| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <87qzz6znfu.fsf@kernel.org>
Date: Thu, 26 Jun 2025 14:39:49 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>
Cc: <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>,
<lkmm@...ts.linux.dev>, <linux-arch@...r.kernel.org>, "Miguel Ojeda"
<ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "Gary Guo"
<gary@...yguo.net>, Björn Roy Baron
<bjorn3_gh@...tonmail.com>, "Benno
Lossin" <lossin@...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>
Subject: Re: [PATCH v5 06/10] rust: sync: atomic: Add the framework of
arithmetic operations
"Boqun Feng" <boqun.feng@...il.com> writes:
> 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 `AllowAtomic` 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 add a subtrait of `AllowAtomic` describing
> which types have and can do atomic arithemtic operations.
>
> A few things about this `AllowAtomicArithmetic` trait:
>
> * It has an associate type `Delta` instead of using
> `AllowAllowAtomic::Repr` because, a `Bar(u32)` (whose `Repr` is `i32`)
> may not wants an `add(&self, i32)`, but an `add(&self, u32)`.
>
> * `AtomicImpl` types already implement an `AtomicHasArithmeticOps`
> trait, so add blanket implementation for them. In the future, `i8` and
> `i16` may impl `AtomicImpl` but not `AtomicHasArithmeticOps` if
> arithemtic operations are not available.
>
> Only add() and fetch_add() are added. The rest will be added in the
> future.
>
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> ---
> rust/kernel/sync/atomic/generic.rs | 101 +++++++++++++++++++++++++++++
> 1 file changed, 101 insertions(+)
>
> diff --git a/rust/kernel/sync/atomic/generic.rs b/rust/kernel/sync/atomic/generic.rs
> index bcdbeea45dd8..8c5bd90b2619 100644
> --- a/rust/kernel/sync/atomic/generic.rs
> +++ b/rust/kernel/sync/atomic/generic.rs
> @@ -57,6 +57,23 @@ fn from_repr(repr: Self::Repr) -> Self {
> }
> }
>
> +/// Atomics that allows arithmetic operations with an integer type.
> +pub trait AllowAtomicArithmetic: AllowAtomic {
> + /// The delta types for arithmetic operations.
> + type Delta;
> +
> + /// Converts [`Self::Delta`] into the representation of the atomic type.
> + fn delta_into_repr(d: Self::Delta) -> Self::Repr;
> +}
> +
> +impl<T: AtomicImpl + AtomicHasArithmeticOps> AllowAtomicArithmetic for T {
> + type Delta = Self;
> +
> + fn delta_into_repr(d: Self::Delta) -> Self::Repr {
> + d
> + }
> +}
> +
> impl<T: AllowAtomic> Atomic<T> {
> /// Creates a new atomic.
> pub const fn new(v: T) -> Self {
> @@ -410,3 +427,87 @@ fn try_cmpxchg<Ordering: All>(&self, old: &mut T, new: T, _: Ordering) -> bool {
> }
> }
> }
> +
> +impl<T: AllowAtomicArithmetic> Atomic<T>
> +where
> + T::Repr: AtomicHasArithmeticOps,
> +{
> + /// Atomic add.
> + ///
> + /// The addition is a wrapping addition.
> + ///
> + /// # Examples
> + ///
> + /// ```rust
> + /// 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<Ordering: RelaxedOnly>(&self, v: T::Delta, _: Ordering) {
> + let v = T::delta_into_repr(v);
> + let a = self.as_ptr().cast::<T::Repr>();
> +
> + // SAFETY:
> + // - For calling the atomic_add() function:
> + // - `self.as_ptr()` is a valid pointer, and per the safety requirement of `AllocAtomic`,
Typo, should be `AllowAtomic`.
> + // a `*mut T` is a valid `*mut T::Repr`. Therefore `a` is a valid pointer,
> + // - per the type invariants, the following atomic operation won't cause data races.
> + // - For extra safety requirement of usage on pointers returned by `self.as_ptr():
> + // - atomic operations are used here.
> + unsafe {
> + T::Repr::atomic_add(a, v);
> + }
> + }
> +
> + /// Atomic fetch and add.
> + ///
> + /// The addition is a wrapping addition.
> + ///
> + /// # Examples
> + ///
> + /// ```rust
> + /// 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<Ordering: All>(&self, v: T::Delta, _: Ordering) -> T {
> + let v = T::delta_into_repr(v);
> + let a = self.as_ptr().cast::<T::Repr>();
> +
> + // SAFETY:
> + // - For calling the atomic_fetch_add*() function:
> + // - `self.as_ptr()` is a valid pointer, and per the safety requirement of `AllocAtomic`,
Typo, should be `AllowAtomic`.
Best regards,
Andreas Hindborg
Powered by blists - more mailing lists