linux.git/rust/kernel/sync/atomic, branch v7.3-rc2

rust: sync: Add generic memory barriers

2026-08-04T12:52:54+00:00

Implement a generic interface for memory barriers (full system/DMA/SMP).
The interface uses a parameter to force user to specify their intent
with barriers.

Provide `Read`, `Write`, `Full` orderings which map to the existing
`rmb()`, `wmb()` and `mb()`. Generic is used here instead of providing
individual standalone functions to reduce code duplication; for example,
the `CONFIG_SMP` check in `smp_mb` is uniformly implemented for all SMP
barriers. This could extend to `virt_mb`'s if they're introduced in the
future. It would also make it easier if new ordering types are
introduced in the future (e.g. `Acquire`, `Release`).

Signed-off-by: Gary Guo 
Signed-off-by: Boqun Feng 
Link: https://patch.msgid.link/20260609-rust-barrier-v2-2-30fcc48e1cd0@garyguo.net

rust: make `build_assert` module the home of related macros

2026-06-10T07:07:13+00:00

Given the macro scoping rules, all macros are rendered twice, in the
module and in the top-level of kernel crate.

Add `#[doc(hidden)]` to the macro definition and `#[doc(inline)]` to the
re-export inside `build_assert` module so the top-level items are hidden.

[ Sadly, because the definition is hidden, `rustdoc` decides to not list
  them as re-exports in the `prelude` page anymore, even if we refer to
  the not-actually-hidden item.

    - Miguel ]

Acked-by: Danilo Krummrich 
Reviewed-by: Alice Ryhl 
Acked-by: Alexandre Courbot 
Acked-by: FUJITA Tomonori 
Acked-by: Boqun Feng 
Signed-off-by: Gary Guo 
Link: https://patch.msgid.link/20260609142637.373347-1-gary@kernel.org
[ Kept a single declaration in the prelude, and reworded since they
  already had `no_inline`. Removed other imports from `predefine` since
  we now use the prelude. - Miguel ]
Signed-off-by: Miguel Ojeda

rust: tests: add Kconfig for KUnit test

2026-06-08T00:30:33+00:00

There are 6 individual Rust KUnit test suites (plus the doctests one). All
the tests are compiled unconditionally now, which adds ~200 kB to the
kernel image for me on x86_64. As Rust matures, this bloating will
inevitably grow.

Add Kconfig.test which includes a RUST_KUNIT_TESTS menu, and all
individual tests under it.

As usual, new tests are all enabled if KUNIT_ALL_TESTS=y.

Suggested-by: Alice Ryhl 
Signed-off-by: Yury Norov 
Reviewed-by: David Gow 
Acked-by: Gary Guo 
Link: https://patch.msgid.link/20260417031531.315281-3-ynorov@nvidia.com
[ Fixed capitalization. Used singular for "API" for consistency.
  Reworded to clarify these are suites and that there exists
  the doctests one (which is the biggest at the moment by
  far). - Miguel ]
Signed-off-by: Miguel Ojeda

rust: tests: drop 'use crate' in bitmap and atomic KUnit tests

2026-06-08T00:30:33+00:00

The following patch makes usage of macros::kunit_tests crate conditional
on the corresponding configs. When the configs are disabled, compiler
warns on unused crate. So, embed it in unit test declaration.

Signed-off-by: Yury Norov 
Reviewed-by: David Gow 
Acked-by: Gary Guo 
Link: https://patch.msgid.link/20260417031531.315281-2-ynorov@nvidia.com
Signed-off-by: Miguel Ojeda

rust: atomic: Update a safety comment in impl of `fetch_add()`

2026-03-08T10:06:51+00:00

The safety comment used in the implementation of `fetch_add()` could be
read as just saying something it is true without justifying it. Update
the safety comment to include justification.

Suggested-by: Miguel Ojeda 
Signed-off-by: Andreas Hindborg 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Alice Ryhl 
Link: https://patch.msgid.link/20260220-atomic-sub-v3-3-e63cbed1d2aa@kernel.org
Link: https://patch.msgid.link/20260303201701.12204-14-boqun@kernel.org

rust: sync: atomic: Add fetch_sub()

2026-03-08T10:06:50+00:00

Add `Atomic::fetch_sub()` with implementation and documentation in line
with existing `Atomic::fetch_add()` implementation.

Signed-off-by: Andreas Hindborg 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Alice Ryhl 
Link: https://patch.msgid.link/20260220-atomic-sub-v3-1-e63cbed1d2aa@kernel.org
Link: https://patch.msgid.link/20260303201701.12204-12-boqun@kernel.org

rust: sync: atomic: Add atomic operation helpers over raw pointers

2026-03-08T10:06:50+00:00

In order to synchronize with C or external memory, atomic operations
over raw pointers are need. Although there is already an
`Atomic::from_ptr()` to provide a `&Atomic`, it's more convenient to
have helpers that directly perform atomic operations on raw pointers.
Hence a few are added, which are basically an `Atomic::from_ptr().op()`
wrapper.

Note: for naming, since `atomic_xchg()` and `atomic_cmpxchg()` have a
conflict naming to 32bit C atomic xchg/cmpxchg, hence the helpers are
just named as `xchg()` and `cmpxchg()`. For `atomic_load()` and
`atomic_store()`, their 32bit C counterparts are `atomic_read()` and
`atomic_set()`, so keep the `atomic_` prefix.

[boqun: Fix typo spotted by Alice and fix broken sentence spotted by
Gary]

Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Alice Ryhl 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260120115207.55318-3-boqun.feng@gmail.com
Link: https://patch.msgid.link/20260303201701.12204-11-boqun@kernel.org

rust: sync: atomic: Add performance-optimal Flag type for atomic booleans

2026-03-08T10:06:49+00:00

Add AtomicFlag type for boolean flags.

Document when AtomicFlag is generally preferable to Atomic: in
particular, when RMW operations such as xchg()/cmpxchg() may be used
and minimizing memory usage is not the top priority. On some
architectures without byte-sized RMW instructions, Atomic can be
slower for RMW operations.

Signed-off-by: FUJITA Tomonori 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260129122622.3896144-2-tomo@aliasing.net
Link: https://patch.msgid.link/20260303201701.12204-9-boqun@kernel.org

rust: sync: atomic: Add Atomic<*{mut,const} T> support

2026-03-08T10:06:49+00:00

Atomic pointer support is an important piece of synchronization
algorithm, e.g. RCU, hence provide the support for that.

Note that instead of relying on atomic_long or the implementation of
`Atomic`, a new set of helpers (atomic_ptr_*) is introduced for
atomic pointer specifically, this is because ptr2int casting would
lose the provenance of a pointer and even though in theory there are a
few tricks the provenance can be restored, it'll still be a simpler
implementation if C could provide atomic pointers directly. The side
effects of this approach are: we don't have the arithmetic and logical
operations for pointers yet and the current implementation only works
on ARCH_SUPPORTS_ATOMIC_RMW architectures, but these are implementation
issues and can be added later.

Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Gary Guo 
Reviewed-by: FUJITA Tomonori 
Link: https://patch.msgid.link/20260120140503.62804-3-boqun.feng@gmail.com
Link: https://patch.msgid.link/20260303201701.12204-8-boqun@kernel.org

rust: sync: atomic: Clarify the need of CONFIG_ARCH_SUPPORTS_ATOMIC_RMW

2026-03-08T10:06:49+00:00

Currently, since all the architectures that support Rust all have
CONFIG_ARCH_SUPPORTS_ATOMIC_RMW selected, the helpers of atomic
load/store on i8 and i16 relies on CONFIG_ARCH_SUPPORTS_ATOMIC_RMW=y.
It's generally fine since most of architectures support that.

The plan for CONFIG_ARCH_SUPPORTS_ATOMIC_RMW=n architectures is adding
their (probably lock-based) atomic load/store for i8 and i16 as their
atomic_{read,set}() and atomic64_{read,set}() counterpart when they
plans to support Rust.

Hence use a statis_assert!() to check this and remind the future us the
need of the helpers. This is more clear than the #[cfg] on impl blocks
of i8 and i16.

Suggested-by: Dirk Behme 
Suggested-by: Benno Lossin 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260120140503.62804-2-boqun.feng@gmail.com
Link: https://patch.msgid.link/20260303201701.12204-7-boqun@kernel.org