Re: [PATCH 3/3] rust: workqueue: add KUnit and sample stress tests

["Onur Özkan" <work@onurozkan.dev>]

On Thu, 02 Apr 2026 08:53:48 +0530
Aakash Bollineni via B4 Relay
<devnull+aakash.bollineni.multicorewareinc.com@kernel.org> wrote:

> From: Aakash Bollineni <aakash.bollineni@multicorewareinc.com>
> 
> To ensure the safety and correctness of the improved workqueue API,
> this patch adds comprehensive testing infrastructure:
> 1. KUnit Tests: Adds an internal 'rust_kernel_workqueue' test suite
>    to rust/kernel/workqueue.rs. These tests verify basic and
>    synchronous cancellation, refcount stability, and concurrency
>    safety for both standard and delayed work.
> 2. Sample Module: Adds samples/rust/rust_workqueue_test.rs as a
>    standalone module that performs a 1000-iteration stress test
>    designed to verify race-free pointer handover during concurrent
>    enqueue/cancel operations.
> The tests use distinct types for standard and delayed work items to
> ensure clear trait dispatch and prevent field offset conflicts.
> 

This seems like the opposite what you did with the TestItem type? It
contains both the standard and delayed work inside.

> Signed-off-by: Aakash Bollineni
> <aakash.bollineni@multicorewareinc.com> ---
>  samples/rust/Makefile               |   2 +
>  samples/rust/rust_workqueue_test.rs | 214
> ++++++++++++++++++++++++++++++++++++ 2 files changed, 216
> insertions(+)
> 
> diff --git a/samples/rust/Makefile b/samples/rust/Makefile
> index 6c0aaa58cccc..0f304bd90997 100644
> --- a/samples/rust/Makefile
> +++ b/samples/rust/Makefile
> @@ -20,3 +20,5 @@ obj-$(CONFIG_SAMPLE_RUST_SOC)
> 	+= rust_soc.o rust_print-y := rust_print_main.o
> rust_print_events.o 
>  subdir-$(CONFIG_SAMPLE_RUST_HOSTPROGS)		+= hostprogs
> +
> +obj-y += rust_workqueue_test.o
> diff --git a/samples/rust/rust_workqueue_test.rs
> b/samples/rust/rust_workqueue_test.rs new file mode 100644
> index 000000000000..c055ec1964c0
> --- /dev/null
> +++ b/samples/rust/rust_workqueue_test.rs
> @@ -0,0 +1,214 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Robust stress test for Rust workqueue API.
> +
> +use kernel::prelude::*;
> +use kernel::sync::Arc;
> +use kernel::time::msecs_to_jiffies;
> +use kernel::workqueue::{self, new_work, Work, WorkItem};
> +
> +#[pin_data]
> +struct TestItem {
> +    #[pin]
> +    work: Work<TestItem>,
> +    value: i32,
> +    #[pin]
> +    delayed_work: workqueue::DelayedWork<TestItem>,
> +}
> +
> +kernel::impl_has_work! {
> +    impl HasWork<Self> for TestItem { self.work }
> +}
> +
> +// SAFETY: The `delayed_work` field is at a fixed offset and is
> valid for the lifetime of +// `TestItem`.
> +unsafe impl workqueue::HasDelayedWork<Self> for TestItem {}
> +
> +impl WorkItem for TestItem {
> +    type Pointer = Arc<TestItem>;
> +
> +    fn run(this: Arc<TestItem>) {
> +        pr_info!(
> +            "Rust workqueue test: Work item running (value: {})\n",
> +            this.value
> +        );
> +    }
> +}
> +
> +/// Helper to get Arc strong count for verification in tests.
> +/// This uses internal layout knowledge of Arc.
> +fn get_arc_count<T: Sized>(arc: &Arc<T>) -> i32 {
> +    // SAFETY: ArcInner has refcount as its first field. Arc points
> to data at DATA_OFFSET.
> +    unsafe {
> +        let ptr = Arc::as_ptr(arc);
> +        let inner_ptr = (ptr as *const
> u8).sub(Arc::<T>::DATA_OFFSET);
> +        // The first field of ArcInner is Refcount, which is a
> transparent wrapper around
> +        // refcount_t. In the kernel, refcount_t is an atomic_t
> (i32).
> +        let refcount_ptr = inner_ptr as *const i32;
> +        // We use a relaxed load to get the current value.
> +        core::ptr::read_volatile(refcount_ptr)
> +    }
> +}
> +
> +struct RustWorkqueueTest;
> +
> +impl kernel::Module for RustWorkqueueTest {
> +    fn init(_module: &'static ThisModule) -> Result<Self> {
> +        pr_info!("Rust workqueue test: starting robust
> verification\n"); +
> +        // 1. Basic Lifecycle with Refcount Validation
> +        {
> +            let test_item = Arc::pin_init(
> +                pin_init!(TestItem {
> +                    work <- new_work!("TestItem::work"),
> +                    value: 42,
> +                    delayed_work <-
> workqueue::new_delayed_work!("TestItem::delayed_work"),
> +                }),
> +                GFP_KERNEL,
> +            )?;
> +
> +            let initial_count = get_arc_count(&test_item);
> +            pr_info!("Initial Arc strong count: {}\n",
> initial_count); +
> +            // Enqueue
> +            let enqueued_item = test_item.clone();
> +
> +            if let Err(returned_item) =
> workqueue::system().enqueue(enqueued_item) {
> +                pr_warn!("Work already pending, unexpected!\n");
> +                let _ = returned_item;
> +            } else {
> +                pr_info!(
> +                    "Work enqueued successfully. Strong count: {}\n",
> +                    get_arc_count(&test_item)
> +                );
> +            }
> +
> +            // Cancel immediately (best effort)
> +            if let Some(reclaimed) = test_item.work.cancel() {
> +                let count_after_cancel = get_arc_count(&test_item);
> +                pr_info!(
> +                    "Success: Work cancelled and Arc reclaimed.
> Strong count: {}\n",
> +                    count_after_cancel
> +                );
> +
> +                // VALIDATION: Reclamation must restore the refcount
> (minus the clone we just
> +                // reclaimed)
> +                if count_after_cancel != initial_count + 1 {
> +                    pr_err!(
> +                        "ERROR: Refcount mismatch after cancel!
> Expected {}, got {}\n",
> +                        initial_count + 1,
> +                        count_after_cancel
> +                    );
> +                    return Err(ENXIO);
> +                }
> +                drop(reclaimed);
> +                if get_arc_count(&test_item) != initial_count {
> +                    pr_err!(
> +                        "ERROR: Refcount mismatch after drop!
> Expected {}, got {}\n",
> +                        initial_count,
> +                        get_arc_count(&test_item)
> +                    );
> +                    return Err(ENXIO);
> +                }
> +            } else {
> +                pr_info!("Work already running or finished, could
> not reclaim via cancel().\n");
> +            }
> +        }
> +
> +        // 2. Stress Testing: Enqueue/Cancel Sync Loop
> +        {
> +            pr_info!("Starting stress test (1000 iterations)...\n");
> +            let test_item = Arc::pin_init(
> +                pin_init!(TestItem {
> +                    work <- new_work!("TestItem::work"),
> +                    value: 99,
> +                    delayed_work <-
> workqueue::new_delayed_work!("TestItem::delayed_work"),
> +                }),
> +                GFP_KERNEL,
> +            )?;
> +
> +            for i in 0..1000 {
> +                let _ =
> workqueue::system().enqueue(test_item.clone());
> +                // Use cancel_sync to ensure determinism for the
> next iteration
> +                let _ = test_item.work.cancel_sync();
> +
> +                if i % 250 == 0 {
> +                    pr_info!("Stress test progress: {}/1000\n", i);
> +                }
> +            }
> +
> +            if get_arc_count(&test_item) != 1 {
> +                pr_err!(
> +                    "ERROR: Refcount leak detected after stress
> test! count: {}\n",
> +                    get_arc_count(&test_item)
> +                );
> +                return Err(ENXIO);
> +            } else {
> +                pr_info!("Stress test completed successfully. No
> refcount leaks.\n");
> +            }
> +        }
> +
> +        // 3. Delayed Work Cancellation Test
> +        {
> +            let test_item = Arc::pin_init(
> +                pin_init!(TestItem {
> +                    work <- new_work!("TestItem::work"),
> +                    value: 7,
> +                    delayed_work <-
> workqueue::new_delayed_work!("TestItem::delayed_work"),
> +                }),
> +                GFP_KERNEL,
> +            )?;
> +
> +            let initial_count = get_arc_count(&test_item);
> +
> +            // Schedule with a long delay
> +            let to_enqueue = test_item.clone();
> +            let res = workqueue::system()
> +                .enqueue_delayed(to_enqueue, msecs_to_jiffies(5000));
> +            if let Err(returned) = res {
> +                pr_warn!("Delayed work already pending, returned
> item.\n");
> +                drop(returned);
> +            } else {
> +                pr_info!("Delayed work enqueued. count: {}\n",
> get_arc_count(&test_item));
> +            }
> +
> +            if test_item.delayed_work.is_pending() {
> +                pr_info!("Delayed work is pending as expected.\n");
> +            }
> +
> +            if let Some(reclaimed) = test_item.delayed_work.cancel()
> {
> +                pr_info!("Success: Delayed work reclaimed. No
> leak.\n");
> +                drop(reclaimed);
> +            } else {
> +                pr_warn!("Notice: Delayed work not reclaimed
> (running or never enqueued).\n");
> +            }
> +
> +            let final_count = get_arc_count(&test_item);
> +            if final_count != initial_count {
> +                pr_err!(
> +                    "ERROR: Refcount leak after delayed cancel!
> expected {}, got {}\n",
> +                    initial_count,
> +                    final_count
> +                );
> +                return Err(ENXIO);
> +            }
> +        }
> +
> +        pr_info!("Rust workqueue test: all robust checks passed\n");
> +        Ok(RustWorkqueueTest)
> +    }
> +}
> +
> +impl Drop for RustWorkqueueTest {
> +    fn drop(&mut self) {
> +        pr_info!("Rust workqueue test: exit\n");
> +    }
> +}
> +
> +module! {
> +    type: RustWorkqueueTest,
> +    name: "rust_workqueue_test",
> +    authors: ["Aakash Bollineni"],
> +    description: "Robust stress test for Rust workqueue API",
> +    license: "GPL",
> +}
>