2.6.32-longterm review patch. If anyone has any objections, please let me know. ------------------ From: Liu Yu <allanyuliu@xxxxxxxxxxx> commit b9f47a3aaeab (tcp_cubic: limit delayed_ack ratio to prevent divide error) try to prevent divide error, but there is still a little chance that delayed_ack can reach zero. In case the param cnt get negative value, then ratio+cnt would overflow and may happen to be zero. As a result, min(ratio, ACK_RATIO_LIMIT) will calculate to be zero. In some old kernels, such as 2.6.32, there is a bug that would pass negative param, which then ultimately leads to this divide error. commit 5b35e1e6e9c (tcp: fix tcp_trim_head() to adjust segment count with skb MSS) fixed the negative param issue. However, it's safe that we fix the range of delayed_ack as well, to make sure we do not hit a divide by zero. CC: Stephen Hemminger <shemminger@xxxxxxxxxx> Signed-off-by: Liu Yu <allanyuliu@xxxxxxxxxxx> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> (cherry picked from commit 0cda345d1b2201dd15591b163e3c92bad5191745) Signed-off-by: Willy Tarreau <w@xxxxxx> --- net/ipv4/tcp_cubic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index 1b6b8c2..db41113 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -385,7 +385,7 @@ static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us) ratio -= ca->delayed_ack >> ACK_RATIO_SHIFT; ratio += cnt; - ca->delayed_ack = min(ratio, ACK_RATIO_LIMIT); + ca->delayed_ack = clamp(ratio, 1U, ACK_RATIO_LIMIT); } /* Some calls are for duplicates without timetamps */ -- 1.7.12.2.21.g234cd45.dirty -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html