Re: [PATCH 2/2] rust: kcsan: add KUnit test for data race detection

[Marco Elver <elver@google.com>]

On Tue, Oct 13, 2026 at 11:38AM +0200, Alexander Potapenko wrote:
> > +        // SAFETY: `probe_console` has the signature expected by the `console` tracepoint. Being
> > +        // part of the kernel image, it and `OBSERVED` outlive the registration, so there is no
> > +        // need to synchronize with in-flight probes after unregistering.
> > +        to_result(unsafe {
> > +            bindings::tracepoint_probe_register(
> > +                &raw mut bindings::__tracepoint_console,
> > +                probe_console as *mut c_void,
> > +                ptr::null_mut(),
> > +            )
> > +        })?;
> > +        let _unregister = ScopeGuard::new(|| {
> > +            // SAFETY: The probe was registered above.
> > +            unsafe {
> > +                bindings::tracepoint_probe_unregister(
> > +                    &raw mut bindings::__tracepoint_console,
> > +                    probe_console as *mut c_void,
> > +                    ptr::null_mut(),
> > +                );
> > +            }
> > +        });
> > +
> > +        let worker = ctx.clone();
> > +        workqueue::system_unbound().try_spawn(GFP_KERNEL, move || {
> 
> I ran this locally and got the following warning:
> 
> [  623.232012] workqueue: work func
> _RNvXsb_NtCskctMpSfuwL9_6kernel9workqueueINtNtCs1G77UTwpz6o_4core3pin3PinINtNtNtB7_5alloc4kbox3BoxINtB5_11ClosureWorkNCNvNtNtB7_10kcsan_test5tests9data_races_0ENtNtB1d_9allocator7KmallocEEINtB5_15WorkItemPointerKy0_E3runB7_
> enqueued on deprecated workqueue. Use system_{percpu|dfl}_wq instead.
> 
> Do we need to use a different workqueue?

Looks like it, and we need this patch to use system_dfl_wq:


From: Marco Elver <elver@google.com>
Date: Tue, 13 Oct 2026 10:05:52 +0000
Subject: [PATCH] rust: workqueue: add system_dfl()

The C kernel deprecated system_unbound_wq in favor of system_dfl_wq
(commit 64d8eae3f895 ("workqueue: Add warnings and fallback if
system_{unbound}_wq is used")).

Add `system_dfl()` to provide a safe wrapper around `system_dfl_wq`.

Signed-off-by: Marco Elver <elver@google.com>
---
 rust/kernel/workqueue.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index 7e253b6f299c..e46d3acf903d 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -1063,6 +1063,16 @@ pub fn system_unbound() -> &'static Queue {
     unsafe { Queue::from_raw(bindings::system_unbound_wq) }
 }
 
+/// Returns the system default work queue (`system_dfl_wq`).
+///
+/// Workers are not bound to any specific CPU, not concurrency managed, and all queued work items
+/// are executed immediately as long as `max_active` limit is not reached and resources are
+/// available.
+pub fn system_dfl() -> &'static Queue {
+    // SAFETY: `system_dfl_wq` is a C global, always available.
+    unsafe { Queue::from_raw(bindings::system_dfl_wq) }
+}
+
 /// Returns the system freezable work queue (`system_freezable_wq`).
 ///
 /// It is equivalent to the one returned by [`system`] except that it's freezable.
-- 
2.56.0.385.gd3acb90ef8-goog