[TCP]: Congestion control API RTT sampling fix

Commit 164891aadf1721fca4dce473bb0e0998181537c6 broke RTT
sampling of congestion control modules. Inaccurate timestamps
could be fed to them without providing any way for them to
identify such cases. Previously RTT sampler was called only if
FLAG_RETRANS_DATA_ACKED was not set filtering inaccurate
timestamps nicely. In addition, the new behavior could give an
invalid timestamp (zero) to RTT sampler if only skbs with
TCPCB_RETRANS were ACKed. This solves both problems.

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

1 files changed, 3 insertions, 0 deletions

diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c
index 4adc47c55351..b2b2256d3b84 100644
--- a/net/ipv4/tcp_illinois.c
+++ b/net/ipv4/tcp_illinois.c
@@ -90,6 +90,9 @@ static void tcp_illinois_acked(struct sock *sk, u32 pkts_acked, ktime_t last)
 
         ca->acked = pkts_acked;
 
+        if (ktime_equal(last, net_invalid_timestamp()))
+                return;
+
         rtt = ktime_to_us(net_timedelta(last));
 
         /* ignore bogus values, this prevents wraparound in alpha math */