4.9-stable review patch. If anyone has any objections, please let me know.
------------------ From: Yuchung Cheng <[email protected]> [ Upstream commit 44abafc4cc094214a99f860f778c48ecb23422fc ] 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 <[email protected]> Signed-off-by: Soheil Hassas Yeganeh <[email protected]> Signed-off-by: Neal Cardwell <[email protected]> Signed-off-by: Eric Dumazet <[email protected]> Signed-off-by: David S. Miller <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- net/ipv4/tcp_cong.c | 1 + 1 file changed, 1 insertion(+) --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -179,6 +179,7 @@ void tcp_init_congestion_control(struct { const struct inet_connection_sock *icsk = inet_csk(sk); + tcp_sk(sk)->prior_ssthresh = 0; if (icsk->icsk_ca_ops->init) icsk->icsk_ca_ops->init(sk); if (tcp_ca_needs_ecn(sk))
