From: Boqun Feng <boqun.feng@gmail.com>
To: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
lkmm@lists.linux.dev
Cc: "Will Deacon" <will@kernel.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"Mark Rutland" <mark.rutland@arm.com>,
"Ingo Molnar" <mingo@kernel.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Paul E. McKenney" <paulmck@kernel.org>,
stern@rowland.harvard.edu, "Miguel Ojeda" <ojeda@kernel.org>,
alex.gaynor@gmail.com, "Gary Guo" <gary@garyguo.net>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
"Benno Lossin" <lossin@kernel.org>,
"Alice Ryhl" <aliceryhl@google.com>,
"Trevor Gross" <tmgross@umich.edu>,
"Danilo Krummrich" <dakr@kernel.org>,
"Andreas Hindborg" <a.hindborg@kernel.org>,
"Boqun Feng" <boqun.feng@gmail.com>
Subject: [PATCH 06/14] rust: sync: atomic: Add the framework of arithmetic operations
Date: Thu, 4 Sep 2025 21:41:33 -0700 [thread overview]
Message-ID: <20250905044141.77868-7-boqun.feng@gmail.com> (raw)
In-Reply-To: <20250905044141.77868-1-boqun.feng@gmail.com>
One important set of atomic operations is the arithmetic operations,
i.e. add(), sub(), fetch_add(), add_return(), etc. However it may not
make senses for all the types that `AtomicType` to have arithmetic
operations, for example a `Foo(u32)` may not have a reasonable add() or
sub(), plus subword types (`u8` and `u16`) currently don't have
atomic arithmetic operations even on C side and might not have them in
the future in Rust (because they are usually suboptimal on a few
architecures). Therefore the plan is to add a few subtraits of
`AtomicType` describing which types have and can do atomic arithemtic
operations.
One trait `AtomicAdd` is added, and only add() and fetch_add() are
added. The rest will be added in the future.
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/all/20250719030827.61357-7-boqun.feng@gmail.com/
---
rust/kernel/sync/atomic.rs | 94 +++++++++++++++++++++++++++-
rust/kernel/sync/atomic/predefine.rs | 14 +++++
2 files changed, 106 insertions(+), 2 deletions(-)
diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs
index 4c32d12dc61e..016a6bcaf080 100644
--- a/rust/kernel/sync/atomic.rs
+++ b/rust/kernel/sync/atomic.rs
@@ -16,7 +16,6 @@
//!
//! [`LKMM`]: srctree/tools/memory-model/
-#[allow(dead_code, unreachable_pub)]
mod internal;
pub mod ordering;
mod predefine;
@@ -25,7 +24,7 @@
pub use ordering::{Acquire, Full, Relaxed, Release};
use crate::build_error;
-use internal::{AtomicBasicOps, AtomicExchangeOps, AtomicRepr};
+use internal::{AtomicArithmeticOps, AtomicBasicOps, AtomicExchangeOps, AtomicRepr};
use ordering::OrderingType;
/// A memory location which can be safely modified from multiple execution contexts.
@@ -112,6 +111,19 @@ pub unsafe trait AtomicType: Sized + Send + Copy {
type Repr: AtomicImpl;
}
+/// Types that support atomic add operations.
+///
+/// # Safety
+///
+// TODO: Properly defines `wrapping_add` in the following comment.
+/// `wrapping_add` any value of type `Self::Repr::Delta` obtained by [`Self::rhs_into_delta()`] to
+/// any value of type `Self::Repr` obtained through transmuting a value of type `Self` to must
+/// yield a value with a bit pattern also valid for `Self`.
+pub unsafe trait AtomicAdd<Rhs = Self>: AtomicType {
+ /// Converts `Rhs` into the `Delta` type of the atomic implementation.
+ fn rhs_into_delta(rhs: Rhs) -> <Self::Repr as AtomicImpl>::Delta;
+}
+
#[inline(always)]
const fn into_repr<T: AtomicType>(v: T) -> T::Repr {
// SAFETY: Per the safety requirement of `AtomicType`, `T` is round-trip transmutable to
@@ -459,3 +471,81 @@ fn try_cmpxchg<Ordering: ordering::Ordering>(&self, old: &mut T, new: T, _: Orde
ret
}
}
+
+impl<T: AtomicType> Atomic<T>
+where
+ T::Repr: AtomicArithmeticOps,
+{
+ /// Atomic add.
+ ///
+ /// Atomically updates `*self` to `(*self).wrapping_add(v)`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use kernel::sync::atomic::{Atomic, Relaxed};
+ ///
+ /// let x = Atomic::new(42);
+ ///
+ /// assert_eq!(42, x.load(Relaxed));
+ ///
+ /// x.add(12, Relaxed);
+ ///
+ /// assert_eq!(54, x.load(Relaxed));
+ /// ```
+ #[inline(always)]
+ pub fn add<Rhs>(&self, v: Rhs, _: ordering::Relaxed)
+ where
+ T: AtomicAdd<Rhs>,
+ {
+ let v = T::rhs_into_delta(v);
+
+ // INVARIANT: `self.0` is a valid `T` after `atomic_add()` due to safety requirement of
+ // `AtomicAdd`.
+ T::Repr::atomic_add(&self.0, v);
+ }
+
+ /// Atomic fetch and add.
+ ///
+ /// Atomically updates `*self` to `(*self).wrapping_add(v)`, and returns the value of `*self`
+ /// before the update.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use kernel::sync::atomic::{Atomic, Acquire, Full, Relaxed};
+ ///
+ /// let x = Atomic::new(42);
+ ///
+ /// assert_eq!(42, x.load(Relaxed));
+ ///
+ /// assert_eq!(54, { x.fetch_add(12, Acquire); x.load(Relaxed) });
+ ///
+ /// let x = Atomic::new(42);
+ ///
+ /// assert_eq!(42, x.load(Relaxed));
+ ///
+ /// assert_eq!(54, { x.fetch_add(12, Full); x.load(Relaxed) } );
+ /// ```
+ #[inline(always)]
+ pub fn fetch_add<Rhs, Ordering: ordering::Ordering>(&self, v: Rhs, _: Ordering) -> T
+ where
+ T: AtomicAdd<Rhs>,
+ {
+ let v = T::rhs_into_delta(v);
+
+ // INVARIANT: `self.0` is a valid `T` after `atomic_fetch_add*()` due to safety requirement
+ // of `AtomicAdd`.
+ let ret = {
+ match Ordering::TYPE {
+ OrderingType::Full => T::Repr::atomic_fetch_add(&self.0, v),
+ OrderingType::Acquire => T::Repr::atomic_fetch_add_acquire(&self.0, v),
+ OrderingType::Release => T::Repr::atomic_fetch_add_release(&self.0, v),
+ OrderingType::Relaxed => T::Repr::atomic_fetch_add_relaxed(&self.0, v),
+ }
+ };
+
+ // SAFETY: `ret` comes from reading `self.0`, which is a valid `T` per type invariants.
+ unsafe { from_repr(ret) }
+ }
+}
diff --git a/rust/kernel/sync/atomic/predefine.rs b/rust/kernel/sync/atomic/predefine.rs
index 33356deee952..a6e5883be7cb 100644
--- a/rust/kernel/sync/atomic/predefine.rs
+++ b/rust/kernel/sync/atomic/predefine.rs
@@ -8,8 +8,22 @@ unsafe impl super::AtomicType for i32 {
type Repr = i32;
}
+// SAFETY: The wrapping add result of two `i32`s is a valid `i32`.
+unsafe impl super::AtomicAdd<i32> for i32 {
+ fn rhs_into_delta(rhs: i32) -> i32 {
+ rhs
+ }
+}
+
// SAFETY: `i64` has the same size and alignment with itself, and is round-trip transmutable to
// itself.
unsafe impl super::AtomicType for i64 {
type Repr = i64;
}
+
+// SAFETY: The wrapping add result of two `i64`s is a valid `i64`.
+unsafe impl super::AtomicAdd<i64> for i64 {
+ fn rhs_into_delta(rhs: i64) -> i64 {
+ rhs
+ }
+}
--
2.51.0
next prev parent reply other threads:[~2025-09-05 4:42 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-05 4:41 [GIT PULL] [PATCH 00/14] Rust atomic changes for v6.18 Boqun Feng
2025-09-05 4:41 ` [PATCH 01/14] rust: Introduce atomic API helpers Boqun Feng
2025-09-06 4:22 ` Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 02/14] rust: sync: Add basic atomic operation mapping framework Boqun Feng
2025-09-06 4:22 ` Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 03/14] rust: sync: atomic: Add ordering annotation types Boqun Feng
2025-09-06 4:22 ` Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 04/14] rust: sync: atomic: Add generic atomics Boqun Feng
2025-09-06 4:23 ` Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 05/14] rust: sync: atomic: Add atomic {cmp,}xchg operations Boqun Feng
2025-09-06 4:23 ` Elle Rhumsaa
2025-09-05 4:41 ` Boqun Feng [this message]
2025-09-06 4:23 ` [PATCH 06/14] rust: sync: atomic: Add the framework of arithmetic operations Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 07/14] rust: sync: atomic: Add Atomic<u{32,64}> Boqun Feng
2025-09-06 4:24 ` Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 08/14] rust: sync: atomic: Add Atomic<{usize,isize}> Boqun Feng
2025-09-06 4:24 ` Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 09/14] rust: sync: Add memory barriers Boqun Feng
2025-09-06 4:25 ` Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 10/14] rust: implement `kernel::sync::Refcount` Boqun Feng
2025-09-06 4:25 ` Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 11/14] rust: make `Arc::into_unique_or_drop` associated function Boqun Feng
2025-09-06 4:25 ` Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 12/14] rust: convert `Arc` to use `Refcount` Boqun Feng
2025-09-06 4:26 ` Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 13/14] rust: block: convert `block::mq` " Boqun Feng
2025-09-06 4:26 ` Elle Rhumsaa
2025-09-05 4:41 ` [PATCH 14/14] MAINTAINERS: update atomic infrastructure entry to include Rust Boqun Feng
2025-09-06 4:26 ` Elle Rhumsaa
2025-09-10 5:27 ` [GIT PULL] [PATCH 00/14] Rust atomic changes for v6.18 Boqun Feng
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