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-rw-r--r--lib/rbtree.c28
1 files changed, 17 insertions, 11 deletions
diff --git a/lib/rbtree.c b/lib/rbtree.c
index 41cf19b2fe51..baf7c835c57c 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -259,10 +259,22 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
{
struct rb_node *other;
- while ((!node || rb_is_black(node)) && node != root->rb_node)
- {
- if (parent->rb_left == node)
- {
+ while (true) {
+ /*
+ * Loop invariant: all leaf paths going through node have a
+ * black node count that is 1 lower than other leaf paths.
+ *
+ * If node is red, we can flip it to black to adjust.
+ * If node is the root, all leaf paths go through it.
+ * Otherwise, we need to adjust the tree through color flips
+ * and tree rotations as per one of the 4 cases below.
+ */
+ if (node && rb_is_red(node)) {
+ rb_set_black(node);
+ break;
+ } else if (!parent) {
+ break;
+ } else if (parent->rb_left == node) {
other = parent->rb_right;
if (rb_is_red(other))
{
@@ -291,12 +303,9 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
rb_set_black(parent);
rb_set_black(other->rb_right);
__rb_rotate_left(parent, root);
- node = root->rb_node;
break;
}
- }
- else
- {
+ } else {
other = parent->rb_left;
if (rb_is_red(other))
{
@@ -325,13 +334,10 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
rb_set_black(parent);
rb_set_black(other->rb_left);
__rb_rotate_right(parent, root);
- node = root->rb_node;
break;
}
}
}
- if (node)
- rb_set_black(node);
}
void rb_erase(struct rb_node *node, struct rb_root *root)