rcu: Add comments to final rcu_gp_cleanup() "if" statement

	/* Advance CBs to reduce false positives below. */

	offloaded = rcu_rdp_is_offloaded(rdp);

	if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {

		// We get here if a grace period was needed (“needgp”)

		// and the above call to rcu_accelerate_cbs() did not set

		// the RCU_GP_FLAG_INIT bit in ->gp_state (which records

		// the need for another grace period).  The purpose

		// of the “offloaded” check is to avoid invoking

		// rcu_accelerate_cbs() on an offloaded CPU because we do not

		// hold the ->nocb_lock needed to safely access an offloaded

		// ->cblist.  We do not want to acquire that lock because

		// it can be heavily contended during callback floods.

		WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);

		WRITE_ONCE(rcu_state.gp_req_activity, jiffies);

		trace_rcu_grace_period(rcu_state.name,

				       rcu_state.gp_seq,

				       TPS("newreq"));

		trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq"));

	} else {

		WRITE_ONCE(rcu_state.gp_flags,

			   rcu_state.gp_flags & RCU_GP_FLAG_INIT);

		// We get here either if there is no need for an

		// additional grace period or if rcu_accelerate_cbs() has

		// already set the RCU_GP_FLAG_INIT bit in ->gp_flags. 

		// So all we need to do is to clear all of the other

		// ->gp_flags bits.

		WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT);

	}

	raw_spin_unlock_irq_rcu_node(rnp);