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

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Message-ID: <20200831231240.GG2855@paulmck-ThinkPad-P72>
Date:   Mon, 31 Aug 2020 16:12:40 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Akira Yokosawa <akiyks@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        kernel-team@...com, mingo@...nel.org, 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
Subject: Re: [PATCH kcsan 8/9] tools/memory-model: Document categories of
 ordering primitives

On Tue, Sep 01, 2020 at 07:34:20AM +0900, Akira Yokosawa wrote:
> 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/ ?

Indeed I did, good catch, thank you!

							Thanx, Paul

>         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.
> [...]