3.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Neal Cardwell <ncardwell@xxxxxxxxxx>
[ Upstream commit 9949afa42be0b76f5832db112ce51bb6b35b2abb ]
The recent change to tcp_cong_avoid_ai() to handle stretch ACKs
introduced a bug where snd_cwnd_cnt could accumulate a very large
value while w was large, and then if w was reduced snd_cwnd could be
incremented by a large delta, leading to a large burst and high packet
loss. This was tickled when CUBIC's bictcp_update() sets "ca->cnt =
100 * cwnd".
This bug crept in while preparing the upstream version of
814d488c6126.
Testing: This patch has been tested in datacenter netperf transfers
and live youtube.com and google.com servers.
Fixes: 814d488c6126 ("tcp: fix the timid additive increase on stretch ACKs")
Signed-off-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: Yuchung Cheng <ycheng@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/tcp_cong.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -309,6 +309,12 @@ EXPORT_SYMBOL_GPL(tcp_slow_start);
*/
void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
{
+ /* If credits accumulated at a higher w, apply them gently now. */
+ if (tp->snd_cwnd_cnt >= w) {
+ tp->snd_cwnd_cnt = 0;
+ tp->snd_cwnd++;
+ }
+
tp->snd_cwnd_cnt += acked;
if (tp->snd_cwnd_cnt >= w) {
u32 delta = tp->snd_cwnd_cnt / w;
--
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