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

[Alan Stern <stern@rowland.harvard.edu>]

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