From 4a5dc632e0b603ec1cbbf87b78de86b4b6359cff Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Tue, 3 Mar 2026 12:16:49 -0800 Subject: rust: sync: atomic: Remove bound `T: Sync` for `Atomic::from_ptr()` Originally, `Atomic::from_ptr()` requires `T` being a `Sync` because I thought having the ability to do `from_ptr()` meant multiplle `&Atomic`s shared by different threads, which was identical (or similar) to multiple `&T`s shared by different threads. Hence `T` was required to be `Sync`. However this is not true, since `&Atomic` is not the same at `&T`. Moreover, having this bound makes `Atomic::<*mut T>::from_ptr()` impossible, which is definitely not intended. Therefore remove the `T: Sync` bound. [boqun: Fix title typo spotted by Alice & Gary] Fixes: 29c32c405e53 ("rust: sync: atomic: Add generic atomics") Signed-off-by: Boqun Feng Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Alice Ryhl Reviewed-by: Gary Guo Link: https://patch.msgid.link/20260120115207.55318-2-boqun.feng@gmail.com Link: https://patch.msgid.link/20260303201701.12204-2-boqun@kernel.org --- rust/kernel/sync/atomic.rs | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) (limited to 'rust') diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index 4aebeacb961a..296b25e83bbb 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -204,10 +204,7 @@ impl Atomic { /// // no data race. /// unsafe { Atomic::from_ptr(foo_a_ptr) }.store(2, Release); /// ``` - pub unsafe fn from_ptr<'a>(ptr: *mut T) -> &'a Self - where - T: Sync, - { + pub unsafe fn from_ptr<'a>(ptr: *mut T) -> &'a Self { // CAST: `T` and `Atomic` have the same size, alignment and bit validity. // SAFETY: Per function safety requirement, `ptr` is a valid pointer and the object will // live long enough. It's safe to return a `&Atomic` because function safety requirement -- cgit From bebf7bdc62537b9ef4700c6402f1c2aa206a9b50 Mon Sep 17 00:00:00 2001 From: FUJITA Tomonori Date: Tue, 3 Mar 2026 12:16:50 -0800 Subject: rust: sync: atomic: Add example for Atomic::get_mut() Add an example for Atomic::get_mut(). No functional change. Signed-off-by: FUJITA Tomonori Signed-off-by: Boqun Feng Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Alice Ryhl Reviewed-by: Gary Guo Link: https://patch.msgid.link/20260128123313.3850604-1-tomo@aliasing.net Link: https://patch.msgid.link/20260303201701.12204-3-boqun@kernel.org --- rust/kernel/sync/atomic.rs | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'rust') diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index 296b25e83bbb..e262b0cb53ae 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -232,6 +232,17 @@ impl Atomic { /// Returns a mutable reference to the underlying atomic `T`. /// /// This is safe because the mutable reference of the atomic `T` guarantees exclusive access. + /// + /// # Examples + /// + /// ``` + /// use kernel::sync::atomic::{Atomic, Relaxed}; + /// + /// let mut atomic_val = Atomic::new(0u32); + /// let val_mut = atomic_val.get_mut(); + /// *val_mut = 101; + /// assert_eq!(101, atomic_val.load(Relaxed)); + /// ``` pub fn get_mut(&mut self) -> &mut T { // CAST: `T` and `T::Repr` has the same size and alignment per the safety requirement of // `AtomicType`, and per the type invariants `self.0` is a valid `T`, therefore the casting -- cgit From ecc8e9fbaac35c8e5cced26f740f846506c4737b Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Tue, 3 Mar 2026 12:16:51 -0800 Subject: rust: helpers: Generify the definitions of rust_helper_*_{read,set}* To support atomic pointers, more {read,set} helpers will be introduced, hence define macros to generate these helpers to ease the introduction of the future helpers. Signed-off-by: Boqun Feng Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20260117122243.24404-2-boqun.feng@gmail.com Link: https://patch.msgid.link/20260303201701.12204-4-boqun@kernel.org --- rust/helpers/atomic_ext.c | 53 ++++++++++++++++++++--------------------------- 1 file changed, 23 insertions(+), 30 deletions(-) (limited to 'rust') diff --git a/rust/helpers/atomic_ext.c b/rust/helpers/atomic_ext.c index 7d0c2bd340da..f471c1ff123d 100644 --- a/rust/helpers/atomic_ext.c +++ b/rust/helpers/atomic_ext.c @@ -4,45 +4,38 @@ #include #include -__rust_helper s8 rust_helper_atomic_i8_read(s8 *ptr) -{ - return READ_ONCE(*ptr); -} - -__rust_helper s8 rust_helper_atomic_i8_read_acquire(s8 *ptr) -{ - return smp_load_acquire(ptr); -} - -__rust_helper s16 rust_helper_atomic_i16_read(s16 *ptr) -{ - return READ_ONCE(*ptr); +#define GEN_READ_HELPER(tname, type) \ +__rust_helper type rust_helper_atomic_##tname##_read(type *ptr) \ +{ \ + return READ_ONCE(*ptr); \ } -__rust_helper s16 rust_helper_atomic_i16_read_acquire(s16 *ptr) -{ - return smp_load_acquire(ptr); +#define GEN_SET_HELPER(tname, type) \ +__rust_helper void rust_helper_atomic_##tname##_set(type *ptr, type val) \ +{ \ + WRITE_ONCE(*ptr, val); \ } -__rust_helper void rust_helper_atomic_i8_set(s8 *ptr, s8 val) -{ - WRITE_ONCE(*ptr, val); +#define GEN_READ_ACQUIRE_HELPER(tname, type) \ +__rust_helper type rust_helper_atomic_##tname##_read_acquire(type *ptr) \ +{ \ + return smp_load_acquire(ptr); \ } -__rust_helper void rust_helper_atomic_i8_set_release(s8 *ptr, s8 val) -{ - smp_store_release(ptr, val); +#define GEN_SET_RELEASE_HELPER(tname, type) \ +__rust_helper void rust_helper_atomic_##tname##_set_release(type *ptr, type val)\ +{ \ + smp_store_release(ptr, val); \ } -__rust_helper void rust_helper_atomic_i16_set(s16 *ptr, s16 val) -{ - WRITE_ONCE(*ptr, val); -} +#define GEN_READ_SET_HELPERS(tname, type) \ + GEN_READ_HELPER(tname, type) \ + GEN_SET_HELPER(tname, type) \ + GEN_READ_ACQUIRE_HELPER(tname, type) \ + GEN_SET_RELEASE_HELPER(tname, type) \ -__rust_helper void rust_helper_atomic_i16_set_release(s16 *ptr, s16 val) -{ - smp_store_release(ptr, val); -} +GEN_READ_SET_HELPERS(i8, s8) +GEN_READ_SET_HELPERS(i16, s16) /* * xchg helpers depend on ARCH_SUPPORTS_ATOMIC_RMW and on the -- cgit From f92d22b00e3f75fad2efd965b20d49b4e763b792 Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Tue, 3 Mar 2026 12:16:52 -0800 Subject: rust: helpers: Generify the definitions of rust_helper_*_xchg* To support atomic pointers, more xchg helpers will be introduced, hence define macros to generate these helpers to ease the introduction of the future helpers. Signed-off-by: Boqun Feng Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20260117122243.24404-3-boqun.feng@gmail.com Link: https://patch.msgid.link/20260303201701.12204-5-boqun@kernel.org --- rust/helpers/atomic_ext.c | 48 ++++++++++++----------------------------------- 1 file changed, 12 insertions(+), 36 deletions(-) (limited to 'rust') diff --git a/rust/helpers/atomic_ext.c b/rust/helpers/atomic_ext.c index f471c1ff123d..c5f665bbe785 100644 --- a/rust/helpers/atomic_ext.c +++ b/rust/helpers/atomic_ext.c @@ -44,45 +44,21 @@ GEN_READ_SET_HELPERS(i16, s16) * The architectures that currently support Rust (x86_64, armv7, * arm64, riscv, and loongarch) satisfy these requirements. */ -__rust_helper s8 rust_helper_atomic_i8_xchg(s8 *ptr, s8 new) -{ - return xchg(ptr, new); -} - -__rust_helper s16 rust_helper_atomic_i16_xchg(s16 *ptr, s16 new) -{ - return xchg(ptr, new); -} - -__rust_helper s8 rust_helper_atomic_i8_xchg_acquire(s8 *ptr, s8 new) -{ - return xchg_acquire(ptr, new); -} - -__rust_helper s16 rust_helper_atomic_i16_xchg_acquire(s16 *ptr, s16 new) -{ - return xchg_acquire(ptr, new); -} - -__rust_helper s8 rust_helper_atomic_i8_xchg_release(s8 *ptr, s8 new) -{ - return xchg_release(ptr, new); -} - -__rust_helper s16 rust_helper_atomic_i16_xchg_release(s16 *ptr, s16 new) -{ - return xchg_release(ptr, new); +#define GEN_XCHG_HELPER(tname, type, suffix) \ +__rust_helper type \ +rust_helper_atomic_##tname##_xchg##suffix(type *ptr, type new) \ +{ \ + return xchg##suffix(ptr, new); \ } -__rust_helper s8 rust_helper_atomic_i8_xchg_relaxed(s8 *ptr, s8 new) -{ - return xchg_relaxed(ptr, new); -} +#define GEN_XCHG_HELPERS(tname, type) \ + GEN_XCHG_HELPER(tname, type, ) \ + GEN_XCHG_HELPER(tname, type, _acquire) \ + GEN_XCHG_HELPER(tname, type, _release) \ + GEN_XCHG_HELPER(tname, type, _relaxed) \ -__rust_helper s16 rust_helper_atomic_i16_xchg_relaxed(s16 *ptr, s16 new) -{ - return xchg_relaxed(ptr, new); -} +GEN_XCHG_HELPERS(i8, s8) +GEN_XCHG_HELPERS(i16, s16) /* * try_cmpxchg helpers depend on ARCH_SUPPORTS_ATOMIC_RMW and on the -- cgit From a92236bf239cc01fd40d9cbe98fc8b9924c42a82 Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Tue, 3 Mar 2026 12:16:53 -0800 Subject: rust: helpers: Generify the definitions of rust_helper_*_cmpxchg* To support atomic pointers, more cmpxchg helpers will be introduced, hence define macros to generate these helpers to ease the introduction of the future helpers. Signed-off-by: Boqun Feng Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20260117122243.24404-4-boqun.feng@gmail.com Link: https://patch.msgid.link/20260303201701.12204-6-boqun@kernel.org --- rust/helpers/atomic_ext.c | 48 ++++++++++++----------------------------------- 1 file changed, 12 insertions(+), 36 deletions(-) (limited to 'rust') diff --git a/rust/helpers/atomic_ext.c b/rust/helpers/atomic_ext.c index c5f665bbe785..240218e2e708 100644 --- a/rust/helpers/atomic_ext.c +++ b/rust/helpers/atomic_ext.c @@ -67,42 +67,18 @@ GEN_XCHG_HELPERS(i16, s16) * The architectures that currently support Rust (x86_64, armv7, * arm64, riscv, and loongarch) satisfy these requirements. */ -__rust_helper bool rust_helper_atomic_i8_try_cmpxchg(s8 *ptr, s8 *old, s8 new) -{ - return try_cmpxchg(ptr, old, new); -} - -__rust_helper bool rust_helper_atomic_i16_try_cmpxchg(s16 *ptr, s16 *old, s16 new) -{ - return try_cmpxchg(ptr, old, new); -} - -__rust_helper bool rust_helper_atomic_i8_try_cmpxchg_acquire(s8 *ptr, s8 *old, s8 new) -{ - return try_cmpxchg_acquire(ptr, old, new); -} - -__rust_helper bool rust_helper_atomic_i16_try_cmpxchg_acquire(s16 *ptr, s16 *old, s16 new) -{ - return try_cmpxchg_acquire(ptr, old, new); -} - -__rust_helper bool rust_helper_atomic_i8_try_cmpxchg_release(s8 *ptr, s8 *old, s8 new) -{ - return try_cmpxchg_release(ptr, old, new); -} - -__rust_helper bool rust_helper_atomic_i16_try_cmpxchg_release(s16 *ptr, s16 *old, s16 new) -{ - return try_cmpxchg_release(ptr, old, new); +#define GEN_TRY_CMPXCHG_HELPER(tname, type, suffix) \ +__rust_helper bool \ +rust_helper_atomic_##tname##_try_cmpxchg##suffix(type *ptr, type *old, type new)\ +{ \ + return try_cmpxchg##suffix(ptr, old, new); \ } -__rust_helper bool rust_helper_atomic_i8_try_cmpxchg_relaxed(s8 *ptr, s8 *old, s8 new) -{ - return try_cmpxchg_relaxed(ptr, old, new); -} +#define GEN_TRY_CMPXCHG_HELPERS(tname, type) \ + GEN_TRY_CMPXCHG_HELPER(tname, type, ) \ + GEN_TRY_CMPXCHG_HELPER(tname, type, _acquire) \ + GEN_TRY_CMPXCHG_HELPER(tname, type, _release) \ + GEN_TRY_CMPXCHG_HELPER(tname, type, _relaxed) \ -__rust_helper bool rust_helper_atomic_i16_try_cmpxchg_relaxed(s16 *ptr, s16 *old, s16 new) -{ - return try_cmpxchg_relaxed(ptr, old, new); -} +GEN_TRY_CMPXCHG_HELPERS(i8, s8) +GEN_TRY_CMPXCHG_HELPERS(i16, s16) -- cgit From 553c02fb588d4310193eba80f75b43b20befd1d2 Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Tue, 3 Mar 2026 12:16:54 -0800 Subject: rust: sync: atomic: Clarify the need of CONFIG_ARCH_SUPPORTS_ATOMIC_RMW 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 --- rust/kernel/sync/atomic/internal.rs | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) (limited to 'rust') diff --git a/rust/kernel/sync/atomic/internal.rs b/rust/kernel/sync/atomic/internal.rs index 0dac58bca2b3..ef516bcb02ee 100644 --- a/rust/kernel/sync/atomic/internal.rs +++ b/rust/kernel/sync/atomic/internal.rs @@ -37,16 +37,23 @@ pub trait AtomicImpl: Sized + Send + Copy + private::Sealed { type Delta; } -// The current helpers of load/store uses `{WRITE,READ}_ONCE()` hence the atomicity is only -// guaranteed against read-modify-write operations if the architecture supports native atomic RmW. -#[cfg(CONFIG_ARCH_SUPPORTS_ATOMIC_RMW)] +// The current helpers of load/store of atomic `i8` and `i16` use `{WRITE,READ}_ONCE()` hence the +// atomicity is only guaranteed against read-modify-write operations if the architecture supports +// native atomic RmW. +// +// In the future when a CONFIG_ARCH_SUPPORTS_ATOMIC_RMW=n architecture plans to support Rust, the +// load/store helpers that guarantee atomicity against RmW operations (usually via a lock) need to +// be added. +crate::static_assert!( + cfg!(CONFIG_ARCH_SUPPORTS_ATOMIC_RMW), + "The current implementation of atomic i8/i16/ptr relies on the architecure being \ + ARCH_SUPPORTS_ATOMIC_RMW" +); + impl AtomicImpl for i8 { type Delta = Self; } -// The current helpers of load/store uses `{WRITE,READ}_ONCE()` hence the atomicity is only -// guaranteed against read-modify-write operations if the architecture supports native atomic RmW. -#[cfg(CONFIG_ARCH_SUPPORTS_ATOMIC_RMW)] impl AtomicImpl for i16 { type Delta = Self; } -- cgit From ac8f06ade38a49f7725cc219fc6e90d1d4708d2b Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Tue, 3 Mar 2026 12:16:55 -0800 Subject: rust: sync: atomic: Add Atomic<*{mut,const} T> support 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/helpers/atomic_ext.c | 3 +++ rust/kernel/sync/atomic.rs | 12 +++++++++- rust/kernel/sync/atomic/internal.rs | 24 ++++++++++++------- rust/kernel/sync/atomic/predefine.rs | 46 ++++++++++++++++++++++++++++++++++++ 4 files changed, 75 insertions(+), 10 deletions(-) (limited to 'rust') diff --git a/rust/helpers/atomic_ext.c b/rust/helpers/atomic_ext.c index 240218e2e708..c267d5190529 100644 --- a/rust/helpers/atomic_ext.c +++ b/rust/helpers/atomic_ext.c @@ -36,6 +36,7 @@ __rust_helper void rust_helper_atomic_##tname##_set_release(type *ptr, type val) GEN_READ_SET_HELPERS(i8, s8) GEN_READ_SET_HELPERS(i16, s16) +GEN_READ_SET_HELPERS(ptr, const void *) /* * xchg helpers depend on ARCH_SUPPORTS_ATOMIC_RMW and on the @@ -59,6 +60,7 @@ rust_helper_atomic_##tname##_xchg##suffix(type *ptr, type new) \ GEN_XCHG_HELPERS(i8, s8) GEN_XCHG_HELPERS(i16, s16) +GEN_XCHG_HELPERS(ptr, const void *) /* * try_cmpxchg helpers depend on ARCH_SUPPORTS_ATOMIC_RMW and on the @@ -82,3 +84,4 @@ rust_helper_atomic_##tname##_try_cmpxchg##suffix(type *ptr, type *old, type new) GEN_TRY_CMPXCHG_HELPERS(i8, s8) GEN_TRY_CMPXCHG_HELPERS(i16, s16) +GEN_TRY_CMPXCHG_HELPERS(ptr, const void *) diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index e262b0cb53ae..f4c3ab15c8a7 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -51,6 +51,10 @@ use ordering::OrderingType; #[repr(transparent)] pub struct Atomic(AtomicRepr); +// SAFETY: `Atomic` is safe to transfer between execution contexts because of the safety +// requirement of `AtomicType`. +unsafe impl Send for Atomic {} + // SAFETY: `Atomic` is safe to share among execution contexts because all accesses are atomic. unsafe impl Sync for Atomic {} @@ -68,6 +72,11 @@ unsafe impl Sync for Atomic {} /// /// - [`Self`] must have the same size and alignment as [`Self::Repr`]. /// - [`Self`] must be [round-trip transmutable] to [`Self::Repr`]. +/// - [`Self`] must be safe to transfer between execution contexts, if it's [`Send`], this is +/// automatically satisfied. The exception is pointer types that are even though marked as +/// `!Send` (e.g. raw pointers and [`NonNull`]) but requiring `unsafe` to do anything +/// meaningful on them. This is because transferring pointer values between execution contexts is +/// safe as long as the actual `unsafe` dereferencing is justified. /// /// Note that this is more relaxed than requiring the bi-directional transmutability (i.e. /// [`transmute()`] is always sound between `U` and `T`) because of the support for atomic @@ -108,7 +117,8 @@ unsafe impl Sync for Atomic {} /// [`transmute()`]: core::mem::transmute /// [round-trip transmutable]: AtomicType#round-trip-transmutability /// [Examples]: AtomicType#examples -pub unsafe trait AtomicType: Sized + Send + Copy { +/// [`NonNull`]: core::ptr::NonNull +pub unsafe trait AtomicType: Sized + Copy { /// The backing atomic implementation type. type Repr: AtomicImpl; } diff --git a/rust/kernel/sync/atomic/internal.rs b/rust/kernel/sync/atomic/internal.rs index ef516bcb02ee..e301db4eaf91 100644 --- a/rust/kernel/sync/atomic/internal.rs +++ b/rust/kernel/sync/atomic/internal.rs @@ -7,6 +7,7 @@ use crate::bindings; use crate::macros::paste; use core::cell::UnsafeCell; +use ffi::c_void; mod private { /// Sealed trait marker to disable customized impls on atomic implementation traits. @@ -14,10 +15,11 @@ mod private { } // The C side supports atomic primitives only for `i32` and `i64` (`atomic_t` and `atomic64_t`), -// while the Rust side also layers provides atomic support for `i8` and `i16` -// on top of lower-level C primitives. +// while the Rust side also provides atomic support for `i8`, `i16` and `*const c_void` on top of +// lower-level C primitives. impl private::Sealed for i8 {} impl private::Sealed for i16 {} +impl private::Sealed for *const c_void {} impl private::Sealed for i32 {} impl private::Sealed for i64 {} @@ -26,10 +28,10 @@ impl private::Sealed for i64 {} /// This trait is sealed, and only types that map directly to the C side atomics /// or can be implemented with lower-level C primitives are allowed to implement this: /// -/// - `i8` and `i16` are implemented with lower-level C primitives. +/// - `i8`, `i16` and `*const c_void` are implemented with lower-level C primitives. /// - `i32` map to `atomic_t` /// - `i64` map to `atomic64_t` -pub trait AtomicImpl: Sized + Send + Copy + private::Sealed { +pub trait AtomicImpl: Sized + Copy + private::Sealed { /// The type of the delta in arithmetic or logical operations. /// /// For example, in `atomic_add(ptr, v)`, it's the type of `v`. Usually it's the same type of @@ -37,9 +39,9 @@ pub trait AtomicImpl: Sized + Send + Copy + private::Sealed { type Delta; } -// The current helpers of load/store of atomic `i8` and `i16` use `{WRITE,READ}_ONCE()` hence the -// atomicity is only guaranteed against read-modify-write operations if the architecture supports -// native atomic RmW. +// The current helpers of load/store of atomic `i8`, `i16` and pointers use `{WRITE,READ}_ONCE()` +// hence the atomicity is only guaranteed against read-modify-write operations if the architecture +// supports native atomic RmW. // // In the future when a CONFIG_ARCH_SUPPORTS_ATOMIC_RMW=n architecture plans to support Rust, the // load/store helpers that guarantee atomicity against RmW operations (usually via a lock) need to @@ -58,6 +60,10 @@ impl AtomicImpl for i16 { type Delta = Self; } +impl AtomicImpl for *const c_void { + type Delta = isize; +} + // `atomic_t` implements atomic operations on `i32`. impl AtomicImpl for i32 { type Delta = Self; @@ -269,7 +275,7 @@ macro_rules! declare_and_impl_atomic_methods { } declare_and_impl_atomic_methods!( - [ i8 => atomic_i8, i16 => atomic_i16, i32 => atomic, i64 => atomic64 ] + [ i8 => atomic_i8, i16 => atomic_i16, *const c_void => atomic_ptr, i32 => atomic, i64 => atomic64 ] /// Basic atomic operations pub trait AtomicBasicOps { /// Atomic read (load). @@ -287,7 +293,7 @@ declare_and_impl_atomic_methods!( ); declare_and_impl_atomic_methods!( - [ i8 => atomic_i8, i16 => atomic_i16, i32 => atomic, i64 => atomic64 ] + [ i8 => atomic_i8, i16 => atomic_i16, *const c_void => atomic_ptr, i32 => atomic, i64 => atomic64 ] /// Exchange and compare-and-exchange atomic operations pub trait AtomicExchangeOps { /// Atomic exchange. diff --git a/rust/kernel/sync/atomic/predefine.rs b/rust/kernel/sync/atomic/predefine.rs index 67a0406d3ea4..6f2c60529b64 100644 --- a/rust/kernel/sync/atomic/predefine.rs +++ b/rust/kernel/sync/atomic/predefine.rs @@ -4,6 +4,7 @@ use crate::static_assert; use core::mem::{align_of, size_of}; +use ffi::c_void; // Ensure size and alignment requirements are checked. static_assert!(size_of::() == size_of::()); @@ -28,6 +29,26 @@ unsafe impl super::AtomicType for i16 { type Repr = i16; } +// SAFETY: +// +// - `*mut T` has the same size and alignment with `*const c_void`, and is round-trip +// transmutable to `*const c_void`. +// - `*mut T` is safe to transfer between execution contexts. See the safety requirement of +// [`AtomicType`]. +unsafe impl super::AtomicType for *mut T { + type Repr = *const c_void; +} + +// SAFETY: +// +// - `*const T` has the same size and alignment with `*const c_void`, and is round-trip +// transmutable to `*const c_void`. +// - `*const T` is safe to transfer between execution contexts. See the safety requirement of +// [`AtomicType`]. +unsafe impl super::AtomicType for *const T { + type Repr = *const c_void; +} + // SAFETY: `i32` has the same size and alignment with itself, and is round-trip transmutable to // itself. unsafe impl super::AtomicType for i32 { @@ -226,4 +247,29 @@ mod tests { assert_eq!(false, x.load(Relaxed)); assert_eq!(Ok(false), x.cmpxchg(false, true, Full)); } + + #[test] + fn atomic_ptr_tests() { + let mut v = 42; + let mut u = 43; + let x = Atomic::new(&raw mut v); + + assert_eq!(x.load(Acquire), &raw mut v); + assert_eq!(x.cmpxchg(&raw mut u, &raw mut u, Relaxed), Err(&raw mut v)); + assert_eq!(x.cmpxchg(&raw mut v, &raw mut u, Relaxed), Ok(&raw mut v)); + assert_eq!(x.load(Relaxed), &raw mut u); + + let x = Atomic::new(&raw const v); + + assert_eq!(x.load(Acquire), &raw const v); + assert_eq!( + x.cmpxchg(&raw const u, &raw const u, Relaxed), + Err(&raw const v) + ); + assert_eq!( + x.cmpxchg(&raw const v, &raw const u, Relaxed), + Ok(&raw const v) + ); + assert_eq!(x.load(Relaxed), &raw const u); + } } -- cgit From ec6fc66ac39b1a6c0b06a828eff8d21928e56b60 Mon Sep 17 00:00:00 2001 From: FUJITA Tomonori Date: Tue, 3 Mar 2026 12:16:56 -0800 Subject: rust: sync: atomic: Add performance-optimal Flag type for atomic booleans 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/kernel/sync/atomic.rs | 125 +++++++++++++++++++++++++++++++++++ rust/kernel/sync/atomic/predefine.rs | 17 +++++ 2 files changed, 142 insertions(+) (limited to 'rust') diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index f4c3ab15c8a7..f80cebce5bc1 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -578,3 +578,128 @@ where unsafe { from_repr(ret) } } } + +#[cfg(any(CONFIG_X86_64, CONFIG_UML, CONFIG_ARM, CONFIG_ARM64))] +#[repr(C)] +#[derive(Clone, Copy)] +struct Flag { + bool_field: bool, +} + +/// # Invariants +/// +/// `padding` must be all zeroes. +#[cfg(not(any(CONFIG_X86_64, CONFIG_UML, CONFIG_ARM, CONFIG_ARM64)))] +#[repr(C, align(4))] +#[derive(Clone, Copy)] +struct Flag { + #[cfg(target_endian = "big")] + padding: [u8; 3], + bool_field: bool, + #[cfg(target_endian = "little")] + padding: [u8; 3], +} + +impl Flag { + #[inline(always)] + const fn new(b: bool) -> Self { + // INVARIANT: `padding` is all zeroes. + Self { + bool_field: b, + #[cfg(not(any(CONFIG_X86_64, CONFIG_UML, CONFIG_ARM, CONFIG_ARM64)))] + padding: [0; 3], + } + } +} + +// SAFETY: `Flag` and `Repr` have the same size and alignment, and `Flag` is round-trip +// transmutable to the selected representation (`i8` or `i32`). +unsafe impl AtomicType for Flag { + #[cfg(any(CONFIG_X86_64, CONFIG_UML, CONFIG_ARM, CONFIG_ARM64))] + type Repr = i8; + #[cfg(not(any(CONFIG_X86_64, CONFIG_UML, CONFIG_ARM, CONFIG_ARM64)))] + type Repr = i32; +} + +/// An atomic flag type intended to be backed by performance-optimal integer type. +/// +/// The backing integer type is an implementation detail; it may vary by architecture and change +/// in the future. +/// +/// [`AtomicFlag`] is generally preferable to [`Atomic`] when you need read-modify-write +/// (RMW) operations (e.g. [`Atomic::xchg()`]/[`Atomic::cmpxchg()`]) or when [`Atomic`] does +/// not save memory due to padding. On some architectures that do not support byte-sized atomic +/// RMW operations, RMW operations on [`Atomic`] are slower. +/// +/// If you only use [`Atomic::load()`]/[`Atomic::store()`], [`Atomic`] is fine. +/// +/// # Examples +/// +/// ``` +/// use kernel::sync::atomic::{AtomicFlag, Relaxed}; +/// +/// let flag = AtomicFlag::new(false); +/// assert_eq!(false, flag.load(Relaxed)); +/// flag.store(true, Relaxed); +/// assert_eq!(true, flag.load(Relaxed)); +/// ``` +pub struct AtomicFlag(Atomic); + +impl AtomicFlag { + /// Creates a new atomic flag. + #[inline(always)] + pub const fn new(b: bool) -> Self { + Self(Atomic::new(Flag::new(b))) + } + + /// Returns a mutable reference to the underlying flag as a [`bool`]. + /// + /// This is safe because the mutable reference of the atomic flag guarantees exclusive access. + /// + /// # Examples + /// + /// ``` + /// use kernel::sync::atomic::{AtomicFlag, Relaxed}; + /// + /// let mut atomic_flag = AtomicFlag::new(false); + /// assert_eq!(false, atomic_flag.load(Relaxed)); + /// *atomic_flag.get_mut() = true; + /// assert_eq!(true, atomic_flag.load(Relaxed)); + /// ``` + #[inline(always)] + pub fn get_mut(&mut self) -> &mut bool { + &mut self.0.get_mut().bool_field + } + + /// Loads the value from the atomic flag. + #[inline(always)] + pub fn load(&self, o: Ordering) -> bool { + self.0.load(o).bool_field + } + + /// Stores a value to the atomic flag. + #[inline(always)] + pub fn store(&self, v: bool, o: Ordering) { + self.0.store(Flag::new(v), o); + } + + /// Stores a value to the atomic flag and returns the previous value. + #[inline(always)] + pub fn xchg(&self, new: bool, o: Ordering) -> bool { + self.0.xchg(Flag::new(new), o).bool_field + } + + /// Store a value to the atomic flag if the current value is equal to `old`. + #[inline(always)] + pub fn cmpxchg( + &self, + old: bool, + new: bool, + o: Ordering, + ) -> Result { + match self.0.cmpxchg(Flag::new(old), Flag::new(new), o) { + Ok(_) => Ok(old), + Err(f) => Err(f.bool_field), + } + } +} diff --git a/rust/kernel/sync/atomic/predefine.rs b/rust/kernel/sync/atomic/predefine.rs index 6f2c60529b64..ceb3caed9784 100644 --- a/rust/kernel/sync/atomic/predefine.rs +++ b/rust/kernel/sync/atomic/predefine.rs @@ -272,4 +272,21 @@ mod tests { ); assert_eq!(x.load(Relaxed), &raw const u); } + + #[test] + fn atomic_flag_tests() { + let mut flag = AtomicFlag::new(false); + + assert_eq!(false, flag.load(Relaxed)); + + *flag.get_mut() = true; + assert_eq!(true, flag.load(Relaxed)); + + assert_eq!(true, flag.xchg(false, Relaxed)); + assert_eq!(false, flag.load(Relaxed)); + + *flag.get_mut() = true; + assert_eq!(Ok(true), flag.cmpxchg(true, false, Full)); + assert_eq!(false, flag.load(Relaxed)); + } } -- cgit From 282866207020b15c2afc4d43b1ca0c5d96c9032d Mon Sep 17 00:00:00 2001 From: FUJITA Tomonori Date: Tue, 3 Mar 2026 12:16:57 -0800 Subject: rust: list: Use AtomicFlag in AtomicTracker Make AtomicTracker use AtomicFlag instead of Atomic to avoid slow byte-sized RMWs on architectures that don't support them. 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/20260129122622.3896144-3-tomo@aliasing.net Link: https://patch.msgid.link/20260303201701.12204-10-boqun@kernel.org --- rust/kernel/list/arc.rs | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'rust') diff --git a/rust/kernel/list/arc.rs b/rust/kernel/list/arc.rs index 2282f33913ee..5e84f500a3fe 100644 --- a/rust/kernel/list/arc.rs +++ b/rust/kernel/list/arc.rs @@ -6,7 +6,7 @@ use crate::alloc::{AllocError, Flags}; use crate::prelude::*; -use crate::sync::atomic::{ordering, Atomic}; +use crate::sync::atomic::{ordering, AtomicFlag}; use crate::sync::{Arc, ArcBorrow, UniqueArc}; use core::marker::PhantomPinned; use core::ops::Deref; @@ -469,7 +469,7 @@ where /// If the boolean is `false`, then there is no [`ListArc`] for this value. #[repr(transparent)] pub struct AtomicTracker { - inner: Atomic, + inner: AtomicFlag, // This value needs to be pinned to justify the INVARIANT: comment in `AtomicTracker::new`. _pin: PhantomPinned, } @@ -480,12 +480,12 @@ impl AtomicTracker { // INVARIANT: Pin-init initializers can't be used on an existing `Arc`, so this value will // not be constructed in an `Arc` that already has a `ListArc`. Self { - inner: Atomic::new(false), + inner: AtomicFlag::new(false), _pin: PhantomPinned, } } - fn project_inner(self: Pin<&mut Self>) -> &mut Atomic { + fn project_inner(self: Pin<&mut Self>) -> &mut AtomicFlag { // SAFETY: The `inner` field is not structurally pinned, so we may obtain a mutable // reference to it even if we only have a pinned reference to `self`. unsafe { &mut Pin::into_inner_unchecked(self).inner } -- cgit From e2f9c86f33abb89d3e52436018f58e5fb951cc04 Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Tue, 3 Mar 2026 12:16:58 -0800 Subject: rust: sync: atomic: Add atomic operation helpers over raw pointers 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/kernel/sync/atomic.rs | 104 +++++++++++++++++++++++++++++++++++ rust/kernel/sync/atomic/predefine.rs | 46 ++++++++++++++++ 2 files changed, 150 insertions(+) (limited to 'rust') diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index f80cebce5bc1..1bb1fc2be177 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -703,3 +703,107 @@ impl AtomicFlag { } } } + +/// Atomic load over raw pointers. +/// +/// This function provides a short-cut of `Atomic::from_ptr().load(..)`, and can be used to work +/// with C side on synchronizations: +/// +/// - `atomic_load(.., Relaxed)` maps to `READ_ONCE()` when used for inter-thread communication. +/// - `atomic_load(.., Acquire)` maps to `smp_load_acquire()`. +/// +/// # Safety +/// +/// - `ptr` is a valid pointer to `T` and aligned to `align_of::()`. +/// - If there is a concurrent store from kernel (C or Rust), it has to be atomic. +#[doc(alias("READ_ONCE", "smp_load_acquire"))] +#[inline(always)] +pub unsafe fn atomic_load( + ptr: *mut T, + o: Ordering, +) -> T +where + T::Repr: AtomicBasicOps, +{ + // SAFETY: Per the function safety requirement, `ptr` is valid and aligned to + // `align_of::()`, and all concurrent stores from kernel are atomic, hence no data race per + // LKMM. + unsafe { Atomic::from_ptr(ptr) }.load(o) +} + +/// Atomic store over raw pointers. +/// +/// This function provides a short-cut of `Atomic::from_ptr().load(..)`, and can be used to work +/// with C side on synchronizations: +/// +/// - `atomic_store(.., Relaxed)` maps to `WRITE_ONCE()` when used for inter-thread communication. +/// - `atomic_load(.., Release)` maps to `smp_store_release()`. +/// +/// # Safety +/// +/// - `ptr` is a valid pointer to `T` and aligned to `align_of::()`. +/// - If there is a concurrent access from kernel (C or Rust), it has to be atomic. +#[doc(alias("WRITE_ONCE", "smp_store_release"))] +#[inline(always)] +pub unsafe fn atomic_store( + ptr: *mut T, + v: T, + o: Ordering, +) where + T::Repr: AtomicBasicOps, +{ + // SAFETY: Per the function safety requirement, `ptr` is valid and aligned to + // `align_of::()`, and all concurrent accesses from kernel are atomic, hence no data race + // per LKMM. + unsafe { Atomic::from_ptr(ptr) }.store(v, o); +} + +/// Atomic exchange over raw pointers. +/// +/// This function provides a short-cut of `Atomic::from_ptr().xchg(..)`, and can be used to work +/// with C side on synchronizations. +/// +/// # Safety +/// +/// - `ptr` is a valid pointer to `T` and aligned to `align_of::()`. +/// - If there is a concurrent access from kernel (C or Rust), it has to be atomic. +#[inline(always)] +pub unsafe fn xchg( + ptr: *mut T, + new: T, + o: Ordering, +) -> T +where + T::Repr: AtomicExchangeOps, +{ + // SAFETY: Per the function safety requirement, `ptr` is valid and aligned to + // `align_of::()`, and all concurrent accesses from kernel are atomic, hence no data race + // per LKMM. + unsafe { Atomic::from_ptr(ptr) }.xchg(new, o) +} + +/// Atomic compare and exchange over raw pointers. +/// +/// This function provides a short-cut of `Atomic::from_ptr().cmpxchg(..)`, and can be used to work +/// with C side on synchronizations. +/// +/// # Safety +/// +/// - `ptr` is a valid pointer to `T` and aligned to `align_of::()`. +/// - If there is a concurrent access from kernel (C or Rust), it has to be atomic. +#[doc(alias("try_cmpxchg"))] +#[inline(always)] +pub unsafe fn cmpxchg( + ptr: *mut T, + old: T, + new: T, + o: Ordering, +) -> Result +where + T::Repr: AtomicExchangeOps, +{ + // SAFETY: Per the function safety requirement, `ptr` is valid and aligned to + // `align_of::()`, and all concurrent accesses from kernel are atomic, hence no data race + // per LKMM. + unsafe { Atomic::from_ptr(ptr) }.cmpxchg(old, new, o) +} diff --git a/rust/kernel/sync/atomic/predefine.rs b/rust/kernel/sync/atomic/predefine.rs index ceb3caed9784..1d53834fcb12 100644 --- a/rust/kernel/sync/atomic/predefine.rs +++ b/rust/kernel/sync/atomic/predefine.rs @@ -178,6 +178,14 @@ mod tests { assert_eq!(v, x.load(Relaxed)); }); + + for_each_type!(42 in [i8, i16, i32, i64, u32, u64, isize, usize] |v| { + let x = Atomic::new(v); + let ptr = x.as_ptr(); + + // SAFETY: `ptr` is a valid pointer and no concurrent access. + assert_eq!(v, unsafe { atomic_load(ptr, Relaxed) }); + }); } #[test] @@ -188,6 +196,17 @@ mod tests { x.store(v, Release); assert_eq!(v, x.load(Acquire)); }); + + for_each_type!(42 in [i8, i16, i32, i64, u32, u64, isize, usize] |v| { + let x = Atomic::new(0); + let ptr = x.as_ptr(); + + // SAFETY: `ptr` is a valid pointer and no concurrent access. + unsafe { atomic_store(ptr, v, Release) }; + + // SAFETY: `ptr` is a valid pointer and no concurrent access. + assert_eq!(v, unsafe { atomic_load(ptr, Acquire) }); + }); } #[test] @@ -201,6 +220,18 @@ mod tests { assert_eq!(old, x.xchg(new, Full)); assert_eq!(new, x.load(Relaxed)); }); + + for_each_type!(42 in [i8, i16, i32, i64, u32, u64, isize, usize] |v| { + let x = Atomic::new(v); + let ptr = x.as_ptr(); + + let old = v; + let new = v + 1; + + // SAFETY: `ptr` is a valid pointer and no concurrent access. + assert_eq!(old, unsafe { xchg(ptr, new, Full) }); + assert_eq!(new, x.load(Relaxed)); + }); } #[test] @@ -216,6 +247,21 @@ mod tests { assert_eq!(Ok(old), x.cmpxchg(old, new, Relaxed)); assert_eq!(new, x.load(Relaxed)); }); + + for_each_type!(42 in [i8, i16, i32, i64, u32, u64, isize, usize] |v| { + let x = Atomic::new(v); + let ptr = x.as_ptr(); + + let old = v; + let new = v + 1; + + // SAFETY: `ptr` is a valid pointer and no concurrent access. + assert_eq!(Err(old), unsafe { cmpxchg(ptr, new, new, Full) }); + assert_eq!(old, x.load(Relaxed)); + // SAFETY: `ptr` is a valid pointer and no concurrent access. + assert_eq!(Ok(old), unsafe { cmpxchg(ptr, old, new, Relaxed) }); + assert_eq!(new, x.load(Relaxed)); + }); } #[test] -- cgit From c49cf341090b53d2afa4dc7c8007ddeefbb3b37f Mon Sep 17 00:00:00 2001 From: Andreas Hindborg Date: Tue, 3 Mar 2026 12:16:59 -0800 Subject: rust: sync: atomic: Add fetch_sub() 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/kernel/sync/atomic.rs | 43 +++++++++++++++++++++++++++++++++++++ rust/kernel/sync/atomic/internal.rs | 5 +++++ 2 files changed, 48 insertions(+) (limited to 'rust') diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index 1bb1fc2be177..545a8d37ba78 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -577,6 +577,49 @@ where // SAFETY: `ret` comes from reading `self.0`, which is a valid `T` per type invariants. unsafe { from_repr(ret) } } + + /// Atomic fetch and subtract. + /// + /// Atomically updates `*self` to `(*self).wrapping_sub(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!(42, x.fetch_sub(12, Acquire)); + /// assert_eq!(30, x.load(Relaxed)); + /// + /// let x = Atomic::new(42); + /// assert_eq!(42, x.load(Relaxed)); + /// assert_eq!(42, x.fetch_sub(12, Full)); + /// assert_eq!(30, x.load(Relaxed)); + /// ``` + #[inline(always)] + pub fn fetch_sub(&self, v: Rhs, _: Ordering) -> T + where + // Types that support addition also support subtraction. + T: AtomicAdd, + { + let v = T::rhs_into_delta(v); + + // INVARIANT: `self.0` is a valid `T` after `atomic_fetch_sub*()` due to safety requirement + // of `AtomicAdd`. + let ret = { + match Ordering::TYPE { + OrderingType::Full => T::Repr::atomic_fetch_sub(&self.0, v), + OrderingType::Acquire => T::Repr::atomic_fetch_sub_acquire(&self.0, v), + OrderingType::Release => T::Repr::atomic_fetch_sub_release(&self.0, v), + OrderingType::Relaxed => T::Repr::atomic_fetch_sub_relaxed(&self.0, v), + } + }; + + // SAFETY: `ret` comes from reading `self.0`, which is a valid `T` per type invariants. + unsafe { from_repr(ret) } + } } #[cfg(any(CONFIG_X86_64, CONFIG_UML, CONFIG_ARM, CONFIG_ARM64))] diff --git a/rust/kernel/sync/atomic/internal.rs b/rust/kernel/sync/atomic/internal.rs index e301db4eaf91..b762dbdf6d18 100644 --- a/rust/kernel/sync/atomic/internal.rs +++ b/rust/kernel/sync/atomic/internal.rs @@ -340,5 +340,10 @@ declare_and_impl_atomic_methods!( // SAFETY: `a.as_ptr()` is valid and properly aligned. unsafe { bindings::#call(v, a.as_ptr().cast()) } } + + fn fetch_sub[acquire, release, relaxed](a: &AtomicRepr, v: Self::Delta) -> Self { + // SAFETY: `a.as_ptr()` guarantees the returned pointer is valid and properly aligned. + unsafe { bindings::#call(v, a.as_ptr().cast()) } + } } ); -- cgit From 0b864375d93d1509821def9c4b15f845d314a5d2 Mon Sep 17 00:00:00 2001 From: Andreas Hindborg Date: Tue, 3 Mar 2026 12:17:00 -0800 Subject: rust: sync: atomic: Update documentation for `fetch_add()` The documentation for `fetch_add()` does not indicate that the original value is returned by `fetch_add()`. Update the documentation so this is clear. 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-v3-2-e63cbed1d2aa@kernel.org Link: https://patch.msgid.link/20260303201701.12204-13-boqun@kernel.org --- rust/kernel/sync/atomic.rs | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) (limited to 'rust') diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index 545a8d37ba78..9cd009d57e35 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -545,16 +545,14 @@ where /// 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) }); + /// assert_eq!(42, x.fetch_add(12, Acquire)); + /// assert_eq!(54, 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) } ); + /// assert_eq!(42, x.fetch_add(12, Full)); + /// assert_eq!(54, x.load(Relaxed)); /// ``` #[inline(always)] pub fn fetch_add(&self, v: Rhs, _: Ordering) -> T -- cgit From b91d5d4bcf1266257a9e0199e1b4ad7fa8771baa Mon Sep 17 00:00:00 2001 From: Andreas Hindborg Date: Tue, 3 Mar 2026 12:17:01 -0800 Subject: rust: atomic: Update a safety comment in impl of `fetch_add()` 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/kernel/sync/atomic/internal.rs | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'rust') diff --git a/rust/kernel/sync/atomic/internal.rs b/rust/kernel/sync/atomic/internal.rs index b762dbdf6d18..ad810c2172ec 100644 --- a/rust/kernel/sync/atomic/internal.rs +++ b/rust/kernel/sync/atomic/internal.rs @@ -337,7 +337,7 @@ declare_and_impl_atomic_methods!( /// Atomically updates `*a` to `(*a).wrapping_add(v)`, and returns the value of `*a` /// before the update. fn fetch_add[acquire, release, relaxed](a: &AtomicRepr, v: Self::Delta) -> Self { - // SAFETY: `a.as_ptr()` is valid and properly aligned. + // SAFETY: `a.as_ptr()` guarantees the returned pointer is valid and properly aligned. unsafe { bindings::#call(v, a.as_ptr().cast()) } } -- cgit