linux-kernel - Re: [RFC 2/3] tools/memory-model: Add a litmus test for atomic

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Date:   Fri, 14 Feb 2020 09:12:13 +0100
From:   Andrea Parri <parri.andrea@...il.com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        Jonathan Corbet <corbet@....net>, linux-arch@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [RFC 2/3] tools/memory-model: Add a litmus test for atomic_set()

> @@ -0,0 +1,24 @@
> +C Atomic-set-observable-to-RMW
> +
> +(*
> + * Result: Never
> + *
> + * Test of the result of atomic_set() must be observable to atomic RMWs.
> + *)
> +
> +{
> +	atomic_t v = ATOMIC_INIT(1);
> +}
> +
> +P0(atomic_t *v)
> +{
> +	(void)atomic_add_unless(v,1,0);

We blacklisted this primitive some time ago, cf. section "LIMITATIONS",
entry (6b) in tools/memory-model/README; the discussion was here:

  https://lkml.kernel.org/r/20180829211053.20531-3-paulmck@linux.vnet.ibm.com

but unfortunately I can't remember other details at the moment: maybe
it is just a matter of or the proper time to update that section.

Thanks,
  Andrea