Re: [PATCH v3 2.6.39-rc1-tip 5/26] 5: uprobes: Adding and remove a uprobe in a rb tree.

[Peter Zijlstra <peterz@infradead.org>]

On Fri, 2011-04-01 at 20:03 +0530, Srikar Dronamraju wrote:
> +static int match_inode(struct uprobe *uprobe, struct inode *inode,
> +                                               struct rb_node **p)
> +{
> +       struct rb_node *n = *p;
> +
> +       if (inode < uprobe->inode)
> +               *p = n->rb_left;
> +       else if (inode > uprobe->inode)
> +               *p = n->rb_right;
> +       else
> +               return 1;
> +       return 0;
> +}
> +
> +static int match_offset(struct uprobe *uprobe, loff_t offset,
> +                                               struct rb_node **p)
> +{
> +       struct rb_node *n = *p;
> +
> +       if (offset < uprobe->offset)
> +               *p = n->rb_left;
> +       else if (offset > uprobe->offset)
> +               *p = n->rb_right;
> +       else
> +               return 1;
> +       return 0;
> +}
>+
> +/* Called with treelock held */
> +static struct uprobe *__find_uprobe(struct inode * inode,
> +                        loff_t offset, struct rb_node **near_match)
> +{
> +       struct rb_node *n = uprobes_tree.rb_node;
> +       struct uprobe *uprobe, *u = NULL;
> +
> +       while (n) {
> +               uprobe = rb_entry(n, struct uprobe, rb_node);
> +               if (match_inode(uprobe, inode, &n)) {
> +                       if (near_match)
> +                               *near_match = n;
> +                       if (match_offset(uprobe, offset, &n)) {
> +                               /* get access ref */
> +                               atomic_inc(&uprobe->ref);
> +                               u = uprobe;
> +                               break;
> +                       }
> +               }
> +       }
> +       return u;
> +}

Here you break out the match functions for some reason.

> +/*
> + * Find a uprobe corresponding to a given inode:offset
> + * Acquires treelock
> + */
> +static struct uprobe *find_uprobe(struct inode * inode, loff_t offset)
> +{
> +       struct uprobe *uprobe;
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&treelock, flags);
> +       uprobe = __find_uprobe(inode, offset, NULL);
> +       spin_unlock_irqrestore(&treelock, flags);
> +       return uprobe;
> +}
> +
> +/*
> + * Acquires treelock.
> + * Matching uprobe already exists in rbtree;
> + *     increment (access refcount) and return the matching uprobe.
> + *
> + * No matching uprobe; insert the uprobe in rb_tree;
> + *     get a double refcount (access + creation) and return NULL.
> + */
> +static struct uprobe *insert_uprobe(struct uprobe *uprobe)
> +{
> +       struct rb_node **p = &uprobes_tree.rb_node;
> +       struct rb_node *parent = NULL;
> +       struct uprobe *u;
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&treelock, flags);
> +       while (*p) {
> +               parent = *p;
> +               u = rb_entry(parent, struct uprobe, rb_node);
> +               if (u->inode > uprobe->inode)
> +                       p = &(*p)->rb_left;
> +               else if (u->inode < uprobe->inode)
> +                       p = &(*p)->rb_right;
> +               else {
> +                       if (u->offset > uprobe->offset)
> +                               p = &(*p)->rb_left;
> +                       else if (u->offset < uprobe->offset)
> +                               p = &(*p)->rb_right;
> +                       else {
> +                               /* get access ref */
> +                               atomic_inc(&u->ref);
> +                               goto unlock_return;
> +                       }
> +               }
> +       }
> +       u = NULL;
> +       rb_link_node(&uprobe->rb_node, parent, p);
> +       rb_insert_color(&uprobe->rb_node, &uprobes_tree);
> +       /* get access + drop ref */
> +       atomic_set(&uprobe->ref, 2);
> +
> +unlock_return:
> +       spin_unlock_irqrestore(&treelock, flags);
> +       return u;
> +} 

And here you open-code the match functions..

Why not have something like:

static int match_probe(struct uprobe *l, struct uprobe *r)
{
	if (l->inode < r->inode)
		return -1;
	else if (l->inode > r->inode)
		return 1;
	else {
		if (l->offset < r->offset)
			return -1;
		else if (l->offset > r->offset)
			return 1;
	}

	return 0;
}

And use that as:

static struct uprobe *
__find_uprobe(struct inode *inode, loff_t offset)
{
	struct uprobe r = { .inode = inode, .offset = offset };
	struct rb_node *n = uprobes_tree.rb_node;
	struct uprobe *uprobe;
	int match;

	while (n) {
		uprobe = rb_node(n, struct uprobe, rb_node);
		match = match_probe(uprobe, &r);
		if (!match) {
			atomic_inc(&uprobe->ref);
			return uprobe;
		}
		if (match < 0)
			n = n->rb_left;
		else
			n = n->rb_right;
	}

	return NULL;
}

static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
{
	struct rb_node **p = &uprobes_tree.rb_node;
	struct rn_node *parent = NULL;
	struct uprobe *u;
	int match;

	while (*p) {
		parent = *p;
		u = rb_entry(parent, struct uprobe, rb_node);
		match = match_uprobe(u, uprobe);
		if (!match) {
			atomic_inc(&u->ref);
			return u;
		}
		if (match < 0)
			p = &parent->rb_left;
		else
			p = &parent->rb_right;
	}

	atomic_set(&uprobe->ref, 2);
	rb_link_node(&uprobe->rb_node, parent, p);
	rb_insert_color(&uprobe->rb_node, &uprobes_tree);
	return uprobe;
}

Isn't that much nicer?