git: 4b86a24a76a4 - main - tcp: In rack, we must only convert restored rtt when the hostcache does restore them.

[Randall Stewart]

The branch main has been updated by rrs:

URL: https://cgit.FreeBSD.org/src/commit/?id=4b86a24a76a4d58c1d870fcb2252b321f61cb3cc

commit 4b86a24a76a4d58c1d870fcb2252b321f61cb3cc
Author:     Randall Stewart <rrs at FreeBSD.org>
AuthorDate: 2021-05-11 12:15:05 +0000
Commit:     Randall Stewart <rrs at FreeBSD.org>
CommitDate: 2021-05-11 12:15:05 +0000

    tcp: In rack, we must only convert restored rtt when the hostcache does restore them.
    
    Rack now after the previous commit is very careful to translate any
    value in the hostcache for srtt/rttvar into its proper format. However
    there is a snafu here in that if tp->srtt is 0 is the only time that
    the HC will actually restore the srtt. We need to then only convert
    the srtt restored when it is actually restored. We do this by making
    sure it was zero before the call to cc_conn_init and it is non-zero
    afterwards.
    
    Reviewed by:    Michael Tuexen
    Sponsored by: Netflix Inc
    Differential Revision:  https://reviews.freebsd.org/D30213
---
 sys/netinet/tcp_stacks/rack.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/sys/netinet/tcp_stacks/rack.c b/sys/netinet/tcp_stacks/rack.c
index 865e54c90e6a..e6b2ef60cef7 100644
--- a/sys/netinet/tcp_stacks/rack.c
+++ b/sys/netinet/tcp_stacks/rack.c
@@ -6614,14 +6614,17 @@ static void
 rack_cc_conn_init(struct tcpcb *tp)
 {
 	struct tcp_rack *rack;
+	uint32_t srtt;
 
 	rack = (struct tcp_rack *)tp->t_fb_ptr;
-
+	srtt = tp->t_srtt;
 	cc_conn_init(tp);
 	/*
-	 * Now convert to rack's internal format.
+	 * Now convert to rack's internal format,
+	 * if required.
 	 */
-	rack_convert_rtts(tp);
+	if ((srtt == 0) && (tp->t_srtt != 0))
+		rack_convert_rtts(tp);
 	/*
 	 * We want a chance to stay in slowstart as
 	 * we create a connection. TCP spec says that