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rbtree: provide rb_find_rcu() / rb_find_add_rcu()

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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
This commit is contained in:
Peter Zijlstra 2024-09-03 10:46:01 -07:00
parent 04b01625da
commit 50a38035ed
1 changed files with 67 additions and 0 deletions
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67
include/linux/rbtree.h
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@ -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