*/
#include <linux/rbtree_augmented.h>
+#include <linux/export.h>
/*
* red-black trees properties: http://en.wikipedia.org/wiki/Rbtree
* parentheses and have some accompanying text comment.
*/
+/*
+ * Notes on lockless lookups:
+ *
+ * All stores to the tree structure (rb_left and rb_right) must be done using
+ * WRITE_ONCE(). And we must not inadvertently cause (temporary) loops in the
+ * tree structure as seen in program order.
+ *
+ * These two requirements will allow lockless iteration of the tree -- not
+ * correct iteration mind you, tree rotations are not atomic so a lookup might
+ * miss entire subtrees.
+ *
+ * But they do guarantee that any such traversal will only see valid elements
+ * and that it will indeed complete -- does not get stuck in a loop.
+ *
+ * It also guarantees that if the lookup returns an element it is the 'correct'
+ * one. But not returning an element does _NOT_ mean it's not present.
+ *
+ * NOTE:
+ *
+ * Stores to __rb_parent_color are not important for simple lookups so those
+ * are left undone as of now. Nor did I check for loops involving parent
+ * pointers.
+ */
+
static inline void rb_set_black(struct rb_node *rb)
{
rb->__rb_parent_color |= RB_BLACK;
static __always_inline void
__rb_insert(struct rb_node *node, struct rb_root *root,
+ bool newleft, struct rb_node **leftmost,
void (*augment_rotate)(struct rb_node *old, struct rb_node *new))
{
struct rb_node *parent = rb_red_parent(node), *gparent, *tmp;
+ if (newleft)
+ *leftmost = node;
+
while (true) {
/*
- * Loop invariant: node is red
- *
- * If there is a black parent, we are done.
- * Otherwise, take some corrective action as we don't
- * want a red root or two consecutive red nodes.
+ * Loop invariant: node is red.
*/
- if (!parent) {
+ if (unlikely(!parent)) {
+ /*
+ * The inserted node is root. Either this is the
+ * first node, or we recursed at Case 1 below and
+ * are no longer violating 4).
+ */
rb_set_parent_color(node, NULL, RB_BLACK);
break;
- } else if (rb_is_black(parent))
+ }
+
+ /*
+ * If there is a black parent, we are done.
+ * Otherwise, take some corrective action as,
+ * per 4), we don't want a red root or two
+ * consecutive red nodes.
+ */
+ if(rb_is_black(parent))
break;
gparent = rb_red_parent(parent);
if (parent != tmp) { /* parent == gparent->rb_left */
if (tmp && rb_is_red(tmp)) {
/*
- * Case 1 - color flips
+ * Case 1 - node's uncle is red (color flips).
*
* G g
* / \ / \
tmp = parent->rb_right;
if (node == tmp) {
/*
- * Case 2 - left rotate at parent
+ * Case 2 - node's uncle is black and node is
+ * the parent's right child (left rotate at parent).
*
* G G
* / \ / \
* This still leaves us in violation of 4), the
* continuation into Case 3 will fix that.
*/
- parent->rb_right = tmp = node->rb_left;
- node->rb_left = parent;
+ tmp = node->rb_left;
+ WRITE_ONCE(parent->rb_right, tmp);
+ WRITE_ONCE(node->rb_left, parent);
if (tmp)
rb_set_parent_color(tmp, parent,
RB_BLACK);
}
/*
- * Case 3 - right rotate at gparent
+ * Case 3 - node's uncle is black and node is
+ * the parent's left child (right rotate at gparent).
*
* G P
* / \ / \
* / \
* n U
*/
- gparent->rb_left = tmp; /* == parent->rb_right */
- parent->rb_right = gparent;
+ WRITE_ONCE(gparent->rb_left, tmp); /* == parent->rb_right */
+ WRITE_ONCE(parent->rb_right, gparent);
if (tmp)
rb_set_parent_color(tmp, gparent, RB_BLACK);
__rb_rotate_set_parents(gparent, parent, root, RB_RED);
tmp = parent->rb_left;
if (node == tmp) {
/* Case 2 - right rotate at parent */
- parent->rb_left = tmp = node->rb_right;
- node->rb_right = parent;
+ tmp = node->rb_right;
+ WRITE_ONCE(parent->rb_left, tmp);
+ WRITE_ONCE(node->rb_right, parent);
if (tmp)
rb_set_parent_color(tmp, parent,
RB_BLACK);
}
/* Case 3 - left rotate at gparent */
- gparent->rb_right = tmp; /* == parent->rb_left */
- parent->rb_left = gparent;
+ WRITE_ONCE(gparent->rb_right, tmp); /* == parent->rb_left */
+ WRITE_ONCE(parent->rb_left, gparent);
if (tmp)
rb_set_parent_color(tmp, gparent, RB_BLACK);
__rb_rotate_set_parents(gparent, parent, root, RB_RED);
* / \ / \
* Sl Sr N Sl
*/
- parent->rb_right = tmp1 = sibling->rb_left;
- sibling->rb_left = parent;
+ tmp1 = sibling->rb_left;
+ WRITE_ONCE(parent->rb_right, tmp1);
+ WRITE_ONCE(sibling->rb_left, parent);
rb_set_parent_color(tmp1, parent, RB_BLACK);
__rb_rotate_set_parents(parent, sibling, root,
RB_RED);
*
* (p) (p)
* / \ / \
- * N S --> N Sl
+ * N S --> N sl
* / \ \
- * sl Sr s
+ * sl Sr S
* \
* Sr
+ *
+ * Note: p might be red, and then both
+ * p and sl are red after rotation(which
+ * breaks property 4). This is fixed in
+ * Case 4 (in __rb_rotate_set_parents()
+ * which set sl the color of p
+ * and set p RB_BLACK)
+ *
+ * (p) (sl)
+ * / \ / \
+ * N sl --> P S
+ * \ / \
+ * S N Sr
+ * \
+ * Sr
*/
- sibling->rb_left = tmp1 = tmp2->rb_right;
- tmp2->rb_right = sibling;
- parent->rb_right = tmp2;
+ tmp1 = tmp2->rb_right;
+ WRITE_ONCE(sibling->rb_left, tmp1);
+ WRITE_ONCE(tmp2->rb_right, sibling);
+ WRITE_ONCE(parent->rb_right, tmp2);
if (tmp1)
rb_set_parent_color(tmp1, sibling,
RB_BLACK);
* / \ / \
* (sl) sr N (sl)
*/
- parent->rb_right = tmp2 = sibling->rb_left;
- sibling->rb_left = parent;
+ tmp2 = sibling->rb_left;
+ WRITE_ONCE(parent->rb_right, tmp2);
+ WRITE_ONCE(sibling->rb_left, parent);
rb_set_parent_color(tmp1, sibling, RB_BLACK);
if (tmp2)
rb_set_parent(tmp2, parent);
sibling = parent->rb_left;
if (rb_is_red(sibling)) {
/* Case 1 - right rotate at parent */
- parent->rb_left = tmp1 = sibling->rb_right;
- sibling->rb_right = parent;
+ tmp1 = sibling->rb_right;
+ WRITE_ONCE(parent->rb_left, tmp1);
+ WRITE_ONCE(sibling->rb_right, parent);
rb_set_parent_color(tmp1, parent, RB_BLACK);
__rb_rotate_set_parents(parent, sibling, root,
RB_RED);
}
break;
}
- /* Case 3 - right rotate at sibling */
- sibling->rb_right = tmp1 = tmp2->rb_left;
- tmp2->rb_left = sibling;
- parent->rb_left = tmp2;
+ /* Case 3 - left rotate at sibling */
+ tmp1 = tmp2->rb_left;
+ WRITE_ONCE(sibling->rb_right, tmp1);
+ WRITE_ONCE(tmp2->rb_left, sibling);
+ WRITE_ONCE(parent->rb_left, tmp2);
if (tmp1)
rb_set_parent_color(tmp1, sibling,
RB_BLACK);
tmp1 = sibling;
sibling = tmp2;
}
- /* Case 4 - left rotate at parent + color flips */
- parent->rb_left = tmp2 = sibling->rb_right;
- sibling->rb_right = parent;
+ /* Case 4 - right rotate at parent + color flips */
+ tmp2 = sibling->rb_right;
+ WRITE_ONCE(parent->rb_left, tmp2);
+ WRITE_ONCE(sibling->rb_right, parent);
rb_set_parent_color(tmp1, sibling, RB_BLACK);
if (tmp2)
rb_set_parent(tmp2, parent);
static inline void dummy_rotate(struct rb_node *old, struct rb_node *new) {}
static const struct rb_augment_callbacks dummy_callbacks = {
- dummy_propagate, dummy_copy, dummy_rotate
+ .propagate = dummy_propagate,
+ .copy = dummy_copy,
+ .rotate = dummy_rotate
};
void rb_insert_color(struct rb_node *node, struct rb_root *root)
{
- __rb_insert(node, root, dummy_rotate);
+ __rb_insert(node, root, false, NULL, dummy_rotate);
}
void rb_erase(struct rb_node *node, struct rb_root *root)
{
struct rb_node *rebalance;
- rebalance = __rb_erase_augmented(node, root, &dummy_callbacks);
+ rebalance = __rb_erase_augmented(node, root,
+ NULL, &dummy_callbacks);
if (rebalance)
____rb_erase_color(rebalance, root, dummy_rotate);
}
+void rb_insert_color_cached(struct rb_node *node,
+ struct rb_root_cached *root, bool leftmost)
+{
+ __rb_insert(node, &root->rb_root, leftmost,
+ &root->rb_leftmost, dummy_rotate);
+}
+
+void rb_erase_cached(struct rb_node *node, struct rb_root_cached *root)
+{
+ struct rb_node *rebalance;
+ rebalance = __rb_erase_augmented(node, &root->rb_root,
+ &root->rb_leftmost, &dummy_callbacks);
+ if (rebalance)
+ ____rb_erase_color(rebalance, &root->rb_root, dummy_rotate);
+}
+
/*
* Augmented rbtree manipulation functions.
*
*/
void __rb_insert_augmented(struct rb_node *node, struct rb_root *root,
+ bool newleft, struct rb_node **leftmost,
void (*augment_rotate)(struct rb_node *old, struct rb_node *new))
{
- __rb_insert(node, root, augment_rotate);
+ __rb_insert(node, root, newleft, leftmost, augment_rotate);
}
/*
{
struct rb_node *parent = rb_parent(victim);
+ /* Copy the pointers/colour from the victim to the replacement */
+ *new = *victim;
+
/* Set the surrounding nodes to point to the replacement */
- __rb_change_child(victim, new, parent, root);
if (victim->rb_left)
rb_set_parent(victim->rb_left, new);
if (victim->rb_right)
rb_set_parent(victim->rb_right, new);
+ __rb_change_child(victim, new, parent, root);
+}
- /* Copy the pointers/colour from the victim to the replacement */
- *new = *victim;
+void rb_replace_node_cached(struct rb_node *victim, struct rb_node *new,
+ struct rb_root_cached *root)
+{
+ rb_replace_node(victim, new, &root->rb_root);
+
+ if (root->rb_leftmost == victim)
+ root->rb_leftmost = new;
}
static struct rb_node *rb_left_deepest_node(const struct rb_node *node)
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