[PATCH v6 9/9] rust: sync: atomic: Add Atomic<{usize,isize}>

Boqun Feng
2025-07-10T06:01:12Z

Add generic atomic support for `usize` and `isize`. Note that instead of
mapping directly to `atomic_long_t`, the represention type
(`AllowAtomic::Repr`) is selected based on CONFIG_64BIT. This reduces
the necessity of creating `atomic_long_*` helpers, which could save
the binary size of kernel if inline helpers are not available.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
rust/kernel/sync/atomic.rs | 48 ++++++++++++++++++++++++++++++++++----
1 file changed, 44 insertions(+), 4 deletions(-)

diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs
index e676bc7d9275..e1e40757d7b5 100644
--- a/rust/kernel/sync/atomic.rs
+++ b/rust/kernel/sync/atomic.rs
@@ -53,6 +53,26 @@ fn delta_into_repr(d: Self::Delta) -> Self::Repr {
}
}

+// SAFETY: For 32bit kernel, `isize` has the same size and alignment with `i32` and is round-trip
+// transmutable to it, for 64bit kernel `isize` has the same size and alignment with `i64` and is
+// round-trip transmutable to it.
+unsafe impl generic::AllowAtomic for isize {
+ #[cfg(not(CONFIG_64BIT))]
+ type Repr = i32;
+ #[cfg(CONFIG_64BIT)]
+ type Repr = i64;
+}
+
+// SAFETY: `isize` is always sound to transmute back from `i32` or `i64` when their sizes are the
+// same.
+unsafe impl generic::AllowAtomicArithmetic for isize {
+ type Delta = Self;
+
+ fn delta_into_repr(d: Self::Delta) -> Self::Repr {
+ d as Self::Repr
+ }
+}
+
// SAFETY: `u32` and `i32` has the same size and alignment, and `u32` is round-trip transmutable to
// `i32`.
unsafe impl generic::AllowAtomic for u32 {
@@ -83,6 +103,26 @@ fn delta_into_repr(d: Self::Delta) -> Self::Repr {
}
}

+// SAFETY: For 32bit kernel, `usize` has the same size and alignment with `i32` and is round-trip
+// transmutable to it, for 64bit kernel `usize` has the same size and alignment with `i64` and is
+// round-trip transmutable to it.
+unsafe impl generic::AllowAtomic for usize {
+ #[cfg(not(CONFIG_64BIT))]
+ type Repr = i32;
+ #[cfg(CONFIG_64BIT)]
+ type Repr = i64;
+}
+
+// SAFETY: `usize` is always sound to transmute back from `i32` or `i64` when their sizes are the
+// same.
+unsafe impl generic::AllowAtomicArithmetic for usize {
+ type Delta = Self;
+
+ fn delta_into_repr(d: Self::Delta) -> Self::Repr {
+ d as Self::Repr
+ }
+}
+
use crate::macros::kunit_tests;

#[kunit_tests(rust_atomics)]
@@ -102,7 +142,7 @@ macro_rules! for_each_type {

#[test]
fn atomic_basic_tests() {
- for_each_type!(42 in [i32, i64, u32, u64] |v| {
+ for_each_type!(42 in [i32, i64, u32, u64, isize, usize] |v| {
let x = Atomic::new(v);

assert_eq!(v, x.load(Relaxed));
@@ -111,7 +151,7 @@ fn atomic_basic_tests() {

#[test]
fn atomic_xchg_tests() {
- for_each_type!(42 in [i32, i64, u32, u64] |v| {
+ for_each_type!(42 in [i32, i64, u32, u64, isize, usize] |v| {
let x = Atomic::new(v);

let old = v;
@@ -124,7 +164,7 @@ fn atomic_xchg_tests() {

#[test]
fn atomic_cmpxchg_tests() {
- for_each_type!(42 in [i32, i64, u32, u64] |v| {
+ for_each_type!(42 in [i32, i64, u32, u64, isize, usize] |v| {
let x = Atomic::new(v);

let old = v;
@@ -139,7 +179,7 @@ fn atomic_cmpxchg_tests() {

#[test]
fn atomic_arithmetic_tests() {
- for_each_type!(42 in [i32, i64, u32, u64] |v| {
+ for_each_type!(42 in [i32, i64, u32, u64, isize, usize] |v| {
let x = Atomic::new(v);

assert_eq!(v, x.fetch_add(12, Full));
--
2.39.5 (Apple Git-154)