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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200901012309.GA571008@rowland.harvard.edu>
Date:   Mon, 31 Aug 2020 21:23:09 -0400
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 kcsan 8/9] tools/memory-model: Document categories of
 ordering primitives

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!

Alan