From eddb362fbb44793cbd9b9fe28f5ac1da617394e9 Mon Sep 17 00:00:00 2001 From: Neal Cardwell Date: Wed, 1 May 2019 20:16:25 -0400 Subject: [PATCH] net-tcp_bbr: v2: adjust skb tx.in_flight upon split in tcp_fragment() When we fragment an skb that has already been sent, we need to update the tx.in_flight for the first skb in the resulting pair ("buff"). Because we were not updating the tx.in_flight, the tx.in_flight value was inconsistent with the pcount of the "buff" skb (tx.in_flight would be too high). That meant that if the "buff" skb was lost, then bbr2_inflight_hi_from_lost_skb() would calculate an inflight_hi value that is too high. This could result in longer queues and higher packet loss. Packetdrill testing verified that without this commit, when the second half of an skb is SACKed and then later the first half of that skb is marked lost, the calculated inflight_hi was incorrect. Effort: net-tcp_bbr Origin-9xx-SHA1: 385f1ddc610798fab2837f9f372857438b25f874 Origin-9xx-SHA1: a0eb099690af net-tcp_bbr: v2: fix tcp_fragment() tx.in_flight recomputation [prod feb 8 2021; use as a fixup] Origin-9xx-SHA1: 885503228153ff0c9114e net-tcp_bbr: v2: introduce tcp_skb_tx_in_flight_is_suspicious() helper for warnings Change-Id: I617f8cab4e9be7a0b8e8d30b047bf8645393354d Signed-off-by: Juhyung Park --- include/net/tcp.h | 15 +++++++++++++++ net/ipv4/tcp_output.c | 26 +++++++++++++++++++++++++- 2 files changed, 40 insertions(+), 1 deletion(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index 0aafdd327..7e462e4fc 100755 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1196,6 +1196,21 @@ void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost, bool is_sack_reneg, struct rate_sample *rs); void tcp_rate_check_app_limited(struct sock *sk); +/* If a retransmit failed due to local qdisc congestion or other local issues, + * then we may have called tcp_set_skb_tso_segs() to increase the number of + * segments in the skb without increasing the tx.in_flight. In all other cases, + * the tx.in_flight should be at least as big as the pcount of the sk_buff. We + * do not have the state to know whether a retransmit failed due to local qdisc + * congestion or other local issues, so to avoid spurious warnings we consider + * that any skb marked lost may have suffered that fate. + */ +static inline bool tcp_skb_tx_in_flight_is_suspicious(u32 skb_pcount, + u32 skb_sacked_flags, + u32 tx_in_flight) +{ + return (skb_pcount > tx_in_flight) && !(skb_sacked_flags & TCPCB_LOST); +} + /* These functions determine how the current flow behaves in respect of SACK * handling. SACK is negotiated with the peer, and therefore it can vary * between different flows. diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index b62d7f9f3..77d7350d5 100755 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1549,7 +1549,7 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue, { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *buff; - int nsize, old_factor; + int nsize, old_factor, inflight_prev; long limit; int nlen; u8 flags; @@ -1627,6 +1627,30 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue, if (diff) tcp_adjust_pcount(sk, skb, diff); + + inflight_prev = TCP_SKB_CB(skb)->tx.in_flight - old_factor; + if (inflight_prev < 0) { + WARN_ONCE(tcp_skb_tx_in_flight_is_suspicious( + old_factor, + TCP_SKB_CB(skb)->sacked, + TCP_SKB_CB(skb)->tx.in_flight), + "inconsistent: tx.in_flight: %u " + "old_factor: %d mss: %u sacked: %u " + "1st pcount: %d 2nd pcount: %d " + "1st len: %u 2nd len: %u ", + TCP_SKB_CB(skb)->tx.in_flight, old_factor, + mss_now, TCP_SKB_CB(skb)->sacked, + tcp_skb_pcount(skb), tcp_skb_pcount(buff), + skb->len, buff->len); + inflight_prev = 0; + } + /* Set 1st tx.in_flight as if 1st were sent by itself: */ + TCP_SKB_CB(skb)->tx.in_flight = inflight_prev + + tcp_skb_pcount(skb); + /* Set 2nd tx.in_flight with new 1st and 2nd pcounts: */ + TCP_SKB_CB(buff)->tx.in_flight = inflight_prev + + tcp_skb_pcount(skb) + + tcp_skb_pcount(buff); } /* Link BUFF into the send queue. */