void ipc_rcu_putref(void *ptr, void (*func)(struct rcu_head *head))
{
	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;

	if (!atomic_dec_and_test(&p->refcount))
		return;

	call_rcu(&p->rcu, func);
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.