From d09a61024f6b78c6a08892fc916cdafd87b50365 Mon Sep 17 00:00:00 2001
From: Alice Ryhl <aliceryhl@google.com>
Date: Wed, 31 May 2023 14:59:39 +0000
Subject: [PATCH] rust: task: add `Send` marker to `Task`
When a type also implements `Sync`, the meaning of `Send` is just "this
type may be accessed mutably from threads other than the one it is
created on". That's ok for this type.
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20230531145939.3714886-5-aliceryhl@google.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
rust/kernel/task.rs | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
index 526d29a0ae278..7eda15e5f1b37 100644
--- a/rust/kernel/task.rs
+++ b/rust/kernel/task.rs
@@ -64,8 +64,14 @@ macro_rules! current {
#[repr(transparent)]
pub struct Task(pub(crate) Opaque<bindings::task_struct>);
-// SAFETY: It's OK to access `Task` through references from other threads because we're either
-// accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
+// SAFETY: By design, the only way to access a `Task` is via the `current` function or via an
+// `ARef<Task>` obtained through the `AlwaysRefCounted` impl. This means that the only situation in
+// which a `Task` can be accessed mutably is when the refcount drops to zero and the destructor
+// runs. It is safe for that to happen on any thread, so it is ok for this type to be `Send`.
+unsafe impl Send for Task {}
+
+// SAFETY: It's OK to access `Task` through shared references from other threads because we're
+// either accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
// synchronised by C code (e.g., `signal_pending`).
unsafe impl Sync for Task {}
--
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