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

Alan Stern
2020-09-01T01:23:12Z

On Mon, Aug 31, 2020 at 11:20:36AM -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>
> ---

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