Commit 50a38035 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

rbtree: provide rb_find_rcu() / rb_find_add_rcu() 



Much like latch_tree, add two RCU methods for the regular RB-tree,
which can be used in conjunction with a seqcount to provide lockless
lookups.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatar"Peter Zijlstra (Intel)" <peterz@infradead.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
Reviewed-by: default avatar"Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20240903174603.3554182-7-andrii@kernel.org
parent 04b01625

include/linux/rbtree.h

+67 −0
Original line number Diff line number Diff line
@@ -244,6 +244,42 @@ rb_find_add(struct rb_node *node, struct rb_root *tree, 
	return NULL;

}



/**

 * rb_find_add_rcu() - find equivalent @node in @tree, or add @node

 * @node: node to look-for / insert

 * @tree: tree to search / modify

 * @cmp: operator defining the node order

 *

 * Adds a Store-Release for link_node.

 *

 * Returns the rb_node matching @node, or NULL when no match is found and @node

 * is inserted.

 */

static __always_inline struct rb_node *

rb_find_add_rcu(struct rb_node *node, struct rb_root *tree,

		int (*cmp)(struct rb_node *, const struct rb_node *))

{

	struct rb_node **link = &tree->rb_node;

	struct rb_node *parent = NULL;

	int c;



	while (*link) {

		parent = *link;

		c = cmp(node, parent);



		if (c < 0)

			link = &parent->rb_left;

		else if (c > 0)

			link = &parent->rb_right;

		else

			return parent;

	}



	rb_link_node_rcu(node, parent, link);

	rb_insert_color(node, tree);

	return NULL;

}



/**

 * rb_find() - find @key in tree @tree

 * @key: key to match
@@ -272,6 +308,37 @@ rb_find(const void *key, const struct rb_root *tree, 
	return NULL;

}



/**

 * rb_find_rcu() - find @key in tree @tree

 * @key: key to match

 * @tree: tree to search

 * @cmp: operator defining the node order

 *

 * Notably, tree descent vs concurrent tree rotations is unsound and can result

 * in false-negatives.

 *

 * Returns the rb_node matching @key or NULL.

 */

static __always_inline struct rb_node *

rb_find_rcu(const void *key, const struct rb_root *tree,

	    int (*cmp)(const void *key, const struct rb_node *))

{

	struct rb_node *node = tree->rb_node;



	while (node) {

		int c = cmp(key, node);



		if (c < 0)

			node = rcu_dereference_raw(node->rb_left);

		else if (c > 0)

			node = rcu_dereference_raw(node->rb_right);

		else

			return node;

	}



	return NULL;

}



/**

 * rb_find_first() - find the first @key in @tree

 * @key: key to match