[tip: perf/core] rbtree: provide rb_find_rcu() / rb_find_add_rcu()

tip-bot2 for Peter Zijlstra
2024-09-05T15:03:26Z

The following commit has been merged into the perf/core branch of tip:

Commit-ID: 50a38035ed5ccc2ab8a28eaf70c3c7a87e060345
Gitweb: https://git.kernel.org/tip/50a38035ed5ccc2ab8a28eaf70c3c7a87e060345
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 03 Sep 2024 10:46:01 -07:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 05 Sep 2024 16:56:15 +02:00

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: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20240903174603.3554182-7-andrii@kernel.org
---
include/linux/rbtree.h | 67 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 67 insertions(+)

diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h
index f7edca3..7c173aa 100644
--- a/include/linux/rbtree.h
+++ b/include/linux/rbtree.h
@@ -245,6 +245,42 @@ rb_find_add(struct rb_node *node, struct rb_root *tree,
}

/**
+ * 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
* @tree: tree to search
@@ -273,6 +309,37 @@ rb_find(const void *key, const struct rb_root *tree,
}

/**
+ * 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
* @tree: tree to search