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

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Message-ID: <20200901025854.GA29330@paulmck-ThinkPad-P72>
Date:   Mon, 31 Aug 2020 19:58:54 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        kernel-team@...com, mingo@...nel.org, 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, Aug 31, 2020 at 09:23:09PM -0400, Alan Stern wrote:
> On Mon, Aug 31, 2020 at 11:20:36AM -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>
> > ---
> 
> This document could use some careful editing.  But one pair of errors
> stands out in particular:
> 
> > diff --git a/tools/memory-model/Documentation/ordering.txt b/tools/memory-model/Documentation/ordering.txt
> > new file mode 100644
> > index 0000000..4b2cc55
> > --- /dev/null
> > +++ b/tools/memory-model/Documentation/ordering.txt
> 
> > +2.	Ordered memory accesses.  These operations order themselves
> > +	against some or all of the CPUs prior or subsequent accesses,
> > +	depending on the category of operation.
> > +
> > +	a.	Release operations.  This category includes
> > +		smp_store_release(), atomic_set_release(),
> > +		rcu_assign_pointer(), and value-returning RMW operations
> > +		whose names end in _release.  These operations order
> > +		their own store against all of the CPU's subsequent
> ---------------------------------------------------------^^^^^^^^^^
> > +		memory accesses.
> > +
> > +	b.	Acquire operations.  This category includes
> > +		smp_load_acquire(), atomic_read_acquire(), and
> > +		value-returning RMW operations whose names end in
> > +		_acquire.  These operations order their own load against
> > +		all of the CPU's prior memory accesses.
> ---------------------------------^^^^^
> 
> Double-oops!

Hey, at least I am consistently wrong!  ;-)

Fixed, thank you!

							Thanx, Paul