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Commit 796f82ea authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: fix delayed acks behavior for SO_RCVLOWAT 



We should not delay acks if there are not enough bytes
in receive queue to satisfy SO_RCVLOWAT.

Since [E]POLLIN event is not going to be generated, there is little
hope for a delayed ack to be useful.

In fact, delaying ACK prevents sender from completing
the transfer.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d1361840

net/ipv4/tcp_input.c

+5 −2
Original line number Diff line number Diff line
@@ -5026,9 +5026,12 @@ static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible) 
	    /* More than one full frame received... */

	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&

	     /* ... and right edge of window advances far enough.

	      * (tcp_recvmsg() will send ACK otherwise). Or...

	      * (tcp_recvmsg() will send ACK otherwise).

	      * If application uses SO_RCVLOWAT, we want send ack now if

	      * we have not received enough bytes to satisfy the condition.

	      */

	     __tcp_select_window(sk) >= tp->rcv_wnd) ||

	    (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||

	     __tcp_select_window(sk) >= tp->rcv_wnd)) ||

	    /* We ACK each frame or... */

	    tcp_in_quickack_mode(sk) ||

	    /* We have out of order data. */