linux-kernel - [tip: locking/core] rust: sync: set

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Message-ID: <176830141082.510.4677710192596737229.tip-bot2@tip-bot2>
Date: Tue, 13 Jan 2026 10:50:10 -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>,
 Andreas Hindborg <a.hindborg@...nel.org>, Gary Guo <gary@...yguo.net>,
 Boqun Feng <boqun.feng@...il.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: locking/core] rust: sync: set_once: Implement Send and Sync

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

Commit-ID:     8a581130b1cbc17c702298b8325e3df98c792760
Gitweb:        https://git.kernel.org/tip/8a581130b1cbc17c702298b8325e3df98c792760
Author:        FUJITA Tomonori <fujita.tomonori@...il.com>
AuthorDate:    Tue, 16 Dec 2025 09:09:01 +09:00
Committer:     Boqun Feng <boqun.feng@...il.com>
CommitterDate: Fri, 09 Jan 2026 19:01:40 +08:00

rust: sync: set_once: Implement Send and Sync

Implement Send and Sync for SetOnce<T> to allow it to be used across
thread boundaries.

Send: SetOnce<T> can be transferred across threads when T: Send, as
the contained value is also transferred and will be dropped on the
destination thread.

Sync: SetOnce<T> can be shared across threads when T: Sync, as
as_ref() provides shared references &T and atomic operations ensure
proper synchronization. Since the inner T may be dropped on any
thread, we also require T: Send.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>
Reviewed-by: Gary Guo <gary@...yguo.net>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Link: https://patch.msgid.link/20251216000901.221375-1-fujita.tomonori@gmail.com
---
 rust/kernel/sync/set_once.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/rust/kernel/sync/set_once.rs b/rust/kernel/sync/set_once.rs
index bdba601..139cef0 100644
--- a/rust/kernel/sync/set_once.rs
+++ b/rust/kernel/sync/set_once.rs
@@ -123,3 +123,11 @@ impl<T> Drop for SetOnce<T> {
         }
     }
 }
+
+// SAFETY: `SetOnce` can be transferred across thread boundaries iff the data it contains can.
+unsafe impl<T: Send> Send for SetOnce<T> {}
+
+// SAFETY: `SetOnce` synchronises access to the inner value via atomic operations,
+// so shared references are safe when `T: Sync`. Since the inner `T` may be dropped
+// on any thread, we also require `T: Send`.
+unsafe impl<T: Send + Sync> Sync for SetOnce<T> {}