Commit ed254971 authored Aug 01, 2017 by Yuchung Cheng Committed by David S. Miller Aug 02, 2017

tcp: avoid setting cwnd to invalid ssthresh after cwnd reduction states



If the sender switches the congestion control during ECN-triggered
cwnd-reduction state (CA_CWR), upon exiting recovery cwnd is set to
the ssthresh value calculated by the previous congestion control. If
the previous congestion control is BBR that always keep ssthresh
to TCP_INIFINITE_SSTHRESH, cwnd ends up being infinite. The safe
step is to avoid assigning invalid ssthresh value when recovery ends.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 4d96f12a

net/ipv4/tcp_input.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -2520,8 +2520,8 @@ static inline void tcp_end_cwnd_reduction(struct sock *sk)
		return;

		/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
		if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR \|\|
		(tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
		if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
		(inet_csk(sk)->icsk_ca_state == TCP_CA_CWR \|\| tp->undo_marker)) {
		tp->snd_cwnd = tp->snd_ssthresh;
		tp->snd_cwnd_stamp = tcp_jiffies32;
		}

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