Commit 905ae1b1 authored by Yuchung Cheng's avatar Yuchung Cheng Committed by Greg Kroah-Hartman

tcp: disallow cwnd undo when switching congestion control


[ Upstream commit 44abafc4 ]

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: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent fb62fe10
...@@ -180,6 +180,7 @@ void tcp_init_congestion_control(struct sock *sk) ...@@ -180,6 +180,7 @@ void tcp_init_congestion_control(struct sock *sk)
{ {
const struct inet_connection_sock *icsk = inet_csk(sk); const struct inet_connection_sock *icsk = inet_csk(sk);
tcp_sk(sk)->prior_ssthresh = 0;
if (icsk->icsk_ca_ops->init) if (icsk->icsk_ca_ops->init)
icsk->icsk_ca_ops->init(sk); icsk->icsk_ca_ops->init(sk);
if (tcp_ca_needs_ecn(sk)) if (tcp_ca_needs_ecn(sk))
......
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