| From foo@baz Tue Jan 26 21:35:03 PST 2016 |
| From: Neal Cardwell <ncardwell@google.com> |
| Date: Mon, 11 Jan 2016 13:42:43 -0500 |
| Subject: tcp_yeah: don't set ssthresh below 2 |
| |
| From: Neal Cardwell <ncardwell@google.com> |
| |
| [ 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@natalenko.name> |
| Signed-off-by: Neal Cardwell <ncardwell@google.com> |
| Signed-off-by: Yuchung Cheng <ycheng@google.com> |
| Signed-off-by: Eric Dumazet <edumazet@google.com> |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| 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 = { |
