On Thu, Jul 11, 2024 at 4:07 AM Peter Zijlstra <pet...@infradead.org> wrote: > > 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) <pet...@infradead.org> > Reviewed-by: Masami Hiramatsu (Google) <mhira...@kernel.org> > --- > include/linux/rbtree.h | 67 > +++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 67 insertions(+) > > --- a/include/linux/rbtree.h > +++ b/include/linux/rbtree.h > @@ -245,6 +245,42 @@ rb_find_add(struct rb_node *node, struct > } > > /** > + * 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 *))
I don't get the point of the RCU version of rb_find_add as RCU itself doesn't provide enough protection for modification of the tree, right? So in uprobes code you do rb_find_add_rcu() under uprobes_treelock + uprobes_seqcount locks. Wouldn't it be just as fine to do plain non-RCU rb_find_add() in that case? After all, you do plain rb_erase under the same set of locks. So what's the point of this one? > +{ > + 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; > +} > + [...]