From: Yuchung Cheng <ycheng@xxxxxxxxxx> commit 44abafc4cc094214a99f860f778c48ecb23422fc upstream. When the sender switches its congestion control during loss recovery, if the recovery is spurious then it may incorrectly revert cwnd and ssthresh to the older values set by a previous congestion control. Consider a congestion control (like BBR) that does not use ssthresh and keeps it infinite: the connection may incorrectly revert cwnd to an infinite value when switching from BBR to another congestion control. This patch fixes it by disallowing such cwnd undo operation upon switching congestion control. Note that undo_marker is not reset s.t. the packets that were incorrectly marked lost would be corrected. We only avoid undoing the cwnd in tcp_undo_cwnd_reduction(). Signed-off-by: Yuchung Cheng <ycheng@xxxxxxxxxx> Signed-off-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx> Signed-off-by: Neal Cardwell <ncardwell@xxxxxxxxxx> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Willy Tarreau <w@xxxxxx> --- net/ipv4/tcp_cong.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index 019c238..2ca6c08 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -95,6 +95,7 @@ void tcp_init_congestion_control(struct sock *sk) rcu_read_unlock(); } + tcp_sk(sk)->prior_ssthresh = 0; if (icsk->icsk_ca_ops->init) icsk->icsk_ca_ops->init(sk); } -- 2.8.0.rc2.1.gbe9624a