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authorAlice Ryhl <aliceryhl@google.com>2023-05-31 16:59:37 +0200
committerMiguel Ojeda <ojeda@kernel.org>2023-05-31 18:53:10 +0200
commitd701e061cb14f589f8c4f48fd7fbe81c0e34b7e7 (patch)
treecd4df82f1656a5d98eeb6a7e48c34cad1fad7de5
parentrust: sync: reword the `Arc` safety comment for `Send` (diff)
downloadlinux-d701e061cb14f589f8c4f48fd7fbe81c0e34b7e7.tar.xz
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rust: sync: reword the `Arc` safety comment for `Sync`
The safety comment on `impl Sync for Arc` references the Send safety comment. This commit avoids that in case the two comments drift apart in the future. Suggested-by: Andreas Hindborg <a.hindborg@samsung.com> Signed-off-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> Reviewed-by: Benno Lossin <benno.lossin@proton.me> Link: https://lore.kernel.org/r/20230531145939.3714886-3-aliceryhl@google.com Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
-rw-r--r--rust/kernel/sync/arc.rs8
1 files changed, 5 insertions, 3 deletions
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index a8c2177950cd..a89843cacaad 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -150,9 +150,11 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<Arc<U>> for Ar
// mutable reference when the reference count reaches zero and `T` is dropped.
unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
-// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync` for the
-// same reason as above. `T` needs to be `Send` as well because a thread can clone an `&Arc<T>`
-// into an `Arc<T>`, which may lead to `T` being accessed by the same reasoning as above.
+// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync`
+// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
+// it needs `T` to be `Send` because any thread that has a `&Arc<T>` may clone it and get an
+// `Arc<T>` on that thread, so the thread may ultimately access `T` using a mutable reference when
+// the reference count reaches zero and `T` is dropped.
unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
impl<T> Arc<T> {