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rust: sync: atomic: Clarify the need of CONFIG_ARCH_SUPPORTS_ATOMIC_RMW

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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 <dirk.behme@gmail.com>
Suggested-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260120140503.62804-2-boqun.feng@gmail.com
Link: https://patch.msgid.link/20260303201701.12204-7-boqun@kernel.org
This commit is contained in:
Boqun Feng
2026-03-03 12:16:54 -08:00
committed by Peter Zijlstra
parent a92236bf23
commit 553c02fb58
1 changed files with 13 additions and 6 deletions
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19
rust/kernel/sync/atomic/internal.rs
View File

@@ -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;
}