRE..."

  Andrea