linux-kernel - Re: [PATCH v2 2/2] rust: workqueue: add creation of workqueues

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Message-ID: <aRb6GPDZo3kaoeKm@google.com>
Date: Fri, 14 Nov 2025 09:44:56 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Tejun Heo <tj@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Lai Jiangshan <jiangshanlai@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, 
	Daniel Almeida <daniel.almeida@...labora.com>, John Hubbard <jhubbard@...dia.com>, 
	Philipp Stanner <phasta@...nel.org>, Tamir Duberstein <tamird@...il.com>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Benno Lossin <lossin@...nel.org>
Subject: Re: [PATCH v2 2/2] rust: workqueue: add creation of workqueues

On Thu, Nov 13, 2025 at 11:52:17AM -0800, Boqun Feng wrote:
> On Thu, Nov 13, 2025 at 10:01:07AM +0000, Alice Ryhl wrote:
> > Creating workqueues is needed by various GPU drivers. Not only does it
> > give you better control over execution, it also allows devices to ensure
> > that all tasks have exited before the device is unbound (or similar) by
> > running the workqueue destructor.
> > 
> > A wrapper type Flags is provided for workqueue flags. It allows you to
> > build any valid flag combination, while using a type-level marker for
> > whether WQ_BH is used to prevent invalid flag combinations. The Flags wrapper
> > also forces you to explicitly pick one of percpu, unbound, or bh.
> > 
> > Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> [...]
> > +/// An owned kernel work queue.
> > +///
> > +/// Dropping a workqueue blocks on all pending work.
> > +///
> > +/// # Invariants
> > +///
> > +/// `queue` points at a valid workqueue that is owned by this `OwnedQueue`.
> > +pub struct OwnedQueue {
> > +    queue: NonNull<Queue>,
> 
> I hope Owned/Ownable can make it just a Owned<Queue> here ;-) And
> that'll make Owned<Queue> automatically Send + Sync. I think it's not a
> rare ask for `OwnedQueue` to be Send + Sync.

Oh yeah it should be Send/Sync.

And hopefully we get Owned eventually.

> > +}
> > +
> > +#[expect(clippy::manual_c_str_literals)]
> > +impl OwnedQueue {
> > +    /// Allocates a new workqueue.
> > +    ///
> > +    /// The provided name is used verbatim as the workqueue name.
> > +    ///
> > +    /// # Examples
> > +    ///
> > +    /// ```
> > +    /// use kernel::c_str;
> > +    /// use kernel::workqueue::{OwnedQueue, Flags};
> > +    ///
> > +    /// let wq = OwnedQueue::new(c_str!("my-wq"), Flags::unbound().sysfs(), 0)?;
> > +    /// wq.try_spawn(
> > +    ///     GFP_KERNEL,
> > +    ///     || pr_warn!("Printing from my-wq"),
> > +    /// )?;
> > +    /// # Ok::<(), Error>(())
> > +    /// ```
> > +    #[inline]
> > +    pub fn new<const BH: bool>(
> > +        name: &CStr,
> > +        flags: Flags<BH>,
> > +        max_active: usize,
> 
> Do we need to support `max_active` as `usize` when the underlying C
> code only support i32?

Negative values don't really make sense. But maybe it's a good idea,
yeah.

Alice