linux-kernel - [tip: locking/core] rust: helpers: Add i8/i16 relaxed atomic helpers

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Message-ID: <176830140769.510.10398950538996490358.tip-bot2@tip-bot2>
Date: Tue, 13 Jan 2026 10:50:07 -0000
From: "tip-bot2 for FUJITA Tomonori" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: FUJITA Tomonori <fujita.tomonori@...il.com>, Gary Guo <gary@...yguo.net>,
 Joel Fernandes <joelagnelf@...dia.com>, Boqun Feng <boqun.feng@...il.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: locking/core] rust: helpers: Add i8/i16 relaxed atomic helpers

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     300e53b3d3b59e72a972a12ee5c6438aab4860a4
Gitweb:        https://git.kernel.org/tip/300e53b3d3b59e72a972a12ee5c6438aab4860a4
Author:        FUJITA Tomonori <fujita.tomonori@...il.com>
AuthorDate:    Thu, 11 Dec 2025 20:38:24 +09:00
Committer:     Boqun Feng <boqun.feng@...il.com>
CommitterDate: Fri, 09 Jan 2026 19:01:40 +08:00

rust: helpers: Add i8/i16 relaxed atomic helpers

Add READ_ONCE/WRITE_ONCE based helpers for i8 and i16 types to support
relaxed atomic operations in Rust.

While relaxed operations could be implemented purely in Rust using
read_volatile() and write_volatile(), using C's READ_ONCE() and
WRITE_ONCE() macros ensures complete consistency with the kernel
memory model.

These helpers expose different symbol names than their C counterparts
so they are split into atomic_ext.c instead of atomic.c. The symbol
names; the names make the interface Rust/C clear, consistent with
i32/i64.

[boqun: Rename the functions from {load,store} to {read,set} to avoid
future adjustment]

Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
Reviewed-by: Gary Guo <gary@...yguo.net>
Reviewed-by: Joel Fernandes <joelagnelf@...dia.com>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Link: https://patch.msgid.link/20251211113826.1299077-3-fujita.tomonori@gmail.com
---
 rust/helpers/atomic_ext.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/rust/helpers/atomic_ext.c b/rust/helpers/atomic_ext.c
index 1fb6241..02e05b4 100644
--- a/rust/helpers/atomic_ext.c
+++ b/rust/helpers/atomic_ext.c
@@ -1,22 +1,43 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include <asm/barrier.h>
+#include <asm/rwonce.h>
+
+__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);
+}
+
 __rust_helper s16 rust_helper_atomic_i16_read_acquire(s16 *ptr)
 {
 	return smp_load_acquire(ptr);
 }
 
+__rust_helper void rust_helper_atomic_i8_set(s8 *ptr, s8 val)
+{
+	WRITE_ONCE(*ptr, val);
+}
+
 __rust_helper void rust_helper_atomic_i8_set_release(s8 *ptr, s8 val)
 {
 	smp_store_release(ptr, val);
 }
 
+__rust_helper void rust_helper_atomic_i16_set(s16 *ptr, s16 val)
+{
+	WRITE_ONCE(*ptr, val);
+}
+
 __rust_helper void rust_helper_atomic_i16_set_release(s16 *ptr, s16 val)
 {
 	smp_store_release(ptr, val);