From: FUJITA Tomonori <fujita.tomonori@gmail.com>
Date: Tue, 16 Dec 2025 00:09:01 +0000 (+0900)
Subject: rust: sync: set_once: Implement Send and Sync
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8a581130b1cbc17c702298b8325e3df98c792760;p=thirdparty%2Fkernel%2Flinux.git

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@gmail.com>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://patch.msgid.link/20251216000901.221375-1-fujita.tomonori@gmail.com
---

diff --git a/rust/kernel/sync/set_once.rs b/rust/kernel/sync/set_once.rs
index bdba601807d8b..139cef05e935f 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> {}