Introduce rb_replace_node_rcu()
Implement an RCU-safe variant of rb_replace_node() and rearrange
rb_replace_node() to do things in the same order.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h
index b690009..e585018 100644
--- a/include/linux/rbtree.h
+++ b/include/linux/rbtree.h
@@ -76,6 +76,8 @@
/* Fast replacement of a single node without remove/rebalance/add/rebalance */
extern void rb_replace_node(struct rb_node *victim, struct rb_node *new,
struct rb_root *root);
+extern void rb_replace_node_rcu(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)
diff --git a/include/linux/rbtree_augmented.h b/include/linux/rbtree_augmented.h
index 14d7b83..d076183 100644
--- a/include/linux/rbtree_augmented.h
+++ b/include/linux/rbtree_augmented.h
@@ -130,6 +130,19 @@
WRITE_ONCE(root->rb_node, new);
}
+static inline void
+__rb_change_child_rcu(struct rb_node *old, struct rb_node *new,
+ struct rb_node *parent, struct rb_root *root)
+{
+ if (parent) {
+ if (parent->rb_left == old)
+ rcu_assign_pointer(parent->rb_left, new);
+ else
+ rcu_assign_pointer(parent->rb_right, new);
+ } else
+ rcu_assign_pointer(root->rb_node, new);
+}
+
extern void __rb_erase_color(struct rb_node *parent, struct rb_root *root,
void (*augment_rotate)(struct rb_node *old, struct rb_node *new));
diff --git a/lib/rbtree.c b/lib/rbtree.c
index 1356454..eb8a19f 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -539,17 +539,39 @@
{
struct rb_node *parent = rb_parent(victim);
+ /* Copy the pointers/colour from the victim to the replacement */
+ *new = *victim;
+
/* Set the surrounding nodes to point to the replacement */
+ if (victim->rb_left)
+ rb_set_parent(victim->rb_left, new);
+ if (victim->rb_right)
+ rb_set_parent(victim->rb_right, new);
__rb_change_child(victim, new, parent, root);
+}
+EXPORT_SYMBOL(rb_replace_node);
+
+void rb_replace_node_rcu(struct rb_node *victim, struct rb_node *new,
+ struct rb_root *root)
+{
+ struct rb_node *parent = rb_parent(victim);
+
+ /* Copy the pointers/colour from the victim to the replacement */
+ *new = *victim;
+
+ /* Set the surrounding nodes to point to the replacement */
if (victim->rb_left)
rb_set_parent(victim->rb_left, new);
if (victim->rb_right)
rb_set_parent(victim->rb_right, new);
- /* Copy the pointers/colour from the victim to the replacement */
- *new = *victim;
+ /* Set the parent's pointer to the new node last after an RCU barrier
+ * so that the pointers onwards are seen to be set correctly when doing
+ * an RCU walk over the tree.
+ */
+ __rb_change_child_rcu(victim, new, parent, root);
}
-EXPORT_SYMBOL(rb_replace_node);
+EXPORT_SYMBOL(rb_replace_node_rcu);
static struct rb_node *rb_left_deepest_node(const struct rb_node *node)
{