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fix overlapping references in BTree #58431

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merged 2 commits into from
Feb 23, 2019
Merged

fix overlapping references in BTree #58431

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d87df69
fix overlapping mutable and shared references in BTreeMap's into_slic…
RalfJung Feb 13, 2019
f0bef49
fix invalidating references in BTree iterators
RalfJung Feb 13, 2019
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fix invalidating references in BTree iterators
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@RalfJung
RalfJung committed Feb 13, 2019
commit f0bef49cf10c19b72b7d025aedb407ab5745c365
32 changes: 20 additions & 12 deletions src/liballoc/collections/btree/map.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1634,9 +1634,11 @@ impl<'a, K, V> RangeMut<'a, K, V> {

let mut cur_handle = match handle.right_kv() {
Ok(kv) => {
let (k, v) = ptr::read(&kv).into_kv_mut();
self.front = kv.right_edge();
return (k, v);
self.front = ptr::read(&kv).right_edge();
// Doing the descend invalidates the references returned by `into_kv_mut`,
// so we have to do this last.
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I struggle with this comment because there's no descend here, right? Maybe the right_edge also invalidates references, or the change is just here to match the code below where a descend happens.

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Well, there's still a call to right_edge so I wanted to be sure that wouldn't cause any problems, without actually checking in detail what that function does. The comment is probably a copy-paste mistake though.

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I've taken the plunge and collapsed the two copies in each iterator in my #66747 PR

let (k, v) = kv.into_kv_mut();
return (k, v); // coerce k from `&mut K` to `&K`
}
Err(last_edge) => {
let next_level = last_edge.into_node().ascend().ok();
Expand All @@ -1647,9 +1649,11 @@ impl<'a, K, V> RangeMut<'a, K, V> {
loop {
match cur_handle.right_kv() {
Ok(kv) => {
let (k, v) = ptr::read(&kv).into_kv_mut();
self.front = first_leaf_edge(kv.right_edge().descend());
return (k, v);
self.front = first_leaf_edge(ptr::read(&kv).right_edge().descend());
// Doing the descend invalidates the references returned by `into_kv_mut`,
// so we have to do this last.
let (k, v) = kv.into_kv_mut();
return (k, v); // coerce k from `&mut K` to `&K`
}
Err(last_edge) => {
let next_level = last_edge.into_node().ascend().ok();
Expand Down Expand Up @@ -1680,9 +1684,11 @@ impl<'a, K, V> RangeMut<'a, K, V> {

let mut cur_handle = match handle.left_kv() {
Ok(kv) => {
let (k, v) = ptr::read(&kv).into_kv_mut();
self.back = kv.left_edge();
return (k, v);
self.back = ptr::read(&kv).left_edge();
// Doing the descend invalidates the references returned by `into_kv_mut`,
// so we have to do this last.
let (k, v) = kv.into_kv_mut();
return (k, v); // coerce k from `&mut K` to `&K`
}
Err(last_edge) => {
let next_level = last_edge.into_node().ascend().ok();
Expand All @@ -1693,9 +1699,11 @@ impl<'a, K, V> RangeMut<'a, K, V> {
loop {
match cur_handle.left_kv() {
Ok(kv) => {
let (k, v) = ptr::read(&kv).into_kv_mut();
self.back = last_leaf_edge(kv.left_edge().descend());
return (k, v);
self.back = last_leaf_edge(ptr::read(&kv).left_edge().descend());
// Doing the descend invalidates the references returned by `into_kv_mut`,
// so we have to do this last.
let (k, v) = kv.into_kv_mut();
return (k, v); // coerce k from `&mut K` to `&K`
}
Err(last_edge) => {
let next_level = last_edge.into_node().ascend().ok();
Expand Down
2 changes: 1 addition & 1 deletion src/liballoc/collections/btree/node.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -675,7 +675,7 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
// invalidates the reference returned by the first.
// More precisely, it is the call to `len` that is the culprit,
// because that creates a shared reference to the header, which *can*
// overlap with the keys.
// overlap with the keys (and even the values, for ZST keys).
unsafe {
let len = self.len();
let leaf = self.as_leaf_mut();
Expand Down