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Mon, 27 Apr 2026 20:40:06 -0700 (PDT) From: Sagar Taunk To: ojeda@kernel.org Cc: boqun@kernel.org, lossin@kernel.org, tmgross@umich.edu, dakr@kernel.org, aliceryhl@google.com, bjorn3_gh@protonmail.com, gary@garyguo.net, a.hindborg@kernel.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, Sagar Taunk Subject: [PATCH v2] rust: sync: atomic: clarify AtomicAdd safety comment Date: Tue, 28 Apr 2026 09:09:35 +0530 Message-ID: <20260428033935.16875-1-sagartaunk2@gmail.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260427203258.22148-1-sagartaunk2@gmail.com> References: <20260427203258.22148-1-sagartaunk2@gmail.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The previous safety comment for AtomicAdd was marked with a TODO and contained a grammatically broken sentence that was difficult to parse. Rewrite the comment to fix the grammar and clearly define the safety contract, including what `wrapping_add` means in the context and why `Self::Repr::Delta` may differ from `Self::Repr`. Signed-off-by: Sagar Taunk --- rust/kernel/sync/atomic.rs | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index 9cd009d57e35..4000fff16e69 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -127,10 +127,14 @@ pub unsafe trait AtomicType: Sized + Copy { /// /// # 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`. +/// `Self::Repr::Delta` is the type of value being added in the underlying +/// C atomic operation, and may differ from `Self::Repr` (e.g., `i32` for 32-bit +/// integer atomics or `isize` rather than the pointer value `*const c_void` for pointer atomics, +/// where the C function expects a byte offset rather than the pointer itself). +/// Thus, for any `Self::Repr` obtained by transmuting a valid `Self`, +/// adding any `Self::Repr::Delta` value produced by `Self::rhs_into_delta()` using +/// `wrapping_add`, where `wrapping_add` denotes addition that wraps on overflow +/// rather than causing undefined behavior, must yield a bit pattern that is valid for `Self`. pub unsafe trait AtomicAdd: AtomicType { /// Converts `Rhs` into the `Delta` type of the atomic implementation. fn rhs_into_delta(rhs: Rhs) -> ::Delta; -- 2.54.0