From: Wedson Almeida Filho <wedsonaf@gmail.com>

Add mutable Iterator implementation for `RBTree`,
allowing iteration over (key, value) pairs in key order. Only values are
mutable, as mutating keys implies modifying a node's position in the tree.

Mutable iteration is used by the binder driver during shutdown to
clean up the tree maintained by the "range allocator" [1].

Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-6-08ba9197f637@google.com/ [1]
Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Matt Gilbride <mattgilbride@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Alice Ryhl <aliceryhl@google.com>
---
 rust/kernel/rbtree.rs | 98 ++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 86 insertions(+), 12 deletions(-)

diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
index d10074e4ac58..d7514ebadfa8 100644
--- a/rust/kernel/rbtree.rs
+++ b/rust/kernel/rbtree.rs
@@ -197,8 +197,26 @@ pub fn iter(&self) -> Iter<'_, K, V> {
         // INVARIANT: `bindings::rb_first` returns a valid pointer to a tree node given a valid pointer to a tree root.
         Iter {
             _tree: PhantomData,
-            // SAFETY: `self.root` is a valid pointer to the tree root.
-            next: unsafe { bindings::rb_first(&self.root) },
+            iter_raw: IterRaw {
+                // SAFETY: by the invariants, all pointers are valid.
+                next: unsafe { bindings::rb_first(&self.root) },
+                _phantom: PhantomData,
+            },
+        }
+    }
+
+    /// Returns a mutable iterator over the tree nodes, sorted by key.
+    pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
+        IterMut {
+            _tree: PhantomData,
+            // INVARIANT:
+            //   - `self.root` is a valid pointer to a tree root.
+            //   - `bindings::rb_first` produces a valid pointer to a node given `root` is valid.
+            iter_raw: IterRaw {
+                // SAFETY: by the invariants, all pointers are valid.
+                next: unsafe { bindings::rb_first(&self.root) },
+                _phantom: PhantomData,
+            },
         }
     }
 
@@ -211,6 +229,11 @@ pub fn keys(&self) -> impl Iterator<Item = &'_ K> {
     pub fn values(&self) -> impl Iterator<Item = &'_ V> {
         self.iter().map(|(_, v)| v)
     }
+
+    /// Returns a mutable iterator over the values of the nodes in the tree, sorted by key.
+    pub fn values_mut(&mut self) -> impl Iterator<Item = &'_ mut V> {
+        self.iter_mut().map(|(_, v)| v)
+    }
 }
 
 impl<K, V> RBTree<K, V>
@@ -414,13 +437,9 @@ fn into_iter(self) -> Self::IntoIter {
 /// An iterator over the nodes of a [`RBTree`].
 ///
 /// Instances are created by calling [`RBTree::iter`].
-///
-/// # Invariants
-/// - `self.next` is a valid pointer.
-/// - `self.next` points to a node stored inside of a valid `RBTree`.
 pub struct Iter<'a, K, V> {
     _tree: PhantomData<&'a RBTree<K, V>>,
-    next: *mut bindings::rb_node,
+    iter_raw: IterRaw<K, V>,
 }
 
 // SAFETY: The [`Iter`] gives out immutable references to K and V, so it has the same
@@ -434,21 +453,76 @@ unsafe impl<'a, K: Sync, V: Sync> Sync for Iter<'a, K, V> {}
 impl<'a, K, V> Iterator for Iter<'a, K, V> {
     type Item = (&'a K, &'a V);
 
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter_raw.next().map(|(k, v)|
+            // SAFETY: Due to `self._tree`, `k` and `v` are valid for the lifetime of `'a`.
+            unsafe { (&*k, &*v) })
+    }
+}
+
+impl<'a, K, V> IntoIterator for &'a mut RBTree<K, V> {
+    type Item = (&'a K, &'a mut V);
+    type IntoIter = IterMut<'a, K, V>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter_mut()
+    }
+}
+
+/// A mutable iterator over the nodes of a [`RBTree`].
+///
+/// Instances are created by calling [`RBTree::iter_mut`].
+pub struct IterMut<'a, K, V> {
+    _tree: PhantomData<&'a mut RBTree<K, V>>,
+    iter_raw: IterRaw<K, V>,
+}
+
+// SAFETY: The [`IterMut`] gives out immutable references to K and mutable references to V, so it has the same
+// thread safety requirements as mutable references.
+unsafe impl<'a, K: Send, V: Send> Send for IterMut<'a, K, V> {}
+
+// SAFETY: The [`IterMut`] gives out immutable references to K and mutable references to V, so it has the same
+// thread safety requirements as mutable references.
+unsafe impl<'a, K: Sync, V: Sync> Sync for IterMut<'a, K, V> {}
+
+impl<'a, K, V> Iterator for IterMut<'a, K, V> {
+    type Item = (&'a K, &'a mut V);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter_raw.next().map(|(k, v)|
+            // SAFETY: Due to `&mut self`, we have exclusive access to `k` and `v`, for the lifetime of `'a`.
+            unsafe { (&*k, &mut *v) })
+    }
+}
+
+/// A raw iterator over the nodes of a [`RBTree`].
+///
+/// # Invariants
+/// - `self.next` is a valid pointer.
+/// - `self.next` points to a node stored inside of a valid `RBTree`.
+struct IterRaw<K, V> {
+    next: *mut bindings::rb_node,
+    _phantom: PhantomData<fn() -> (K, V)>,
+}
+
+impl<K, V> Iterator for IterRaw<K, V> {
+    type Item = (*mut K, *mut V);
+
     fn next(&mut self) -> Option<Self::Item> {
         if self.next.is_null() {
             return None;
         }
 
-        // SAFETY: By the type invariant of `Iter`, `self.next` is a valid node in an `RBTree`,
+        // SAFETY: By the type invariant of `IterRaw`, `self.next` is a valid node in an `RBTree`,
         // and by the type invariant of `RBTree`, all nodes point to the links field of `Node<K, V>` objects.
-        let cur = unsafe { container_of!(self.next, Node<K, V>, links) };
+        let cur: *mut Node<K, V> =
+            unsafe { container_of!(self.next, Node<K, V>, links) }.cast_mut();
 
         // SAFETY: `self.next` is a valid tree node by the type invariants.
         self.next = unsafe { bindings::rb_next(self.next) };
 
-        // SAFETY: By the same reasoning above, it is safe to dereference the node. Additionally,
-        // it is ok to return a reference to members because the iterator must outlive it.
-        Some(unsafe { (&(*cur).key, &(*cur).value) })
+        // SAFETY: By the same reasoning above, it is safe to dereference the node.
+        Some(unsafe { (addr_of_mut!((*cur).key), addr_of_mut!((*cur).value)) })
     }
 }
 

-- 
2.46.0.rc1.232.g9752f9e123-goog

On 27.07.24 22:30, Matt Gilbride wrote:
> From: Wedson Almeida Filho <wedsonaf@gmail.com>
> 
> Add mutable Iterator implementation for `RBTree`,
> allowing iteration over (key, value) pairs in key order. Only values are
> mutable, as mutating keys implies modifying a node's position in the tree.
> 
> Mutable iteration is used by the binder driver during shutdown to
> clean up the tree maintained by the "range allocator" [1].
> 
> Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-6-08ba9197f637@google.com/ [1]
> Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
> Signed-off-by: Matt Gilbride <mattgilbride@google.com>
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> Tested-by: Alice Ryhl <aliceryhl@google.com>
> ---
>  rust/kernel/rbtree.rs | 98 ++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 86 insertions(+), 12 deletions(-)
> 
> diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
> index d10074e4ac58..d7514ebadfa8 100644
> --- a/rust/kernel/rbtree.rs
> +++ b/rust/kernel/rbtree.rs
> @@ -197,8 +197,26 @@ pub fn iter(&self) -> Iter<'_, K, V> {
>          // INVARIANT: `bindings::rb_first` returns a valid pointer to a tree node given a valid pointer to a tree root.

This INVARIANT is out of place, `Iter` doesn't have any INVARIANT any
more.

>          Iter {
>              _tree: PhantomData,
> -            // SAFETY: `self.root` is a valid pointer to the tree root.
> -            next: unsafe { bindings::rb_first(&self.root) },
> +            iter_raw: IterRaw {

This `IterRaw` construction is missing an INVARIANT comment. I think you
can copy paste from below.

> +                // SAFETY: by the invariants, all pointers are valid.
> +                next: unsafe { bindings::rb_first(&self.root) },
> +                _phantom: PhantomData,
> +            },
> +        }
> +    }
> +
> +    /// Returns a mutable iterator over the tree nodes, sorted by key.
> +    pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
> +        IterMut {
> +            _tree: PhantomData,
> +            // INVARIANT:
> +            //   - `self.root` is a valid pointer to a tree root.
> +            //   - `bindings::rb_first` produces a valid pointer to a node given `root` is valid.
> +            iter_raw: IterRaw {
> +                // SAFETY: by the invariants, all pointers are valid.
> +                next: unsafe { bindings::rb_first(&self.root) },

Does this really derive a mutable reference? Ie shouldn't this be:?

    next: unsafe { bindings::rb_first(&mut self.root) },

> +                _phantom: PhantomData,
> +            },
>          }
>      }
> 
> @@ -211,6 +229,11 @@ pub fn keys(&self) -> impl Iterator<Item = &'_ K> {
>      pub fn values(&self) -> impl Iterator<Item = &'_ V> {
>          self.iter().map(|(_, v)| v)
>      }
> +
> +    /// Returns a mutable iterator over the values of the nodes in the tree, sorted by key.
> +    pub fn values_mut(&mut self) -> impl Iterator<Item = &'_ mut V> {
> +        self.iter_mut().map(|(_, v)| v)
> +    }
>  }
> 
>  impl<K, V> RBTree<K, V>
> @@ -414,13 +437,9 @@ fn into_iter(self) -> Self::IntoIter {
>  /// An iterator over the nodes of a [`RBTree`].
>  ///
>  /// Instances are created by calling [`RBTree::iter`].
> -///
> -/// # Invariants
> -/// - `self.next` is a valid pointer.
> -/// - `self.next` points to a node stored inside of a valid `RBTree`.
>  pub struct Iter<'a, K, V> {
>      _tree: PhantomData<&'a RBTree<K, V>>,
> -    next: *mut bindings::rb_node,
> +    iter_raw: IterRaw<K, V>,
>  }
> 
>  // SAFETY: The [`Iter`] gives out immutable references to K and V, so it has the same
> @@ -434,21 +453,76 @@ unsafe impl<'a, K: Sync, V: Sync> Sync for Iter<'a, K, V> {}
>  impl<'a, K, V> Iterator for Iter<'a, K, V> {
>      type Item = (&'a K, &'a V);
> 
> +    fn next(&mut self) -> Option<Self::Item> {
> +        self.iter_raw.next().map(|(k, v)|
> +            // SAFETY: Due to `self._tree`, `k` and `v` are valid for the lifetime of `'a`.
> +            unsafe { (&*k, &*v) })

I don't really like the formatting here, can you move the SAFETY one
line upwards? It should format nicely then.

> +    }
> +}
> +
> +impl<'a, K, V> IntoIterator for &'a mut RBTree<K, V> {
> +    type Item = (&'a K, &'a mut V);
> +    type IntoIter = IterMut<'a, K, V>;
> +
> +    fn into_iter(self) -> Self::IntoIter {
> +        self.iter_mut()
> +    }
> +}
> +
> +/// A mutable iterator over the nodes of a [`RBTree`].
> +///
> +/// Instances are created by calling [`RBTree::iter_mut`].
> +pub struct IterMut<'a, K, V> {
> +    _tree: PhantomData<&'a mut RBTree<K, V>>,
> +    iter_raw: IterRaw<K, V>,
> +}
> +
> +// SAFETY: The [`IterMut`] gives out immutable references to K and mutable references to V, so it has the same
> +// thread safety requirements as mutable references.
> +unsafe impl<'a, K: Send, V: Send> Send for IterMut<'a, K, V> {}

Since we only borrow `K` immutably, would it make sense to have `K:
Sync`?

---
Cheers,
Benno

> +
> +// SAFETY: The [`IterMut`] gives out immutable references to K and mutable references to V, so it has the same
> +// thread safety requirements as mutable references.
> +unsafe impl<'a, K: Sync, V: Sync> Sync for IterMut<'a, K, V> {}
> +
> +impl<'a, K, V> Iterator for IterMut<'a, K, V> {
> +    type Item = (&'a K, &'a mut V);
> +
> +    fn next(&mut self) -> Option<Self::Item> {
> +        self.iter_raw.next().map(|(k, v)|
> +            // SAFETY: Due to `&mut self`, we have exclusive access to `k` and `v`, for the lifetime of `'a`.
> +            unsafe { (&*k, &mut *v) })
> +    }
> +}
> +
> +/// A raw iterator over the nodes of a [`RBTree`].
> +///
> +/// # Invariants
> +/// - `self.next` is a valid pointer.
> +/// - `self.next` points to a node stored inside of a valid `RBTree`.
> +struct IterRaw<K, V> {
> +    next: *mut bindings::rb_node,
> +    _phantom: PhantomData<fn() -> (K, V)>,
> +}
> +
> +impl<K, V> Iterator for IterRaw<K, V> {
> +    type Item = (*mut K, *mut V);
> +
>      fn next(&mut self) -> Option<Self::Item> {
>          if self.next.is_null() {
>              return None;
>          }
> 
> -        // SAFETY: By the type invariant of `Iter`, `self.next` is a valid node in an `RBTree`,
> +        // SAFETY: By the type invariant of `IterRaw`, `self.next` is a valid node in an `RBTree`,
>          // and by the type invariant of `RBTree`, all nodes point to the links field of `Node<K, V>` objects.
> -        let cur = unsafe { container_of!(self.next, Node<K, V>, links) };
> +        let cur: *mut Node<K, V> =
> +            unsafe { container_of!(self.next, Node<K, V>, links) }.cast_mut();
> 
>          // SAFETY: `self.next` is a valid tree node by the type invariants.
>          self.next = unsafe { bindings::rb_next(self.next) };
> 
> -        // SAFETY: By the same reasoning above, it is safe to dereference the node. Additionally,
> -        // it is ok to return a reference to members because the iterator must outlive it.
> -        Some(unsafe { (&(*cur).key, &(*cur).value) })
> +        // SAFETY: By the same reasoning above, it is safe to dereference the node.
> +        Some(unsafe { (addr_of_mut!((*cur).key), addr_of_mut!((*cur).value)) })
>      }
>  }
> 
> 
> --
> 2.46.0.rc1.232.g9752f9e123-goog
> 

On Mon, Aug 5, 2024 at 9:22 PM Benno Lossin <benno.lossin@proton.me> wrote:
>
> On 27.07.24 22:30, Matt Gilbride wrote:
> > From: Wedson Almeida Filho <wedsonaf@gmail.com>
> >
> > Add mutable Iterator implementation for `RBTree`,
> > allowing iteration over (key, value) pairs in key order. Only values are
> > mutable, as mutating keys implies modifying a node's position in the tree.
> >
> > Mutable iteration is used by the binder driver during shutdown to
> > clean up the tree maintained by the "range allocator" [1].
> >
> > Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-6-08ba9197f637@google.com/ [1]
> > Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
> > Signed-off-by: Matt Gilbride <mattgilbride@google.com>
> > Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> > Tested-by: Alice Ryhl <aliceryhl@google.com>
> > ---
> >  rust/kernel/rbtree.rs | 98 ++++++++++++++++++++++++++++++++++++++++++++-------
> >  1 file changed, 86 insertions(+), 12 deletions(-)
> >
> > diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
> > index d10074e4ac58..d7514ebadfa8 100644
> > --- a/rust/kernel/rbtree.rs
> > +++ b/rust/kernel/rbtree.rs
> > @@ -197,8 +197,26 @@ pub fn iter(&self) -> Iter<'_, K, V> {
> >          // INVARIANT: `bindings::rb_first` returns a valid pointer to a tree node given a valid pointer to a tree root.
>
> This INVARIANT is out of place, `Iter` doesn't have any INVARIANT any
> more.

We can delete it.

> >          Iter {
> >              _tree: PhantomData,
> > -            // SAFETY: `self.root` is a valid pointer to the tree root.
> > -            next: unsafe { bindings::rb_first(&self.root) },
> > +            iter_raw: IterRaw {
>
> This `IterRaw` construction is missing an INVARIANT comment. I think you
> can copy paste from below.

We can copy from below.

> > +                // SAFETY: by the invariants, all pointers are valid.
> > +                next: unsafe { bindings::rb_first(&self.root) },
> > +                _phantom: PhantomData,
> > +            },
> > +        }
> > +    }
> > +
> > +    /// Returns a mutable iterator over the tree nodes, sorted by key.
> > +    pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
> > +        IterMut {
> > +            _tree: PhantomData,
> > +            // INVARIANT:
> > +            //   - `self.root` is a valid pointer to a tree root.
> > +            //   - `bindings::rb_first` produces a valid pointer to a node given `root` is valid.
> > +            iter_raw: IterRaw {
> > +                // SAFETY: by the invariants, all pointers are valid.
> > +                next: unsafe { bindings::rb_first(&self.root) },
>
> Does this really derive a mutable reference? Ie shouldn't this be:?
>
>     next: unsafe { bindings::rb_first(&mut self.root) },

Let's change this to:

next: unsafe { bindings::rb_first(ptr::from_mut(&mut self.root)) }

This way, the pointer will be derived from a mutable reference even if
it becomes a `*const` through intermediate operations.


> > +                _phantom: PhantomData,
> > +            },
> >          }
> >      }
> >
> > @@ -211,6 +229,11 @@ pub fn keys(&self) -> impl Iterator<Item = &'_ K> {
> >      pub fn values(&self) -> impl Iterator<Item = &'_ V> {
> >          self.iter().map(|(_, v)| v)
> >      }
> > +
> > +    /// Returns a mutable iterator over the values of the nodes in the tree, sorted by key.
> > +    pub fn values_mut(&mut self) -> impl Iterator<Item = &'_ mut V> {
> > +        self.iter_mut().map(|(_, v)| v)
> > +    }
> >  }
> >
> >  impl<K, V> RBTree<K, V>
> > @@ -414,13 +437,9 @@ fn into_iter(self) -> Self::IntoIter {
> >  /// An iterator over the nodes of a [`RBTree`].
> >  ///
> >  /// Instances are created by calling [`RBTree::iter`].
> > -///
> > -/// # Invariants
> > -/// - `self.next` is a valid pointer.
> > -/// - `self.next` points to a node stored inside of a valid `RBTree`.
> >  pub struct Iter<'a, K, V> {
> >      _tree: PhantomData<&'a RBTree<K, V>>,
> > -    next: *mut bindings::rb_node,
> > +    iter_raw: IterRaw<K, V>,
> >  }
> >
> >  // SAFETY: The [`Iter`] gives out immutable references to K and V, so it has the same
> > @@ -434,21 +453,76 @@ unsafe impl<'a, K: Sync, V: Sync> Sync for Iter<'a, K, V> {}
> >  impl<'a, K, V> Iterator for Iter<'a, K, V> {
> >      type Item = (&'a K, &'a V);
> >
> > +    fn next(&mut self) -> Option<Self::Item> {
> > +        self.iter_raw.next().map(|(k, v)|
> > +            // SAFETY: Due to `self._tree`, `k` and `v` are valid for the lifetime of `'a`.
> > +            unsafe { (&*k, &*v) })
>
> I don't really like the formatting here, can you move the SAFETY one
> line upwards? It should format nicely then.

You suggested exactly the reverse formatting change on RBTreeCursor?

> > +    }
> > +}
> > +
> > +impl<'a, K, V> IntoIterator for &'a mut RBTree<K, V> {
> > +    type Item = (&'a K, &'a mut V);
> > +    type IntoIter = IterMut<'a, K, V>;
> > +
> > +    fn into_iter(self) -> Self::IntoIter {
> > +        self.iter_mut()
> > +    }
> > +}
> > +
> > +/// A mutable iterator over the nodes of a [`RBTree`].
> > +///
> > +/// Instances are created by calling [`RBTree::iter_mut`].
> > +pub struct IterMut<'a, K, V> {
> > +    _tree: PhantomData<&'a mut RBTree<K, V>>,
> > +    iter_raw: IterRaw<K, V>,
> > +}
> > +
> > +// SAFETY: The [`IterMut`] gives out immutable references to K and mutable references to V, so it has the same
> > +// thread safety requirements as mutable references.
> > +unsafe impl<'a, K: Send, V: Send> Send for IterMut<'a, K, V> {}
>
> Since we only borrow `K` immutably, would it make sense to have `K:
> Sync`?

No, `K: Send` is better because it's less restrictive in practice.

Alice

On 06.08.24 10:30, Alice Ryhl wrote:
> On Mon, Aug 5, 2024 at 9:22 PM Benno Lossin <benno.lossin@proton.me> wrote:
>>
>> On 27.07.24 22:30, Matt Gilbride wrote:
>>> From: Wedson Almeida Filho <wedsonaf@gmail.com>
>>>
>>> Add mutable Iterator implementation for `RBTree`,
>>> allowing iteration over (key, value) pairs in key order. Only values are
>>> mutable, as mutating keys implies modifying a node's position in the tree.
>>>
>>> Mutable iteration is used by the binder driver during shutdown to
>>> clean up the tree maintained by the "range allocator" [1].
>>>
>>> Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-6-08ba9197f637@google.com/ [1]
>>> Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
>>> Signed-off-by: Matt Gilbride <mattgilbride@google.com>
>>> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
>>> Tested-by: Alice Ryhl <aliceryhl@google.com>
>>> ---
>>>  rust/kernel/rbtree.rs | 98 ++++++++++++++++++++++++++++++++++++++++++++-------
>>>  1 file changed, 86 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
>>> index d10074e4ac58..d7514ebadfa8 100644
>>> --- a/rust/kernel/rbtree.rs
>>> +++ b/rust/kernel/rbtree.rs
>>> @@ -197,8 +197,26 @@ pub fn iter(&self) -> Iter<'_, K, V> {
>>>          // INVARIANT: `bindings::rb_first` returns a valid pointer to a tree node given a valid pointer to a tree root.
>>
>> This INVARIANT is out of place, `Iter` doesn't have any INVARIANT any
>> more.
> 
> We can delete it.
> 
>>>          Iter {
>>>              _tree: PhantomData,
>>> -            // SAFETY: `self.root` is a valid pointer to the tree root.
>>> -            next: unsafe { bindings::rb_first(&self.root) },
>>> +            iter_raw: IterRaw {
>>
>> This `IterRaw` construction is missing an INVARIANT comment. I think you
>> can copy paste from below.
> 
> We can copy from below.
> 
>>> +                // SAFETY: by the invariants, all pointers are valid.
>>> +                next: unsafe { bindings::rb_first(&self.root) },
>>> +                _phantom: PhantomData,
>>> +            },
>>> +        }
>>> +    }
>>> +
>>> +    /// Returns a mutable iterator over the tree nodes, sorted by key.
>>> +    pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
>>> +        IterMut {
>>> +            _tree: PhantomData,
>>> +            // INVARIANT:
>>> +            //   - `self.root` is a valid pointer to a tree root.
>>> +            //   - `bindings::rb_first` produces a valid pointer to a node given `root` is valid.
>>> +            iter_raw: IterRaw {
>>> +                // SAFETY: by the invariants, all pointers are valid.
>>> +                next: unsafe { bindings::rb_first(&self.root) },
>>
>> Does this really derive a mutable reference? Ie shouldn't this be:?
>>
>>     next: unsafe { bindings::rb_first(&mut self.root) },
> 
> Let's change this to:
> 
> next: unsafe { bindings::rb_first(ptr::from_mut(&mut self.root)) }
> 
> This way, the pointer will be derived from a mutable reference even if
> it becomes a `*const` through intermediate operations.

SGTM

> 
> 
>>> +                _phantom: PhantomData,
>>> +            },
>>>          }
>>>      }
>>>
>>> @@ -211,6 +229,11 @@ pub fn keys(&self) -> impl Iterator<Item = &'_ K> {
>>>      pub fn values(&self) -> impl Iterator<Item = &'_ V> {
>>>          self.iter().map(|(_, v)| v)
>>>      }
>>> +
>>> +    /// Returns a mutable iterator over the values of the nodes in the tree, sorted by key.
>>> +    pub fn values_mut(&mut self) -> impl Iterator<Item = &'_ mut V> {
>>> +        self.iter_mut().map(|(_, v)| v)
>>> +    }
>>>  }
>>>
>>>  impl<K, V> RBTree<K, V>
>>> @@ -414,13 +437,9 @@ fn into_iter(self) -> Self::IntoIter {
>>>  /// An iterator over the nodes of a [`RBTree`].
>>>  ///
>>>  /// Instances are created by calling [`RBTree::iter`].
>>> -///
>>> -/// # Invariants
>>> -/// - `self.next` is a valid pointer.
>>> -/// - `self.next` points to a node stored inside of a valid `RBTree`.
>>>  pub struct Iter<'a, K, V> {
>>>      _tree: PhantomData<&'a RBTree<K, V>>,
>>> -    next: *mut bindings::rb_node,
>>> +    iter_raw: IterRaw<K, V>,
>>>  }
>>>
>>>  // SAFETY: The [`Iter`] gives out immutable references to K and V, so it has the same
>>> @@ -434,21 +453,76 @@ unsafe impl<'a, K: Sync, V: Sync> Sync for Iter<'a, K, V> {}
>>>  impl<'a, K, V> Iterator for Iter<'a, K, V> {
>>>      type Item = (&'a K, &'a V);
>>>
>>> +    fn next(&mut self) -> Option<Self::Item> {
>>> +        self.iter_raw.next().map(|(k, v)|
>>> +            // SAFETY: Due to `self._tree`, `k` and `v` are valid for the lifetime of `'a`.
>>> +            unsafe { (&*k, &*v) })
>>
>> I don't really like the formatting here, can you move the SAFETY one
>> line upwards? It should format nicely then.
> 
> You suggested exactly the reverse formatting change on RBTreeCursor?

Do you mean on this version or in a previous one? If you mean in this
one, then I would argue that they are not "reverses" of each other. For
this instance I would prefer

        // SAFETY: Due to `self._tree`, `k` and `v` are valid for the lifetime of `'a`.
        self.iter_raw.next().map(|(k, v)| unsafe { (&*k, &*v) })

or

        self.iter_raw.next().map(|(k, v)| {
            // SAFETY: Due to `self._tree`, `k` and `v` are valid for the lifetime of `'a`.
            unsafe { (&*k, &*v) }
        })

I hope that this seems consistent, my motivation behind the suggestions 
are that I don't like the comment splitting the single line.

---
Cheers,
Benno