Re: [PATCH v2 5/6] rust: workqueue: add ScopedQueue for lifetime bound items

[Daniel Almeida]

> On 7 Aug 2026, at 13:52, Danilo Krummrich <dakr@xxxxxxxxxx> wrote:
> 
> From: Onur Özkan <work@xxxxxxxxxxxxx>
> 
> Add a workqueue wrapper for work items that are not 'static.
> 
> Tyr reset work is queued from a handle that owns a Controller<'bound>
> where the work item holds references tied to the lifetime of the bound
> device and its mapped IO state. The existing API only accepts 'static
> work items which cannot express that relationship.
> 
> Introduce ScopedQueue for this case. It owns the underlying workqueue
> and ties enqueued work to the queue lifetime so borrowed state cannot
> outlive the queue that may still run it.
> 
> Construction is unsafe because the queue must not be leaked.
> 
> `compile_fail` doc-tests are ignored for now as KUnit doesn't support
> that. Enabling those tests as regular code block would raise this error:
> 
>    ERROR:root:error[E0597]: `data` does not live long enough
> --> rust/doctests_kernel_generated.rs:22029:44
>  |
>    22027 |         let data = ();
>  |             ---- binding `data` declared here
>    22028 |         // SAFETY: Queue is not leaked.
>    22029 |         queue = unsafe { new_queue(&data)? };
>  |                                            ^^^^^ borrowed value does not live long enough
>    22030 |     }
>  |     - `data` dropped here while still borrowed
>    ...
>    22034 | }
>  | - borrow might be used here, when `queue` is dropped and runs the `Drop` code for type `ScopedQueue`
>  |
>  = note: values in a scope are dropped in the opposite order they are defined
> 
> which is exactly the constraint ScopedQueue is meant to enforce.
> 
> Suggested-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> Signed-off-by: Onur Özkan <work@xxxxxxxxxxxxx>
> [ Move from scoped_queue.rs to scoped.rs, which can be shared with
>  ScopedWork; add missing inline annotations. - Danilo ]
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> ---
> rust/kernel/workqueue/mod.rs    |   3 +
> rust/kernel/workqueue/scoped.rs | 190 ++++++++++++++++++++++++++++++++
> 2 files changed, 193 insertions(+)
> create mode 100644 rust/kernel/workqueue/scoped.rs
> 
> diff --git a/rust/kernel/workqueue/mod.rs b/rust/kernel/workqueue/mod.rs
> index 8eb2d037be83..551fa1401b85 100644
> --- a/rust/kernel/workqueue/mod.rs
> +++ b/rust/kernel/workqueue/mod.rs
> @@ -212,6 +212,9 @@
> mod builder;
> pub use self::builder::Builder;
> 
> +mod scoped;
> +pub use self::scoped::ScopedQueue;
> +
> /// Creates a [`Work`] initialiser with the given name and a newly-created lock class.
> #[macro_export]
> macro_rules! new_work {
> diff --git a/rust/kernel/workqueue/scoped.rs b/rust/kernel/workqueue/scoped.rs
> new file mode 100644
> index 000000000000..18a4b6f6cf18
> --- /dev/null
> +++ b/rust/kernel/workqueue/scoped.rs
> @@ -0,0 +1,190 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Lifetime-scoped workqueues.
> +//!
> +//! Provides [`ScopedQueue`] for work items that may borrow data with some
> +//! non-`'static` lifetime.
> +//!
> +//! Unlike [`Queue`] which only accepts `'static` work items, [`ScopedQueue`]
> +//! owns its underlying queue and relies on that queue being dropped to drain
> +//! pending and running work before borrowed data can go out of scope.
> +//!
> +//! TODO: Remove `ignore` once KUnit supports `compile_fail` on doc-tests.
> +//! ```compile_fail,ignore
> +//! use kernel::prelude::*;
> +//! use kernel::workqueue::ScopedQueue;
> +//!
> +//! /// # Safety
> +//! ///
> +//! /// Returned queue must not be leaked.
> +//! unsafe fn new_queue<'bound>(_: &'bound ()) -> Result<ScopedQueue<'bound>> {

nit: is it me, or “bound” sounds out of place here? Perhaps ’scope instead?

Same comment throughout the whole example.

> +//!     // SAFETY: Caller guarantees that the returned queue is not leaked.
> +//!     unsafe { ScopedQueue::new(c"scoped_queue") }
> +//! }
> +//!
> +//! fn queue_outlives_borrowed_data() -> Result {
> +//!     let queue;
> +//!
> +//!     {
> +//!         let data = ();
> +//!         // SAFETY: Queue is not leaked.
> +//!         queue = unsafe { new_queue(&data)? };
> +//!     }
> +//!     // Here the `compile_fail` is fulfilled as `queue` would be dropped
> +//!     // after `data`.
> +//!     Ok(())
> +//! }
> +//! ```
> +//!
> +//! TODO: Remove `ignore` once KUnit supports `compile_fail` on doc-tests.
> +//! ```compile_fail,ignore
> +//! use kernel::prelude::*;
> +//! use kernel::sync::Arc;
> +//! use kernel::workqueue::{
> +//!     impl_has_work,
> +//!     new_work,
> +//!     ScopedQueue,
> +//!     Work,
> +//!     WorkItem,
> +//! };
> +//!
> +//! #[pin_data]
> +//! struct BorrowedWork<'bound> {
> +//!     data: &'bound (),
> +//!     #[pin]
> +//!     work: Work<BorrowedWork<'bound>>,
> +//! }
> +//!
> +//! impl_has_work! {
> +//!     impl{'bound} HasWork<BorrowedWork<'bound>> for BorrowedWork<'bound> { self.work }
> +//! }
> +//!
> +//! impl<'bound> WorkItem for BorrowedWork<'bound> {
> +//!     type Pointer = Arc<Self>;
> +//!
> +//!     fn run(_this: Arc<Self>) {}
> +//! }
> +//!
> +//! impl<'bound> BorrowedWork<'bound> {
> +//!     fn new(data: &'bound ()) -> Result<Arc<Self>> {
> +//!         Arc::pin_init(
> +//!             pin_init!(Self {
> +//!                 data,
> +//!                 work <- new_work!("BorrowedWork::work"),
> +//!             }),
> +//!             GFP_KERNEL,
> +//!         )
> +//!     }
> +//! }
> +//!
> +//! struct Handle<'bound> {
> +//!     work: Arc<BorrowedWork<'bound>>,
> +//!     wq: ScopedQueue<'bound>,
> +//! }
> +//!
> +//! impl<'bound> Handle<'bound> {
> +//!     /// # Safety
> +//!     ///
> +//!     /// Returned handle must not be leaked.
> +//!     unsafe fn new(data: &'bound ()) -> Result<Self> {
> +//!         Ok(Self {
> +//!             work: BorrowedWork::new(data)?,
> +//!             // SAFETY: Caller guarantees that the returned handle is not leaked.
> +//!             wq: unsafe { ScopedQueue::new(c"handle_wq")? },
> +//!         })
> +//!     }
> +//! }
> +//!
> +//! fn handle_outlives_borrowed_data() -> Result {
> +//!     let handle;
> +//!
> +//!     {
> +//!         let data = ();
> +//!         // SAFETY: Handle is not leaked.
> +//!         handle = unsafe { Handle::new(&data)? };
> +//!
> +//!         let _ = handle.wq.enqueue(handle.work.clone());
> +//!     }
> +//!     // Here the `compile_fail` is fulfilled as `handle` would be dropped
> +//!     // after `data`.
> +//!     Ok(())
> +//! }
> +//! ```
> +
> +use super::{
> +    OwnedQueue,
> +    Queue,
> +    RawWorkItem, //
> +};
> +
> +use crate::{
> +    bindings,
> +    ffi,
> +    prelude::*, //
> +};
> +
> +use core::marker::PhantomData;
> +
> +/// An owned workqueue that can enqueue work items borrowing from `'scope`.
> +///
> +/// A `ScopedQueue` must not outlive data borrowed by its work items.
> +pub struct ScopedQueue<'scope> {
> +    inner: OwnedQueue,
> +    _scope: PhantomData<&'scope mut &'scope ()>,
> +}
> +
> +impl<'scope> ScopedQueue<'scope> {
> +    /// Creates an ordered scoped workqueue.
> +    ///
> +    /// # Safety
> +    ///
> +    /// The caller must not leak the returned queue or otherwise prevent its
> +    /// [`Drop`] implementation from running since dropping the queue drains
> +    /// pending and running work that may borrow from `'scope`.
> +    #[inline]
> +    pub unsafe fn new(name: &'static CStr) -> Result<Self> {

Does this really need to be ’static?

> +        Ok(Self {
> +            inner: Queue::new_ordered().build(name)?,
> +            _scope: PhantomData,
> +        })
> +    }
> +
> +    /// Enqueues a work item on this scoped queue.
> +    #[inline]
> +    pub fn enqueue<W, const ID: u64>(&self, work: W) -> W::EnqueueOutput
> +    where
> +        W: RawWorkItem<ID> + Send + 'scope,
> +    {
> +        let queue_ptr = self.inner.0.get();
> +
> +        // SAFETY:
> +        // - Closure returns `false` only if `queue_work_on` returns `false`
> +        //   and that means `work_ptr` is already in a workqueue.
> +        //
> +        // - `W: 'scope` and dropck keep borrowed data alive until this queue is
> +        //   dropped. The constructor requires that the queue is not leaked and
> +        //   dropping `inner` drains pending and running work so the function
> +        //   pointer is not called after any lifetime in `W` expires.
> +        //
> +        // - The last requirement of `__enqueue` is not relevant here because `W`
> +        //   is `Send`.
> +        unsafe {
> +            work.__enqueue(move |work_ptr| {
> +                bindings::queue_work_on(
> +                    bindings::wq_misc_consts_WORK_CPU_UNBOUND as ffi::c_int,
> +                    queue_ptr,
> +                    work_ptr,
> +                )
> +            })
> +        }
> +    }
> +}
> +
> +impl Drop for ScopedQueue<'_> {
> +    #[inline]
> +    fn drop(&mut self) {
> +        // This impl makes dropck require `'scope` to outlive `OwnedQueue`.
> +        // See: https://doc.rust-lang.org/nomicon/phantom-data.html#generic-parameters-and-drop-checking
> +        let _ = &self._scope;
> +    }
> +}
> -- 
> 2.55.0
> 

Would a conversion from OwnedQueue to ScopedQueue
make sense in the future?

Reviewed-by: Daniel Almeida <daniel.almeida@xxxxxxxxxxxxx>