From be7724cdbbca22e0cbde1edf30941a7aa4378ded Mon Sep 17 00:00:00 2001 From: Alice Ryhl Date: Wed, 31 May 2023 14:59:38 +0000 Subject: [PATCH] rust: specify when `ARef` is thread safe An `ARef` behaves just like the `Arc` when it comes to thread safety, so we can reuse the thread safety comments from `Arc` here. This is necessary because without this change, the Rust compiler will assume that things are not thread safe even though they are. Signed-off-by: Alice Ryhl Reviewed-by: Andreas Hindborg Reviewed-by: Boqun Feng Reviewed-by: Martin Rodriguez Reboredo Reviewed-by: Benno Lossin Link: https://lore.kernel.org/r/20230531145939.3714886-4-aliceryhl@google.com Signed-off-by: Miguel Ojeda --- rust/kernel/types.rs | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index 29db59d..1e5380b 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -321,6 +321,19 @@ pub struct ARef { _p: PhantomData, } +// SAFETY: It is safe to send `ARef` 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 an `ARef` may ultimately access `T` using a +// mutable reference, for example, when the reference count reaches zero and `T` is dropped. +unsafe impl Send for ARef {} + +// SAFETY: It is safe to send `&ARef` 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 `&ARef` may clone it and get an +// `ARef` on that thread, so the thread may ultimately access `T` using a mutable reference, for +// example, when the reference count reaches zero and `T` is dropped. +unsafe impl Sync for ARef {} + impl ARef { /// Creates a new instance of [`ARef`]. /// -- 2.7.4