43 		/* Send ACK. Note, we do not put the bucket,  in tcp_timewait_check_oow_rate_limit()
56  *   when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
108 		/* Out of window, send ACK */  in tcp_timewait_state_process()
122 		/* Dup ACK? */  in tcp_timewait_state_process()
123 		if (!th->ack ||  in tcp_timewait_state_process()
169 		/* In window segment, it may be only reset or bare ack. */  in tcp_timewait_state_process()
206 	   old duplicate (i.e. we receive RST in reply to SYN-ACK),  in tcp_timewait_state_process()
211 	if (th->syn && !th->rst && !th->ack && !paws_reject &&  in tcp_timewait_state_process()
232 		if (paws_reject || th->ack)  in tcp_timewait_state_process()
253 	 * so the timewait ack generating code has the key.  in tcp_time_wait_init()
594  * XXX (TFO) - The current impl contains a special check for ack
639 		 * To be more exact, it says that we should send ACK,  in tcp_check_req()
649 		 * Enforce "SYN-ACK" according to figure 8, figure 6  in tcp_check_req()
683 	   and to do that we first verify the ACK (as per RFC793, page  in tcp_check_req()
685 	   To convince ourselves, let us consider a way in which the ACK  in tcp_check_req()
696 		A: sends SYN|ACK, seq=7, ack_seq=8  in tcp_check_req()
697 		B: sends SYN|ACK, seq=7, ack_seq=8  in tcp_check_req()
699 	   So we are now A eating this SYN|ACK, ACK test passes.  So  in tcp_check_req()
701 	   it a bare ACK.  in tcp_check_req()
704 	   bare ACK.  Otherwise, we create an established connection.  Both  in tcp_check_req()
711 	   But generally, we should (RFC lies!) to accept ACK  in tcp_check_req()
723 	 *                  sent (the segment carries an unacceptable ACK) ...  in tcp_check_req()
726 	 * Invalid ACK: reset will be sent by listening socket.  in tcp_check_req()
727 	 * Note that the ACK validity check for a Fast Open socket is done  in tcp_check_req()
737 	 * is essentially ACK extension and too early or too late values  in tcp_check_req()
745 		/* Out of window: send ACK and drop. */  in tcp_check_req()
778 	/* ACK sequence verified above, just make sure ACK is  in tcp_check_req()
779 	 * set.  If ACK not set, just silently drop the packet.  in tcp_check_req()
793 	/* While TCP_DEFER_ACCEPT is active, drop bare ACK. */  in tcp_check_req()
801 	/* OK, ACK is valid, create big socket and  in tcp_check_req()