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

[Alan Stern]

On Mon, Aug 31, 2020 at 11:20:36AM -0700, paulmck@xxxxxxxxxx wrote:
> From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> ---

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