This is a note to let you know that I've just added the patch titled
tcp_yeah: don't set ssthresh below 2
to the 4.4-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_yeah-don-t-set-ssthresh-below-2.patch
and it can be found in the queue-4.4 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 Jan 26 21:31:27 PST 2016
From: Neal Cardwell <ncardwell@xxxxxxxxxx>
Date: Mon, 11 Jan 2016 13:42:43 -0500
Subject: tcp_yeah: don't set ssthresh below 2
From: Neal Cardwell <ncardwell@xxxxxxxxxx>
[ Upstream commit 83d15e70c4d8909d722c0d64747d8fb42e38a48f ]
For tcp_yeah, use an ssthresh floor of 2, the same floor used by Reno
and CUBIC, per RFC 5681 (equation 4).
tcp_yeah_ssthresh() was sometimes returning a 0 or negative ssthresh
value if the intended reduction is as big or bigger than the current
cwnd. Congestion control modules should never return a zero or
negative ssthresh. A zero ssthresh generally results in a zero cwnd,
causing the connection to stall. A negative ssthresh value will be
interpreted as a u32 and will set a target cwnd for PRR near 4
billion.
Oleksandr Natalenko reported that a system using tcp_yeah with ECN
could see a warning about a prior_cwnd of 0 in
tcp_cwnd_reduction(). Testing verified that this was due to
tcp_yeah_ssthresh() misbehaving in this way.
Reported-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
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_yeah.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/ipv4/tcp_yeah.c
+++ b/net/ipv4/tcp_yeah.c
@@ -219,7 +219,7 @@ static u32 tcp_yeah_ssthresh(struct sock
yeah->fast_count = 0;
yeah->reno_count = max(yeah->reno_count>>1, 2U);
- return tp->snd_cwnd - reduction;
+ return max_t(int, tp->snd_cwnd - reduction, 2);
}
static struct tcp_congestion_ops tcp_yeah __read_mostly = {
Patches currently in stable-queue which might be from ncardwell@xxxxxxxxxx are
queue-4.4/tcp_yeah-don-t-set-ssthresh-below-2.patch
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