git: 9e69e009c86f - stable/12 - tcp: send ACKs when requested

The branch stable/12 has been updated by rscheff:

URL: https://cgit.FreeBSD.org/src/commit/?id=9e69e009c86f259653610f3c337253b79381c7a7

commit 9e69e009c86f259653610f3c337253b79381c7a7
Author:     Michael Tuexen <tuexen@FreeBSD.org>
AuthorDate: 2022-09-22 10:12:11 +0000
Commit:     Richard Scheffenegger <rscheff@FreeBSD.org>
CommitDate: 2022-09-25 08:46:54 +0000

    tcp: send ACKs when requested
    
    When doing Limited Transmit send an ACK when needed by the protocol
    processing (like sending ACKs with a DSACK block).
    
    PR:                     264257
    PR:                     263445
    PR:                     260393
    Reviewed by:            rscheff@
    MFC after:              3 days
    Sponsored by:           Netflix, Inc.
    Differential Revision:  https://reviews.freebsd.org/D36631
    
    (cherry picked from commit 5ae83e0d871bc7cbe4dcc9a33d37eb689e631efe)
---
 sys/netinet/tcp_input.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index 755d645d338c..fd55a5a09369 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -2695,14 +2695,14 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 					    maxseg;
 					/*
 					 * Only call tcp_output when there
-					 * is new data available to be sent.
-					 * Otherwise we would send pure ACKs.
+					 * is new data available to be sent
+					 * or we need to send an ACK.
 					 */
 					SOCKBUF_LOCK(&so->so_snd);
 					avail = sbavail(&so->so_snd) -
 					    (tp->snd_nxt - tp->snd_una);
 					SOCKBUF_UNLOCK(&so->so_snd);
-					if (avail > 0)
+					if (avail > 0 || tp->t_flags & TF_ACKNOW)
 						(void) tp->t_fb->tfb_tcp_output(tp);
 					sent = tp->snd_max - oldsndmax;
 					if (sent > maxseg) {