[PATCH v6 09/14] rust: hrtimer: implement `UnsafeHrTimerPointer` for `Pin<&mut T>`

[Andreas Hindborg <a.hindborg@kernel.org>]

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

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/time/hrtimer.rs         |  1 +
 rust/kernel/time/hrtimer/pin_mut.rs | 97 +++++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+)

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index d776e93584a87dfdc646816a16bacf19e444217d..9220a8f559271c7eda8d457dbd52cf9e4800ec14 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -395,3 +395,4 @@ unsafe fn raw_get_timer(ptr: *const Self) ->
 
 mod arc;
 mod pin;
+mod pin_mut;
diff --git a/rust/kernel/time/hrtimer/pin_mut.rs b/rust/kernel/time/hrtimer/pin_mut.rs
new file mode 100644
index 0000000000000000000000000000000000000000..adcbba2b5ca9759fbdcc235ba75e006e35724d10
--- /dev/null
+++ b/rust/kernel/time/hrtimer/pin_mut.rs
@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use super::HasHrTimer;
+use super::HrTimer;
+use super::HrTimerCallback;
+use super::HrTimerHandle;
+use super::RawHrTimerCallback;
+use super::UnsafeHrTimerPointer;
+use crate::time::Ktime;
+use core::pin::Pin;
+
+/// A handle for a `Pin<&mut HasHrTimer>`. When the handle exists, the timer might
+/// be running.
+pub struct PinMutHrTimerHandle<'a, U>
+where
+    U: HasHrTimer<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> HrTimerHandle for PinMutHrTimerHandle<'a, U>
+where
+    U: HasHrTimer<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 HasHrTimer<U>>::raw_get_timer(self_ptr) };
+
+        // SAFETY: As `timer_ptr` is derived from a reference, it must point to
+        // a valid and initialized `HrTimer`.
+        unsafe { HrTimer::<U>::raw_cancel(timer_ptr) }
+    }
+}
+
+impl<'a, U> Drop for PinMutHrTimerHandle<'a, U>
+where
+    U: HasHrTimer<U>,
+{
+    fn drop(&mut self) {
+        self.cancel();
+    }
+}
+
+// SAFETY: We capture the lifetime of `Self` when we create a
+// `PinMutHrTimerHandle`, so `Self` will outlive the handle.
+unsafe impl<'a, U> UnsafeHrTimerPointer for Pin<&'a mut U>
+where
+    U: Send + Sync,
+    U: HasHrTimer<U>,
+    U: HrTimerCallback<CallbackTarget<'a> = Self>,
+{
+    type TimerHandle = PinMutHrTimerHandle<'a, U>;
+
+    unsafe fn start(self, expires: Ktime) -> Self::TimerHandle {
+        // Cast to pointer
+        let self_ptr: *const U = <Self as core::ops::Deref>::deref(&self);
+
+        // SAFETY: As we derive `self_ptr` from a reference above, it must point
+        // to a valid `U`.
+        unsafe { U::start(self_ptr, expires) };
+
+        PinMutHrTimerHandle { inner: self }
+    }
+}
+
+impl<'a, U> RawHrTimerCallback for Pin<&'a mut U>
+where
+    U: HasHrTimer<U>,
+    U: HrTimerCallback<CallbackTarget<'a> = Self>,
+    U: HrTimerCallback<CallbackTargetParameter<'a> = Self>,
+{
+    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
+        // `HrTimer` is `repr(C)`
+        let timer_ptr = ptr as *mut HrTimer<U>;
+
+        // SAFETY: By the safety requirement of this function, `timer_ptr`
+        // points to a `HrTimer<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 `HrTimer<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()
+    }
+}

-- 
2.47.0