RCU dependency chain 3

 1 /* Does this work? */
 2 struct foo my_foo = { 5, 10 };
 3
 4 struct foo *insert_struct(struct foo *p)
 5 {
 6   struct foo *q;
 7
 8   if (data < 0)
 9     return NULL;
10   spin_lock(gp_lock);
11   q = atomic_xchg(&gp, p);
12   spin_unlock(gp_lock);
13   synchronize_rcu();
14   return q;
15 }
16
17 ...
18   WARN_ON_ONCE(insert_struct(&my_foo));
19 ...
20
21 int lookup3(int key)
22 {
23   struct foo *p;
24   int data;
25
26   rcu_read_lock();
27   p = rcu_dereference(gp);
28   if (p != NULL && p->key == key)
29     data = p->data;
30   else if (p == &myfoo)
31     data = p->data * p->data;
32   else
33     data = -1;
34   rcu_read_unlock();
35   return data;
36 }