tcp_cubic: fix comparison of jiffies

Jiffies wraps around therefore the correct way to compare is
to use cast to signed value.

Note: cubic is not using full jiffies value on 64 bit arch
because using full unsigned long makes struct bictcp grow too
large for the available ca_priv area.

Includes correction from Sangtae Ha to improve ack train detection.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 71d5f2f29fa6..43bb34c9b8bf 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -342,9 +342,11 @@ static void hystart_update(struct sock *sk, u32 delay)
                 u32 curr_jiffies = jiffies;
 
                 /* first detection parameter - ack-train detection */
-                if (curr_jiffies - ca->last_jiffies <= msecs_to_jiffies(2)) {
+                if ((s32)(curr_jiffies - ca->last_jiffies) <=
+                    msecs_to_jiffies(2)) {
                         ca->last_jiffies = curr_jiffies;
-                        if (curr_jiffies - ca->round_start >= ca->delay_min>>4)
+                        if ((s32) (curr_jiffies - ca->round_start) >
+                            ca->delay_min >> 4)
                                 ca->found |= HYSTART_ACK_TRAIN;
                 }