Function rcu_barrier 

pub fn rcu_barrier()

Wait until all in-flight call_rcu() callbacks complete.

Note that this primitive does not necessarily wait for an RCU grace period to complete. For example, if there are no RCU callbacks queued anywhere in the system, then rcu_barrier() is within its rights to return immediately, without waiting for anything, much less an RCU grace period. In fact, rcu_barrier() will normally not result in any RCU grace periods beyond those that were already destined to be executed.

In kernels built with CONFIG_RCU_LAZY=y, this function also hurries all pending lazy RCU callbacks.

Note that this is one of the RCU primitives which must not be called in atomic context.