linux-kernel - Re: [PATCH v3 4/5] Documentation/locking/atomic: Add a litmus test for atomic

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Date:   Thu, 27 Feb 2020 18:43:04 +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>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 4/5] Documentation/locking/atomic: Add a litmus test
 for atomic_set()

On Thu, Feb 27, 2020 at 08:40:48AM +0800, Boqun Feng wrote:
> We already use a litmus test in atomic_t.txt to describe the behavior of
> an atomic_set() with the an atomic RMW, so add it into atomic-tests
> directory to make it easily accessible for anyone who cares about the
> semantics of our atomic APIs.
> 
> Additionally, change the sentences describing the test in atomic_t.txt
> with better wording.
> 
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> ---
>  ...c-RMW-ops-are-atomic-WRT-atomic_set.litmus | 24 +++++++++++++++++++
>  Documentation/atomic-tests/README             |  7 ++++++
>  Documentation/atomic_t.txt                    |  6 ++---
>  3 files changed, 34 insertions(+), 3 deletions(-)
>  create mode 100644 Documentation/atomic-tests/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
> 
> diff --git a/Documentation/atomic-tests/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus b/Documentation/atomic-tests/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
> new file mode 100644
> index 000000000000..5dd7f04e504a
> --- /dev/null
> +++ b/Documentation/atomic-tests/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
> @@ -0,0 +1,24 @@
> +C Atomic-set-observable-to-RMW

Nit: s/Atomic-set-observable-to-RMW/Atomic-RMW-ops-are-atomic-WRT-atomic_set


> +
> +(*
> + * Result: Never
> + *
> + * Test that atomic_set() cannot break the atomicity of atomic RMWs.
> + *)
> +
> +{
> +	atomic_t v = ATOMIC_INIT(1);
> +}
> +
> +P0(atomic_t *v)
> +{
> +	(void)atomic_add_unless(v,1,0);

Nit: spaces after commas


> +}
> +
> +P1(atomic_t *v)
> +{
> +	atomic_set(v, 0);
> +}
> +
> +exists
> +(v=2)
> diff --git a/Documentation/atomic-tests/README b/Documentation/atomic-tests/README
> index ae61201a4271..a1b72410b539 100644
> --- a/Documentation/atomic-tests/README
> +++ b/Documentation/atomic-tests/README
> @@ -2,3 +2,10 @@ This directory contains litmus tests that are typical to describe the semantics
>  of our atomic APIs. For more information about how to "run" a litmus test or
>  how to generate a kernel test module based on a litmus test, please see
>  tools/memory-model/README.
> +
> +============
> +LITMUS TESTS
> +============
> +
> +Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
> +	Test that atomic_set() cannot break the atomicity of atomic RMWs.
> diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
> index ceb85ada378e..67d1d99f8589 100644
> --- a/Documentation/atomic_t.txt
> +++ b/Documentation/atomic_t.txt
> @@ -85,10 +85,10 @@ smp_store_release() respectively. Therefore, if you find yourself only using
>  the Non-RMW operations of atomic_t, you do not in fact need atomic_t at all
>  and are doing it wrong.
>  
> -A subtle detail of atomic_set{}() is that it should be observable to the RMW
> -ops. That is:
> +A note for the implementation of atomic_set{}() is that it must not break the
> +atomicity of the RMW ops. That is:
>  
> -  C atomic-set
> +  C Atomic-RMW-ops-are-atomic-WRT-atomic_set
>  
>    {
>      atomic_t v = ATOMIC_INIT(1);
> -- 
> 2.25.0
>