linux-kernel - [PATCH v7 7/9] rust: sync: atomic: Add Atomic<u{32,64}>

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Message-Id: <20250714053656.66712-8-boqun.feng@gmail.com>
Date: Sun, 13 Jul 2025 22:36:54 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org,
	lkmm@...ts.linux.dev,
	linux-arch@...r.kernel.org
Cc: "Miguel Ojeda" <ojeda@...nel.org>,
	"Alex Gaynor" <alex.gaynor@...il.com>,
	"Boqun Feng" <boqun.feng@...il.com>,
	"Gary Guo" <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	"Benno Lossin" <lossin@...nel.org>,
	"Andreas Hindborg" <a.hindborg@...nel.org>,
	"Alice Ryhl" <aliceryhl@...gle.com>,
	"Trevor Gross" <tmgross@...ch.edu>,
	"Danilo Krummrich" <dakr@...nel.org>,
	"Will Deacon" <will@...nel.org>,
	"Peter Zijlstra" <peterz@...radead.org>,
	"Mark Rutland" <mark.rutland@....com>,
	"Wedson Almeida Filho" <wedsonaf@...il.com>,
	"Viresh Kumar" <viresh.kumar@...aro.org>,
	"Lyude Paul" <lyude@...hat.com>,
	"Ingo Molnar" <mingo@...nel.org>,
	"Mitchell Levy" <levymitchell0@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	Alan Stern <stern@...land.harvard.edu>
Subject: [PATCH v7 7/9] rust: sync: atomic: Add Atomic<u{32,64}>

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@...gle.com>
Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>
Reviewed-by: Benno Lossin <lossin@...nel.org>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 rust/kernel/sync/atomic.rs | 95 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)

diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs
index 54f5b4618337..eb4a47d7e2f3 100644
--- a/rust/kernel/sync/atomic.rs
+++ b/rust/kernel/sync/atomic.rs
@@ -48,3 +48,98 @@ 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 generic::AllowAtomic for u32 {
+    type Repr = i32;
+}
+
+// SAFETY: The wrapping add result of two `i32`s is a valid `u32`.
+unsafe impl generic::AllowAtomicAdd<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 generic::AllowAtomic for u64 {
+    type Repr = i64;
+}
+
+// SAFETY: The wrapping add result of two `i64`s is a valid `u64`.
+unsafe impl generic::AllowAtomicAdd<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::*;
+
+    // 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));
+        });
+    }
+}
-- 
2.39.5 (Apple Git-154)