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rust: add safety comment in workqueue traits

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Add missing safety comments for the implementation of the unsafe traits
WorkItemPointer and RawWorkItem for Arc<T> in workqueue.rs

Link: https://github.com/Rust-for-Linux/linux/issues/351.
Co-developed-by: Vangelis Mamalakis <mamalakis@google.com>
Signed-off-by: Vangelis Mamalakis <mamalakis@google.com>
Suggested-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Konstantin Andrikopoulos <kernel@mandragore.io>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Konstantin Andrikopoulos 2024-11-27 15:07:38 +00:00 committed by Tejun Heo
parent 40384c840e
commit b03917e02b
1 changed files with 16 additions and 2 deletions
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18
rust/kernel/workqueue.rs
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@ -519,7 +519,15 @@ unsafe fn raw_get_work(ptr: *mut Self) -> *mut $crate::workqueue::Work<$work_typ
impl{T} HasWork<Self> for ClosureWork<T> { self.work }
}
// SAFETY: TODO.
// SAFETY: The `__enqueue` implementation in RawWorkItem uses a `work_struct` initialized with the
// `run` method of this trait as the function pointer because:
// - `__enqueue` gets the `work_struct` from the `Work` field, using `T::raw_get_work`.
// - The only safe way to create a `Work` object is through `Work::new`.
// - `Work::new` makes sure that `T::Pointer::run` is passed to `init_work_with_key`.
// - Finally `Work` and `RawWorkItem` guarantee that the correct `Work` field
// will be used because of the ID const generic bound. This makes sure that `T::raw_get_work`
// uses the correct offset for the `Work` field, and `Work::new` picks the correct
// implementation of `WorkItemPointer` for `Arc<T>`.
unsafe impl<T, const ID: u64> WorkItemPointer<ID> for Arc<T>
where
T: WorkItem<ID, Pointer = Self>,
@ -537,7 +545,13 @@ unsafe impl<T, const ID: u64> WorkItemPointer<ID> for Arc<T>
}
}
// SAFETY: TODO.
// SAFETY: The `work_struct` raw pointer is guaranteed to be valid for the duration of the call to
// the closure because we get it from an `Arc`, which means that the ref count will be at least 1,
// and we don't drop the `Arc` ourselves. If `queue_work_on` returns true, it is further guaranteed
// to be valid until a call to the function pointer in `work_struct` because we leak the memory it
// points to, and only reclaim it if the closure returns false, or in `WorkItemPointer::run`, which
// is what the function pointer in the `work_struct` must be pointing to, according to the safety
// requirements of `WorkItemPointer`.
unsafe impl<T, const ID: u64> RawWorkItem<ID> for Arc<T>
where
T: WorkItem<ID, Pointer = Self>,