[PATCH v5 08/10] rust: sync: atomic: Add Atomic<{usize,isize}>

Boqun Feng
2025-06-18T16:49:50Z

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 necessarity of creating `atomic_long_*` helpers, which could save
the binary size of kernel if inline helpers are not available.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
rust/kernel/sync/atomic.rs | 58 +++++++++++++++++++++++++++++++++++---
1 file changed, 54 insertions(+), 4 deletions(-)

diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs
index 965a3db554d9..829511f4d582 100644
--- a/rust/kernel/sync/atomic.rs
+++ b/rust/kernel/sync/atomic.rs
@@ -65,6 +65,56 @@ fn delta_into_repr(d: Self::Delta) -> Self::Repr {
}
}

+// SAFETY: `usize` has the same size and the alignment as `i64` for 64bit and the same as `i32` for
+// 32bit.
+unsafe impl generic::AllowAtomic for usize {
+ #[cfg(CONFIG_64BIT)]
+ type Repr = i64;
+ #[cfg(not(CONFIG_64BIT))]
+ type Repr = i32;
+
+ fn into_repr(self) -> Self::Repr {
+ self as Self::Repr
+ }
+
+ fn from_repr(repr: Self::Repr) -> Self {
+ repr as Self
+ }
+}
+
+impl generic::AllowAtomicArithmetic for usize {
+ type Delta = usize;
+
+ fn delta_into_repr(d: Self::Delta) -> Self::Repr {
+ d as Self::Repr
+ }
+}
+
+// SAFETY: `isize` has the same size and the alignment as `i64` for 64bit and the same as `i32` for
+// 32bit.
+unsafe impl generic::AllowAtomic for isize {
+ #[cfg(CONFIG_64BIT)]
+ type Repr = i64;
+ #[cfg(not(CONFIG_64BIT))]
+ type Repr = i32;
+
+ fn into_repr(self) -> Self::Repr {
+ self as Self::Repr
+ }
+
+ fn from_repr(repr: Self::Repr) -> Self {
+ repr as Self
+ }
+}
+
+impl generic::AllowAtomicArithmetic for isize {
+ type Delta = isize;
+
+ fn delta_into_repr(d: Self::Delta) -> Self::Repr {
+ d as Self::Repr
+ }
+}
+
use crate::macros::kunit_tests;

#[kunit_tests(rust_atomics)]
@@ -84,7 +134,7 @@ 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));
@@ -93,7 +143,7 @@ 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;
@@ -106,7 +156,7 @@ 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;
@@ -121,7 +171,7 @@ 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)