1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/tcp.h> 3 #include <net/tcp.h> 4 5 void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb) 6 { 7 struct tcp_sock *tp = tcp_sk(sk); 8 9 tcp_skb_mark_lost_uncond_verify(tp, skb); 10 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) { 11 /* Account for retransmits that are lost again */ 12 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; 13 tp->retrans_out -= tcp_skb_pcount(skb); 14 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT, 15 tcp_skb_pcount(skb)); 16 } 17 } 18 19 static bool tcp_rack_sent_after(u64 t1, u64 t2, u32 seq1, u32 seq2) 20 { 21 return t1 > t2 || (t1 == t2 && after(seq1, seq2)); 22 } 23 24 static u32 tcp_rack_reo_wnd(const struct sock *sk) 25 { 26 struct tcp_sock *tp = tcp_sk(sk); 27 28 if (!tp->reord_seen) { 29 /* If reordering has not been observed, be aggressive during 30 * the recovery or starting the recovery by DUPACK threshold. 31 */ 32 if (inet_csk(sk)->icsk_ca_state >= TCP_CA_Recovery) 33 return 0; 34 35 if (tp->sacked_out >= tp->reordering && 36 !(sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_NO_DUPTHRESH)) 37 return 0; 38 } 39 40 /* To be more reordering resilient, allow min_rtt/4 settling delay. 41 * Use min_rtt instead of the smoothed RTT because reordering is 42 * often a path property and less related to queuing or delayed ACKs. 43 * Upon receiving DSACKs, linearly increase the window up to the 44 * smoothed RTT. 45 */ 46 return min((tcp_min_rtt(tp) >> 2) * tp->rack.reo_wnd_steps, 47 tp->srtt_us >> 3); 48 } 49 50 s32 tcp_rack_skb_timeout(struct tcp_sock *tp, struct sk_buff *skb, u32 reo_wnd) 51 { 52 return tp->rack.rtt_us + reo_wnd - 53 tcp_stamp_us_delta(tp->tcp_mstamp, skb->skb_mstamp); 54 } 55 56 /* RACK loss detection (IETF draft draft-ietf-tcpm-rack-01): 57 * 58 * Marks a packet lost, if some packet sent later has been (s)acked. 59 * The underlying idea is similar to the traditional dupthresh and FACK 60 * but they look at different metrics: 61 * 62 * dupthresh: 3 OOO packets delivered (packet count) 63 * FACK: sequence delta to highest sacked sequence (sequence space) 64 * RACK: sent time delta to the latest delivered packet (time domain) 65 * 66 * The advantage of RACK is it applies to both original and retransmitted 67 * packet and therefore is robust against tail losses. Another advantage 68 * is being more resilient to reordering by simply allowing some 69 * "settling delay", instead of tweaking the dupthresh. 70 * 71 * When tcp_rack_detect_loss() detects some packets are lost and we 72 * are not already in the CA_Recovery state, either tcp_rack_reo_timeout() 73 * or tcp_time_to_recover()'s "Trick#1: the loss is proven" code path will 74 * make us enter the CA_Recovery state. 75 */ 76 static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout) 77 { 78 struct tcp_sock *tp = tcp_sk(sk); 79 struct sk_buff *skb, *n; 80 u32 reo_wnd; 81 82 *reo_timeout = 0; 83 reo_wnd = tcp_rack_reo_wnd(sk); 84 list_for_each_entry_safe(skb, n, &tp->tsorted_sent_queue, 85 tcp_tsorted_anchor) { 86 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 87 s32 remaining; 88 89 /* Skip ones marked lost but not yet retransmitted */ 90 if ((scb->sacked & TCPCB_LOST) && 91 !(scb->sacked & TCPCB_SACKED_RETRANS)) 92 continue; 93 94 if (!tcp_rack_sent_after(tp->rack.mstamp, skb->skb_mstamp, 95 tp->rack.end_seq, scb->end_seq)) 96 break; 97 98 /* A packet is lost if it has not been s/acked beyond 99 * the recent RTT plus the reordering window. 100 */ 101 remaining = tcp_rack_skb_timeout(tp, skb, reo_wnd); 102 if (remaining <= 0) { 103 tcp_mark_skb_lost(sk, skb); 104 list_del_init(&skb->tcp_tsorted_anchor); 105 } else { 106 /* Record maximum wait time */ 107 *reo_timeout = max_t(u32, *reo_timeout, remaining); 108 } 109 } 110 } 111 112 void tcp_rack_mark_lost(struct sock *sk) 113 { 114 struct tcp_sock *tp = tcp_sk(sk); 115 u32 timeout; 116 117 if (!tp->rack.advanced) 118 return; 119 120 /* Reset the advanced flag to avoid unnecessary queue scanning */ 121 tp->rack.advanced = 0; 122 tcp_rack_detect_loss(sk, &timeout); 123 if (timeout) { 124 timeout = usecs_to_jiffies(timeout) + TCP_TIMEOUT_MIN; 125 inet_csk_reset_xmit_timer(sk, ICSK_TIME_REO_TIMEOUT, 126 timeout, inet_csk(sk)->icsk_rto); 127 } 128 } 129 130 /* Record the most recently (re)sent time among the (s)acked packets 131 * This is "Step 3: Advance RACK.xmit_time and update RACK.RTT" from 132 * draft-cheng-tcpm-rack-00.txt 133 */ 134 void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq, 135 u64 xmit_time) 136 { 137 u32 rtt_us; 138 139 rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, xmit_time); 140 if (rtt_us < tcp_min_rtt(tp) && (sacked & TCPCB_RETRANS)) { 141 /* If the sacked packet was retransmitted, it's ambiguous 142 * whether the retransmission or the original (or the prior 143 * retransmission) was sacked. 144 * 145 * If the original is lost, there is no ambiguity. Otherwise 146 * we assume the original can be delayed up to aRTT + min_rtt. 147 * the aRTT term is bounded by the fast recovery or timeout, 148 * so it's at least one RTT (i.e., retransmission is at least 149 * an RTT later). 150 */ 151 return; 152 } 153 tp->rack.advanced = 1; 154 tp->rack.rtt_us = rtt_us; 155 if (tcp_rack_sent_after(xmit_time, tp->rack.mstamp, 156 end_seq, tp->rack.end_seq)) { 157 tp->rack.mstamp = xmit_time; 158 tp->rack.end_seq = end_seq; 159 } 160 } 161 162 /* We have waited long enough to accommodate reordering. Mark the expired 163 * packets lost and retransmit them. 164 */ 165 void tcp_rack_reo_timeout(struct sock *sk) 166 { 167 struct tcp_sock *tp = tcp_sk(sk); 168 u32 timeout, prior_inflight; 169 170 prior_inflight = tcp_packets_in_flight(tp); 171 tcp_rack_detect_loss(sk, &timeout); 172 if (prior_inflight != tcp_packets_in_flight(tp)) { 173 if (inet_csk(sk)->icsk_ca_state != TCP_CA_Recovery) { 174 tcp_enter_recovery(sk, false); 175 if (!inet_csk(sk)->icsk_ca_ops->cong_control) 176 tcp_cwnd_reduction(sk, 1, 0); 177 } 178 tcp_xmit_retransmit_queue(sk); 179 } 180 if (inet_csk(sk)->icsk_pending != ICSK_TIME_RETRANS) 181 tcp_rearm_rto(sk); 182 } 183 184 /* Updates the RACK's reo_wnd based on DSACK and no. of recoveries. 185 * 186 * If DSACK is received, increment reo_wnd by min_rtt/4 (upper bounded 187 * by srtt), since there is possibility that spurious retransmission was 188 * due to reordering delay longer than reo_wnd. 189 * 190 * Persist the current reo_wnd value for TCP_RACK_RECOVERY_THRESH (16) 191 * no. of successful recoveries (accounts for full DSACK-based loss 192 * recovery undo). After that, reset it to default (min_rtt/4). 193 * 194 * At max, reo_wnd is incremented only once per rtt. So that the new 195 * DSACK on which we are reacting, is due to the spurious retx (approx) 196 * after the reo_wnd has been updated last time. 197 * 198 * reo_wnd is tracked in terms of steps (of min_rtt/4), rather than 199 * absolute value to account for change in rtt. 200 */ 201 void tcp_rack_update_reo_wnd(struct sock *sk, struct rate_sample *rs) 202 { 203 struct tcp_sock *tp = tcp_sk(sk); 204 205 if (sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_STATIC_REO_WND || 206 !rs->prior_delivered) 207 return; 208 209 /* Disregard DSACK if a rtt has not passed since we adjusted reo_wnd */ 210 if (before(rs->prior_delivered, tp->rack.last_delivered)) 211 tp->rack.dsack_seen = 0; 212 213 /* Adjust the reo_wnd if update is pending */ 214 if (tp->rack.dsack_seen) { 215 tp->rack.reo_wnd_steps = min_t(u32, 0xFF, 216 tp->rack.reo_wnd_steps + 1); 217 tp->rack.dsack_seen = 0; 218 tp->rack.last_delivered = tp->delivered; 219 tp->rack.reo_wnd_persist = TCP_RACK_RECOVERY_THRESH; 220 } else if (!tp->rack.reo_wnd_persist) { 221 tp->rack.reo_wnd_steps = 1; 222 } 223 } 224 225 /* RFC6582 NewReno recovery for non-SACK connection. It simply retransmits 226 * the next unacked packet upon receiving 227 * a) three or more DUPACKs to start the fast recovery 228 * b) an ACK acknowledging new data during the fast recovery. 229 */ 230 void tcp_newreno_mark_lost(struct sock *sk, bool snd_una_advanced) 231 { 232 const u8 state = inet_csk(sk)->icsk_ca_state; 233 struct tcp_sock *tp = tcp_sk(sk); 234 235 if ((state < TCP_CA_Recovery && tp->sacked_out >= tp->reordering) || 236 (state == TCP_CA_Recovery && snd_una_advanced)) { 237 struct sk_buff *skb = tcp_rtx_queue_head(sk); 238 u32 mss; 239 240 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) 241 return; 242 243 mss = tcp_skb_mss(skb); 244 if (tcp_skb_pcount(skb) > 1 && skb->len > mss) 245 tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb, 246 mss, mss, GFP_ATOMIC); 247 248 tcp_skb_mark_lost_uncond_verify(tp, skb); 249 } 250 } 251