From 1cda61fbda205920517f7b63af90c97c38ff9af6 Mon Sep 17 00:00:00 2001
From: Emil Fresk <emil.fresk@gmail.com>
Date: Sat, 18 Feb 2023 09:43:06 +0100
Subject: Make some linked list operations unsafe, and document their safety at
 usage

---
 rtic-common/src/lib.rs        |  4 ++++
 rtic-common/src/wait_queue.rs | 38 ++++++++++++++++++++------------------
 2 files changed, 24 insertions(+), 18 deletions(-)

(limited to 'rtic-common/src')

diff --git a/rtic-common/src/lib.rs b/rtic-common/src/lib.rs
index b8b5e0d9..03d03063 100644
--- a/rtic-common/src/lib.rs
+++ b/rtic-common/src/lib.rs
@@ -4,6 +4,10 @@
 #![deny(missing_docs)]
 //deny_warnings_placeholder_for_ci
 
+#[cfg(test)]
+#[macro_use]
+extern crate std;
+
 pub mod dropper;
 pub mod wait_queue;
 pub mod waker_registration;
diff --git a/rtic-common/src/wait_queue.rs b/rtic-common/src/wait_queue.rs
index 4ced6ab9..7387a984 100644
--- a/rtic-common/src/wait_queue.rs
+++ b/rtic-common/src/wait_queue.rs
@@ -68,7 +68,9 @@ impl<T: Clone> LinkedList<T> {
     }
 
     /// Put an element at the back of the queue.
-    pub fn push(&self, link: Pin<&mut Link<T>>) {
+    ///
+    /// SAFETY: The link must live until it is removed from the queue.
+    pub unsafe fn push(&self, link: Pin<&Link<T>>) {
         cs::with(|_| {
             // Make sure all previous writes are visible
             core::sync::atomic::fence(Ordering::SeqCst);
@@ -76,17 +78,17 @@ impl<T: Clone> LinkedList<T> {
             let tail = self.tail.load(Self::R);
 
             // SAFETY: This datastructure does not move the underlying value.
-            let link = unsafe { link.get_unchecked_mut() };
+            let link = link.get_ref();
 
             if let Some(tail_ref) = unsafe { tail.as_ref() } {
                 // Queue is not empty
                 link.prev.store(tail, Self::R);
-                self.tail.store(link, Self::R);
-                tail_ref.next.store(link, Self::R);
+                self.tail.store(link as *const _ as *mut _, Self::R);
+                tail_ref.next.store(link as *const _ as *mut _, Self::R);
             } else {
                 // Queue is empty
-                self.tail.store(link, Self::R);
-                self.head.store(link, Self::R);
+                self.tail.store(link as *const _ as *mut _, Self::R);
+                self.head.store(link as *const _ as *mut _, Self::R);
             }
         });
     }
@@ -126,7 +128,7 @@ impl<T: Clone> Link<T> {
     }
 
     /// Remove this link from a linked list.
-    pub fn remove_from_list(&mut self, list: &LinkedList<T>) {
+    pub fn remove_from_list(&self, list: &LinkedList<T>) {
         cs::with(|_| {
             // Make sure all previous writes are visible
             core::sync::atomic::fence(Ordering::SeqCst);
@@ -230,17 +232,17 @@ mod tests {
     fn linked_list() {
         let wq = LinkedList::<u32>::new();
 
-        let mut i1 = Link::new(10);
-        let mut i2 = Link::new(11);
-        let mut i3 = Link::new(12);
-        let mut i4 = Link::new(13);
-        let mut i5 = Link::new(14);
-
-        wq.push(unsafe { Pin::new_unchecked(&mut i1) });
-        wq.push(unsafe { Pin::new_unchecked(&mut i2) });
-        wq.push(unsafe { Pin::new_unchecked(&mut i3) });
-        wq.push(unsafe { Pin::new_unchecked(&mut i4) });
-        wq.push(unsafe { Pin::new_unchecked(&mut i5) });
+        let i1 = Link::new(10);
+        let i2 = Link::new(11);
+        let i3 = Link::new(12);
+        let i4 = Link::new(13);
+        let i5 = Link::new(14);
+
+        unsafe { wq.push(Pin::new_unchecked(&i1)) };
+        unsafe { wq.push(Pin::new_unchecked(&i2)) };
+        unsafe { wq.push(Pin::new_unchecked(&i3)) };
+        unsafe { wq.push(Pin::new_unchecked(&i4)) };
+        unsafe { wq.push(Pin::new_unchecked(&i5)) };
 
         wq.print();
 
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