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, tcp_skb_timestamp_us(skb)); 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, 95 tcp_skb_timestamp_us(skb), 96 tp->rack.end_seq, scb->end_seq)) 97 break; 98 99 /* A packet is lost if it has not been s/acked beyond 100 * the recent RTT plus the reordering window. 101 */ 102 remaining = tcp_rack_skb_timeout(tp, skb, reo_wnd); 103 if (remaining <= 0) { 104 tcp_mark_skb_lost(sk, skb); 105 list_del_init(&skb->tcp_tsorted_anchor); 106 } else { 107 /* Record maximum wait time */ 108 *reo_timeout = max_t(u32, *reo_timeout, remaining); 109 } 110 } 111 } 112 113 void tcp_rack_mark_lost(struct sock *sk) 114 { 115 struct tcp_sock *tp = tcp_sk(sk); 116 u32 timeout; 117 118 if (!tp->rack.advanced) 119 return; 120 121 /* Reset the advanced flag to avoid unnecessary queue scanning */ 122 tp->rack.advanced = 0; 123 tcp_rack_detect_loss(sk, &timeout); 124 if (timeout) { 125 timeout = usecs_to_jiffies(timeout) + TCP_TIMEOUT_MIN; 126 inet_csk_reset_xmit_timer(sk, ICSK_TIME_REO_TIMEOUT, 127 timeout, inet_csk(sk)->icsk_rto); 128 } 129 } 130 131 /* Record the most recently (re)sent time among the (s)acked packets 132 * This is "Step 3: Advance RACK.xmit_time and update RACK.RTT" from 133 * draft-cheng-tcpm-rack-00.txt 134 */ 135 void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq, 136 u64 xmit_time) 137 { 138 u32 rtt_us; 139 140 rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, xmit_time); 141 if (rtt_us < tcp_min_rtt(tp) && (sacked & TCPCB_RETRANS)) { 142 /* If the sacked packet was retransmitted, it's ambiguous 143 * whether the retransmission or the original (or the prior 144 * retransmission) was sacked. 145 * 146 * If the original is lost, there is no ambiguity. Otherwise 147 * we assume the original can be delayed up to aRTT + min_rtt. 148 * the aRTT term is bounded by the fast recovery or timeout, 149 * so it's at least one RTT (i.e., retransmission is at least 150 * an RTT later). 151 */ 152 return; 153 } 154 tp->rack.advanced = 1; 155 tp->rack.rtt_us = rtt_us; 156 if (tcp_rack_sent_after(xmit_time, tp->rack.mstamp, 157 end_seq, tp->rack.end_seq)) { 158 tp->rack.mstamp = xmit_time; 159 tp->rack.end_seq = end_seq; 160 } 161 } 162 163 /* We have waited long enough to accommodate reordering. Mark the expired 164 * packets lost and retransmit them. 165 */ 166 void tcp_rack_reo_timeout(struct sock *sk) 167 { 168 struct tcp_sock *tp = tcp_sk(sk); 169 u32 timeout, prior_inflight; 170 171 prior_inflight = tcp_packets_in_flight(tp); 172 tcp_rack_detect_loss(sk, &timeout); 173 if (prior_inflight != tcp_packets_in_flight(tp)) { 174 if (inet_csk(sk)->icsk_ca_state != TCP_CA_Recovery) { 175 tcp_enter_recovery(sk, false); 176 if (!inet_csk(sk)->icsk_ca_ops->cong_control) 177 tcp_cwnd_reduction(sk, 1, 0); 178 } 179 tcp_xmit_retransmit_queue(sk); 180 } 181 if (inet_csk(sk)->icsk_pending != ICSK_TIME_RETRANS) 182 tcp_rearm_rto(sk); 183 } 184 185 /* Updates the RACK's reo_wnd based on DSACK and no. of recoveries. 186 * 187 * If DSACK is received, increment reo_wnd by min_rtt/4 (upper bounded 188 * by srtt), since there is possibility that spurious retransmission was 189 * due to reordering delay longer than reo_wnd. 190 * 191 * Persist the current reo_wnd value for TCP_RACK_RECOVERY_THRESH (16) 192 * no. of successful recoveries (accounts for full DSACK-based loss 193 * recovery undo). After that, reset it to default (min_rtt/4). 194 * 195 * At max, reo_wnd is incremented only once per rtt. So that the new 196 * DSACK on which we are reacting, is due to the spurious retx (approx) 197 * after the reo_wnd has been updated last time. 198 * 199 * reo_wnd is tracked in terms of steps (of min_rtt/4), rather than 200 * absolute value to account for change in rtt. 201 */ 202 void tcp_rack_update_reo_wnd(struct sock *sk, struct rate_sample *rs) 203 { 204 struct tcp_sock *tp = tcp_sk(sk); 205 206 if (sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_STATIC_REO_WND || 207 !rs->prior_delivered) 208 return; 209 210 /* Disregard DSACK if a rtt has not passed since we adjusted reo_wnd */ 211 if (before(rs->prior_delivered, tp->rack.last_delivered)) 212 tp->rack.dsack_seen = 0; 213 214 /* Adjust the reo_wnd if update is pending */ 215 if (tp->rack.dsack_seen) { 216 tp->rack.reo_wnd_steps = min_t(u32, 0xFF, 217 tp->rack.reo_wnd_steps + 1); 218 tp->rack.dsack_seen = 0; 219 tp->rack.last_delivered = tp->delivered; 220 tp->rack.reo_wnd_persist = TCP_RACK_RECOVERY_THRESH; 221 } else if (!tp->rack.reo_wnd_persist) { 222 tp->rack.reo_wnd_steps = 1; 223 } 224 } 225 226 /* RFC6582 NewReno recovery for non-SACK connection. It simply retransmits 227 * the next unacked packet upon receiving 228 * a) three or more DUPACKs to start the fast recovery 229 * b) an ACK acknowledging new data during the fast recovery. 230 */ 231 void tcp_newreno_mark_lost(struct sock *sk, bool snd_una_advanced) 232 { 233 const u8 state = inet_csk(sk)->icsk_ca_state; 234 struct tcp_sock *tp = tcp_sk(sk); 235 236 if ((state < TCP_CA_Recovery && tp->sacked_out >= tp->reordering) || 237 (state == TCP_CA_Recovery && snd_una_advanced)) { 238 struct sk_buff *skb = tcp_rtx_queue_head(sk); 239 u32 mss; 240 241 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) 242 return; 243 244 mss = tcp_skb_mss(skb); 245 if (tcp_skb_pcount(skb) > 1 && skb->len > mss) 246 tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb, 247 mss, mss, GFP_ATOMIC); 248 249 tcp_skb_mark_lost_uncond_verify(tp, skb); 250 } 251 } 252