From cf5397d1776489e1c66b7db01f6a58c431ab08f1 Mon Sep 17 00:00:00 2001 From: Wedson Almeida Filho Date: Thu, 22 Aug 2024 16:37:55 +0000 Subject: [PATCH] rust: rbtree: add mutable iterator 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 Reviewed-by: Alice Ryhl Tested-by: Alice Ryhl Reviewed-by: Boqun Feng Reviewed-by: Benno Lossin Signed-off-by: Matt Gilbride Link: https://lore.kernel.org/r/20240822-b4-rbtree-v12-3-014561758a57@google.com Signed-off-by: Miguel Ojeda --- rust/kernel/rbtree.rs | 103 ++++++++++++++++++++++++++++++++++++------ 1 file changed, 89 insertions(+), 14 deletions(-) diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs index ca19d79053de..b07a21b5d8b0 100644 --- a/rust/kernel/rbtree.rs +++ b/rust/kernel/rbtree.rs @@ -12,7 +12,7 @@ use core::{ cmp::{Ord, Ordering}, marker::PhantomData, mem::MaybeUninit, - ptr::{addr_of_mut, NonNull}, + ptr::{addr_of_mut, from_mut, NonNull}, }; /// A red-black tree with owned nodes. @@ -194,11 +194,31 @@ impl RBTree { /// Returns an iterator over the tree nodes, sorted by key. 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) }, + // 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, + }, + } + } + + /// 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(from_mut(&mut self.root)) }, + _phantom: PhantomData, + }, } } @@ -211,6 +231,11 @@ impl RBTree { pub fn values(&self) -> impl Iterator { 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 { + self.iter_mut().map(|(_, v)| v) + } } impl RBTree @@ -414,13 +439,9 @@ impl<'a, K, V> IntoIterator for &'a RBTree { /// 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>, - next: *mut bindings::rb_node, + iter_raw: IterRaw, } // SAFETY: The [`Iter`] gives out immutable references to K and V, so it has the same @@ -434,21 +455,75 @@ 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 { + // 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) }) + } +} + +impl<'a, K, V> IntoIterator for &'a mut RBTree { + 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>, + iter_raw: IterRaw, +} + +// SAFETY: The [`IterMut`] has exclusive access to both `K` and `V`, so it is sufficient to require them to be `Send`. +// The iterator only gives out immutable references to the keys, but since the iterator has excusive access to those same +// keys, `Send` is sufficient. `Sync` would be okay, but it is more restrictive to the user. +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.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 { + next: *mut bindings::rb_node, + _phantom: PhantomData (K, V)>, +} + +impl Iterator for IterRaw { + type Item = (*mut K, *mut V); + fn next(&mut self) -> Option { 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` objects. - let cur = unsafe { container_of!(self.next, Node, links) }; + let cur = unsafe { container_of!(self.next, Node, 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)) }) } }