Re: [PATCH v5 04/10] rust: sync: atomic: Add generic atomics

Alan Stern
2025-06-30T14:44:45Z

On Mon, Jun 30, 2025 at 11:52:35AM +0200, Andreas Hindborg wrote:
> "Boqun Feng" <boqun.feng@gmail.com> writes:
> > Well, a non-atomic read vs an atomic read is not a data race (for both
> > Rust memory model and LKMM), so your proposal is overly restricted.
>
> OK, my mistake then. I thought mixing marked and plain accesses would be
> considered a race. I got hat from
> `tools/memory-model/Documentation/explanation.txt`:
>
> A "data race"
> occurs when there are two memory accesses such that:
>
> 1. they access the same location,
>
> 2. at least one of them is a store,
>
> 3. at least one of them is plain,
>
> 4. they occur on different CPUs (or in different threads on the
> same CPU), and
>
> 5. they execute concurrently.
>
> I did not study all that documentation, so I might be missing a point or
> two.

You missed point 2 above: at least one of the accesses has to be a
store. When you're looking at a non-atomic read vs. an atomic read,
both of them are loads and so it isn't a data race.

Alan