Commit 83d15e70 authored by Neal Cardwell's avatar Neal Cardwell Committed by David S. Miller
Browse files

tcp_yeah: don't set ssthresh below 2

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

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: default avatarOleksandr Natalenko <>
Signed-off-by: default avatarNeal Cardwell <>
Signed-off-by: default avatarYuchung Cheng <>
Signed-off-by: default avatarEric Dumazet <>
Signed-off-by: default avatarDavid S. Miller <>
parent 649621e3
...@@ -219,7 +219,7 @@ static u32 tcp_yeah_ssthresh(struct sock *sk) ...@@ -219,7 +219,7 @@ static u32 tcp_yeah_ssthresh(struct sock *sk)
yeah->fast_count = 0; yeah->fast_count = 0;
yeah->reno_count = max(yeah->reno_count>>1, 2U); 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 = { static struct tcp_congestion_ops tcp_yeah __read_mostly = {
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