linux-kernel - Re: [RFC v2 3/4] Documentation/locking/atomic: Add a litmus test for atomic

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Message-ID: <Pine.LNX.4.44L0.2002191004420.1514-100000@iolanthe.rowland.org>
Date:   Wed, 19 Feb 2020 10:07:09 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Boqun Feng <boqun.feng@...il.com>
cc:     linux-kernel@...r.kernel.org,
        Andrea Parri <parri.andrea@...il.com>,
        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: [RFC v2 3/4] Documentation/locking/atomic: Add a litmus test
 for atomic_set()

On Wed, 19 Feb 2020, 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.

One very minor point about the new working in atomic_t.txt:

> diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
> index ceb85ada378e..d30cb3d87375 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 cannot break the
> +atomicity of the RMW ops. That is:

This would be slightly better if you changed it to: "it must not break".

The comments in the litmus test and README file are okay as they stand.

Alan