// SPDX-License-Identifier: GPL-2.0 #include <linux/tcp.h> #include <net/tcp.h> static bool tcp_rack_sent_after(u64 t1, u64 t2, u32 seq1, u32 seq2) { return t1 > t2 || (t1 == t2 && after(seq1, seq2)); } static u32 tcp_rack_reo_wnd(const struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); if (!tp->reord_seen) { /* If reordering has not been observed, be aggressive during * the recovery or starting the recovery by DUPACK threshold. */ if (inet_csk(sk)->icsk_ca_state >= TCP_CA_Recovery) return 0; if (tp->sacked_out >= tp->reordering && !(sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_NO_DUPTHRESH)) return 0; } /* To be more reordering resilient, allow min_rtt/4 settling delay. * Use min_rtt instead of the smoothed RTT because reordering is * often a path property and less related to queuing or delayed ACKs. * Upon receiving DSACKs, linearly increase the window up to the * smoothed RTT. */ return min((tcp_min_rtt(tp) >> 2) * tp->rack.reo_wnd_steps, tp->srtt_us >> 3); } s32 tcp_rack_skb_timeout(struct tcp_sock *tp, struct sk_buff *skb, u32 reo_wnd) { return tp->rack.rtt_us + reo_wnd - tcp_stamp_us_delta(tp->tcp_mstamp, tcp_skb_timestamp_us(skb)); } /* RACK loss detection (IETF draft draft-ietf-tcpm-rack-01): * * Marks a packet lost, if some packet sent later has been (s)acked. * The underlying idea is similar to the traditional dupthresh and FACK * but they look at different metrics: * * dupthresh: 3 OOO packets delivered (packet count) * FACK: sequence delta to highest sacked sequence (sequence space) * RACK: sent time delta to the latest delivered packet (time domain) * * The advantage of RACK is it applies to both original and retransmitted * packet and therefore is robust against tail losses. Another advantage * is being more resilient to reordering by simply allowing some * "settling delay", instead of tweaking the dupthresh. * * When tcp_rack_detect_loss() detects some packets are lost and we * are not already in the CA_Recovery state, either tcp_rack_reo_timeout() * or tcp_time_to_recover()'s "Trick#1: the loss is proven" code path will * make us enter the CA_Recovery state. */ static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb, *n; u32 reo_wnd; *reo_timeout = 0; reo_wnd = tcp_rack_reo_wnd(sk); list_for_each_entry_safe(skb, n, &tp->tsorted_sent_queue, tcp_tsorted_anchor) { struct tcp_skb_cb *scb = TCP_SKB_CB(skb); s32 remaining; /* Skip ones marked lost but not yet retransmitted */ if ((scb->sacked & TCPCB_LOST) && !(scb->sacked & TCPCB_SACKED_RETRANS)) continue; if (!tcp_rack_sent_after(tp->rack.mstamp, tcp_skb_timestamp_us(skb), tp->rack.end_seq, scb->end_seq)) break; /* A packet is lost if it has not been s/acked beyond * the recent RTT plus the reordering window. */ remaining = tcp_rack_skb_timeout(tp, skb, reo_wnd); if (remaining <= 0) { tcp_mark_skb_lost(sk, skb); list_del_init(&skb->tcp_tsorted_anchor); } else { /* Record maximum wait time */ *reo_timeout = max_t(u32, *reo_timeout, remaining); } } } bool tcp_rack_mark_lost(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); u32 timeout; if (!tp->rack.advanced) return false; /* Reset the advanced flag to avoid unnecessary queue scanning */ tp->rack.advanced = 0; tcp_rack_detect_loss(sk, &timeout); if (timeout) { timeout = usecs_to_jiffies(timeout) + TCP_TIMEOUT_MIN; inet_csk_reset_xmit_timer(sk, ICSK_TIME_REO_TIMEOUT, timeout, inet_csk(sk)->icsk_rto); } return !!timeout; } /* Record the most recently (re)sent time among the (s)acked packets * This is "Step 3: Advance RACK.xmit_time and update RACK.RTT" from * draft-cheng-tcpm-rack-00.txt */ void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq, u64 xmit_time) { u32 rtt_us; rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, xmit_time); if (rtt_us < tcp_min_rtt(tp) && (sacked & TCPCB_RETRANS)) { /* If the sacked packet was retransmitted, it's ambiguous * whether the retransmission or the original (or the prior * retransmission) was sacked. * * If the original is lost, there is no ambiguity. Otherwise * we assume the original can be delayed up to aRTT + min_rtt. * the aRTT term is bounded by the fast recovery or timeout, * so it's at least one RTT (i.e., retransmission is at least * an RTT later). */ return; } tp->rack.advanced = 1; tp->rack.rtt_us = rtt_us; if (tcp_rack_sent_after(xmit_time, tp->rack.mstamp, end_seq, tp->rack.end_seq)) { tp->rack.mstamp = xmit_time; tp->rack.end_seq = end_seq; } } /* We have waited long enough to accommodate reordering. Mark the expired * packets lost and retransmit them. */ void tcp_rack_reo_timeout(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); u32 timeout, prior_inflight; u32 lost = tp->lost; prior_inflight = tcp_packets_in_flight(tp); tcp_rack_detect_loss(sk, &timeout); if (prior_inflight != tcp_packets_in_flight(tp)) { if (inet_csk(sk)->icsk_ca_state != TCP_CA_Recovery) { tcp_enter_recovery(sk, false); if (!inet_csk(sk)->icsk_ca_ops->cong_control) tcp_cwnd_reduction(sk, 1, tp->lost - lost, 0); } tcp_xmit_retransmit_queue(sk); } if (inet_csk(sk)->icsk_pending != ICSK_TIME_RETRANS) tcp_rearm_rto(sk); } /* Updates the RACK's reo_wnd based on DSACK and no. of recoveries. * * If a DSACK is received that seems like it may have been due to reordering * triggering fast recovery, increment reo_wnd by min_rtt/4 (upper bounded * by srtt), since there is possibility that spurious retransmission was * due to reordering delay longer than reo_wnd. * * Persist the current reo_wnd value for TCP_RACK_RECOVERY_THRESH (16) * no. of successful recoveries (accounts for full DSACK-based loss * recovery undo). After that, reset it to default (min_rtt/4). * * At max, reo_wnd is incremented only once per rtt. So that the new * DSACK on which we are reacting, is due to the spurious retx (approx) * after the reo_wnd has been updated last time. * * reo_wnd is tracked in terms of steps (of min_rtt/4), rather than * absolute value to account for change in rtt. */ void tcp_rack_update_reo_wnd(struct sock *sk, struct rate_sample *rs) { struct tcp_sock *tp = tcp_sk(sk); if (sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_STATIC_REO_WND || !rs->prior_delivered) return; /* Disregard DSACK if a rtt has not passed since we adjusted reo_wnd */ if (before(rs->prior_delivered, tp->rack.last_delivered)) tp->rack.dsack_seen = 0; /* Adjust the reo_wnd if update is pending */ if (tp->rack.dsack_seen) { tp->rack.reo_wnd_steps = min_t(u32, 0xFF, tp->rack.reo_wnd_steps + 1); tp->rack.dsack_seen = 0; tp->rack.last_delivered = tp->delivered; tp->rack.reo_wnd_persist = TCP_RACK_RECOVERY_THRESH; } else if (!tp->rack.reo_wnd_persist) { tp->rack.reo_wnd_steps = 1; } } /* RFC6582 NewReno recovery for non-SACK connection. It simply retransmits * the next unacked packet upon receiving * a) three or more DUPACKs to start the fast recovery * b) an ACK acknowledging new data during the fast recovery. */ void tcp_newreno_mark_lost(struct sock *sk, bool snd_una_advanced) { const u8 state = inet_csk(sk)->icsk_ca_state; struct tcp_sock *tp = tcp_sk(sk); if ((state < TCP_CA_Recovery && tp->sacked_out >= tp->reordering) || (state == TCP_CA_Recovery && snd_una_advanced)) { struct sk_buff *skb = tcp_rtx_queue_head(sk); u32 mss; if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) return; mss = tcp_skb_mss(skb); if (tcp_skb_pcount(skb) > 1 && skb->len > mss) tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb, mss, mss, GFP_ATOMIC); tcp_mark_skb_lost(sk, skb); } }