Message-Id: <20241017-hrtimer-v3-v6-12-rc2-v3-8-59a75cbb44da@kernel.org>
Date: Thu, 17 Oct 2024 15:04:35 +0200
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>
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>, 
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Andreas Hindborg <a.hindborg@...nel.org>
Subject: [PATCH v3 08/13] rust: hrtimer: implement `UnsafeTimerPointer` for
 `Pin<&mut T>`

Allow pinned mutable references to structs that contain a `Timer` node to
be scheduled with the `hrtimer` subsystem.

Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
---
 rust/kernel/hrtimer.rs         |  1 +
 rust/kernel/hrtimer/pin_mut.rs | 99 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 100 insertions(+)

diff --git a/rust/kernel/hrtimer.rs b/rust/kernel/hrtimer.rs
index ceedf330a803ec2db7ff6c25713ae48e2fd1f4ca..940390aa2a6c6a222534b545d8d2fbd639a19f64 100644
--- a/rust/kernel/hrtimer.rs
+++ b/rust/kernel/hrtimer.rs
@@ -363,3 +363,4 @@ unsafe fn raw_get_timer(ptr: *const Self) ->
 
 mod arc;
 mod pin;
+mod pin_mut;
diff --git a/rust/kernel/hrtimer/pin_mut.rs b/rust/kernel/hrtimer/pin_mut.rs
new file mode 100644
index 0000000000000000000000000000000000000000..d6c85647a762066776cf292620a8b19c12721876
--- /dev/null
+++ b/rust/kernel/hrtimer/pin_mut.rs
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use super::HasTimer;
+use super::RawTimerCallback;
+use super::Timer;
+use super::TimerCallback;
+use super::TimerHandle;
+use super::UnsafeTimerPointer;
+use crate::time::Ktime;
+use core::pin::Pin;
+
+/// A handle for a `Pin<&mut HasTimer>`. When the handle exists, the timer might
+/// be running.
+pub struct PinMutTimerHandle<'a, U>
+where
+    U: HasTimer<U>,
+{
+    pub(crate) inner: Pin<&'a mut U>,
+}
+
+// SAFETY: We cancel the timer when the handle is dropped. The implementation of
+// the `cancel` method will block if the timer handler is running.
+unsafe impl<'a, U> TimerHandle for PinMutTimerHandle<'a, U>
+where
+    U: HasTimer<U>,
+{
+    fn cancel(&mut self) -> bool {
+        // SAFETY: We are not moving out of `self` or handing out mutable
+        // references to `self`.
+        let self_ptr = unsafe { self.inner.as_mut().get_unchecked_mut() as *mut U };
+
+        // SAFETY: As we got `self_ptr` from a reference above, it must point to
+        // a valid `U`.
+        let timer_ptr = unsafe { <U as HasTimer<U>>::raw_get_timer(self_ptr) };
+
+        // SAFETY: As `timer_ptr` is derived from a reference, it must point to
+        // a valid and initialized `Timer`.
+        unsafe { Timer::<U>::raw_cancel(timer_ptr) }
+    }
+}
+
+impl<'a, U> Drop for PinMutTimerHandle<'a, U>
+where
+    U: HasTimer<U>,
+{
+    fn drop(&mut self) {
+        self.cancel();
+    }
+}
+
+// SAFETY: We capture the lifetime of `Self` when we create a
+// `PinMutTimerHandle`, so `Self` will outlive the handle.
+unsafe impl<'a, U> UnsafeTimerPointer for Pin<&'a mut U>
+where
+    U: Send + Sync,
+    U: HasTimer<U>,
+    U: TimerCallback<CallbackTarget<'a> = Self>,
+{
+    type TimerHandle = PinMutTimerHandle<'a, U>;
+
+    unsafe fn start(self, expires: Ktime) -> Self::TimerHandle {
+        use core::ops::Deref;
+
+        // Cast to pointer
+        let self_ptr = self.deref() as *const U;
+
+        // SAFETY: As we derive `self_ptr` from a reference above, it must point
+        // to a valid `U`.
+        unsafe { U::start(self_ptr, expires) };
+
+        PinMutTimerHandle { inner: self }
+    }
+}
+
+impl<'a, U> RawTimerCallback for Pin<&'a mut U>
+where
+    U: HasTimer<U>,
+    U: TimerCallback<CallbackTarget<'a> = Self>,
+    U: TimerCallback<CallbackTargetParameter<'a> = Self>,
+{
+    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
+        // `Timer` is `repr(C)`
+        let timer_ptr = ptr as *mut Timer<U>;
+
+        // SAFETY: By the safety requirement of this function, `timer_ptr`
+        // points to a `Timer<U>` contained in an `U`.
+        let receiver_ptr = unsafe { U::timer_container_of(timer_ptr) };
+
+        // SAFETY: By the safety requirement of this function, `timer_ptr`
+        // points to a `Timer<U>` contained in an `U`.
+        let receiver_ref = unsafe { &mut *receiver_ptr };
+
+        // SAFETY: `receiver_ref` only exists as pinned, so it is safe to pin it
+        // here.
+        let receiver_pin = unsafe { Pin::new_unchecked(receiver_ref) };
+
+        U::run(receiver_pin).into()
+    }
+}

-- 
2.46.0

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