From 8e995bf14fdb7e33681d5c3312b602fa342b878a Mon Sep 17 00:00:00 2001 From: Kevin Yang Date: Wed, 22 Aug 2018 17:43:16 -0400 Subject: [PATCH] tcp_bbr: apply PROBE_RTT cwnd cap even if acked==0 This commit fixes a corner case where TCP BBR would enter PROBE_RTT mode but not reduce its cwnd. If a TCP receiver ACKed less than one full segment, the number of delivered/acked packets was 0, so that bbr_set_cwnd() would short-circuit and exit early, without cutting cwnd to the value we want for PROBE_RTT. The fix is to instead make sure that even when 0 full packets are ACKed, we do apply all the appropriate caps, including the cap that applies in PROBE_RTT mode. Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control") Signed-off-by: Kevin Yang Signed-off-by: Neal Cardwell Reviewed-by: Yuchung Cheng Reviewed-by: Soheil Hassas Yeganeh Signed-off-by: David S. Miller --- net/ipv4/tcp_bbr.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c index 1d4bdd3b5e4d..02ff2dde9609 100644 --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -420,10 +420,10 @@ static void bbr_set_cwnd(struct sock *sk, const struct rate_sample *rs, { struct tcp_sock *tp = tcp_sk(sk); struct bbr *bbr = inet_csk_ca(sk); - u32 cwnd = 0, target_cwnd = 0; + u32 cwnd = tp->snd_cwnd, target_cwnd = 0; if (!acked) - return; + goto done; /* no packet fully ACKed; just apply caps */ if (bbr_set_cwnd_to_recover_or_restore(sk, rs, acked, &cwnd)) goto done; -- 2.39.5