This is a note to let you know that I've just added the patch titled
tcp: fix tcp_cong_avoid_ai() credit accumulation bug with decreases in w
to the 3.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tcp-fix-tcp_cong_avoid_ai-credit-accumulation-bug-with-decreases-in-w.patch
and it can be found in the queue-3.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Tue Mar 24 11:00:07 CET 2015
From: Neal Cardwell <ncardwell@xxxxxxxxxx>
Date: Tue, 10 Mar 2015 17:17:03 -0400
Subject: tcp: fix tcp_cong_avoid_ai() credit accumulation bug with decreases in w
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;
Patches currently in stable-queue which might be from ncardwell@xxxxxxxxxx are
queue-3.19/tcp-fix-tcp_cong_avoid_ai-credit-accumulation-bug-with-decreases-in-w.patch
queue-3.19/tcp-restore-1.5x-per-rtt-limit-to-cubic-cwnd-growth-in-congestion-avoidance.patch
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