static DEFINE_MUTEX(rcu_barrier_mutex);
static struct completion rcu_barrier_completion;
-/* Because of FASTCALL declaration of complete, we use this wrapper */
+/*
+ * Awaken the corresponding synchronize_rcu() instance now that a
+ * grace period has elapsed.
+ */
static void wakeme_after_rcu(struct rcu_head *head)
{
struct rcu_synchronize *rcu;
mutex_lock(&rcu_barrier_mutex);
init_completion(&rcu_barrier_completion);
atomic_set(&rcu_barrier_cpu_count, 0);
+ /*
+ * The queueing of callbacks in all CPUs must be atomic with
+ * respect to RCU, otherwise one CPU may queue a callback,
+ * wait for a grace period, decrement barrier count and call
+ * complete(), while other CPUs have not yet queued anything.
+ * So, we need to make sure that grace periods cannot complete
+ * until all the callbacks are queued.
+ */
+ rcu_read_lock();
on_each_cpu(rcu_barrier_func, NULL, 0, 1);
+ rcu_read_unlock();
wait_for_completion(&rcu_barrier_completion);
mutex_unlock(&rcu_barrier_mutex);
}