2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
6 * Implementation of the Transmission Control Protocol(TCP).
9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 * Mark Evans, <evansmp@uhura.aston.ac.uk>
11 * Corey Minyard <wf-rch!minyard@relay.EU.net>
12 * Florian La Roche, <flla@stud.uni-sb.de>
13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 * Linus Torvalds, <torvalds@cs.helsinki.fi>
15 * Alan Cox, <gw4pts@gw4pts.ampr.org>
16 * Matthew Dillon, <dillon@apollo.west.oic.com>
17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 * Jorge Cwik, <jorge@laser.satlink.net>
23 * Pedro Roque : Fast Retransmit/Recovery.
25 * Retransmit queue handled by TCP.
26 * Better retransmit timer handling.
27 * New congestion avoidance.
31 * Eric : Fast Retransmit.
32 * Randy Scott : MSS option defines.
33 * Eric Schenk : Fixes to slow start algorithm.
34 * Eric Schenk : Yet another double ACK bug.
35 * Eric Schenk : Delayed ACK bug fixes.
36 * Eric Schenk : Floyd style fast retrans war avoidance.
37 * David S. Miller : Don't allow zero congestion window.
38 * Eric Schenk : Fix retransmitter so that it sends
39 * next packet on ack of previous packet.
40 * Andi Kleen : Moved open_request checking here
41 * and process RSTs for open_requests.
42 * Andi Kleen : Better prune_queue, and other fixes.
43 * Andrey Savochkin: Fix RTT measurements in the presence of
45 * Andrey Savochkin: Check sequence numbers correctly when
46 * removing SACKs due to in sequence incoming
48 * Andi Kleen: Make sure we never ack data there is not
49 * enough room for. Also make this condition
50 * a fatal error if it might still happen.
51 * Andi Kleen: Add tcp_measure_rcv_mss to make
52 * connections with MSS<min(MTU,ann. MSS)
53 * work without delayed acks.
54 * Andi Kleen: Process packets with PSH set in the
56 * J Hadi Salim: ECN support
59 * Panu Kuhlberg: Experimental audit of TCP (re)transmission
60 * engine. Lots of bugs are found.
61 * Pasi Sarolahti: F-RTO for dealing with spurious RTOs
64 #define pr_fmt(fmt) "TCP: " fmt
67 #include <linux/slab.h>
68 #include <linux/module.h>
69 #include <linux/sysctl.h>
70 #include <linux/kernel.h>
71 #include <linux/prefetch.h>
74 #include <net/inet_common.h>
75 #include <linux/ipsec.h>
76 #include <asm/unaligned.h>
77 #include <linux/errqueue.h>
79 int sysctl_tcp_timestamps __read_mostly = 1;
80 int sysctl_tcp_window_scaling __read_mostly = 1;
81 int sysctl_tcp_sack __read_mostly = 1;
82 int sysctl_tcp_fack __read_mostly = 1;
83 int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
84 int sysctl_tcp_max_reordering __read_mostly = 300;
85 EXPORT_SYMBOL(sysctl_tcp_reordering);
86 int sysctl_tcp_dsack __read_mostly = 1;
87 int sysctl_tcp_app_win __read_mostly = 31;
88 int sysctl_tcp_adv_win_scale __read_mostly = 1;
89 EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
91 /* rfc5961 challenge ack rate limiting */
92 int sysctl_tcp_challenge_ack_limit = 100;
94 int sysctl_tcp_stdurg __read_mostly;
95 int sysctl_tcp_rfc1337 __read_mostly;
96 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
97 int sysctl_tcp_frto __read_mostly = 2;
99 int sysctl_tcp_thin_dupack __read_mostly;
101 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
102 int sysctl_tcp_early_retrans __read_mostly = 3;
103 int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
105 #define FLAG_DATA 0x01 /* Incoming frame contained data. */
106 #define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */
107 #define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */
108 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */
109 #define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */
110 #define FLAG_DATA_SACKED 0x20 /* New SACK. */
111 #define FLAG_ECE 0x40 /* ECE in this ACK */
112 #define FLAG_LOST_RETRANS 0x80 /* This ACK marks some retransmission lost */
113 #define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/
114 #define FLAG_ORIG_SACK_ACKED 0x200 /* Never retransmitted data are (s)acked */
115 #define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
116 #define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */
117 #define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */
118 #define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */
120 #define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
121 #define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
122 #define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE)
123 #define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED)
125 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
126 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
128 /* Adapt the MSS value used to make delayed ack decision to the
131 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
133 struct inet_connection_sock *icsk = inet_csk(sk);
134 const unsigned int lss = icsk->icsk_ack.last_seg_size;
137 icsk->icsk_ack.last_seg_size = 0;
139 /* skb->len may jitter because of SACKs, even if peer
140 * sends good full-sized frames.
142 len = skb_shinfo(skb)->gso_size ? : skb->len;
143 if (len >= icsk->icsk_ack.rcv_mss) {
144 icsk->icsk_ack.rcv_mss = len;
146 /* Otherwise, we make more careful check taking into account,
147 * that SACKs block is variable.
149 * "len" is invariant segment length, including TCP header.
151 len += skb->data - skb_transport_header(skb);
152 if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
153 /* If PSH is not set, packet should be
154 * full sized, provided peer TCP is not badly broken.
155 * This observation (if it is correct 8)) allows
156 * to handle super-low mtu links fairly.
158 (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
159 !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
160 /* Subtract also invariant (if peer is RFC compliant),
161 * tcp header plus fixed timestamp option length.
162 * Resulting "len" is MSS free of SACK jitter.
164 len -= tcp_sk(sk)->tcp_header_len;
165 icsk->icsk_ack.last_seg_size = len;
167 icsk->icsk_ack.rcv_mss = len;
171 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
172 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
173 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
177 static void tcp_incr_quickack(struct sock *sk)
179 struct inet_connection_sock *icsk = inet_csk(sk);
180 unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
184 if (quickacks > icsk->icsk_ack.quick)
185 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
188 static void tcp_enter_quickack_mode(struct sock *sk)
190 struct inet_connection_sock *icsk = inet_csk(sk);
191 tcp_incr_quickack(sk);
192 icsk->icsk_ack.pingpong = 0;
193 icsk->icsk_ack.ato = TCP_ATO_MIN;
196 /* Send ACKs quickly, if "quick" count is not exhausted
197 * and the session is not interactive.
200 static bool tcp_in_quickack_mode(struct sock *sk)
202 const struct inet_connection_sock *icsk = inet_csk(sk);
203 const struct dst_entry *dst = __sk_dst_get(sk);
205 return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
206 (icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong);
209 static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
211 if (tp->ecn_flags & TCP_ECN_OK)
212 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
215 static void tcp_ecn_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
217 if (tcp_hdr(skb)->cwr)
218 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
221 static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
223 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
226 static void __tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
228 switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
229 case INET_ECN_NOT_ECT:
230 /* Funny extension: if ECT is not set on a segment,
231 * and we already seen ECT on a previous segment,
232 * it is probably a retransmit.
234 if (tp->ecn_flags & TCP_ECN_SEEN)
235 tcp_enter_quickack_mode((struct sock *)tp);
238 if (tcp_ca_needs_ecn((struct sock *)tp))
239 tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_IS_CE);
241 if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
242 /* Better not delay acks, sender can have a very low cwnd */
243 tcp_enter_quickack_mode((struct sock *)tp);
244 tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
246 tp->ecn_flags |= TCP_ECN_SEEN;
249 if (tcp_ca_needs_ecn((struct sock *)tp))
250 tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_NO_CE);
251 tp->ecn_flags |= TCP_ECN_SEEN;
256 static void tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
258 if (tp->ecn_flags & TCP_ECN_OK)
259 __tcp_ecn_check_ce(tp, skb);
262 static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
264 if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
265 tp->ecn_flags &= ~TCP_ECN_OK;
268 static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
270 if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
271 tp->ecn_flags &= ~TCP_ECN_OK;
274 static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
276 if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
281 /* Buffer size and advertised window tuning.
283 * 1. Tuning sk->sk_sndbuf, when connection enters established state.
286 static void tcp_sndbuf_expand(struct sock *sk)
288 const struct tcp_sock *tp = tcp_sk(sk);
292 /* Worst case is non GSO/TSO : each frame consumes one skb
293 * and skb->head is kmalloced using power of two area of memory
295 per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
297 SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
299 per_mss = roundup_pow_of_two(per_mss) +
300 SKB_DATA_ALIGN(sizeof(struct sk_buff));
302 nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
303 nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
305 /* Fast Recovery (RFC 5681 3.2) :
306 * Cubic needs 1.7 factor, rounded to 2 to include
307 * extra cushion (application might react slowly to POLLOUT)
309 sndmem = 2 * nr_segs * per_mss;
311 if (sk->sk_sndbuf < sndmem)
312 sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
315 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
317 * All tcp_full_space() is split to two parts: "network" buffer, allocated
318 * forward and advertised in receiver window (tp->rcv_wnd) and
319 * "application buffer", required to isolate scheduling/application
320 * latencies from network.
321 * window_clamp is maximal advertised window. It can be less than
322 * tcp_full_space(), in this case tcp_full_space() - window_clamp
323 * is reserved for "application" buffer. The less window_clamp is
324 * the smoother our behaviour from viewpoint of network, but the lower
325 * throughput and the higher sensitivity of the connection to losses. 8)
327 * rcv_ssthresh is more strict window_clamp used at "slow start"
328 * phase to predict further behaviour of this connection.
329 * It is used for two goals:
330 * - to enforce header prediction at sender, even when application
331 * requires some significant "application buffer". It is check #1.
332 * - to prevent pruning of receive queue because of misprediction
333 * of receiver window. Check #2.
335 * The scheme does not work when sender sends good segments opening
336 * window and then starts to feed us spaghetti. But it should work
337 * in common situations. Otherwise, we have to rely on queue collapsing.
340 /* Slow part of check#2. */
341 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
343 struct tcp_sock *tp = tcp_sk(sk);
345 int truesize = tcp_win_from_space(skb->truesize) >> 1;
346 int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
348 while (tp->rcv_ssthresh <= window) {
349 if (truesize <= skb->len)
350 return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
358 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
360 struct tcp_sock *tp = tcp_sk(sk);
363 if (tp->rcv_ssthresh < tp->window_clamp &&
364 (int)tp->rcv_ssthresh < tcp_space(sk) &&
365 !tcp_under_memory_pressure(sk)) {
368 /* Check #2. Increase window, if skb with such overhead
369 * will fit to rcvbuf in future.
371 if (tcp_win_from_space(skb->truesize) <= skb->len)
372 incr = 2 * tp->advmss;
374 incr = __tcp_grow_window(sk, skb);
377 incr = max_t(int, incr, 2 * skb->len);
378 tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
380 inet_csk(sk)->icsk_ack.quick |= 1;
385 /* 3. Tuning rcvbuf, when connection enters established state. */
386 static void tcp_fixup_rcvbuf(struct sock *sk)
388 u32 mss = tcp_sk(sk)->advmss;
391 rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) *
392 tcp_default_init_rwnd(mss);
394 /* Dynamic Right Sizing (DRS) has 2 to 3 RTT latency
395 * Allow enough cushion so that sender is not limited by our window
397 if (sysctl_tcp_moderate_rcvbuf)
400 if (sk->sk_rcvbuf < rcvmem)
401 sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
404 /* 4. Try to fixup all. It is made immediately after connection enters
407 void tcp_init_buffer_space(struct sock *sk)
409 struct tcp_sock *tp = tcp_sk(sk);
412 if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
413 tcp_fixup_rcvbuf(sk);
414 if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
415 tcp_sndbuf_expand(sk);
417 tp->rcvq_space.space = tp->rcv_wnd;
418 tp->rcvq_space.time = tcp_time_stamp;
419 tp->rcvq_space.seq = tp->copied_seq;
421 maxwin = tcp_full_space(sk);
423 if (tp->window_clamp >= maxwin) {
424 tp->window_clamp = maxwin;
426 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
427 tp->window_clamp = max(maxwin -
428 (maxwin >> sysctl_tcp_app_win),
432 /* Force reservation of one segment. */
433 if (sysctl_tcp_app_win &&
434 tp->window_clamp > 2 * tp->advmss &&
435 tp->window_clamp + tp->advmss > maxwin)
436 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
438 tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
439 tp->snd_cwnd_stamp = tcp_time_stamp;
442 /* 5. Recalculate window clamp after socket hit its memory bounds. */
443 static void tcp_clamp_window(struct sock *sk)
445 struct tcp_sock *tp = tcp_sk(sk);
446 struct inet_connection_sock *icsk = inet_csk(sk);
448 icsk->icsk_ack.quick = 0;
450 if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
451 !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
452 !tcp_under_memory_pressure(sk) &&
453 sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
454 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
457 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
458 tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
461 /* Initialize RCV_MSS value.
462 * RCV_MSS is an our guess about MSS used by the peer.
463 * We haven't any direct information about the MSS.
464 * It's better to underestimate the RCV_MSS rather than overestimate.
465 * Overestimations make us ACKing less frequently than needed.
466 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
468 void tcp_initialize_rcv_mss(struct sock *sk)
470 const struct tcp_sock *tp = tcp_sk(sk);
471 unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
473 hint = min(hint, tp->rcv_wnd / 2);
474 hint = min(hint, TCP_MSS_DEFAULT);
475 hint = max(hint, TCP_MIN_MSS);
477 inet_csk(sk)->icsk_ack.rcv_mss = hint;
479 EXPORT_SYMBOL(tcp_initialize_rcv_mss);
481 /* Receiver "autotuning" code.
483 * The algorithm for RTT estimation w/o timestamps is based on
484 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
485 * <http://public.lanl.gov/radiant/pubs.html#DRS>
487 * More detail on this code can be found at
488 * <http://staff.psc.edu/jheffner/>,
489 * though this reference is out of date. A new paper
492 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
494 u32 new_sample = tp->rcv_rtt_est.rtt;
500 if (new_sample != 0) {
501 /* If we sample in larger samples in the non-timestamp
502 * case, we could grossly overestimate the RTT especially
503 * with chatty applications or bulk transfer apps which
504 * are stalled on filesystem I/O.
506 * Also, since we are only going for a minimum in the
507 * non-timestamp case, we do not smooth things out
508 * else with timestamps disabled convergence takes too
512 m -= (new_sample >> 3);
520 /* No previous measure. */
524 if (tp->rcv_rtt_est.rtt != new_sample)
525 tp->rcv_rtt_est.rtt = new_sample;
528 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
530 if (tp->rcv_rtt_est.time == 0)
532 if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
534 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rcv_rtt_est.time, 1);
537 tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
538 tp->rcv_rtt_est.time = tcp_time_stamp;
541 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
542 const struct sk_buff *skb)
544 struct tcp_sock *tp = tcp_sk(sk);
545 if (tp->rx_opt.rcv_tsecr &&
546 (TCP_SKB_CB(skb)->end_seq -
547 TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
548 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
552 * This function should be called every time data is copied to user space.
553 * It calculates the appropriate TCP receive buffer space.
555 void tcp_rcv_space_adjust(struct sock *sk)
557 struct tcp_sock *tp = tcp_sk(sk);
561 time = tcp_time_stamp - tp->rcvq_space.time;
562 if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
565 /* Number of bytes copied to user in last RTT */
566 copied = tp->copied_seq - tp->rcvq_space.seq;
567 if (copied <= tp->rcvq_space.space)
571 * copied = bytes received in previous RTT, our base window
572 * To cope with packet losses, we need a 2x factor
573 * To cope with slow start, and sender growing its cwin by 100 %
574 * every RTT, we need a 4x factor, because the ACK we are sending
575 * now is for the next RTT, not the current one :
576 * <prev RTT . ><current RTT .. ><next RTT .... >
579 if (sysctl_tcp_moderate_rcvbuf &&
580 !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
581 int rcvwin, rcvmem, rcvbuf;
583 /* minimal window to cope with packet losses, assuming
584 * steady state. Add some cushion because of small variations.
586 rcvwin = (copied << 1) + 16 * tp->advmss;
588 /* If rate increased by 25%,
589 * assume slow start, rcvwin = 3 * copied
590 * If rate increased by 50%,
591 * assume sender can use 2x growth, rcvwin = 4 * copied
594 tp->rcvq_space.space + (tp->rcvq_space.space >> 2)) {
596 tp->rcvq_space.space + (tp->rcvq_space.space >> 1))
599 rcvwin += (rcvwin >> 1);
602 rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
603 while (tcp_win_from_space(rcvmem) < tp->advmss)
606 rcvbuf = min(rcvwin / tp->advmss * rcvmem, sysctl_tcp_rmem[2]);
607 if (rcvbuf > sk->sk_rcvbuf) {
608 sk->sk_rcvbuf = rcvbuf;
610 /* Make the window clamp follow along. */
611 tp->window_clamp = rcvwin;
614 tp->rcvq_space.space = copied;
617 tp->rcvq_space.seq = tp->copied_seq;
618 tp->rcvq_space.time = tcp_time_stamp;
621 /* There is something which you must keep in mind when you analyze the
622 * behavior of the tp->ato delayed ack timeout interval. When a
623 * connection starts up, we want to ack as quickly as possible. The
624 * problem is that "good" TCP's do slow start at the beginning of data
625 * transmission. The means that until we send the first few ACK's the
626 * sender will sit on his end and only queue most of his data, because
627 * he can only send snd_cwnd unacked packets at any given time. For
628 * each ACK we send, he increments snd_cwnd and transmits more of his
631 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
633 struct tcp_sock *tp = tcp_sk(sk);
634 struct inet_connection_sock *icsk = inet_csk(sk);
637 inet_csk_schedule_ack(sk);
639 tcp_measure_rcv_mss(sk, skb);
641 tcp_rcv_rtt_measure(tp);
643 now = tcp_time_stamp;
645 if (!icsk->icsk_ack.ato) {
646 /* The _first_ data packet received, initialize
647 * delayed ACK engine.
649 tcp_incr_quickack(sk);
650 icsk->icsk_ack.ato = TCP_ATO_MIN;
652 int m = now - icsk->icsk_ack.lrcvtime;
654 if (m <= TCP_ATO_MIN / 2) {
655 /* The fastest case is the first. */
656 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
657 } else if (m < icsk->icsk_ack.ato) {
658 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
659 if (icsk->icsk_ack.ato > icsk->icsk_rto)
660 icsk->icsk_ack.ato = icsk->icsk_rto;
661 } else if (m > icsk->icsk_rto) {
662 /* Too long gap. Apparently sender failed to
663 * restart window, so that we send ACKs quickly.
665 tcp_incr_quickack(sk);
669 icsk->icsk_ack.lrcvtime = now;
671 tcp_ecn_check_ce(tp, skb);
674 tcp_grow_window(sk, skb);
677 /* Called to compute a smoothed rtt estimate. The data fed to this
678 * routine either comes from timestamps, or from segments that were
679 * known _not_ to have been retransmitted [see Karn/Partridge
680 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
681 * piece by Van Jacobson.
682 * NOTE: the next three routines used to be one big routine.
683 * To save cycles in the RFC 1323 implementation it was better to break
684 * it up into three procedures. -- erics
686 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
688 struct tcp_sock *tp = tcp_sk(sk);
689 long m = mrtt_us; /* RTT */
690 u32 srtt = tp->srtt_us;
692 /* The following amusing code comes from Jacobson's
693 * article in SIGCOMM '88. Note that rtt and mdev
694 * are scaled versions of rtt and mean deviation.
695 * This is designed to be as fast as possible
696 * m stands for "measurement".
698 * On a 1990 paper the rto value is changed to:
699 * RTO = rtt + 4 * mdev
701 * Funny. This algorithm seems to be very broken.
702 * These formulae increase RTO, when it should be decreased, increase
703 * too slowly, when it should be increased quickly, decrease too quickly
704 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
705 * does not matter how to _calculate_ it. Seems, it was trap
706 * that VJ failed to avoid. 8)
709 m -= (srtt >> 3); /* m is now error in rtt est */
710 srtt += m; /* rtt = 7/8 rtt + 1/8 new */
712 m = -m; /* m is now abs(error) */
713 m -= (tp->mdev_us >> 2); /* similar update on mdev */
714 /* This is similar to one of Eifel findings.
715 * Eifel blocks mdev updates when rtt decreases.
716 * This solution is a bit different: we use finer gain
717 * for mdev in this case (alpha*beta).
718 * Like Eifel it also prevents growth of rto,
719 * but also it limits too fast rto decreases,
720 * happening in pure Eifel.
725 m -= (tp->mdev_us >> 2); /* similar update on mdev */
727 tp->mdev_us += m; /* mdev = 3/4 mdev + 1/4 new */
728 if (tp->mdev_us > tp->mdev_max_us) {
729 tp->mdev_max_us = tp->mdev_us;
730 if (tp->mdev_max_us > tp->rttvar_us)
731 tp->rttvar_us = tp->mdev_max_us;
733 if (after(tp->snd_una, tp->rtt_seq)) {
734 if (tp->mdev_max_us < tp->rttvar_us)
735 tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
736 tp->rtt_seq = tp->snd_nxt;
737 tp->mdev_max_us = tcp_rto_min_us(sk);
740 /* no previous measure. */
741 srtt = m << 3; /* take the measured time to be rtt */
742 tp->mdev_us = m << 1; /* make sure rto = 3*rtt */
743 tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
744 tp->mdev_max_us = tp->rttvar_us;
745 tp->rtt_seq = tp->snd_nxt;
747 tp->srtt_us = max(1U, srtt);
750 /* Set the sk_pacing_rate to allow proper sizing of TSO packets.
751 * Note: TCP stack does not yet implement pacing.
752 * FQ packet scheduler can be used to implement cheap but effective
753 * TCP pacing, to smooth the burst on large writes when packets
754 * in flight is significantly lower than cwnd (or rwin)
756 static void tcp_update_pacing_rate(struct sock *sk)
758 const struct tcp_sock *tp = tcp_sk(sk);
761 /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
762 rate = (u64)tp->mss_cache * 2 * (USEC_PER_SEC << 3);
764 rate *= max(tp->snd_cwnd, tp->packets_out);
766 if (likely(tp->srtt_us))
767 do_div(rate, tp->srtt_us);
769 /* ACCESS_ONCE() is needed because sch_fq fetches sk_pacing_rate
770 * without any lock. We want to make sure compiler wont store
771 * intermediate values in this location.
773 ACCESS_ONCE(sk->sk_pacing_rate) = min_t(u64, rate,
774 sk->sk_max_pacing_rate);
777 /* Calculate rto without backoff. This is the second half of Van Jacobson's
778 * routine referred to above.
780 static void tcp_set_rto(struct sock *sk)
782 const struct tcp_sock *tp = tcp_sk(sk);
783 /* Old crap is replaced with new one. 8)
786 * 1. If rtt variance happened to be less 50msec, it is hallucination.
787 * It cannot be less due to utterly erratic ACK generation made
788 * at least by solaris and freebsd. "Erratic ACKs" has _nothing_
789 * to do with delayed acks, because at cwnd>2 true delack timeout
790 * is invisible. Actually, Linux-2.4 also generates erratic
791 * ACKs in some circumstances.
793 inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
795 /* 2. Fixups made earlier cannot be right.
796 * If we do not estimate RTO correctly without them,
797 * all the algo is pure shit and should be replaced
798 * with correct one. It is exactly, which we pretend to do.
801 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
802 * guarantees that rto is higher.
807 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
809 __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
812 cwnd = TCP_INIT_CWND;
813 return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
817 * Packet counting of FACK is based on in-order assumptions, therefore TCP
818 * disables it when reordering is detected
820 void tcp_disable_fack(struct tcp_sock *tp)
822 /* RFC3517 uses different metric in lost marker => reset on change */
824 tp->lost_skb_hint = NULL;
825 tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED;
828 /* Take a notice that peer is sending D-SACKs */
829 static void tcp_dsack_seen(struct tcp_sock *tp)
831 tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
834 static void tcp_update_reordering(struct sock *sk, const int metric,
837 struct tcp_sock *tp = tcp_sk(sk);
838 if (metric > tp->reordering) {
841 tp->reordering = min(sysctl_tcp_max_reordering, metric);
843 /* This exciting event is worth to be remembered. 8) */
845 mib_idx = LINUX_MIB_TCPTSREORDER;
846 else if (tcp_is_reno(tp))
847 mib_idx = LINUX_MIB_TCPRENOREORDER;
848 else if (tcp_is_fack(tp))
849 mib_idx = LINUX_MIB_TCPFACKREORDER;
851 mib_idx = LINUX_MIB_TCPSACKREORDER;
853 NET_INC_STATS_BH(sock_net(sk), mib_idx);
854 #if FASTRETRANS_DEBUG > 1
855 pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
856 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
860 tp->undo_marker ? tp->undo_retrans : 0);
862 tcp_disable_fack(tp);
866 tcp_disable_early_retrans(tp);
869 /* This must be called before lost_out is incremented */
870 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
872 if (!tp->retransmit_skb_hint ||
873 before(TCP_SKB_CB(skb)->seq,
874 TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
875 tp->retransmit_skb_hint = skb;
878 after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
879 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
882 static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
884 if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
885 tcp_verify_retransmit_hint(tp, skb);
887 tp->lost_out += tcp_skb_pcount(skb);
888 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
892 static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
895 tcp_verify_retransmit_hint(tp, skb);
897 if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
898 tp->lost_out += tcp_skb_pcount(skb);
899 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
903 /* This procedure tags the retransmission queue when SACKs arrive.
905 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
906 * Packets in queue with these bits set are counted in variables
907 * sacked_out, retrans_out and lost_out, correspondingly.
909 * Valid combinations are:
910 * Tag InFlight Description
911 * 0 1 - orig segment is in flight.
912 * S 0 - nothing flies, orig reached receiver.
913 * L 0 - nothing flies, orig lost by net.
914 * R 2 - both orig and retransmit are in flight.
915 * L|R 1 - orig is lost, retransmit is in flight.
916 * S|R 1 - orig reached receiver, retrans is still in flight.
917 * (L|S|R is logically valid, it could occur when L|R is sacked,
918 * but it is equivalent to plain S and code short-curcuits it to S.
919 * L|S is logically invalid, it would mean -1 packet in flight 8))
921 * These 6 states form finite state machine, controlled by the following events:
922 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
923 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
924 * 3. Loss detection event of two flavors:
925 * A. Scoreboard estimator decided the packet is lost.
926 * A'. Reno "three dupacks" marks head of queue lost.
927 * A''. Its FACK modification, head until snd.fack is lost.
928 * B. SACK arrives sacking SND.NXT at the moment, when the
929 * segment was retransmitted.
930 * 4. D-SACK added new rule: D-SACK changes any tag to S.
932 * It is pleasant to note, that state diagram turns out to be commutative,
933 * so that we are allowed not to be bothered by order of our actions,
934 * when multiple events arrive simultaneously. (see the function below).
936 * Reordering detection.
937 * --------------------
938 * Reordering metric is maximal distance, which a packet can be displaced
939 * in packet stream. With SACKs we can estimate it:
941 * 1. SACK fills old hole and the corresponding segment was not
942 * ever retransmitted -> reordering. Alas, we cannot use it
943 * when segment was retransmitted.
944 * 2. The last flaw is solved with D-SACK. D-SACK arrives
945 * for retransmitted and already SACKed segment -> reordering..
946 * Both of these heuristics are not used in Loss state, when we cannot
947 * account for retransmits accurately.
949 * SACK block validation.
950 * ----------------------
952 * SACK block range validation checks that the received SACK block fits to
953 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
954 * Note that SND.UNA is not included to the range though being valid because
955 * it means that the receiver is rather inconsistent with itself reporting
956 * SACK reneging when it should advance SND.UNA. Such SACK block this is
957 * perfectly valid, however, in light of RFC2018 which explicitly states
958 * that "SACK block MUST reflect the newest segment. Even if the newest
959 * segment is going to be discarded ...", not that it looks very clever
960 * in case of head skb. Due to potentional receiver driven attacks, we
961 * choose to avoid immediate execution of a walk in write queue due to
962 * reneging and defer head skb's loss recovery to standard loss recovery
963 * procedure that will eventually trigger (nothing forbids us doing this).
965 * Implements also blockage to start_seq wrap-around. Problem lies in the
966 * fact that though start_seq (s) is before end_seq (i.e., not reversed),
967 * there's no guarantee that it will be before snd_nxt (n). The problem
968 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
971 * <- outs wnd -> <- wrapzone ->
972 * u e n u_w e_w s n_w
974 * |<------------+------+----- TCP seqno space --------------+---------->|
975 * ...-- <2^31 ->| |<--------...
976 * ...---- >2^31 ------>| |<--------...
978 * Current code wouldn't be vulnerable but it's better still to discard such
979 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
980 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
981 * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
982 * equal to the ideal case (infinite seqno space without wrap caused issues).
984 * With D-SACK the lower bound is extended to cover sequence space below
985 * SND.UNA down to undo_marker, which is the last point of interest. Yet
986 * again, D-SACK block must not to go across snd_una (for the same reason as
987 * for the normal SACK blocks, explained above). But there all simplicity
988 * ends, TCP might receive valid D-SACKs below that. As long as they reside
989 * fully below undo_marker they do not affect behavior in anyway and can
990 * therefore be safely ignored. In rare cases (which are more or less
991 * theoretical ones), the D-SACK will nicely cross that boundary due to skb
992 * fragmentation and packet reordering past skb's retransmission. To consider
993 * them correctly, the acceptable range must be extended even more though
994 * the exact amount is rather hard to quantify. However, tp->max_window can
995 * be used as an exaggerated estimate.
997 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
998 u32 start_seq, u32 end_seq)
1000 /* Too far in future, or reversed (interpretation is ambiguous) */
1001 if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1004 /* Nasty start_seq wrap-around check (see comments above) */
1005 if (!before(start_seq, tp->snd_nxt))
1008 /* In outstanding window? ...This is valid exit for D-SACKs too.
1009 * start_seq == snd_una is non-sensical (see comments above)
1011 if (after(start_seq, tp->snd_una))
1014 if (!is_dsack || !tp->undo_marker)
1017 /* ...Then it's D-SACK, and must reside below snd_una completely */
1018 if (after(end_seq, tp->snd_una))
1021 if (!before(start_seq, tp->undo_marker))
1025 if (!after(end_seq, tp->undo_marker))
1028 /* Undo_marker boundary crossing (overestimates a lot). Known already:
1029 * start_seq < undo_marker and end_seq >= undo_marker.
1031 return !before(start_seq, end_seq - tp->max_window);
1034 /* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1035 * Event "B". Later note: FACK people cheated me again 8), we have to account
1036 * for reordering! Ugly, but should help.
1038 * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1039 * less than what is now known to be received by the other end (derived from
1040 * highest SACK block). Also calculate the lowest snd_nxt among the remaining
1041 * retransmitted skbs to avoid some costly processing per ACKs.
1043 static void tcp_mark_lost_retrans(struct sock *sk, int *flag)
1045 const struct inet_connection_sock *icsk = inet_csk(sk);
1046 struct tcp_sock *tp = tcp_sk(sk);
1047 struct sk_buff *skb;
1049 u32 new_low_seq = tp->snd_nxt;
1050 u32 received_upto = tcp_highest_sack_seq(tp);
1052 if (!tcp_is_fack(tp) || !tp->retrans_out ||
1053 !after(received_upto, tp->lost_retrans_low) ||
1054 icsk->icsk_ca_state != TCP_CA_Recovery)
1057 tcp_for_write_queue(skb, sk) {
1058 u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1060 if (skb == tcp_send_head(sk))
1062 if (cnt == tp->retrans_out)
1064 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1067 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1070 /* TODO: We would like to get rid of tcp_is_fack(tp) only
1071 * constraint here (see above) but figuring out that at
1072 * least tp->reordering SACK blocks reside between ack_seq
1073 * and received_upto is not easy task to do cheaply with
1074 * the available datastructures.
1076 * Whether FACK should check here for tp->reordering segs
1077 * in-between one could argue for either way (it would be
1078 * rather simple to implement as we could count fack_count
1079 * during the walk and do tp->fackets_out - fack_count).
1081 if (after(received_upto, ack_seq)) {
1082 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1083 tp->retrans_out -= tcp_skb_pcount(skb);
1084 *flag |= FLAG_LOST_RETRANS;
1085 tcp_skb_mark_lost_uncond_verify(tp, skb);
1086 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
1088 if (before(ack_seq, new_low_seq))
1089 new_low_seq = ack_seq;
1090 cnt += tcp_skb_pcount(skb);
1094 if (tp->retrans_out)
1095 tp->lost_retrans_low = new_low_seq;
1098 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1099 struct tcp_sack_block_wire *sp, int num_sacks,
1102 struct tcp_sock *tp = tcp_sk(sk);
1103 u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1104 u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1105 bool dup_sack = false;
1107 if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1110 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1111 } else if (num_sacks > 1) {
1112 u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1113 u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1115 if (!after(end_seq_0, end_seq_1) &&
1116 !before(start_seq_0, start_seq_1)) {
1119 NET_INC_STATS_BH(sock_net(sk),
1120 LINUX_MIB_TCPDSACKOFORECV);
1124 /* D-SACK for already forgotten data... Do dumb counting. */
1125 if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
1126 !after(end_seq_0, prior_snd_una) &&
1127 after(end_seq_0, tp->undo_marker))
1133 struct tcp_sacktag_state {
1136 /* Timestamps for earliest and latest never-retransmitted segment
1137 * that was SACKed. RTO needs the earliest RTT to stay conservative,
1138 * but congestion control should still get an accurate delay signal.
1140 struct skb_mstamp first_sackt;
1141 struct skb_mstamp last_sackt;
1145 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1146 * the incoming SACK may not exactly match but we can find smaller MSS
1147 * aligned portion of it that matches. Therefore we might need to fragment
1148 * which may fail and creates some hassle (caller must handle error case
1151 * FIXME: this could be merged to shift decision code
1153 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1154 u32 start_seq, u32 end_seq)
1158 unsigned int pkt_len;
1161 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1162 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1164 if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1165 after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1166 mss = tcp_skb_mss(skb);
1167 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1170 pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1174 pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1179 /* Round if necessary so that SACKs cover only full MSSes
1180 * and/or the remaining small portion (if present)
1182 if (pkt_len > mss) {
1183 unsigned int new_len = (pkt_len / mss) * mss;
1184 if (!in_sack && new_len < pkt_len) {
1186 if (new_len >= skb->len)
1191 err = tcp_fragment(sk, skb, pkt_len, mss, GFP_ATOMIC);
1199 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1200 static u8 tcp_sacktag_one(struct sock *sk,
1201 struct tcp_sacktag_state *state, u8 sacked,
1202 u32 start_seq, u32 end_seq,
1203 int dup_sack, int pcount,
1204 const struct skb_mstamp *xmit_time)
1206 struct tcp_sock *tp = tcp_sk(sk);
1207 int fack_count = state->fack_count;
1209 /* Account D-SACK for retransmitted packet. */
1210 if (dup_sack && (sacked & TCPCB_RETRANS)) {
1211 if (tp->undo_marker && tp->undo_retrans > 0 &&
1212 after(end_seq, tp->undo_marker))
1214 if (sacked & TCPCB_SACKED_ACKED)
1215 state->reord = min(fack_count, state->reord);
1218 /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1219 if (!after(end_seq, tp->snd_una))
1222 if (!(sacked & TCPCB_SACKED_ACKED)) {
1223 if (sacked & TCPCB_SACKED_RETRANS) {
1224 /* If the segment is not tagged as lost,
1225 * we do not clear RETRANS, believing
1226 * that retransmission is still in flight.
1228 if (sacked & TCPCB_LOST) {
1229 sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1230 tp->lost_out -= pcount;
1231 tp->retrans_out -= pcount;
1234 if (!(sacked & TCPCB_RETRANS)) {
1235 /* New sack for not retransmitted frame,
1236 * which was in hole. It is reordering.
1238 if (before(start_seq,
1239 tcp_highest_sack_seq(tp)))
1240 state->reord = min(fack_count,
1242 if (!after(end_seq, tp->high_seq))
1243 state->flag |= FLAG_ORIG_SACK_ACKED;
1244 if (state->first_sackt.v64 == 0)
1245 state->first_sackt = *xmit_time;
1246 state->last_sackt = *xmit_time;
1249 if (sacked & TCPCB_LOST) {
1250 sacked &= ~TCPCB_LOST;
1251 tp->lost_out -= pcount;
1255 sacked |= TCPCB_SACKED_ACKED;
1256 state->flag |= FLAG_DATA_SACKED;
1257 tp->sacked_out += pcount;
1259 fack_count += pcount;
1261 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1262 if (!tcp_is_fack(tp) && tp->lost_skb_hint &&
1263 before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1264 tp->lost_cnt_hint += pcount;
1266 if (fack_count > tp->fackets_out)
1267 tp->fackets_out = fack_count;
1270 /* D-SACK. We can detect redundant retransmission in S|R and plain R
1271 * frames and clear it. undo_retrans is decreased above, L|R frames
1272 * are accounted above as well.
1274 if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1275 sacked &= ~TCPCB_SACKED_RETRANS;
1276 tp->retrans_out -= pcount;
1282 /* Shift newly-SACKed bytes from this skb to the immediately previous
1283 * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1285 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1286 struct tcp_sacktag_state *state,
1287 unsigned int pcount, int shifted, int mss,
1290 struct tcp_sock *tp = tcp_sk(sk);
1291 struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1292 u32 start_seq = TCP_SKB_CB(skb)->seq; /* start of newly-SACKed */
1293 u32 end_seq = start_seq + shifted; /* end of newly-SACKed */
1297 /* Adjust counters and hints for the newly sacked sequence
1298 * range but discard the return value since prev is already
1299 * marked. We must tag the range first because the seq
1300 * advancement below implicitly advances
1301 * tcp_highest_sack_seq() when skb is highest_sack.
1303 tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1304 start_seq, end_seq, dup_sack, pcount,
1307 if (skb == tp->lost_skb_hint)
1308 tp->lost_cnt_hint += pcount;
1310 TCP_SKB_CB(prev)->end_seq += shifted;
1311 TCP_SKB_CB(skb)->seq += shifted;
1313 tcp_skb_pcount_add(prev, pcount);
1314 BUG_ON(tcp_skb_pcount(skb) < pcount);
1315 tcp_skb_pcount_add(skb, -pcount);
1317 /* When we're adding to gso_segs == 1, gso_size will be zero,
1318 * in theory this shouldn't be necessary but as long as DSACK
1319 * code can come after this skb later on it's better to keep
1320 * setting gso_size to something.
1322 if (!TCP_SKB_CB(prev)->tcp_gso_size)
1323 TCP_SKB_CB(prev)->tcp_gso_size = mss;
1325 /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1326 if (tcp_skb_pcount(skb) <= 1)
1327 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1329 /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1330 TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1333 BUG_ON(!tcp_skb_pcount(skb));
1334 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1338 /* Whole SKB was eaten :-) */
1340 if (skb == tp->retransmit_skb_hint)
1341 tp->retransmit_skb_hint = prev;
1342 if (skb == tp->lost_skb_hint) {
1343 tp->lost_skb_hint = prev;
1344 tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1347 TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1348 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1349 TCP_SKB_CB(prev)->end_seq++;
1351 if (skb == tcp_highest_sack(sk))
1352 tcp_advance_highest_sack(sk, skb);
1354 tcp_unlink_write_queue(skb, sk);
1355 sk_wmem_free_skb(sk, skb);
1357 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1362 /* I wish gso_size would have a bit more sane initialization than
1363 * something-or-zero which complicates things
1365 static int tcp_skb_seglen(const struct sk_buff *skb)
1367 return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1370 /* Shifting pages past head area doesn't work */
1371 static int skb_can_shift(const struct sk_buff *skb)
1373 return !skb_headlen(skb) && skb_is_nonlinear(skb);
1376 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1379 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1380 struct tcp_sacktag_state *state,
1381 u32 start_seq, u32 end_seq,
1384 struct tcp_sock *tp = tcp_sk(sk);
1385 struct sk_buff *prev;
1391 if (!sk_can_gso(sk))
1394 /* Normally R but no L won't result in plain S */
1396 (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1398 if (!skb_can_shift(skb))
1400 /* This frame is about to be dropped (was ACKed). */
1401 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1404 /* Can only happen with delayed DSACK + discard craziness */
1405 if (unlikely(skb == tcp_write_queue_head(sk)))
1407 prev = tcp_write_queue_prev(sk, skb);
1409 if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1412 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1413 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1417 pcount = tcp_skb_pcount(skb);
1418 mss = tcp_skb_seglen(skb);
1420 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1421 * drop this restriction as unnecessary
1423 if (mss != tcp_skb_seglen(prev))
1426 if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1428 /* CHECKME: This is non-MSS split case only?, this will
1429 * cause skipped skbs due to advancing loop btw, original
1430 * has that feature too
1432 if (tcp_skb_pcount(skb) <= 1)
1435 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1437 /* TODO: head merge to next could be attempted here
1438 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1439 * though it might not be worth of the additional hassle
1441 * ...we can probably just fallback to what was done
1442 * previously. We could try merging non-SACKed ones
1443 * as well but it probably isn't going to buy off
1444 * because later SACKs might again split them, and
1445 * it would make skb timestamp tracking considerably
1451 len = end_seq - TCP_SKB_CB(skb)->seq;
1453 BUG_ON(len > skb->len);
1455 /* MSS boundaries should be honoured or else pcount will
1456 * severely break even though it makes things bit trickier.
1457 * Optimize common case to avoid most of the divides
1459 mss = tcp_skb_mss(skb);
1461 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1462 * drop this restriction as unnecessary
1464 if (mss != tcp_skb_seglen(prev))
1469 } else if (len < mss) {
1477 /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1478 if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1481 if (!skb_shift(prev, skb, len))
1483 if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1486 /* Hole filled allows collapsing with the next as well, this is very
1487 * useful when hole on every nth skb pattern happens
1489 if (prev == tcp_write_queue_tail(sk))
1491 skb = tcp_write_queue_next(sk, prev);
1493 if (!skb_can_shift(skb) ||
1494 (skb == tcp_send_head(sk)) ||
1495 ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1496 (mss != tcp_skb_seglen(skb)))
1500 if (skb_shift(prev, skb, len)) {
1501 pcount += tcp_skb_pcount(skb);
1502 tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1506 state->fack_count += pcount;
1513 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1517 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1518 struct tcp_sack_block *next_dup,
1519 struct tcp_sacktag_state *state,
1520 u32 start_seq, u32 end_seq,
1523 struct tcp_sock *tp = tcp_sk(sk);
1524 struct sk_buff *tmp;
1526 tcp_for_write_queue_from(skb, sk) {
1528 bool dup_sack = dup_sack_in;
1530 if (skb == tcp_send_head(sk))
1533 /* queue is in-order => we can short-circuit the walk early */
1534 if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1538 before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1539 in_sack = tcp_match_skb_to_sack(sk, skb,
1540 next_dup->start_seq,
1546 /* skb reference here is a bit tricky to get right, since
1547 * shifting can eat and free both this skb and the next,
1548 * so not even _safe variant of the loop is enough.
1551 tmp = tcp_shift_skb_data(sk, skb, state,
1552 start_seq, end_seq, dup_sack);
1561 in_sack = tcp_match_skb_to_sack(sk, skb,
1567 if (unlikely(in_sack < 0))
1571 TCP_SKB_CB(skb)->sacked =
1574 TCP_SKB_CB(skb)->sacked,
1575 TCP_SKB_CB(skb)->seq,
1576 TCP_SKB_CB(skb)->end_seq,
1578 tcp_skb_pcount(skb),
1581 if (!before(TCP_SKB_CB(skb)->seq,
1582 tcp_highest_sack_seq(tp)))
1583 tcp_advance_highest_sack(sk, skb);
1586 state->fack_count += tcp_skb_pcount(skb);
1591 /* Avoid all extra work that is being done by sacktag while walking in
1594 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1595 struct tcp_sacktag_state *state,
1598 tcp_for_write_queue_from(skb, sk) {
1599 if (skb == tcp_send_head(sk))
1602 if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1605 state->fack_count += tcp_skb_pcount(skb);
1610 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1612 struct tcp_sack_block *next_dup,
1613 struct tcp_sacktag_state *state,
1619 if (before(next_dup->start_seq, skip_to_seq)) {
1620 skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1621 skb = tcp_sacktag_walk(skb, sk, NULL, state,
1622 next_dup->start_seq, next_dup->end_seq,
1629 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1631 return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1635 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1636 u32 prior_snd_una, struct tcp_sacktag_state *state)
1638 struct tcp_sock *tp = tcp_sk(sk);
1639 const unsigned char *ptr = (skb_transport_header(ack_skb) +
1640 TCP_SKB_CB(ack_skb)->sacked);
1641 struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1642 struct tcp_sack_block sp[TCP_NUM_SACKS];
1643 struct tcp_sack_block *cache;
1644 struct sk_buff *skb;
1645 int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1647 bool found_dup_sack = false;
1649 int first_sack_index;
1652 state->reord = tp->packets_out;
1654 if (!tp->sacked_out) {
1655 if (WARN_ON(tp->fackets_out))
1656 tp->fackets_out = 0;
1657 tcp_highest_sack_reset(sk);
1660 found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1661 num_sacks, prior_snd_una);
1663 state->flag |= FLAG_DSACKING_ACK;
1665 /* Eliminate too old ACKs, but take into
1666 * account more or less fresh ones, they can
1667 * contain valid SACK info.
1669 if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1672 if (!tp->packets_out)
1676 first_sack_index = 0;
1677 for (i = 0; i < num_sacks; i++) {
1678 bool dup_sack = !i && found_dup_sack;
1680 sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1681 sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1683 if (!tcp_is_sackblock_valid(tp, dup_sack,
1684 sp[used_sacks].start_seq,
1685 sp[used_sacks].end_seq)) {
1689 if (!tp->undo_marker)
1690 mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1692 mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1694 /* Don't count olds caused by ACK reordering */
1695 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1696 !after(sp[used_sacks].end_seq, tp->snd_una))
1698 mib_idx = LINUX_MIB_TCPSACKDISCARD;
1701 NET_INC_STATS_BH(sock_net(sk), mib_idx);
1703 first_sack_index = -1;
1707 /* Ignore very old stuff early */
1708 if (!after(sp[used_sacks].end_seq, prior_snd_una))
1714 /* order SACK blocks to allow in order walk of the retrans queue */
1715 for (i = used_sacks - 1; i > 0; i--) {
1716 for (j = 0; j < i; j++) {
1717 if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1718 swap(sp[j], sp[j + 1]);
1720 /* Track where the first SACK block goes to */
1721 if (j == first_sack_index)
1722 first_sack_index = j + 1;
1727 skb = tcp_write_queue_head(sk);
1728 state->fack_count = 0;
1731 if (!tp->sacked_out) {
1732 /* It's already past, so skip checking against it */
1733 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1735 cache = tp->recv_sack_cache;
1736 /* Skip empty blocks in at head of the cache */
1737 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1742 while (i < used_sacks) {
1743 u32 start_seq = sp[i].start_seq;
1744 u32 end_seq = sp[i].end_seq;
1745 bool dup_sack = (found_dup_sack && (i == first_sack_index));
1746 struct tcp_sack_block *next_dup = NULL;
1748 if (found_dup_sack && ((i + 1) == first_sack_index))
1749 next_dup = &sp[i + 1];
1751 /* Skip too early cached blocks */
1752 while (tcp_sack_cache_ok(tp, cache) &&
1753 !before(start_seq, cache->end_seq))
1756 /* Can skip some work by looking recv_sack_cache? */
1757 if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1758 after(end_seq, cache->start_seq)) {
1761 if (before(start_seq, cache->start_seq)) {
1762 skb = tcp_sacktag_skip(skb, sk, state,
1764 skb = tcp_sacktag_walk(skb, sk, next_dup,
1771 /* Rest of the block already fully processed? */
1772 if (!after(end_seq, cache->end_seq))
1775 skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1779 /* ...tail remains todo... */
1780 if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1781 /* ...but better entrypoint exists! */
1782 skb = tcp_highest_sack(sk);
1785 state->fack_count = tp->fackets_out;
1790 skb = tcp_sacktag_skip(skb, sk, state, cache->end_seq);
1791 /* Check overlap against next cached too (past this one already) */
1796 if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1797 skb = tcp_highest_sack(sk);
1800 state->fack_count = tp->fackets_out;
1802 skb = tcp_sacktag_skip(skb, sk, state, start_seq);
1805 skb = tcp_sacktag_walk(skb, sk, next_dup, state,
1806 start_seq, end_seq, dup_sack);
1812 /* Clear the head of the cache sack blocks so we can skip it next time */
1813 for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1814 tp->recv_sack_cache[i].start_seq = 0;
1815 tp->recv_sack_cache[i].end_seq = 0;
1817 for (j = 0; j < used_sacks; j++)
1818 tp->recv_sack_cache[i++] = sp[j];
1820 if ((state->reord < tp->fackets_out) &&
1821 ((inet_csk(sk)->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker))
1822 tcp_update_reordering(sk, tp->fackets_out - state->reord, 0);
1824 tcp_mark_lost_retrans(sk, &state->flag);
1825 tcp_verify_left_out(tp);
1828 #if FASTRETRANS_DEBUG > 0
1829 WARN_ON((int)tp->sacked_out < 0);
1830 WARN_ON((int)tp->lost_out < 0);
1831 WARN_ON((int)tp->retrans_out < 0);
1832 WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1837 /* Limits sacked_out so that sum with lost_out isn't ever larger than
1838 * packets_out. Returns false if sacked_out adjustement wasn't necessary.
1840 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
1844 holes = max(tp->lost_out, 1U);
1845 holes = min(holes, tp->packets_out);
1847 if ((tp->sacked_out + holes) > tp->packets_out) {
1848 tp->sacked_out = tp->packets_out - holes;
1854 /* If we receive more dupacks than we expected counting segments
1855 * in assumption of absent reordering, interpret this as reordering.
1856 * The only another reason could be bug in receiver TCP.
1858 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1860 struct tcp_sock *tp = tcp_sk(sk);
1861 if (tcp_limit_reno_sacked(tp))
1862 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1865 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1867 static void tcp_add_reno_sack(struct sock *sk)
1869 struct tcp_sock *tp = tcp_sk(sk);
1871 tcp_check_reno_reordering(sk, 0);
1872 tcp_verify_left_out(tp);
1875 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1877 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1879 struct tcp_sock *tp = tcp_sk(sk);
1882 /* One ACK acked hole. The rest eat duplicate ACKs. */
1883 if (acked - 1 >= tp->sacked_out)
1886 tp->sacked_out -= acked - 1;
1888 tcp_check_reno_reordering(sk, acked);
1889 tcp_verify_left_out(tp);
1892 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1897 void tcp_clear_retrans(struct tcp_sock *tp)
1899 tp->retrans_out = 0;
1901 tp->undo_marker = 0;
1902 tp->undo_retrans = -1;
1903 tp->fackets_out = 0;
1907 static inline void tcp_init_undo(struct tcp_sock *tp)
1909 tp->undo_marker = tp->snd_una;
1910 /* Retransmission still in flight may cause DSACKs later. */
1911 tp->undo_retrans = tp->retrans_out ? : -1;
1914 /* Enter Loss state. If we detect SACK reneging, forget all SACK information
1915 * and reset tags completely, otherwise preserve SACKs. If receiver
1916 * dropped its ofo queue, we will know this due to reneging detection.
1918 void tcp_enter_loss(struct sock *sk)
1920 const struct inet_connection_sock *icsk = inet_csk(sk);
1921 struct tcp_sock *tp = tcp_sk(sk);
1922 struct sk_buff *skb;
1923 bool new_recovery = false;
1924 bool is_reneg; /* is receiver reneging on SACKs? */
1926 /* Reduce ssthresh if it has not yet been made inside this window. */
1927 if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1928 !after(tp->high_seq, tp->snd_una) ||
1929 (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1930 new_recovery = true;
1931 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1932 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1933 tcp_ca_event(sk, CA_EVENT_LOSS);
1937 tp->snd_cwnd_cnt = 0;
1938 tp->snd_cwnd_stamp = tcp_time_stamp;
1940 tp->retrans_out = 0;
1943 if (tcp_is_reno(tp))
1944 tcp_reset_reno_sack(tp);
1946 skb = tcp_write_queue_head(sk);
1947 is_reneg = skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED);
1949 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
1951 tp->fackets_out = 0;
1953 tcp_clear_all_retrans_hints(tp);
1955 tcp_for_write_queue(skb, sk) {
1956 if (skb == tcp_send_head(sk))
1959 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1960 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || is_reneg) {
1961 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1962 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1963 tp->lost_out += tcp_skb_pcount(skb);
1964 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
1967 tcp_verify_left_out(tp);
1969 /* Timeout in disordered state after receiving substantial DUPACKs
1970 * suggests that the degree of reordering is over-estimated.
1972 if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
1973 tp->sacked_out >= sysctl_tcp_reordering)
1974 tp->reordering = min_t(unsigned int, tp->reordering,
1975 sysctl_tcp_reordering);
1976 tcp_set_ca_state(sk, TCP_CA_Loss);
1977 tp->high_seq = tp->snd_nxt;
1978 tcp_ecn_queue_cwr(tp);
1980 /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
1981 * loss recovery is underway except recurring timeout(s) on
1982 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
1984 tp->frto = sysctl_tcp_frto &&
1985 (new_recovery || icsk->icsk_retransmits) &&
1986 !inet_csk(sk)->icsk_mtup.probe_size;
1989 /* If ACK arrived pointing to a remembered SACK, it means that our
1990 * remembered SACKs do not reflect real state of receiver i.e.
1991 * receiver _host_ is heavily congested (or buggy).
1993 * To avoid big spurious retransmission bursts due to transient SACK
1994 * scoreboard oddities that look like reneging, we give the receiver a
1995 * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
1996 * restore sanity to the SACK scoreboard. If the apparent reneging
1997 * persists until this RTO then we'll clear the SACK scoreboard.
1999 static bool tcp_check_sack_reneging(struct sock *sk, int flag)
2001 if (flag & FLAG_SACK_RENEGING) {
2002 struct tcp_sock *tp = tcp_sk(sk);
2003 unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
2004 msecs_to_jiffies(10));
2006 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2007 delay, TCP_RTO_MAX);
2013 static inline int tcp_fackets_out(const struct tcp_sock *tp)
2015 return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
2018 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2019 * counter when SACK is enabled (without SACK, sacked_out is used for
2022 * Instead, with FACK TCP uses fackets_out that includes both SACKed
2023 * segments up to the highest received SACK block so far and holes in
2026 * With reordering, holes may still be in flight, so RFC3517 recovery
2027 * uses pure sacked_out (total number of SACKed segments) even though
2028 * it violates the RFC that uses duplicate ACKs, often these are equal
2029 * but when e.g. out-of-window ACKs or packet duplication occurs,
2030 * they differ. Since neither occurs due to loss, TCP should really
2033 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2035 return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
2038 static bool tcp_pause_early_retransmit(struct sock *sk, int flag)
2040 struct tcp_sock *tp = tcp_sk(sk);
2041 unsigned long delay;
2043 /* Delay early retransmit and entering fast recovery for
2044 * max(RTT/4, 2msec) unless ack has ECE mark, no RTT samples
2045 * available, or RTO is scheduled to fire first.
2047 if (sysctl_tcp_early_retrans < 2 || sysctl_tcp_early_retrans > 3 ||
2048 (flag & FLAG_ECE) || !tp->srtt_us)
2051 delay = max(usecs_to_jiffies(tp->srtt_us >> 5),
2052 msecs_to_jiffies(2));
2054 if (!time_after(inet_csk(sk)->icsk_timeout, (jiffies + delay)))
2057 inet_csk_reset_xmit_timer(sk, ICSK_TIME_EARLY_RETRANS, delay,
2062 /* Linux NewReno/SACK/FACK/ECN state machine.
2063 * --------------------------------------
2065 * "Open" Normal state, no dubious events, fast path.
2066 * "Disorder" In all the respects it is "Open",
2067 * but requires a bit more attention. It is entered when
2068 * we see some SACKs or dupacks. It is split of "Open"
2069 * mainly to move some processing from fast path to slow one.
2070 * "CWR" CWND was reduced due to some Congestion Notification event.
2071 * It can be ECN, ICMP source quench, local device congestion.
2072 * "Recovery" CWND was reduced, we are fast-retransmitting.
2073 * "Loss" CWND was reduced due to RTO timeout or SACK reneging.
2075 * tcp_fastretrans_alert() is entered:
2076 * - each incoming ACK, if state is not "Open"
2077 * - when arrived ACK is unusual, namely:
2082 * Counting packets in flight is pretty simple.
2084 * in_flight = packets_out - left_out + retrans_out
2086 * packets_out is SND.NXT-SND.UNA counted in packets.
2088 * retrans_out is number of retransmitted segments.
2090 * left_out is number of segments left network, but not ACKed yet.
2092 * left_out = sacked_out + lost_out
2094 * sacked_out: Packets, which arrived to receiver out of order
2095 * and hence not ACKed. With SACKs this number is simply
2096 * amount of SACKed data. Even without SACKs
2097 * it is easy to give pretty reliable estimate of this number,
2098 * counting duplicate ACKs.
2100 * lost_out: Packets lost by network. TCP has no explicit
2101 * "loss notification" feedback from network (for now).
2102 * It means that this number can be only _guessed_.
2103 * Actually, it is the heuristics to predict lossage that
2104 * distinguishes different algorithms.
2106 * F.e. after RTO, when all the queue is considered as lost,
2107 * lost_out = packets_out and in_flight = retrans_out.
2109 * Essentially, we have now two algorithms counting
2112 * FACK: It is the simplest heuristics. As soon as we decided
2113 * that something is lost, we decide that _all_ not SACKed
2114 * packets until the most forward SACK are lost. I.e.
2115 * lost_out = fackets_out - sacked_out and left_out = fackets_out.
2116 * It is absolutely correct estimate, if network does not reorder
2117 * packets. And it loses any connection to reality when reordering
2118 * takes place. We use FACK by default until reordering
2119 * is suspected on the path to this destination.
2121 * NewReno: when Recovery is entered, we assume that one segment
2122 * is lost (classic Reno). While we are in Recovery and
2123 * a partial ACK arrives, we assume that one more packet
2124 * is lost (NewReno). This heuristics are the same in NewReno
2127 * Imagine, that's all! Forget about all this shamanism about CWND inflation
2128 * deflation etc. CWND is real congestion window, never inflated, changes
2129 * only according to classic VJ rules.
2131 * Really tricky (and requiring careful tuning) part of algorithm
2132 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2133 * The first determines the moment _when_ we should reduce CWND and,
2134 * hence, slow down forward transmission. In fact, it determines the moment
2135 * when we decide that hole is caused by loss, rather than by a reorder.
2137 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2138 * holes, caused by lost packets.
2140 * And the most logically complicated part of algorithm is undo
2141 * heuristics. We detect false retransmits due to both too early
2142 * fast retransmit (reordering) and underestimated RTO, analyzing
2143 * timestamps and D-SACKs. When we detect that some segments were
2144 * retransmitted by mistake and CWND reduction was wrong, we undo
2145 * window reduction and abort recovery phase. This logic is hidden
2146 * inside several functions named tcp_try_undo_<something>.
2149 /* This function decides, when we should leave Disordered state
2150 * and enter Recovery phase, reducing congestion window.
2152 * Main question: may we further continue forward transmission
2153 * with the same cwnd?
2155 static bool tcp_time_to_recover(struct sock *sk, int flag)
2157 struct tcp_sock *tp = tcp_sk(sk);
2160 /* Trick#1: The loss is proven. */
2164 /* Not-A-Trick#2 : Classic rule... */
2165 if (tcp_dupack_heuristics(tp) > tp->reordering)
2168 /* Trick#4: It is still not OK... But will it be useful to delay
2171 packets_out = tp->packets_out;
2172 if (packets_out <= tp->reordering &&
2173 tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2174 !tcp_may_send_now(sk)) {
2175 /* We have nothing to send. This connection is limited
2176 * either by receiver window or by application.
2181 /* If a thin stream is detected, retransmit after first
2182 * received dupack. Employ only if SACK is supported in order
2183 * to avoid possible corner-case series of spurious retransmissions
2184 * Use only if there are no unsent data.
2186 if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
2187 tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
2188 tcp_is_sack(tp) && !tcp_send_head(sk))
2191 /* Trick#6: TCP early retransmit, per RFC5827. To avoid spurious
2192 * retransmissions due to small network reorderings, we implement
2193 * Mitigation A.3 in the RFC and delay the retransmission for a short
2194 * interval if appropriate.
2196 if (tp->do_early_retrans && !tp->retrans_out && tp->sacked_out &&
2197 (tp->packets_out >= (tp->sacked_out + 1) && tp->packets_out < 4) &&
2198 !tcp_may_send_now(sk))
2199 return !tcp_pause_early_retransmit(sk, flag);
2204 /* Detect loss in event "A" above by marking head of queue up as lost.
2205 * For FACK or non-SACK(Reno) senders, the first "packets" number of segments
2206 * are considered lost. For RFC3517 SACK, a segment is considered lost if it
2207 * has at least tp->reordering SACKed seqments above it; "packets" refers to
2208 * the maximum SACKed segments to pass before reaching this limit.
2210 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2212 struct tcp_sock *tp = tcp_sk(sk);
2213 struct sk_buff *skb;
2217 /* Use SACK to deduce losses of new sequences sent during recovery */
2218 const u32 loss_high = tcp_is_sack(tp) ? tp->snd_nxt : tp->high_seq;
2220 WARN_ON(packets > tp->packets_out);
2221 if (tp->lost_skb_hint) {
2222 skb = tp->lost_skb_hint;
2223 cnt = tp->lost_cnt_hint;
2224 /* Head already handled? */
2225 if (mark_head && skb != tcp_write_queue_head(sk))
2228 skb = tcp_write_queue_head(sk);
2232 tcp_for_write_queue_from(skb, sk) {
2233 if (skb == tcp_send_head(sk))
2235 /* TODO: do this better */
2236 /* this is not the most efficient way to do this... */
2237 tp->lost_skb_hint = skb;
2238 tp->lost_cnt_hint = cnt;
2240 if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2244 if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2245 (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2246 cnt += tcp_skb_pcount(skb);
2248 if (cnt > packets) {
2249 if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
2250 (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
2251 (oldcnt >= packets))
2254 mss = tcp_skb_mss(skb);
2255 err = tcp_fragment(sk, skb, (packets - oldcnt) * mss,
2262 tcp_skb_mark_lost(tp, skb);
2267 tcp_verify_left_out(tp);
2270 /* Account newly detected lost packet(s) */
2272 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2274 struct tcp_sock *tp = tcp_sk(sk);
2276 if (tcp_is_reno(tp)) {
2277 tcp_mark_head_lost(sk, 1, 1);
2278 } else if (tcp_is_fack(tp)) {
2279 int lost = tp->fackets_out - tp->reordering;
2282 tcp_mark_head_lost(sk, lost, 0);
2284 int sacked_upto = tp->sacked_out - tp->reordering;
2285 if (sacked_upto >= 0)
2286 tcp_mark_head_lost(sk, sacked_upto, 0);
2287 else if (fast_rexmit)
2288 tcp_mark_head_lost(sk, 1, 1);
2292 /* CWND moderation, preventing bursts due to too big ACKs
2293 * in dubious situations.
2295 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2297 tp->snd_cwnd = min(tp->snd_cwnd,
2298 tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2299 tp->snd_cwnd_stamp = tcp_time_stamp;
2302 /* Nothing was retransmitted or returned timestamp is less
2303 * than timestamp of the first retransmission.
2305 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2307 return !tp->retrans_stamp ||
2308 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2309 before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
2312 /* Undo procedures. */
2314 /* We can clear retrans_stamp when there are no retransmissions in the
2315 * window. It would seem that it is trivially available for us in
2316 * tp->retrans_out, however, that kind of assumptions doesn't consider
2317 * what will happen if errors occur when sending retransmission for the
2318 * second time. ...It could the that such segment has only
2319 * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2320 * the head skb is enough except for some reneging corner cases that
2321 * are not worth the effort.
2323 * Main reason for all this complexity is the fact that connection dying
2324 * time now depends on the validity of the retrans_stamp, in particular,
2325 * that successive retransmissions of a segment must not advance
2326 * retrans_stamp under any conditions.
2328 static bool tcp_any_retrans_done(const struct sock *sk)
2330 const struct tcp_sock *tp = tcp_sk(sk);
2331 struct sk_buff *skb;
2333 if (tp->retrans_out)
2336 skb = tcp_write_queue_head(sk);
2337 if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2343 #if FASTRETRANS_DEBUG > 1
2344 static void DBGUNDO(struct sock *sk, const char *msg)
2346 struct tcp_sock *tp = tcp_sk(sk);
2347 struct inet_sock *inet = inet_sk(sk);
2349 if (sk->sk_family == AF_INET) {
2350 pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2352 &inet->inet_daddr, ntohs(inet->inet_dport),
2353 tp->snd_cwnd, tcp_left_out(tp),
2354 tp->snd_ssthresh, tp->prior_ssthresh,
2357 #if IS_ENABLED(CONFIG_IPV6)
2358 else if (sk->sk_family == AF_INET6) {
2359 struct ipv6_pinfo *np = inet6_sk(sk);
2360 pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2362 &np->daddr, ntohs(inet->inet_dport),
2363 tp->snd_cwnd, tcp_left_out(tp),
2364 tp->snd_ssthresh, tp->prior_ssthresh,
2370 #define DBGUNDO(x...) do { } while (0)
2373 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2375 struct tcp_sock *tp = tcp_sk(sk);
2378 struct sk_buff *skb;
2380 tcp_for_write_queue(skb, sk) {
2381 if (skb == tcp_send_head(sk))
2383 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2386 tcp_clear_all_retrans_hints(tp);
2389 if (tp->prior_ssthresh) {
2390 const struct inet_connection_sock *icsk = inet_csk(sk);
2392 if (icsk->icsk_ca_ops->undo_cwnd)
2393 tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2395 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2397 if (tp->prior_ssthresh > tp->snd_ssthresh) {
2398 tp->snd_ssthresh = tp->prior_ssthresh;
2399 tcp_ecn_withdraw_cwr(tp);
2402 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2404 tp->snd_cwnd_stamp = tcp_time_stamp;
2405 tp->undo_marker = 0;
2408 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2410 return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2413 /* People celebrate: "We love our President!" */
2414 static bool tcp_try_undo_recovery(struct sock *sk)
2416 struct tcp_sock *tp = tcp_sk(sk);
2418 if (tcp_may_undo(tp)) {
2421 /* Happy end! We did not retransmit anything
2422 * or our original transmission succeeded.
2424 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2425 tcp_undo_cwnd_reduction(sk, false);
2426 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2427 mib_idx = LINUX_MIB_TCPLOSSUNDO;
2429 mib_idx = LINUX_MIB_TCPFULLUNDO;
2431 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2433 if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2434 /* Hold old state until something *above* high_seq
2435 * is ACKed. For Reno it is MUST to prevent false
2436 * fast retransmits (RFC2582). SACK TCP is safe. */
2437 tcp_moderate_cwnd(tp);
2438 if (!tcp_any_retrans_done(sk))
2439 tp->retrans_stamp = 0;
2442 tcp_set_ca_state(sk, TCP_CA_Open);
2446 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2447 static bool tcp_try_undo_dsack(struct sock *sk)
2449 struct tcp_sock *tp = tcp_sk(sk);
2451 if (tp->undo_marker && !tp->undo_retrans) {
2452 DBGUNDO(sk, "D-SACK");
2453 tcp_undo_cwnd_reduction(sk, false);
2454 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2460 /* Undo during loss recovery after partial ACK or using F-RTO. */
2461 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2463 struct tcp_sock *tp = tcp_sk(sk);
2465 if (frto_undo || tcp_may_undo(tp)) {
2466 tcp_undo_cwnd_reduction(sk, true);
2468 DBGUNDO(sk, "partial loss");
2469 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2471 NET_INC_STATS_BH(sock_net(sk),
2472 LINUX_MIB_TCPSPURIOUSRTOS);
2473 inet_csk(sk)->icsk_retransmits = 0;
2474 if (frto_undo || tcp_is_sack(tp))
2475 tcp_set_ca_state(sk, TCP_CA_Open);
2481 /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2482 * It computes the number of packets to send (sndcnt) based on packets newly
2484 * 1) If the packets in flight is larger than ssthresh, PRR spreads the
2485 * cwnd reductions across a full RTT.
2486 * 2) Otherwise PRR uses packet conservation to send as much as delivered.
2487 * But when the retransmits are acked without further losses, PRR
2488 * slow starts cwnd up to ssthresh to speed up the recovery.
2490 static void tcp_init_cwnd_reduction(struct sock *sk)
2492 struct tcp_sock *tp = tcp_sk(sk);
2494 tp->high_seq = tp->snd_nxt;
2495 tp->tlp_high_seq = 0;
2496 tp->snd_cwnd_cnt = 0;
2497 tp->prior_cwnd = tp->snd_cwnd;
2498 tp->prr_delivered = 0;
2500 tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2501 tcp_ecn_queue_cwr(tp);
2504 static void tcp_cwnd_reduction(struct sock *sk, const int prior_unsacked,
2505 int fast_rexmit, int flag)
2507 struct tcp_sock *tp = tcp_sk(sk);
2509 int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2510 int newly_acked_sacked = prior_unsacked -
2511 (tp->packets_out - tp->sacked_out);
2513 tp->prr_delivered += newly_acked_sacked;
2515 u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2517 sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2518 } else if ((flag & FLAG_RETRANS_DATA_ACKED) &&
2519 !(flag & FLAG_LOST_RETRANS)) {
2520 sndcnt = min_t(int, delta,
2521 max_t(int, tp->prr_delivered - tp->prr_out,
2522 newly_acked_sacked) + 1);
2524 sndcnt = min(delta, newly_acked_sacked);
2526 sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
2527 tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
2530 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2532 struct tcp_sock *tp = tcp_sk(sk);
2534 /* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2535 if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
2536 (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
2537 tp->snd_cwnd = tp->snd_ssthresh;
2538 tp->snd_cwnd_stamp = tcp_time_stamp;
2540 tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2543 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2544 void tcp_enter_cwr(struct sock *sk)
2546 struct tcp_sock *tp = tcp_sk(sk);
2548 tp->prior_ssthresh = 0;
2549 if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2550 tp->undo_marker = 0;
2551 tcp_init_cwnd_reduction(sk);
2552 tcp_set_ca_state(sk, TCP_CA_CWR);
2555 EXPORT_SYMBOL(tcp_enter_cwr);
2557 static void tcp_try_keep_open(struct sock *sk)
2559 struct tcp_sock *tp = tcp_sk(sk);
2560 int state = TCP_CA_Open;
2562 if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2563 state = TCP_CA_Disorder;
2565 if (inet_csk(sk)->icsk_ca_state != state) {
2566 tcp_set_ca_state(sk, state);
2567 tp->high_seq = tp->snd_nxt;
2571 static void tcp_try_to_open(struct sock *sk, int flag, const int prior_unsacked)
2573 struct tcp_sock *tp = tcp_sk(sk);
2575 tcp_verify_left_out(tp);
2577 if (!tcp_any_retrans_done(sk))
2578 tp->retrans_stamp = 0;
2580 if (flag & FLAG_ECE)
2583 if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2584 tcp_try_keep_open(sk);
2586 tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
2590 static void tcp_mtup_probe_failed(struct sock *sk)
2592 struct inet_connection_sock *icsk = inet_csk(sk);
2594 icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2595 icsk->icsk_mtup.probe_size = 0;
2598 static void tcp_mtup_probe_success(struct sock *sk)
2600 struct tcp_sock *tp = tcp_sk(sk);
2601 struct inet_connection_sock *icsk = inet_csk(sk);
2603 /* FIXME: breaks with very large cwnd */
2604 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2605 tp->snd_cwnd = tp->snd_cwnd *
2606 tcp_mss_to_mtu(sk, tp->mss_cache) /
2607 icsk->icsk_mtup.probe_size;
2608 tp->snd_cwnd_cnt = 0;
2609 tp->snd_cwnd_stamp = tcp_time_stamp;
2610 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2612 icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2613 icsk->icsk_mtup.probe_size = 0;
2614 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2617 /* Do a simple retransmit without using the backoff mechanisms in
2618 * tcp_timer. This is used for path mtu discovery.
2619 * The socket is already locked here.
2621 void tcp_simple_retransmit(struct sock *sk)
2623 const struct inet_connection_sock *icsk = inet_csk(sk);
2624 struct tcp_sock *tp = tcp_sk(sk);
2625 struct sk_buff *skb;
2626 unsigned int mss = tcp_current_mss(sk);
2627 u32 prior_lost = tp->lost_out;
2629 tcp_for_write_queue(skb, sk) {
2630 if (skb == tcp_send_head(sk))
2632 if (tcp_skb_seglen(skb) > mss &&
2633 !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2634 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2635 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2636 tp->retrans_out -= tcp_skb_pcount(skb);
2638 tcp_skb_mark_lost_uncond_verify(tp, skb);
2642 tcp_clear_retrans_hints_partial(tp);
2644 if (prior_lost == tp->lost_out)
2647 if (tcp_is_reno(tp))
2648 tcp_limit_reno_sacked(tp);
2650 tcp_verify_left_out(tp);
2652 /* Don't muck with the congestion window here.
2653 * Reason is that we do not increase amount of _data_
2654 * in network, but units changed and effective
2655 * cwnd/ssthresh really reduced now.
2657 if (icsk->icsk_ca_state != TCP_CA_Loss) {
2658 tp->high_seq = tp->snd_nxt;
2659 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2660 tp->prior_ssthresh = 0;
2661 tp->undo_marker = 0;
2662 tcp_set_ca_state(sk, TCP_CA_Loss);
2664 tcp_xmit_retransmit_queue(sk);
2666 EXPORT_SYMBOL(tcp_simple_retransmit);
2668 static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2670 struct tcp_sock *tp = tcp_sk(sk);
2673 if (tcp_is_reno(tp))
2674 mib_idx = LINUX_MIB_TCPRENORECOVERY;
2676 mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2678 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2680 tp->prior_ssthresh = 0;
2683 if (!tcp_in_cwnd_reduction(sk)) {
2685 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2686 tcp_init_cwnd_reduction(sk);
2688 tcp_set_ca_state(sk, TCP_CA_Recovery);
2691 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2692 * recovered or spurious. Otherwise retransmits more on partial ACKs.
2694 static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
2696 struct tcp_sock *tp = tcp_sk(sk);
2697 bool recovered = !before(tp->snd_una, tp->high_seq);
2699 if ((flag & FLAG_SND_UNA_ADVANCED) &&
2700 tcp_try_undo_loss(sk, false))
2703 if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2704 /* Step 3.b. A timeout is spurious if not all data are
2705 * lost, i.e., never-retransmitted data are (s)acked.
2707 if ((flag & FLAG_ORIG_SACK_ACKED) &&
2708 tcp_try_undo_loss(sk, true))
2711 if (after(tp->snd_nxt, tp->high_seq)) {
2712 if (flag & FLAG_DATA_SACKED || is_dupack)
2713 tp->frto = 0; /* Step 3.a. loss was real */
2714 } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2715 tp->high_seq = tp->snd_nxt;
2716 __tcp_push_pending_frames(sk, tcp_current_mss(sk),
2718 if (after(tp->snd_nxt, tp->high_seq))
2719 return; /* Step 2.b */
2725 /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2726 tcp_try_undo_recovery(sk);
2729 if (tcp_is_reno(tp)) {
2730 /* A Reno DUPACK means new data in F-RTO step 2.b above are
2731 * delivered. Lower inflight to clock out (re)tranmissions.
2733 if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
2734 tcp_add_reno_sack(sk);
2735 else if (flag & FLAG_SND_UNA_ADVANCED)
2736 tcp_reset_reno_sack(tp);
2738 tcp_xmit_retransmit_queue(sk);
2741 /* Undo during fast recovery after partial ACK. */
2742 static bool tcp_try_undo_partial(struct sock *sk, const int acked,
2743 const int prior_unsacked, int flag)
2745 struct tcp_sock *tp = tcp_sk(sk);
2747 if (tp->undo_marker && tcp_packet_delayed(tp)) {
2748 /* Plain luck! Hole if filled with delayed
2749 * packet, rather than with a retransmit.
2751 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2753 /* We are getting evidence that the reordering degree is higher
2754 * than we realized. If there are no retransmits out then we
2755 * can undo. Otherwise we clock out new packets but do not
2756 * mark more packets lost or retransmit more.
2758 if (tp->retrans_out) {
2759 tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
2763 if (!tcp_any_retrans_done(sk))
2764 tp->retrans_stamp = 0;
2766 DBGUNDO(sk, "partial recovery");
2767 tcp_undo_cwnd_reduction(sk, true);
2768 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2769 tcp_try_keep_open(sk);
2775 /* Process an event, which can update packets-in-flight not trivially.
2776 * Main goal of this function is to calculate new estimate for left_out,
2777 * taking into account both packets sitting in receiver's buffer and
2778 * packets lost by network.
2780 * Besides that it does CWND reduction, when packet loss is detected
2781 * and changes state of machine.
2783 * It does _not_ decide what to send, it is made in function
2784 * tcp_xmit_retransmit_queue().
2786 static void tcp_fastretrans_alert(struct sock *sk, const int acked,
2787 const int prior_unsacked,
2788 bool is_dupack, int flag)
2790 struct inet_connection_sock *icsk = inet_csk(sk);
2791 struct tcp_sock *tp = tcp_sk(sk);
2792 bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2793 (tcp_fackets_out(tp) > tp->reordering));
2794 int fast_rexmit = 0;
2796 if (WARN_ON(!tp->packets_out && tp->sacked_out))
2798 if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2799 tp->fackets_out = 0;
2801 /* Now state machine starts.
2802 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2803 if (flag & FLAG_ECE)
2804 tp->prior_ssthresh = 0;
2806 /* B. In all the states check for reneging SACKs. */
2807 if (tcp_check_sack_reneging(sk, flag))
2810 /* C. Check consistency of the current state. */
2811 tcp_verify_left_out(tp);
2813 /* D. Check state exit conditions. State can be terminated
2814 * when high_seq is ACKed. */
2815 if (icsk->icsk_ca_state == TCP_CA_Open) {
2816 WARN_ON(tp->retrans_out != 0);
2817 tp->retrans_stamp = 0;
2818 } else if (!before(tp->snd_una, tp->high_seq)) {
2819 switch (icsk->icsk_ca_state) {
2821 /* CWR is to be held something *above* high_seq
2822 * is ACKed for CWR bit to reach receiver. */
2823 if (tp->snd_una != tp->high_seq) {
2824 tcp_end_cwnd_reduction(sk);
2825 tcp_set_ca_state(sk, TCP_CA_Open);
2829 case TCP_CA_Recovery:
2830 if (tcp_is_reno(tp))
2831 tcp_reset_reno_sack(tp);
2832 if (tcp_try_undo_recovery(sk))
2834 tcp_end_cwnd_reduction(sk);
2839 /* E. Process state. */
2840 switch (icsk->icsk_ca_state) {
2841 case TCP_CA_Recovery:
2842 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2843 if (tcp_is_reno(tp) && is_dupack)
2844 tcp_add_reno_sack(sk);
2846 if (tcp_try_undo_partial(sk, acked, prior_unsacked, flag))
2848 /* Partial ACK arrived. Force fast retransmit. */
2849 do_lost = tcp_is_reno(tp) ||
2850 tcp_fackets_out(tp) > tp->reordering;
2852 if (tcp_try_undo_dsack(sk)) {
2853 tcp_try_keep_open(sk);
2858 tcp_process_loss(sk, flag, is_dupack);
2859 if (icsk->icsk_ca_state != TCP_CA_Open &&
2860 !(flag & FLAG_LOST_RETRANS))
2862 /* Change state if cwnd is undone or retransmits are lost */
2864 if (tcp_is_reno(tp)) {
2865 if (flag & FLAG_SND_UNA_ADVANCED)
2866 tcp_reset_reno_sack(tp);
2868 tcp_add_reno_sack(sk);
2871 if (icsk->icsk_ca_state <= TCP_CA_Disorder)
2872 tcp_try_undo_dsack(sk);
2874 if (!tcp_time_to_recover(sk, flag)) {
2875 tcp_try_to_open(sk, flag, prior_unsacked);
2879 /* MTU probe failure: don't reduce cwnd */
2880 if (icsk->icsk_ca_state < TCP_CA_CWR &&
2881 icsk->icsk_mtup.probe_size &&
2882 tp->snd_una == tp->mtu_probe.probe_seq_start) {
2883 tcp_mtup_probe_failed(sk);
2884 /* Restores the reduction we did in tcp_mtup_probe() */
2886 tcp_simple_retransmit(sk);
2890 /* Otherwise enter Recovery state */
2891 tcp_enter_recovery(sk, (flag & FLAG_ECE));
2896 tcp_update_scoreboard(sk, fast_rexmit);
2897 tcp_cwnd_reduction(sk, prior_unsacked, fast_rexmit, flag);
2898 tcp_xmit_retransmit_queue(sk);
2901 static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
2902 long seq_rtt_us, long sack_rtt_us)
2904 const struct tcp_sock *tp = tcp_sk(sk);
2906 /* Prefer RTT measured from ACK's timing to TS-ECR. This is because
2907 * broken middle-boxes or peers may corrupt TS-ECR fields. But
2908 * Karn's algorithm forbids taking RTT if some retransmitted data
2909 * is acked (RFC6298).
2911 if (flag & FLAG_RETRANS_DATA_ACKED)
2915 seq_rtt_us = sack_rtt_us;
2917 /* RTTM Rule: A TSecr value received in a segment is used to
2918 * update the averaged RTT measurement only if the segment
2919 * acknowledges some new data, i.e., only if it advances the
2920 * left edge of the send window.
2921 * See draft-ietf-tcplw-high-performance-00, section 3.3.
2923 if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2925 seq_rtt_us = jiffies_to_usecs(tcp_time_stamp - tp->rx_opt.rcv_tsecr);
2930 tcp_rtt_estimator(sk, seq_rtt_us);
2933 /* RFC6298: only reset backoff on valid RTT measurement. */
2934 inet_csk(sk)->icsk_backoff = 0;
2938 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
2939 static void tcp_synack_rtt_meas(struct sock *sk, const u32 synack_stamp)
2941 struct tcp_sock *tp = tcp_sk(sk);
2942 long seq_rtt_us = -1L;
2944 if (synack_stamp && !tp->total_retrans)
2945 seq_rtt_us = jiffies_to_usecs(tcp_time_stamp - synack_stamp);
2947 /* If the ACK acks both the SYNACK and the (Fast Open'd) data packets
2948 * sent in SYN_RECV, SYNACK RTT is the smooth RTT computed in tcp_ack()
2951 tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, seq_rtt_us, -1L);
2954 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
2956 const struct inet_connection_sock *icsk = inet_csk(sk);
2958 icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
2959 tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
2962 /* Restart timer after forward progress on connection.
2963 * RFC2988 recommends to restart timer to now+rto.
2965 void tcp_rearm_rto(struct sock *sk)
2967 const struct inet_connection_sock *icsk = inet_csk(sk);
2968 struct tcp_sock *tp = tcp_sk(sk);
2970 /* If the retrans timer is currently being used by Fast Open
2971 * for SYN-ACK retrans purpose, stay put.
2973 if (tp->fastopen_rsk)
2976 if (!tp->packets_out) {
2977 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
2979 u32 rto = inet_csk(sk)->icsk_rto;
2980 /* Offset the time elapsed after installing regular RTO */
2981 if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
2982 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
2983 struct sk_buff *skb = tcp_write_queue_head(sk);
2984 const u32 rto_time_stamp =
2985 tcp_skb_timestamp(skb) + rto;
2986 s32 delta = (s32)(rto_time_stamp - tcp_time_stamp);
2987 /* delta may not be positive if the socket is locked
2988 * when the retrans timer fires and is rescheduled.
2993 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
2998 /* This function is called when the delayed ER timer fires. TCP enters
2999 * fast recovery and performs fast-retransmit.
3001 void tcp_resume_early_retransmit(struct sock *sk)
3003 struct tcp_sock *tp = tcp_sk(sk);
3007 /* Stop if ER is disabled after the delayed ER timer is scheduled */
3008 if (!tp->do_early_retrans)
3011 tcp_enter_recovery(sk, false);
3012 tcp_update_scoreboard(sk, 1);
3013 tcp_xmit_retransmit_queue(sk);
3016 /* If we get here, the whole TSO packet has not been acked. */
3017 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3019 struct tcp_sock *tp = tcp_sk(sk);
3022 BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3024 packets_acked = tcp_skb_pcount(skb);
3025 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3027 packets_acked -= tcp_skb_pcount(skb);
3029 if (packets_acked) {
3030 BUG_ON(tcp_skb_pcount(skb) == 0);
3031 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3034 return packets_acked;
3037 static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3040 const struct skb_shared_info *shinfo;
3042 /* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3043 if (likely(!(sk->sk_tsflags & SOF_TIMESTAMPING_TX_ACK)))
3046 shinfo = skb_shinfo(skb);
3047 if ((shinfo->tx_flags & SKBTX_ACK_TSTAMP) &&
3048 between(shinfo->tskey, prior_snd_una, tcp_sk(sk)->snd_una - 1))
3049 __skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
3052 /* Remove acknowledged frames from the retransmission queue. If our packet
3053 * is before the ack sequence we can discard it as it's confirmed to have
3054 * arrived at the other end.
3056 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3058 struct tcp_sacktag_state *sack)
3060 const struct inet_connection_sock *icsk = inet_csk(sk);
3061 struct skb_mstamp first_ackt, last_ackt, now;
3062 struct tcp_sock *tp = tcp_sk(sk);
3063 u32 prior_sacked = tp->sacked_out;
3064 u32 reord = tp->packets_out;
3065 bool fully_acked = true;
3066 long sack_rtt_us = -1L;
3067 long seq_rtt_us = -1L;
3068 long ca_rtt_us = -1L;
3069 struct sk_buff *skb;
3076 while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3077 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3078 u8 sacked = scb->sacked;
3081 tcp_ack_tstamp(sk, skb, prior_snd_una);
3083 /* Determine how many packets and what bytes were acked, tso and else */
3084 if (after(scb->end_seq, tp->snd_una)) {
3085 if (tcp_skb_pcount(skb) == 1 ||
3086 !after(tp->snd_una, scb->seq))
3089 acked_pcount = tcp_tso_acked(sk, skb);
3093 fully_acked = false;
3095 /* Speedup tcp_unlink_write_queue() and next loop */
3096 prefetchw(skb->next);
3097 acked_pcount = tcp_skb_pcount(skb);
3100 if (unlikely(sacked & TCPCB_RETRANS)) {
3101 if (sacked & TCPCB_SACKED_RETRANS)
3102 tp->retrans_out -= acked_pcount;
3103 flag |= FLAG_RETRANS_DATA_ACKED;
3104 } else if (!(sacked & TCPCB_SACKED_ACKED)) {
3105 last_ackt = skb->skb_mstamp;
3106 WARN_ON_ONCE(last_ackt.v64 == 0);
3107 if (!first_ackt.v64)
3108 first_ackt = last_ackt;
3110 reord = min(pkts_acked, reord);
3111 if (!after(scb->end_seq, tp->high_seq))
3112 flag |= FLAG_ORIG_SACK_ACKED;
3115 if (sacked & TCPCB_SACKED_ACKED)
3116 tp->sacked_out -= acked_pcount;
3117 if (sacked & TCPCB_LOST)
3118 tp->lost_out -= acked_pcount;
3120 tp->packets_out -= acked_pcount;
3121 pkts_acked += acked_pcount;
3123 /* Initial outgoing SYN's get put onto the write_queue
3124 * just like anything else we transmit. It is not
3125 * true data, and if we misinform our callers that
3126 * this ACK acks real data, we will erroneously exit
3127 * connection startup slow start one packet too
3128 * quickly. This is severely frowned upon behavior.
3130 if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3131 flag |= FLAG_DATA_ACKED;
3133 flag |= FLAG_SYN_ACKED;
3134 tp->retrans_stamp = 0;
3140 tcp_unlink_write_queue(skb, sk);
3141 sk_wmem_free_skb(sk, skb);
3142 if (unlikely(skb == tp->retransmit_skb_hint))
3143 tp->retransmit_skb_hint = NULL;
3144 if (unlikely(skb == tp->lost_skb_hint))
3145 tp->lost_skb_hint = NULL;
3148 if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3149 tp->snd_up = tp->snd_una;
3151 if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3152 flag |= FLAG_SACK_RENEGING;
3154 skb_mstamp_get(&now);
3155 if (likely(first_ackt.v64)) {
3156 seq_rtt_us = skb_mstamp_us_delta(&now, &first_ackt);
3157 ca_rtt_us = skb_mstamp_us_delta(&now, &last_ackt);
3159 if (sack->first_sackt.v64) {
3160 sack_rtt_us = skb_mstamp_us_delta(&now, &sack->first_sackt);
3161 ca_rtt_us = skb_mstamp_us_delta(&now, &sack->last_sackt);
3164 rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us);
3166 if (flag & FLAG_ACKED) {
3168 if (unlikely(icsk->icsk_mtup.probe_size &&
3169 !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3170 tcp_mtup_probe_success(sk);
3173 if (tcp_is_reno(tp)) {
3174 tcp_remove_reno_sacks(sk, pkts_acked);
3178 /* Non-retransmitted hole got filled? That's reordering */
3179 if (reord < prior_fackets)
3180 tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3182 delta = tcp_is_fack(tp) ? pkts_acked :
3183 prior_sacked - tp->sacked_out;
3184 tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3187 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3189 } else if (skb && rtt_update && sack_rtt_us >= 0 &&
3190 sack_rtt_us > skb_mstamp_us_delta(&now, &skb->skb_mstamp)) {
3191 /* Do not re-arm RTO if the sack RTT is measured from data sent
3192 * after when the head was last (re)transmitted. Otherwise the
3193 * timeout may continue to extend in loss recovery.
3198 if (icsk->icsk_ca_ops->pkts_acked)
3199 icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked, ca_rtt_us);
3201 #if FASTRETRANS_DEBUG > 0
3202 WARN_ON((int)tp->sacked_out < 0);
3203 WARN_ON((int)tp->lost_out < 0);
3204 WARN_ON((int)tp->retrans_out < 0);
3205 if (!tp->packets_out && tcp_is_sack(tp)) {
3206 icsk = inet_csk(sk);
3208 pr_debug("Leak l=%u %d\n",
3209 tp->lost_out, icsk->icsk_ca_state);
3212 if (tp->sacked_out) {
3213 pr_debug("Leak s=%u %d\n",
3214 tp->sacked_out, icsk->icsk_ca_state);
3217 if (tp->retrans_out) {
3218 pr_debug("Leak r=%u %d\n",
3219 tp->retrans_out, icsk->icsk_ca_state);
3220 tp->retrans_out = 0;
3227 static void tcp_ack_probe(struct sock *sk)
3229 const struct tcp_sock *tp = tcp_sk(sk);
3230 struct inet_connection_sock *icsk = inet_csk(sk);
3232 /* Was it a usable window open? */
3234 if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3235 icsk->icsk_backoff = 0;
3236 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3237 /* Socket must be waked up by subsequent tcp_data_snd_check().
3238 * This function is not for random using!
3241 unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
3243 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3248 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3250 return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3251 inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3254 /* Decide wheather to run the increase function of congestion control. */
3255 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3257 if (tcp_in_cwnd_reduction(sk))
3260 /* If reordering is high then always grow cwnd whenever data is
3261 * delivered regardless of its ordering. Otherwise stay conservative
3262 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3263 * new SACK or ECE mark may first advance cwnd here and later reduce
3264 * cwnd in tcp_fastretrans_alert() based on more states.
3266 if (tcp_sk(sk)->reordering > sysctl_tcp_reordering)
3267 return flag & FLAG_FORWARD_PROGRESS;
3269 return flag & FLAG_DATA_ACKED;
3272 /* Check that window update is acceptable.
3273 * The function assumes that snd_una<=ack<=snd_next.
3275 static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3276 const u32 ack, const u32 ack_seq,
3279 return after(ack, tp->snd_una) ||
3280 after(ack_seq, tp->snd_wl1) ||
3281 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3284 /* If we update tp->snd_una, also update tp->bytes_acked */
3285 static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3287 u32 delta = ack - tp->snd_una;
3289 u64_stats_update_begin(&tp->syncp);
3290 tp->bytes_acked += delta;
3291 u64_stats_update_end(&tp->syncp);
3295 /* If we update tp->rcv_nxt, also update tp->bytes_received */
3296 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3298 u32 delta = seq - tp->rcv_nxt;
3300 u64_stats_update_begin(&tp->syncp);
3301 tp->bytes_received += delta;
3302 u64_stats_update_end(&tp->syncp);
3306 /* Update our send window.
3308 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3309 * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3311 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3314 struct tcp_sock *tp = tcp_sk(sk);
3316 u32 nwin = ntohs(tcp_hdr(skb)->window);
3318 if (likely(!tcp_hdr(skb)->syn))
3319 nwin <<= tp->rx_opt.snd_wscale;
3321 if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3322 flag |= FLAG_WIN_UPDATE;
3323 tcp_update_wl(tp, ack_seq);
3325 if (tp->snd_wnd != nwin) {
3328 /* Note, it is the only place, where
3329 * fast path is recovered for sending TCP.
3332 tcp_fast_path_check(sk);
3334 if (nwin > tp->max_window) {
3335 tp->max_window = nwin;
3336 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3341 tcp_snd_una_update(tp, ack);
3346 /* Return true if we're currently rate-limiting out-of-window ACKs and
3347 * thus shouldn't send a dupack right now. We rate-limit dupacks in
3348 * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3349 * attacks that send repeated SYNs or ACKs for the same connection. To
3350 * do this, we do not send a duplicate SYNACK or ACK if the remote
3351 * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3353 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3354 int mib_idx, u32 *last_oow_ack_time)
3356 /* Data packets without SYNs are not likely part of an ACK loop. */
3357 if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3359 goto not_rate_limited;
3361 if (*last_oow_ack_time) {
3362 s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
3364 if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
3365 NET_INC_STATS_BH(net, mib_idx);
3366 return true; /* rate-limited: don't send yet! */
3370 *last_oow_ack_time = tcp_time_stamp;
3373 return false; /* not rate-limited: go ahead, send dupack now! */
3376 /* RFC 5961 7 [ACK Throttling] */
3377 static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
3379 /* unprotected vars, we dont care of overwrites */
3380 static u32 challenge_timestamp;
3381 static unsigned int challenge_count;
3382 struct tcp_sock *tp = tcp_sk(sk);
3385 /* First check our per-socket dupack rate limit. */
3386 if (tcp_oow_rate_limited(sock_net(sk), skb,
3387 LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3388 &tp->last_oow_ack_time))
3391 /* Then check the check host-wide RFC 5961 rate limit. */
3393 if (now != challenge_timestamp) {
3394 challenge_timestamp = now;
3395 challenge_count = 0;
3397 if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
3398 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
3403 static void tcp_store_ts_recent(struct tcp_sock *tp)
3405 tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3406 tp->rx_opt.ts_recent_stamp = get_seconds();
3409 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3411 if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3412 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3413 * extra check below makes sure this can only happen
3414 * for pure ACK frames. -DaveM
3416 * Not only, also it occurs for expired timestamps.
3419 if (tcp_paws_check(&tp->rx_opt, 0))
3420 tcp_store_ts_recent(tp);
3424 /* This routine deals with acks during a TLP episode.
3425 * We mark the end of a TLP episode on receiving TLP dupack or when
3426 * ack is after tlp_high_seq.
3427 * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
3429 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3431 struct tcp_sock *tp = tcp_sk(sk);
3433 if (before(ack, tp->tlp_high_seq))
3436 if (flag & FLAG_DSACKING_ACK) {
3437 /* This DSACK means original and TLP probe arrived; no loss */
3438 tp->tlp_high_seq = 0;
3439 } else if (after(ack, tp->tlp_high_seq)) {
3440 /* ACK advances: there was a loss, so reduce cwnd. Reset
3441 * tlp_high_seq in tcp_init_cwnd_reduction()
3443 tcp_init_cwnd_reduction(sk);
3444 tcp_set_ca_state(sk, TCP_CA_CWR);
3445 tcp_end_cwnd_reduction(sk);
3446 tcp_try_keep_open(sk);
3447 NET_INC_STATS_BH(sock_net(sk),
3448 LINUX_MIB_TCPLOSSPROBERECOVERY);
3449 } else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3450 FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3451 /* Pure dupack: original and TLP probe arrived; no loss */
3452 tp->tlp_high_seq = 0;
3456 static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
3458 const struct inet_connection_sock *icsk = inet_csk(sk);
3460 if (icsk->icsk_ca_ops->in_ack_event)
3461 icsk->icsk_ca_ops->in_ack_event(sk, flags);
3464 /* This routine deals with incoming acks, but not outgoing ones. */
3465 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3467 struct inet_connection_sock *icsk = inet_csk(sk);
3468 struct tcp_sock *tp = tcp_sk(sk);
3469 struct tcp_sacktag_state sack_state;
3470 u32 prior_snd_una = tp->snd_una;
3471 u32 ack_seq = TCP_SKB_CB(skb)->seq;
3472 u32 ack = TCP_SKB_CB(skb)->ack_seq;
3473 bool is_dupack = false;
3475 int prior_packets = tp->packets_out;
3476 const int prior_unsacked = tp->packets_out - tp->sacked_out;
3477 int acked = 0; /* Number of packets newly acked */
3479 sack_state.first_sackt.v64 = 0;
3481 /* We very likely will need to access write queue head. */
3482 prefetchw(sk->sk_write_queue.next);
3484 /* If the ack is older than previous acks
3485 * then we can probably ignore it.
3487 if (before(ack, prior_snd_una)) {
3488 /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3489 if (before(ack, prior_snd_una - tp->max_window)) {
3490 tcp_send_challenge_ack(sk, skb);
3496 /* If the ack includes data we haven't sent yet, discard
3497 * this segment (RFC793 Section 3.9).
3499 if (after(ack, tp->snd_nxt))
3502 if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
3503 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
3506 if (after(ack, prior_snd_una)) {
3507 flag |= FLAG_SND_UNA_ADVANCED;
3508 icsk->icsk_retransmits = 0;
3511 prior_fackets = tp->fackets_out;
3513 /* ts_recent update must be made after we are sure that the packet
3516 if (flag & FLAG_UPDATE_TS_RECENT)
3517 tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3519 if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3520 /* Window is constant, pure forward advance.
3521 * No more checks are required.
3522 * Note, we use the fact that SND.UNA>=SND.WL2.
3524 tcp_update_wl(tp, ack_seq);
3525 tcp_snd_una_update(tp, ack);
3526 flag |= FLAG_WIN_UPDATE;
3528 tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
3530 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3532 u32 ack_ev_flags = CA_ACK_SLOWPATH;
3534 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3537 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3539 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3541 if (TCP_SKB_CB(skb)->sacked)
3542 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3545 if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
3547 ack_ev_flags |= CA_ACK_ECE;
3550 if (flag & FLAG_WIN_UPDATE)
3551 ack_ev_flags |= CA_ACK_WIN_UPDATE;
3553 tcp_in_ack_event(sk, ack_ev_flags);
3556 /* We passed data and got it acked, remove any soft error
3557 * log. Something worked...
3559 sk->sk_err_soft = 0;
3560 icsk->icsk_probes_out = 0;
3561 tp->rcv_tstamp = tcp_time_stamp;
3565 /* See if we can take anything off of the retransmit queue. */
3566 acked = tp->packets_out;
3567 flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una,
3569 acked -= tp->packets_out;
3571 /* Advance cwnd if state allows */
3572 if (tcp_may_raise_cwnd(sk, flag))
3573 tcp_cong_avoid(sk, ack, acked);
3575 if (tcp_ack_is_dubious(sk, flag)) {
3576 is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
3577 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3580 if (tp->tlp_high_seq)
3581 tcp_process_tlp_ack(sk, ack, flag);
3583 if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) {
3584 struct dst_entry *dst = __sk_dst_get(sk);
3589 if (icsk->icsk_pending == ICSK_TIME_RETRANS)
3590 tcp_schedule_loss_probe(sk);
3591 tcp_update_pacing_rate(sk);
3595 /* If data was DSACKed, see if we can undo a cwnd reduction. */
3596 if (flag & FLAG_DSACKING_ACK)
3597 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3599 /* If this ack opens up a zero window, clear backoff. It was
3600 * being used to time the probes, and is probably far higher than
3601 * it needs to be for normal retransmission.
3603 if (tcp_send_head(sk))
3606 if (tp->tlp_high_seq)
3607 tcp_process_tlp_ack(sk, ack, flag);
3611 SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3615 /* If data was SACKed, tag it and see if we should send more data.
3616 * If data was DSACKed, see if we can undo a cwnd reduction.
3618 if (TCP_SKB_CB(skb)->sacked) {
3619 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3621 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3625 SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3629 static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
3630 bool syn, struct tcp_fastopen_cookie *foc,
3633 /* Valid only in SYN or SYN-ACK with an even length. */
3634 if (!foc || !syn || len < 0 || (len & 1))
3637 if (len >= TCP_FASTOPEN_COOKIE_MIN &&
3638 len <= TCP_FASTOPEN_COOKIE_MAX)
3639 memcpy(foc->val, cookie, len);
3646 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3647 * But, this can also be called on packets in the established flow when
3648 * the fast version below fails.
3650 void tcp_parse_options(const struct sk_buff *skb,
3651 struct tcp_options_received *opt_rx, int estab,
3652 struct tcp_fastopen_cookie *foc)
3654 const unsigned char *ptr;
3655 const struct tcphdr *th = tcp_hdr(skb);
3656 int length = (th->doff * 4) - sizeof(struct tcphdr);
3658 ptr = (const unsigned char *)(th + 1);
3659 opt_rx->saw_tstamp = 0;
3661 while (length > 0) {
3662 int opcode = *ptr++;
3668 case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */
3673 if (opsize < 2) /* "silly options" */
3675 if (opsize > length)
3676 return; /* don't parse partial options */
3679 if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3680 u16 in_mss = get_unaligned_be16(ptr);
3682 if (opt_rx->user_mss &&
3683 opt_rx->user_mss < in_mss)
3684 in_mss = opt_rx->user_mss;
3685 opt_rx->mss_clamp = in_mss;
3690 if (opsize == TCPOLEN_WINDOW && th->syn &&
3691 !estab && sysctl_tcp_window_scaling) {
3692 __u8 snd_wscale = *(__u8 *)ptr;
3693 opt_rx->wscale_ok = 1;
3694 if (snd_wscale > 14) {
3695 net_info_ratelimited("%s: Illegal window scaling value %d >14 received\n",
3700 opt_rx->snd_wscale = snd_wscale;
3703 case TCPOPT_TIMESTAMP:
3704 if ((opsize == TCPOLEN_TIMESTAMP) &&
3705 ((estab && opt_rx->tstamp_ok) ||
3706 (!estab && sysctl_tcp_timestamps))) {
3707 opt_rx->saw_tstamp = 1;
3708 opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3709 opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3712 case TCPOPT_SACK_PERM:
3713 if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3714 !estab && sysctl_tcp_sack) {
3715 opt_rx->sack_ok = TCP_SACK_SEEN;
3716 tcp_sack_reset(opt_rx);
3721 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3722 !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3724 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3727 #ifdef CONFIG_TCP_MD5SIG
3730 * The MD5 Hash has already been
3731 * checked (see tcp_v{4,6}_do_rcv()).
3735 case TCPOPT_FASTOPEN:
3736 tcp_parse_fastopen_option(
3737 opsize - TCPOLEN_FASTOPEN_BASE,
3738 ptr, th->syn, foc, false);
3742 /* Fast Open option shares code 254 using a
3743 * 16 bits magic number.
3745 if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
3746 get_unaligned_be16(ptr) ==
3747 TCPOPT_FASTOPEN_MAGIC)
3748 tcp_parse_fastopen_option(opsize -
3749 TCPOLEN_EXP_FASTOPEN_BASE,
3750 ptr + 2, th->syn, foc, true);
3759 EXPORT_SYMBOL(tcp_parse_options);
3761 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
3763 const __be32 *ptr = (const __be32 *)(th + 1);
3765 if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3766 | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3767 tp->rx_opt.saw_tstamp = 1;
3769 tp->rx_opt.rcv_tsval = ntohl(*ptr);
3772 tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
3774 tp->rx_opt.rcv_tsecr = 0;
3780 /* Fast parse options. This hopes to only see timestamps.
3781 * If it is wrong it falls back on tcp_parse_options().
3783 static bool tcp_fast_parse_options(const struct sk_buff *skb,
3784 const struct tcphdr *th, struct tcp_sock *tp)
3786 /* In the spirit of fast parsing, compare doff directly to constant
3787 * values. Because equality is used, short doff can be ignored here.
3789 if (th->doff == (sizeof(*th) / 4)) {
3790 tp->rx_opt.saw_tstamp = 0;
3792 } else if (tp->rx_opt.tstamp_ok &&
3793 th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
3794 if (tcp_parse_aligned_timestamp(tp, th))
3798 tcp_parse_options(skb, &tp->rx_opt, 1, NULL);
3799 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3800 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
3805 #ifdef CONFIG_TCP_MD5SIG
3807 * Parse MD5 Signature option
3809 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
3811 int length = (th->doff << 2) - sizeof(*th);
3812 const u8 *ptr = (const u8 *)(th + 1);
3814 /* If the TCP option is too short, we can short cut */
3815 if (length < TCPOLEN_MD5SIG)
3818 while (length > 0) {
3819 int opcode = *ptr++;
3830 if (opsize < 2 || opsize > length)
3832 if (opcode == TCPOPT_MD5SIG)
3833 return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
3840 EXPORT_SYMBOL(tcp_parse_md5sig_option);
3843 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3845 * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3846 * it can pass through stack. So, the following predicate verifies that
3847 * this segment is not used for anything but congestion avoidance or
3848 * fast retransmit. Moreover, we even are able to eliminate most of such
3849 * second order effects, if we apply some small "replay" window (~RTO)
3850 * to timestamp space.
3852 * All these measures still do not guarantee that we reject wrapped ACKs
3853 * on networks with high bandwidth, when sequence space is recycled fastly,
3854 * but it guarantees that such events will be very rare and do not affect
3855 * connection seriously. This doesn't look nice, but alas, PAWS is really
3858 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3859 * states that events when retransmit arrives after original data are rare.
3860 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3861 * the biggest problem on large power networks even with minor reordering.
3862 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3863 * up to bandwidth of 18Gigabit/sec. 8) ]
3866 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3868 const struct tcp_sock *tp = tcp_sk(sk);
3869 const struct tcphdr *th = tcp_hdr(skb);
3870 u32 seq = TCP_SKB_CB(skb)->seq;
3871 u32 ack = TCP_SKB_CB(skb)->ack_seq;
3873 return (/* 1. Pure ACK with correct sequence number. */
3874 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3876 /* 2. ... and duplicate ACK. */
3877 ack == tp->snd_una &&
3879 /* 3. ... and does not update window. */
3880 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3882 /* 4. ... and sits in replay window. */
3883 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3886 static inline bool tcp_paws_discard(const struct sock *sk,
3887 const struct sk_buff *skb)
3889 const struct tcp_sock *tp = tcp_sk(sk);
3891 return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
3892 !tcp_disordered_ack(sk, skb);
3895 /* Check segment sequence number for validity.
3897 * Segment controls are considered valid, if the segment
3898 * fits to the window after truncation to the window. Acceptability
3899 * of data (and SYN, FIN, of course) is checked separately.
3900 * See tcp_data_queue(), for example.
3902 * Also, controls (RST is main one) are accepted using RCV.WUP instead
3903 * of RCV.NXT. Peer still did not advance his SND.UNA when we
3904 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3905 * (borrowed from freebsd)
3908 static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
3910 return !before(end_seq, tp->rcv_wup) &&
3911 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3914 /* When we get a reset we do this. */
3915 void tcp_reset(struct sock *sk)
3917 /* We want the right error as BSD sees it (and indeed as we do). */
3918 switch (sk->sk_state) {
3920 sk->sk_err = ECONNREFUSED;
3922 case TCP_CLOSE_WAIT:
3928 sk->sk_err = ECONNRESET;
3930 /* This barrier is coupled with smp_rmb() in tcp_poll() */
3933 if (!sock_flag(sk, SOCK_DEAD))
3934 sk->sk_error_report(sk);
3940 * Process the FIN bit. This now behaves as it is supposed to work
3941 * and the FIN takes effect when it is validly part of sequence
3942 * space. Not before when we get holes.
3944 * If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3945 * (and thence onto LAST-ACK and finally, CLOSE, we never enter
3948 * If we are in FINWAIT-1, a received FIN indicates simultaneous
3949 * close and we go into CLOSING (and later onto TIME-WAIT)
3951 * If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3953 static void tcp_fin(struct sock *sk)
3955 struct tcp_sock *tp = tcp_sk(sk);
3957 inet_csk_schedule_ack(sk);
3959 sk->sk_shutdown |= RCV_SHUTDOWN;
3960 sock_set_flag(sk, SOCK_DONE);
3962 switch (sk->sk_state) {
3964 case TCP_ESTABLISHED:
3965 /* Move to CLOSE_WAIT */
3966 tcp_set_state(sk, TCP_CLOSE_WAIT);
3967 inet_csk(sk)->icsk_ack.pingpong = 1;
3970 case TCP_CLOSE_WAIT:
3972 /* Received a retransmission of the FIN, do
3977 /* RFC793: Remain in the LAST-ACK state. */
3981 /* This case occurs when a simultaneous close
3982 * happens, we must ack the received FIN and
3983 * enter the CLOSING state.
3986 tcp_set_state(sk, TCP_CLOSING);
3989 /* Received a FIN -- send ACK and enter TIME_WAIT. */
3991 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
3994 /* Only TCP_LISTEN and TCP_CLOSE are left, in these
3995 * cases we should never reach this piece of code.
3997 pr_err("%s: Impossible, sk->sk_state=%d\n",
3998 __func__, sk->sk_state);
4002 /* It _is_ possible, that we have something out-of-order _after_ FIN.
4003 * Probably, we should reset in this case. For now drop them.
4005 __skb_queue_purge(&tp->out_of_order_queue);
4006 if (tcp_is_sack(tp))
4007 tcp_sack_reset(&tp->rx_opt);
4010 if (!sock_flag(sk, SOCK_DEAD)) {
4011 sk->sk_state_change(sk);
4013 /* Do not send POLL_HUP for half duplex close. */
4014 if (sk->sk_shutdown == SHUTDOWN_MASK ||
4015 sk->sk_state == TCP_CLOSE)
4016 sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4018 sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4022 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4025 if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4026 if (before(seq, sp->start_seq))
4027 sp->start_seq = seq;
4028 if (after(end_seq, sp->end_seq))
4029 sp->end_seq = end_seq;
4035 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4037 struct tcp_sock *tp = tcp_sk(sk);
4039 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4042 if (before(seq, tp->rcv_nxt))
4043 mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4045 mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4047 NET_INC_STATS_BH(sock_net(sk), mib_idx);
4049 tp->rx_opt.dsack = 1;
4050 tp->duplicate_sack[0].start_seq = seq;
4051 tp->duplicate_sack[0].end_seq = end_seq;
4055 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4057 struct tcp_sock *tp = tcp_sk(sk);
4059 if (!tp->rx_opt.dsack)
4060 tcp_dsack_set(sk, seq, end_seq);
4062 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4065 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4067 struct tcp_sock *tp = tcp_sk(sk);
4069 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4070 before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4071 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4072 tcp_enter_quickack_mode(sk);
4074 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4075 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4077 if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4078 end_seq = tp->rcv_nxt;
4079 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4086 /* These routines update the SACK block as out-of-order packets arrive or
4087 * in-order packets close up the sequence space.
4089 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4092 struct tcp_sack_block *sp = &tp->selective_acks[0];
4093 struct tcp_sack_block *swalk = sp + 1;
4095 /* See if the recent change to the first SACK eats into
4096 * or hits the sequence space of other SACK blocks, if so coalesce.
4098 for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4099 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4102 /* Zap SWALK, by moving every further SACK up by one slot.
4103 * Decrease num_sacks.
4105 tp->rx_opt.num_sacks--;
4106 for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4110 this_sack++, swalk++;
4114 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4116 struct tcp_sock *tp = tcp_sk(sk);
4117 struct tcp_sack_block *sp = &tp->selective_acks[0];
4118 int cur_sacks = tp->rx_opt.num_sacks;
4124 for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4125 if (tcp_sack_extend(sp, seq, end_seq)) {
4126 /* Rotate this_sack to the first one. */
4127 for (; this_sack > 0; this_sack--, sp--)
4128 swap(*sp, *(sp - 1));
4130 tcp_sack_maybe_coalesce(tp);
4135 /* Could not find an adjacent existing SACK, build a new one,
4136 * put it at the front, and shift everyone else down. We
4137 * always know there is at least one SACK present already here.
4139 * If the sack array is full, forget about the last one.
4141 if (this_sack >= TCP_NUM_SACKS) {
4143 tp->rx_opt.num_sacks--;
4146 for (; this_sack > 0; this_sack--, sp--)
4150 /* Build the new head SACK, and we're done. */
4151 sp->start_seq = seq;
4152 sp->end_seq = end_seq;
4153 tp->rx_opt.num_sacks++;
4156 /* RCV.NXT advances, some SACKs should be eaten. */
4158 static void tcp_sack_remove(struct tcp_sock *tp)
4160 struct tcp_sack_block *sp = &tp->selective_acks[0];
4161 int num_sacks = tp->rx_opt.num_sacks;
4164 /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4165 if (skb_queue_empty(&tp->out_of_order_queue)) {
4166 tp->rx_opt.num_sacks = 0;
4170 for (this_sack = 0; this_sack < num_sacks;) {
4171 /* Check if the start of the sack is covered by RCV.NXT. */
4172 if (!before(tp->rcv_nxt, sp->start_seq)) {
4175 /* RCV.NXT must cover all the block! */
4176 WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4178 /* Zap this SACK, by moving forward any other SACKS. */
4179 for (i = this_sack+1; i < num_sacks; i++)
4180 tp->selective_acks[i-1] = tp->selective_acks[i];
4187 tp->rx_opt.num_sacks = num_sacks;
4191 * tcp_try_coalesce - try to merge skb to prior one
4194 * @from: buffer to add in queue
4195 * @fragstolen: pointer to boolean
4197 * Before queueing skb @from after @to, try to merge them
4198 * to reduce overall memory use and queue lengths, if cost is small.
4199 * Packets in ofo or receive queues can stay a long time.
4200 * Better try to coalesce them right now to avoid future collapses.
4201 * Returns true if caller should free @from instead of queueing it
4203 static bool tcp_try_coalesce(struct sock *sk,
4205 struct sk_buff *from,
4210 *fragstolen = false;
4212 /* Its possible this segment overlaps with prior segment in queue */
4213 if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4216 if (!skb_try_coalesce(to, from, fragstolen, &delta))
4219 atomic_add(delta, &sk->sk_rmem_alloc);
4220 sk_mem_charge(sk, delta);
4221 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4222 TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4223 TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4224 TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4228 /* This one checks to see if we can put data from the
4229 * out_of_order queue into the receive_queue.
4231 static void tcp_ofo_queue(struct sock *sk)
4233 struct tcp_sock *tp = tcp_sk(sk);
4234 __u32 dsack_high = tp->rcv_nxt;
4235 struct sk_buff *skb, *tail;
4236 bool fragstolen, eaten;
4238 while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4239 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4242 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4243 __u32 dsack = dsack_high;
4244 if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4245 dsack_high = TCP_SKB_CB(skb)->end_seq;
4246 tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4249 __skb_unlink(skb, &tp->out_of_order_queue);
4250 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4251 SOCK_DEBUG(sk, "ofo packet was already received\n");
4255 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4256 tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4257 TCP_SKB_CB(skb)->end_seq);
4259 tail = skb_peek_tail(&sk->sk_receive_queue);
4260 eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4261 tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4263 __skb_queue_tail(&sk->sk_receive_queue, skb);
4264 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
4267 kfree_skb_partial(skb, fragstolen);
4271 static bool tcp_prune_ofo_queue(struct sock *sk);
4272 static int tcp_prune_queue(struct sock *sk);
4274 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4277 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4278 !sk_rmem_schedule(sk, skb, size)) {
4280 if (tcp_prune_queue(sk) < 0)
4283 if (!sk_rmem_schedule(sk, skb, size)) {
4284 if (!tcp_prune_ofo_queue(sk))
4287 if (!sk_rmem_schedule(sk, skb, size))
4294 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4296 struct tcp_sock *tp = tcp_sk(sk);
4297 struct sk_buff *skb1;
4300 tcp_ecn_check_ce(tp, skb);
4302 if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4303 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFODROP);
4308 /* Disable header prediction. */
4310 inet_csk_schedule_ack(sk);
4312 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4313 SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4314 tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4316 skb1 = skb_peek_tail(&tp->out_of_order_queue);
4318 /* Initial out of order segment, build 1 SACK. */
4319 if (tcp_is_sack(tp)) {
4320 tp->rx_opt.num_sacks = 1;
4321 tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4322 tp->selective_acks[0].end_seq =
4323 TCP_SKB_CB(skb)->end_seq;
4325 __skb_queue_head(&tp->out_of_order_queue, skb);
4329 seq = TCP_SKB_CB(skb)->seq;
4330 end_seq = TCP_SKB_CB(skb)->end_seq;
4332 if (seq == TCP_SKB_CB(skb1)->end_seq) {
4335 if (!tcp_try_coalesce(sk, skb1, skb, &fragstolen)) {
4336 __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4338 tcp_grow_window(sk, skb);
4339 kfree_skb_partial(skb, fragstolen);
4343 if (!tp->rx_opt.num_sacks ||
4344 tp->selective_acks[0].end_seq != seq)
4347 /* Common case: data arrive in order after hole. */
4348 tp->selective_acks[0].end_seq = end_seq;
4352 /* Find place to insert this segment. */
4354 if (!after(TCP_SKB_CB(skb1)->seq, seq))
4356 if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
4360 skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
4363 /* Do skb overlap to previous one? */
4364 if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4365 if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4366 /* All the bits are present. Drop. */
4367 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4370 tcp_dsack_set(sk, seq, end_seq);
4373 if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4374 /* Partial overlap. */
4375 tcp_dsack_set(sk, seq,
4376 TCP_SKB_CB(skb1)->end_seq);
4378 if (skb_queue_is_first(&tp->out_of_order_queue,
4382 skb1 = skb_queue_prev(
4383 &tp->out_of_order_queue,
4388 __skb_queue_head(&tp->out_of_order_queue, skb);
4390 __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4392 /* And clean segments covered by new one as whole. */
4393 while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
4394 skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
4396 if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4398 if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4399 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4403 __skb_unlink(skb1, &tp->out_of_order_queue);
4404 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4405 TCP_SKB_CB(skb1)->end_seq);
4406 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4411 if (tcp_is_sack(tp))
4412 tcp_sack_new_ofo_skb(sk, seq, end_seq);
4415 tcp_grow_window(sk, skb);
4416 skb_set_owner_r(skb, sk);
4420 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen,
4424 struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4426 __skb_pull(skb, hdrlen);
4428 tcp_try_coalesce(sk, tail, skb, fragstolen)) ? 1 : 0;
4429 tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
4431 __skb_queue_tail(&sk->sk_receive_queue, skb);
4432 skb_set_owner_r(skb, sk);
4437 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4439 struct sk_buff *skb;
4445 skb = alloc_skb(size, sk->sk_allocation);
4449 if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
4452 if (memcpy_from_msg(skb_put(skb, size), msg, size))
4455 TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4456 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4457 TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4459 if (tcp_queue_rcv(sk, skb, 0, &fragstolen)) {
4460 WARN_ON_ONCE(fragstolen); /* should not happen */
4471 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4473 struct tcp_sock *tp = tcp_sk(sk);
4475 bool fragstolen = false;
4477 if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4481 __skb_pull(skb, tcp_hdr(skb)->doff * 4);
4483 tcp_ecn_accept_cwr(tp, skb);
4485 tp->rx_opt.dsack = 0;
4487 /* Queue data for delivery to the user.
4488 * Packets in sequence go to the receive queue.
4489 * Out of sequence packets to the out_of_order_queue.
4491 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4492 if (tcp_receive_window(tp) == 0)
4495 /* Ok. In sequence. In window. */
4496 if (tp->ucopy.task == current &&
4497 tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4498 sock_owned_by_user(sk) && !tp->urg_data) {
4499 int chunk = min_t(unsigned int, skb->len,
4502 __set_current_state(TASK_RUNNING);
4505 if (!skb_copy_datagram_msg(skb, 0, tp->ucopy.msg, chunk)) {
4506 tp->ucopy.len -= chunk;
4507 tp->copied_seq += chunk;
4508 eaten = (chunk == skb->len);
4509 tcp_rcv_space_adjust(sk);
4517 if (skb_queue_len(&sk->sk_receive_queue) == 0)
4518 sk_forced_mem_schedule(sk, skb->truesize);
4519 else if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
4522 eaten = tcp_queue_rcv(sk, skb, 0, &fragstolen);
4524 tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4526 tcp_event_data_recv(sk, skb);
4527 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
4530 if (!skb_queue_empty(&tp->out_of_order_queue)) {
4533 /* RFC2581. 4.2. SHOULD send immediate ACK, when
4534 * gap in queue is filled.
4536 if (skb_queue_empty(&tp->out_of_order_queue))
4537 inet_csk(sk)->icsk_ack.pingpong = 0;
4540 if (tp->rx_opt.num_sacks)
4541 tcp_sack_remove(tp);
4543 tcp_fast_path_check(sk);
4546 kfree_skb_partial(skb, fragstolen);
4547 if (!sock_flag(sk, SOCK_DEAD))
4548 sk->sk_data_ready(sk);
4552 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4553 /* A retransmit, 2nd most common case. Force an immediate ack. */
4554 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4555 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4558 tcp_enter_quickack_mode(sk);
4559 inet_csk_schedule_ack(sk);
4565 /* Out of window. F.e. zero window probe. */
4566 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4569 tcp_enter_quickack_mode(sk);
4571 if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4572 /* Partial packet, seq < rcv_next < end_seq */
4573 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4574 tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4575 TCP_SKB_CB(skb)->end_seq);
4577 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4579 /* If window is closed, drop tail of packet. But after
4580 * remembering D-SACK for its head made in previous line.
4582 if (!tcp_receive_window(tp))
4587 tcp_data_queue_ofo(sk, skb);
4590 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4591 struct sk_buff_head *list)
4593 struct sk_buff *next = NULL;
4595 if (!skb_queue_is_last(list, skb))
4596 next = skb_queue_next(list, skb);
4598 __skb_unlink(skb, list);
4600 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4605 /* Collapse contiguous sequence of skbs head..tail with
4606 * sequence numbers start..end.
4608 * If tail is NULL, this means until the end of the list.
4610 * Segments with FIN/SYN are not collapsed (only because this
4614 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4615 struct sk_buff *head, struct sk_buff *tail,
4618 struct sk_buff *skb, *n;
4621 /* First, check that queue is collapsible and find
4622 * the point where collapsing can be useful. */
4626 skb_queue_walk_from_safe(list, skb, n) {
4629 /* No new bits? It is possible on ofo queue. */
4630 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4631 skb = tcp_collapse_one(sk, skb, list);
4637 /* The first skb to collapse is:
4639 * - bloated or contains data before "start" or
4640 * overlaps to the next one.
4642 if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
4643 (tcp_win_from_space(skb->truesize) > skb->len ||
4644 before(TCP_SKB_CB(skb)->seq, start))) {
4645 end_of_skbs = false;
4649 if (!skb_queue_is_last(list, skb)) {
4650 struct sk_buff *next = skb_queue_next(list, skb);
4652 TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
4653 end_of_skbs = false;
4658 /* Decided to skip this, advance start seq. */
4659 start = TCP_SKB_CB(skb)->end_seq;
4662 (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4665 while (before(start, end)) {
4666 int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
4667 struct sk_buff *nskb;
4669 nskb = alloc_skb(copy, GFP_ATOMIC);
4673 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4674 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4675 __skb_queue_before(list, skb, nskb);
4676 skb_set_owner_r(nskb, sk);
4678 /* Copy data, releasing collapsed skbs. */
4680 int offset = start - TCP_SKB_CB(skb)->seq;
4681 int size = TCP_SKB_CB(skb)->end_seq - start;
4685 size = min(copy, size);
4686 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4688 TCP_SKB_CB(nskb)->end_seq += size;
4692 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4693 skb = tcp_collapse_one(sk, skb, list);
4696 (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4703 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4704 * and tcp_collapse() them until all the queue is collapsed.
4706 static void tcp_collapse_ofo_queue(struct sock *sk)
4708 struct tcp_sock *tp = tcp_sk(sk);
4709 struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4710 struct sk_buff *head;
4716 start = TCP_SKB_CB(skb)->seq;
4717 end = TCP_SKB_CB(skb)->end_seq;
4721 struct sk_buff *next = NULL;
4723 if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
4724 next = skb_queue_next(&tp->out_of_order_queue, skb);
4727 /* Segment is terminated when we see gap or when
4728 * we are at the end of all the queue. */
4730 after(TCP_SKB_CB(skb)->seq, end) ||
4731 before(TCP_SKB_CB(skb)->end_seq, start)) {
4732 tcp_collapse(sk, &tp->out_of_order_queue,
4733 head, skb, start, end);
4737 /* Start new segment */
4738 start = TCP_SKB_CB(skb)->seq;
4739 end = TCP_SKB_CB(skb)->end_seq;
4741 if (before(TCP_SKB_CB(skb)->seq, start))
4742 start = TCP_SKB_CB(skb)->seq;
4743 if (after(TCP_SKB_CB(skb)->end_seq, end))
4744 end = TCP_SKB_CB(skb)->end_seq;
4750 * Purge the out-of-order queue.
4751 * Return true if queue was pruned.
4753 static bool tcp_prune_ofo_queue(struct sock *sk)
4755 struct tcp_sock *tp = tcp_sk(sk);
4758 if (!skb_queue_empty(&tp->out_of_order_queue)) {
4759 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
4760 __skb_queue_purge(&tp->out_of_order_queue);
4762 /* Reset SACK state. A conforming SACK implementation will
4763 * do the same at a timeout based retransmit. When a connection
4764 * is in a sad state like this, we care only about integrity
4765 * of the connection not performance.
4767 if (tp->rx_opt.sack_ok)
4768 tcp_sack_reset(&tp->rx_opt);
4775 /* Reduce allocated memory if we can, trying to get
4776 * the socket within its memory limits again.
4778 * Return less than zero if we should start dropping frames
4779 * until the socket owning process reads some of the data
4780 * to stabilize the situation.
4782 static int tcp_prune_queue(struct sock *sk)
4784 struct tcp_sock *tp = tcp_sk(sk);
4786 SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4788 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
4790 if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4791 tcp_clamp_window(sk);
4792 else if (tcp_under_memory_pressure(sk))
4793 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4795 tcp_collapse_ofo_queue(sk);
4796 if (!skb_queue_empty(&sk->sk_receive_queue))
4797 tcp_collapse(sk, &sk->sk_receive_queue,
4798 skb_peek(&sk->sk_receive_queue),
4800 tp->copied_seq, tp->rcv_nxt);
4803 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4806 /* Collapsing did not help, destructive actions follow.
4807 * This must not ever occur. */
4809 tcp_prune_ofo_queue(sk);
4811 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4814 /* If we are really being abused, tell the caller to silently
4815 * drop receive data on the floor. It will get retransmitted
4816 * and hopefully then we'll have sufficient space.
4818 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
4820 /* Massive buffer overcommit. */
4825 static bool tcp_should_expand_sndbuf(const struct sock *sk)
4827 const struct tcp_sock *tp = tcp_sk(sk);
4829 /* If the user specified a specific send buffer setting, do
4832 if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4835 /* If we are under global TCP memory pressure, do not expand. */
4836 if (tcp_under_memory_pressure(sk))
4839 /* If we are under soft global TCP memory pressure, do not expand. */
4840 if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
4843 /* If we filled the congestion window, do not expand. */
4844 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
4850 /* When incoming ACK allowed to free some skb from write_queue,
4851 * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4852 * on the exit from tcp input handler.
4854 * PROBLEM: sndbuf expansion does not work well with largesend.
4856 static void tcp_new_space(struct sock *sk)
4858 struct tcp_sock *tp = tcp_sk(sk);
4860 if (tcp_should_expand_sndbuf(sk)) {
4861 tcp_sndbuf_expand(sk);
4862 tp->snd_cwnd_stamp = tcp_time_stamp;
4865 sk->sk_write_space(sk);
4868 static void tcp_check_space(struct sock *sk)
4870 if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4871 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4872 /* pairs with tcp_poll() */
4873 smp_mb__after_atomic();
4874 if (sk->sk_socket &&
4875 test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4880 static inline void tcp_data_snd_check(struct sock *sk)
4882 tcp_push_pending_frames(sk);
4883 tcp_check_space(sk);
4887 * Check if sending an ack is needed.
4889 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4891 struct tcp_sock *tp = tcp_sk(sk);
4893 /* More than one full frame received... */
4894 if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
4895 /* ... and right edge of window advances far enough.
4896 * (tcp_recvmsg() will send ACK otherwise). Or...
4898 __tcp_select_window(sk) >= tp->rcv_wnd) ||
4899 /* We ACK each frame or... */
4900 tcp_in_quickack_mode(sk) ||
4901 /* We have out of order data. */
4902 (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
4903 /* Then ack it now */
4906 /* Else, send delayed ack. */
4907 tcp_send_delayed_ack(sk);
4911 static inline void tcp_ack_snd_check(struct sock *sk)
4913 if (!inet_csk_ack_scheduled(sk)) {
4914 /* We sent a data segment already. */
4917 __tcp_ack_snd_check(sk, 1);
4921 * This routine is only called when we have urgent data
4922 * signaled. Its the 'slow' part of tcp_urg. It could be
4923 * moved inline now as tcp_urg is only called from one
4924 * place. We handle URGent data wrong. We have to - as
4925 * BSD still doesn't use the correction from RFC961.
4926 * For 1003.1g we should support a new option TCP_STDURG to permit
4927 * either form (or just set the sysctl tcp_stdurg).
4930 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
4932 struct tcp_sock *tp = tcp_sk(sk);
4933 u32 ptr = ntohs(th->urg_ptr);
4935 if (ptr && !sysctl_tcp_stdurg)
4937 ptr += ntohl(th->seq);
4939 /* Ignore urgent data that we've already seen and read. */
4940 if (after(tp->copied_seq, ptr))
4943 /* Do not replay urg ptr.
4945 * NOTE: interesting situation not covered by specs.
4946 * Misbehaving sender may send urg ptr, pointing to segment,
4947 * which we already have in ofo queue. We are not able to fetch
4948 * such data and will stay in TCP_URG_NOTYET until will be eaten
4949 * by recvmsg(). Seems, we are not obliged to handle such wicked
4950 * situations. But it is worth to think about possibility of some
4951 * DoSes using some hypothetical application level deadlock.
4953 if (before(ptr, tp->rcv_nxt))
4956 /* Do we already have a newer (or duplicate) urgent pointer? */
4957 if (tp->urg_data && !after(ptr, tp->urg_seq))
4960 /* Tell the world about our new urgent pointer. */
4963 /* We may be adding urgent data when the last byte read was
4964 * urgent. To do this requires some care. We cannot just ignore
4965 * tp->copied_seq since we would read the last urgent byte again
4966 * as data, nor can we alter copied_seq until this data arrives
4967 * or we break the semantics of SIOCATMARK (and thus sockatmark())
4969 * NOTE. Double Dutch. Rendering to plain English: author of comment
4970 * above did something sort of send("A", MSG_OOB); send("B", MSG_OOB);
4971 * and expect that both A and B disappear from stream. This is _wrong_.
4972 * Though this happens in BSD with high probability, this is occasional.
4973 * Any application relying on this is buggy. Note also, that fix "works"
4974 * only in this artificial test. Insert some normal data between A and B and we will
4975 * decline of BSD again. Verdict: it is better to remove to trap
4978 if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
4979 !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
4980 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
4982 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
4983 __skb_unlink(skb, &sk->sk_receive_queue);
4988 tp->urg_data = TCP_URG_NOTYET;
4991 /* Disable header prediction. */
4995 /* This is the 'fast' part of urgent handling. */
4996 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
4998 struct tcp_sock *tp = tcp_sk(sk);
5000 /* Check if we get a new urgent pointer - normally not. */
5002 tcp_check_urg(sk, th);
5004 /* Do we wait for any urgent data? - normally not... */
5005 if (tp->urg_data == TCP_URG_NOTYET) {
5006 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5009 /* Is the urgent pointer pointing into this packet? */
5010 if (ptr < skb->len) {
5012 if (skb_copy_bits(skb, ptr, &tmp, 1))
5014 tp->urg_data = TCP_URG_VALID | tmp;
5015 if (!sock_flag(sk, SOCK_DEAD))
5016 sk->sk_data_ready(sk);
5021 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
5023 struct tcp_sock *tp = tcp_sk(sk);
5024 int chunk = skb->len - hlen;
5028 if (skb_csum_unnecessary(skb))
5029 err = skb_copy_datagram_msg(skb, hlen, tp->ucopy.msg, chunk);
5031 err = skb_copy_and_csum_datagram_msg(skb, hlen, tp->ucopy.msg);
5034 tp->ucopy.len -= chunk;
5035 tp->copied_seq += chunk;
5036 tcp_rcv_space_adjust(sk);
5043 static __sum16 __tcp_checksum_complete_user(struct sock *sk,
5044 struct sk_buff *skb)
5048 if (sock_owned_by_user(sk)) {
5050 result = __tcp_checksum_complete(skb);
5053 result = __tcp_checksum_complete(skb);
5058 static inline bool tcp_checksum_complete_user(struct sock *sk,
5059 struct sk_buff *skb)
5061 return !skb_csum_unnecessary(skb) &&
5062 __tcp_checksum_complete_user(sk, skb);
5065 /* Does PAWS and seqno based validation of an incoming segment, flags will
5066 * play significant role here.
5068 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5069 const struct tcphdr *th, int syn_inerr)
5071 struct tcp_sock *tp = tcp_sk(sk);
5073 /* RFC1323: H1. Apply PAWS check first. */
5074 if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
5075 tcp_paws_discard(sk, skb)) {
5077 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5078 if (!tcp_oow_rate_limited(sock_net(sk), skb,
5079 LINUX_MIB_TCPACKSKIPPEDPAWS,
5080 &tp->last_oow_ack_time))
5081 tcp_send_dupack(sk, skb);
5084 /* Reset is accepted even if it did not pass PAWS. */
5087 /* Step 1: check sequence number */
5088 if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5089 /* RFC793, page 37: "In all states except SYN-SENT, all reset
5090 * (RST) segments are validated by checking their SEQ-fields."
5091 * And page 69: "If an incoming segment is not acceptable,
5092 * an acknowledgment should be sent in reply (unless the RST
5093 * bit is set, if so drop the segment and return)".
5098 if (!tcp_oow_rate_limited(sock_net(sk), skb,
5099 LINUX_MIB_TCPACKSKIPPEDSEQ,
5100 &tp->last_oow_ack_time))
5101 tcp_send_dupack(sk, skb);
5106 /* Step 2: check RST bit */
5109 * If sequence number exactly matches RCV.NXT, then
5110 * RESET the connection
5112 * Send a challenge ACK
5114 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt)
5117 tcp_send_challenge_ack(sk, skb);
5121 /* step 3: check security and precedence [ignored] */
5123 /* step 4: Check for a SYN
5124 * RFC 5961 4.2 : Send a challenge ack
5129 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5130 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5131 tcp_send_challenge_ack(sk, skb);
5143 * TCP receive function for the ESTABLISHED state.
5145 * It is split into a fast path and a slow path. The fast path is
5147 * - A zero window was announced from us - zero window probing
5148 * is only handled properly in the slow path.
5149 * - Out of order segments arrived.
5150 * - Urgent data is expected.
5151 * - There is no buffer space left
5152 * - Unexpected TCP flags/window values/header lengths are received
5153 * (detected by checking the TCP header against pred_flags)
5154 * - Data is sent in both directions. Fast path only supports pure senders
5155 * or pure receivers (this means either the sequence number or the ack
5156 * value must stay constant)
5157 * - Unexpected TCP option.
5159 * When these conditions are not satisfied it drops into a standard
5160 * receive procedure patterned after RFC793 to handle all cases.
5161 * The first three cases are guaranteed by proper pred_flags setting,
5162 * the rest is checked inline. Fast processing is turned on in
5163 * tcp_data_queue when everything is OK.
5165 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5166 const struct tcphdr *th, unsigned int len)
5168 struct tcp_sock *tp = tcp_sk(sk);
5170 if (unlikely(!sk->sk_rx_dst))
5171 inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5173 * Header prediction.
5174 * The code loosely follows the one in the famous
5175 * "30 instruction TCP receive" Van Jacobson mail.
5177 * Van's trick is to deposit buffers into socket queue
5178 * on a device interrupt, to call tcp_recv function
5179 * on the receive process context and checksum and copy
5180 * the buffer to user space. smart...
5182 * Our current scheme is not silly either but we take the
5183 * extra cost of the net_bh soft interrupt processing...
5184 * We do checksum and copy also but from device to kernel.
5187 tp->rx_opt.saw_tstamp = 0;
5189 /* pred_flags is 0xS?10 << 16 + snd_wnd
5190 * if header_prediction is to be made
5191 * 'S' will always be tp->tcp_header_len >> 2
5192 * '?' will be 0 for the fast path, otherwise pred_flags is 0 to
5193 * turn it off (when there are holes in the receive
5194 * space for instance)
5195 * PSH flag is ignored.
5198 if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5199 TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5200 !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5201 int tcp_header_len = tp->tcp_header_len;
5203 /* Timestamp header prediction: tcp_header_len
5204 * is automatically equal to th->doff*4 due to pred_flags
5208 /* Check timestamp */
5209 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5210 /* No? Slow path! */
5211 if (!tcp_parse_aligned_timestamp(tp, th))
5214 /* If PAWS failed, check it more carefully in slow path */
5215 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5218 /* DO NOT update ts_recent here, if checksum fails
5219 * and timestamp was corrupted part, it will result
5220 * in a hung connection since we will drop all
5221 * future packets due to the PAWS test.
5225 if (len <= tcp_header_len) {
5226 /* Bulk data transfer: sender */
5227 if (len == tcp_header_len) {
5228 /* Predicted packet is in window by definition.
5229 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5230 * Hence, check seq<=rcv_wup reduces to:
5232 if (tcp_header_len ==
5233 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5234 tp->rcv_nxt == tp->rcv_wup)
5235 tcp_store_ts_recent(tp);
5237 /* We know that such packets are checksummed
5240 tcp_ack(sk, skb, 0);
5242 tcp_data_snd_check(sk);
5244 } else { /* Header too small */
5245 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5250 bool fragstolen = false;
5252 if (tp->ucopy.task == current &&
5253 tp->copied_seq == tp->rcv_nxt &&
5254 len - tcp_header_len <= tp->ucopy.len &&
5255 sock_owned_by_user(sk)) {
5256 __set_current_state(TASK_RUNNING);
5258 if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
5259 /* Predicted packet is in window by definition.
5260 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5261 * Hence, check seq<=rcv_wup reduces to:
5263 if (tcp_header_len ==
5264 (sizeof(struct tcphdr) +
5265 TCPOLEN_TSTAMP_ALIGNED) &&
5266 tp->rcv_nxt == tp->rcv_wup)
5267 tcp_store_ts_recent(tp);
5269 tcp_rcv_rtt_measure_ts(sk, skb);
5271 __skb_pull(skb, tcp_header_len);
5272 tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
5273 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5278 if (tcp_checksum_complete_user(sk, skb))
5281 if ((int)skb->truesize > sk->sk_forward_alloc)
5284 /* Predicted packet is in window by definition.
5285 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5286 * Hence, check seq<=rcv_wup reduces to:
5288 if (tcp_header_len ==
5289 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5290 tp->rcv_nxt == tp->rcv_wup)
5291 tcp_store_ts_recent(tp);
5293 tcp_rcv_rtt_measure_ts(sk, skb);
5295 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5297 /* Bulk data transfer: receiver */
5298 eaten = tcp_queue_rcv(sk, skb, tcp_header_len,
5302 tcp_event_data_recv(sk, skb);
5304 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5305 /* Well, only one small jumplet in fast path... */
5306 tcp_ack(sk, skb, FLAG_DATA);
5307 tcp_data_snd_check(sk);
5308 if (!inet_csk_ack_scheduled(sk))
5312 __tcp_ack_snd_check(sk, 0);
5315 kfree_skb_partial(skb, fragstolen);
5316 sk->sk_data_ready(sk);
5322 if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5325 if (!th->ack && !th->rst && !th->syn)
5329 * Standard slow path.
5332 if (!tcp_validate_incoming(sk, skb, th, 1))
5336 if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
5339 tcp_rcv_rtt_measure_ts(sk, skb);
5341 /* Process urgent data. */
5342 tcp_urg(sk, skb, th);
5344 /* step 7: process the segment text */
5345 tcp_data_queue(sk, skb);
5347 tcp_data_snd_check(sk);
5348 tcp_ack_snd_check(sk);
5352 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_CSUMERRORS);
5353 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5358 EXPORT_SYMBOL(tcp_rcv_established);
5360 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
5362 struct tcp_sock *tp = tcp_sk(sk);
5363 struct inet_connection_sock *icsk = inet_csk(sk);
5365 tcp_set_state(sk, TCP_ESTABLISHED);
5368 icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
5369 security_inet_conn_established(sk, skb);
5372 /* Make sure socket is routed, for correct metrics. */
5373 icsk->icsk_af_ops->rebuild_header(sk);
5375 tcp_init_metrics(sk);
5377 tcp_init_congestion_control(sk);
5379 /* Prevent spurious tcp_cwnd_restart() on first data
5382 tp->lsndtime = tcp_time_stamp;
5384 tcp_init_buffer_space(sk);
5386 if (sock_flag(sk, SOCK_KEEPOPEN))
5387 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5389 if (!tp->rx_opt.snd_wscale)
5390 __tcp_fast_path_on(tp, tp->snd_wnd);
5394 if (!sock_flag(sk, SOCK_DEAD)) {
5395 sk->sk_state_change(sk);
5396 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5400 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
5401 struct tcp_fastopen_cookie *cookie)
5403 struct tcp_sock *tp = tcp_sk(sk);
5404 struct sk_buff *data = tp->syn_data ? tcp_write_queue_head(sk) : NULL;
5405 u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
5406 bool syn_drop = false;
5408 if (mss == tp->rx_opt.user_mss) {
5409 struct tcp_options_received opt;
5411 /* Get original SYNACK MSS value if user MSS sets mss_clamp */
5412 tcp_clear_options(&opt);
5413 opt.user_mss = opt.mss_clamp = 0;
5414 tcp_parse_options(synack, &opt, 0, NULL);
5415 mss = opt.mss_clamp;
5418 if (!tp->syn_fastopen) {
5419 /* Ignore an unsolicited cookie */
5421 } else if (tp->total_retrans) {
5422 /* SYN timed out and the SYN-ACK neither has a cookie nor
5423 * acknowledges data. Presumably the remote received only
5424 * the retransmitted (regular) SYNs: either the original
5425 * SYN-data or the corresponding SYN-ACK was dropped.
5427 syn_drop = (cookie->len < 0 && data);
5428 } else if (cookie->len < 0 && !tp->syn_data) {
5429 /* We requested a cookie but didn't get it. If we did not use
5430 * the (old) exp opt format then try so next time (try_exp=1).
5431 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
5433 try_exp = tp->syn_fastopen_exp ? 2 : 1;
5436 tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
5438 if (data) { /* Retransmit unacked data in SYN */
5439 tcp_for_write_queue_from(data, sk) {
5440 if (data == tcp_send_head(sk) ||
5441 __tcp_retransmit_skb(sk, data))
5445 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
5448 tp->syn_data_acked = tp->syn_data;
5449 if (tp->syn_data_acked)
5450 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
5454 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5455 const struct tcphdr *th, unsigned int len)
5457 struct inet_connection_sock *icsk = inet_csk(sk);
5458 struct tcp_sock *tp = tcp_sk(sk);
5459 struct tcp_fastopen_cookie foc = { .len = -1 };
5460 int saved_clamp = tp->rx_opt.mss_clamp;
5462 tcp_parse_options(skb, &tp->rx_opt, 0, &foc);
5463 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
5464 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
5468 * "If the state is SYN-SENT then
5469 * first check the ACK bit
5470 * If the ACK bit is set
5471 * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5472 * a reset (unless the RST bit is set, if so drop
5473 * the segment and return)"
5475 if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
5476 after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
5477 goto reset_and_undo;
5479 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5480 !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5482 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
5483 goto reset_and_undo;
5486 /* Now ACK is acceptable.
5488 * "If the RST bit is set
5489 * If the ACK was acceptable then signal the user "error:
5490 * connection reset", drop the segment, enter CLOSED state,
5491 * delete TCB, and return."
5500 * "fifth, if neither of the SYN or RST bits is set then
5501 * drop the segment and return."
5507 goto discard_and_undo;
5510 * "If the SYN bit is on ...
5511 * are acceptable then ...
5512 * (our SYN has been ACKed), change the connection
5513 * state to ESTABLISHED..."
5516 tcp_ecn_rcv_synack(tp, th);
5518 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5519 tcp_ack(sk, skb, FLAG_SLOWPATH);
5521 /* Ok.. it's good. Set up sequence numbers and
5522 * move to established.
5524 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5525 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5527 /* RFC1323: The window in SYN & SYN/ACK segments is
5530 tp->snd_wnd = ntohs(th->window);
5532 if (!tp->rx_opt.wscale_ok) {
5533 tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5534 tp->window_clamp = min(tp->window_clamp, 65535U);
5537 if (tp->rx_opt.saw_tstamp) {
5538 tp->rx_opt.tstamp_ok = 1;
5539 tp->tcp_header_len =
5540 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5541 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5542 tcp_store_ts_recent(tp);
5544 tp->tcp_header_len = sizeof(struct tcphdr);
5547 if (tcp_is_sack(tp) && sysctl_tcp_fack)
5548 tcp_enable_fack(tp);
5551 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5552 tcp_initialize_rcv_mss(sk);
5554 /* Remember, tcp_poll() does not lock socket!
5555 * Change state from SYN-SENT only after copied_seq
5556 * is initialized. */
5557 tp->copied_seq = tp->rcv_nxt;
5561 tcp_finish_connect(sk, skb);
5563 if ((tp->syn_fastopen || tp->syn_data) &&
5564 tcp_rcv_fastopen_synack(sk, skb, &foc))
5567 if (sk->sk_write_pending ||
5568 icsk->icsk_accept_queue.rskq_defer_accept ||
5569 icsk->icsk_ack.pingpong) {
5570 /* Save one ACK. Data will be ready after
5571 * several ticks, if write_pending is set.
5573 * It may be deleted, but with this feature tcpdumps
5574 * look so _wonderfully_ clever, that I was not able
5575 * to stand against the temptation 8) --ANK
5577 inet_csk_schedule_ack(sk);
5578 icsk->icsk_ack.lrcvtime = tcp_time_stamp;
5579 tcp_enter_quickack_mode(sk);
5580 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5581 TCP_DELACK_MAX, TCP_RTO_MAX);
5592 /* No ACK in the segment */
5596 * "If the RST bit is set
5598 * Otherwise (no ACK) drop the segment and return."
5601 goto discard_and_undo;
5605 if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5606 tcp_paws_reject(&tp->rx_opt, 0))
5607 goto discard_and_undo;
5610 /* We see SYN without ACK. It is attempt of
5611 * simultaneous connect with crossed SYNs.
5612 * Particularly, it can be connect to self.
5614 tcp_set_state(sk, TCP_SYN_RECV);
5616 if (tp->rx_opt.saw_tstamp) {
5617 tp->rx_opt.tstamp_ok = 1;
5618 tcp_store_ts_recent(tp);
5619 tp->tcp_header_len =
5620 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5622 tp->tcp_header_len = sizeof(struct tcphdr);
5625 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5626 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5628 /* RFC1323: The window in SYN & SYN/ACK segments is
5631 tp->snd_wnd = ntohs(th->window);
5632 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
5633 tp->max_window = tp->snd_wnd;
5635 tcp_ecn_rcv_syn(tp, th);
5638 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5639 tcp_initialize_rcv_mss(sk);
5641 tcp_send_synack(sk);
5643 /* Note, we could accept data and URG from this segment.
5644 * There are no obstacles to make this (except that we must
5645 * either change tcp_recvmsg() to prevent it from returning data
5646 * before 3WHS completes per RFC793, or employ TCP Fast Open).
5648 * However, if we ignore data in ACKless segments sometimes,
5649 * we have no reasons to accept it sometimes.
5650 * Also, seems the code doing it in step6 of tcp_rcv_state_process
5651 * is not flawless. So, discard packet for sanity.
5652 * Uncomment this return to process the data.
5659 /* "fifth, if neither of the SYN or RST bits is set then
5660 * drop the segment and return."
5664 tcp_clear_options(&tp->rx_opt);
5665 tp->rx_opt.mss_clamp = saved_clamp;
5669 tcp_clear_options(&tp->rx_opt);
5670 tp->rx_opt.mss_clamp = saved_clamp;
5675 * This function implements the receiving procedure of RFC 793 for
5676 * all states except ESTABLISHED and TIME_WAIT.
5677 * It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5678 * address independent.
5681 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
5682 const struct tcphdr *th, unsigned int len)
5684 struct tcp_sock *tp = tcp_sk(sk);
5685 struct inet_connection_sock *icsk = inet_csk(sk);
5686 struct request_sock *req;
5691 tp->rx_opt.saw_tstamp = 0;
5693 switch (sk->sk_state) {
5707 if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
5710 /* Now we have several options: In theory there is
5711 * nothing else in the frame. KA9Q has an option to
5712 * send data with the syn, BSD accepts data with the
5713 * syn up to the [to be] advertised window and
5714 * Solaris 2.1 gives you a protocol error. For now
5715 * we just ignore it, that fits the spec precisely
5716 * and avoids incompatibilities. It would be nice in
5717 * future to drop through and process the data.
5719 * Now that TTCP is starting to be used we ought to
5721 * But, this leaves one open to an easy denial of
5722 * service attack, and SYN cookies can't defend
5723 * against this problem. So, we drop the data
5724 * in the interest of security over speed unless
5725 * it's still in use.
5733 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
5737 /* Do step6 onward by hand. */
5738 tcp_urg(sk, skb, th);
5740 tcp_data_snd_check(sk);
5744 req = tp->fastopen_rsk;
5746 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
5747 sk->sk_state != TCP_FIN_WAIT1);
5749 if (!tcp_check_req(sk, skb, req, true))
5753 if (!th->ack && !th->rst && !th->syn)
5756 if (!tcp_validate_incoming(sk, skb, th, 0))
5759 /* step 5: check the ACK field */
5760 acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
5761 FLAG_UPDATE_TS_RECENT) > 0;
5763 switch (sk->sk_state) {
5768 /* Once we leave TCP_SYN_RECV, we no longer need req
5772 synack_stamp = tcp_rsk(req)->snt_synack;
5773 tp->total_retrans = req->num_retrans;
5774 reqsk_fastopen_remove(sk, req, false);
5776 synack_stamp = tp->lsndtime;
5777 /* Make sure socket is routed, for correct metrics. */
5778 icsk->icsk_af_ops->rebuild_header(sk);
5779 tcp_init_congestion_control(sk);
5782 tp->copied_seq = tp->rcv_nxt;
5783 tcp_init_buffer_space(sk);
5786 tcp_set_state(sk, TCP_ESTABLISHED);
5787 sk->sk_state_change(sk);
5789 /* Note, that this wakeup is only for marginal crossed SYN case.
5790 * Passively open sockets are not waked up, because
5791 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
5794 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5796 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5797 tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
5798 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5799 tcp_synack_rtt_meas(sk, synack_stamp);
5801 if (tp->rx_opt.tstamp_ok)
5802 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5805 /* Re-arm the timer because data may have been sent out.
5806 * This is similar to the regular data transmission case
5807 * when new data has just been ack'ed.
5809 * (TFO) - we could try to be more aggressive and
5810 * retransmitting any data sooner based on when they
5815 tcp_init_metrics(sk);
5817 tcp_update_pacing_rate(sk);
5819 /* Prevent spurious tcp_cwnd_restart() on first data packet */
5820 tp->lsndtime = tcp_time_stamp;
5822 tcp_initialize_rcv_mss(sk);
5823 tcp_fast_path_on(tp);
5826 case TCP_FIN_WAIT1: {
5827 struct dst_entry *dst;
5830 /* If we enter the TCP_FIN_WAIT1 state and we are a
5831 * Fast Open socket and this is the first acceptable
5832 * ACK we have received, this would have acknowledged
5833 * our SYNACK so stop the SYNACK timer.
5836 /* Return RST if ack_seq is invalid.
5837 * Note that RFC793 only says to generate a
5838 * DUPACK for it but for TCP Fast Open it seems
5839 * better to treat this case like TCP_SYN_RECV
5844 /* We no longer need the request sock. */
5845 reqsk_fastopen_remove(sk, req, false);
5848 if (tp->snd_una != tp->write_seq)
5851 tcp_set_state(sk, TCP_FIN_WAIT2);
5852 sk->sk_shutdown |= SEND_SHUTDOWN;
5854 dst = __sk_dst_get(sk);
5858 if (!sock_flag(sk, SOCK_DEAD)) {
5859 /* Wake up lingering close() */
5860 sk->sk_state_change(sk);
5864 if (tp->linger2 < 0 ||
5865 (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5866 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5868 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5872 tmo = tcp_fin_time(sk);
5873 if (tmo > TCP_TIMEWAIT_LEN) {
5874 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5875 } else if (th->fin || sock_owned_by_user(sk)) {
5876 /* Bad case. We could lose such FIN otherwise.
5877 * It is not a big problem, but it looks confusing
5878 * and not so rare event. We still can lose it now,
5879 * if it spins in bh_lock_sock(), but it is really
5882 inet_csk_reset_keepalive_timer(sk, tmo);
5884 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5891 if (tp->snd_una == tp->write_seq) {
5892 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
5898 if (tp->snd_una == tp->write_seq) {
5899 tcp_update_metrics(sk);
5906 /* step 6: check the URG bit */
5907 tcp_urg(sk, skb, th);
5909 /* step 7: process the segment text */
5910 switch (sk->sk_state) {
5911 case TCP_CLOSE_WAIT:
5914 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5918 /* RFC 793 says to queue data in these states,
5919 * RFC 1122 says we MUST send a reset.
5920 * BSD 4.4 also does reset.
5922 if (sk->sk_shutdown & RCV_SHUTDOWN) {
5923 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5924 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
5925 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5931 case TCP_ESTABLISHED:
5932 tcp_data_queue(sk, skb);
5937 /* tcp_data could move socket to TIME-WAIT */
5938 if (sk->sk_state != TCP_CLOSE) {
5939 tcp_data_snd_check(sk);
5940 tcp_ack_snd_check(sk);
5949 EXPORT_SYMBOL(tcp_rcv_state_process);
5951 static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
5953 struct inet_request_sock *ireq = inet_rsk(req);
5955 if (family == AF_INET)
5956 net_dbg_ratelimited("drop open request from %pI4/%u\n",
5957 &ireq->ir_rmt_addr, port);
5958 #if IS_ENABLED(CONFIG_IPV6)
5959 else if (family == AF_INET6)
5960 net_dbg_ratelimited("drop open request from %pI6/%u\n",
5961 &ireq->ir_v6_rmt_addr, port);
5965 /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
5967 * If we receive a SYN packet with these bits set, it means a
5968 * network is playing bad games with TOS bits. In order to
5969 * avoid possible false congestion notifications, we disable
5970 * TCP ECN negotiation.
5972 * Exception: tcp_ca wants ECN. This is required for DCTCP
5973 * congestion control: Linux DCTCP asserts ECT on all packets,
5974 * including SYN, which is most optimal solution; however,
5975 * others, such as FreeBSD do not.
5977 static void tcp_ecn_create_request(struct request_sock *req,
5978 const struct sk_buff *skb,
5979 const struct sock *listen_sk,
5980 const struct dst_entry *dst)
5982 const struct tcphdr *th = tcp_hdr(skb);
5983 const struct net *net = sock_net(listen_sk);
5984 bool th_ecn = th->ece && th->cwr;
5990 ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
5991 ecn_ok = net->ipv4.sysctl_tcp_ecn || dst_feature(dst, RTAX_FEATURE_ECN);
5993 if ((!ect && ecn_ok) || tcp_ca_needs_ecn(listen_sk))
5994 inet_rsk(req)->ecn_ok = 1;
5997 static void tcp_openreq_init(struct request_sock *req,
5998 const struct tcp_options_received *rx_opt,
5999 struct sk_buff *skb, const struct sock *sk)
6001 struct inet_request_sock *ireq = inet_rsk(req);
6003 req->rcv_wnd = 0; /* So that tcp_send_synack() knows! */
6005 tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
6006 tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
6007 tcp_rsk(req)->snt_synack = tcp_time_stamp;
6008 tcp_rsk(req)->last_oow_ack_time = 0;
6009 req->mss = rx_opt->mss_clamp;
6010 req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
6011 ireq->tstamp_ok = rx_opt->tstamp_ok;
6012 ireq->sack_ok = rx_opt->sack_ok;
6013 ireq->snd_wscale = rx_opt->snd_wscale;
6014 ireq->wscale_ok = rx_opt->wscale_ok;
6017 ireq->ir_rmt_port = tcp_hdr(skb)->source;
6018 ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
6019 ireq->ir_mark = inet_request_mark(sk, skb);
6022 struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
6023 struct sock *sk_listener)
6025 struct request_sock *req = reqsk_alloc(ops, sk_listener);
6028 struct inet_request_sock *ireq = inet_rsk(req);
6030 kmemcheck_annotate_bitfield(ireq, flags);
6032 atomic64_set(&ireq->ir_cookie, 0);
6033 ireq->ireq_state = TCP_NEW_SYN_RECV;
6034 write_pnet(&ireq->ireq_net, sock_net(sk_listener));
6035 ireq->ireq_family = sk_listener->sk_family;
6040 EXPORT_SYMBOL(inet_reqsk_alloc);
6043 * Return true if a syncookie should be sent
6045 static bool tcp_syn_flood_action(struct sock *sk,
6046 const struct sk_buff *skb,
6049 const char *msg = "Dropping request";
6050 bool want_cookie = false;
6051 struct listen_sock *lopt;
6053 #ifdef CONFIG_SYN_COOKIES
6054 if (sysctl_tcp_syncookies) {
6055 msg = "Sending cookies";
6057 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
6060 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
6062 lopt = inet_csk(sk)->icsk_accept_queue.listen_opt;
6063 if (!lopt->synflood_warned && sysctl_tcp_syncookies != 2) {
6064 lopt->synflood_warned = 1;
6065 pr_info("%s: Possible SYN flooding on port %d. %s. Check SNMP counters.\n",
6066 proto, ntohs(tcp_hdr(skb)->dest), msg);
6071 static void tcp_reqsk_record_syn(const struct sock *sk,
6072 struct request_sock *req,
6073 const struct sk_buff *skb)
6075 if (tcp_sk(sk)->save_syn) {
6076 u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
6079 copy = kmalloc(len + sizeof(u32), GFP_ATOMIC);
6082 memcpy(©[1], skb_network_header(skb), len);
6083 req->saved_syn = copy;
6088 int tcp_conn_request(struct request_sock_ops *rsk_ops,
6089 const struct tcp_request_sock_ops *af_ops,
6090 struct sock *sk, struct sk_buff *skb)
6092 struct tcp_options_received tmp_opt;
6093 struct request_sock *req;
6094 struct tcp_sock *tp = tcp_sk(sk);
6095 struct dst_entry *dst = NULL;
6096 __u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
6097 bool want_cookie = false, fastopen;
6099 struct tcp_fastopen_cookie foc = { .len = -1 };
6103 /* TW buckets are converted to open requests without
6104 * limitations, they conserve resources and peer is
6105 * evidently real one.
6107 if ((sysctl_tcp_syncookies == 2 ||
6108 inet_csk_reqsk_queue_is_full(sk)) && !isn) {
6109 want_cookie = tcp_syn_flood_action(sk, skb, rsk_ops->slab_name);
6115 /* Accept backlog is full. If we have already queued enough
6116 * of warm entries in syn queue, drop request. It is better than
6117 * clogging syn queue with openreqs with exponentially increasing
6120 if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) {
6121 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6125 req = inet_reqsk_alloc(rsk_ops, sk);
6129 tcp_rsk(req)->af_specific = af_ops;
6131 tcp_clear_options(&tmp_opt);
6132 tmp_opt.mss_clamp = af_ops->mss_clamp;
6133 tmp_opt.user_mss = tp->rx_opt.user_mss;
6134 tcp_parse_options(skb, &tmp_opt, 0, want_cookie ? NULL : &foc);
6136 if (want_cookie && !tmp_opt.saw_tstamp)
6137 tcp_clear_options(&tmp_opt);
6139 tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
6140 tcp_openreq_init(req, &tmp_opt, skb, sk);
6142 /* Note: tcp_v6_init_req() might override ir_iif for link locals */
6143 inet_rsk(req)->ir_iif = sk->sk_bound_dev_if;
6145 af_ops->init_req(req, sk, skb);
6147 if (security_inet_conn_request(sk, skb, req))
6150 if (!want_cookie && !isn) {
6151 /* VJ's idea. We save last timestamp seen
6152 * from the destination in peer table, when entering
6153 * state TIME-WAIT, and check against it before
6154 * accepting new connection request.
6156 * If "isn" is not zero, this request hit alive
6157 * timewait bucket, so that all the necessary checks
6158 * are made in the function processing timewait state.
6160 if (tcp_death_row.sysctl_tw_recycle) {
6163 dst = af_ops->route_req(sk, &fl, req, &strict);
6165 if (dst && strict &&
6166 !tcp_peer_is_proven(req, dst, true,
6167 tmp_opt.saw_tstamp)) {
6168 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSPASSIVEREJECTED);
6169 goto drop_and_release;
6172 /* Kill the following clause, if you dislike this way. */
6173 else if (!sysctl_tcp_syncookies &&
6174 (sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
6175 (sysctl_max_syn_backlog >> 2)) &&
6176 !tcp_peer_is_proven(req, dst, false,
6177 tmp_opt.saw_tstamp)) {
6178 /* Without syncookies last quarter of
6179 * backlog is filled with destinations,
6180 * proven to be alive.
6181 * It means that we continue to communicate
6182 * to destinations, already remembered
6183 * to the moment of synflood.
6185 pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
6187 goto drop_and_release;
6190 isn = af_ops->init_seq(skb);
6193 dst = af_ops->route_req(sk, &fl, req, NULL);
6198 tcp_ecn_create_request(req, skb, sk, dst);
6201 isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
6202 req->cookie_ts = tmp_opt.tstamp_ok;
6203 if (!tmp_opt.tstamp_ok)
6204 inet_rsk(req)->ecn_ok = 0;
6207 tcp_rsk(req)->snt_isn = isn;
6208 tcp_openreq_init_rwin(req, sk, dst);
6209 fastopen = !want_cookie &&
6210 tcp_try_fastopen(sk, skb, req, &foc, dst);
6211 err = af_ops->send_synack(sk, dst, &fl, req,
6212 skb_get_queue_mapping(skb), &foc);
6214 if (err || want_cookie)
6217 tcp_rsk(req)->tfo_listener = false;
6218 af_ops->queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
6220 tcp_reqsk_record_syn(sk, req, skb);
6229 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
6232 EXPORT_SYMBOL(tcp_conn_request);