On Tue Jan 20, 2026 at 9:03 PM GMT, Boqun Feng wrote:
> 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
TIL! I thought Rust and C has the same behaviour with this respect.
I have been using `indoc!` to strip the additional whitespaces, but I suppose
it's only for multiline strings but no line continuation.
Best,
Gary
