Re: [PATCH v1] rust: workqueue: add cancel_sync support

[Alice Ryhl <aliceryhl@google.com>]

On Sun, May 10, 2026 at 11:21:57AM +0300, Onur Özkan wrote:
> Drivers can use this during teardown to cancel pending work and wait for
> running work to finish before dropping related resources.
> 
> This is not implemented for Pin<KBox<T>> because queuing a boxed work
> item transfers ownership of the box to the workqueue. There is therefore
> no separate safe owner that can cancel the boxed work while it is pending.
> 
> The immediate motivation is the Tyr reset infrastructure [1], which needs
> to cancel pending reset work and wait for any running reset work during
> teardown before dropping the resources used by that work.
> 
> [1]: https://lore.kernel.org/all/20260416171728.205141-1-work@onurozkan.dev
> 
> Signed-off-by: Onur Özkan <work@onurozkan.dev>
> ---
>  rust/kernel/workqueue.rs | 134 ++++++++++++++++++++++++++++++++-------
>  1 file changed, 112 insertions(+), 22 deletions(-)
> 
> diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
> index 7e253b6f299c..a10daa2763ac 100644
> --- a/rust/kernel/workqueue.rs
> +++ b/rust/kernel/workqueue.rs
> @@ -442,23 +442,44 @@ pub unsafe trait RawDelayedWorkItem<const ID: u64>: RawWorkItem<ID> {}
>  ///
>  /// # Safety
>  ///
> -/// Implementers must ensure that [`__enqueue`] uses a `work_struct` initialized with the [`run`]
> -/// method of this trait as the function pointer.
> +/// Implementers must ensure that [`__enqueue`] uses a `work_struct` initialized with [`run`] as
> +/// its function pointer, and that [`from_raw_work`] rebuilds the exact ownership transferred by
> +/// a successful [`__enqueue`] call.
>  ///
>  /// [`__enqueue`]: RawWorkItem::__enqueue
> +/// [`from_raw_work`]: WorkItemPointer::from_raw_work
>  /// [`run`]: WorkItemPointer::run
> -pub unsafe trait WorkItemPointer<const ID: u64>: RawWorkItem<ID> {
> -    /// Run this work item.
> +pub unsafe trait WorkItemPointer<const ID: u64>: RawWorkItem<ID> + Sized {
> +    /// The work item type containing the embedded `work_struct`.
> +    type Item: WorkItem<ID, Pointer = Self> + ?Sized;
> +
> +    /// Rebuild this work item's pointer from its embedded `work_struct`.
>      ///
>      /// # Safety
>      ///
> -    /// The provided `work_struct` pointer must originate from a previous call to [`__enqueue`]
> -    /// where the `queue_work_on` closure returned true, and the pointer must still be valid.
> +    /// The provided `work_struct` pointer must originate from a previous call to
> +    /// [`RawWorkItem::__enqueue`] where the `queue_work_on` closure returned true
> +    /// and the pointer must still be valid.
> +    unsafe fn from_raw_work(ptr: *mut bindings::work_struct) -> Self;
> +
> +    /// Run this work item.
>      ///
> -    /// [`__enqueue`]: RawWorkItem::__enqueue
> -    unsafe extern "C" fn run(ptr: *mut bindings::work_struct);
> +    /// # Safety
> +    ///
> +    /// The provided `work_struct` pointer must satisfy the same requirements as
> +    /// [`WorkItemPointer::from_raw_work`].
> +    #[inline]
> +    unsafe extern "C" fn run(ptr: *mut bindings::work_struct) {
> +        <Self::Item as WorkItem<ID>>::run(
> +            // SAFETY: The requirements for `run` are exactly those of `from_raw_work`.
> +            unsafe { Self::from_raw_work(ptr) },
> +        );
> +    }
>  }
>  
> +/// Marker for work item types that support cancellation.
> +pub trait SupportsCancelling<const ID: u64>: WorkItemPointer<ID> {}

Shouldn't 'from_raw_work()' be a method on SupportsCancelling instead?

Alice