Re: [PATCH v5 02/10] rust: sync: Add basic atomic operation mapping framework

Andreas Hindborg
2025-06-26T08:50:17Z

"Boqun Feng" <boqun.feng@gmail.com> writes:

> Preparation for generic atomic implementation. To unify the
> implementation of a generic method over `i32` and `i64`, the C side
> atomic methods need to be grouped so that in a generic method, they can
> be referred as <type>::<method>, otherwise their parameters and return
> value are different between `i32` and `i64`, which would require using
> `transmute()` to unify the type into a `T`.
>
> Introduce `AtomicImpl` to represent a basic type in Rust that has the
> direct mapping to an atomic implementation from C. This trait is sealed,
> and currently only `i32` and `i64` impl this.
>
> Further, different methods are put into different `*Ops` trait groups,
> and this is for the future when smaller types like `i8`/`i16` are
> supported but only with a limited set of API (e.g. only set(), load(),
> xchg() and cmpxchg(), no add() or sub() etc).
>
> While the atomic mod is introduced, documentation is also added for
> memory models and data races.
>
> Also bump my role to the maintainer of ATOMIC INFRASTRUCTURE to reflect
> my responsiblity on the Rust atomic mod.
>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> ---
> MAINTAINERS | 4 +-
> rust/kernel/sync.rs | 1 +
> rust/kernel/sync/atomic.rs | 19 ++++
> rust/kernel/sync/atomic/ops.rs | 199 +++++++++++++++++++++++++++++++++
> 4 files changed, 222 insertions(+), 1 deletion(-)
> create mode 100644 rust/kernel/sync/atomic.rs
> create mode 100644 rust/kernel/sync/atomic/ops.rs
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 0c1d245bf7b8..5eef524975ca 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3894,7 +3894,7 @@ F: drivers/input/touchscreen/atmel_mxt_ts.c
> ATOMIC INFRASTRUCTURE
> M: Will Deacon <will@kernel.org>
> M: Peter Zijlstra <peterz@infradead.org>
> -R: Boqun Feng <boqun.feng@gmail.com>
> +M: Boqun Feng <boqun.feng@gmail.com>
> R: Mark Rutland <mark.rutland@arm.com>
> L: linux-kernel@vger.kernel.org
> S: Maintained
> @@ -3903,6 +3903,8 @@ F: arch/*/include/asm/atomic*.h
> F: include/*/atomic*.h
> F: include/linux/refcount.h
> F: scripts/atomic/
> +F: rust/kernel/sync/atomic.rs
> +F: rust/kernel/sync/atomic/
>
> ATTO EXPRESSSAS SAS/SATA RAID SCSI DRIVER
> M: Bradley Grove <linuxdrivers@attotech.com>
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index 36a719015583..b620027e0641 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -10,6 +10,7 @@
> use pin_init;
>
> mod arc;
> +pub mod atomic;
> mod condvar;
> pub mod lock;
> mod locked_by;
> diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs
> new file mode 100644
> index 000000000000..65e41dba97b7
> --- /dev/null
> +++ b/rust/kernel/sync/atomic.rs
> @@ -0,0 +1,19 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Atomic primitives.
> +//!
> +//! These primitives have the same semantics as their C counterparts: and the precise definitions of
> +//! semantics can be found at [`LKMM`]. Note that Linux Kernel Memory (Consistency) Model is the
> +//! only model for Rust code in kernel, and Rust's own atomics should be avoided.
> +//!
> +//! # Data races
> +//!
> +//! [`LKMM`] atomics have different rules regarding data races:
> +//!
> +//! - A normal write from C side is treated as an atomic write if
> +//! CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=y.
> +//! - Mixed-size atomic accesses don't cause data races.
> +//!
> +//! [`LKMM`]: srctree/tools/memory-mode/

Typo in the link destination.

Best regards,
Andreas Hindborg