Wait until a grace period has elapsed.
void synchronize_rcu(void);
void
no arguments
Control will return to the caller some time after a full grace period has elapsed, in other words after all currently executing RCU read-side critical sections have completed. Note, however, that upon return from synchronize_rcu, the caller might well be executing concurrently with new RCU read-side critical sections that began while synchronize_rcu was waiting. RCU read-side critical sections are delimited by rcu_read_lock and rcu_read_unlock, and may be nested.
See the description of synchronize_sched for more detailed information on memory ordering guarantees.