[TCP]: Extend reordering detection to cover CA_Loss partially

This implements more accurately what is stated in sacktag's
overall comment:

  "Both of these heuristics are not used in Loss state, when
   we cannot account for retransmits accurately."

When CA_Loss state is entered, the state changer ensures that
undo_marker is only set if no TCPCB_RETRANS skbs were found,
thus having non-zero undo_marker in CA_Loss basically tells
that the R-bits still accurately reflect the current state
of TCP.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 901240f40688..26713e5d89db 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1511,7 +1511,8 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
 
         tcp_verify_left_out(tp);
 
-        if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss &&
+        if ((reord < tp->fackets_out) &&
+            ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
             (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
                 tcp_update_reordering(sk, tp->fackets_out - reord, 0);