Re: [PATCH v5 3.1.0-rc4-tip 1/26] uprobes: Auxillary routines toinsert, find, delete uprobes

[Peter Zijlstra]

On Tue, 2011-09-20 at 17:29 +0530, Srikar Dronamraju wrote:
> +static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
> +{
> +       struct rb_node **p = &uprobes_tree.rb_node;
> +       struct rb_node *parent = NULL;
> +       struct uprobe *u;
> +       int match;
> +
> +       while (*p) {
> +               parent = *p;
> +               u = rb_entry(parent, struct uprobe, rb_node);
> +               match = match_uprobe(uprobe, u);
> +               if (!match) {
> +                       atomic_inc(&u->ref);
> +                       return u;
> +               }
> +
> +               if (match < 0)
> +                       p = &parent->rb_left;
> +               else
> +                       p = &parent->rb_right;
> +
> +       }
> +       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);
> +       return u;
> +} 

If you ever want to make a 'lockless' lookup work you need to set the
refcount of the new object before its fully visible, instead of after.

Now much of a problem now since its fully serialized by that
uprobes_treelock thing.
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