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tcp_bbr: apply PROBE_RTT cwnd cap even if acked==0

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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: 0f8782ea14 ("tcp_bbr: add BBR congestion control")
Signed-off-by: Kevin Yang <yyd@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Yuchung Cheng <ycheng@google.com>
Reviewed-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Kevin Yang 2018-08-22 17:43:16 -04:00 committed by David S. Miller
parent 5490b32dce
commit 8e995bf14f
1 changed files with 2 additions and 2 deletions
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4
net/ipv4/tcp_bbr.c
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@ -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;