On Tue, Jan 20, 2026 at 04:54:51PM +0000, Gary Guo wrote:
> On Tue Jan 20, 2026 at 2:05 PM GMT, Boqun Feng wrote:
> > Currently, since all the architectures that support Rust all have
> > CONFIG_ARCH_SUPPORTS_ATOMIC_RMW selected, the helpers of atomic
> > load/store on i8 and i16 relies on CONFIG_ARCH_SUPPORTS_ATOMIC_RMW=y.
> > It's generally fine since most of architectures support that.
> >
> > The plan for CONFIG_ARCH_SUPPORTS_ATOMIC_RMW=n architectures is adding
> > their (probably lock-based) atomic load/store for i8 and i16 as their
> > atomic_{read,set}() and atomic64_{read,set}() counterpart when they
> > plans to support Rust.
> >
> > Hence use a statis_assert!() to check this and remind the future us the
> > need of the helpers. This is more clear than the #[cfg] on impl blocks
> > of i8 and i16.
> >
> > Suggested-by: Dirk Behme <[email protected]>
> > Suggested-by: Benno Lossin <[email protected]>
> > Signed-off-by: Boqun Feng <[email protected]>
>
> Reviewed-by: Gary Guo <[email protected]>
>
Thanks!
> > ---
> > rust/kernel/sync/atomic/internal.rs | 19 +++++++++++++------
> > 1 file changed, 13 insertions(+), 6 deletions(-)
> >
> > diff --git a/rust/kernel/sync/atomic/internal.rs
> > b/rust/kernel/sync/atomic/internal.rs
> > index 0dac58bca2b3..ef516bcb02ee 100644
> > --- a/rust/kernel/sync/atomic/internal.rs
> > +++ b/rust/kernel/sync/atomic/internal.rs
> > @@ -37,16 +37,23 @@ pub trait AtomicImpl: Sized + Send + Copy +
> > private::Sealed {
> > type Delta;
> > }
> >
> > -// The current helpers of load/store uses `{WRITE,READ}_ONCE()` hence the
> > atomicity is only
> > -// guaranteed against read-modify-write operations if the architecture
> > supports native atomic RmW.
> > -#[cfg(CONFIG_ARCH_SUPPORTS_ATOMIC_RMW)]
> > +// The current helpers of load/store of atomic `i8` and `i16` use
> > `{WRITE,READ}_ONCE()` hence the
> > +// atomicity is only guaranteed against read-modify-write operations if
> > the architecture supports
> > +// native atomic RmW.
> > +//
> > +// In the future when a CONFIG_ARCH_SUPPORTS_ATOMIC_RMW=n architecture
> > plans to support Rust, the
> > +// load/store helpers that guarantee atomicity against RmW operations
> > (usually via a lock) need to
> > +// be added.
> > +crate::static_assert!(
> > + cfg!(CONFIG_ARCH_SUPPORTS_ATOMIC_RMW),
> > + "The current implementation of atomic i8/i16/ptr relies on the
> > architecure being \
> > + ARCH_SUPPORTS_ATOMIC_RMW"
>
> The printed string when assertion fails will have 5 spaces between "being" and
> "ARCH", although it probably doesn't matter..
>
Are you sure? My test result shows:
ERROR:root:error[E0080]: evaluation panicked: The current implementation of
atomic i8/i16/ptr relies on the architecure being ARCH_SUPPORTS_ATOMIC_RMW
similar is the following playground example:
https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=5dd0098247503be792bc35cda8f2630f
Regards,
Boqun
> Best,
> Gary
>
> > +);
> > +
> > impl AtomicImpl for i8 {
> > type Delta = Self;
> > }
> >
> > -// The current helpers of load/store uses `{WRITE,READ}_ONCE()` hence the
> > atomicity is only
> > -// guaranteed against read-modify-write operations if the architecture
> > supports native atomic RmW.
> > -#[cfg(CONFIG_ARCH_SUPPORTS_ATOMIC_RMW)]
> > impl AtomicImpl for i16 {
> > type Delta = Self;
> > }
>
