Date: Wed, 5 Feb 2025 17:58:52 GMT From: Michael Tuexen <tuexen@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: cb9ee81985f2 - stable/13 - tcp: fix the initial CWND when a SYN retransmission happened Message-ID: <202502051758.515HwqC0062108@gitrepo.freebsd.org>
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The branch stable/13 has been updated by tuexen: URL: https://cgit.FreeBSD.org/src/commit/?id=cb9ee81985f2951b94294a87b203181401125769 commit cb9ee81985f2951b94294a87b203181401125769 Author: Michael Tuexen <tuexen@FreeBSD.org> AuthorDate: 2024-11-05 08:52:42 +0000 Commit: Michael Tuexen <tuexen@FreeBSD.org> CommitDate: 2025-02-05 17:57:51 +0000 tcp: fix the initial CWND when a SYN retransmission happened According to RFC 3390 the CWND should be set to one MSS if the SYN or SYN-ACK has been retransmitted. This is handled in the code by setting CWND to 1 and cc_conn_init() translates this to MSS. Unfortunately, cc_cong_signal() was overwriting the special value of 1 in case of a lost SYN, and therefore the initial CWND was not as it was supposed to be. Fix this by not overwriting the special value of 1. Reviewed by: cc, rscheff Sponsored by: Netflix, Inc. Differential Revision: https://reviews.freebsd.org/D47439 (cherry picked from commit 625835c8b5e897e54a1a023788a3a9c3b16631c9) --- sys/netinet/tcp_timer.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/sys/netinet/tcp_timer.c b/sys/netinet/tcp_timer.c index fb021608f7da..4dce11d1d580 100644 --- a/sys/netinet/tcp_timer.c +++ b/sys/netinet/tcp_timer.c @@ -876,7 +876,9 @@ tcp_timer_rexmt(void * xtp) */ tp->t_rtttime = 0; - cc_cong_signal(tp, NULL, CC_RTO); + /* Do not overwrite the snd_cwnd on SYN retransmissions. */ + if (tp->t_state != TCPS_SYN_SENT) + cc_cong_signal(tp, NULL, CC_RTO); NET_EPOCH_ENTER(et); (void) tp->t_fb->tfb_tcp_output(tp); NET_EPOCH_EXIT(et);
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