linux-kernel - [PATCH v2 07/14] rust: hrtimer: add `UnsafeTimerPointer`

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Message-ID: <20240917222739.1298275-8-a.hindborg@kernel.org>
Date: Wed, 18 Sep 2024 00:27:31 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc: Andreas Hindborg <a.hindborg@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Alice Ryhl <aliceryhl@...gle.com>,
	rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 07/14] rust: hrtimer: add `UnsafeTimerPointer`

Add a trait to allow unsafely queuing stack allocated timers.

Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
---
 rust/kernel/hrtimer.rs | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/rust/kernel/hrtimer.rs b/rust/kernel/hrtimer.rs
index d6c3fa89f77e..bb6349f440e2 100644
--- a/rust/kernel/hrtimer.rs
+++ b/rust/kernel/hrtimer.rs
@@ -191,6 +191,39 @@ pub trait TimerPointer: Sync + Sized {
     fn schedule(self, expires: Ktime) -> Self::TimerHandle;
 }
 
+/// Unsafe version of [`TimerPointer`] for situations where leaking the
+/// `TimerHandle` returned by `schedule` would be unsound. This is the case for
+/// stack allocated timers.
+///
+/// Typical implementers are pinned references such as [`Pin<&T>].
+///
+/// # Safety
+///
+/// Implementers of this trait must ensure that instances of types implementing
+/// [`UnsafeTimerPointer`] outlives any associated [`TimerPointer::TimerHandle`]
+/// instances.
+///
+/// [`Pin<&T>`]: Box
+pub unsafe trait UnsafeTimerPointer: Sync + Sized {
+    /// A handle representing a scheduled timer.
+    ///
+    /// # Safety
+    ///
+    /// If the timer is armed, or if the timer callback is running when the
+    /// handle is dropped, the drop method of `TimerHandle` must not return
+    /// until the timer is unarmed and the callback has completed.
+    type TimerHandle: TimerHandle;
+
+    /// Schedule the timer after `expires` time units. If the timer was already
+    /// scheduled, it is rescheduled at the new expiry time.
+    ///
+    /// # Safety
+    ///
+    /// Caller promises keep the timer structure alive until the timer is dead.
+    /// Caller can ensure this by not leaking the returned `Self::TimerHandle`.
+    unsafe fn schedule(self, expires: Ktime) -> Self::TimerHandle;
+}
+
 /// Implemented by [`TimerPointer`] implementers to give the C timer callback a
 /// function to call.
 // This is split from `TimerPointer` to make it easier to specify trait bounds.
-- 
2.46.0