[PATCH 2/7] rust: workqueue: restrict delayed work to global wqs

[Danilo Krummrich <dakr@kernel.org>]

From: Alice Ryhl <aliceryhl@google.com>

When a workqueue is shut down, delayed work that is pending but not
scheduled does not get properly cleaned up, so it's not safe to use
`enqueue_delayed` on a workqueue that might be destroyed. To fix this,
restricted `enqueue_delayed` to static queues.

This may be fixed in the future by an approach along the lines of [1].

Cc: stable@vger.kernel.org
Fixes: 7c098cd5eaae ("workqueue: rust: add delayed work items")
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://lore.kernel.org/r/20250423-destroy-workqueue-flush-v1-1-3d74820780a5@google.com [1]
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/workqueue.rs | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index 3194b9c441aa..b6e02ba427b3 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -302,8 +302,15 @@ pub fn enqueue<W, const ID: u64>(&self, w: W) -> W::EnqueueOutput
     ///
     /// This may fail if the work item is already enqueued in a workqueue.
     ///
+    /// This is only valid for global workqueues (with static lifetimes) because those are the only
+    /// ones that outlive all possible delayed work items.
+    ///
     /// The work item will be submitted using `WORK_CPU_UNBOUND`.
-    pub fn enqueue_delayed<W, const ID: u64>(&self, w: W, delay: Jiffies) -> W::EnqueueOutput
+    pub fn enqueue_delayed<W, const ID: u64>(
+        &'static self,
+        w: W,
+        delay: Jiffies,
+    ) -> W::EnqueueOutput
     where
         W: RawDelayedWorkItem<ID> + Send + 'static,
     {
-- 
2.55.0