| // SPDX-License-Identifier: GPL-2.0 |
| /* |
| * INET An implementation of the TCP/IP protocol suite for the LINUX |
| * operating system. INET is implemented using the BSD Socket |
| * interface as the means of communication with the user level. |
| * |
| * Implementation of the Transmission Control Protocol(TCP). |
| * |
| * Authors: Ross Biro |
| * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> |
| * Mark Evans, <evansmp@uhura.aston.ac.uk> |
| * Corey Minyard <wf-rch!minyard@relay.EU.net> |
| * Florian La Roche, <flla@stud.uni-sb.de> |
| * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> |
| * Linus Torvalds, <torvalds@cs.helsinki.fi> |
| * Alan Cox, <gw4pts@gw4pts.ampr.org> |
| * Matthew Dillon, <dillon@apollo.west.oic.com> |
| * Arnt Gulbrandsen, <agulbra@nvg.unit.no> |
| * Jorge Cwik, <jorge@laser.satlink.net> |
| */ |
| |
| /* |
| * Changes: |
| * Pedro Roque : Fast Retransmit/Recovery. |
| * Two receive queues. |
| * Retransmit queue handled by TCP. |
| * Better retransmit timer handling. |
| * New congestion avoidance. |
| * Header prediction. |
| * Variable renaming. |
| * |
| * Eric : Fast Retransmit. |
| * Randy Scott : MSS option defines. |
| * Eric Schenk : Fixes to slow start algorithm. |
| * Eric Schenk : Yet another double ACK bug. |
| * Eric Schenk : Delayed ACK bug fixes. |
| * Eric Schenk : Floyd style fast retrans war avoidance. |
| * David S. Miller : Don't allow zero congestion window. |
| * Eric Schenk : Fix retransmitter so that it sends |
| * next packet on ack of previous packet. |
| * Andi Kleen : Moved open_request checking here |
| * and process RSTs for open_requests. |
| * Andi Kleen : Better prune_queue, and other fixes. |
| * Andrey Savochkin: Fix RTT measurements in the presence of |
| * timestamps. |
| * Andrey Savochkin: Check sequence numbers correctly when |
| * removing SACKs due to in sequence incoming |
| * data segments. |
| * Andi Kleen: Make sure we never ack data there is not |
| * enough room for. Also make this condition |
| * a fatal error if it might still happen. |
| * Andi Kleen: Add tcp_measure_rcv_mss to make |
| * connections with MSS<min(MTU,ann. MSS) |
| * work without delayed acks. |
| * Andi Kleen: Process packets with PSH set in the |
| * fast path. |
| * J Hadi Salim: ECN support |
| * Andrei Gurtov, |
| * Pasi Sarolahti, |
| * Panu Kuhlberg: Experimental audit of TCP (re)transmission |
| * engine. Lots of bugs are found. |
| * Pasi Sarolahti: F-RTO for dealing with spurious RTOs |
| */ |
| |
| #define pr_fmt(fmt) "TCP: " fmt |
| |
| #include <linux/mm.h> |
| #include <linux/slab.h> |
| #include <linux/module.h> |
| #include <linux/sysctl.h> |
| #include <linux/kernel.h> |
| #include <linux/prefetch.h> |
| #include <net/dst.h> |
| #include <net/tcp.h> |
| #include <net/proto_memory.h> |
| #include <net/inet_common.h> |
| #include <linux/ipsec.h> |
| #include <asm/unaligned.h> |
| #include <linux/errqueue.h> |
| #include <trace/events/tcp.h> |
| #include <linux/jump_label_ratelimit.h> |
| #include <net/busy_poll.h> |
| #include <net/mptcp.h> |
| |
| int sysctl_tcp_max_orphans __read_mostly = NR_FILE; |
| |
| #define FLAG_DATA 0x01 /* Incoming frame contained data. */ |
| #define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */ |
| #define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */ |
| #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */ |
| #define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */ |
| #define FLAG_DATA_SACKED 0x20 /* New SACK. */ |
| #define FLAG_ECE 0x40 /* ECE in this ACK */ |
| #define FLAG_LOST_RETRANS 0x80 /* This ACK marks some retransmission lost */ |
| #define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/ |
| #define FLAG_ORIG_SACK_ACKED 0x200 /* Never retransmitted data are (s)acked */ |
| #define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */ |
| #define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */ |
| #define FLAG_SET_XMIT_TIMER 0x1000 /* Set TLP or RTO timer */ |
| #define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */ |
| #define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */ |
| #define FLAG_NO_CHALLENGE_ACK 0x8000 /* do not call tcp_send_challenge_ack() */ |
| #define FLAG_ACK_MAYBE_DELAYED 0x10000 /* Likely a delayed ACK */ |
| #define FLAG_DSACK_TLP 0x20000 /* DSACK for tail loss probe */ |
| |
| #define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED) |
| #define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED) |
| #define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK) |
| #define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED) |
| |
| #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH) |
| #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH)) |
| |
| #define REXMIT_NONE 0 /* no loss recovery to do */ |
| #define REXMIT_LOST 1 /* retransmit packets marked lost */ |
| #define REXMIT_NEW 2 /* FRTO-style transmit of unsent/new packets */ |
| |
| #if IS_ENABLED(CONFIG_TLS_DEVICE) |
| static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ); |
| |
| void clean_acked_data_enable(struct inet_connection_sock *icsk, |
| void (*cad)(struct sock *sk, u32 ack_seq)) |
| { |
| icsk->icsk_clean_acked = cad; |
| static_branch_deferred_inc(&clean_acked_data_enabled); |
| } |
| EXPORT_SYMBOL_GPL(clean_acked_data_enable); |
| |
| void clean_acked_data_disable(struct inet_connection_sock *icsk) |
| { |
| static_branch_slow_dec_deferred(&clean_acked_data_enabled); |
| icsk->icsk_clean_acked = NULL; |
| } |
| EXPORT_SYMBOL_GPL(clean_acked_data_disable); |
| |
| void clean_acked_data_flush(void) |
| { |
| static_key_deferred_flush(&clean_acked_data_enabled); |
| } |
| EXPORT_SYMBOL_GPL(clean_acked_data_flush); |
| #endif |
| |
| #ifdef CONFIG_CGROUP_BPF |
| static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb) |
| { |
| bool unknown_opt = tcp_sk(sk)->rx_opt.saw_unknown && |
| BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk), |
| BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG); |
| bool parse_all_opt = BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk), |
| BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG); |
| struct bpf_sock_ops_kern sock_ops; |
| |
| if (likely(!unknown_opt && !parse_all_opt)) |
| return; |
| |
| /* The skb will be handled in the |
| * bpf_skops_established() or |
| * bpf_skops_write_hdr_opt(). |
| */ |
| switch (sk->sk_state) { |
| case TCP_SYN_RECV: |
| case TCP_SYN_SENT: |
| case TCP_LISTEN: |
| return; |
| } |
| |
| sock_owned_by_me(sk); |
| |
| memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp)); |
| sock_ops.op = BPF_SOCK_OPS_PARSE_HDR_OPT_CB; |
| sock_ops.is_fullsock = 1; |
| sock_ops.sk = sk; |
| bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb)); |
| |
| BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops); |
| } |
| |
| static void bpf_skops_established(struct sock *sk, int bpf_op, |
| struct sk_buff *skb) |
| { |
| struct bpf_sock_ops_kern sock_ops; |
| |
| sock_owned_by_me(sk); |
| |
| memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp)); |
| sock_ops.op = bpf_op; |
| sock_ops.is_fullsock = 1; |
| sock_ops.sk = sk; |
| /* sk with TCP_REPAIR_ON does not have skb in tcp_finish_connect */ |
| if (skb) |
| bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb)); |
| |
| BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops); |
| } |
| #else |
| static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb) |
| { |
| } |
| |
| static void bpf_skops_established(struct sock *sk, int bpf_op, |
| struct sk_buff *skb) |
| { |
| } |
| #endif |
| |
| static __cold void tcp_gro_dev_warn(const struct sock *sk, const struct sk_buff *skb, |
| unsigned int len) |
| { |
| struct net_device *dev; |
| |
| rcu_read_lock(); |
| dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif); |
| if (!dev || len >= READ_ONCE(dev->mtu)) |
| pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n", |
| dev ? dev->name : "Unknown driver"); |
| rcu_read_unlock(); |
| } |
| |
| /* Adapt the MSS value used to make delayed ack decision to the |
| * real world. |
| */ |
| static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb) |
| { |
| struct inet_connection_sock *icsk = inet_csk(sk); |
| const unsigned int lss = icsk->icsk_ack.last_seg_size; |
| unsigned int len; |
| |
| icsk->icsk_ack.last_seg_size = 0; |
| |
| /* skb->len may jitter because of SACKs, even if peer |
| * sends good full-sized frames. |
| */ |
| len = skb_shinfo(skb)->gso_size ? : skb->len; |
| if (len >= icsk->icsk_ack.rcv_mss) { |
| /* Note: divides are still a bit expensive. |
| * For the moment, only adjust scaling_ratio |
| * when we update icsk_ack.rcv_mss. |
| */ |
| if (unlikely(len != icsk->icsk_ack.rcv_mss)) { |
| u64 val = (u64)skb->len << TCP_RMEM_TO_WIN_SCALE; |
| |
| do_div(val, skb->truesize); |
| tcp_sk(sk)->scaling_ratio = val ? val : 1; |
| } |
| icsk->icsk_ack.rcv_mss = min_t(unsigned int, len, |
| tcp_sk(sk)->advmss); |
| /* Account for possibly-removed options */ |
| DO_ONCE_LITE_IF(len > icsk->icsk_ack.rcv_mss + MAX_TCP_OPTION_SPACE, |
| tcp_gro_dev_warn, sk, skb, len); |
| /* If the skb has a len of exactly 1*MSS and has the PSH bit |
| * set then it is likely the end of an application write. So |
| * more data may not be arriving soon, and yet the data sender |
| * may be waiting for an ACK if cwnd-bound or using TX zero |
| * copy. So we set ICSK_ACK_PUSHED here so that |
| * tcp_cleanup_rbuf() will send an ACK immediately if the app |
| * reads all of the data and is not ping-pong. If len > MSS |
| * then this logic does not matter (and does not hurt) because |
| * tcp_cleanup_rbuf() will always ACK immediately if the app |
| * reads data and there is more than an MSS of unACKed data. |
| */ |
| if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_PSH) |
| icsk->icsk_ack.pending |= ICSK_ACK_PUSHED; |
| } else { |
| /* Otherwise, we make more careful check taking into account, |
| * that SACKs block is variable. |
| * |
| * "len" is invariant segment length, including TCP header. |
| */ |
| len += skb->data - skb_transport_header(skb); |
| if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) || |
| /* If PSH is not set, packet should be |
| * full sized, provided peer TCP is not badly broken. |
| * This observation (if it is correct 8)) allows |
| * to handle super-low mtu links fairly. |
| */ |
| (len >= TCP_MIN_MSS + sizeof(struct tcphdr) && |
| !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) { |
| /* Subtract also invariant (if peer is RFC compliant), |
| * tcp header plus fixed timestamp option length. |
| * Resulting "len" is MSS free of SACK jitter. |
| */ |
| len -= tcp_sk(sk)->tcp_header_len; |
| icsk->icsk_ack.last_seg_size = len; |
| if (len == lss) { |
| icsk->icsk_ack.rcv_mss = len; |
| return; |
| } |
| } |
| if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED) |
| icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2; |
| icsk->icsk_ack.pending |= ICSK_ACK_PUSHED; |
| } |
| } |
| |
| static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks) |
| { |
| struct inet_connection_sock *icsk = inet_csk(sk); |
| unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss); |
| |
| if (quickacks == 0) |
| quickacks = 2; |
| quickacks = min(quickacks, max_quickacks); |
| if (quickacks > icsk->icsk_ack.quick) |
| icsk->icsk_ack.quick = quickacks; |
| } |
| |
| static void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks) |
| { |
| struct inet_connection_sock *icsk = inet_csk(sk); |
| |
| tcp_incr_quickack(sk, max_quickacks); |
| inet_csk_exit_pingpong_mode(sk); |
| icsk->icsk_ack.ato = TCP_ATO_MIN; |
| } |
| |
| /* Send ACKs quickly, if "quick" count is not exhausted |
| * and the session is not interactive. |
| */ |
| |
| static bool tcp_in_quickack_mode(struct sock *sk) |
| { |
| const struct inet_connection_sock *icsk = inet_csk(sk); |
| const struct dst_entry *dst = __sk_dst_get(sk); |
| |
| return (dst && dst_metric(dst, RTAX_QUICKACK)) || |
| (icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk)); |
| } |
| |
| static void tcp_ecn_queue_cwr(struct tcp_sock *tp) |
| { |
| if (tp->ecn_flags & TCP_ECN_OK) |
| tp->ecn_flags |= TCP_ECN_QUEUE_CWR; |
| } |
| |
| static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb) |
| { |
| if (tcp_hdr(skb)->cwr) { |
| tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR; |
| |
| /* If the sender is telling us it has entered CWR, then its |
| * cwnd may be very low (even just 1 packet), so we should ACK |
| * immediately. |
| */ |
| if (TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) |
| inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW; |
| } |
| } |
| |
| static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp) |
| { |
| tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR; |
| } |
| |
| static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) { |
| case INET_ECN_NOT_ECT: |
| /* Funny extension: if ECT is not set on a segment, |
| * and we already seen ECT on a previous segment, |
| * it is probably a retransmit. |
| */ |
| if (tp->ecn_flags & TCP_ECN_SEEN) |
| tcp_enter_quickack_mode(sk, 2); |
| break; |
| case INET_ECN_CE: |
| if (tcp_ca_needs_ecn(sk)) |
| tcp_ca_event(sk, CA_EVENT_ECN_IS_CE); |
| |
| if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) { |
| /* Better not delay acks, sender can have a very low cwnd */ |
| tcp_enter_quickack_mode(sk, 2); |
| tp->ecn_flags |= TCP_ECN_DEMAND_CWR; |
| } |
| tp->ecn_flags |= TCP_ECN_SEEN; |
| break; |
| default: |
| if (tcp_ca_needs_ecn(sk)) |
| tcp_ca_event(sk, CA_EVENT_ECN_NO_CE); |
| tp->ecn_flags |= TCP_ECN_SEEN; |
| break; |
| } |
| } |
| |
| static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb) |
| { |
| if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK) |
| __tcp_ecn_check_ce(sk, skb); |
| } |
| |
| static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th) |
| { |
| if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr)) |
| tp->ecn_flags &= ~TCP_ECN_OK; |
| } |
| |
| static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th) |
| { |
| if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr)) |
| tp->ecn_flags &= ~TCP_ECN_OK; |
| } |
| |
| static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th) |
| { |
| if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK)) |
| return true; |
| return false; |
| } |
| |
| /* Buffer size and advertised window tuning. |
| * |
| * 1. Tuning sk->sk_sndbuf, when connection enters established state. |
| */ |
| |
| static void tcp_sndbuf_expand(struct sock *sk) |
| { |
| const struct tcp_sock *tp = tcp_sk(sk); |
| const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops; |
| int sndmem, per_mss; |
| u32 nr_segs; |
| |
| /* Worst case is non GSO/TSO : each frame consumes one skb |
| * and skb->head is kmalloced using power of two area of memory |
| */ |
| per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) + |
| MAX_TCP_HEADER + |
| SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); |
| |
| per_mss = roundup_pow_of_two(per_mss) + |
| SKB_DATA_ALIGN(sizeof(struct sk_buff)); |
| |
| nr_segs = max_t(u32, TCP_INIT_CWND, tcp_snd_cwnd(tp)); |
| nr_segs = max_t(u32, nr_segs, tp->reordering + 1); |
| |
| /* Fast Recovery (RFC 5681 3.2) : |
| * Cubic needs 1.7 factor, rounded to 2 to include |
| * extra cushion (application might react slowly to EPOLLOUT) |
| */ |
| sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2; |
| sndmem *= nr_segs * per_mss; |
| |
| if (sk->sk_sndbuf < sndmem) |
| WRITE_ONCE(sk->sk_sndbuf, |
| min(sndmem, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_wmem[2]))); |
| } |
| |
| /* 2. Tuning advertised window (window_clamp, rcv_ssthresh) |
| * |
| * All tcp_full_space() is split to two parts: "network" buffer, allocated |
| * forward and advertised in receiver window (tp->rcv_wnd) and |
| * "application buffer", required to isolate scheduling/application |
| * latencies from network. |
| * window_clamp is maximal advertised window. It can be less than |
| * tcp_full_space(), in this case tcp_full_space() - window_clamp |
| * is reserved for "application" buffer. The less window_clamp is |
| * the smoother our behaviour from viewpoint of network, but the lower |
| * throughput and the higher sensitivity of the connection to losses. 8) |
| * |
| * rcv_ssthresh is more strict window_clamp used at "slow start" |
| * phase to predict further behaviour of this connection. |
| * It is used for two goals: |
| * - to enforce header prediction at sender, even when application |
| * requires some significant "application buffer". It is check #1. |
| * - to prevent pruning of receive queue because of misprediction |
| * of receiver window. Check #2. |
| * |
| * The scheme does not work when sender sends good segments opening |
| * window and then starts to feed us spaghetti. But it should work |
| * in common situations. Otherwise, we have to rely on queue collapsing. |
| */ |
| |
| /* Slow part of check#2. */ |
| static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb, |
| unsigned int skbtruesize) |
| { |
| const struct tcp_sock *tp = tcp_sk(sk); |
| /* Optimize this! */ |
| int truesize = tcp_win_from_space(sk, skbtruesize) >> 1; |
| int window = tcp_win_from_space(sk, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2])) >> 1; |
| |
| while (tp->rcv_ssthresh <= window) { |
| if (truesize <= skb->len) |
| return 2 * inet_csk(sk)->icsk_ack.rcv_mss; |
| |
| truesize >>= 1; |
| window >>= 1; |
| } |
| return 0; |
| } |
| |
| /* Even if skb appears to have a bad len/truesize ratio, TCP coalescing |
| * can play nice with us, as sk_buff and skb->head might be either |
| * freed or shared with up to MAX_SKB_FRAGS segments. |
| * Only give a boost to drivers using page frag(s) to hold the frame(s), |
| * and if no payload was pulled in skb->head before reaching us. |
| */ |
| static u32 truesize_adjust(bool adjust, const struct sk_buff *skb) |
| { |
| u32 truesize = skb->truesize; |
| |
| if (adjust && !skb_headlen(skb)) { |
| truesize -= SKB_TRUESIZE(skb_end_offset(skb)); |
| /* paranoid check, some drivers might be buggy */ |
| if (unlikely((int)truesize < (int)skb->len)) |
| truesize = skb->truesize; |
| } |
| return truesize; |
| } |
| |
| static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb, |
| bool adjust) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| int room; |
| |
| room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh; |
| |
| if (room <= 0) |
| return; |
| |
| /* Check #1 */ |
| if (!tcp_under_memory_pressure(sk)) { |
| unsigned int truesize = truesize_adjust(adjust, skb); |
| int incr; |
| |
| /* Check #2. Increase window, if skb with such overhead |
| * will fit to rcvbuf in future. |
| */ |
| if (tcp_win_from_space(sk, truesize) <= skb->len) |
| incr = 2 * tp->advmss; |
| else |
| incr = __tcp_grow_window(sk, skb, truesize); |
| |
| if (incr) { |
| incr = max_t(int, incr, 2 * skb->len); |
| tp->rcv_ssthresh += min(room, incr); |
| inet_csk(sk)->icsk_ack.quick |= 1; |
| } |
| } else { |
| /* Under pressure: |
| * Adjust rcv_ssthresh according to reserved mem |
| */ |
| tcp_adjust_rcv_ssthresh(sk); |
| } |
| } |
| |
| /* 3. Try to fixup all. It is made immediately after connection enters |
| * established state. |
| */ |
| static void tcp_init_buffer_space(struct sock *sk) |
| { |
| int tcp_app_win = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_app_win); |
| struct tcp_sock *tp = tcp_sk(sk); |
| int maxwin; |
| |
| if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) |
| tcp_sndbuf_expand(sk); |
| |
| tcp_mstamp_refresh(tp); |
| tp->rcvq_space.time = tp->tcp_mstamp; |
| tp->rcvq_space.seq = tp->copied_seq; |
| |
| maxwin = tcp_full_space(sk); |
| |
| if (tp->window_clamp >= maxwin) { |
| WRITE_ONCE(tp->window_clamp, maxwin); |
| |
| if (tcp_app_win && maxwin > 4 * tp->advmss) |
| WRITE_ONCE(tp->window_clamp, |
| max(maxwin - (maxwin >> tcp_app_win), |
| 4 * tp->advmss)); |
| } |
| |
| /* Force reservation of one segment. */ |
| if (tcp_app_win && |
| tp->window_clamp > 2 * tp->advmss && |
| tp->window_clamp + tp->advmss > maxwin) |
| WRITE_ONCE(tp->window_clamp, |
| max(2 * tp->advmss, maxwin - tp->advmss)); |
| |
| tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp); |
| tp->snd_cwnd_stamp = tcp_jiffies32; |
| tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd, |
| (u32)TCP_INIT_CWND * tp->advmss); |
| } |
| |
| /* 4. Recalculate window clamp after socket hit its memory bounds. */ |
| static void tcp_clamp_window(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct inet_connection_sock *icsk = inet_csk(sk); |
| struct net *net = sock_net(sk); |
| int rmem2; |
| |
| icsk->icsk_ack.quick = 0; |
| rmem2 = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]); |
| |
| if (sk->sk_rcvbuf < rmem2 && |
| !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) && |
| !tcp_under_memory_pressure(sk) && |
| sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) { |
| WRITE_ONCE(sk->sk_rcvbuf, |
| min(atomic_read(&sk->sk_rmem_alloc), rmem2)); |
| } |
| if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) |
| tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss); |
| } |
| |
| /* Initialize RCV_MSS value. |
| * RCV_MSS is an our guess about MSS used by the peer. |
| * We haven't any direct information about the MSS. |
| * It's better to underestimate the RCV_MSS rather than overestimate. |
| * Overestimations make us ACKing less frequently than needed. |
| * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss(). |
| */ |
| void tcp_initialize_rcv_mss(struct sock *sk) |
| { |
| const struct tcp_sock *tp = tcp_sk(sk); |
| unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache); |
| |
| hint = min(hint, tp->rcv_wnd / 2); |
| hint = min(hint, TCP_MSS_DEFAULT); |
| hint = max(hint, TCP_MIN_MSS); |
| |
| inet_csk(sk)->icsk_ack.rcv_mss = hint; |
| } |
| EXPORT_SYMBOL(tcp_initialize_rcv_mss); |
| |
| /* Receiver "autotuning" code. |
| * |
| * The algorithm for RTT estimation w/o timestamps is based on |
| * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL. |
| * <https://public.lanl.gov/radiant/pubs.html#DRS> |
| * |
| * More detail on this code can be found at |
| * <http://staff.psc.edu/jheffner/>, |
| * though this reference is out of date. A new paper |
| * is pending. |
| */ |
| static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep) |
| { |
| u32 new_sample = tp->rcv_rtt_est.rtt_us; |
| long m = sample; |
| |
| if (new_sample != 0) { |
| /* If we sample in larger samples in the non-timestamp |
| * case, we could grossly overestimate the RTT especially |
| * with chatty applications or bulk transfer apps which |
| * are stalled on filesystem I/O. |
| * |
| * Also, since we are only going for a minimum in the |
| * non-timestamp case, we do not smooth things out |
| * else with timestamps disabled convergence takes too |
| * long. |
| */ |
| if (!win_dep) { |
| m -= (new_sample >> 3); |
| new_sample += m; |
| } else { |
| m <<= 3; |
| if (m < new_sample) |
| new_sample = m; |
| } |
| } else { |
| /* No previous measure. */ |
| new_sample = m << 3; |
| } |
| |
| tp->rcv_rtt_est.rtt_us = new_sample; |
| } |
| |
| static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp) |
| { |
| u32 delta_us; |
| |
| if (tp->rcv_rtt_est.time == 0) |
| goto new_measure; |
| if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq)) |
| return; |
| delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time); |
| if (!delta_us) |
| delta_us = 1; |
| tcp_rcv_rtt_update(tp, delta_us, 1); |
| |
| new_measure: |
| tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd; |
| tp->rcv_rtt_est.time = tp->tcp_mstamp; |
| } |
| |
| static s32 tcp_rtt_tsopt_us(const struct tcp_sock *tp) |
| { |
| u32 delta, delta_us; |
| |
| delta = tcp_time_stamp_ts(tp) - tp->rx_opt.rcv_tsecr; |
| if (tp->tcp_usec_ts) |
| return delta; |
| |
| if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) { |
| if (!delta) |
| delta = 1; |
| delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ); |
| return delta_us; |
| } |
| return -1; |
| } |
| |
| static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, |
| const struct sk_buff *skb) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr) |
| return; |
| tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr; |
| |
| if (TCP_SKB_CB(skb)->end_seq - |
| TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) { |
| s32 delta = tcp_rtt_tsopt_us(tp); |
| |
| if (delta >= 0) |
| tcp_rcv_rtt_update(tp, delta, 0); |
| } |
| } |
| |
| /* |
| * This function should be called every time data is copied to user space. |
| * It calculates the appropriate TCP receive buffer space. |
| */ |
| void tcp_rcv_space_adjust(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| u32 copied; |
| int time; |
| |
| trace_tcp_rcv_space_adjust(sk); |
| |
| tcp_mstamp_refresh(tp); |
| time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time); |
| if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0) |
| return; |
| |
| /* Number of bytes copied to user in last RTT */ |
| copied = tp->copied_seq - tp->rcvq_space.seq; |
| if (copied <= tp->rcvq_space.space) |
| goto new_measure; |
| |
| /* A bit of theory : |
| * copied = bytes received in previous RTT, our base window |
| * To cope with packet losses, we need a 2x factor |
| * To cope with slow start, and sender growing its cwin by 100 % |
| * every RTT, we need a 4x factor, because the ACK we are sending |
| * now is for the next RTT, not the current one : |
| * <prev RTT . ><current RTT .. ><next RTT .... > |
| */ |
| |
| if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) && |
| !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) { |
| u64 rcvwin, grow; |
| int rcvbuf; |
| |
| /* minimal window to cope with packet losses, assuming |
| * steady state. Add some cushion because of small variations. |
| */ |
| rcvwin = ((u64)copied << 1) + 16 * tp->advmss; |
| |
| /* Accommodate for sender rate increase (eg. slow start) */ |
| grow = rcvwin * (copied - tp->rcvq_space.space); |
| do_div(grow, tp->rcvq_space.space); |
| rcvwin += (grow << 1); |
| |
| rcvbuf = min_t(u64, tcp_space_from_win(sk, rcvwin), |
| READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2])); |
| if (rcvbuf > sk->sk_rcvbuf) { |
| WRITE_ONCE(sk->sk_rcvbuf, rcvbuf); |
| |
| /* Make the window clamp follow along. */ |
| WRITE_ONCE(tp->window_clamp, |
| tcp_win_from_space(sk, rcvbuf)); |
| } |
| } |
| tp->rcvq_space.space = copied; |
| |
| new_measure: |
| tp->rcvq_space.seq = tp->copied_seq; |
| tp->rcvq_space.time = tp->tcp_mstamp; |
| } |
| |
| static void tcp_save_lrcv_flowlabel(struct sock *sk, const struct sk_buff *skb) |
| { |
| #if IS_ENABLED(CONFIG_IPV6) |
| struct inet_connection_sock *icsk = inet_csk(sk); |
| |
| if (skb->protocol == htons(ETH_P_IPV6)) |
| icsk->icsk_ack.lrcv_flowlabel = ntohl(ip6_flowlabel(ipv6_hdr(skb))); |
| #endif |
| } |
| |
| /* There is something which you must keep in mind when you analyze the |
| * behavior of the tp->ato delayed ack timeout interval. When a |
| * connection starts up, we want to ack as quickly as possible. The |
| * problem is that "good" TCP's do slow start at the beginning of data |
| * transmission. The means that until we send the first few ACK's the |
| * sender will sit on his end and only queue most of his data, because |
| * he can only send snd_cwnd unacked packets at any given time. For |
| * each ACK we send, he increments snd_cwnd and transmits more of his |
| * queue. -DaveM |
| */ |
| static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct inet_connection_sock *icsk = inet_csk(sk); |
| u32 now; |
| |
| inet_csk_schedule_ack(sk); |
| |
| tcp_measure_rcv_mss(sk, skb); |
| |
| tcp_rcv_rtt_measure(tp); |
| |
| now = tcp_jiffies32; |
| |
| if (!icsk->icsk_ack.ato) { |
| /* The _first_ data packet received, initialize |
| * delayed ACK engine. |
| */ |
| tcp_incr_quickack(sk, TCP_MAX_QUICKACKS); |
| icsk->icsk_ack.ato = TCP_ATO_MIN; |
| } else { |
| int m = now - icsk->icsk_ack.lrcvtime; |
| |
| if (m <= TCP_ATO_MIN / 2) { |
| /* The fastest case is the first. */ |
| icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2; |
| } else if (m < icsk->icsk_ack.ato) { |
| icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m; |
| if (icsk->icsk_ack.ato > icsk->icsk_rto) |
| icsk->icsk_ack.ato = icsk->icsk_rto; |
| } else if (m > icsk->icsk_rto) { |
| /* Too long gap. Apparently sender failed to |
| * restart window, so that we send ACKs quickly. |
| */ |
| tcp_incr_quickack(sk, TCP_MAX_QUICKACKS); |
| } |
| } |
| icsk->icsk_ack.lrcvtime = now; |
| tcp_save_lrcv_flowlabel(sk, skb); |
| |
| tcp_ecn_check_ce(sk, skb); |
| |
| if (skb->len >= 128) |
| tcp_grow_window(sk, skb, true); |
| } |
| |
| /* Called to compute a smoothed rtt estimate. The data fed to this |
| * routine either comes from timestamps, or from segments that were |
| * known _not_ to have been retransmitted [see Karn/Partridge |
| * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88 |
| * piece by Van Jacobson. |
| * NOTE: the next three routines used to be one big routine. |
| * To save cycles in the RFC 1323 implementation it was better to break |
| * it up into three procedures. -- erics |
| */ |
| static void tcp_rtt_estimator(struct sock *sk, long mrtt_us) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| long m = mrtt_us; /* RTT */ |
| u32 srtt = tp->srtt_us; |
| |
| /* The following amusing code comes from Jacobson's |
| * article in SIGCOMM '88. Note that rtt and mdev |
| * are scaled versions of rtt and mean deviation. |
| * This is designed to be as fast as possible |
| * m stands for "measurement". |
| * |
| * On a 1990 paper the rto value is changed to: |
| * RTO = rtt + 4 * mdev |
| * |
| * Funny. This algorithm seems to be very broken. |
| * These formulae increase RTO, when it should be decreased, increase |
| * too slowly, when it should be increased quickly, decrease too quickly |
| * etc. I guess in BSD RTO takes ONE value, so that it is absolutely |
| * does not matter how to _calculate_ it. Seems, it was trap |
| * that VJ failed to avoid. 8) |
| */ |
| if (srtt != 0) { |
| m -= (srtt >> 3); /* m is now error in rtt est */ |
| srtt += m; /* rtt = 7/8 rtt + 1/8 new */ |
| if (m < 0) { |
| m = -m; /* m is now abs(error) */ |
| m -= (tp->mdev_us >> 2); /* similar update on mdev */ |
| /* This is similar to one of Eifel findings. |
| * Eifel blocks mdev updates when rtt decreases. |
| * This solution is a bit different: we use finer gain |
| * for mdev in this case (alpha*beta). |
| * Like Eifel it also prevents growth of rto, |
| * but also it limits too fast rto decreases, |
| * happening in pure Eifel. |
| */ |
| if (m > 0) |
| m >>= 3; |
| } else { |
| m -= (tp->mdev_us >> 2); /* similar update on mdev */ |
| } |
| tp->mdev_us += m; /* mdev = 3/4 mdev + 1/4 new */ |
| if (tp->mdev_us > tp->mdev_max_us) { |
| tp->mdev_max_us = tp->mdev_us; |
| if (tp->mdev_max_us > tp->rttvar_us) |
| tp->rttvar_us = tp->mdev_max_us; |
| } |
| if (after(tp->snd_una, tp->rtt_seq)) { |
| if (tp->mdev_max_us < tp->rttvar_us) |
| tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2; |
| tp->rtt_seq = tp->snd_nxt; |
| tp->mdev_max_us = tcp_rto_min_us(sk); |
| |
| tcp_bpf_rtt(sk, mrtt_us, srtt); |
| } |
| } else { |
| /* no previous measure. */ |
| srtt = m << 3; /* take the measured time to be rtt */ |
| tp->mdev_us = m << 1; /* make sure rto = 3*rtt */ |
| tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk)); |
| tp->mdev_max_us = tp->rttvar_us; |
| tp->rtt_seq = tp->snd_nxt; |
| |
| tcp_bpf_rtt(sk, mrtt_us, srtt); |
| } |
| tp->srtt_us = max(1U, srtt); |
| } |
| |
| static void tcp_update_pacing_rate(struct sock *sk) |
| { |
| const struct tcp_sock *tp = tcp_sk(sk); |
| u64 rate; |
| |
| /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */ |
| rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3); |
| |
| /* current rate is (cwnd * mss) / srtt |
| * In Slow Start [1], set sk_pacing_rate to 200 % the current rate. |
| * In Congestion Avoidance phase, set it to 120 % the current rate. |
| * |
| * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh) |
| * If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching |
| * end of slow start and should slow down. |
| */ |
| if (tcp_snd_cwnd(tp) < tp->snd_ssthresh / 2) |
| rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio); |
| else |
| rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio); |
| |
| rate *= max(tcp_snd_cwnd(tp), tp->packets_out); |
| |
| if (likely(tp->srtt_us)) |
| do_div(rate, tp->srtt_us); |
| |
| /* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate |
| * without any lock. We want to make sure compiler wont store |
| * intermediate values in this location. |
| */ |
| WRITE_ONCE(sk->sk_pacing_rate, |
| min_t(u64, rate, READ_ONCE(sk->sk_max_pacing_rate))); |
| } |
| |
| /* Calculate rto without backoff. This is the second half of Van Jacobson's |
| * routine referred to above. |
| */ |
| static void tcp_set_rto(struct sock *sk) |
| { |
| const struct tcp_sock *tp = tcp_sk(sk); |
| /* Old crap is replaced with new one. 8) |
| * |
| * More seriously: |
| * 1. If rtt variance happened to be less 50msec, it is hallucination. |
| * It cannot be less due to utterly erratic ACK generation made |
| * at least by solaris and freebsd. "Erratic ACKs" has _nothing_ |
| * to do with delayed acks, because at cwnd>2 true delack timeout |
| * is invisible. Actually, Linux-2.4 also generates erratic |
| * ACKs in some circumstances. |
| */ |
| inet_csk(sk)->icsk_rto = __tcp_set_rto(tp); |
| |
| /* 2. Fixups made earlier cannot be right. |
| * If we do not estimate RTO correctly without them, |
| * all the algo is pure shit and should be replaced |
| * with correct one. It is exactly, which we pretend to do. |
| */ |
| |
| /* NOTE: clamping at TCP_RTO_MIN is not required, current algo |
| * guarantees that rto is higher. |
| */ |
| tcp_bound_rto(sk); |
| } |
| |
| __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst) |
| { |
| __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0); |
| |
| if (!cwnd) |
| cwnd = TCP_INIT_CWND; |
| return min_t(__u32, cwnd, tp->snd_cwnd_clamp); |
| } |
| |
| struct tcp_sacktag_state { |
| /* Timestamps for earliest and latest never-retransmitted segment |
| * that was SACKed. RTO needs the earliest RTT to stay conservative, |
| * but congestion control should still get an accurate delay signal. |
| */ |
| u64 first_sackt; |
| u64 last_sackt; |
| u32 reord; |
| u32 sack_delivered; |
| int flag; |
| unsigned int mss_now; |
| struct rate_sample *rate; |
| }; |
| |
| /* Take a notice that peer is sending D-SACKs. Skip update of data delivery |
| * and spurious retransmission information if this DSACK is unlikely caused by |
| * sender's action: |
| * - DSACKed sequence range is larger than maximum receiver's window. |
| * - Total no. of DSACKed segments exceed the total no. of retransmitted segs. |
| */ |
| static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq, |
| u32 end_seq, struct tcp_sacktag_state *state) |
| { |
| u32 seq_len, dup_segs = 1; |
| |
| if (!before(start_seq, end_seq)) |
| return 0; |
| |
| seq_len = end_seq - start_seq; |
| /* Dubious DSACK: DSACKed range greater than maximum advertised rwnd */ |
| if (seq_len > tp->max_window) |
| return 0; |
| if (seq_len > tp->mss_cache) |
| dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache); |
| else if (tp->tlp_high_seq && tp->tlp_high_seq == end_seq) |
| state->flag |= FLAG_DSACK_TLP; |
| |
| tp->dsack_dups += dup_segs; |
| /* Skip the DSACK if dup segs weren't retransmitted by sender */ |
| if (tp->dsack_dups > tp->total_retrans) |
| return 0; |
| |
| tp->rx_opt.sack_ok |= TCP_DSACK_SEEN; |
| /* We increase the RACK ordering window in rounds where we receive |
| * DSACKs that may have been due to reordering causing RACK to trigger |
| * a spurious fast recovery. Thus RACK ignores DSACKs that happen |
| * without having seen reordering, or that match TLP probes (TLP |
| * is timer-driven, not triggered by RACK). |
| */ |
| if (tp->reord_seen && !(state->flag & FLAG_DSACK_TLP)) |
| tp->rack.dsack_seen = 1; |
| |
| state->flag |= FLAG_DSACKING_ACK; |
| /* A spurious retransmission is delivered */ |
| state->sack_delivered += dup_segs; |
| |
| return dup_segs; |
| } |
| |
| /* It's reordering when higher sequence was delivered (i.e. sacked) before |
| * some lower never-retransmitted sequence ("low_seq"). The maximum reordering |
| * distance is approximated in full-mss packet distance ("reordering"). |
| */ |
| static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq, |
| const int ts) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| const u32 mss = tp->mss_cache; |
| u32 fack, metric; |
| |
| fack = tcp_highest_sack_seq(tp); |
| if (!before(low_seq, fack)) |
| return; |
| |
| metric = fack - low_seq; |
| if ((metric > tp->reordering * mss) && mss) { |
| #if FASTRETRANS_DEBUG > 1 |
| pr_debug("Disorder%d %d %u f%u s%u rr%d\n", |
| tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state, |
| tp->reordering, |
| 0, |
| tp->sacked_out, |
| tp->undo_marker ? tp->undo_retrans : 0); |
| #endif |
| tp->reordering = min_t(u32, (metric + mss - 1) / mss, |
| READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering)); |
| } |
| |
| /* This exciting event is worth to be remembered. 8) */ |
| tp->reord_seen++; |
| NET_INC_STATS(sock_net(sk), |
| ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER); |
| } |
| |
| /* This must be called before lost_out or retrans_out are updated |
| * on a new loss, because we want to know if all skbs previously |
| * known to be lost have already been retransmitted, indicating |
| * that this newly lost skb is our next skb to retransmit. |
| */ |
| static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb) |
| { |
| if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) || |
| (tp->retransmit_skb_hint && |
| before(TCP_SKB_CB(skb)->seq, |
| TCP_SKB_CB(tp->retransmit_skb_hint)->seq))) |
| tp->retransmit_skb_hint = skb; |
| } |
| |
| /* Sum the number of packets on the wire we have marked as lost, and |
| * notify the congestion control module that the given skb was marked lost. |
| */ |
| static void tcp_notify_skb_loss_event(struct tcp_sock *tp, const struct sk_buff *skb) |
| { |
| tp->lost += tcp_skb_pcount(skb); |
| } |
| |
| void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb) |
| { |
| __u8 sacked = TCP_SKB_CB(skb)->sacked; |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (sacked & TCPCB_SACKED_ACKED) |
| return; |
| |
| tcp_verify_retransmit_hint(tp, skb); |
| if (sacked & TCPCB_LOST) { |
| if (sacked & TCPCB_SACKED_RETRANS) { |
| /* Account for retransmits that are lost again */ |
| TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; |
| tp->retrans_out -= tcp_skb_pcount(skb); |
| NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT, |
| tcp_skb_pcount(skb)); |
| tcp_notify_skb_loss_event(tp, skb); |
| } |
| } else { |
| tp->lost_out += tcp_skb_pcount(skb); |
| TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; |
| tcp_notify_skb_loss_event(tp, skb); |
| } |
| } |
| |
| /* Updates the delivered and delivered_ce counts */ |
| static void tcp_count_delivered(struct tcp_sock *tp, u32 delivered, |
| bool ece_ack) |
| { |
| tp->delivered += delivered; |
| if (ece_ack) |
| tp->delivered_ce += delivered; |
| } |
| |
| /* This procedure tags the retransmission queue when SACKs arrive. |
| * |
| * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L). |
| * Packets in queue with these bits set are counted in variables |
| * sacked_out, retrans_out and lost_out, correspondingly. |
| * |
| * Valid combinations are: |
| * Tag InFlight Description |
| * 0 1 - orig segment is in flight. |
| * S 0 - nothing flies, orig reached receiver. |
| * L 0 - nothing flies, orig lost by net. |
| * R 2 - both orig and retransmit are in flight. |
| * L|R 1 - orig is lost, retransmit is in flight. |
| * S|R 1 - orig reached receiver, retrans is still in flight. |
| * (L|S|R is logically valid, it could occur when L|R is sacked, |
| * but it is equivalent to plain S and code short-circuits it to S. |
| * L|S is logically invalid, it would mean -1 packet in flight 8)) |
| * |
| * These 6 states form finite state machine, controlled by the following events: |
| * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue()) |
| * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue()) |
| * 3. Loss detection event of two flavors: |
| * A. Scoreboard estimator decided the packet is lost. |
| * A'. Reno "three dupacks" marks head of queue lost. |
| * B. SACK arrives sacking SND.NXT at the moment, when the |
| * segment was retransmitted. |
| * 4. D-SACK added new rule: D-SACK changes any tag to S. |
| * |
| * It is pleasant to note, that state diagram turns out to be commutative, |
| * so that we are allowed not to be bothered by order of our actions, |
| * when multiple events arrive simultaneously. (see the function below). |
| * |
| * Reordering detection. |
| * -------------------- |
| * Reordering metric is maximal distance, which a packet can be displaced |
| * in packet stream. With SACKs we can estimate it: |
| * |
| * 1. SACK fills old hole and the corresponding segment was not |
| * ever retransmitted -> reordering. Alas, we cannot use it |
| * when segment was retransmitted. |
| * 2. The last flaw is solved with D-SACK. D-SACK arrives |
| * for retransmitted and already SACKed segment -> reordering.. |
| * Both of these heuristics are not used in Loss state, when we cannot |
| * account for retransmits accurately. |
| * |
| * SACK block validation. |
| * ---------------------- |
| * |
| * SACK block range validation checks that the received SACK block fits to |
| * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT. |
| * Note that SND.UNA is not included to the range though being valid because |
| * it means that the receiver is rather inconsistent with itself reporting |
| * SACK reneging when it should advance SND.UNA. Such SACK block this is |
| * perfectly valid, however, in light of RFC2018 which explicitly states |
| * that "SACK block MUST reflect the newest segment. Even if the newest |
| * segment is going to be discarded ...", not that it looks very clever |
| * in case of head skb. Due to potentional receiver driven attacks, we |
| * choose to avoid immediate execution of a walk in write queue due to |
| * reneging and defer head skb's loss recovery to standard loss recovery |
| * procedure that will eventually trigger (nothing forbids us doing this). |
| * |
| * Implements also blockage to start_seq wrap-around. Problem lies in the |
| * fact that though start_seq (s) is before end_seq (i.e., not reversed), |
| * there's no guarantee that it will be before snd_nxt (n). The problem |
| * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt |
| * wrap (s_w): |
| * |
| * <- outs wnd -> <- wrapzone -> |
| * u e n u_w e_w s n_w |
| * | | | | | | | |
| * |<------------+------+----- TCP seqno space --------------+---------->| |
| * ...-- <2^31 ->| |<--------... |
| * ...---- >2^31 ------>| |<--------... |
| * |
| * Current code wouldn't be vulnerable but it's better still to discard such |
| * crazy SACK blocks. Doing this check for start_seq alone closes somewhat |
| * similar case (end_seq after snd_nxt wrap) as earlier reversed check in |
| * snd_nxt wrap -> snd_una region will then become "well defined", i.e., |
| * equal to the ideal case (infinite seqno space without wrap caused issues). |
| * |
| * With D-SACK the lower bound is extended to cover sequence space below |
| * SND.UNA down to undo_marker, which is the last point of interest. Yet |
| * again, D-SACK block must not to go across snd_una (for the same reason as |
| * for the normal SACK blocks, explained above). But there all simplicity |
| * ends, TCP might receive valid D-SACKs below that. As long as they reside |
| * fully below undo_marker they do not affect behavior in anyway and can |
| * therefore be safely ignored. In rare cases (which are more or less |
| * theoretical ones), the D-SACK will nicely cross that boundary due to skb |
| * fragmentation and packet reordering past skb's retransmission. To consider |
| * them correctly, the acceptable range must be extended even more though |
| * the exact amount is rather hard to quantify. However, tp->max_window can |
| * be used as an exaggerated estimate. |
| */ |
| static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack, |
| u32 start_seq, u32 end_seq) |
| { |
| /* Too far in future, or reversed (interpretation is ambiguous) */ |
| if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq)) |
| return false; |
| |
| /* Nasty start_seq wrap-around check (see comments above) */ |
| if (!before(start_seq, tp->snd_nxt)) |
| return false; |
| |
| /* In outstanding window? ...This is valid exit for D-SACKs too. |
| * start_seq == snd_una is non-sensical (see comments above) |
| */ |
| if (after(start_seq, tp->snd_una)) |
| return true; |
| |
| if (!is_dsack || !tp->undo_marker) |
| return false; |
| |
| /* ...Then it's D-SACK, and must reside below snd_una completely */ |
| if (after(end_seq, tp->snd_una)) |
| return false; |
| |
| if (!before(start_seq, tp->undo_marker)) |
| return true; |
| |
| /* Too old */ |
| if (!after(end_seq, tp->undo_marker)) |
| return false; |
| |
| /* Undo_marker boundary crossing (overestimates a lot). Known already: |
| * start_seq < undo_marker and end_seq >= undo_marker. |
| */ |
| return !before(start_seq, end_seq - tp->max_window); |
| } |
| |
| static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb, |
| struct tcp_sack_block_wire *sp, int num_sacks, |
| u32 prior_snd_una, struct tcp_sacktag_state *state) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq); |
| u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq); |
| u32 dup_segs; |
| |
| if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) { |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV); |
| } else if (num_sacks > 1) { |
| u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq); |
| u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq); |
| |
| if (after(end_seq_0, end_seq_1) || before(start_seq_0, start_seq_1)) |
| return false; |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKOFORECV); |
| } else { |
| return false; |
| } |
| |
| dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state); |
| if (!dup_segs) { /* Skip dubious DSACK */ |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKIGNOREDDUBIOUS); |
| return false; |
| } |
| |
| NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECVSEGS, dup_segs); |
| |
| /* D-SACK for already forgotten data... Do dumb counting. */ |
| if (tp->undo_marker && tp->undo_retrans > 0 && |
| !after(end_seq_0, prior_snd_una) && |
| after(end_seq_0, tp->undo_marker)) |
| tp->undo_retrans = max_t(int, 0, tp->undo_retrans - dup_segs); |
| |
| return true; |
| } |
| |
| /* Check if skb is fully within the SACK block. In presence of GSO skbs, |
| * the incoming SACK may not exactly match but we can find smaller MSS |
| * aligned portion of it that matches. Therefore we might need to fragment |
| * which may fail and creates some hassle (caller must handle error case |
| * returns). |
| * |
| * FIXME: this could be merged to shift decision code |
| */ |
| static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb, |
| u32 start_seq, u32 end_seq) |
| { |
| int err; |
| bool in_sack; |
| unsigned int pkt_len; |
| unsigned int mss; |
| |
| in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && |
| !before(end_seq, TCP_SKB_CB(skb)->end_seq); |
| |
| if (tcp_skb_pcount(skb) > 1 && !in_sack && |
| after(TCP_SKB_CB(skb)->end_seq, start_seq)) { |
| mss = tcp_skb_mss(skb); |
| in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq); |
| |
| if (!in_sack) { |
| pkt_len = start_seq - TCP_SKB_CB(skb)->seq; |
| if (pkt_len < mss) |
| pkt_len = mss; |
| } else { |
| pkt_len = end_seq - TCP_SKB_CB(skb)->seq; |
| if (pkt_len < mss) |
| return -EINVAL; |
| } |
| |
| /* Round if necessary so that SACKs cover only full MSSes |
| * and/or the remaining small portion (if present) |
| */ |
| if (pkt_len > mss) { |
| unsigned int new_len = (pkt_len / mss) * mss; |
| if (!in_sack && new_len < pkt_len) |
| new_len += mss; |
| pkt_len = new_len; |
| } |
| |
| if (pkt_len >= skb->len && !in_sack) |
| return 0; |
| |
| err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb, |
| pkt_len, mss, GFP_ATOMIC); |
| if (err < 0) |
| return err; |
| } |
| |
| return in_sack; |
| } |
| |
| /* Mark the given newly-SACKed range as such, adjusting counters and hints. */ |
| static u8 tcp_sacktag_one(struct sock *sk, |
| struct tcp_sacktag_state *state, u8 sacked, |
| u32 start_seq, u32 end_seq, |
| int dup_sack, int pcount, |
| u64 xmit_time) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| /* Account D-SACK for retransmitted packet. */ |
| if (dup_sack && (sacked & TCPCB_RETRANS)) { |
| if (tp->undo_marker && tp->undo_retrans > 0 && |
| after(end_seq, tp->undo_marker)) |
| tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount); |
| if ((sacked & TCPCB_SACKED_ACKED) && |
| before(start_seq, state->reord)) |
| state->reord = start_seq; |
| } |
| |
| /* Nothing to do; acked frame is about to be dropped (was ACKed). */ |
| if (!after(end_seq, tp->snd_una)) |
| return sacked; |
| |
| if (!(sacked & TCPCB_SACKED_ACKED)) { |
| tcp_rack_advance(tp, sacked, end_seq, xmit_time); |
| |
| if (sacked & TCPCB_SACKED_RETRANS) { |
| /* If the segment is not tagged as lost, |
| * we do not clear RETRANS, believing |
| * that retransmission is still in flight. |
| */ |
| if (sacked & TCPCB_LOST) { |
| sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS); |
| tp->lost_out -= pcount; |
| tp->retrans_out -= pcount; |
| } |
| } else { |
| if (!(sacked & TCPCB_RETRANS)) { |
| /* New sack for not retransmitted frame, |
| * which was in hole. It is reordering. |
| */ |
| if (before(start_seq, |
| tcp_highest_sack_seq(tp)) && |
| before(start_seq, state->reord)) |
| state->reord = start_seq; |
| |
| if (!after(end_seq, tp->high_seq)) |
| state->flag |= FLAG_ORIG_SACK_ACKED; |
| if (state->first_sackt == 0) |
| state->first_sackt = xmit_time; |
| state->last_sackt = xmit_time; |
| } |
| |
| if (sacked & TCPCB_LOST) { |
| sacked &= ~TCPCB_LOST; |
| tp->lost_out -= pcount; |
| } |
| } |
| |
| sacked |= TCPCB_SACKED_ACKED; |
| state->flag |= FLAG_DATA_SACKED; |
| tp->sacked_out += pcount; |
| /* Out-of-order packets delivered */ |
| state->sack_delivered += pcount; |
| |
| /* Lost marker hint past SACKed? Tweak RFC3517 cnt */ |
| if (tp->lost_skb_hint && |
| before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq)) |
| tp->lost_cnt_hint += pcount; |
| } |
| |
| /* D-SACK. We can detect redundant retransmission in S|R and plain R |
| * frames and clear it. undo_retrans is decreased above, L|R frames |
| * are accounted above as well. |
| */ |
| if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) { |
| sacked &= ~TCPCB_SACKED_RETRANS; |
| tp->retrans_out -= pcount; |
| } |
| |
| return sacked; |
| } |
| |
| /* Shift newly-SACKed bytes from this skb to the immediately previous |
| * already-SACKed sk_buff. Mark the newly-SACKed bytes as such. |
| */ |
| static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev, |
| struct sk_buff *skb, |
| struct tcp_sacktag_state *state, |
| unsigned int pcount, int shifted, int mss, |
| bool dup_sack) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| u32 start_seq = TCP_SKB_CB(skb)->seq; /* start of newly-SACKed */ |
| u32 end_seq = start_seq + shifted; /* end of newly-SACKed */ |
| |
| BUG_ON(!pcount); |
| |
| /* Adjust counters and hints for the newly sacked sequence |
| * range but discard the return value since prev is already |
| * marked. We must tag the range first because the seq |
| * advancement below implicitly advances |
| * tcp_highest_sack_seq() when skb is highest_sack. |
| */ |
| tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked, |
| start_seq, end_seq, dup_sack, pcount, |
| tcp_skb_timestamp_us(skb)); |
| tcp_rate_skb_delivered(sk, skb, state->rate); |
| |
| if (skb == tp->lost_skb_hint) |
| tp->lost_cnt_hint += pcount; |
| |
| TCP_SKB_CB(prev)->end_seq += shifted; |
| TCP_SKB_CB(skb)->seq += shifted; |
| |
| tcp_skb_pcount_add(prev, pcount); |
| WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount); |
| tcp_skb_pcount_add(skb, -pcount); |
| |
| /* When we're adding to gso_segs == 1, gso_size will be zero, |
| * in theory this shouldn't be necessary but as long as DSACK |
| * code can come after this skb later on it's better to keep |
| * setting gso_size to something. |
| */ |
| if (!TCP_SKB_CB(prev)->tcp_gso_size) |
| TCP_SKB_CB(prev)->tcp_gso_size = mss; |
| |
| /* CHECKME: To clear or not to clear? Mimics normal skb currently */ |
| if (tcp_skb_pcount(skb) <= 1) |
| TCP_SKB_CB(skb)->tcp_gso_size = 0; |
| |
| /* Difference in this won't matter, both ACKed by the same cumul. ACK */ |
| TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS); |
| |
| if (skb->len > 0) { |
| BUG_ON(!tcp_skb_pcount(skb)); |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED); |
| return false; |
| } |
| |
| /* Whole SKB was eaten :-) */ |
| |
| if (skb == tp->retransmit_skb_hint) |
| tp->retransmit_skb_hint = prev; |
| if (skb == tp->lost_skb_hint) { |
| tp->lost_skb_hint = prev; |
| tp->lost_cnt_hint -= tcp_skb_pcount(prev); |
| } |
| |
| TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags; |
| TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor; |
| if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) |
| TCP_SKB_CB(prev)->end_seq++; |
| |
| if (skb == tcp_highest_sack(sk)) |
| tcp_advance_highest_sack(sk, skb); |
| |
| tcp_skb_collapse_tstamp(prev, skb); |
| if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp)) |
| TCP_SKB_CB(prev)->tx.delivered_mstamp = 0; |
| |
| tcp_rtx_queue_unlink_and_free(skb, sk); |
| |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED); |
| |
| return true; |
| } |
| |
| /* I wish gso_size would have a bit more sane initialization than |
| * something-or-zero which complicates things |
| */ |
| static int tcp_skb_seglen(const struct sk_buff *skb) |
| { |
| return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb); |
| } |
| |
| /* Shifting pages past head area doesn't work */ |
| static int skb_can_shift(const struct sk_buff *skb) |
| { |
| return !skb_headlen(skb) && skb_is_nonlinear(skb); |
| } |
| |
| int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from, |
| int pcount, int shiftlen) |
| { |
| /* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE) |
| * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need |
| * to make sure not storing more than 65535 * 8 bytes per skb, |
| * even if current MSS is bigger. |
| */ |
| if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE)) |
| return 0; |
| if (unlikely(tcp_skb_pcount(to) + pcount > 65535)) |
| return 0; |
| return skb_shift(to, from, shiftlen); |
| } |
| |
| /* Try collapsing SACK blocks spanning across multiple skbs to a single |
| * skb. |
| */ |
| static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb, |
| struct tcp_sacktag_state *state, |
| u32 start_seq, u32 end_seq, |
| bool dup_sack) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct sk_buff *prev; |
| int mss; |
| int pcount = 0; |
| int len; |
| int in_sack; |
| |
| /* Normally R but no L won't result in plain S */ |
| if (!dup_sack && |
| (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS) |
| goto fallback; |
| if (!skb_can_shift(skb)) |
| goto fallback; |
| /* This frame is about to be dropped (was ACKed). */ |
| if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) |
| goto fallback; |
| |
| /* Can only happen with delayed DSACK + discard craziness */ |
| prev = skb_rb_prev(skb); |
| if (!prev) |
| goto fallback; |
| |
| if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) |
| goto fallback; |
| |
| if (!tcp_skb_can_collapse(prev, skb)) |
| goto fallback; |
| |
| in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && |
| !before(end_seq, TCP_SKB_CB(skb)->end_seq); |
| |
| if (in_sack) { |
| len = skb->len; |
| pcount = tcp_skb_pcount(skb); |
| mss = tcp_skb_seglen(skb); |
| |
| /* TODO: Fix DSACKs to not fragment already SACKed and we can |
| * drop this restriction as unnecessary |
| */ |
| if (mss != tcp_skb_seglen(prev)) |
| goto fallback; |
| } else { |
| if (!after(TCP_SKB_CB(skb)->end_seq, start_seq)) |
| goto noop; |
| /* CHECKME: This is non-MSS split case only?, this will |
| * cause skipped skbs due to advancing loop btw, original |
| * has that feature too |
| */ |
| if (tcp_skb_pcount(skb) <= 1) |
| goto noop; |
| |
| in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq); |
| if (!in_sack) { |
| /* TODO: head merge to next could be attempted here |
| * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)), |
| * though it might not be worth of the additional hassle |
| * |
| * ...we can probably just fallback to what was done |
| * previously. We could try merging non-SACKed ones |
| * as well but it probably isn't going to buy off |
| * because later SACKs might again split them, and |
| * it would make skb timestamp tracking considerably |
| * harder problem. |
| */ |
| goto fallback; |
| } |
| |
| len = end_seq - TCP_SKB_CB(skb)->seq; |
| BUG_ON(len < 0); |
| BUG_ON(len > skb->len); |
| |
| /* MSS boundaries should be honoured or else pcount will |
| * severely break even though it makes things bit trickier. |
| * Optimize common case to avoid most of the divides |
| */ |
| mss = tcp_skb_mss(skb); |
| |
| /* TODO: Fix DSACKs to not fragment already SACKed and we can |
| * drop this restriction as unnecessary |
| */ |
| if (mss != tcp_skb_seglen(prev)) |
| goto fallback; |
| |
| if (len == mss) { |
| pcount = 1; |
| } else if (len < mss) { |
| goto noop; |
| } else { |
| pcount = len / mss; |
| len = pcount * mss; |
| } |
| } |
| |
| /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */ |
| if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una)) |
| goto fallback; |
| |
| if (!tcp_skb_shift(prev, skb, pcount, len)) |
| goto fallback; |
| if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack)) |
| goto out; |
| |
| /* Hole filled allows collapsing with the next as well, this is very |
| * useful when hole on every nth skb pattern happens |
| */ |
| skb = skb_rb_next(prev); |
| if (!skb) |
| goto out; |
| |
| if (!skb_can_shift(skb) || |
| ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) || |
| (mss != tcp_skb_seglen(skb))) |
| goto out; |
| |
| if (!tcp_skb_can_collapse(prev, skb)) |
| goto out; |
| len = skb->len; |
| pcount = tcp_skb_pcount(skb); |
| if (tcp_skb_shift(prev, skb, pcount, len)) |
| tcp_shifted_skb(sk, prev, skb, state, pcount, |
| len, mss, 0); |
| |
| out: |
| return prev; |
| |
| noop: |
| return skb; |
| |
| fallback: |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK); |
| return NULL; |
| } |
| |
| static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk, |
| struct tcp_sack_block *next_dup, |
| struct tcp_sacktag_state *state, |
| u32 start_seq, u32 end_seq, |
| bool dup_sack_in) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct sk_buff *tmp; |
| |
| skb_rbtree_walk_from(skb) { |
| int in_sack = 0; |
| bool dup_sack = dup_sack_in; |
| |
| /* queue is in-order => we can short-circuit the walk early */ |
| if (!before(TCP_SKB_CB(skb)->seq, end_seq)) |
| break; |
| |
| if (next_dup && |
| before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) { |
| in_sack = tcp_match_skb_to_sack(sk, skb, |
| next_dup->start_seq, |
| next_dup->end_seq); |
| if (in_sack > 0) |
| dup_sack = true; |
| } |
| |
| /* skb reference here is a bit tricky to get right, since |
| * shifting can eat and free both this skb and the next, |
| * so not even _safe variant of the loop is enough. |
| */ |
| if (in_sack <= 0) { |
| tmp = tcp_shift_skb_data(sk, skb, state, |
| start_seq, end_seq, dup_sack); |
| if (tmp) { |
| if (tmp != skb) { |
| skb = tmp; |
| continue; |
| } |
| |
| in_sack = 0; |
| } else { |
| in_sack = tcp_match_skb_to_sack(sk, skb, |
| start_seq, |
| end_seq); |
| } |
| } |
| |
| if (unlikely(in_sack < 0)) |
| break; |
| |
| if (in_sack) { |
| TCP_SKB_CB(skb)->sacked = |
| tcp_sacktag_one(sk, |
| state, |
| TCP_SKB_CB(skb)->sacked, |
| TCP_SKB_CB(skb)->seq, |
| TCP_SKB_CB(skb)->end_seq, |
| dup_sack, |
| tcp_skb_pcount(skb), |
| tcp_skb_timestamp_us(skb)); |
| tcp_rate_skb_delivered(sk, skb, state->rate); |
| if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) |
| list_del_init(&skb->tcp_tsorted_anchor); |
| |
| if (!before(TCP_SKB_CB(skb)->seq, |
| tcp_highest_sack_seq(tp))) |
| tcp_advance_highest_sack(sk, skb); |
| } |
| } |
| return skb; |
| } |
| |
| static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq) |
| { |
| struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node; |
| struct sk_buff *skb; |
| |
| while (*p) { |
| parent = *p; |
| skb = rb_to_skb(parent); |
| if (before(seq, TCP_SKB_CB(skb)->seq)) { |
| p = &parent->rb_left; |
| continue; |
| } |
| if (!before(seq, TCP_SKB_CB(skb)->end_seq)) { |
| p = &parent->rb_right; |
| continue; |
| } |
| return skb; |
| } |
| return NULL; |
| } |
| |
| static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk, |
| u32 skip_to_seq) |
| { |
| if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq)) |
| return skb; |
| |
| return tcp_sacktag_bsearch(sk, skip_to_seq); |
| } |
| |
| static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb, |
| struct sock *sk, |
| struct tcp_sack_block *next_dup, |
| struct tcp_sacktag_state *state, |
| u32 skip_to_seq) |
| { |
| if (!next_dup) |
| return skb; |
| |
| if (before(next_dup->start_seq, skip_to_seq)) { |
| skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq); |
| skb = tcp_sacktag_walk(skb, sk, NULL, state, |
| next_dup->start_seq, next_dup->end_seq, |
| 1); |
| } |
| |
| return skb; |
| } |
| |
| static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache) |
| { |
| return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache); |
| } |
| |
| static int |
| tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb, |
| u32 prior_snd_una, struct tcp_sacktag_state *state) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| const unsigned char *ptr = (skb_transport_header(ack_skb) + |
| TCP_SKB_CB(ack_skb)->sacked); |
| struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2); |
| struct tcp_sack_block sp[TCP_NUM_SACKS]; |
| struct tcp_sack_block *cache; |
| struct sk_buff *skb; |
| int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3); |
| int used_sacks; |
| bool found_dup_sack = false; |
| int i, j; |
| int first_sack_index; |
| |
| state->flag = 0; |
| state->reord = tp->snd_nxt; |
| |
| if (!tp->sacked_out) |
| tcp_highest_sack_reset(sk); |
| |
| found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire, |
| num_sacks, prior_snd_una, state); |
| |
| /* Eliminate too old ACKs, but take into |
| * account more or less fresh ones, they can |
| * contain valid SACK info. |
| */ |
| if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window)) |
| return 0; |
| |
| if (!tp->packets_out) |
| goto out; |
| |
| used_sacks = 0; |
| first_sack_index = 0; |
| for (i = 0; i < num_sacks; i++) { |
| bool dup_sack = !i && found_dup_sack; |
| |
| sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq); |
| sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq); |
| |
| if (!tcp_is_sackblock_valid(tp, dup_sack, |
| sp[used_sacks].start_seq, |
| sp[used_sacks].end_seq)) { |
| int mib_idx; |
| |
| if (dup_sack) { |
| if (!tp->undo_marker) |
| mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO; |
| else |
| mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD; |
| } else { |
| /* Don't count olds caused by ACK reordering */ |
| if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) && |
| !after(sp[used_sacks].end_seq, tp->snd_una)) |
| continue; |
| mib_idx = LINUX_MIB_TCPSACKDISCARD; |
| } |
| |
| NET_INC_STATS(sock_net(sk), mib_idx); |
| if (i == 0) |
| first_sack_index = -1; |
| continue; |
| } |
| |
| /* Ignore very old stuff early */ |
| if (!after(sp[used_sacks].end_seq, prior_snd_una)) { |
| if (i == 0) |
| first_sack_index = -1; |
| continue; |
| } |
| |
| used_sacks++; |
| } |
| |
| /* order SACK blocks to allow in order walk of the retrans queue */ |
| for (i = used_sacks - 1; i > 0; i--) { |
| for (j = 0; j < i; j++) { |
| if (after(sp[j].start_seq, sp[j + 1].start_seq)) { |
| swap(sp[j], sp[j + 1]); |
| |
| /* Track where the first SACK block goes to */ |
| if (j == first_sack_index) |
| first_sack_index = j + 1; |
| } |
| } |
| } |
| |
| state->mss_now = tcp_current_mss(sk); |
| skb = NULL; |
| i = 0; |
| |
| if (!tp->sacked_out) { |
| /* It's already past, so skip checking against it */ |
| cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache); |
| } else { |
| cache = tp->recv_sack_cache; |
| /* Skip empty blocks in at head of the cache */ |
| while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq && |
| !cache->end_seq) |
| cache++; |
| } |
| |
| while (i < used_sacks) { |
| u32 start_seq = sp[i].start_seq; |
| u32 end_seq = sp[i].end_seq; |
| bool dup_sack = (found_dup_sack && (i == first_sack_index)); |
| struct tcp_sack_block *next_dup = NULL; |
| |
| if (found_dup_sack && ((i + 1) == first_sack_index)) |
| next_dup = &sp[i + 1]; |
| |
| /* Skip too early cached blocks */ |
| while (tcp_sack_cache_ok(tp, cache) && |
| !before(start_seq, cache->end_seq)) |
| cache++; |
| |
| /* Can skip some work by looking recv_sack_cache? */ |
| if (tcp_sack_cache_ok(tp, cache) && !dup_sack && |
| after(end_seq, cache->start_seq)) { |
| |
| /* Head todo? */ |
| if (before(start_seq, cache->start_seq)) { |
| skb = tcp_sacktag_skip(skb, sk, start_seq); |
| skb = tcp_sacktag_walk(skb, sk, next_dup, |
| state, |
| start_seq, |
| cache->start_seq, |
| dup_sack); |
| } |
| |
| /* Rest of the block already fully processed? */ |
| if (!after(end_seq, cache->end_seq)) |
| goto advance_sp; |
| |
| skb = tcp_maybe_skipping_dsack(skb, sk, next_dup, |
| state, |
| cache->end_seq); |
| |
| /* ...tail remains todo... */ |
| if (tcp_highest_sack_seq(tp) == cache->end_seq) { |
| /* ...but better entrypoint exists! */ |
| skb = tcp_highest_sack(sk); |
| if (!skb) |
| break; |
| cache++; |
| goto walk; |
| } |
| |
| skb = tcp_sacktag_skip(skb, sk, cache->end_seq); |
| /* Check overlap against next cached too (past this one already) */ |
| cache++; |
| continue; |
| } |
| |
| if (!before(start_seq, tcp_highest_sack_seq(tp))) { |
| skb = tcp_highest_sack(sk); |
| if (!skb) |
| break; |
| } |
| skb = tcp_sacktag_skip(skb, sk, start_seq); |
| |
| walk: |
| skb = tcp_sacktag_walk(skb, sk, next_dup, state, |
| start_seq, end_seq, dup_sack); |
| |
| advance_sp: |
| i++; |
| } |
| |
| /* Clear the head of the cache sack blocks so we can skip it next time */ |
| for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) { |
| tp->recv_sack_cache[i].start_seq = 0; |
| tp->recv_sack_cache[i].end_seq = 0; |
| } |
| for (j = 0; j < used_sacks; j++) |
| tp->recv_sack_cache[i++] = sp[j]; |
| |
| if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker) |
| tcp_check_sack_reordering(sk, state->reord, 0); |
| |
| tcp_verify_left_out(tp); |
| out: |
| |
| #if FASTRETRANS_DEBUG > 0 |
| WARN_ON((int)tp->sacked_out < 0); |
| WARN_ON((int)tp->lost_out < 0); |
| WARN_ON((int)tp->retrans_out < 0); |
| WARN_ON((int)tcp_packets_in_flight(tp) < 0); |
| #endif |
| return state->flag; |
| } |
| |
| /* Limits sacked_out so that sum with lost_out isn't ever larger than |
| * packets_out. Returns false if sacked_out adjustement wasn't necessary. |
| */ |
| static bool tcp_limit_reno_sacked(struct tcp_sock *tp) |
| { |
| u32 holes; |
| |
| holes = max(tp->lost_out, 1U); |
| holes = min(holes, tp->packets_out); |
| |
| if ((tp->sacked_out + holes) > tp->packets_out) { |
| tp->sacked_out = tp->packets_out - holes; |
| return true; |
| } |
| return false; |
| } |
| |
| /* If we receive more dupacks than we expected counting segments |
| * in assumption of absent reordering, interpret this as reordering. |
| * The only another reason could be bug in receiver TCP. |
| */ |
| static void tcp_check_reno_reordering(struct sock *sk, const int addend) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (!tcp_limit_reno_sacked(tp)) |
| return; |
| |
| tp->reordering = min_t(u32, tp->packets_out + addend, |
| READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering)); |
| tp->reord_seen++; |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER); |
| } |
| |
| /* Emulate SACKs for SACKless connection: account for a new dupack. */ |
| |
| static void tcp_add_reno_sack(struct sock *sk, int num_dupack, bool ece_ack) |
| { |
| if (num_dupack) { |
| struct tcp_sock *tp = tcp_sk(sk); |
| u32 prior_sacked = tp->sacked_out; |
| s32 delivered; |
| |
| tp->sacked_out += num_dupack; |
| tcp_check_reno_reordering(sk, 0); |
| delivered = tp->sacked_out - prior_sacked; |
| if (delivered > 0) |
| tcp_count_delivered(tp, delivered, ece_ack); |
| tcp_verify_left_out(tp); |
| } |
| } |
| |
| /* Account for ACK, ACKing some data in Reno Recovery phase. */ |
| |
| static void tcp_remove_reno_sacks(struct sock *sk, int acked, bool ece_ack) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (acked > 0) { |
| /* One ACK acked hole. The rest eat duplicate ACKs. */ |
| tcp_count_delivered(tp, max_t(int, acked - tp->sacked_out, 1), |
| ece_ack); |
| if (acked - 1 >= tp->sacked_out) |
| tp->sacked_out = 0; |
| else |
| tp->sacked_out -= acked - 1; |
| } |
| tcp_check_reno_reordering(sk, acked); |
| tcp_verify_left_out(tp); |
| } |
| |
| static inline void tcp_reset_reno_sack(struct tcp_sock *tp) |
| { |
| tp->sacked_out = 0; |
| } |
| |
| void tcp_clear_retrans(struct tcp_sock *tp) |
| { |
| tp->retrans_out = 0; |
| tp->lost_out = 0; |
| tp->undo_marker = 0; |
| tp->undo_retrans = -1; |
| tp->sacked_out = 0; |
| tp->rto_stamp = 0; |
| tp->total_rto = 0; |
| tp->total_rto_recoveries = 0; |
| tp->total_rto_time = 0; |
| } |
| |
| static inline void tcp_init_undo(struct tcp_sock *tp) |
| { |
| tp->undo_marker = tp->snd_una; |
| |
| /* Retransmission still in flight may cause DSACKs later. */ |
| /* First, account for regular retransmits in flight: */ |
| tp->undo_retrans = tp->retrans_out; |
| /* Next, account for TLP retransmits in flight: */ |
| if (tp->tlp_high_seq && tp->tlp_retrans) |
| tp->undo_retrans++; |
| /* Finally, avoid 0, because undo_retrans==0 means "can undo now": */ |
| if (!tp->undo_retrans) |
| tp->undo_retrans = -1; |
| } |
| |
| static bool tcp_is_rack(const struct sock *sk) |
| { |
| return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_recovery) & |
| TCP_RACK_LOSS_DETECTION; |
| } |
| |
| /* If we detect SACK reneging, forget all SACK information |
| * and reset tags completely, otherwise preserve SACKs. If receiver |
| * dropped its ofo queue, we will know this due to reneging detection. |
| */ |
| static void tcp_timeout_mark_lost(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct sk_buff *skb, *head; |
| bool is_reneg; /* is receiver reneging on SACKs? */ |
| |
| head = tcp_rtx_queue_head(sk); |
| is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED); |
| if (is_reneg) { |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING); |
| tp->sacked_out = 0; |
| /* Mark SACK reneging until we recover from this loss event. */ |
| tp->is_sack_reneg = 1; |
| } else if (tcp_is_reno(tp)) { |
| tcp_reset_reno_sack(tp); |
| } |
| |
| skb = head; |
| skb_rbtree_walk_from(skb) { |
| if (is_reneg) |
| TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED; |
| else if (tcp_is_rack(sk) && skb != head && |
| tcp_rack_skb_timeout(tp, skb, 0) > 0) |
| continue; /* Don't mark recently sent ones lost yet */ |
| tcp_mark_skb_lost(sk, skb); |
| } |
| tcp_verify_left_out(tp); |
| tcp_clear_all_retrans_hints(tp); |
| } |
| |
| /* Enter Loss state. */ |
| void tcp_enter_loss(struct sock *sk) |
| { |
| const struct inet_connection_sock *icsk = inet_csk(sk); |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct net *net = sock_net(sk); |
| bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery; |
| u8 reordering; |
| |
| tcp_timeout_mark_lost(sk); |
| |
| /* Reduce ssthresh if it has not yet been made inside this window. */ |
| if (icsk->icsk_ca_state <= TCP_CA_Disorder || |
| !after(tp->high_seq, tp->snd_una) || |
| (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) { |
| tp->prior_ssthresh = tcp_current_ssthresh(sk); |
| tp->prior_cwnd = tcp_snd_cwnd(tp); |
| tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); |
| tcp_ca_event(sk, CA_EVENT_LOSS); |
| tcp_init_undo(tp); |
| } |
| tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + 1); |
| tp->snd_cwnd_cnt = 0; |
| tp->snd_cwnd_stamp = tcp_jiffies32; |
| |
| /* Timeout in disordered state after receiving substantial DUPACKs |
| * suggests that the degree of reordering is over-estimated. |
| */ |
| reordering = READ_ONCE(net->ipv4.sysctl_tcp_reordering); |
| if (icsk->icsk_ca_state <= TCP_CA_Disorder && |
| tp->sacked_out >= reordering) |
| tp->reordering = min_t(unsigned int, tp->reordering, |
| reordering); |
| |
| tcp_set_ca_state(sk, TCP_CA_Loss); |
| tp->high_seq = tp->snd_nxt; |
| tp->tlp_high_seq = 0; |
| tcp_ecn_queue_cwr(tp); |
| |
| /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous |
| * loss recovery is underway except recurring timeout(s) on |
| * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing |
| */ |
| tp->frto = READ_ONCE(net->ipv4.sysctl_tcp_frto) && |
| (new_recovery || icsk->icsk_retransmits) && |
| !inet_csk(sk)->icsk_mtup.probe_size; |
| } |
| |
| /* If ACK arrived pointing to a remembered SACK, it means that our |
| * remembered SACKs do not reflect real state of receiver i.e. |
| * receiver _host_ is heavily congested (or buggy). |
| * |
| * To avoid big spurious retransmission bursts due to transient SACK |
| * scoreboard oddities that look like reneging, we give the receiver a |
| * little time (max(RTT/2, 10ms)) to send us some more ACKs that will |
| * restore sanity to the SACK scoreboard. If the apparent reneging |
| * persists until this RTO then we'll clear the SACK scoreboard. |
| */ |
| static bool tcp_check_sack_reneging(struct sock *sk, int *ack_flag) |
| { |
| if (*ack_flag & FLAG_SACK_RENEGING && |
| *ack_flag & FLAG_SND_UNA_ADVANCED) { |
| struct tcp_sock *tp = tcp_sk(sk); |
| unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4), |
| msecs_to_jiffies(10)); |
| |
| inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, |
| delay, TCP_RTO_MAX); |
| *ack_flag &= ~FLAG_SET_XMIT_TIMER; |
| return true; |
| } |
| return false; |
| } |
| |
| /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs |
| * counter when SACK is enabled (without SACK, sacked_out is used for |
| * that purpose). |
| * |
| * With reordering, holes may still be in flight, so RFC3517 recovery |
| * uses pure sacked_out (total number of SACKed segments) even though |
| * it violates the RFC that uses duplicate ACKs, often these are equal |
| * but when e.g. out-of-window ACKs or packet duplication occurs, |
| * they differ. Since neither occurs due to loss, TCP should really |
| * ignore them. |
| */ |
| static inline int tcp_dupack_heuristics(const struct tcp_sock *tp) |
| { |
| return tp->sacked_out + 1; |
| } |
| |
| /* Linux NewReno/SACK/ECN state machine. |
| * -------------------------------------- |
| * |
| * "Open" Normal state, no dubious events, fast path. |
| * "Disorder" In all the respects it is "Open", |
| * but requires a bit more attention. It is entered when |
| * we see some SACKs or dupacks. It is split of "Open" |
| * mainly to move some processing from fast path to slow one. |
| * "CWR" CWND was reduced due to some Congestion Notification event. |
| * It can be ECN, ICMP source quench, local device congestion. |
| * "Recovery" CWND was reduced, we are fast-retransmitting. |
| * "Loss" CWND was reduced due to RTO timeout or SACK reneging. |
| * |
| * tcp_fastretrans_alert() is entered: |
| * - each incoming ACK, if state is not "Open" |
| * - when arrived ACK is unusual, namely: |
| * * SACK |
| * * Duplicate ACK. |
| * * ECN ECE. |
| * |
| * Counting packets in flight is pretty simple. |
| * |
| * in_flight = packets_out - left_out + retrans_out |
| * |
| * packets_out is SND.NXT-SND.UNA counted in packets. |
| * |
| * retrans_out is number of retransmitted segments. |
| * |
| * left_out is number of segments left network, but not ACKed yet. |
| * |
| * left_out = sacked_out + lost_out |
| * |
| * sacked_out: Packets, which arrived to receiver out of order |
| * and hence not ACKed. With SACKs this number is simply |
| * amount of SACKed data. Even without SACKs |
| * it is easy to give pretty reliable estimate of this number, |
| * counting duplicate ACKs. |
| * |
| * lost_out: Packets lost by network. TCP has no explicit |
| * "loss notification" feedback from network (for now). |
| * It means that this number can be only _guessed_. |
| * Actually, it is the heuristics to predict lossage that |
| * distinguishes different algorithms. |
| * |
| * F.e. after RTO, when all the queue is considered as lost, |
| * lost_out = packets_out and in_flight = retrans_out. |
| * |
| * Essentially, we have now a few algorithms detecting |
| * lost packets. |
| * |
| * If the receiver supports SACK: |
| * |
| * RFC6675/3517: It is the conventional algorithm. A packet is |
| * considered lost if the number of higher sequence packets |
| * SACKed is greater than or equal the DUPACK thoreshold |
| * (reordering). This is implemented in tcp_mark_head_lost and |
| * tcp_update_scoreboard. |
| * |
| * RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm |
| * (2017-) that checks timing instead of counting DUPACKs. |
| * Essentially a packet is considered lost if it's not S/ACKed |
| * after RTT + reordering_window, where both metrics are |
| * dynamically measured and adjusted. This is implemented in |
| * tcp_rack_mark_lost. |
| * |
| * If the receiver does not support SACK: |
| * |
| * NewReno (RFC6582): in Recovery we assume that one segment |
| * is lost (classic Reno). While we are in Recovery and |
| * a partial ACK arrives, we assume that one more packet |
| * is lost (NewReno). This heuristics are the same in NewReno |
| * and SACK. |
| * |
| * Really tricky (and requiring careful tuning) part of algorithm |
| * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue(). |
| * The first determines the moment _when_ we should reduce CWND and, |
| * hence, slow down forward transmission. In fact, it determines the moment |
| * when we decide that hole is caused by loss, rather than by a reorder. |
| * |
| * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill |
| * holes, caused by lost packets. |
| * |
| * And the most logically complicated part of algorithm is undo |
| * heuristics. We detect false retransmits due to both too early |
| * fast retransmit (reordering) and underestimated RTO, analyzing |
| * timestamps and D-SACKs. When we detect that some segments were |
| * retransmitted by mistake and CWND reduction was wrong, we undo |
| * window reduction and abort recovery phase. This logic is hidden |
| * inside several functions named tcp_try_undo_<something>. |
| */ |
| |
| /* This function decides, when we should leave Disordered state |
| * and enter Recovery phase, reducing congestion window. |
| * |
| * Main question: may we further continue forward transmission |
| * with the same cwnd? |
| */ |
| static bool tcp_time_to_recover(struct sock *sk, int flag) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| /* Trick#1: The loss is proven. */ |
| if (tp->lost_out) |
| return true; |
| |
| /* Not-A-Trick#2 : Classic rule... */ |
| if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering) |
| return true; |
| |
| return false; |
| } |
| |
| /* Detect loss in event "A" above by marking head of queue up as lost. |
| * For RFC3517 SACK, a segment is considered lost if it |
| * has at least tp->reordering SACKed seqments above it; "packets" refers to |
| * the maximum SACKed segments to pass before reaching this limit. |
| */ |
| static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct sk_buff *skb; |
| int cnt; |
| /* Use SACK to deduce losses of new sequences sent during recovery */ |
| const u32 loss_high = tp->snd_nxt; |
| |
| WARN_ON(packets > tp->packets_out); |
| skb = tp->lost_skb_hint; |
| if (skb) { |
| /* Head already handled? */ |
| if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una)) |
| return; |
| cnt = tp->lost_cnt_hint; |
| } else { |
| skb = tcp_rtx_queue_head(sk); |
| cnt = 0; |
| } |
| |
| skb_rbtree_walk_from(skb) { |
| /* TODO: do this better */ |
| /* this is not the most efficient way to do this... */ |
| tp->lost_skb_hint = skb; |
| tp->lost_cnt_hint = cnt; |
| |
| if (after(TCP_SKB_CB(skb)->end_seq, loss_high)) |
| break; |
| |
| if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) |
| cnt += tcp_skb_pcount(skb); |
| |
| if (cnt > packets) |
| break; |
| |
| if (!(TCP_SKB_CB(skb)->sacked & TCPCB_LOST)) |
| tcp_mark_skb_lost(sk, skb); |
| |
| if (mark_head) |
| break; |
| } |
| tcp_verify_left_out(tp); |
| } |
| |
| /* Account newly detected lost packet(s) */ |
| |
| static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (tcp_is_sack(tp)) { |
| int sacked_upto = tp->sacked_out - tp->reordering; |
| if (sacked_upto >= 0) |
| tcp_mark_head_lost(sk, sacked_upto, 0); |
| else if (fast_rexmit) |
| tcp_mark_head_lost(sk, 1, 1); |
| } |
| } |
| |
| static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when) |
| { |
| return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && |
| before(tp->rx_opt.rcv_tsecr, when); |
| } |
| |
| /* skb is spurious retransmitted if the returned timestamp echo |
| * reply is prior to the skb transmission time |
| */ |
| static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp, |
| const struct sk_buff *skb) |
| { |
| return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) && |
| tcp_tsopt_ecr_before(tp, tcp_skb_timestamp_ts(tp->tcp_usec_ts, skb)); |
| } |
| |
| /* Nothing was retransmitted or returned timestamp is less |
| * than timestamp of the first retransmission. |
| */ |
| static inline bool tcp_packet_delayed(const struct tcp_sock *tp) |
| { |
| return tp->retrans_stamp && |
| tcp_tsopt_ecr_before(tp, tp->retrans_stamp); |
| } |
| |
| /* Undo procedures. */ |
| |
| /* We can clear retrans_stamp when there are no retransmissions in the |
| * window. It would seem that it is trivially available for us in |
| * tp->retrans_out, however, that kind of assumptions doesn't consider |
| * what will happen if errors occur when sending retransmission for the |
| * second time. ...It could the that such segment has only |
| * TCPCB_EVER_RETRANS set at the present time. It seems that checking |
| * the head skb is enough except for some reneging corner cases that |
| * are not worth the effort. |
| * |
| * Main reason for all this complexity is the fact that connection dying |
| * time now depends on the validity of the retrans_stamp, in particular, |
| * that successive retransmissions of a segment must not advance |
| * retrans_stamp under any conditions. |
| */ |
| static bool tcp_any_retrans_done(const struct sock *sk) |
| { |
| const struct tcp_sock *tp = tcp_sk(sk); |
| struct sk_buff *skb; |
| |
| if (tp->retrans_out) |
| return true; |
| |
| skb = tcp_rtx_queue_head(sk); |
| if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS)) |
| return true; |
| |
| return false; |
| } |
| |
| static void DBGUNDO(struct sock *sk, const char *msg) |
| { |
| #if FASTRETRANS_DEBUG > 1 |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct inet_sock *inet = inet_sk(sk); |
| |
| if (sk->sk_family == AF_INET) { |
| pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n", |
| msg, |
| &inet->inet_daddr, ntohs(inet->inet_dport), |
| tcp_snd_cwnd(tp), tcp_left_out(tp), |
| tp->snd_ssthresh, tp->prior_ssthresh, |
| tp->packets_out); |
| } |
| #if IS_ENABLED(CONFIG_IPV6) |
| else if (sk->sk_family == AF_INET6) { |
| pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n", |
| msg, |
| &sk->sk_v6_daddr, ntohs(inet->inet_dport), |
| tcp_snd_cwnd(tp), tcp_left_out(tp), |
| tp->snd_ssthresh, tp->prior_ssthresh, |
| tp->packets_out); |
| } |
| #endif |
| #endif |
| } |
| |
| static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (unmark_loss) { |
| struct sk_buff *skb; |
| |
| skb_rbtree_walk(skb, &sk->tcp_rtx_queue) { |
| TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; |
| } |
| tp->lost_out = 0; |
| tcp_clear_all_retrans_hints(tp); |
| } |
| |
| if (tp->prior_ssthresh) { |
| const struct inet_connection_sock *icsk = inet_csk(sk); |
| |
| tcp_snd_cwnd_set(tp, icsk->icsk_ca_ops->undo_cwnd(sk)); |
| |
| if (tp->prior_ssthresh > tp->snd_ssthresh) { |
| tp->snd_ssthresh = tp->prior_ssthresh; |
| tcp_ecn_withdraw_cwr(tp); |
| } |
| } |
| tp->snd_cwnd_stamp = tcp_jiffies32; |
| tp->undo_marker = 0; |
| tp->rack.advanced = 1; /* Force RACK to re-exam losses */ |
| } |
| |
| static inline bool tcp_may_undo(const struct tcp_sock *tp) |
| { |
| return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp)); |
| } |
| |
| static bool tcp_is_non_sack_preventing_reopen(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) { |
| /* Hold old state until something *above* high_seq |
| * is ACKed. For Reno it is MUST to prevent false |
| * fast retransmits (RFC2582). SACK TCP is safe. */ |
| if (!tcp_any_retrans_done(sk)) |
| tp->retrans_stamp = 0; |
| return true; |
| } |
| return false; |
| } |
| |
| /* People celebrate: "We love our President!" */ |
| static bool tcp_try_undo_recovery(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (tcp_may_undo(tp)) { |
| int mib_idx; |
| |
| /* Happy end! We did not retransmit anything |
| * or our original transmission succeeded. |
| */ |
| DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans"); |
| tcp_undo_cwnd_reduction(sk, false); |
| if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss) |
| mib_idx = LINUX_MIB_TCPLOSSUNDO; |
| else |
| mib_idx = LINUX_MIB_TCPFULLUNDO; |
| |
| NET_INC_STATS(sock_net(sk), mib_idx); |
| } else if (tp->rack.reo_wnd_persist) { |
| tp->rack.reo_wnd_persist--; |
| } |
| if (tcp_is_non_sack_preventing_reopen(sk)) |
| return true; |
| tcp_set_ca_state(sk, TCP_CA_Open); |
| tp->is_sack_reneg = 0; |
| return false; |
| } |
| |
| /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */ |
| static bool tcp_try_undo_dsack(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (tp->undo_marker && !tp->undo_retrans) { |
| tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH, |
| tp->rack.reo_wnd_persist + 1); |
| DBGUNDO(sk, "D-SACK"); |
| tcp_undo_cwnd_reduction(sk, false); |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO); |
| return true; |
| } |
| return false; |
| } |
| |
| /* Undo during loss recovery after partial ACK or using F-RTO. */ |
| static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (frto_undo || tcp_may_undo(tp)) { |
| tcp_undo_cwnd_reduction(sk, true); |
| |
| DBGUNDO(sk, "partial loss"); |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO); |
| if (frto_undo) |
| NET_INC_STATS(sock_net(sk), |
| LINUX_MIB_TCPSPURIOUSRTOS); |
| inet_csk(sk)->icsk_retransmits = 0; |
| if (tcp_is_non_sack_preventing_reopen(sk)) |
| return true; |
| if (frto_undo || tcp_is_sack(tp)) { |
| tcp_set_ca_state(sk, TCP_CA_Open); |
| tp->is_sack_reneg = 0; |
| } |
| return true; |
| } |
| return false; |
| } |
| |
| /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937. |
| * It computes the number of packets to send (sndcnt) based on packets newly |
| * delivered: |
| * 1) If the packets in flight is larger than ssthresh, PRR spreads the |
| * cwnd reductions across a full RTT. |
| * 2) Otherwise PRR uses packet conservation to send as much as delivered. |
| * But when SND_UNA is acked without further losses, |
| * slow starts cwnd up to ssthresh to speed up the recovery. |
| */ |
| static void tcp_init_cwnd_reduction(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| tp->high_seq = tp->snd_nxt; |
| tp->tlp_high_seq = 0; |
| tp->snd_cwnd_cnt = 0; |
| tp->prior_cwnd = tcp_snd_cwnd(tp); |
| tp->prr_delivered = 0; |
| tp->prr_out = 0; |
| tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk); |
| tcp_ecn_queue_cwr(tp); |
| } |
| |
| void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost, int flag) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| int sndcnt = 0; |
| int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp); |
| |
| if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd)) |
| return; |
| |
| tp->prr_delivered += newly_acked_sacked; |
| if (delta < 0) { |
| u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered + |
| tp->prior_cwnd - 1; |
| sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out; |
| } else { |
| sndcnt = max_t(int, tp->prr_delivered - tp->prr_out, |
| newly_acked_sacked); |
| if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost) |
| sndcnt++; |
| sndcnt = min(delta, sndcnt); |
| } |
| /* Force a fast retransmit upon entering fast recovery */ |
| sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1)); |
| tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + sndcnt); |
| } |
| |
| static inline void tcp_end_cwnd_reduction(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (inet_csk(sk)->icsk_ca_ops->cong_control) |
| return; |
| |
| /* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */ |
| if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH && |
| (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) { |
| tcp_snd_cwnd_set(tp, tp->snd_ssthresh); |
| tp->snd_cwnd_stamp = tcp_jiffies32; |
| } |
| tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR); |
| } |
| |
| /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */ |
| void tcp_enter_cwr(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| tp->prior_ssthresh = 0; |
| if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) { |
| tp->undo_marker = 0; |
| tcp_init_cwnd_reduction(sk); |
| tcp_set_ca_state(sk, TCP_CA_CWR); |
| } |
| } |
| EXPORT_SYMBOL(tcp_enter_cwr); |
| |
| static void tcp_try_keep_open(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| int state = TCP_CA_Open; |
| |
| if (tcp_left_out(tp) || tcp_any_retrans_done(sk)) |
| state = TCP_CA_Disorder; |
| |
| if (inet_csk(sk)->icsk_ca_state != state) { |
| tcp_set_ca_state(sk, state); |
| tp->high_seq = tp->snd_nxt; |
| } |
| } |
| |
| static void tcp_try_to_open(struct sock *sk, int flag) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| tcp_verify_left_out(tp); |
| |
| if (!tcp_any_retrans_done(sk)) |
| tp->retrans_stamp = 0; |
| |
| if (flag & FLAG_ECE) |
| tcp_enter_cwr(sk); |
| |
| if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) { |
| tcp_try_keep_open(sk); |
| } |
| } |
| |
| static void tcp_mtup_probe_failed(struct sock *sk) |
| { |
| struct inet_connection_sock *icsk = inet_csk(sk); |
| |
| icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1; |
| icsk->icsk_mtup.probe_size = 0; |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL); |
| } |
| |
| static void tcp_mtup_probe_success(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct inet_connection_sock *icsk = inet_csk(sk); |
| u64 val; |
| |
| tp->prior_ssthresh = tcp_current_ssthresh(sk); |
| |
| val = (u64)tcp_snd_cwnd(tp) * tcp_mss_to_mtu(sk, tp->mss_cache); |
| do_div(val, icsk->icsk_mtup.probe_size); |
| DEBUG_NET_WARN_ON_ONCE((u32)val != val); |
| tcp_snd_cwnd_set(tp, max_t(u32, 1U, val)); |
| |
| tp->snd_cwnd_cnt = 0; |
| tp->snd_cwnd_stamp = tcp_jiffies32; |
| tp->snd_ssthresh = tcp_current_ssthresh(sk); |
| |
| icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size; |
| icsk->icsk_mtup.probe_size = 0; |
| tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS); |
| } |
| |
| /* Sometimes we deduce that packets have been dropped due to reasons other than |
| * congestion, like path MTU reductions or failed client TFO attempts. In these |
| * cases we call this function to retransmit as many packets as cwnd allows, |
| * without reducing cwnd. Given that retransmits will set retrans_stamp to a |
| * non-zero value (and may do so in a later calling context due to TSQ), we |
| * also enter CA_Loss so that we track when all retransmitted packets are ACKed |
| * and clear retrans_stamp when that happens (to ensure later recurring RTOs |
| * are using the correct retrans_stamp and don't declare ETIMEDOUT |
| * prematurely). |
| */ |
| static void tcp_non_congestion_loss_retransmit(struct sock *sk) |
| { |
| const struct inet_connection_sock *icsk = inet_csk(sk); |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (icsk->icsk_ca_state != TCP_CA_Loss) { |
| tp->high_seq = tp->snd_nxt; |
| tp->snd_ssthresh = tcp_current_ssthresh(sk); |
| tp->prior_ssthresh = 0; |
| tp->undo_marker = 0; |
| tcp_set_ca_state(sk, TCP_CA_Loss); |
| } |
| tcp_xmit_retransmit_queue(sk); |
| } |
| |
| /* Do a simple retransmit without using the backoff mechanisms in |
| * tcp_timer. This is used for path mtu discovery. |
| * The socket is already locked here. |
| */ |
| void tcp_simple_retransmit(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct sk_buff *skb; |
| int mss; |
| |
| /* A fastopen SYN request is stored as two separate packets within |
| * the retransmit queue, this is done by tcp_send_syn_data(). |
| * As a result simply checking the MSS of the frames in the queue |
| * will not work for the SYN packet. |
| * |
| * Us being here is an indication of a path MTU issue so we can |
| * assume that the fastopen SYN was lost and just mark all the |
| * frames in the retransmit queue as lost. We will use an MSS of |
| * -1 to mark all frames as lost, otherwise compute the current MSS. |
| */ |
| if (tp->syn_data && sk->sk_state == TCP_SYN_SENT) |
| mss = -1; |
| else |
| mss = tcp_current_mss(sk); |
| |
| skb_rbtree_walk(skb, &sk->tcp_rtx_queue) { |
| if (tcp_skb_seglen(skb) > mss) |
| tcp_mark_skb_lost(sk, skb); |
| } |
| |
| tcp_clear_retrans_hints_partial(tp); |
| |
| if (!tp->lost_out) |
| return; |
| |
| if (tcp_is_reno(tp)) |
| tcp_limit_reno_sacked(tp); |
| |
| tcp_verify_left_out(tp); |
| |
| /* Don't muck with the congestion window here. |
| * Reason is that we do not increase amount of _data_ |
| * in network, but units changed and effective |
| * cwnd/ssthresh really reduced now. |
| */ |
| tcp_non_congestion_loss_retransmit(sk); |
| } |
| EXPORT_SYMBOL(tcp_simple_retransmit); |
| |
| void tcp_enter_recovery(struct sock *sk, bool ece_ack) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| int mib_idx; |
| |
| if (tcp_is_reno(tp)) |
| mib_idx = LINUX_MIB_TCPRENORECOVERY; |
| else |
| mib_idx = LINUX_MIB_TCPSACKRECOVERY; |
| |
| NET_INC_STATS(sock_net(sk), mib_idx); |
| |
| tp->prior_ssthresh = 0; |
| tcp_init_undo(tp); |
| |
| if (!tcp_in_cwnd_reduction(sk)) { |
| if (!ece_ack) |
| tp->prior_ssthresh = tcp_current_ssthresh(sk); |
| tcp_init_cwnd_reduction(sk); |
| } |
| tcp_set_ca_state(sk, TCP_CA_Recovery); |
| } |
| |
| static void tcp_update_rto_time(struct tcp_sock *tp) |
| { |
| if (tp->rto_stamp) { |
| tp->total_rto_time += tcp_time_stamp_ms(tp) - tp->rto_stamp; |
| tp->rto_stamp = 0; |
| } |
| } |
| |
| /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are |
| * recovered or spurious. Otherwise retransmits more on partial ACKs. |
| */ |
| static void tcp_process_loss(struct sock *sk, int flag, int num_dupack, |
| int *rexmit) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| bool recovered = !before(tp->snd_una, tp->high_seq); |
| |
| if ((flag & FLAG_SND_UNA_ADVANCED || rcu_access_pointer(tp->fastopen_rsk)) && |
| tcp_try_undo_loss(sk, false)) |
| return; |
| |
| if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */ |
| /* Step 3.b. A timeout is spurious if not all data are |
| * lost, i.e., never-retransmitted data are (s)acked. |
| */ |
| if ((flag & FLAG_ORIG_SACK_ACKED) && |
| tcp_try_undo_loss(sk, true)) |
| return; |
| |
| if (after(tp->snd_nxt, tp->high_seq)) { |
| if (flag & FLAG_DATA_SACKED || num_dupack) |
| tp->frto = 0; /* Step 3.a. loss was real */ |
| } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) { |
| tp->high_seq = tp->snd_nxt; |
| /* Step 2.b. Try send new data (but deferred until cwnd |
| * is updated in tcp_ack()). Otherwise fall back to |
| * the conventional recovery. |
| */ |
| if (!tcp_write_queue_empty(sk) && |
| after(tcp_wnd_end(tp), tp->snd_nxt)) { |
| *rexmit = REXMIT_NEW; |
| return; |
| } |
| tp->frto = 0; |
| } |
| } |
| |
| if (recovered) { |
| /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */ |
| tcp_try_undo_recovery(sk); |
| return; |
| } |
| if (tcp_is_reno(tp)) { |
| /* A Reno DUPACK means new data in F-RTO step 2.b above are |
| * delivered. Lower inflight to clock out (re)transmissions. |
| */ |
| if (after(tp->snd_nxt, tp->high_seq) && num_dupack) |
| tcp_add_reno_sack(sk, num_dupack, flag & FLAG_ECE); |
| else if (flag & FLAG_SND_UNA_ADVANCED) |
| tcp_reset_reno_sack(tp); |
| } |
| *rexmit = REXMIT_LOST; |
| } |
| |
| static bool tcp_force_fast_retransmit(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| return after(tcp_highest_sack_seq(tp), |
| tp->snd_una + tp->reordering * tp->mss_cache); |
| } |
| |
| /* Undo during fast recovery after partial ACK. */ |
| static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una, |
| bool *do_lost) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (tp->undo_marker && tcp_packet_delayed(tp)) { |
| /* Plain luck! Hole if filled with delayed |
| * packet, rather than with a retransmit. Check reordering. |
| */ |
| tcp_check_sack_reordering(sk, prior_snd_una, 1); |
| |
| /* We are getting evidence that the reordering degree is higher |
| * than we realized. If there are no retransmits out then we |
| * can undo. Otherwise we clock out new packets but do not |
| * mark more packets lost or retransmit more. |
| */ |
| if (tp->retrans_out) |
| return true; |
| |
| if (!tcp_any_retrans_done(sk)) |
| tp->retrans_stamp = 0; |
| |
| DBGUNDO(sk, "partial recovery"); |
| tcp_undo_cwnd_reduction(sk, true); |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO); |
| tcp_try_keep_open(sk); |
| } else { |
| /* Partial ACK arrived. Force fast retransmit. */ |
| *do_lost = tcp_force_fast_retransmit(sk); |
| } |
| return false; |
| } |
| |
| static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (tcp_rtx_queue_empty(sk)) |
| return; |
| |
| if (unlikely(tcp_is_reno(tp))) { |
| tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED); |
| } else if (tcp_is_rack(sk)) { |
| u32 prior_retrans = tp->retrans_out; |
| |
| if (tcp_rack_mark_lost(sk)) |
| *ack_flag &= ~FLAG_SET_XMIT_TIMER; |
| if (prior_retrans > tp->retrans_out) |
| *ack_flag |= FLAG_LOST_RETRANS; |
| } |
| } |
| |
| /* Process an event, which can update packets-in-flight not trivially. |
| * Main goal of this function is to calculate new estimate for left_out, |
| * taking into account both packets sitting in receiver's buffer and |
| * packets lost by network. |
| * |
| * Besides that it updates the congestion state when packet loss or ECN |
| * is detected. But it does not reduce the cwnd, it is done by the |
| * congestion control later. |
| * |
| * It does _not_ decide what to send, it is made in function |
| * tcp_xmit_retransmit_queue(). |
| */ |
| static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una, |
| int num_dupack, int *ack_flag, int *rexmit) |
| { |
| struct inet_connection_sock *icsk = inet_csk(sk); |
| struct tcp_sock *tp = tcp_sk(sk); |
| int fast_rexmit = 0, flag = *ack_flag; |
| bool ece_ack = flag & FLAG_ECE; |
| bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) && |
| tcp_force_fast_retransmit(sk)); |
| |
| if (!tp->packets_out && tp->sacked_out) |
| tp->sacked_out = 0; |
| |
| /* Now state machine starts. |
| * A. ECE, hence prohibit cwnd undoing, the reduction is required. */ |
| if (ece_ack) |
| tp->prior_ssthresh = 0; |
| |
| /* B. In all the states check for reneging SACKs. */ |
| if (tcp_check_sack_reneging(sk, ack_flag)) |
| return; |
| |
| /* C. Check consistency of the current state. */ |
| tcp_verify_left_out(tp); |
| |
| /* D. Check state exit conditions. State can be terminated |
| * when high_seq is ACKed. */ |
| if (icsk->icsk_ca_state == TCP_CA_Open) { |
| WARN_ON(tp->retrans_out != 0 && !tp->syn_data); |
| tp->retrans_stamp = 0; |
| } else if (!before(tp->snd_una, tp->high_seq)) { |
| switch (icsk->icsk_ca_state) { |
| case TCP_CA_CWR: |
| /* CWR is to be held something *above* high_seq |
| * is ACKed for CWR bit to reach receiver. */ |
| if (tp->snd_una != tp->high_seq) { |
| tcp_end_cwnd_reduction(sk); |
| tcp_set_ca_state(sk, TCP_CA_Open); |
| } |
| break; |
| |
| case TCP_CA_Recovery: |
| if (tcp_is_reno(tp)) |
| tcp_reset_reno_sack(tp); |
| if (tcp_try_undo_recovery(sk)) |
| return; |
| tcp_end_cwnd_reduction(sk); |
| break; |
| } |
| } |
| |
| /* E. Process state. */ |
| switch (icsk->icsk_ca_state) { |
| case TCP_CA_Recovery: |
| if (!(flag & FLAG_SND_UNA_ADVANCED)) { |
| if (tcp_is_reno(tp)) |
| tcp_add_reno_sack(sk, num_dupack, ece_ack); |
| } else if (tcp_try_undo_partial(sk, prior_snd_una, &do_lost)) |
| return; |
| |
| if (tcp_try_undo_dsack(sk)) |
| tcp_try_to_open(sk, flag); |
| |
| tcp_identify_packet_loss(sk, ack_flag); |
| if (icsk->icsk_ca_state != TCP_CA_Recovery) { |
| if (!tcp_time_to_recover(sk, flag)) |
| return; |
| /* Undo reverts the recovery state. If loss is evident, |
| * starts a new recovery (e.g. reordering then loss); |
| */ |
| tcp_enter_recovery(sk, ece_ack); |
| } |
| break; |
| case TCP_CA_Loss: |
| tcp_process_loss(sk, flag, num_dupack, rexmit); |
| if (icsk->icsk_ca_state != TCP_CA_Loss) |
|