linux-kernel - Re: [PATCH memory-model 5/8] tools/memory-model: Add a glossary of LKMM terms

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Date:   Fri, 6 Nov 2020 11:59:30 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     paulmck@...nel.org
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 memory-model 5/8] tools/memory-model: Add a glossary of
 LKMM terms

On Thu, Nov 05, 2020 at 02:00:14PM -0800, paulmck@...nel.org wrote:
> From: "Paul E. McKenney" <paulmck@...nel.org>
> 
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>  tools/memory-model/Documentation/glossary.txt | 155 ++++++++++++++++++++++++++
>  1 file changed, 155 insertions(+)
>  create mode 100644 tools/memory-model/Documentation/glossary.txt
> 
> diff --git a/tools/memory-model/Documentation/glossary.txt b/tools/memory-model/Documentation/glossary.txt
> new file mode 100644
> index 0000000..036fa28
> --- /dev/null
> +++ b/tools/memory-model/Documentation/glossary.txt
> @@ -0,0 +1,155 @@
> +This document contains brief definitions of LKMM-related terms.  Like most
> +glossaries, it is not intended to be read front to back (except perhaps
> +as a way of confirming a diagnosis of OCD), but rather to be searched
> +for specific terms.
> +
> +
> +Address Dependency:  When the address of a later memory access is computed
> +	based on the value returned by an earlier load, an "address
> +	dependency" extends from that load extending to the later access.
> +	Address dependencies are quite common in RCU read-side critical
> +	sections:
> +
> +	 1 rcu_read_lock();
> +	 2 p = rcu_dereference(gp);
> +	 3 do_something(p->a);
> +	 4 rcu_read_unlock();
> +
> +	 In this case, because the address of "p->a" on line 3 is computed
> +	 from the value returned by the rcu_dereference() on line 2, the
> +	 address dependency extends from that rcu_dereference() to that
> +	 "p->a".  In rare cases, optimizing compilers can destroy address
> +	 dependencies.	Please see Documentation/RCU/rcu_dereference.txt
> +	 for more information.
> +
> +	 See also "Control Dependency".

There should also be an entry for "Data Dependency", linked from here
and from Control Dependency.

> +Marked Access:  An access to a variable that uses an special function or
> +	macro such as "r1 = READ_ONCE()" or "smp_store_release(&a, 1)".

How about "r1 = READ_ONCE(x)"?

Alan