Re: [PATCH 07/14] rust: sync: atomic: Add Atomic<u{32,64}>

[Elle Rhumsaa <elle@weathered-steel.dev>]

On Thu, Sep 04, 2025 at 09:41:34PM -0700, Boqun Feng wrote:
> Add generic atomic support for basic unsigned types that have an
> `AtomicImpl` with the same size and alignment.
> 
> Unit tests are added including Atomic<i32> and Atomic<i64>.
> 
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
> Reviewed-by: Benno Lossin <lossin@kernel.org>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> Link: https://lore.kernel.org/all/20250719030827.61357-8-boqun.feng@gmail.com/
> ---
>  rust/kernel/sync/atomic/predefine.rs | 95 ++++++++++++++++++++++++++++
>  1 file changed, 95 insertions(+)
> 
> diff --git a/rust/kernel/sync/atomic/predefine.rs b/rust/kernel/sync/atomic/predefine.rs
> index a6e5883be7cb..d0875812f6ad 100644
> --- a/rust/kernel/sync/atomic/predefine.rs
> +++ b/rust/kernel/sync/atomic/predefine.rs
> @@ -27,3 +27,98 @@ fn rhs_into_delta(rhs: i64) -> i64 {
>          rhs
>      }
>  }
> +
> +// SAFETY: `u32` and `i32` has the same size and alignment, and `u32` is round-trip transmutable to
> +// `i32`.
> +unsafe impl super::AtomicType for u32 {
> +    type Repr = i32;
> +}
> +
> +// SAFETY: The wrapping add result of two `i32`s is a valid `u32`.
> +unsafe impl super::AtomicAdd<u32> for u32 {
> +    fn rhs_into_delta(rhs: u32) -> i32 {
> +        rhs as i32
> +    }
> +}
> +
> +// SAFETY: `u64` and `i64` has the same size and alignment, and `u64` is round-trip transmutable to
> +// `i64`.
> +unsafe impl super::AtomicType for u64 {
> +    type Repr = i64;
> +}
> +
> +// SAFETY: The wrapping add result of two `i64`s is a valid `u64`.
> +unsafe impl super::AtomicAdd<u64> for u64 {
> +    fn rhs_into_delta(rhs: u64) -> i64 {
> +        rhs as i64
> +    }
> +}
> +
> +use crate::macros::kunit_tests;
> +
> +#[kunit_tests(rust_atomics)]
> +mod tests {
> +    use super::super::*;
> +
> +    // Call $fn($val) with each $type of $val.
> +    macro_rules! for_each_type {
> +        ($val:literal in [$($type:ty),*] $fn:expr) => {
> +            $({
> +                let v: $type = $val;
> +
> +                $fn(v);
> +            })*
> +        }
> +    }
> +
> +    #[test]
> +    fn atomic_basic_tests() {
> +        for_each_type!(42 in [i32, i64, u32, u64] |v| {
> +            let x = Atomic::new(v);
> +
> +            assert_eq!(v, x.load(Relaxed));
> +        });
> +    }
> +
> +    #[test]
> +    fn atomic_xchg_tests() {
> +        for_each_type!(42 in [i32, i64, u32, u64] |v| {
> +            let x = Atomic::new(v);
> +
> +            let old = v;
> +            let new = v + 1;
> +
> +            assert_eq!(old, x.xchg(new, Full));
> +            assert_eq!(new, x.load(Relaxed));
> +        });
> +    }
> +
> +    #[test]
> +    fn atomic_cmpxchg_tests() {
> +        for_each_type!(42 in [i32, i64, u32, u64] |v| {
> +            let x = Atomic::new(v);
> +
> +            let old = v;
> +            let new = v + 1;
> +
> +            assert_eq!(Err(old), x.cmpxchg(new, new, Full));
> +            assert_eq!(old, x.load(Relaxed));
> +            assert_eq!(Ok(old), x.cmpxchg(old, new, Relaxed));
> +            assert_eq!(new, x.load(Relaxed));
> +        });
> +    }
> +
> +    #[test]
> +    fn atomic_arithmetic_tests() {
> +        for_each_type!(42 in [i32, i64, u32, u64] |v| {
> +            let x = Atomic::new(v);
> +
> +            assert_eq!(v, x.fetch_add(12, Full));
> +            assert_eq!(v + 12, x.load(Relaxed));
> +
> +            x.add(13, Relaxed);
> +
> +            assert_eq!(v + 25, x.load(Relaxed));
> +        });
> +    }
> +}
> -- 
> 2.51.0
> 
> 

Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>