43 		/* Send ACK. Note, we do not put the bucket,  in tcp_timewait_check_oow_rate_limit()
68  *   when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
120 		/* Out of window, send ACK */  in tcp_timewait_state_process()
134 		/* Dup ACK? */  in tcp_timewait_state_process()
135 		if (!th->ack ||  in tcp_timewait_state_process()
182 		/* In window segment, it may be only reset or bare ack. */  in tcp_timewait_state_process()
219 	   old duplicate (i.e. we receive RST in reply to SYN-ACK),  in tcp_timewait_state_process()
224 	if (th->syn && !th->rst && !th->ack && !paws_reject &&  in tcp_timewait_state_process()
245 		if (paws_reject || th->ack)  in tcp_timewait_state_process()
266 	 * so the timewait ack generating code has the key.  in tcp_time_wait_init()
641  * XXX (TFO) - The current impl contains a special check for ack
686 		 * To be more exact, it says that we should send ACK,  in tcp_check_req()
696 		 * Enforce "SYN-ACK" according to figure 8, figure 6  in tcp_check_req()
730 	   and to do that we first verify the ACK (as per RFC793, page  in tcp_check_req()
732 	   To convince ourselves, let us consider a way in which the ACK  in tcp_check_req()
743 		A: sends SYN|ACK, seq=7, ack_seq=8  in tcp_check_req()
744 		B: sends SYN|ACK, seq=7, ack_seq=8  in tcp_check_req()
746 	   So we are now A eating this SYN|ACK, ACK test passes.  So  in tcp_check_req()
748 	   it a bare ACK.  in tcp_check_req()
751 	   bare ACK.  Otherwise, we create an established connection.  Both  in tcp_check_req()
758 	   But generally, we should (RFC lies!) to accept ACK  in tcp_check_req()
770 	 *                  sent (the segment carries an unacceptable ACK) ...  in tcp_check_req()
773 	 * Invalid ACK: reset will be sent by listening socket.  in tcp_check_req()
774 	 * Note that the ACK validity check for a Fast Open socket is done  in tcp_check_req()
784 	 * is essentially ACK extension and too early or too late values  in tcp_check_req()
792 		/* Out of window: send ACK and drop. */  in tcp_check_req()
825 	/* ACK sequence verified above, just make sure ACK is  in tcp_check_req()
826 	 * set.  If ACK not set, just silently drop the packet.  in tcp_check_req()
840 	/* While TCP_DEFER_ACCEPT is active, drop bare ACK. */  in tcp_check_req()
848 	/* OK, ACK is valid, create big socket and  in tcp_check_req()