From: Eric Dumazet Date: Mon, 16 Apr 2018 17:33:36 +0000 (-0700) Subject: tcp: fix delayed acks behavior for SO_RCVLOWAT X-Git-Tag: for-linus-20180616~56^2~455^2~3 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=796f82eafcd96629c2f9a0332dbb4f474854aaf8;p=linux-block.git 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: Eric Dumazet Signed-off-by: David S. Miller --- diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 367def6ddeda..d854363a4387 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -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. */