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@xxxxxxxxxxxxx> AuthorDate: Tue, 03 Sep 2024 10:46:01 -07:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> Signed-off-by: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Reviewed-by: Oleg Nesterov <oleg@xxxxxxxxxx> Reviewed-by: "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> Link: https://lore.kernel.org/r/20240903174603.3554182-7-andrii@xxxxxxxxxx --- 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
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