diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h index fb31765e935a..830c4992088d 100644 --- a/include/linux/rbtree.h +++ b/include/linux/rbtree.h @@ -31,6 +31,7 @@ #include #include +#include struct rb_node { unsigned long __rb_parent_color; @@ -73,11 +74,11 @@ extern struct rb_node *rb_first_postorder(const struct rb_root *); extern struct rb_node *rb_next_postorder(const struct rb_node *); /* Fast replacement of a single node without remove/rebalance/add/rebalance */ -extern void rb_replace_node(struct rb_node *victim, struct rb_node *new, +extern void rb_replace_node(struct rb_node *victim, struct rb_node *new, struct rb_root *root); -static inline void rb_link_node(struct rb_node * node, struct rb_node * parent, - struct rb_node ** rb_link) +static inline void rb_link_node(struct rb_node *node, struct rb_node *parent, + struct rb_node **rb_link) { node->__rb_parent_color = (unsigned long)parent; node->rb_left = node->rb_right = NULL; @@ -85,6 +86,15 @@ static inline void rb_link_node(struct rb_node * node, struct rb_node * parent, *rb_link = node; } +static inline void rb_link_node_rcu(struct rb_node *node, struct rb_node *parent, + struct rb_node **rb_link) +{ + node->__rb_parent_color = (unsigned long)parent; + node->rb_left = node->rb_right = NULL; + + rcu_assign_pointer(*rb_link, node); +} + #define rb_entry_safe(ptr, type, member) \ ({ typeof(ptr) ____ptr = (ptr); \ ____ptr ? rb_entry(____ptr, type, member) : NULL; \ diff --git a/include/linux/rbtree_augmented.h b/include/linux/rbtree_augmented.h index 378c5ee75f78..14d7b831b63a 100644 --- a/include/linux/rbtree_augmented.h +++ b/include/linux/rbtree_augmented.h @@ -123,11 +123,11 @@ __rb_change_child(struct rb_node *old, struct rb_node *new, { if (parent) { if (parent->rb_left == old) - parent->rb_left = new; + WRITE_ONCE(parent->rb_left, new); else - parent->rb_right = new; + WRITE_ONCE(parent->rb_right, new); } else - root->rb_node = new; + WRITE_ONCE(root->rb_node, new); } extern void __rb_erase_color(struct rb_node *parent, struct rb_root *root, @@ -137,7 +137,8 @@ static __always_inline struct rb_node * __rb_erase_augmented(struct rb_node *node, struct rb_root *root, const struct rb_augment_callbacks *augment) { - struct rb_node *child = node->rb_right, *tmp = node->rb_left; + struct rb_node *child = node->rb_right; + struct rb_node *tmp = node->rb_left; struct rb_node *parent, *rebalance; unsigned long pc; @@ -167,6 +168,7 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root, tmp = parent; } else { struct rb_node *successor = child, *child2; + tmp = child->rb_left; if (!tmp) { /* @@ -180,6 +182,7 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root, */ parent = successor; child2 = successor->rb_right; + augment->copy(node, successor); } else { /* @@ -201,19 +204,23 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root, successor = tmp; tmp = tmp->rb_left; } while (tmp); - parent->rb_left = child2 = successor->rb_right; - successor->rb_right = child; + child2 = successor->rb_right; + WRITE_ONCE(parent->rb_left, child2); + WRITE_ONCE(successor->rb_right, child); rb_set_parent(child, successor); + augment->copy(node, successor); augment->propagate(parent, successor); } - successor->rb_left = tmp = node->rb_left; + tmp = node->rb_left; + WRITE_ONCE(successor->rb_left, tmp); rb_set_parent(tmp, successor); pc = node->__rb_parent_color; tmp = __rb_parent(pc); __rb_change_child(node, successor, tmp, root); + if (child2) { successor->__rb_parent_color = pc; rb_set_parent_color(child2, parent, RB_BLACK); diff --git a/lib/rbtree.c b/lib/rbtree.c index c16c81a3d430..1356454e36de 100644 --- a/lib/rbtree.c +++ b/lib/rbtree.c @@ -44,6 +44,30 @@ * 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; @@ -129,8 +153,9 @@ __rb_insert(struct rb_node *node, struct rb_root *root, * 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); @@ -149,8 +174,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root, * / \ * 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); @@ -171,8 +196,9 @@ __rb_insert(struct rb_node *node, struct rb_root *root, 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); @@ -183,8 +209,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root, } /* 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); @@ -224,8 +250,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root, * / \ / \ * 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); @@ -275,9 +302,10 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root, * \ * 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); @@ -297,8 +325,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root, * / \ / \ * (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); @@ -310,8 +339,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root, 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); @@ -336,9 +366,10 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root, break; } /* Case 3 - right rotate at sibling */ - sibling->rb_right = tmp1 = tmp2->rb_left; - tmp2->rb_left = sibling; - parent->rb_left = tmp2; + 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); @@ -347,8 +378,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root, sibling = tmp2; } /* Case 4 - left rotate at parent + color flips */ - parent->rb_left = tmp2 = sibling->rb_right; - sibling->rb_right = parent; + 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);