From 9dc274151a548ffd215caecec5a8872db8799447 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 20 Jul 2012 05:02:33 +0000 Subject: tcp: fix ABC in tcp_slow_start() When/if sysctl_tcp_abc > 1, we expect to increase cwnd by 2 if the received ACK acknowledges more than 2*MSS bytes, in tcp_slow_start() Problem is this RFC 3465 statement is not correctly coded, as the while () loop increases snd_cwnd one by one. Add a new variable to avoid this off-by one error. Signed-off-by: Eric Dumazet Cc: Tom Herbert Cc: Yuchung Cheng Cc: Neal Cardwell Cc: Nandita Dukkipati Cc: John Heffner Cc: Stephen Hemminger Acked-by: Yuchung Cheng Acked-by: Neal Cardwell Signed-off-by: David S. Miller --- net/ipv4/tcp_cong.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'net/ipv4') diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index 04dbd7ae7c62..4d4db16e336e 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -307,6 +307,7 @@ EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited); void tcp_slow_start(struct tcp_sock *tp) { int cnt; /* increase in packets */ + unsigned int delta = 0; /* RFC3465: ABC Slow start * Increase only after a full MSS of bytes is acked @@ -333,9 +334,9 @@ void tcp_slow_start(struct tcp_sock *tp) tp->snd_cwnd_cnt += cnt; while (tp->snd_cwnd_cnt >= tp->snd_cwnd) { tp->snd_cwnd_cnt -= tp->snd_cwnd; - if (tp->snd_cwnd < tp->snd_cwnd_clamp) - tp->snd_cwnd++; + delta++; } + tp->snd_cwnd = min(tp->snd_cwnd + delta, tp->snd_cwnd_clamp); } EXPORT_SYMBOL_GPL(tcp_slow_start); -- cgit v1.2.3-58-ga151