linux-kernel - Re: [PATCH 1/3] rust: completion: implement initial abstraction

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Message-ID: <aEq0tA7yuBPxTSXq@pollux>
Date: Thu, 12 Jun 2025 13:06:28 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <lossin@...nel.org>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, ojeda@...nel.org,
	alex.gaynor@...il.com, boqun.feng@...il.com, gary@...yguo.net,
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me,
	a.hindborg@...nel.org, aliceryhl@...gle.com, tmgross@...ch.edu,
	chrisi.schrefl@...il.com, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>
Subject: Re: [PATCH 1/3] rust: completion: implement initial abstraction

On Thu, Jun 12, 2025 at 12:53:45PM +0200, Benno Lossin wrote:
> On Thu Jun 12, 2025 at 12:35 PM CEST, Danilo Krummrich wrote:
> > On Thu, Jun 12, 2025 at 10:15:55AM +0200, Benno Lossin wrote:
> >> On Tue Jun 3, 2025 at 10:48 PM CEST, Danilo Krummrich wrote:
> >> > +    /// Signal all tasks waiting on this completion.
> >> > +    ///
> >> > +    /// This method wakes up all tasks waiting on this completion; after this operation the
> >> > +    /// completion is permanently done.
> >> > +    pub fn complete_all(&self) {
> >> > +        // SAFETY: `self.as_raw()` is a pointer to a valid `struct completion`.
> >> > +        unsafe { bindings::complete_all(self.as_raw()) };
> >> > +    }
> >> > +
> >> > +    /// Wait for completion of a task.
> >> > +    ///
> >> > +    /// This method waits for the completion of a task; it is not interruptible and there is no
> >> > +    /// timeout.
> >> 
> >> Another thing that we should document is weather this function returns
> >> immediately when `complete_all` was already called in the past.
> >
> > The details are all documented in [1], which is also linked in the module
> > documentation of this file.
> >
> > [1] https://docs.kernel.org/scheduler/completion.html
> 
> I dislike that we don't have the docs right there on the function.
> Following that link, there is also a lot of other stuff there that don't
> apply to Rust (eg initializing completions, and the
> wait_for_completion*() variants).
> 
> After a bit of reading, I found the part that I was looking for (by
> searching for `complete_all`...):
> 
>     A thread that wants to signal that the conditions for continuation have
>     been achieved calls `complete()` to signal exactly one of the waiters
>     that it can continue:
>     
>     ```c
>     void complete(struct completion *done)
>     ```
>     
>     ... or calls `complete_all()` to signal all current and future waiters:
>     
>     ```c
>     void complete_all(struct completion *done)
>     ```
> 
> Let's just put this information on the `complete_all` function.

It's already there, no?

"after this operation the completion is permanently done"