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authorstephen hemminger <shemminger@vyatta.com>2011-05-04 10:04:56 +0000
committerWilly Tarreau <w@1wt.eu>2014-05-19 07:54:28 +0200
commitb7daa2a2f4d09b288026b0c99f86677d513b976d (patch)
tree65b57b1439ff0f003d2eb39ee36d2d3143dd1be7
parent18fbf564ddc8a54e5b22961cb50ece22b50cbfba (diff)
downloadlinux-linaro-stable-b7daa2a2f4d09b288026b0c99f86677d513b976d.tar.gz
tcp_cubic: limit delayed_ack ratio to prevent divide error
TCP Cubic keeps a metric that estimates the amount of delayed acknowledgements to use in adjusting the window. If an abnormally large number of packets are acknowledged at once, then the update could wrap and reach zero. This kind of ACK could only happen when there was a large window and huge number of ACK's were lost. This patch limits the value of delayed ack ratio. The choice of 32 is just a conservative value since normally it should be range of 1 to 4 packets. Signed-off-by: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: David S. Miller <davem@davemloft.net> (cherry picked from commit b9f47a3aaeabdce3b42829bbb27765fa340f76ba) [wt: in 2.6.32, this fix is needed for the next one] Signed-off-by: Willy Tarreau <w@1wt.eu>
-rw-r--r--net/ipv4/tcp_cubic.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 0d41c2657f45..1b6b8c2f9fa0 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -90,6 +90,7 @@ struct bictcp {
u32 ack_cnt; /* number of acks */
u32 tcp_cwnd; /* estimated tcp cwnd */
#define ACK_RATIO_SHIFT 4
+#define ACK_RATIO_LIMIT (32u << ACK_RATIO_SHIFT)
u16 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
u8 sample_cnt; /* number of samples to decide curr_rtt */
u8 found; /* the exit point is found? */
@@ -379,8 +380,12 @@ static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
u32 delay;
if (icsk->icsk_ca_state == TCP_CA_Open) {
- cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
- ca->delayed_ack += cnt;
+ u32 ratio = ca->delayed_ack;
+
+ ratio -= ca->delayed_ack >> ACK_RATIO_SHIFT;
+ ratio += cnt;
+
+ ca->delayed_ack = min(ratio, ACK_RATIO_LIMIT);
}
/* Some calls are for duplicates without timetamps */