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Message-ID: <20260203152818.317806-3-marco.crivellari@suse.com>
Date: Tue, 3 Feb 2026 16:28:17 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
rust-for-linux@...r.kernel.org
Cc: Tejun Heo <tj@...nel.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
Frederic Weisbecker <frederic@...nel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Marco Crivellari <marco.crivellari@...e.com>,
Michal Hocko <mhocko@...e.com>,
Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH v4 2/2] rust: add system_percpu() and per-cpu enqueue functions
The C code defines 2 new workqueues: system_percpu_wq and system_dfl_wq,
respectively the futures replacement for system_wq and system_unbound_wq.
This change introduce system_percpu(), that use the new system_percpu_wq.
In order to enqueue on a specific CPU, two new functions have been added
to the Queue implementation:
enqueue_cpu() - that receive a u32 CPU id as 2nd argument
enqueue_delayed_cpu() - that receive a u32 CPU id as 3rd argument
system_wq (and so workqueue::system()) will be removed in a future
release cycle and should not be used.
Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
rust/kernel/sync/completion.rs | 2 +-
rust/kernel/workqueue.rs | 96 +++++++++++++++++++++++++++++++---
2 files changed, 91 insertions(+), 7 deletions(-)
diff --git a/rust/kernel/sync/completion.rs b/rust/kernel/sync/completion.rs
index c50012a940a3..ee6aa8f18507 100644
--- a/rust/kernel/sync/completion.rs
+++ b/rust/kernel/sync/completion.rs
@@ -38,7 +38,7 @@
/// done <- Completion::new(),
/// }), GFP_KERNEL)?;
///
-/// let _ = workqueue::system().enqueue(this.clone());
+/// let _ = workqueue::system_percpu().enqueue(this.clone());
///
/// Ok(this)
/// }
diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index 300cc2bfe012..81a68d5062b7 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -67,7 +67,7 @@
//! /// This method will enqueue the struct for execution on the system workqueue, where its value
//! /// will be printed.
//! fn print_later(val: Arc<MyStruct>) {
-//! let _ = workqueue::system().enqueue(val);
+//! let _ = workqueue::system_percpu().enqueue(val);
//! }
//! # print_later(MyStruct::new(42).unwrap());
//! ```
@@ -121,11 +121,11 @@
//! }
//!
//! fn print_1_later(val: Arc<MyStruct>) {
-//! let _ = workqueue::system().enqueue::<Arc<MyStruct>, 1>(val);
+//! let _ = workqueue::system_percpu().enqueue::<Arc<MyStruct>, 1>(val);
//! }
//!
//! fn print_2_later(val: Arc<MyStruct>) {
-//! let _ = workqueue::system().enqueue::<Arc<MyStruct>, 2>(val);
+//! let _ = workqueue::system_percpu().enqueue::<Arc<MyStruct>, 2>(val);
//! }
//! # print_1_later(MyStruct::new(24, 25).unwrap());
//! # print_2_later(MyStruct::new(41, 42).unwrap());
@@ -171,13 +171,13 @@
//! /// This method will enqueue the struct for execution on the system workqueue, where its value
//! /// will be printed 12 jiffies later.
//! fn print_later(val: Arc<MyStruct>) {
-//! let _ = workqueue::system().enqueue_delayed(val, 12);
+//! let _ = workqueue::system_percpu().enqueue_delayed(val, 12);
//! }
//!
//! /// It is also possible to use the ordinary `enqueue` method together with `DelayedWork`. This
//! /// is equivalent to calling `enqueue_delayed` with a delay of zero.
//! fn print_now(val: Arc<MyStruct>) {
-//! let _ = workqueue::system().enqueue(val);
+//! let _ = workqueue::system_percpu().enqueue(val);
//! }
//! # print_later(MyStruct::new(42).unwrap());
//! # print_now(MyStruct::new(42).unwrap());
@@ -292,6 +292,39 @@ pub fn enqueue<W, const ID: u64>(&self, w: W) -> W::EnqueueOutput
}
}
+ /// Enqueues a work item on a specific CPU.
+ ///
+ /// This may fail if the work item is already enqueued in a workqueue.
+ ///
+ /// The work item will be submitted on cpu_id.
+ pub fn enqueue_cpu<W, const ID: u64>(&self, w: W, cpu_id: u32) -> W::EnqueueOutput
+ where
+ W: RawWorkItem<ID> + Send + 'static,
+ {
+ let queue_ptr = self.0.get();
+
+ // SAFETY: We only return `false` if the `work_struct` is already in a workqueue. The other
+ // `__enqueue` requirements are not relevant since `W` is `Send` and static.
+ //
+ // The call to `bindings::queue_work_on` will dereference the provided raw pointer, which
+ // is ok because `__enqueue` guarantees that the pointer is valid for the duration of this
+ // closure.
+ //
+ // Furthermore, if the C workqueue code accesses the pointer after this call to
+ // `__enqueue`, then the work item was successfully enqueued, and `bindings::queue_work_on`
+ // will have returned true. In this case, `__enqueue` promises that the raw pointer will
+ // stay valid until we call the function pointer in the `work_struct`, so the access is ok.
+ unsafe {
+ w.__enqueue(move |work_ptr| {
+ bindings::queue_work_on(
+ cpu_id as ffi::c_int,
+ queue_ptr,
+ work_ptr,
+ )
+ })
+ }
+ }
+
/// Enqueues a delayed work item.
///
/// This may fail if the work item is already enqueued in a workqueue.
@@ -328,6 +361,42 @@ pub fn enqueue_delayed<W, const ID: u64>(&self, w: W, delay: Jiffies) -> W::Enqu
}
}
+ /// Enqueues a delayed work item on a specific CPU.
+ ///
+ /// This may fail if the work item is already enqueued in a workqueue.
+ ///
+ /// The work item will be submitted on cpu_id.
+ pub fn enqueue_delayed_cpu<W, const ID: u64>(&self, w: W, delay: Jiffies, cpu_id: u32) -> W::EnqueueOutput
+ where
+ W: RawDelayedWorkItem<ID> + Send + 'static,
+ {
+ let queue_ptr = self.0.get();
+
+ // SAFETY: We only return `false` if the `work_struct` is already in a workqueue. The other
+ // `__enqueue` requirements are not relevant since `W` is `Send` and static.
+ //
+ // The call to `bindings::queue_delayed_work_on` will dereference the provided raw pointer,
+ // which is ok because `__enqueue` guarantees that the pointer is valid for the duration of
+ // this closure, and the safety requirements of `RawDelayedWorkItem` expands this
+ // requirement to apply to the entire `delayed_work`.
+ //
+ // Furthermore, if the C workqueue code accesses the pointer after this call to
+ // `__enqueue`, then the work item was successfully enqueued, and
+ // `bindings::queue_delayed_work_on` will have returned true. In this case, `__enqueue`
+ // promises that the raw pointer will stay valid until we call the function pointer in the
+ // `work_struct`, so the access is ok.
+ unsafe {
+ w.__enqueue(move |work_ptr| {
+ bindings::queue_delayed_work_on(
+ cpu_id as ffi::c_int,
+ queue_ptr,
+ container_of!(work_ptr, bindings::delayed_work, work),
+ delay,
+ )
+ })
+ }
+ }
+
/// Tries to spawn the given function or closure as a work item.
///
/// This method can fail because it allocates memory to store the work item.
@@ -934,17 +1003,32 @@ unsafe impl<T, const ID: u64> RawDelayedWorkItem<ID> for Pin<KBox<T>>
{
}
-/// Returns the system work queue (`system_wq`).
+/// Returns the per-cpu system work queue (`system_wq`).
///
/// It is the one used by `schedule[_delayed]_work[_on]()`. Multi-CPU multi-threaded. There are
/// users which expect relatively short queue flush time.
///
/// Callers shouldn't queue work items which can run for too long.
+///
+/// Note: `system_wq` will be removed in a future release cycle. Use [`system_percpu_wq`] instead.
pub fn system() -> &'static Queue {
// SAFETY: `system_wq` is a C global, always available.
unsafe { Queue::from_raw(bindings::system_wq) }
}
+/// Returns the per-cpu system work queue (`system_percpu_wq`).
+///
+/// It is the one used by `schedule[_delayed]_work[_on]()`. Multi-CPU multi-threaded. There are
+/// users which expect relatively short queue flush time.
+///
+/// Callers shouldn't queue work items which can run for too long.
+///
+/// Note: `system_percpu_wq` will replace `system_wq` in a future release cycle.
+pub fn system_percpu() -> &'static Queue {
+ // SAFETY: `system_percpu_wq` is a C global, always available.
+ unsafe { Queue::from_raw(bindings::system_percpu_wq) }
+}
+
/// Returns the system high-priority work queue (`system_highpri_wq`).
///
/// It is similar to the one returned by [`system`] but for work items which require higher
--
2.52.0
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