linux-kernel - Re: [PATCH kcsan 8/9] tools/memory-model: Document categories of ordering primitives

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Date:   Tue, 1 Sep 2020 07:34:20 +0900
From:   Akira Yokosawa <akiyks@...il.com>
To:     paulmck@...nel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, kernel-team@...com, mingo@...nel.org
Cc:     stern@...land.harvard.edu, parri.andrea@...il.com, will@...nel.org,
        peterz@...radead.org, boqun.feng@...il.com, npiggin@...il.com,
        dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
        akiyks@...il.com
Subject: Re: [PATCH kcsan 8/9] tools/memory-model: Document categories of
 ordering primitives

On Mon, 31 Aug 2020 11:20:36 -0700, paulmck@...nel.org wrote:
> From: "Paul E. McKenney" <paulmck@...nel.org>
> 
> The Linux kernel has a number of categories of ordering primitives, which
> are recorded in the LKMM implementation and hinted at by cheatsheet.txt.
> But there is no overview of these categories, and such an overview
> is needed in order to understand multithreaded LKMM litmus tests.
> This commit therefore adds an ordering.txt as well as extracting a
> control-dependencies.txt from memory-barriers.txt.  It also updates the
> README file.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>  tools/memory-model/Documentation/README       |  24 +-
>  tools/memory-model/Documentation/ordering.txt | 462 ++++++++++++++++++++++++++
>  tools/memory-model/control-dependencies.txt   | 256 ++++++++++++++
>  3 files changed, 740 insertions(+), 2 deletions(-)
>  create mode 100644 tools/memory-model/Documentation/ordering.txt
>  create mode 100644 tools/memory-model/control-dependencies.txt

Hi Paul,

Didn't you mean to put control-dependencies.txt under tools/memory-model/Documentation/ ?

        Thanks, Akira

> 
> diff --git a/tools/memory-model/Documentation/README b/tools/memory-model/Documentation/README
> index 4326603..16177aa 100644
> --- a/tools/memory-model/Documentation/README
> +++ b/tools/memory-model/Documentation/README
> @@ -8,10 +8,19 @@ number of places.
>  
>  This document therefore describes a number of places to start reading
>  the documentation in this directory, depending on what you know and what
> -you would like to learn:
> +you would like to learn.  These are cumulative, that is, understanding
> +of the documents earlier in this list is required by the documents later
> +in this list.
>  
>  o	You are new to Linux-kernel concurrency: simple.txt
>  
> +o	You have some background in Linux-kernel concurrency, and would
> +	like an overview of the types of low-level concurrency primitives
> +	that are provided:  ordering.txt
> +
> +	Here, "low level" means atomic operations to single locations in
> +	memory.
> +
>  o	You are familiar with the concurrency facilities that you
>  	need, and just want to get started with LKMM litmus tests:
>  	litmus-tests.txt
> @@ -20,6 +29,9 @@ o	You are familiar with Linux-kernel concurrency, and would
>  	like a detailed intuitive understanding of LKMM, including
>  	situations involving more than two threads: recipes.txt
>  
> +o	You would like a detailed understanding of what your compiler can
> +	and cannot do to control dependencies: control-dependencies.txt
> +
>  o	You are familiar with Linux-kernel concurrency and the
>  	use of LKMM, and would like a cheat sheet to remind you
>  	of LKMM's guarantees: cheatsheet.txt
> @@ -37,12 +49,16 @@ o	You are interested in the publications related to LKMM, including
>  DESCRIPTION OF FILES
>  ====================
>  
> -Documentation/README
> +README
>  	This file.
>  
>  Documentation/cheatsheet.txt
>  	Quick-reference guide to the Linux-kernel memory model.
>  
> +Documentation/control-dependencies.txt
> +	A guide to preventing compiler optimizations from destroying
> +	your control dependencies.
> +
>  Documentation/explanation.txt
>  	Describes the memory model in detail.
[...]