// SPDX-License-Identifier: GPL-2.0
#include <linux/tcp.h>
#include <net/tcp.h>
static u32 tcp_rack_reo_wnd(const struct sock *sk)
{
const 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 &&
!(READ_ONCE(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_skb_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_US);
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_skb_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 ((READ_ONCE(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);
}
}
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