linux-kernel - [PATCH v6 06/14] rust: hrtimer: add `UnsafeHrTimerPointer`

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Message-Id: <20250110-hrtimer-v3-v6-12-rc2-v6-6-f71d50f16482@kernel.org>
Date: Fri, 10 Jan 2025 21:15:29 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Miguel Ojeda <ojeda@...nel.org>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>, 
 Frederic Weisbecker <frederic@...nel.org>, 
 Thomas Gleixner <tglx@...utronix.de>, Danilo Krummrich <dakr@...nel.org>
Cc: Alex Gaynor <alex.gaynor@...il.com>, 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>, 
 Trevor Gross <tmgross@...ch.edu>, Lyude Paul <lyude@...hat.com>, 
 Guangbo Cui <2407018371@...com>, Dirk Behme <dirk.behme@...il.com>, 
 Daniel Almeida <daniel.almeida@...labora.com>, 
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Andreas Hindborg <a.hindborg@...nel.org>
Subject: [PATCH v6 06/14] rust: hrtimer: add `UnsafeHrTimerPointer`

Add a trait to allow unsafely queuing stack allocated timers.

Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
---
 rust/kernel/time/hrtimer.rs | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index 50e8c23578b5cf7196893ac88d9547fc027f1f04..aab998b02f19b774d5b04ae2c89b669f13c4b0c7 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -142,6 +142,37 @@ pub trait HrTimerPointer: Sync + Sized {
     fn start(self, expires: Ktime) -> Self::TimerHandle;
 }
 
+/// Unsafe version of [`HrTimerPointer`] for situations where leaking the
+/// [`HrTimerHandle`] returned by `start` 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
+/// [`UnsafeHrTimerPointer`] outlives any associated [`HrTimerPointer::TimerHandle`]
+/// instances.
+pub unsafe trait UnsafeHrTimerPointer: Sync + Sized {
+    /// A handle representing a running timer.
+    ///
+    /// # Safety
+    ///
+    /// If the timer is running, or if the timer callback is executing when the
+    /// handle is dropped, the drop method of [`Self::TimerHandle`] must not return
+    /// until the timer is stopped and the callback has completed.
+    type TimerHandle: HrTimerHandle;
+
+    /// Start the timer after `expires` time units. If the timer was already
+    /// running, it is restarted 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 start(self, expires: Ktime) -> Self::TimerHandle;
+}
+
 /// Implemented by [`HrTimerPointer`] implementers to give the C timer callback a
 /// function to call.
 // This is split from `HrTimerPointer` to make it easier to specify trait bounds.

-- 
2.47.0