From: Liu Yu <allanliuyu@gmail•com>
To: eric.dumazet@gmail•com, ncardwell@google•com,
shemminger@vyatta•com, "David S. Miller" <davem@davemloft•net>
Cc: netdev@vger•kernel.org
Subject: [PATCH] tcp_cubic: fix the range of delayed_ack
Date: Wed, 30 Apr 2014 17:34:09 +0800 [thread overview]
Message-ID: <5360C391.2040202@gmail.com> (raw)
From: Liu Yu <allanyuliu@tencent•com>
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@vyatta•com>
Signed-off-by: Liu Yu <allanyuliu@tencent•com>
---
net/ipv4/tcp_cubic.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 8bf2245..b4f1b29 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -409,7 +409,7 @@ 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 */
--
1.7.1
next reply other threads:[~2014-04-30 9:32 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-30 9:34 Liu Yu [this message]
2014-04-30 14:18 ` [PATCH] tcp_cubic: fix the range of delayed_ack Eric Dumazet
2014-04-30 14:53 ` Neal Cardwell
2014-04-30 20:16 ` David Miller
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