From 882bebaaca4bb1484078d44ef011f918c0e1e14e Mon Sep 17 00:00:00 2001 From: Ilpo Järvinen Date: Mon, 7 Apr 2008 22:33:07 -0700 Subject: [TCP]: tcp_simple_retransmit can cause S+L MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This fixes Bugzilla #10384 tcp_simple_retransmit does L increment without any checking whatsoever for overflowing S+L when Reno is in use. The simplest scenario I can currently think of is rather complex in practice (there might be some more straightforward cases though). Ie., if mss is reduced during mtu probing, it may end up marking everything lost and if some duplicate ACKs arrived prior to that sacked_out will be non-zero as well, leading to S+L > packets_out, tcp_clean_rtx_queue on the next cumulative ACK or tcp_fastretrans_alert on the next duplicate ACK will fix the S counter. More straightforward (but questionable) solution would be to just call tcp_reset_reno_sack() in tcp_simple_retransmit but it would negatively impact the probe's retransmission, ie., the retransmissions would not occur if some duplicate ACKs had arrived. So I had to add reno sacked_out reseting to CA_Loss state when the first cumulative ACK arrives (this stale sacked_out might actually be the explanation for the reports of left_out overflows in kernel prior to 2.6.23 and S+L overflow reports of 2.6.24). However, this alone won't be enough to fix kernel before 2.6.24 because it is building on top of the commit 1b6d427bb7e ([TCP]: Reduce sacked_out with reno when purging write_queue) to keep the sacked_out from overflowing. Signed-off-by: Ilpo Järvinen Reported-by: Alessandro Suardi Signed-off-by: David S. Miller --- include/net/tcp.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include') diff --git a/include/net/tcp.h b/include/net/tcp.h index 7de4ea3a04d9..4fd3eb2f8ec2 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -752,6 +752,8 @@ static inline unsigned int tcp_packets_in_flight(const struct tcp_sock *tp) return tp->packets_out - tcp_left_out(tp) + tp->retrans_out; } +extern int tcp_limit_reno_sacked(struct tcp_sock *tp); + /* If cwnd > ssthresh, we may raise ssthresh to be half-way to cwnd. * The exception is rate halving phase, when cwnd is decreasing towards * ssthresh. -- cgit v1.2.3-58-ga151