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

Paul E. McKenney
2020-08-31T23:12:43Z

On Tue, Sep 01, 2020 at 07:34:20AM +0900, Akira Yokosawa wrote:
> On Mon, 31 Aug 2020 11:20:36 -0700, paulmck@kernel.org wrote:
> > From: "Paul E. McKenney" <paulmck@kernel.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@kernel.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.
> …