* Peter Zijlstra [off-list ref] [2011-09-26 13:18:40]:

On Tue, 2011-09-20 at 17:29 +0530, Srikar Dronamraju wrote:

quoted

+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.

Agree, 

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

Will stick with this for now; If and when we do a lockless lookup we
could fix this.

-- 
Thanks and Regards
Srikar

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