linux-kernel - [PATCH v7 07/14] rust: hrtimer: add `hrtimer::ScopedHrTimerPointer`

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Message-Id: <20250203-hrtimer-v3-v6-12-rc2-v7-7-189144725399@kernel.org>
Date: Mon, 03 Feb 2025 16:07:53 +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>, 
 Tamir Duberstein <tamird@...il.com>, rust-for-linux@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Andreas Hindborg <a.hindborg@...nel.org>
Subject: [PATCH v7 07/14] rust: hrtimer: add
 `hrtimer::ScopedHrTimerPointer`

Add the trait `ScopedHrTimerPointer` to allow safe use of stack allocated
timers. Safety is achieved by pinning the stack in place while timers are
running.

Implement the trait for all types that implement `UnsafeHrTimerPointer`.

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

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index f5b360c9472b2a4a90c608be1a470222204ffcf5..4d39c3526a897cba3b76589f21d0866beaae0c4f 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -188,6 +188,39 @@ pub unsafe trait UnsafeHrTimerPointer: Sync + Sized {
     unsafe fn start(self, expires: Ktime) -> Self::TimerHandle;
 }
 
+/// A trait for stack allocated timers.
+///
+/// # Safety
+///
+/// Implementers must ensure that `start_scoped` does not return until the
+/// timer is dead and the timer handler is not running.
+pub unsafe trait ScopedHrTimerPointer {
+    /// Start the timer to run after `expires` time units and immediately
+    /// after call `f`. When `f` returns, the timer is cancelled.
+    fn start_scoped<T, F>(self, expires: Ktime, f: F) -> T
+    where
+        F: FnOnce() -> T;
+}
+
+// SAFETY: By the safety requirement of [`UnsafeHrTimerPointer`], dropping the
+// handle returned by [`UnsafeHrTimerPointer::start`] ensures that the timer is
+// killed.
+unsafe impl<T> ScopedHrTimerPointer for T
+where
+    T: UnsafeHrTimerPointer,
+{
+    fn start_scoped<U, F>(self, expires: Ktime, f: F) -> U
+    where
+        F: FnOnce() -> U,
+    {
+        // SAFETY: We drop the timer handle below before returning.
+        let handle = unsafe { UnsafeHrTimerPointer::start(self, expires) };
+        let t = f();
+        drop(handle);
+        t
+    }
+}
+
 /// 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