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;
98 int sysctl_tcp_min_rtt_wlen __read_mostly = 300;
100 int sysctl_tcp_thin_dupack __read_mostly;
102 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
103 int sysctl_tcp_early_retrans __read_mostly = 3;
104 int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
106 #define FLAG_DATA 0x01 /* Incoming frame contained data. */
107 #define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */
108 #define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */
109 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */
110 #define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */
111 #define FLAG_DATA_SACKED 0x20 /* New SACK. */
112 #define FLAG_ECE 0x40 /* ECE in this ACK */
113 #define FLAG_LOST_RETRANS 0x80 /* This ACK marks some retransmission lost */
114 #define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/
115 #define FLAG_ORIG_SACK_ACKED 0x200 /* Never retransmitted data are (s)acked */
116 #define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
117 #define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */
118 #define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */
119 #define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */
121 #define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
122 #define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
123 #define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE)
124 #define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED)
126 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
127 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
129 /* Adapt the MSS value used to make delayed ack decision to the
132 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
134 struct inet_connection_sock *icsk = inet_csk(sk);
135 const unsigned int lss = icsk->icsk_ack.last_seg_size;
138 icsk->icsk_ack.last_seg_size = 0;
140 /* skb->len may jitter because of SACKs, even if peer
141 * sends good full-sized frames.
143 len = skb_shinfo(skb)->gso_size ? : skb->len;
144 if (len >= icsk->icsk_ack.rcv_mss) {
145 icsk->icsk_ack.rcv_mss = len;
147 /* Otherwise, we make more careful check taking into account,
148 * that SACKs block is variable.
150 * "len" is invariant segment length, including TCP header.
152 len += skb->data - skb_transport_header(skb);
153 if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
154 /* If PSH is not set, packet should be
155 * full sized, provided peer TCP is not badly broken.
156 * This observation (if it is correct 8)) allows
157 * to handle super-low mtu links fairly.
159 (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
160 !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
161 /* Subtract also invariant (if peer is RFC compliant),
162 * tcp header plus fixed timestamp option length.
163 * Resulting "len" is MSS free of SACK jitter.
165 len -= tcp_sk(sk)->tcp_header_len;
166 icsk->icsk_ack.last_seg_size = len;
168 icsk->icsk_ack.rcv_mss = len;
172 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
173 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
174 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
178 static void tcp_incr_quickack(struct sock *sk)
180 struct inet_connection_sock *icsk = inet_csk(sk);
181 unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
185 if (quickacks > icsk->icsk_ack.quick)
186 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
189 static void tcp_enter_quickack_mode(struct sock *sk)
191 struct inet_connection_sock *icsk = inet_csk(sk);
192 tcp_incr_quickack(sk);
193 icsk->icsk_ack.pingpong = 0;
194 icsk->icsk_ack.ato = TCP_ATO_MIN;
197 /* Send ACKs quickly, if "quick" count is not exhausted
198 * and the session is not interactive.
201 static bool tcp_in_quickack_mode(struct sock *sk)
203 const struct inet_connection_sock *icsk = inet_csk(sk);
204 const struct dst_entry *dst = __sk_dst_get(sk);
206 return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
207 (icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong);
210 static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
212 if (tp->ecn_flags & TCP_ECN_OK)
213 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
216 static void tcp_ecn_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
218 if (tcp_hdr(skb)->cwr)
219 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
222 static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
224 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
227 static void __tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
229 switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
230 case INET_ECN_NOT_ECT:
231 /* Funny extension: if ECT is not set on a segment,
232 * and we already seen ECT on a previous segment,
233 * it is probably a retransmit.
235 if (tp->ecn_flags & TCP_ECN_SEEN)
236 tcp_enter_quickack_mode((struct sock *)tp);
239 if (tcp_ca_needs_ecn((struct sock *)tp))
240 tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_IS_CE);
242 if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
243 /* Better not delay acks, sender can have a very low cwnd */
244 tcp_enter_quickack_mode((struct sock *)tp);
245 tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
247 tp->ecn_flags |= TCP_ECN_SEEN;
250 if (tcp_ca_needs_ecn((struct sock *)tp))
251 tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_NO_CE);
252 tp->ecn_flags |= TCP_ECN_SEEN;
257 static void tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
259 if (tp->ecn_flags & TCP_ECN_OK)
260 __tcp_ecn_check_ce(tp, skb);
263 static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
265 if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
266 tp->ecn_flags &= ~TCP_ECN_OK;
269 static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
271 if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
272 tp->ecn_flags &= ~TCP_ECN_OK;
275 static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
277 if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
282 /* Buffer size and advertised window tuning.
284 * 1. Tuning sk->sk_sndbuf, when connection enters established state.
287 static void tcp_sndbuf_expand(struct sock *sk)
289 const struct tcp_sock *tp = tcp_sk(sk);
293 /* Worst case is non GSO/TSO : each frame consumes one skb
294 * and skb->head is kmalloced using power of two area of memory
296 per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
298 SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
300 per_mss = roundup_pow_of_two(per_mss) +
301 SKB_DATA_ALIGN(sizeof(struct sk_buff));
303 nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
304 nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
306 /* Fast Recovery (RFC 5681 3.2) :
307 * Cubic needs 1.7 factor, rounded to 2 to include
308 * extra cushion (application might react slowly to POLLOUT)
310 sndmem = 2 * nr_segs * per_mss;
312 if (sk->sk_sndbuf < sndmem)
313 sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
316 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
318 * All tcp_full_space() is split to two parts: "network" buffer, allocated
319 * forward and advertised in receiver window (tp->rcv_wnd) and
320 * "application buffer", required to isolate scheduling/application
321 * latencies from network.
322 * window_clamp is maximal advertised window. It can be less than
323 * tcp_full_space(), in this case tcp_full_space() - window_clamp
324 * is reserved for "application" buffer. The less window_clamp is
325 * the smoother our behaviour from viewpoint of network, but the lower
326 * throughput and the higher sensitivity of the connection to losses. 8)
328 * rcv_ssthresh is more strict window_clamp used at "slow start"
329 * phase to predict further behaviour of this connection.
330 * It is used for two goals:
331 * - to enforce header prediction at sender, even when application
332 * requires some significant "application buffer". It is check #1.
333 * - to prevent pruning of receive queue because of misprediction
334 * of receiver window. Check #2.
336 * The scheme does not work when sender sends good segments opening
337 * window and then starts to feed us spaghetti. But it should work
338 * in common situations. Otherwise, we have to rely on queue collapsing.
341 /* Slow part of check#2. */
342 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
344 struct tcp_sock *tp = tcp_sk(sk);
346 int truesize = tcp_win_from_space(skb->truesize) >> 1;
347 int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
349 while (tp->rcv_ssthresh <= window) {
350 if (truesize <= skb->len)
351 return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
359 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
361 struct tcp_sock *tp = tcp_sk(sk);
364 if (tp->rcv_ssthresh < tp->window_clamp &&
365 (int)tp->rcv_ssthresh < tcp_space(sk) &&
366 !tcp_under_memory_pressure(sk)) {
369 /* Check #2. Increase window, if skb with such overhead
370 * will fit to rcvbuf in future.
372 if (tcp_win_from_space(skb->truesize) <= skb->len)
373 incr = 2 * tp->advmss;
375 incr = __tcp_grow_window(sk, skb);
378 incr = max_t(int, incr, 2 * skb->len);
379 tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
381 inet_csk(sk)->icsk_ack.quick |= 1;
386 /* 3. Tuning rcvbuf, when connection enters established state. */
387 static void tcp_fixup_rcvbuf(struct sock *sk)
389 u32 mss = tcp_sk(sk)->advmss;
392 rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) *
393 tcp_default_init_rwnd(mss);
395 /* Dynamic Right Sizing (DRS) has 2 to 3 RTT latency
396 * Allow enough cushion so that sender is not limited by our window
398 if (sysctl_tcp_moderate_rcvbuf)
401 if (sk->sk_rcvbuf < rcvmem)
402 sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
405 /* 4. Try to fixup all. It is made immediately after connection enters
408 void tcp_init_buffer_space(struct sock *sk)
410 struct tcp_sock *tp = tcp_sk(sk);
413 if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
414 tcp_fixup_rcvbuf(sk);
415 if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
416 tcp_sndbuf_expand(sk);
418 tp->rcvq_space.space = tp->rcv_wnd;
419 tp->rcvq_space.time = tcp_time_stamp;
420 tp->rcvq_space.seq = tp->copied_seq;
422 maxwin = tcp_full_space(sk);
424 if (tp->window_clamp >= maxwin) {
425 tp->window_clamp = maxwin;
427 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
428 tp->window_clamp = max(maxwin -
429 (maxwin >> sysctl_tcp_app_win),
433 /* Force reservation of one segment. */
434 if (sysctl_tcp_app_win &&
435 tp->window_clamp > 2 * tp->advmss &&
436 tp->window_clamp + tp->advmss > maxwin)
437 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
439 tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
440 tp->snd_cwnd_stamp = tcp_time_stamp;
443 /* 5. Recalculate window clamp after socket hit its memory bounds. */
444 static void tcp_clamp_window(struct sock *sk)
446 struct tcp_sock *tp = tcp_sk(sk);
447 struct inet_connection_sock *icsk = inet_csk(sk);
449 icsk->icsk_ack.quick = 0;
451 if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
452 !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
453 !tcp_under_memory_pressure(sk) &&
454 sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
455 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
458 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
459 tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
462 /* Initialize RCV_MSS value.
463 * RCV_MSS is an our guess about MSS used by the peer.
464 * We haven't any direct information about the MSS.
465 * It's better to underestimate the RCV_MSS rather than overestimate.
466 * Overestimations make us ACKing less frequently than needed.
467 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
469 void tcp_initialize_rcv_mss(struct sock *sk)
471 const struct tcp_sock *tp = tcp_sk(sk);
472 unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
474 hint = min(hint, tp->rcv_wnd / 2);
475 hint = min(hint, TCP_MSS_DEFAULT);
476 hint = max(hint, TCP_MIN_MSS);
478 inet_csk(sk)->icsk_ack.rcv_mss = hint;
480 EXPORT_SYMBOL(tcp_initialize_rcv_mss);
482 /* Receiver "autotuning" code.
484 * The algorithm for RTT estimation w/o timestamps is based on
485 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
486 * <http://public.lanl.gov/radiant/pubs.html#DRS>
488 * More detail on this code can be found at
489 * <http://staff.psc.edu/jheffner/>,
490 * though this reference is out of date. A new paper
493 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
495 u32 new_sample = tp->rcv_rtt_est.rtt;
501 if (new_sample != 0) {
502 /* If we sample in larger samples in the non-timestamp
503 * case, we could grossly overestimate the RTT especially
504 * with chatty applications or bulk transfer apps which
505 * are stalled on filesystem I/O.
507 * Also, since we are only going for a minimum in the
508 * non-timestamp case, we do not smooth things out
509 * else with timestamps disabled convergence takes too
513 m -= (new_sample >> 3);
521 /* No previous measure. */
525 if (tp->rcv_rtt_est.rtt != new_sample)
526 tp->rcv_rtt_est.rtt = new_sample;
529 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
531 if (tp->rcv_rtt_est.time == 0)
533 if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
535 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rcv_rtt_est.time, 1);
538 tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
539 tp->rcv_rtt_est.time = tcp_time_stamp;
542 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
543 const struct sk_buff *skb)
545 struct tcp_sock *tp = tcp_sk(sk);
546 if (tp->rx_opt.rcv_tsecr &&
547 (TCP_SKB_CB(skb)->end_seq -
548 TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
549 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
553 * This function should be called every time data is copied to user space.
554 * It calculates the appropriate TCP receive buffer space.
556 void tcp_rcv_space_adjust(struct sock *sk)
558 struct tcp_sock *tp = tcp_sk(sk);
562 time = tcp_time_stamp - tp->rcvq_space.time;
563 if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
566 /* Number of bytes copied to user in last RTT */
567 copied = tp->copied_seq - tp->rcvq_space.seq;
568 if (copied <= tp->rcvq_space.space)
572 * copied = bytes received in previous RTT, our base window
573 * To cope with packet losses, we need a 2x factor
574 * To cope with slow start, and sender growing its cwin by 100 %
575 * every RTT, we need a 4x factor, because the ACK we are sending
576 * now is for the next RTT, not the current one :
577 * <prev RTT . ><current RTT .. ><next RTT .... >
580 if (sysctl_tcp_moderate_rcvbuf &&
581 !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
582 int rcvwin, rcvmem, rcvbuf;
584 /* minimal window to cope with packet losses, assuming
585 * steady state. Add some cushion because of small variations.
587 rcvwin = (copied << 1) + 16 * tp->advmss;
589 /* If rate increased by 25%,
590 * assume slow start, rcvwin = 3 * copied
591 * If rate increased by 50%,
592 * assume sender can use 2x growth, rcvwin = 4 * copied
595 tp->rcvq_space.space + (tp->rcvq_space.space >> 2)) {
597 tp->rcvq_space.space + (tp->rcvq_space.space >> 1))
600 rcvwin += (rcvwin >> 1);
603 rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
604 while (tcp_win_from_space(rcvmem) < tp->advmss)
607 rcvbuf = min(rcvwin / tp->advmss * rcvmem, sysctl_tcp_rmem[2]);
608 if (rcvbuf > sk->sk_rcvbuf) {
609 sk->sk_rcvbuf = rcvbuf;
611 /* Make the window clamp follow along. */
612 tp->window_clamp = rcvwin;
615 tp->rcvq_space.space = copied;
618 tp->rcvq_space.seq = tp->copied_seq;
619 tp->rcvq_space.time = tcp_time_stamp;
622 /* There is something which you must keep in mind when you analyze the
623 * behavior of the tp->ato delayed ack timeout interval. When a
624 * connection starts up, we want to ack as quickly as possible. The
625 * problem is that "good" TCP's do slow start at the beginning of data
626 * transmission. The means that until we send the first few ACK's the
627 * sender will sit on his end and only queue most of his data, because
628 * he can only send snd_cwnd unacked packets at any given time. For
629 * each ACK we send, he increments snd_cwnd and transmits more of his
632 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
634 struct tcp_sock *tp = tcp_sk(sk);
635 struct inet_connection_sock *icsk = inet_csk(sk);
638 inet_csk_schedule_ack(sk);
640 tcp_measure_rcv_mss(sk, skb);
642 tcp_rcv_rtt_measure(tp);
644 now = tcp_time_stamp;
646 if (!icsk->icsk_ack.ato) {
647 /* The _first_ data packet received, initialize
648 * delayed ACK engine.
650 tcp_incr_quickack(sk);
651 icsk->icsk_ack.ato = TCP_ATO_MIN;
653 int m = now - icsk->icsk_ack.lrcvtime;
655 if (m <= TCP_ATO_MIN / 2) {
656 /* The fastest case is the first. */
657 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
658 } else if (m < icsk->icsk_ack.ato) {
659 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
660 if (icsk->icsk_ack.ato > icsk->icsk_rto)
661 icsk->icsk_ack.ato = icsk->icsk_rto;
662 } else if (m > icsk->icsk_rto) {
663 /* Too long gap. Apparently sender failed to
664 * restart window, so that we send ACKs quickly.
666 tcp_incr_quickack(sk);
670 icsk->icsk_ack.lrcvtime = now;
672 tcp_ecn_check_ce(tp, skb);
675 tcp_grow_window(sk, skb);
678 /* Called to compute a smoothed rtt estimate. The data fed to this
679 * routine either comes from timestamps, or from segments that were
680 * known _not_ to have been retransmitted [see Karn/Partridge
681 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
682 * piece by Van Jacobson.
683 * NOTE: the next three routines used to be one big routine.
684 * To save cycles in the RFC 1323 implementation it was better to break
685 * it up into three procedures. -- erics
687 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
689 struct tcp_sock *tp = tcp_sk(sk);
690 long m = mrtt_us; /* RTT */
691 u32 srtt = tp->srtt_us;
693 /* The following amusing code comes from Jacobson's
694 * article in SIGCOMM '88. Note that rtt and mdev
695 * are scaled versions of rtt and mean deviation.
696 * This is designed to be as fast as possible
697 * m stands for "measurement".
699 * On a 1990 paper the rto value is changed to:
700 * RTO = rtt + 4 * mdev
702 * Funny. This algorithm seems to be very broken.
703 * These formulae increase RTO, when it should be decreased, increase
704 * too slowly, when it should be increased quickly, decrease too quickly
705 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
706 * does not matter how to _calculate_ it. Seems, it was trap
707 * that VJ failed to avoid. 8)
710 m -= (srtt >> 3); /* m is now error in rtt est */
711 srtt += m; /* rtt = 7/8 rtt + 1/8 new */
713 m = -m; /* m is now abs(error) */
714 m -= (tp->mdev_us >> 2); /* similar update on mdev */
715 /* This is similar to one of Eifel findings.
716 * Eifel blocks mdev updates when rtt decreases.
717 * This solution is a bit different: we use finer gain
718 * for mdev in this case (alpha*beta).
719 * Like Eifel it also prevents growth of rto,
720 * but also it limits too fast rto decreases,
721 * happening in pure Eifel.
726 m -= (tp->mdev_us >> 2); /* similar update on mdev */
728 tp->mdev_us += m; /* mdev = 3/4 mdev + 1/4 new */
729 if (tp->mdev_us > tp->mdev_max_us) {
730 tp->mdev_max_us = tp->mdev_us;
731 if (tp->mdev_max_us > tp->rttvar_us)
732 tp->rttvar_us = tp->mdev_max_us;
734 if (after(tp->snd_una, tp->rtt_seq)) {
735 if (tp->mdev_max_us < tp->rttvar_us)
736 tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
737 tp->rtt_seq = tp->snd_nxt;
738 tp->mdev_max_us = tcp_rto_min_us(sk);
741 /* no previous measure. */
742 srtt = m << 3; /* take the measured time to be rtt */
743 tp->mdev_us = m << 1; /* make sure rto = 3*rtt */
744 tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
745 tp->mdev_max_us = tp->rttvar_us;
746 tp->rtt_seq = tp->snd_nxt;
748 tp->srtt_us = max(1U, srtt);
751 /* Set the sk_pacing_rate to allow proper sizing of TSO packets.
752 * Note: TCP stack does not yet implement pacing.
753 * FQ packet scheduler can be used to implement cheap but effective
754 * TCP pacing, to smooth the burst on large writes when packets
755 * in flight is significantly lower than cwnd (or rwin)
757 int sysctl_tcp_pacing_ss_ratio __read_mostly = 200;
758 int sysctl_tcp_pacing_ca_ratio __read_mostly = 120;
760 static void tcp_update_pacing_rate(struct sock *sk)
762 const struct tcp_sock *tp = tcp_sk(sk);
765 /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
766 rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
768 /* current rate is (cwnd * mss) / srtt
769 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
770 * In Congestion Avoidance phase, set it to 120 % the current rate.
772 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
773 * If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
774 * end of slow start and should slow down.
776 if (tp->snd_cwnd < tp->snd_ssthresh / 2)
777 rate *= sysctl_tcp_pacing_ss_ratio;
779 rate *= sysctl_tcp_pacing_ca_ratio;
781 rate *= max(tp->snd_cwnd, tp->packets_out);
783 if (likely(tp->srtt_us))
784 do_div(rate, tp->srtt_us);
786 /* ACCESS_ONCE() is needed because sch_fq fetches sk_pacing_rate
787 * without any lock. We want to make sure compiler wont store
788 * intermediate values in this location.
790 ACCESS_ONCE(sk->sk_pacing_rate) = min_t(u64, rate,
791 sk->sk_max_pacing_rate);
794 /* Calculate rto without backoff. This is the second half of Van Jacobson's
795 * routine referred to above.
797 static void tcp_set_rto(struct sock *sk)
799 const struct tcp_sock *tp = tcp_sk(sk);
800 /* Old crap is replaced with new one. 8)
803 * 1. If rtt variance happened to be less 50msec, it is hallucination.
804 * It cannot be less due to utterly erratic ACK generation made
805 * at least by solaris and freebsd. "Erratic ACKs" has _nothing_
806 * to do with delayed acks, because at cwnd>2 true delack timeout
807 * is invisible. Actually, Linux-2.4 also generates erratic
808 * ACKs in some circumstances.
810 inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
812 /* 2. Fixups made earlier cannot be right.
813 * If we do not estimate RTO correctly without them,
814 * all the algo is pure shit and should be replaced
815 * with correct one. It is exactly, which we pretend to do.
818 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
819 * guarantees that rto is higher.
824 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
826 __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
829 cwnd = TCP_INIT_CWND;
830 return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
834 * Packet counting of FACK is based on in-order assumptions, therefore TCP
835 * disables it when reordering is detected
837 void tcp_disable_fack(struct tcp_sock *tp)
839 /* RFC3517 uses different metric in lost marker => reset on change */
841 tp->lost_skb_hint = NULL;
842 tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED;
845 /* Take a notice that peer is sending D-SACKs */
846 static void tcp_dsack_seen(struct tcp_sock *tp)
848 tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
851 static void tcp_update_reordering(struct sock *sk, const int metric,
854 struct tcp_sock *tp = tcp_sk(sk);
855 if (metric > tp->reordering) {
858 tp->reordering = min(sysctl_tcp_max_reordering, metric);
860 /* This exciting event is worth to be remembered. 8) */
862 mib_idx = LINUX_MIB_TCPTSREORDER;
863 else if (tcp_is_reno(tp))
864 mib_idx = LINUX_MIB_TCPRENOREORDER;
865 else if (tcp_is_fack(tp))
866 mib_idx = LINUX_MIB_TCPFACKREORDER;
868 mib_idx = LINUX_MIB_TCPSACKREORDER;
870 NET_INC_STATS_BH(sock_net(sk), mib_idx);
871 #if FASTRETRANS_DEBUG > 1
872 pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
873 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
877 tp->undo_marker ? tp->undo_retrans : 0);
879 tcp_disable_fack(tp);
883 tcp_disable_early_retrans(tp);
887 /* This must be called before lost_out is incremented */
888 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
890 if (!tp->retransmit_skb_hint ||
891 before(TCP_SKB_CB(skb)->seq,
892 TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
893 tp->retransmit_skb_hint = skb;
896 after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
897 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
900 static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
902 if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
903 tcp_verify_retransmit_hint(tp, skb);
905 tp->lost_out += tcp_skb_pcount(skb);
906 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
910 void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
912 tcp_verify_retransmit_hint(tp, skb);
914 if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
915 tp->lost_out += tcp_skb_pcount(skb);
916 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
920 /* This procedure tags the retransmission queue when SACKs arrive.
922 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
923 * Packets in queue with these bits set are counted in variables
924 * sacked_out, retrans_out and lost_out, correspondingly.
926 * Valid combinations are:
927 * Tag InFlight Description
928 * 0 1 - orig segment is in flight.
929 * S 0 - nothing flies, orig reached receiver.
930 * L 0 - nothing flies, orig lost by net.
931 * R 2 - both orig and retransmit are in flight.
932 * L|R 1 - orig is lost, retransmit is in flight.
933 * S|R 1 - orig reached receiver, retrans is still in flight.
934 * (L|S|R is logically valid, it could occur when L|R is sacked,
935 * but it is equivalent to plain S and code short-curcuits it to S.
936 * L|S is logically invalid, it would mean -1 packet in flight 8))
938 * These 6 states form finite state machine, controlled by the following events:
939 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
940 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
941 * 3. Loss detection event of two flavors:
942 * A. Scoreboard estimator decided the packet is lost.
943 * A'. Reno "three dupacks" marks head of queue lost.
944 * A''. Its FACK modification, head until snd.fack is lost.
945 * B. SACK arrives sacking SND.NXT at the moment, when the
946 * segment was retransmitted.
947 * 4. D-SACK added new rule: D-SACK changes any tag to S.
949 * It is pleasant to note, that state diagram turns out to be commutative,
950 * so that we are allowed not to be bothered by order of our actions,
951 * when multiple events arrive simultaneously. (see the function below).
953 * Reordering detection.
954 * --------------------
955 * Reordering metric is maximal distance, which a packet can be displaced
956 * in packet stream. With SACKs we can estimate it:
958 * 1. SACK fills old hole and the corresponding segment was not
959 * ever retransmitted -> reordering. Alas, we cannot use it
960 * when segment was retransmitted.
961 * 2. The last flaw is solved with D-SACK. D-SACK arrives
962 * for retransmitted and already SACKed segment -> reordering..
963 * Both of these heuristics are not used in Loss state, when we cannot
964 * account for retransmits accurately.
966 * SACK block validation.
967 * ----------------------
969 * SACK block range validation checks that the received SACK block fits to
970 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
971 * Note that SND.UNA is not included to the range though being valid because
972 * it means that the receiver is rather inconsistent with itself reporting
973 * SACK reneging when it should advance SND.UNA. Such SACK block this is
974 * perfectly valid, however, in light of RFC2018 which explicitly states
975 * that "SACK block MUST reflect the newest segment. Even if the newest
976 * segment is going to be discarded ...", not that it looks very clever
977 * in case of head skb. Due to potentional receiver driven attacks, we
978 * choose to avoid immediate execution of a walk in write queue due to
979 * reneging and defer head skb's loss recovery to standard loss recovery
980 * procedure that will eventually trigger (nothing forbids us doing this).
982 * Implements also blockage to start_seq wrap-around. Problem lies in the
983 * fact that though start_seq (s) is before end_seq (i.e., not reversed),
984 * there's no guarantee that it will be before snd_nxt (n). The problem
985 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
988 * <- outs wnd -> <- wrapzone ->
989 * u e n u_w e_w s n_w
991 * |<------------+------+----- TCP seqno space --------------+---------->|
992 * ...-- <2^31 ->| |<--------...
993 * ...---- >2^31 ------>| |<--------...
995 * Current code wouldn't be vulnerable but it's better still to discard such
996 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
997 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
998 * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
999 * equal to the ideal case (infinite seqno space without wrap caused issues).
1001 * With D-SACK the lower bound is extended to cover sequence space below
1002 * SND.UNA down to undo_marker, which is the last point of interest. Yet
1003 * again, D-SACK block must not to go across snd_una (for the same reason as
1004 * for the normal SACK blocks, explained above). But there all simplicity
1005 * ends, TCP might receive valid D-SACKs below that. As long as they reside
1006 * fully below undo_marker they do not affect behavior in anyway and can
1007 * therefore be safely ignored. In rare cases (which are more or less
1008 * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1009 * fragmentation and packet reordering past skb's retransmission. To consider
1010 * them correctly, the acceptable range must be extended even more though
1011 * the exact amount is rather hard to quantify. However, tp->max_window can
1012 * be used as an exaggerated estimate.
1014 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1015 u32 start_seq, u32 end_seq)
1017 /* Too far in future, or reversed (interpretation is ambiguous) */
1018 if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1021 /* Nasty start_seq wrap-around check (see comments above) */
1022 if (!before(start_seq, tp->snd_nxt))
1025 /* In outstanding window? ...This is valid exit for D-SACKs too.
1026 * start_seq == snd_una is non-sensical (see comments above)
1028 if (after(start_seq, tp->snd_una))
1031 if (!is_dsack || !tp->undo_marker)
1034 /* ...Then it's D-SACK, and must reside below snd_una completely */
1035 if (after(end_seq, tp->snd_una))
1038 if (!before(start_seq, tp->undo_marker))
1042 if (!after(end_seq, tp->undo_marker))
1045 /* Undo_marker boundary crossing (overestimates a lot). Known already:
1046 * start_seq < undo_marker and end_seq >= undo_marker.
1048 return !before(start_seq, end_seq - tp->max_window);
1051 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1052 struct tcp_sack_block_wire *sp, int num_sacks,
1055 struct tcp_sock *tp = tcp_sk(sk);
1056 u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1057 u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1058 bool dup_sack = false;
1060 if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1063 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1064 } else if (num_sacks > 1) {
1065 u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1066 u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1068 if (!after(end_seq_0, end_seq_1) &&
1069 !before(start_seq_0, start_seq_1)) {
1072 NET_INC_STATS_BH(sock_net(sk),
1073 LINUX_MIB_TCPDSACKOFORECV);
1077 /* D-SACK for already forgotten data... Do dumb counting. */
1078 if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
1079 !after(end_seq_0, prior_snd_una) &&
1080 after(end_seq_0, tp->undo_marker))
1086 struct tcp_sacktag_state {
1089 /* Timestamps for earliest and latest never-retransmitted segment
1090 * that was SACKed. RTO needs the earliest RTT to stay conservative,
1091 * but congestion control should still get an accurate delay signal.
1093 struct skb_mstamp first_sackt;
1094 struct skb_mstamp last_sackt;
1098 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1099 * the incoming SACK may not exactly match but we can find smaller MSS
1100 * aligned portion of it that matches. Therefore we might need to fragment
1101 * which may fail and creates some hassle (caller must handle error case
1104 * FIXME: this could be merged to shift decision code
1106 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1107 u32 start_seq, u32 end_seq)
1111 unsigned int pkt_len;
1114 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1115 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1117 if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1118 after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1119 mss = tcp_skb_mss(skb);
1120 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1123 pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1127 pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1132 /* Round if necessary so that SACKs cover only full MSSes
1133 * and/or the remaining small portion (if present)
1135 if (pkt_len > mss) {
1136 unsigned int new_len = (pkt_len / mss) * mss;
1137 if (!in_sack && new_len < pkt_len) {
1139 if (new_len >= skb->len)
1144 err = tcp_fragment(sk, skb, pkt_len, mss, GFP_ATOMIC);
1152 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1153 static u8 tcp_sacktag_one(struct sock *sk,
1154 struct tcp_sacktag_state *state, u8 sacked,
1155 u32 start_seq, u32 end_seq,
1156 int dup_sack, int pcount,
1157 const struct skb_mstamp *xmit_time)
1159 struct tcp_sock *tp = tcp_sk(sk);
1160 int fack_count = state->fack_count;
1162 /* Account D-SACK for retransmitted packet. */
1163 if (dup_sack && (sacked & TCPCB_RETRANS)) {
1164 if (tp->undo_marker && tp->undo_retrans > 0 &&
1165 after(end_seq, tp->undo_marker))
1167 if (sacked & TCPCB_SACKED_ACKED)
1168 state->reord = min(fack_count, state->reord);
1171 /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1172 if (!after(end_seq, tp->snd_una))
1175 if (!(sacked & TCPCB_SACKED_ACKED)) {
1176 tcp_rack_advance(tp, xmit_time, sacked);
1178 if (sacked & TCPCB_SACKED_RETRANS) {
1179 /* If the segment is not tagged as lost,
1180 * we do not clear RETRANS, believing
1181 * that retransmission is still in flight.
1183 if (sacked & TCPCB_LOST) {
1184 sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1185 tp->lost_out -= pcount;
1186 tp->retrans_out -= pcount;
1189 if (!(sacked & TCPCB_RETRANS)) {
1190 /* New sack for not retransmitted frame,
1191 * which was in hole. It is reordering.
1193 if (before(start_seq,
1194 tcp_highest_sack_seq(tp)))
1195 state->reord = min(fack_count,
1197 if (!after(end_seq, tp->high_seq))
1198 state->flag |= FLAG_ORIG_SACK_ACKED;
1199 if (state->first_sackt.v64 == 0)
1200 state->first_sackt = *xmit_time;
1201 state->last_sackt = *xmit_time;
1204 if (sacked & TCPCB_LOST) {
1205 sacked &= ~TCPCB_LOST;
1206 tp->lost_out -= pcount;
1210 sacked |= TCPCB_SACKED_ACKED;
1211 state->flag |= FLAG_DATA_SACKED;
1212 tp->sacked_out += pcount;
1214 fack_count += pcount;
1216 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1217 if (!tcp_is_fack(tp) && tp->lost_skb_hint &&
1218 before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1219 tp->lost_cnt_hint += pcount;
1221 if (fack_count > tp->fackets_out)
1222 tp->fackets_out = fack_count;
1225 /* D-SACK. We can detect redundant retransmission in S|R and plain R
1226 * frames and clear it. undo_retrans is decreased above, L|R frames
1227 * are accounted above as well.
1229 if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1230 sacked &= ~TCPCB_SACKED_RETRANS;
1231 tp->retrans_out -= pcount;
1237 /* Shift newly-SACKed bytes from this skb to the immediately previous
1238 * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1240 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1241 struct tcp_sacktag_state *state,
1242 unsigned int pcount, int shifted, int mss,
1245 struct tcp_sock *tp = tcp_sk(sk);
1246 struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1247 u32 start_seq = TCP_SKB_CB(skb)->seq; /* start of newly-SACKed */
1248 u32 end_seq = start_seq + shifted; /* end of newly-SACKed */
1252 /* Adjust counters and hints for the newly sacked sequence
1253 * range but discard the return value since prev is already
1254 * marked. We must tag the range first because the seq
1255 * advancement below implicitly advances
1256 * tcp_highest_sack_seq() when skb is highest_sack.
1258 tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1259 start_seq, end_seq, dup_sack, pcount,
1262 if (skb == tp->lost_skb_hint)
1263 tp->lost_cnt_hint += pcount;
1265 TCP_SKB_CB(prev)->end_seq += shifted;
1266 TCP_SKB_CB(skb)->seq += shifted;
1268 tcp_skb_pcount_add(prev, pcount);
1269 BUG_ON(tcp_skb_pcount(skb) < pcount);
1270 tcp_skb_pcount_add(skb, -pcount);
1272 /* When we're adding to gso_segs == 1, gso_size will be zero,
1273 * in theory this shouldn't be necessary but as long as DSACK
1274 * code can come after this skb later on it's better to keep
1275 * setting gso_size to something.
1277 if (!TCP_SKB_CB(prev)->tcp_gso_size)
1278 TCP_SKB_CB(prev)->tcp_gso_size = mss;
1280 /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1281 if (tcp_skb_pcount(skb) <= 1)
1282 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1284 /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1285 TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1288 BUG_ON(!tcp_skb_pcount(skb));
1289 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1293 /* Whole SKB was eaten :-) */
1295 if (skb == tp->retransmit_skb_hint)
1296 tp->retransmit_skb_hint = prev;
1297 if (skb == tp->lost_skb_hint) {
1298 tp->lost_skb_hint = prev;
1299 tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1302 TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1303 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1304 TCP_SKB_CB(prev)->end_seq++;
1306 if (skb == tcp_highest_sack(sk))
1307 tcp_advance_highest_sack(sk, skb);
1309 tcp_unlink_write_queue(skb, sk);
1310 sk_wmem_free_skb(sk, skb);
1312 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1317 /* I wish gso_size would have a bit more sane initialization than
1318 * something-or-zero which complicates things
1320 static int tcp_skb_seglen(const struct sk_buff *skb)
1322 return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1325 /* Shifting pages past head area doesn't work */
1326 static int skb_can_shift(const struct sk_buff *skb)
1328 return !skb_headlen(skb) && skb_is_nonlinear(skb);
1331 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1334 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1335 struct tcp_sacktag_state *state,
1336 u32 start_seq, u32 end_seq,
1339 struct tcp_sock *tp = tcp_sk(sk);
1340 struct sk_buff *prev;
1346 if (!sk_can_gso(sk))
1349 /* Normally R but no L won't result in plain S */
1351 (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1353 if (!skb_can_shift(skb))
1355 /* This frame is about to be dropped (was ACKed). */
1356 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1359 /* Can only happen with delayed DSACK + discard craziness */
1360 if (unlikely(skb == tcp_write_queue_head(sk)))
1362 prev = tcp_write_queue_prev(sk, skb);
1364 if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1367 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1368 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1372 pcount = tcp_skb_pcount(skb);
1373 mss = tcp_skb_seglen(skb);
1375 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1376 * drop this restriction as unnecessary
1378 if (mss != tcp_skb_seglen(prev))
1381 if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1383 /* CHECKME: This is non-MSS split case only?, this will
1384 * cause skipped skbs due to advancing loop btw, original
1385 * has that feature too
1387 if (tcp_skb_pcount(skb) <= 1)
1390 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1392 /* TODO: head merge to next could be attempted here
1393 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1394 * though it might not be worth of the additional hassle
1396 * ...we can probably just fallback to what was done
1397 * previously. We could try merging non-SACKed ones
1398 * as well but it probably isn't going to buy off
1399 * because later SACKs might again split them, and
1400 * it would make skb timestamp tracking considerably
1406 len = end_seq - TCP_SKB_CB(skb)->seq;
1408 BUG_ON(len > skb->len);
1410 /* MSS boundaries should be honoured or else pcount will
1411 * severely break even though it makes things bit trickier.
1412 * Optimize common case to avoid most of the divides
1414 mss = tcp_skb_mss(skb);
1416 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1417 * drop this restriction as unnecessary
1419 if (mss != tcp_skb_seglen(prev))
1424 } else if (len < mss) {
1432 /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1433 if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1436 if (!skb_shift(prev, skb, len))
1438 if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1441 /* Hole filled allows collapsing with the next as well, this is very
1442 * useful when hole on every nth skb pattern happens
1444 if (prev == tcp_write_queue_tail(sk))
1446 skb = tcp_write_queue_next(sk, prev);
1448 if (!skb_can_shift(skb) ||
1449 (skb == tcp_send_head(sk)) ||
1450 ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1451 (mss != tcp_skb_seglen(skb)))
1455 if (skb_shift(prev, skb, len)) {
1456 pcount += tcp_skb_pcount(skb);
1457 tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1461 state->fack_count += pcount;
1468 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1472 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1473 struct tcp_sack_block *next_dup,
1474 struct tcp_sacktag_state *state,
1475 u32 start_seq, u32 end_seq,
1478 struct tcp_sock *tp = tcp_sk(sk);
1479 struct sk_buff *tmp;
1481 tcp_for_write_queue_from(skb, sk) {
1483 bool dup_sack = dup_sack_in;
1485 if (skb == tcp_send_head(sk))
1488 /* queue is in-order => we can short-circuit the walk early */
1489 if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1493 before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1494 in_sack = tcp_match_skb_to_sack(sk, skb,
1495 next_dup->start_seq,
1501 /* skb reference here is a bit tricky to get right, since
1502 * shifting can eat and free both this skb and the next,
1503 * so not even _safe variant of the loop is enough.
1506 tmp = tcp_shift_skb_data(sk, skb, state,
1507 start_seq, end_seq, dup_sack);
1516 in_sack = tcp_match_skb_to_sack(sk, skb,
1522 if (unlikely(in_sack < 0))
1526 TCP_SKB_CB(skb)->sacked =
1529 TCP_SKB_CB(skb)->sacked,
1530 TCP_SKB_CB(skb)->seq,
1531 TCP_SKB_CB(skb)->end_seq,
1533 tcp_skb_pcount(skb),
1536 if (!before(TCP_SKB_CB(skb)->seq,
1537 tcp_highest_sack_seq(tp)))
1538 tcp_advance_highest_sack(sk, skb);
1541 state->fack_count += tcp_skb_pcount(skb);
1546 /* Avoid all extra work that is being done by sacktag while walking in
1549 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1550 struct tcp_sacktag_state *state,
1553 tcp_for_write_queue_from(skb, sk) {
1554 if (skb == tcp_send_head(sk))
1557 if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1560 state->fack_count += tcp_skb_pcount(skb);
1565 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1567 struct tcp_sack_block *next_dup,
1568 struct tcp_sacktag_state *state,
1574 if (before(next_dup->start_seq, skip_to_seq)) {
1575 skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1576 skb = tcp_sacktag_walk(skb, sk, NULL, state,
1577 next_dup->start_seq, next_dup->end_seq,
1584 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1586 return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1590 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1591 u32 prior_snd_una, struct tcp_sacktag_state *state)
1593 struct tcp_sock *tp = tcp_sk(sk);
1594 const unsigned char *ptr = (skb_transport_header(ack_skb) +
1595 TCP_SKB_CB(ack_skb)->sacked);
1596 struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1597 struct tcp_sack_block sp[TCP_NUM_SACKS];
1598 struct tcp_sack_block *cache;
1599 struct sk_buff *skb;
1600 int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1602 bool found_dup_sack = false;
1604 int first_sack_index;
1607 state->reord = tp->packets_out;
1609 if (!tp->sacked_out) {
1610 if (WARN_ON(tp->fackets_out))
1611 tp->fackets_out = 0;
1612 tcp_highest_sack_reset(sk);
1615 found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1616 num_sacks, prior_snd_una);
1618 state->flag |= FLAG_DSACKING_ACK;
1620 /* Eliminate too old ACKs, but take into
1621 * account more or less fresh ones, they can
1622 * contain valid SACK info.
1624 if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1627 if (!tp->packets_out)
1631 first_sack_index = 0;
1632 for (i = 0; i < num_sacks; i++) {
1633 bool dup_sack = !i && found_dup_sack;
1635 sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1636 sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1638 if (!tcp_is_sackblock_valid(tp, dup_sack,
1639 sp[used_sacks].start_seq,
1640 sp[used_sacks].end_seq)) {
1644 if (!tp->undo_marker)
1645 mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1647 mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1649 /* Don't count olds caused by ACK reordering */
1650 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1651 !after(sp[used_sacks].end_seq, tp->snd_una))
1653 mib_idx = LINUX_MIB_TCPSACKDISCARD;
1656 NET_INC_STATS_BH(sock_net(sk), mib_idx);
1658 first_sack_index = -1;
1662 /* Ignore very old stuff early */
1663 if (!after(sp[used_sacks].end_seq, prior_snd_una))
1669 /* order SACK blocks to allow in order walk of the retrans queue */
1670 for (i = used_sacks - 1; i > 0; i--) {
1671 for (j = 0; j < i; j++) {
1672 if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1673 swap(sp[j], sp[j + 1]);
1675 /* Track where the first SACK block goes to */
1676 if (j == first_sack_index)
1677 first_sack_index = j + 1;
1682 skb = tcp_write_queue_head(sk);
1683 state->fack_count = 0;
1686 if (!tp->sacked_out) {
1687 /* It's already past, so skip checking against it */
1688 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1690 cache = tp->recv_sack_cache;
1691 /* Skip empty blocks in at head of the cache */
1692 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1697 while (i < used_sacks) {
1698 u32 start_seq = sp[i].start_seq;
1699 u32 end_seq = sp[i].end_seq;
1700 bool dup_sack = (found_dup_sack && (i == first_sack_index));
1701 struct tcp_sack_block *next_dup = NULL;
1703 if (found_dup_sack && ((i + 1) == first_sack_index))
1704 next_dup = &sp[i + 1];
1706 /* Skip too early cached blocks */
1707 while (tcp_sack_cache_ok(tp, cache) &&
1708 !before(start_seq, cache->end_seq))
1711 /* Can skip some work by looking recv_sack_cache? */
1712 if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1713 after(end_seq, cache->start_seq)) {
1716 if (before(start_seq, cache->start_seq)) {
1717 skb = tcp_sacktag_skip(skb, sk, state,
1719 skb = tcp_sacktag_walk(skb, sk, next_dup,
1726 /* Rest of the block already fully processed? */
1727 if (!after(end_seq, cache->end_seq))
1730 skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1734 /* ...tail remains todo... */
1735 if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1736 /* ...but better entrypoint exists! */
1737 skb = tcp_highest_sack(sk);
1740 state->fack_count = tp->fackets_out;
1745 skb = tcp_sacktag_skip(skb, sk, state, cache->end_seq);
1746 /* Check overlap against next cached too (past this one already) */
1751 if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1752 skb = tcp_highest_sack(sk);
1755 state->fack_count = tp->fackets_out;
1757 skb = tcp_sacktag_skip(skb, sk, state, start_seq);
1760 skb = tcp_sacktag_walk(skb, sk, next_dup, state,
1761 start_seq, end_seq, dup_sack);
1767 /* Clear the head of the cache sack blocks so we can skip it next time */
1768 for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1769 tp->recv_sack_cache[i].start_seq = 0;
1770 tp->recv_sack_cache[i].end_seq = 0;
1772 for (j = 0; j < used_sacks; j++)
1773 tp->recv_sack_cache[i++] = sp[j];
1775 if ((state->reord < tp->fackets_out) &&
1776 ((inet_csk(sk)->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker))
1777 tcp_update_reordering(sk, tp->fackets_out - state->reord, 0);
1779 tcp_verify_left_out(tp);
1782 #if FASTRETRANS_DEBUG > 0
1783 WARN_ON((int)tp->sacked_out < 0);
1784 WARN_ON((int)tp->lost_out < 0);
1785 WARN_ON((int)tp->retrans_out < 0);
1786 WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1791 /* Limits sacked_out so that sum with lost_out isn't ever larger than
1792 * packets_out. Returns false if sacked_out adjustement wasn't necessary.
1794 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
1798 holes = max(tp->lost_out, 1U);
1799 holes = min(holes, tp->packets_out);
1801 if ((tp->sacked_out + holes) > tp->packets_out) {
1802 tp->sacked_out = tp->packets_out - holes;
1808 /* If we receive more dupacks than we expected counting segments
1809 * in assumption of absent reordering, interpret this as reordering.
1810 * The only another reason could be bug in receiver TCP.
1812 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1814 struct tcp_sock *tp = tcp_sk(sk);
1815 if (tcp_limit_reno_sacked(tp))
1816 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1819 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1821 static void tcp_add_reno_sack(struct sock *sk)
1823 struct tcp_sock *tp = tcp_sk(sk);
1825 tcp_check_reno_reordering(sk, 0);
1826 tcp_verify_left_out(tp);
1829 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1831 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1833 struct tcp_sock *tp = tcp_sk(sk);
1836 /* One ACK acked hole. The rest eat duplicate ACKs. */
1837 if (acked - 1 >= tp->sacked_out)
1840 tp->sacked_out -= acked - 1;
1842 tcp_check_reno_reordering(sk, acked);
1843 tcp_verify_left_out(tp);
1846 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1851 void tcp_clear_retrans(struct tcp_sock *tp)
1853 tp->retrans_out = 0;
1855 tp->undo_marker = 0;
1856 tp->undo_retrans = -1;
1857 tp->fackets_out = 0;
1861 static inline void tcp_init_undo(struct tcp_sock *tp)
1863 tp->undo_marker = tp->snd_una;
1864 /* Retransmission still in flight may cause DSACKs later. */
1865 tp->undo_retrans = tp->retrans_out ? : -1;
1868 /* Enter Loss state. If we detect SACK reneging, forget all SACK information
1869 * and reset tags completely, otherwise preserve SACKs. If receiver
1870 * dropped its ofo queue, we will know this due to reneging detection.
1872 void tcp_enter_loss(struct sock *sk)
1874 const struct inet_connection_sock *icsk = inet_csk(sk);
1875 struct tcp_sock *tp = tcp_sk(sk);
1876 struct sk_buff *skb;
1877 bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
1878 bool is_reneg; /* is receiver reneging on SACKs? */
1880 /* Reduce ssthresh if it has not yet been made inside this window. */
1881 if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1882 !after(tp->high_seq, tp->snd_una) ||
1883 (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1884 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1885 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1886 tcp_ca_event(sk, CA_EVENT_LOSS);
1890 tp->snd_cwnd_cnt = 0;
1891 tp->snd_cwnd_stamp = tcp_time_stamp;
1893 tp->retrans_out = 0;
1896 if (tcp_is_reno(tp))
1897 tcp_reset_reno_sack(tp);
1899 skb = tcp_write_queue_head(sk);
1900 is_reneg = skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED);
1902 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
1904 tp->fackets_out = 0;
1906 tcp_clear_all_retrans_hints(tp);
1908 tcp_for_write_queue(skb, sk) {
1909 if (skb == tcp_send_head(sk))
1912 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1913 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || is_reneg) {
1914 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1915 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1916 tp->lost_out += tcp_skb_pcount(skb);
1917 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
1920 tcp_verify_left_out(tp);
1922 /* Timeout in disordered state after receiving substantial DUPACKs
1923 * suggests that the degree of reordering is over-estimated.
1925 if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
1926 tp->sacked_out >= sysctl_tcp_reordering)
1927 tp->reordering = min_t(unsigned int, tp->reordering,
1928 sysctl_tcp_reordering);
1929 tcp_set_ca_state(sk, TCP_CA_Loss);
1930 tp->high_seq = tp->snd_nxt;
1931 tcp_ecn_queue_cwr(tp);
1933 /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
1934 * loss recovery is underway except recurring timeout(s) on
1935 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
1937 tp->frto = sysctl_tcp_frto &&
1938 (new_recovery || icsk->icsk_retransmits) &&
1939 !inet_csk(sk)->icsk_mtup.probe_size;
1942 /* If ACK arrived pointing to a remembered SACK, it means that our
1943 * remembered SACKs do not reflect real state of receiver i.e.
1944 * receiver _host_ is heavily congested (or buggy).
1946 * To avoid big spurious retransmission bursts due to transient SACK
1947 * scoreboard oddities that look like reneging, we give the receiver a
1948 * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
1949 * restore sanity to the SACK scoreboard. If the apparent reneging
1950 * persists until this RTO then we'll clear the SACK scoreboard.
1952 static bool tcp_check_sack_reneging(struct sock *sk, int flag)
1954 if (flag & FLAG_SACK_RENEGING) {
1955 struct tcp_sock *tp = tcp_sk(sk);
1956 unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
1957 msecs_to_jiffies(10));
1959 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1960 delay, TCP_RTO_MAX);
1966 static inline int tcp_fackets_out(const struct tcp_sock *tp)
1968 return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
1971 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
1972 * counter when SACK is enabled (without SACK, sacked_out is used for
1975 * Instead, with FACK TCP uses fackets_out that includes both SACKed
1976 * segments up to the highest received SACK block so far and holes in
1979 * With reordering, holes may still be in flight, so RFC3517 recovery
1980 * uses pure sacked_out (total number of SACKed segments) even though
1981 * it violates the RFC that uses duplicate ACKs, often these are equal
1982 * but when e.g. out-of-window ACKs or packet duplication occurs,
1983 * they differ. Since neither occurs due to loss, TCP should really
1986 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
1988 return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
1991 static bool tcp_pause_early_retransmit(struct sock *sk, int flag)
1993 struct tcp_sock *tp = tcp_sk(sk);
1994 unsigned long delay;
1996 /* Delay early retransmit and entering fast recovery for
1997 * max(RTT/4, 2msec) unless ack has ECE mark, no RTT samples
1998 * available, or RTO is scheduled to fire first.
2000 if (sysctl_tcp_early_retrans < 2 || sysctl_tcp_early_retrans > 3 ||
2001 (flag & FLAG_ECE) || !tp->srtt_us)
2004 delay = max(usecs_to_jiffies(tp->srtt_us >> 5),
2005 msecs_to_jiffies(2));
2007 if (!time_after(inet_csk(sk)->icsk_timeout, (jiffies + delay)))
2010 inet_csk_reset_xmit_timer(sk, ICSK_TIME_EARLY_RETRANS, delay,
2015 /* Linux NewReno/SACK/FACK/ECN state machine.
2016 * --------------------------------------
2018 * "Open" Normal state, no dubious events, fast path.
2019 * "Disorder" In all the respects it is "Open",
2020 * but requires a bit more attention. It is entered when
2021 * we see some SACKs or dupacks. It is split of "Open"
2022 * mainly to move some processing from fast path to slow one.
2023 * "CWR" CWND was reduced due to some Congestion Notification event.
2024 * It can be ECN, ICMP source quench, local device congestion.
2025 * "Recovery" CWND was reduced, we are fast-retransmitting.
2026 * "Loss" CWND was reduced due to RTO timeout or SACK reneging.
2028 * tcp_fastretrans_alert() is entered:
2029 * - each incoming ACK, if state is not "Open"
2030 * - when arrived ACK is unusual, namely:
2035 * Counting packets in flight is pretty simple.
2037 * in_flight = packets_out - left_out + retrans_out
2039 * packets_out is SND.NXT-SND.UNA counted in packets.
2041 * retrans_out is number of retransmitted segments.
2043 * left_out is number of segments left network, but not ACKed yet.
2045 * left_out = sacked_out + lost_out
2047 * sacked_out: Packets, which arrived to receiver out of order
2048 * and hence not ACKed. With SACKs this number is simply
2049 * amount of SACKed data. Even without SACKs
2050 * it is easy to give pretty reliable estimate of this number,
2051 * counting duplicate ACKs.
2053 * lost_out: Packets lost by network. TCP has no explicit
2054 * "loss notification" feedback from network (for now).
2055 * It means that this number can be only _guessed_.
2056 * Actually, it is the heuristics to predict lossage that
2057 * distinguishes different algorithms.
2059 * F.e. after RTO, when all the queue is considered as lost,
2060 * lost_out = packets_out and in_flight = retrans_out.
2062 * Essentially, we have now two algorithms counting
2065 * FACK: It is the simplest heuristics. As soon as we decided
2066 * that something is lost, we decide that _all_ not SACKed
2067 * packets until the most forward SACK are lost. I.e.
2068 * lost_out = fackets_out - sacked_out and left_out = fackets_out.
2069 * It is absolutely correct estimate, if network does not reorder
2070 * packets. And it loses any connection to reality when reordering
2071 * takes place. We use FACK by default until reordering
2072 * is suspected on the path to this destination.
2074 * NewReno: when Recovery is entered, we assume that one segment
2075 * is lost (classic Reno). While we are in Recovery and
2076 * a partial ACK arrives, we assume that one more packet
2077 * is lost (NewReno). This heuristics are the same in NewReno
2080 * Imagine, that's all! Forget about all this shamanism about CWND inflation
2081 * deflation etc. CWND is real congestion window, never inflated, changes
2082 * only according to classic VJ rules.
2084 * Really tricky (and requiring careful tuning) part of algorithm
2085 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2086 * The first determines the moment _when_ we should reduce CWND and,
2087 * hence, slow down forward transmission. In fact, it determines the moment
2088 * when we decide that hole is caused by loss, rather than by a reorder.
2090 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2091 * holes, caused by lost packets.
2093 * And the most logically complicated part of algorithm is undo
2094 * heuristics. We detect false retransmits due to both too early
2095 * fast retransmit (reordering) and underestimated RTO, analyzing
2096 * timestamps and D-SACKs. When we detect that some segments were
2097 * retransmitted by mistake and CWND reduction was wrong, we undo
2098 * window reduction and abort recovery phase. This logic is hidden
2099 * inside several functions named tcp_try_undo_<something>.
2102 /* This function decides, when we should leave Disordered state
2103 * and enter Recovery phase, reducing congestion window.
2105 * Main question: may we further continue forward transmission
2106 * with the same cwnd?
2108 static bool tcp_time_to_recover(struct sock *sk, int flag)
2110 struct tcp_sock *tp = tcp_sk(sk);
2113 /* Trick#1: The loss is proven. */
2117 /* Not-A-Trick#2 : Classic rule... */
2118 if (tcp_dupack_heuristics(tp) > tp->reordering)
2121 /* Trick#4: It is still not OK... But will it be useful to delay
2124 packets_out = tp->packets_out;
2125 if (packets_out <= tp->reordering &&
2126 tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2127 !tcp_may_send_now(sk)) {
2128 /* We have nothing to send. This connection is limited
2129 * either by receiver window or by application.
2134 /* If a thin stream is detected, retransmit after first
2135 * received dupack. Employ only if SACK is supported in order
2136 * to avoid possible corner-case series of spurious retransmissions
2137 * Use only if there are no unsent data.
2139 if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
2140 tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
2141 tcp_is_sack(tp) && !tcp_send_head(sk))
2144 /* Trick#6: TCP early retransmit, per RFC5827. To avoid spurious
2145 * retransmissions due to small network reorderings, we implement
2146 * Mitigation A.3 in the RFC and delay the retransmission for a short
2147 * interval if appropriate.
2149 if (tp->do_early_retrans && !tp->retrans_out && tp->sacked_out &&
2150 (tp->packets_out >= (tp->sacked_out + 1) && tp->packets_out < 4) &&
2151 !tcp_may_send_now(sk))
2152 return !tcp_pause_early_retransmit(sk, flag);
2157 /* Detect loss in event "A" above by marking head of queue up as lost.
2158 * For FACK or non-SACK(Reno) senders, the first "packets" number of segments
2159 * are considered lost. For RFC3517 SACK, a segment is considered lost if it
2160 * has at least tp->reordering SACKed seqments above it; "packets" refers to
2161 * the maximum SACKed segments to pass before reaching this limit.
2163 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2165 struct tcp_sock *tp = tcp_sk(sk);
2166 struct sk_buff *skb;
2170 /* Use SACK to deduce losses of new sequences sent during recovery */
2171 const u32 loss_high = tcp_is_sack(tp) ? tp->snd_nxt : tp->high_seq;
2173 WARN_ON(packets > tp->packets_out);
2174 if (tp->lost_skb_hint) {
2175 skb = tp->lost_skb_hint;
2176 cnt = tp->lost_cnt_hint;
2177 /* Head already handled? */
2178 if (mark_head && skb != tcp_write_queue_head(sk))
2181 skb = tcp_write_queue_head(sk);
2185 tcp_for_write_queue_from(skb, sk) {
2186 if (skb == tcp_send_head(sk))
2188 /* TODO: do this better */
2189 /* this is not the most efficient way to do this... */
2190 tp->lost_skb_hint = skb;
2191 tp->lost_cnt_hint = cnt;
2193 if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2197 if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2198 (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2199 cnt += tcp_skb_pcount(skb);
2201 if (cnt > packets) {
2202 if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
2203 (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
2204 (oldcnt >= packets))
2207 mss = tcp_skb_mss(skb);
2208 err = tcp_fragment(sk, skb, (packets - oldcnt) * mss,
2215 tcp_skb_mark_lost(tp, skb);
2220 tcp_verify_left_out(tp);
2223 /* Account newly detected lost packet(s) */
2225 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2227 struct tcp_sock *tp = tcp_sk(sk);
2229 if (tcp_is_reno(tp)) {
2230 tcp_mark_head_lost(sk, 1, 1);
2231 } else if (tcp_is_fack(tp)) {
2232 int lost = tp->fackets_out - tp->reordering;
2235 tcp_mark_head_lost(sk, lost, 0);
2237 int sacked_upto = tp->sacked_out - tp->reordering;
2238 if (sacked_upto >= 0)
2239 tcp_mark_head_lost(sk, sacked_upto, 0);
2240 else if (fast_rexmit)
2241 tcp_mark_head_lost(sk, 1, 1);
2245 /* CWND moderation, preventing bursts due to too big ACKs
2246 * in dubious situations.
2248 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2250 tp->snd_cwnd = min(tp->snd_cwnd,
2251 tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2252 tp->snd_cwnd_stamp = tcp_time_stamp;
2255 static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2257 return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2258 before(tp->rx_opt.rcv_tsecr, when);
2261 /* skb is spurious retransmitted if the returned timestamp echo
2262 * reply is prior to the skb transmission time
2264 static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2265 const struct sk_buff *skb)
2267 return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2268 tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
2271 /* Nothing was retransmitted or returned timestamp is less
2272 * than timestamp of the first retransmission.
2274 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2276 return !tp->retrans_stamp ||
2277 tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
2280 /* Undo procedures. */
2282 /* We can clear retrans_stamp when there are no retransmissions in the
2283 * window. It would seem that it is trivially available for us in
2284 * tp->retrans_out, however, that kind of assumptions doesn't consider
2285 * what will happen if errors occur when sending retransmission for the
2286 * second time. ...It could the that such segment has only
2287 * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2288 * the head skb is enough except for some reneging corner cases that
2289 * are not worth the effort.
2291 * Main reason for all this complexity is the fact that connection dying
2292 * time now depends on the validity of the retrans_stamp, in particular,
2293 * that successive retransmissions of a segment must not advance
2294 * retrans_stamp under any conditions.
2296 static bool tcp_any_retrans_done(const struct sock *sk)
2298 const struct tcp_sock *tp = tcp_sk(sk);
2299 struct sk_buff *skb;
2301 if (tp->retrans_out)
2304 skb = tcp_write_queue_head(sk);
2305 if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2311 #if FASTRETRANS_DEBUG > 1
2312 static void DBGUNDO(struct sock *sk, const char *msg)
2314 struct tcp_sock *tp = tcp_sk(sk);
2315 struct inet_sock *inet = inet_sk(sk);
2317 if (sk->sk_family == AF_INET) {
2318 pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2320 &inet->inet_daddr, ntohs(inet->inet_dport),
2321 tp->snd_cwnd, tcp_left_out(tp),
2322 tp->snd_ssthresh, tp->prior_ssthresh,
2325 #if IS_ENABLED(CONFIG_IPV6)
2326 else if (sk->sk_family == AF_INET6) {
2327 struct ipv6_pinfo *np = inet6_sk(sk);
2328 pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2330 &np->daddr, ntohs(inet->inet_dport),
2331 tp->snd_cwnd, tcp_left_out(tp),
2332 tp->snd_ssthresh, tp->prior_ssthresh,
2338 #define DBGUNDO(x...) do { } while (0)
2341 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2343 struct tcp_sock *tp = tcp_sk(sk);
2346 struct sk_buff *skb;
2348 tcp_for_write_queue(skb, sk) {
2349 if (skb == tcp_send_head(sk))
2351 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2354 tcp_clear_all_retrans_hints(tp);
2357 if (tp->prior_ssthresh) {
2358 const struct inet_connection_sock *icsk = inet_csk(sk);
2360 if (icsk->icsk_ca_ops->undo_cwnd)
2361 tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2363 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2365 if (tp->prior_ssthresh > tp->snd_ssthresh) {
2366 tp->snd_ssthresh = tp->prior_ssthresh;
2367 tcp_ecn_withdraw_cwr(tp);
2370 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2372 tp->snd_cwnd_stamp = tcp_time_stamp;
2373 tp->undo_marker = 0;
2376 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2378 return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2381 /* People celebrate: "We love our President!" */
2382 static bool tcp_try_undo_recovery(struct sock *sk)
2384 struct tcp_sock *tp = tcp_sk(sk);
2386 if (tcp_may_undo(tp)) {
2389 /* Happy end! We did not retransmit anything
2390 * or our original transmission succeeded.
2392 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2393 tcp_undo_cwnd_reduction(sk, false);
2394 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2395 mib_idx = LINUX_MIB_TCPLOSSUNDO;
2397 mib_idx = LINUX_MIB_TCPFULLUNDO;
2399 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2401 if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2402 /* Hold old state until something *above* high_seq
2403 * is ACKed. For Reno it is MUST to prevent false
2404 * fast retransmits (RFC2582). SACK TCP is safe. */
2405 tcp_moderate_cwnd(tp);
2406 if (!tcp_any_retrans_done(sk))
2407 tp->retrans_stamp = 0;
2410 tcp_set_ca_state(sk, TCP_CA_Open);
2414 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2415 static bool tcp_try_undo_dsack(struct sock *sk)
2417 struct tcp_sock *tp = tcp_sk(sk);
2419 if (tp->undo_marker && !tp->undo_retrans) {
2420 DBGUNDO(sk, "D-SACK");
2421 tcp_undo_cwnd_reduction(sk, false);
2422 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2428 /* Undo during loss recovery after partial ACK or using F-RTO. */
2429 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2431 struct tcp_sock *tp = tcp_sk(sk);
2433 if (frto_undo || tcp_may_undo(tp)) {
2434 tcp_undo_cwnd_reduction(sk, true);
2436 DBGUNDO(sk, "partial loss");
2437 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2439 NET_INC_STATS_BH(sock_net(sk),
2440 LINUX_MIB_TCPSPURIOUSRTOS);
2441 inet_csk(sk)->icsk_retransmits = 0;
2442 if (frto_undo || tcp_is_sack(tp))
2443 tcp_set_ca_state(sk, TCP_CA_Open);
2449 /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2450 * It computes the number of packets to send (sndcnt) based on packets newly
2452 * 1) If the packets in flight is larger than ssthresh, PRR spreads the
2453 * cwnd reductions across a full RTT.
2454 * 2) Otherwise PRR uses packet conservation to send as much as delivered.
2455 * But when the retransmits are acked without further losses, PRR
2456 * slow starts cwnd up to ssthresh to speed up the recovery.
2458 static void tcp_init_cwnd_reduction(struct sock *sk)
2460 struct tcp_sock *tp = tcp_sk(sk);
2462 tp->high_seq = tp->snd_nxt;
2463 tp->tlp_high_seq = 0;
2464 tp->snd_cwnd_cnt = 0;
2465 tp->prior_cwnd = tp->snd_cwnd;
2466 tp->prr_delivered = 0;
2468 tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2469 tcp_ecn_queue_cwr(tp);
2472 static void tcp_cwnd_reduction(struct sock *sk, const int prior_unsacked,
2473 int fast_rexmit, int flag)
2475 struct tcp_sock *tp = tcp_sk(sk);
2477 int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2478 int newly_acked_sacked = prior_unsacked -
2479 (tp->packets_out - tp->sacked_out);
2481 tp->prr_delivered += newly_acked_sacked;
2483 u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2485 sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2486 } else if ((flag & FLAG_RETRANS_DATA_ACKED) &&
2487 !(flag & FLAG_LOST_RETRANS)) {
2488 sndcnt = min_t(int, delta,
2489 max_t(int, tp->prr_delivered - tp->prr_out,
2490 newly_acked_sacked) + 1);
2492 sndcnt = min(delta, newly_acked_sacked);
2494 sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
2495 tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
2498 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2500 struct tcp_sock *tp = tcp_sk(sk);
2502 /* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2503 if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
2504 (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
2505 tp->snd_cwnd = tp->snd_ssthresh;
2506 tp->snd_cwnd_stamp = tcp_time_stamp;
2508 tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2511 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2512 void tcp_enter_cwr(struct sock *sk)
2514 struct tcp_sock *tp = tcp_sk(sk);
2516 tp->prior_ssthresh = 0;
2517 if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2518 tp->undo_marker = 0;
2519 tcp_init_cwnd_reduction(sk);
2520 tcp_set_ca_state(sk, TCP_CA_CWR);
2523 EXPORT_SYMBOL(tcp_enter_cwr);
2525 static void tcp_try_keep_open(struct sock *sk)
2527 struct tcp_sock *tp = tcp_sk(sk);
2528 int state = TCP_CA_Open;
2530 if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2531 state = TCP_CA_Disorder;
2533 if (inet_csk(sk)->icsk_ca_state != state) {
2534 tcp_set_ca_state(sk, state);
2535 tp->high_seq = tp->snd_nxt;
2539 static void tcp_try_to_open(struct sock *sk, int flag, const int prior_unsacked)
2541 struct tcp_sock *tp = tcp_sk(sk);
2543 tcp_verify_left_out(tp);
2545 if (!tcp_any_retrans_done(sk))
2546 tp->retrans_stamp = 0;
2548 if (flag & FLAG_ECE)
2551 if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2552 tcp_try_keep_open(sk);
2554 tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
2558 static void tcp_mtup_probe_failed(struct sock *sk)
2560 struct inet_connection_sock *icsk = inet_csk(sk);
2562 icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2563 icsk->icsk_mtup.probe_size = 0;
2564 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2567 static void tcp_mtup_probe_success(struct sock *sk)
2569 struct tcp_sock *tp = tcp_sk(sk);
2570 struct inet_connection_sock *icsk = inet_csk(sk);
2572 /* FIXME: breaks with very large cwnd */
2573 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2574 tp->snd_cwnd = tp->snd_cwnd *
2575 tcp_mss_to_mtu(sk, tp->mss_cache) /
2576 icsk->icsk_mtup.probe_size;
2577 tp->snd_cwnd_cnt = 0;
2578 tp->snd_cwnd_stamp = tcp_time_stamp;
2579 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2581 icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2582 icsk->icsk_mtup.probe_size = 0;
2583 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2584 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2587 /* Do a simple retransmit without using the backoff mechanisms in
2588 * tcp_timer. This is used for path mtu discovery.
2589 * The socket is already locked here.
2591 void tcp_simple_retransmit(struct sock *sk)
2593 const struct inet_connection_sock *icsk = inet_csk(sk);
2594 struct tcp_sock *tp = tcp_sk(sk);
2595 struct sk_buff *skb;
2596 unsigned int mss = tcp_current_mss(sk);
2597 u32 prior_lost = tp->lost_out;
2599 tcp_for_write_queue(skb, sk) {
2600 if (skb == tcp_send_head(sk))
2602 if (tcp_skb_seglen(skb) > mss &&
2603 !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2604 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2605 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2606 tp->retrans_out -= tcp_skb_pcount(skb);
2608 tcp_skb_mark_lost_uncond_verify(tp, skb);
2612 tcp_clear_retrans_hints_partial(tp);
2614 if (prior_lost == tp->lost_out)
2617 if (tcp_is_reno(tp))
2618 tcp_limit_reno_sacked(tp);
2620 tcp_verify_left_out(tp);
2622 /* Don't muck with the congestion window here.
2623 * Reason is that we do not increase amount of _data_
2624 * in network, but units changed and effective
2625 * cwnd/ssthresh really reduced now.
2627 if (icsk->icsk_ca_state != TCP_CA_Loss) {
2628 tp->high_seq = tp->snd_nxt;
2629 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2630 tp->prior_ssthresh = 0;
2631 tp->undo_marker = 0;
2632 tcp_set_ca_state(sk, TCP_CA_Loss);
2634 tcp_xmit_retransmit_queue(sk);
2636 EXPORT_SYMBOL(tcp_simple_retransmit);
2638 static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2640 struct tcp_sock *tp = tcp_sk(sk);
2643 if (tcp_is_reno(tp))
2644 mib_idx = LINUX_MIB_TCPRENORECOVERY;
2646 mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2648 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2650 tp->prior_ssthresh = 0;
2653 if (!tcp_in_cwnd_reduction(sk)) {
2655 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2656 tcp_init_cwnd_reduction(sk);
2658 tcp_set_ca_state(sk, TCP_CA_Recovery);
2661 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2662 * recovered or spurious. Otherwise retransmits more on partial ACKs.
2664 static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
2666 struct tcp_sock *tp = tcp_sk(sk);
2667 bool recovered = !before(tp->snd_una, tp->high_seq);
2669 if ((flag & FLAG_SND_UNA_ADVANCED) &&
2670 tcp_try_undo_loss(sk, false))
2673 if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2674 /* Step 3.b. A timeout is spurious if not all data are
2675 * lost, i.e., never-retransmitted data are (s)acked.
2677 if ((flag & FLAG_ORIG_SACK_ACKED) &&
2678 tcp_try_undo_loss(sk, true))
2681 if (after(tp->snd_nxt, tp->high_seq)) {
2682 if (flag & FLAG_DATA_SACKED || is_dupack)
2683 tp->frto = 0; /* Step 3.a. loss was real */
2684 } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2685 tp->high_seq = tp->snd_nxt;
2686 __tcp_push_pending_frames(sk, tcp_current_mss(sk),
2688 if (after(tp->snd_nxt, tp->high_seq))
2689 return; /* Step 2.b */
2695 /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2696 tcp_try_undo_recovery(sk);
2699 if (tcp_is_reno(tp)) {
2700 /* A Reno DUPACK means new data in F-RTO step 2.b above are
2701 * delivered. Lower inflight to clock out (re)tranmissions.
2703 if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
2704 tcp_add_reno_sack(sk);
2705 else if (flag & FLAG_SND_UNA_ADVANCED)
2706 tcp_reset_reno_sack(tp);
2708 tcp_xmit_retransmit_queue(sk);
2711 /* Undo during fast recovery after partial ACK. */
2712 static bool tcp_try_undo_partial(struct sock *sk, const int acked,
2713 const int prior_unsacked, int flag)
2715 struct tcp_sock *tp = tcp_sk(sk);
2717 if (tp->undo_marker && tcp_packet_delayed(tp)) {
2718 /* Plain luck! Hole if filled with delayed
2719 * packet, rather than with a retransmit.
2721 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2723 /* We are getting evidence that the reordering degree is higher
2724 * than we realized. If there are no retransmits out then we
2725 * can undo. Otherwise we clock out new packets but do not
2726 * mark more packets lost or retransmit more.
2728 if (tp->retrans_out) {
2729 tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
2733 if (!tcp_any_retrans_done(sk))
2734 tp->retrans_stamp = 0;
2736 DBGUNDO(sk, "partial recovery");
2737 tcp_undo_cwnd_reduction(sk, true);
2738 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2739 tcp_try_keep_open(sk);
2745 /* Process an event, which can update packets-in-flight not trivially.
2746 * Main goal of this function is to calculate new estimate for left_out,
2747 * taking into account both packets sitting in receiver's buffer and
2748 * packets lost by network.
2750 * Besides that it does CWND reduction, when packet loss is detected
2751 * and changes state of machine.
2753 * It does _not_ decide what to send, it is made in function
2754 * tcp_xmit_retransmit_queue().
2756 static void tcp_fastretrans_alert(struct sock *sk, const int acked,
2757 const int prior_unsacked,
2758 bool is_dupack, int flag)
2760 struct inet_connection_sock *icsk = inet_csk(sk);
2761 struct tcp_sock *tp = tcp_sk(sk);
2762 bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2763 (tcp_fackets_out(tp) > tp->reordering));
2764 int fast_rexmit = 0;
2766 if (WARN_ON(!tp->packets_out && tp->sacked_out))
2768 if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2769 tp->fackets_out = 0;
2771 /* Now state machine starts.
2772 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2773 if (flag & FLAG_ECE)
2774 tp->prior_ssthresh = 0;
2776 /* B. In all the states check for reneging SACKs. */
2777 if (tcp_check_sack_reneging(sk, flag))
2780 /* C. Check consistency of the current state. */
2781 tcp_verify_left_out(tp);
2783 /* D. Check state exit conditions. State can be terminated
2784 * when high_seq is ACKed. */
2785 if (icsk->icsk_ca_state == TCP_CA_Open) {
2786 WARN_ON(tp->retrans_out != 0);
2787 tp->retrans_stamp = 0;
2788 } else if (!before(tp->snd_una, tp->high_seq)) {
2789 switch (icsk->icsk_ca_state) {
2791 /* CWR is to be held something *above* high_seq
2792 * is ACKed for CWR bit to reach receiver. */
2793 if (tp->snd_una != tp->high_seq) {
2794 tcp_end_cwnd_reduction(sk);
2795 tcp_set_ca_state(sk, TCP_CA_Open);
2799 case TCP_CA_Recovery:
2800 if (tcp_is_reno(tp))
2801 tcp_reset_reno_sack(tp);
2802 if (tcp_try_undo_recovery(sk))
2804 tcp_end_cwnd_reduction(sk);
2809 /* Use RACK to detect loss */
2810 if (sysctl_tcp_recovery & TCP_RACK_LOST_RETRANS &&
2811 tcp_rack_mark_lost(sk))
2812 flag |= FLAG_LOST_RETRANS;
2814 /* E. Process state. */
2815 switch (icsk->icsk_ca_state) {
2816 case TCP_CA_Recovery:
2817 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2818 if (tcp_is_reno(tp) && is_dupack)
2819 tcp_add_reno_sack(sk);
2821 if (tcp_try_undo_partial(sk, acked, prior_unsacked, flag))
2823 /* Partial ACK arrived. Force fast retransmit. */
2824 do_lost = tcp_is_reno(tp) ||
2825 tcp_fackets_out(tp) > tp->reordering;
2827 if (tcp_try_undo_dsack(sk)) {
2828 tcp_try_keep_open(sk);
2833 tcp_process_loss(sk, flag, is_dupack);
2834 if (icsk->icsk_ca_state != TCP_CA_Open &&
2835 !(flag & FLAG_LOST_RETRANS))
2837 /* Change state if cwnd is undone or retransmits are lost */
2839 if (tcp_is_reno(tp)) {
2840 if (flag & FLAG_SND_UNA_ADVANCED)
2841 tcp_reset_reno_sack(tp);
2843 tcp_add_reno_sack(sk);
2846 if (icsk->icsk_ca_state <= TCP_CA_Disorder)
2847 tcp_try_undo_dsack(sk);
2849 if (!tcp_time_to_recover(sk, flag)) {
2850 tcp_try_to_open(sk, flag, prior_unsacked);
2854 /* MTU probe failure: don't reduce cwnd */
2855 if (icsk->icsk_ca_state < TCP_CA_CWR &&
2856 icsk->icsk_mtup.probe_size &&
2857 tp->snd_una == tp->mtu_probe.probe_seq_start) {
2858 tcp_mtup_probe_failed(sk);
2859 /* Restores the reduction we did in tcp_mtup_probe() */
2861 tcp_simple_retransmit(sk);
2865 /* Otherwise enter Recovery state */
2866 tcp_enter_recovery(sk, (flag & FLAG_ECE));
2871 tcp_update_scoreboard(sk, fast_rexmit);
2872 tcp_cwnd_reduction(sk, prior_unsacked, fast_rexmit, flag);
2873 tcp_xmit_retransmit_queue(sk);
2876 /* Kathleen Nichols' algorithm for tracking the minimum value of
2877 * a data stream over some fixed time interval. (E.g., the minimum
2878 * RTT over the past five minutes.) It uses constant space and constant
2879 * time per update yet almost always delivers the same minimum as an
2880 * implementation that has to keep all the data in the window.
2882 * The algorithm keeps track of the best, 2nd best & 3rd best min
2883 * values, maintaining an invariant that the measurement time of the
2884 * n'th best >= n-1'th best. It also makes sure that the three values
2885 * are widely separated in the time window since that bounds the worse
2886 * case error when that data is monotonically increasing over the window.
2888 * Upon getting a new min, we can forget everything earlier because it
2889 * has no value - the new min is <= everything else in the window by
2890 * definition and it's the most recent. So we restart fresh on every new min
2891 * and overwrites 2nd & 3rd choices. The same property holds for 2nd & 3rd
2894 static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us)
2896 const u32 now = tcp_time_stamp, wlen = sysctl_tcp_min_rtt_wlen * HZ;
2897 struct rtt_meas *m = tcp_sk(sk)->rtt_min;
2898 struct rtt_meas rttm = { .rtt = (rtt_us ? : 1), .ts = now };
2901 /* Check if the new measurement updates the 1st, 2nd, or 3rd choices */
2902 if (unlikely(rttm.rtt <= m[0].rtt))
2903 m[0] = m[1] = m[2] = rttm;
2904 else if (rttm.rtt <= m[1].rtt)
2906 else if (rttm.rtt <= m[2].rtt)
2909 elapsed = now - m[0].ts;
2910 if (unlikely(elapsed > wlen)) {
2911 /* Passed entire window without a new min so make 2nd choice
2912 * the new min & 3rd choice the new 2nd. So forth and so on.
2917 if (now - m[0].ts > wlen) {
2920 if (now - m[0].ts > wlen)
2923 } else if (m[1].ts == m[0].ts && elapsed > wlen / 4) {
2924 /* Passed a quarter of the window without a new min so
2925 * take 2nd choice from the 2nd quarter of the window.
2928 } else if (m[2].ts == m[1].ts && elapsed > wlen / 2) {
2929 /* Passed half the window without a new min so take the 3rd
2930 * choice from the last half of the window.
2936 static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
2937 long seq_rtt_us, long sack_rtt_us,
2940 const struct tcp_sock *tp = tcp_sk(sk);
2942 /* Prefer RTT measured from ACK's timing to TS-ECR. This is because
2943 * broken middle-boxes or peers may corrupt TS-ECR fields. But
2944 * Karn's algorithm forbids taking RTT if some retransmitted data
2945 * is acked (RFC6298).
2948 seq_rtt_us = sack_rtt_us;
2950 /* RTTM Rule: A TSecr value received in a segment is used to
2951 * update the averaged RTT measurement only if the segment
2952 * acknowledges some new data, i.e., only if it advances the
2953 * left edge of the send window.
2954 * See draft-ietf-tcplw-high-performance-00, section 3.3.
2956 if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2958 seq_rtt_us = ca_rtt_us = jiffies_to_usecs(tcp_time_stamp -
2959 tp->rx_opt.rcv_tsecr);
2963 /* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
2964 * always taken together with ACK, SACK, or TS-opts. Any negative
2965 * values will be skipped with the seq_rtt_us < 0 check above.
2967 tcp_update_rtt_min(sk, ca_rtt_us);
2968 tcp_rtt_estimator(sk, seq_rtt_us);
2971 /* RFC6298: only reset backoff on valid RTT measurement. */
2972 inet_csk(sk)->icsk_backoff = 0;
2976 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
2977 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
2981 if (req && !req->num_retrans && tcp_rsk(req)->snt_synack.v64) {
2982 struct skb_mstamp now;
2984 skb_mstamp_get(&now);
2985 rtt_us = skb_mstamp_us_delta(&now, &tcp_rsk(req)->snt_synack);
2988 tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us);
2992 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
2994 const struct inet_connection_sock *icsk = inet_csk(sk);
2996 icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
2997 tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
3000 /* Restart timer after forward progress on connection.
3001 * RFC2988 recommends to restart timer to now+rto.
3003 void tcp_rearm_rto(struct sock *sk)
3005 const struct inet_connection_sock *icsk = inet_csk(sk);
3006 struct tcp_sock *tp = tcp_sk(sk);
3008 /* If the retrans timer is currently being used by Fast Open
3009 * for SYN-ACK retrans purpose, stay put.
3011 if (tp->fastopen_rsk)
3014 if (!tp->packets_out) {
3015 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3017 u32 rto = inet_csk(sk)->icsk_rto;
3018 /* Offset the time elapsed after installing regular RTO */
3019 if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
3020 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3021 struct sk_buff *skb = tcp_write_queue_head(sk);
3022 const u32 rto_time_stamp =
3023 tcp_skb_timestamp(skb) + rto;
3024 s32 delta = (s32)(rto_time_stamp - tcp_time_stamp);
3025 /* delta may not be positive if the socket is locked
3026 * when the retrans timer fires and is rescheduled.
3031 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
3036 /* This function is called when the delayed ER timer fires. TCP enters
3037 * fast recovery and performs fast-retransmit.
3039 void tcp_resume_early_retransmit(struct sock *sk)
3041 struct tcp_sock *tp = tcp_sk(sk);
3045 /* Stop if ER is disabled after the delayed ER timer is scheduled */
3046 if (!tp->do_early_retrans)
3049 tcp_enter_recovery(sk, false);
3050 tcp_update_scoreboard(sk, 1);
3051 tcp_xmit_retransmit_queue(sk);
3054 /* If we get here, the whole TSO packet has not been acked. */
3055 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3057 struct tcp_sock *tp = tcp_sk(sk);
3060 BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3062 packets_acked = tcp_skb_pcount(skb);
3063 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3065 packets_acked -= tcp_skb_pcount(skb);
3067 if (packets_acked) {
3068 BUG_ON(tcp_skb_pcount(skb) == 0);
3069 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3072 return packets_acked;
3075 static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3078 const struct skb_shared_info *shinfo;
3080 /* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3081 if (likely(!(sk->sk_tsflags & SOF_TIMESTAMPING_TX_ACK)))
3084 shinfo = skb_shinfo(skb);
3085 if ((shinfo->tx_flags & SKBTX_ACK_TSTAMP) &&
3086 between(shinfo->tskey, prior_snd_una, tcp_sk(sk)->snd_una - 1))
3087 __skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
3090 /* Remove acknowledged frames from the retransmission queue. If our packet
3091 * is before the ack sequence we can discard it as it's confirmed to have
3092 * arrived at the other end.
3094 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3096 struct tcp_sacktag_state *sack)
3098 const struct inet_connection_sock *icsk = inet_csk(sk);
3099 struct skb_mstamp first_ackt, last_ackt, now;
3100 struct tcp_sock *tp = tcp_sk(sk);
3101 u32 prior_sacked = tp->sacked_out;
3102 u32 reord = tp->packets_out;
3103 bool fully_acked = true;
3104 long sack_rtt_us = -1L;
3105 long seq_rtt_us = -1L;
3106 long ca_rtt_us = -1L;
3107 struct sk_buff *skb;
3114 while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3115 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3116 u8 sacked = scb->sacked;
3119 tcp_ack_tstamp(sk, skb, prior_snd_una);
3121 /* Determine how many packets and what bytes were acked, tso and else */
3122 if (after(scb->end_seq, tp->snd_una)) {
3123 if (tcp_skb_pcount(skb) == 1 ||
3124 !after(tp->snd_una, scb->seq))
3127 acked_pcount = tcp_tso_acked(sk, skb);
3131 fully_acked = false;
3133 /* Speedup tcp_unlink_write_queue() and next loop */
3134 prefetchw(skb->next);
3135 acked_pcount = tcp_skb_pcount(skb);
3138 if (unlikely(sacked & TCPCB_RETRANS)) {
3139 if (sacked & TCPCB_SACKED_RETRANS)
3140 tp->retrans_out -= acked_pcount;
3141 flag |= FLAG_RETRANS_DATA_ACKED;
3142 } else if (!(sacked & TCPCB_SACKED_ACKED)) {
3143 last_ackt = skb->skb_mstamp;
3144 WARN_ON_ONCE(last_ackt.v64 == 0);
3145 if (!first_ackt.v64)
3146 first_ackt = last_ackt;
3148 reord = min(pkts_acked, reord);
3149 if (!after(scb->end_seq, tp->high_seq))
3150 flag |= FLAG_ORIG_SACK_ACKED;
3153 if (sacked & TCPCB_SACKED_ACKED)
3154 tp->sacked_out -= acked_pcount;
3155 else if (tcp_is_sack(tp) && !tcp_skb_spurious_retrans(tp, skb))
3156 tcp_rack_advance(tp, &skb->skb_mstamp, sacked);
3157 if (sacked & TCPCB_LOST)
3158 tp->lost_out -= acked_pcount;
3160 tp->packets_out -= acked_pcount;
3161 pkts_acked += acked_pcount;
3163 /* Initial outgoing SYN's get put onto the write_queue
3164 * just like anything else we transmit. It is not
3165 * true data, and if we misinform our callers that
3166 * this ACK acks real data, we will erroneously exit
3167 * connection startup slow start one packet too
3168 * quickly. This is severely frowned upon behavior.
3170 if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3171 flag |= FLAG_DATA_ACKED;
3173 flag |= FLAG_SYN_ACKED;
3174 tp->retrans_stamp = 0;
3180 tcp_unlink_write_queue(skb, sk);
3181 sk_wmem_free_skb(sk, skb);
3182 if (unlikely(skb == tp->retransmit_skb_hint))
3183 tp->retransmit_skb_hint = NULL;
3184 if (unlikely(skb == tp->lost_skb_hint))
3185 tp->lost_skb_hint = NULL;
3188 if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3189 tp->snd_up = tp->snd_una;
3191 if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3192 flag |= FLAG_SACK_RENEGING;
3194 skb_mstamp_get(&now);
3195 if (likely(first_ackt.v64) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3196 seq_rtt_us = skb_mstamp_us_delta(&now, &first_ackt);
3197 ca_rtt_us = skb_mstamp_us_delta(&now, &last_ackt);
3199 if (sack->first_sackt.v64) {
3200 sack_rtt_us = skb_mstamp_us_delta(&now, &sack->first_sackt);
3201 ca_rtt_us = skb_mstamp_us_delta(&now, &sack->last_sackt);
3204 rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3207 if (flag & FLAG_ACKED) {
3209 if (unlikely(icsk->icsk_mtup.probe_size &&
3210 !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3211 tcp_mtup_probe_success(sk);
3214 if (tcp_is_reno(tp)) {
3215 tcp_remove_reno_sacks(sk, pkts_acked);
3219 /* Non-retransmitted hole got filled? That's reordering */
3220 if (reord < prior_fackets)
3221 tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3223 delta = tcp_is_fack(tp) ? pkts_acked :
3224 prior_sacked - tp->sacked_out;
3225 tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3228 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3230 } else if (skb && rtt_update && sack_rtt_us >= 0 &&
3231 sack_rtt_us > skb_mstamp_us_delta(&now, &skb->skb_mstamp)) {
3232 /* Do not re-arm RTO if the sack RTT is measured from data sent
3233 * after when the head was last (re)transmitted. Otherwise the
3234 * timeout may continue to extend in loss recovery.
3239 if (icsk->icsk_ca_ops->pkts_acked)
3240 icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked, ca_rtt_us);
3242 #if FASTRETRANS_DEBUG > 0
3243 WARN_ON((int)tp->sacked_out < 0);
3244 WARN_ON((int)tp->lost_out < 0);
3245 WARN_ON((int)tp->retrans_out < 0);
3246 if (!tp->packets_out && tcp_is_sack(tp)) {
3247 icsk = inet_csk(sk);
3249 pr_debug("Leak l=%u %d\n",
3250 tp->lost_out, icsk->icsk_ca_state);
3253 if (tp->sacked_out) {
3254 pr_debug("Leak s=%u %d\n",
3255 tp->sacked_out, icsk->icsk_ca_state);
3258 if (tp->retrans_out) {
3259 pr_debug("Leak r=%u %d\n",
3260 tp->retrans_out, icsk->icsk_ca_state);
3261 tp->retrans_out = 0;
3268 static void tcp_ack_probe(struct sock *sk)
3270 const struct tcp_sock *tp = tcp_sk(sk);
3271 struct inet_connection_sock *icsk = inet_csk(sk);
3273 /* Was it a usable window open? */
3275 if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3276 icsk->icsk_backoff = 0;
3277 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3278 /* Socket must be waked up by subsequent tcp_data_snd_check().
3279 * This function is not for random using!
3282 unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
3284 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3289 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3291 return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3292 inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3295 /* Decide wheather to run the increase function of congestion control. */
3296 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3298 if (tcp_in_cwnd_reduction(sk))
3301 /* If reordering is high then always grow cwnd whenever data is
3302 * delivered regardless of its ordering. Otherwise stay conservative
3303 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3304 * new SACK or ECE mark may first advance cwnd here and later reduce
3305 * cwnd in tcp_fastretrans_alert() based on more states.
3307 if (tcp_sk(sk)->reordering > sysctl_tcp_reordering)
3308 return flag & FLAG_FORWARD_PROGRESS;
3310 return flag & FLAG_DATA_ACKED;
3313 /* Check that window update is acceptable.
3314 * The function assumes that snd_una<=ack<=snd_next.
3316 static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3317 const u32 ack, const u32 ack_seq,
3320 return after(ack, tp->snd_una) ||
3321 after(ack_seq, tp->snd_wl1) ||
3322 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3325 /* If we update tp->snd_una, also update tp->bytes_acked */
3326 static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3328 u32 delta = ack - tp->snd_una;
3330 u64_stats_update_begin(&tp->syncp);
3331 tp->bytes_acked += delta;
3332 u64_stats_update_end(&tp->syncp);
3336 /* If we update tp->rcv_nxt, also update tp->bytes_received */
3337 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3339 u32 delta = seq - tp->rcv_nxt;
3341 u64_stats_update_begin(&tp->syncp);
3342 tp->bytes_received += delta;
3343 u64_stats_update_end(&tp->syncp);
3347 /* Update our send window.
3349 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3350 * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3352 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3355 struct tcp_sock *tp = tcp_sk(sk);
3357 u32 nwin = ntohs(tcp_hdr(skb)->window);
3359 if (likely(!tcp_hdr(skb)->syn))
3360 nwin <<= tp->rx_opt.snd_wscale;
3362 if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3363 flag |= FLAG_WIN_UPDATE;
3364 tcp_update_wl(tp, ack_seq);
3366 if (tp->snd_wnd != nwin) {
3369 /* Note, it is the only place, where
3370 * fast path is recovered for sending TCP.
3373 tcp_fast_path_check(sk);
3375 if (tcp_send_head(sk))
3376 tcp_slow_start_after_idle_check(sk);
3378 if (nwin > tp->max_window) {
3379 tp->max_window = nwin;
3380 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3385 tcp_snd_una_update(tp, ack);
3390 /* Return true if we're currently rate-limiting out-of-window ACKs and
3391 * thus shouldn't send a dupack right now. We rate-limit dupacks in
3392 * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3393 * attacks that send repeated SYNs or ACKs for the same connection. To
3394 * do this, we do not send a duplicate SYNACK or ACK if the remote
3395 * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3397 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3398 int mib_idx, u32 *last_oow_ack_time)
3400 /* Data packets without SYNs are not likely part of an ACK loop. */
3401 if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3403 goto not_rate_limited;
3405 if (*last_oow_ack_time) {
3406 s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
3408 if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
3409 NET_INC_STATS_BH(net, mib_idx);
3410 return true; /* rate-limited: don't send yet! */
3414 *last_oow_ack_time = tcp_time_stamp;
3417 return false; /* not rate-limited: go ahead, send dupack now! */
3420 /* RFC 5961 7 [ACK Throttling] */
3421 static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
3423 /* unprotected vars, we dont care of overwrites */
3424 static u32 challenge_timestamp;
3425 static unsigned int challenge_count;
3426 struct tcp_sock *tp = tcp_sk(sk);
3429 /* First check our per-socket dupack rate limit. */
3430 if (tcp_oow_rate_limited(sock_net(sk), skb,
3431 LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3432 &tp->last_oow_ack_time))
3435 /* Then check the check host-wide RFC 5961 rate limit. */
3437 if (now != challenge_timestamp) {
3438 challenge_timestamp = now;
3439 challenge_count = 0;
3441 if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
3442 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
3447 static void tcp_store_ts_recent(struct tcp_sock *tp)
3449 tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3450 tp->rx_opt.ts_recent_stamp = get_seconds();
3453 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3455 if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3456 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3457 * extra check below makes sure this can only happen
3458 * for pure ACK frames. -DaveM
3460 * Not only, also it occurs for expired timestamps.
3463 if (tcp_paws_check(&tp->rx_opt, 0))
3464 tcp_store_ts_recent(tp);
3468 /* This routine deals with acks during a TLP episode.
3469 * We mark the end of a TLP episode on receiving TLP dupack or when
3470 * ack is after tlp_high_seq.
3471 * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
3473 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3475 struct tcp_sock *tp = tcp_sk(sk);
3477 if (before(ack, tp->tlp_high_seq))
3480 if (flag & FLAG_DSACKING_ACK) {
3481 /* This DSACK means original and TLP probe arrived; no loss */
3482 tp->tlp_high_seq = 0;
3483 } else if (after(ack, tp->tlp_high_seq)) {
3484 /* ACK advances: there was a loss, so reduce cwnd. Reset
3485 * tlp_high_seq in tcp_init_cwnd_reduction()
3487 tcp_init_cwnd_reduction(sk);
3488 tcp_set_ca_state(sk, TCP_CA_CWR);
3489 tcp_end_cwnd_reduction(sk);
3490 tcp_try_keep_open(sk);
3491 NET_INC_STATS_BH(sock_net(sk),
3492 LINUX_MIB_TCPLOSSPROBERECOVERY);
3493 } else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3494 FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3495 /* Pure dupack: original and TLP probe arrived; no loss */
3496 tp->tlp_high_seq = 0;
3500 static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
3502 const struct inet_connection_sock *icsk = inet_csk(sk);
3504 if (icsk->icsk_ca_ops->in_ack_event)
3505 icsk->icsk_ca_ops->in_ack_event(sk, flags);
3508 /* This routine deals with incoming acks, but not outgoing ones. */
3509 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3511 struct inet_connection_sock *icsk = inet_csk(sk);
3512 struct tcp_sock *tp = tcp_sk(sk);
3513 struct tcp_sacktag_state sack_state;
3514 u32 prior_snd_una = tp->snd_una;
3515 u32 ack_seq = TCP_SKB_CB(skb)->seq;
3516 u32 ack = TCP_SKB_CB(skb)->ack_seq;
3517 bool is_dupack = false;
3519 int prior_packets = tp->packets_out;
3520 const int prior_unsacked = tp->packets_out - tp->sacked_out;
3521 int acked = 0; /* Number of packets newly acked */
3523 sack_state.first_sackt.v64 = 0;
3525 /* We very likely will need to access write queue head. */
3526 prefetchw(sk->sk_write_queue.next);
3528 /* If the ack is older than previous acks
3529 * then we can probably ignore it.
3531 if (before(ack, prior_snd_una)) {
3532 /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3533 if (before(ack, prior_snd_una - tp->max_window)) {
3534 tcp_send_challenge_ack(sk, skb);
3540 /* If the ack includes data we haven't sent yet, discard
3541 * this segment (RFC793 Section 3.9).
3543 if (after(ack, tp->snd_nxt))
3546 if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
3547 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
3550 if (after(ack, prior_snd_una)) {
3551 flag |= FLAG_SND_UNA_ADVANCED;
3552 icsk->icsk_retransmits = 0;
3555 prior_fackets = tp->fackets_out;
3557 /* ts_recent update must be made after we are sure that the packet
3560 if (flag & FLAG_UPDATE_TS_RECENT)
3561 tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3563 if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3564 /* Window is constant, pure forward advance.
3565 * No more checks are required.
3566 * Note, we use the fact that SND.UNA>=SND.WL2.
3568 tcp_update_wl(tp, ack_seq);
3569 tcp_snd_una_update(tp, ack);
3570 flag |= FLAG_WIN_UPDATE;
3572 tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
3574 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3576 u32 ack_ev_flags = CA_ACK_SLOWPATH;
3578 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3581 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3583 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3585 if (TCP_SKB_CB(skb)->sacked)
3586 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3589 if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
3591 ack_ev_flags |= CA_ACK_ECE;
3594 if (flag & FLAG_WIN_UPDATE)
3595 ack_ev_flags |= CA_ACK_WIN_UPDATE;
3597 tcp_in_ack_event(sk, ack_ev_flags);
3600 /* We passed data and got it acked, remove any soft error
3601 * log. Something worked...
3603 sk->sk_err_soft = 0;
3604 icsk->icsk_probes_out = 0;
3605 tp->rcv_tstamp = tcp_time_stamp;
3609 /* See if we can take anything off of the retransmit queue. */
3610 acked = tp->packets_out;
3611 flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una,
3613 acked -= tp->packets_out;
3615 if (tcp_ack_is_dubious(sk, flag)) {
3616 is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
3617 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3620 if (tp->tlp_high_seq)
3621 tcp_process_tlp_ack(sk, ack, flag);
3623 /* Advance cwnd if state allows */
3624 if (tcp_may_raise_cwnd(sk, flag))
3625 tcp_cong_avoid(sk, ack, acked);
3627 if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) {
3628 struct dst_entry *dst = __sk_dst_get(sk);
3633 if (icsk->icsk_pending == ICSK_TIME_RETRANS)
3634 tcp_schedule_loss_probe(sk);
3635 tcp_update_pacing_rate(sk);
3639 /* If data was DSACKed, see if we can undo a cwnd reduction. */
3640 if (flag & FLAG_DSACKING_ACK)
3641 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3643 /* If this ack opens up a zero window, clear backoff. It was
3644 * being used to time the probes, and is probably far higher than
3645 * it needs to be for normal retransmission.
3647 if (tcp_send_head(sk))
3650 if (tp->tlp_high_seq)
3651 tcp_process_tlp_ack(sk, ack, flag);
3655 SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3659 /* If data was SACKed, tag it and see if we should send more data.
3660 * If data was DSACKed, see if we can undo a cwnd reduction.
3662 if (TCP_SKB_CB(skb)->sacked) {
3663 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3665 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3669 SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3673 static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
3674 bool syn, struct tcp_fastopen_cookie *foc,
3677 /* Valid only in SYN or SYN-ACK with an even length. */
3678 if (!foc || !syn || len < 0 || (len & 1))
3681 if (len >= TCP_FASTOPEN_COOKIE_MIN &&
3682 len <= TCP_FASTOPEN_COOKIE_MAX)
3683 memcpy(foc->val, cookie, len);
3690 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3691 * But, this can also be called on packets in the established flow when
3692 * the fast version below fails.
3694 void tcp_parse_options(const struct sk_buff *skb,
3695 struct tcp_options_received *opt_rx, int estab,
3696 struct tcp_fastopen_cookie *foc)
3698 const unsigned char *ptr;
3699 const struct tcphdr *th = tcp_hdr(skb);
3700 int length = (th->doff * 4) - sizeof(struct tcphdr);
3702 ptr = (const unsigned char *)(th + 1);
3703 opt_rx->saw_tstamp = 0;
3705 while (length > 0) {
3706 int opcode = *ptr++;
3712 case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */
3717 if (opsize < 2) /* "silly options" */
3719 if (opsize > length)
3720 return; /* don't parse partial options */
3723 if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3724 u16 in_mss = get_unaligned_be16(ptr);
3726 if (opt_rx->user_mss &&
3727 opt_rx->user_mss < in_mss)
3728 in_mss = opt_rx->user_mss;
3729 opt_rx->mss_clamp = in_mss;
3734 if (opsize == TCPOLEN_WINDOW && th->syn &&
3735 !estab && sysctl_tcp_window_scaling) {
3736 __u8 snd_wscale = *(__u8 *)ptr;
3737 opt_rx->wscale_ok = 1;
3738 if (snd_wscale > 14) {
3739 net_info_ratelimited("%s: Illegal window scaling value %d >14 received\n",
3744 opt_rx->snd_wscale = snd_wscale;
3747 case TCPOPT_TIMESTAMP:
3748 if ((opsize == TCPOLEN_TIMESTAMP) &&
3749 ((estab && opt_rx->tstamp_ok) ||
3750 (!estab && sysctl_tcp_timestamps))) {
3751 opt_rx->saw_tstamp = 1;
3752 opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3753 opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3756 case TCPOPT_SACK_PERM:
3757 if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3758 !estab && sysctl_tcp_sack) {
3759 opt_rx->sack_ok = TCP_SACK_SEEN;
3760 tcp_sack_reset(opt_rx);
3765 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3766 !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3768 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3771 #ifdef CONFIG_TCP_MD5SIG
3774 * The MD5 Hash has already been
3775 * checked (see tcp_v{4,6}_do_rcv()).
3779 case TCPOPT_FASTOPEN:
3780 tcp_parse_fastopen_option(
3781 opsize - TCPOLEN_FASTOPEN_BASE,
3782 ptr, th->syn, foc, false);
3786 /* Fast Open option shares code 254 using a
3787 * 16 bits magic number.
3789 if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
3790 get_unaligned_be16(ptr) ==
3791 TCPOPT_FASTOPEN_MAGIC)
3792 tcp_parse_fastopen_option(opsize -
3793 TCPOLEN_EXP_FASTOPEN_BASE,
3794 ptr + 2, th->syn, foc, true);
3803 EXPORT_SYMBOL(tcp_parse_options);
3805 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
3807 const __be32 *ptr = (const __be32 *)(th + 1);
3809 if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3810 | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3811 tp->rx_opt.saw_tstamp = 1;
3813 tp->rx_opt.rcv_tsval = ntohl(*ptr);
3816 tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
3818 tp->rx_opt.rcv_tsecr = 0;
3824 /* Fast parse options. This hopes to only see timestamps.
3825 * If it is wrong it falls back on tcp_parse_options().
3827 static bool tcp_fast_parse_options(const struct sk_buff *skb,
3828 const struct tcphdr *th, struct tcp_sock *tp)
3830 /* In the spirit of fast parsing, compare doff directly to constant
3831 * values. Because equality is used, short doff can be ignored here.
3833 if (th->doff == (sizeof(*th) / 4)) {
3834 tp->rx_opt.saw_tstamp = 0;
3836 } else if (tp->rx_opt.tstamp_ok &&
3837 th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
3838 if (tcp_parse_aligned_timestamp(tp, th))
3842 tcp_parse_options(skb, &tp->rx_opt, 1, NULL);
3843 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3844 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
3849 #ifdef CONFIG_TCP_MD5SIG
3851 * Parse MD5 Signature option
3853 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
3855 int length = (th->doff << 2) - sizeof(*th);
3856 const u8 *ptr = (const u8 *)(th + 1);
3858 /* If the TCP option is too short, we can short cut */
3859 if (length < TCPOLEN_MD5SIG)
3862 while (length > 0) {
3863 int opcode = *ptr++;
3874 if (opsize < 2 || opsize > length)
3876 if (opcode == TCPOPT_MD5SIG)
3877 return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
3884 EXPORT_SYMBOL(tcp_parse_md5sig_option);
3887 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3889 * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3890 * it can pass through stack. So, the following predicate verifies that
3891 * this segment is not used for anything but congestion avoidance or
3892 * fast retransmit. Moreover, we even are able to eliminate most of such
3893 * second order effects, if we apply some small "replay" window (~RTO)
3894 * to timestamp space.
3896 * All these measures still do not guarantee that we reject wrapped ACKs
3897 * on networks with high bandwidth, when sequence space is recycled fastly,
3898 * but it guarantees that such events will be very rare and do not affect
3899 * connection seriously. This doesn't look nice, but alas, PAWS is really
3902 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3903 * states that events when retransmit arrives after original data are rare.
3904 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3905 * the biggest problem on large power networks even with minor reordering.
3906 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3907 * up to bandwidth of 18Gigabit/sec. 8) ]
3910 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3912 const struct tcp_sock *tp = tcp_sk(sk);
3913 const struct tcphdr *th = tcp_hdr(skb);
3914 u32 seq = TCP_SKB_CB(skb)->seq;
3915 u32 ack = TCP_SKB_CB(skb)->ack_seq;
3917 return (/* 1. Pure ACK with correct sequence number. */
3918 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3920 /* 2. ... and duplicate ACK. */
3921 ack == tp->snd_una &&
3923 /* 3. ... and does not update window. */
3924 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3926 /* 4. ... and sits in replay window. */
3927 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3930 static inline bool tcp_paws_discard(const struct sock *sk,
3931 const struct sk_buff *skb)
3933 const struct tcp_sock *tp = tcp_sk(sk);
3935 return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
3936 !tcp_disordered_ack(sk, skb);
3939 /* Check segment sequence number for validity.
3941 * Segment controls are considered valid, if the segment
3942 * fits to the window after truncation to the window. Acceptability
3943 * of data (and SYN, FIN, of course) is checked separately.
3944 * See tcp_data_queue(), for example.
3946 * Also, controls (RST is main one) are accepted using RCV.WUP instead
3947 * of RCV.NXT. Peer still did not advance his SND.UNA when we
3948 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3949 * (borrowed from freebsd)
3952 static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
3954 return !before(end_seq, tp->rcv_wup) &&
3955 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3958 /* When we get a reset we do this. */
3959 void tcp_reset(struct sock *sk)
3961 /* We want the right error as BSD sees it (and indeed as we do). */
3962 switch (sk->sk_state) {
3964 sk->sk_err = ECONNREFUSED;
3966 case TCP_CLOSE_WAIT:
3972 sk->sk_err = ECONNRESET;
3974 /* This barrier is coupled with smp_rmb() in tcp_poll() */
3977 if (!sock_flag(sk, SOCK_DEAD))
3978 sk->sk_error_report(sk);
3984 * Process the FIN bit. This now behaves as it is supposed to work
3985 * and the FIN takes effect when it is validly part of sequence
3986 * space. Not before when we get holes.
3988 * If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3989 * (and thence onto LAST-ACK and finally, CLOSE, we never enter
3992 * If we are in FINWAIT-1, a received FIN indicates simultaneous
3993 * close and we go into CLOSING (and later onto TIME-WAIT)
3995 * If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3997 static void tcp_fin(struct sock *sk)
3999 struct tcp_sock *tp = tcp_sk(sk);
4001 inet_csk_schedule_ack(sk);
4003 sk->sk_shutdown |= RCV_SHUTDOWN;
4004 sock_set_flag(sk, SOCK_DONE);
4006 switch (sk->sk_state) {
4008 case TCP_ESTABLISHED:
4009 /* Move to CLOSE_WAIT */
4010 tcp_set_state(sk, TCP_CLOSE_WAIT);
4011 inet_csk(sk)->icsk_ack.pingpong = 1;
4014 case TCP_CLOSE_WAIT:
4016 /* Received a retransmission of the FIN, do
4021 /* RFC793: Remain in the LAST-ACK state. */
4025 /* This case occurs when a simultaneous close
4026 * happens, we must ack the received FIN and
4027 * enter the CLOSING state.
4030 tcp_set_state(sk, TCP_CLOSING);
4033 /* Received a FIN -- send ACK and enter TIME_WAIT. */
4035 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4038 /* Only TCP_LISTEN and TCP_CLOSE are left, in these
4039 * cases we should never reach this piece of code.
4041 pr_err("%s: Impossible, sk->sk_state=%d\n",
4042 __func__, sk->sk_state);
4046 /* It _is_ possible, that we have something out-of-order _after_ FIN.
4047 * Probably, we should reset in this case. For now drop them.
4049 __skb_queue_purge(&tp->out_of_order_queue);
4050 if (tcp_is_sack(tp))
4051 tcp_sack_reset(&tp->rx_opt);
4054 if (!sock_flag(sk, SOCK_DEAD)) {
4055 sk->sk_state_change(sk);
4057 /* Do not send POLL_HUP for half duplex close. */
4058 if (sk->sk_shutdown == SHUTDOWN_MASK ||
4059 sk->sk_state == TCP_CLOSE)
4060 sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4062 sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4066 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4069 if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4070 if (before(seq, sp->start_seq))
4071 sp->start_seq = seq;
4072 if (after(end_seq, sp->end_seq))
4073 sp->end_seq = end_seq;
4079 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4081 struct tcp_sock *tp = tcp_sk(sk);
4083 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4086 if (before(seq, tp->rcv_nxt))
4087 mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4089 mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4091 NET_INC_STATS_BH(sock_net(sk), mib_idx);
4093 tp->rx_opt.dsack = 1;
4094 tp->duplicate_sack[0].start_seq = seq;
4095 tp->duplicate_sack[0].end_seq = end_seq;
4099 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4101 struct tcp_sock *tp = tcp_sk(sk);
4103 if (!tp->rx_opt.dsack)
4104 tcp_dsack_set(sk, seq, end_seq);
4106 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4109 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4111 struct tcp_sock *tp = tcp_sk(sk);
4113 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4114 before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4115 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4116 tcp_enter_quickack_mode(sk);
4118 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4119 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4121 if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4122 end_seq = tp->rcv_nxt;
4123 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4130 /* These routines update the SACK block as out-of-order packets arrive or
4131 * in-order packets close up the sequence space.
4133 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4136 struct tcp_sack_block *sp = &tp->selective_acks[0];
4137 struct tcp_sack_block *swalk = sp + 1;
4139 /* See if the recent change to the first SACK eats into
4140 * or hits the sequence space of other SACK blocks, if so coalesce.
4142 for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4143 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4146 /* Zap SWALK, by moving every further SACK up by one slot.
4147 * Decrease num_sacks.
4149 tp->rx_opt.num_sacks--;
4150 for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4154 this_sack++, swalk++;
4158 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4160 struct tcp_sock *tp = tcp_sk(sk);
4161 struct tcp_sack_block *sp = &tp->selective_acks[0];
4162 int cur_sacks = tp->rx_opt.num_sacks;
4168 for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4169 if (tcp_sack_extend(sp, seq, end_seq)) {
4170 /* Rotate this_sack to the first one. */
4171 for (; this_sack > 0; this_sack--, sp--)
4172 swap(*sp, *(sp - 1));
4174 tcp_sack_maybe_coalesce(tp);
4179 /* Could not find an adjacent existing SACK, build a new one,
4180 * put it at the front, and shift everyone else down. We
4181 * always know there is at least one SACK present already here.
4183 * If the sack array is full, forget about the last one.
4185 if (this_sack >= TCP_NUM_SACKS) {
4187 tp->rx_opt.num_sacks--;
4190 for (; this_sack > 0; this_sack--, sp--)
4194 /* Build the new head SACK, and we're done. */
4195 sp->start_seq = seq;
4196 sp->end_seq = end_seq;
4197 tp->rx_opt.num_sacks++;
4200 /* RCV.NXT advances, some SACKs should be eaten. */
4202 static void tcp_sack_remove(struct tcp_sock *tp)
4204 struct tcp_sack_block *sp = &tp->selective_acks[0];
4205 int num_sacks = tp->rx_opt.num_sacks;
4208 /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4209 if (skb_queue_empty(&tp->out_of_order_queue)) {
4210 tp->rx_opt.num_sacks = 0;
4214 for (this_sack = 0; this_sack < num_sacks;) {
4215 /* Check if the start of the sack is covered by RCV.NXT. */
4216 if (!before(tp->rcv_nxt, sp->start_seq)) {
4219 /* RCV.NXT must cover all the block! */
4220 WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4222 /* Zap this SACK, by moving forward any other SACKS. */
4223 for (i = this_sack+1; i < num_sacks; i++)
4224 tp->selective_acks[i-1] = tp->selective_acks[i];
4231 tp->rx_opt.num_sacks = num_sacks;
4235 * tcp_try_coalesce - try to merge skb to prior one
4238 * @from: buffer to add in queue
4239 * @fragstolen: pointer to boolean
4241 * Before queueing skb @from after @to, try to merge them
4242 * to reduce overall memory use and queue lengths, if cost is small.
4243 * Packets in ofo or receive queues can stay a long time.
4244 * Better try to coalesce them right now to avoid future collapses.
4245 * Returns true if caller should free @from instead of queueing it
4247 static bool tcp_try_coalesce(struct sock *sk,
4249 struct sk_buff *from,
4254 *fragstolen = false;
4256 /* Its possible this segment overlaps with prior segment in queue */
4257 if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4260 if (!skb_try_coalesce(to, from, fragstolen, &delta))
4263 atomic_add(delta, &sk->sk_rmem_alloc);
4264 sk_mem_charge(sk, delta);
4265 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4266 TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4267 TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4268 TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4272 /* This one checks to see if we can put data from the
4273 * out_of_order queue into the receive_queue.
4275 static void tcp_ofo_queue(struct sock *sk)
4277 struct tcp_sock *tp = tcp_sk(sk);
4278 __u32 dsack_high = tp->rcv_nxt;
4279 struct sk_buff *skb, *tail;
4280 bool fragstolen, eaten;
4282 while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4283 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4286 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4287 __u32 dsack = dsack_high;
4288 if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4289 dsack_high = TCP_SKB_CB(skb)->end_seq;
4290 tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4293 __skb_unlink(skb, &tp->out_of_order_queue);
4294 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4295 SOCK_DEBUG(sk, "ofo packet was already received\n");
4299 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4300 tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4301 TCP_SKB_CB(skb)->end_seq);
4303 tail = skb_peek_tail(&sk->sk_receive_queue);
4304 eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4305 tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4307 __skb_queue_tail(&sk->sk_receive_queue, skb);
4308 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
4311 kfree_skb_partial(skb, fragstolen);
4315 static bool tcp_prune_ofo_queue(struct sock *sk);
4316 static int tcp_prune_queue(struct sock *sk);
4318 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4321 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4322 !sk_rmem_schedule(sk, skb, size)) {
4324 if (tcp_prune_queue(sk) < 0)
4327 if (!sk_rmem_schedule(sk, skb, size)) {
4328 if (!tcp_prune_ofo_queue(sk))
4331 if (!sk_rmem_schedule(sk, skb, size))
4338 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4340 struct tcp_sock *tp = tcp_sk(sk);
4341 struct sk_buff *skb1;
4344 tcp_ecn_check_ce(tp, skb);
4346 if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4347 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFODROP);
4352 /* Disable header prediction. */
4354 inet_csk_schedule_ack(sk);
4356 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4357 SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4358 tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4360 skb1 = skb_peek_tail(&tp->out_of_order_queue);
4362 /* Initial out of order segment, build 1 SACK. */
4363 if (tcp_is_sack(tp)) {
4364 tp->rx_opt.num_sacks = 1;
4365 tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4366 tp->selective_acks[0].end_seq =
4367 TCP_SKB_CB(skb)->end_seq;
4369 __skb_queue_head(&tp->out_of_order_queue, skb);
4373 seq = TCP_SKB_CB(skb)->seq;
4374 end_seq = TCP_SKB_CB(skb)->end_seq;
4376 if (seq == TCP_SKB_CB(skb1)->end_seq) {
4379 if (!tcp_try_coalesce(sk, skb1, skb, &fragstolen)) {
4380 __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4382 tcp_grow_window(sk, skb);
4383 kfree_skb_partial(skb, fragstolen);
4387 if (!tp->rx_opt.num_sacks ||
4388 tp->selective_acks[0].end_seq != seq)
4391 /* Common case: data arrive in order after hole. */
4392 tp->selective_acks[0].end_seq = end_seq;
4396 /* Find place to insert this segment. */
4398 if (!after(TCP_SKB_CB(skb1)->seq, seq))
4400 if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
4404 skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
4407 /* Do skb overlap to previous one? */
4408 if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4409 if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4410 /* All the bits are present. Drop. */
4411 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4414 tcp_dsack_set(sk, seq, end_seq);
4417 if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4418 /* Partial overlap. */
4419 tcp_dsack_set(sk, seq,
4420 TCP_SKB_CB(skb1)->end_seq);
4422 if (skb_queue_is_first(&tp->out_of_order_queue,
4426 skb1 = skb_queue_prev(
4427 &tp->out_of_order_queue,
4432 __skb_queue_head(&tp->out_of_order_queue, skb);
4434 __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4436 /* And clean segments covered by new one as whole. */
4437 while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
4438 skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
4440 if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4442 if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4443 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4447 __skb_unlink(skb1, &tp->out_of_order_queue);
4448 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4449 TCP_SKB_CB(skb1)->end_seq);
4450 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4455 if (tcp_is_sack(tp))
4456 tcp_sack_new_ofo_skb(sk, seq, end_seq);
4459 tcp_grow_window(sk, skb);
4460 skb_set_owner_r(skb, sk);
4464 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen,
4468 struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4470 __skb_pull(skb, hdrlen);
4472 tcp_try_coalesce(sk, tail, skb, fragstolen)) ? 1 : 0;
4473 tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
4475 __skb_queue_tail(&sk->sk_receive_queue, skb);
4476 skb_set_owner_r(skb, sk);
4481 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4483 struct sk_buff *skb;
4491 if (size > PAGE_SIZE) {
4492 int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
4494 data_len = npages << PAGE_SHIFT;
4495 size = data_len + (size & ~PAGE_MASK);
4497 skb = alloc_skb_with_frags(size - data_len, data_len,
4498 PAGE_ALLOC_COSTLY_ORDER,
4499 &err, sk->sk_allocation);
4503 skb_put(skb, size - data_len);
4504 skb->data_len = data_len;
4507 if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
4510 err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
4514 TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4515 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4516 TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4518 if (tcp_queue_rcv(sk, skb, 0, &fragstolen)) {
4519 WARN_ON_ONCE(fragstolen); /* should not happen */
4531 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4533 struct tcp_sock *tp = tcp_sk(sk);
4535 bool fragstolen = false;
4537 if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4541 __skb_pull(skb, tcp_hdr(skb)->doff * 4);
4543 tcp_ecn_accept_cwr(tp, skb);
4545 tp->rx_opt.dsack = 0;
4547 /* Queue data for delivery to the user.
4548 * Packets in sequence go to the receive queue.
4549 * Out of sequence packets to the out_of_order_queue.
4551 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4552 if (tcp_receive_window(tp) == 0)
4555 /* Ok. In sequence. In window. */
4556 if (tp->ucopy.task == current &&
4557 tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4558 sock_owned_by_user(sk) && !tp->urg_data) {
4559 int chunk = min_t(unsigned int, skb->len,
4562 __set_current_state(TASK_RUNNING);
4565 if (!skb_copy_datagram_msg(skb, 0, tp->ucopy.msg, chunk)) {
4566 tp->ucopy.len -= chunk;
4567 tp->copied_seq += chunk;
4568 eaten = (chunk == skb->len);
4569 tcp_rcv_space_adjust(sk);
4577 if (skb_queue_len(&sk->sk_receive_queue) == 0)
4578 sk_forced_mem_schedule(sk, skb->truesize);
4579 else if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
4582 eaten = tcp_queue_rcv(sk, skb, 0, &fragstolen);
4584 tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4586 tcp_event_data_recv(sk, skb);
4587 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
4590 if (!skb_queue_empty(&tp->out_of_order_queue)) {
4593 /* RFC2581. 4.2. SHOULD send immediate ACK, when
4594 * gap in queue is filled.
4596 if (skb_queue_empty(&tp->out_of_order_queue))
4597 inet_csk(sk)->icsk_ack.pingpong = 0;
4600 if (tp->rx_opt.num_sacks)
4601 tcp_sack_remove(tp);
4603 tcp_fast_path_check(sk);
4606 kfree_skb_partial(skb, fragstolen);
4607 if (!sock_flag(sk, SOCK_DEAD))
4608 sk->sk_data_ready(sk);
4612 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4613 /* A retransmit, 2nd most common case. Force an immediate ack. */
4614 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4615 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4618 tcp_enter_quickack_mode(sk);
4619 inet_csk_schedule_ack(sk);
4625 /* Out of window. F.e. zero window probe. */
4626 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4629 tcp_enter_quickack_mode(sk);
4631 if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4632 /* Partial packet, seq < rcv_next < end_seq */
4633 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4634 tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4635 TCP_SKB_CB(skb)->end_seq);
4637 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4639 /* If window is closed, drop tail of packet. But after
4640 * remembering D-SACK for its head made in previous line.
4642 if (!tcp_receive_window(tp))
4647 tcp_data_queue_ofo(sk, skb);
4650 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4651 struct sk_buff_head *list)
4653 struct sk_buff *next = NULL;
4655 if (!skb_queue_is_last(list, skb))
4656 next = skb_queue_next(list, skb);
4658 __skb_unlink(skb, list);
4660 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4665 /* Collapse contiguous sequence of skbs head..tail with
4666 * sequence numbers start..end.
4668 * If tail is NULL, this means until the end of the list.
4670 * Segments with FIN/SYN are not collapsed (only because this
4674 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4675 struct sk_buff *head, struct sk_buff *tail,
4678 struct sk_buff *skb, *n;
4681 /* First, check that queue is collapsible and find
4682 * the point where collapsing can be useful. */
4686 skb_queue_walk_from_safe(list, skb, n) {
4689 /* No new bits? It is possible on ofo queue. */
4690 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4691 skb = tcp_collapse_one(sk, skb, list);
4697 /* The first skb to collapse is:
4699 * - bloated or contains data before "start" or
4700 * overlaps to the next one.
4702 if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
4703 (tcp_win_from_space(skb->truesize) > skb->len ||
4704 before(TCP_SKB_CB(skb)->seq, start))) {
4705 end_of_skbs = false;
4709 if (!skb_queue_is_last(list, skb)) {
4710 struct sk_buff *next = skb_queue_next(list, skb);
4712 TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
4713 end_of_skbs = false;
4718 /* Decided to skip this, advance start seq. */
4719 start = TCP_SKB_CB(skb)->end_seq;
4722 (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4725 while (before(start, end)) {
4726 int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
4727 struct sk_buff *nskb;
4729 nskb = alloc_skb(copy, GFP_ATOMIC);
4733 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4734 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4735 __skb_queue_before(list, skb, nskb);
4736 skb_set_owner_r(nskb, sk);
4738 /* Copy data, releasing collapsed skbs. */
4740 int offset = start - TCP_SKB_CB(skb)->seq;
4741 int size = TCP_SKB_CB(skb)->end_seq - start;
4745 size = min(copy, size);
4746 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4748 TCP_SKB_CB(nskb)->end_seq += size;
4752 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4753 skb = tcp_collapse_one(sk, skb, list);
4756 (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4763 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4764 * and tcp_collapse() them until all the queue is collapsed.
4766 static void tcp_collapse_ofo_queue(struct sock *sk)
4768 struct tcp_sock *tp = tcp_sk(sk);
4769 struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4770 struct sk_buff *head;
4776 start = TCP_SKB_CB(skb)->seq;
4777 end = TCP_SKB_CB(skb)->end_seq;
4781 struct sk_buff *next = NULL;
4783 if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
4784 next = skb_queue_next(&tp->out_of_order_queue, skb);
4787 /* Segment is terminated when we see gap or when
4788 * we are at the end of all the queue. */
4790 after(TCP_SKB_CB(skb)->seq, end) ||
4791 before(TCP_SKB_CB(skb)->end_seq, start)) {
4792 tcp_collapse(sk, &tp->out_of_order_queue,
4793 head, skb, start, end);
4797 /* Start new segment */
4798 start = TCP_SKB_CB(skb)->seq;
4799 end = TCP_SKB_CB(skb)->end_seq;
4801 if (before(TCP_SKB_CB(skb)->seq, start))
4802 start = TCP_SKB_CB(skb)->seq;
4803 if (after(TCP_SKB_CB(skb)->end_seq, end))
4804 end = TCP_SKB_CB(skb)->end_seq;
4810 * Purge the out-of-order queue.
4811 * Return true if queue was pruned.
4813 static bool tcp_prune_ofo_queue(struct sock *sk)
4815 struct tcp_sock *tp = tcp_sk(sk);
4818 if (!skb_queue_empty(&tp->out_of_order_queue)) {
4819 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
4820 __skb_queue_purge(&tp->out_of_order_queue);
4822 /* Reset SACK state. A conforming SACK implementation will
4823 * do the same at a timeout based retransmit. When a connection
4824 * is in a sad state like this, we care only about integrity
4825 * of the connection not performance.
4827 if (tp->rx_opt.sack_ok)
4828 tcp_sack_reset(&tp->rx_opt);
4835 /* Reduce allocated memory if we can, trying to get
4836 * the socket within its memory limits again.
4838 * Return less than zero if we should start dropping frames
4839 * until the socket owning process reads some of the data
4840 * to stabilize the situation.
4842 static int tcp_prune_queue(struct sock *sk)
4844 struct tcp_sock *tp = tcp_sk(sk);
4846 SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4848 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
4850 if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4851 tcp_clamp_window(sk);
4852 else if (tcp_under_memory_pressure(sk))
4853 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4855 tcp_collapse_ofo_queue(sk);
4856 if (!skb_queue_empty(&sk->sk_receive_queue))
4857 tcp_collapse(sk, &sk->sk_receive_queue,
4858 skb_peek(&sk->sk_receive_queue),
4860 tp->copied_seq, tp->rcv_nxt);
4863 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4866 /* Collapsing did not help, destructive actions follow.
4867 * This must not ever occur. */
4869 tcp_prune_ofo_queue(sk);
4871 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4874 /* If we are really being abused, tell the caller to silently
4875 * drop receive data on the floor. It will get retransmitted
4876 * and hopefully then we'll have sufficient space.
4878 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
4880 /* Massive buffer overcommit. */
4885 static bool tcp_should_expand_sndbuf(const struct sock *sk)
4887 const struct tcp_sock *tp = tcp_sk(sk);
4889 /* If the user specified a specific send buffer setting, do
4892 if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4895 /* If we are under global TCP memory pressure, do not expand. */
4896 if (tcp_under_memory_pressure(sk))
4899 /* If we are under soft global TCP memory pressure, do not expand. */
4900 if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
4903 /* If we filled the congestion window, do not expand. */
4904 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
4910 /* When incoming ACK allowed to free some skb from write_queue,
4911 * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4912 * on the exit from tcp input handler.
4914 * PROBLEM: sndbuf expansion does not work well with largesend.
4916 static void tcp_new_space(struct sock *sk)
4918 struct tcp_sock *tp = tcp_sk(sk);
4920 if (tcp_should_expand_sndbuf(sk)) {
4921 tcp_sndbuf_expand(sk);
4922 tp->snd_cwnd_stamp = tcp_time_stamp;
4925 sk->sk_write_space(sk);
4928 static void tcp_check_space(struct sock *sk)
4930 if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4931 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4932 /* pairs with tcp_poll() */
4933 smp_mb__after_atomic();
4934 if (sk->sk_socket &&
4935 test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4940 static inline void tcp_data_snd_check(struct sock *sk)
4942 tcp_push_pending_frames(sk);
4943 tcp_check_space(sk);
4947 * Check if sending an ack is needed.
4949 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4951 struct tcp_sock *tp = tcp_sk(sk);
4953 /* More than one full frame received... */
4954 if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
4955 /* ... and right edge of window advances far enough.
4956 * (tcp_recvmsg() will send ACK otherwise). Or...
4958 __tcp_select_window(sk) >= tp->rcv_wnd) ||
4959 /* We ACK each frame or... */
4960 tcp_in_quickack_mode(sk) ||
4961 /* We have out of order data. */
4962 (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
4963 /* Then ack it now */
4966 /* Else, send delayed ack. */
4967 tcp_send_delayed_ack(sk);
4971 static inline void tcp_ack_snd_check(struct sock *sk)
4973 if (!inet_csk_ack_scheduled(sk)) {
4974 /* We sent a data segment already. */
4977 __tcp_ack_snd_check(sk, 1);
4981 * This routine is only called when we have urgent data
4982 * signaled. Its the 'slow' part of tcp_urg. It could be
4983 * moved inline now as tcp_urg is only called from one
4984 * place. We handle URGent data wrong. We have to - as
4985 * BSD still doesn't use the correction from RFC961.
4986 * For 1003.1g we should support a new option TCP_STDURG to permit
4987 * either form (or just set the sysctl tcp_stdurg).
4990 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
4992 struct tcp_sock *tp = tcp_sk(sk);
4993 u32 ptr = ntohs(th->urg_ptr);
4995 if (ptr && !sysctl_tcp_stdurg)
4997 ptr += ntohl(th->seq);
4999 /* Ignore urgent data that we've already seen and read. */
5000 if (after(tp->copied_seq, ptr))
5003 /* Do not replay urg ptr.
5005 * NOTE: interesting situation not covered by specs.
5006 * Misbehaving sender may send urg ptr, pointing to segment,
5007 * which we already have in ofo queue. We are not able to fetch
5008 * such data and will stay in TCP_URG_NOTYET until will be eaten
5009 * by recvmsg(). Seems, we are not obliged to handle such wicked
5010 * situations. But it is worth to think about possibility of some
5011 * DoSes using some hypothetical application level deadlock.
5013 if (before(ptr, tp->rcv_nxt))
5016 /* Do we already have a newer (or duplicate) urgent pointer? */
5017 if (tp->urg_data && !after(ptr, tp->urg_seq))
5020 /* Tell the world about our new urgent pointer. */
5023 /* We may be adding urgent data when the last byte read was
5024 * urgent. To do this requires some care. We cannot just ignore
5025 * tp->copied_seq since we would read the last urgent byte again
5026 * as data, nor can we alter copied_seq until this data arrives
5027 * or we break the semantics of SIOCATMARK (and thus sockatmark())
5029 * NOTE. Double Dutch. Rendering to plain English: author of comment
5030 * above did something sort of send("A", MSG_OOB); send("B", MSG_OOB);
5031 * and expect that both A and B disappear from stream. This is _wrong_.
5032 * Though this happens in BSD with high probability, this is occasional.
5033 * Any application relying on this is buggy. Note also, that fix "works"
5034 * only in this artificial test. Insert some normal data between A and B and we will
5035 * decline of BSD again. Verdict: it is better to remove to trap
5038 if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5039 !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5040 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5042 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5043 __skb_unlink(skb, &sk->sk_receive_queue);
5048 tp->urg_data = TCP_URG_NOTYET;
5051 /* Disable header prediction. */
5055 /* This is the 'fast' part of urgent handling. */
5056 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5058 struct tcp_sock *tp = tcp_sk(sk);
5060 /* Check if we get a new urgent pointer - normally not. */
5062 tcp_check_urg(sk, th);
5064 /* Do we wait for any urgent data? - normally not... */
5065 if (tp->urg_data == TCP_URG_NOTYET) {
5066 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5069 /* Is the urgent pointer pointing into this packet? */
5070 if (ptr < skb->len) {
5072 if (skb_copy_bits(skb, ptr, &tmp, 1))
5074 tp->urg_data = TCP_URG_VALID | tmp;
5075 if (!sock_flag(sk, SOCK_DEAD))
5076 sk->sk_data_ready(sk);
5081 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
5083 struct tcp_sock *tp = tcp_sk(sk);
5084 int chunk = skb->len - hlen;
5088 if (skb_csum_unnecessary(skb))
5089 err = skb_copy_datagram_msg(skb, hlen, tp->ucopy.msg, chunk);
5091 err = skb_copy_and_csum_datagram_msg(skb, hlen, tp->ucopy.msg);
5094 tp->ucopy.len -= chunk;
5095 tp->copied_seq += chunk;
5096 tcp_rcv_space_adjust(sk);
5103 static __sum16 __tcp_checksum_complete_user(struct sock *sk,
5104 struct sk_buff *skb)
5108 if (sock_owned_by_user(sk)) {
5110 result = __tcp_checksum_complete(skb);
5113 result = __tcp_checksum_complete(skb);
5118 static inline bool tcp_checksum_complete_user(struct sock *sk,
5119 struct sk_buff *skb)
5121 return !skb_csum_unnecessary(skb) &&
5122 __tcp_checksum_complete_user(sk, skb);
5125 /* Does PAWS and seqno based validation of an incoming segment, flags will
5126 * play significant role here.
5128 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5129 const struct tcphdr *th, int syn_inerr)
5131 struct tcp_sock *tp = tcp_sk(sk);
5133 /* RFC1323: H1. Apply PAWS check first. */
5134 if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
5135 tcp_paws_discard(sk, skb)) {
5137 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5138 if (!tcp_oow_rate_limited(sock_net(sk), skb,
5139 LINUX_MIB_TCPACKSKIPPEDPAWS,
5140 &tp->last_oow_ack_time))
5141 tcp_send_dupack(sk, skb);
5144 /* Reset is accepted even if it did not pass PAWS. */
5147 /* Step 1: check sequence number */
5148 if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5149 /* RFC793, page 37: "In all states except SYN-SENT, all reset
5150 * (RST) segments are validated by checking their SEQ-fields."
5151 * And page 69: "If an incoming segment is not acceptable,
5152 * an acknowledgment should be sent in reply (unless the RST
5153 * bit is set, if so drop the segment and return)".
5158 if (!tcp_oow_rate_limited(sock_net(sk), skb,
5159 LINUX_MIB_TCPACKSKIPPEDSEQ,
5160 &tp->last_oow_ack_time))
5161 tcp_send_dupack(sk, skb);
5166 /* Step 2: check RST bit */
5169 * If sequence number exactly matches RCV.NXT, then
5170 * RESET the connection
5172 * Send a challenge ACK
5174 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt)
5177 tcp_send_challenge_ack(sk, skb);
5181 /* step 3: check security and precedence [ignored] */
5183 /* step 4: Check for a SYN
5184 * RFC 5961 4.2 : Send a challenge ack
5189 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5190 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5191 tcp_send_challenge_ack(sk, skb);
5203 * TCP receive function for the ESTABLISHED state.
5205 * It is split into a fast path and a slow path. The fast path is
5207 * - A zero window was announced from us - zero window probing
5208 * is only handled properly in the slow path.
5209 * - Out of order segments arrived.
5210 * - Urgent data is expected.
5211 * - There is no buffer space left
5212 * - Unexpected TCP flags/window values/header lengths are received
5213 * (detected by checking the TCP header against pred_flags)
5214 * - Data is sent in both directions. Fast path only supports pure senders
5215 * or pure receivers (this means either the sequence number or the ack
5216 * value must stay constant)
5217 * - Unexpected TCP option.
5219 * When these conditions are not satisfied it drops into a standard
5220 * receive procedure patterned after RFC793 to handle all cases.
5221 * The first three cases are guaranteed by proper pred_flags setting,
5222 * the rest is checked inline. Fast processing is turned on in
5223 * tcp_data_queue when everything is OK.
5225 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5226 const struct tcphdr *th, unsigned int len)
5228 struct tcp_sock *tp = tcp_sk(sk);
5230 if (unlikely(!sk->sk_rx_dst))
5231 inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5233 * Header prediction.
5234 * The code loosely follows the one in the famous
5235 * "30 instruction TCP receive" Van Jacobson mail.
5237 * Van's trick is to deposit buffers into socket queue
5238 * on a device interrupt, to call tcp_recv function
5239 * on the receive process context and checksum and copy
5240 * the buffer to user space. smart...
5242 * Our current scheme is not silly either but we take the
5243 * extra cost of the net_bh soft interrupt processing...
5244 * We do checksum and copy also but from device to kernel.
5247 tp->rx_opt.saw_tstamp = 0;
5249 /* pred_flags is 0xS?10 << 16 + snd_wnd
5250 * if header_prediction is to be made
5251 * 'S' will always be tp->tcp_header_len >> 2
5252 * '?' will be 0 for the fast path, otherwise pred_flags is 0 to
5253 * turn it off (when there are holes in the receive
5254 * space for instance)
5255 * PSH flag is ignored.
5258 if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5259 TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5260 !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5261 int tcp_header_len = tp->tcp_header_len;
5263 /* Timestamp header prediction: tcp_header_len
5264 * is automatically equal to th->doff*4 due to pred_flags
5268 /* Check timestamp */
5269 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5270 /* No? Slow path! */
5271 if (!tcp_parse_aligned_timestamp(tp, th))
5274 /* If PAWS failed, check it more carefully in slow path */
5275 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5278 /* DO NOT update ts_recent here, if checksum fails
5279 * and timestamp was corrupted part, it will result
5280 * in a hung connection since we will drop all
5281 * future packets due to the PAWS test.
5285 if (len <= tcp_header_len) {
5286 /* Bulk data transfer: sender */
5287 if (len == tcp_header_len) {
5288 /* Predicted packet is in window by definition.
5289 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5290 * Hence, check seq<=rcv_wup reduces to:
5292 if (tcp_header_len ==
5293 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5294 tp->rcv_nxt == tp->rcv_wup)
5295 tcp_store_ts_recent(tp);
5297 /* We know that such packets are checksummed
5300 tcp_ack(sk, skb, 0);
5302 tcp_data_snd_check(sk);
5304 } else { /* Header too small */
5305 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5310 bool fragstolen = false;
5312 if (tp->ucopy.task == current &&
5313 tp->copied_seq == tp->rcv_nxt &&
5314 len - tcp_header_len <= tp->ucopy.len &&
5315 sock_owned_by_user(sk)) {
5316 __set_current_state(TASK_RUNNING);
5318 if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
5319 /* Predicted packet is in window by definition.
5320 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5321 * Hence, check seq<=rcv_wup reduces to:
5323 if (tcp_header_len ==
5324 (sizeof(struct tcphdr) +
5325 TCPOLEN_TSTAMP_ALIGNED) &&
5326 tp->rcv_nxt == tp->rcv_wup)
5327 tcp_store_ts_recent(tp);
5329 tcp_rcv_rtt_measure_ts(sk, skb);
5331 __skb_pull(skb, tcp_header_len);
5332 tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
5333 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5338 if (tcp_checksum_complete_user(sk, skb))
5341 if ((int)skb->truesize > sk->sk_forward_alloc)
5344 /* Predicted packet is in window by definition.
5345 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5346 * Hence, check seq<=rcv_wup reduces to:
5348 if (tcp_header_len ==
5349 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5350 tp->rcv_nxt == tp->rcv_wup)
5351 tcp_store_ts_recent(tp);
5353 tcp_rcv_rtt_measure_ts(sk, skb);
5355 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5357 /* Bulk data transfer: receiver */
5358 eaten = tcp_queue_rcv(sk, skb, tcp_header_len,
5362 tcp_event_data_recv(sk, skb);
5364 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5365 /* Well, only one small jumplet in fast path... */
5366 tcp_ack(sk, skb, FLAG_DATA);
5367 tcp_data_snd_check(sk);
5368 if (!inet_csk_ack_scheduled(sk))
5372 __tcp_ack_snd_check(sk, 0);
5375 kfree_skb_partial(skb, fragstolen);
5376 sk->sk_data_ready(sk);
5382 if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5385 if (!th->ack && !th->rst && !th->syn)
5389 * Standard slow path.
5392 if (!tcp_validate_incoming(sk, skb, th, 1))
5396 if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
5399 tcp_rcv_rtt_measure_ts(sk, skb);
5401 /* Process urgent data. */
5402 tcp_urg(sk, skb, th);
5404 /* step 7: process the segment text */
5405 tcp_data_queue(sk, skb);
5407 tcp_data_snd_check(sk);
5408 tcp_ack_snd_check(sk);
5412 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_CSUMERRORS);
5413 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5418 EXPORT_SYMBOL(tcp_rcv_established);
5420 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
5422 struct tcp_sock *tp = tcp_sk(sk);
5423 struct inet_connection_sock *icsk = inet_csk(sk);
5425 tcp_set_state(sk, TCP_ESTABLISHED);
5428 icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
5429 security_inet_conn_established(sk, skb);
5432 /* Make sure socket is routed, for correct metrics. */
5433 icsk->icsk_af_ops->rebuild_header(sk);
5435 tcp_init_metrics(sk);
5437 tcp_init_congestion_control(sk);
5439 /* Prevent spurious tcp_cwnd_restart() on first data
5442 tp->lsndtime = tcp_time_stamp;
5444 tcp_init_buffer_space(sk);
5446 if (sock_flag(sk, SOCK_KEEPOPEN))
5447 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5449 if (!tp->rx_opt.snd_wscale)
5450 __tcp_fast_path_on(tp, tp->snd_wnd);
5454 if (!sock_flag(sk, SOCK_DEAD)) {
5455 sk->sk_state_change(sk);
5456 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5460 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
5461 struct tcp_fastopen_cookie *cookie)
5463 struct tcp_sock *tp = tcp_sk(sk);
5464 struct sk_buff *data = tp->syn_data ? tcp_write_queue_head(sk) : NULL;
5465 u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
5466 bool syn_drop = false;
5468 if (mss == tp->rx_opt.user_mss) {
5469 struct tcp_options_received opt;
5471 /* Get original SYNACK MSS value if user MSS sets mss_clamp */
5472 tcp_clear_options(&opt);
5473 opt.user_mss = opt.mss_clamp = 0;
5474 tcp_parse_options(synack, &opt, 0, NULL);
5475 mss = opt.mss_clamp;
5478 if (!tp->syn_fastopen) {
5479 /* Ignore an unsolicited cookie */
5481 } else if (tp->total_retrans) {
5482 /* SYN timed out and the SYN-ACK neither has a cookie nor
5483 * acknowledges data. Presumably the remote received only
5484 * the retransmitted (regular) SYNs: either the original
5485 * SYN-data or the corresponding SYN-ACK was dropped.
5487 syn_drop = (cookie->len < 0 && data);
5488 } else if (cookie->len < 0 && !tp->syn_data) {
5489 /* We requested a cookie but didn't get it. If we did not use
5490 * the (old) exp opt format then try so next time (try_exp=1).
5491 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
5493 try_exp = tp->syn_fastopen_exp ? 2 : 1;
5496 tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
5498 if (data) { /* Retransmit unacked data in SYN */
5499 tcp_for_write_queue_from(data, sk) {
5500 if (data == tcp_send_head(sk) ||
5501 __tcp_retransmit_skb(sk, data))
5505 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
5508 tp->syn_data_acked = tp->syn_data;
5509 if (tp->syn_data_acked)
5510 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
5514 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5515 const struct tcphdr *th)
5517 struct inet_connection_sock *icsk = inet_csk(sk);
5518 struct tcp_sock *tp = tcp_sk(sk);
5519 struct tcp_fastopen_cookie foc = { .len = -1 };
5520 int saved_clamp = tp->rx_opt.mss_clamp;
5522 tcp_parse_options(skb, &tp->rx_opt, 0, &foc);
5523 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
5524 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
5528 * "If the state is SYN-SENT then
5529 * first check the ACK bit
5530 * If the ACK bit is set
5531 * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5532 * a reset (unless the RST bit is set, if so drop
5533 * the segment and return)"
5535 if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
5536 after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
5537 goto reset_and_undo;
5539 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5540 !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5542 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
5543 goto reset_and_undo;
5546 /* Now ACK is acceptable.
5548 * "If the RST bit is set
5549 * If the ACK was acceptable then signal the user "error:
5550 * connection reset", drop the segment, enter CLOSED state,
5551 * delete TCB, and return."
5560 * "fifth, if neither of the SYN or RST bits is set then
5561 * drop the segment and return."
5567 goto discard_and_undo;
5570 * "If the SYN bit is on ...
5571 * are acceptable then ...
5572 * (our SYN has been ACKed), change the connection
5573 * state to ESTABLISHED..."
5576 tcp_ecn_rcv_synack(tp, th);
5578 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5579 tcp_ack(sk, skb, FLAG_SLOWPATH);
5581 /* Ok.. it's good. Set up sequence numbers and
5582 * move to established.
5584 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5585 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5587 /* RFC1323: The window in SYN & SYN/ACK segments is
5590 tp->snd_wnd = ntohs(th->window);
5592 if (!tp->rx_opt.wscale_ok) {
5593 tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5594 tp->window_clamp = min(tp->window_clamp, 65535U);
5597 if (tp->rx_opt.saw_tstamp) {
5598 tp->rx_opt.tstamp_ok = 1;
5599 tp->tcp_header_len =
5600 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5601 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5602 tcp_store_ts_recent(tp);
5604 tp->tcp_header_len = sizeof(struct tcphdr);
5607 if (tcp_is_sack(tp) && sysctl_tcp_fack)
5608 tcp_enable_fack(tp);
5611 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5612 tcp_initialize_rcv_mss(sk);
5614 /* Remember, tcp_poll() does not lock socket!
5615 * Change state from SYN-SENT only after copied_seq
5616 * is initialized. */
5617 tp->copied_seq = tp->rcv_nxt;
5621 tcp_finish_connect(sk, skb);
5623 if ((tp->syn_fastopen || tp->syn_data) &&
5624 tcp_rcv_fastopen_synack(sk, skb, &foc))
5627 if (sk->sk_write_pending ||
5628 icsk->icsk_accept_queue.rskq_defer_accept ||
5629 icsk->icsk_ack.pingpong) {
5630 /* Save one ACK. Data will be ready after
5631 * several ticks, if write_pending is set.
5633 * It may be deleted, but with this feature tcpdumps
5634 * look so _wonderfully_ clever, that I was not able
5635 * to stand against the temptation 8) --ANK
5637 inet_csk_schedule_ack(sk);
5638 icsk->icsk_ack.lrcvtime = tcp_time_stamp;
5639 tcp_enter_quickack_mode(sk);
5640 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5641 TCP_DELACK_MAX, TCP_RTO_MAX);
5652 /* No ACK in the segment */
5656 * "If the RST bit is set
5658 * Otherwise (no ACK) drop the segment and return."
5661 goto discard_and_undo;
5665 if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5666 tcp_paws_reject(&tp->rx_opt, 0))
5667 goto discard_and_undo;
5670 /* We see SYN without ACK. It is attempt of
5671 * simultaneous connect with crossed SYNs.
5672 * Particularly, it can be connect to self.
5674 tcp_set_state(sk, TCP_SYN_RECV);
5676 if (tp->rx_opt.saw_tstamp) {
5677 tp->rx_opt.tstamp_ok = 1;
5678 tcp_store_ts_recent(tp);
5679 tp->tcp_header_len =
5680 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5682 tp->tcp_header_len = sizeof(struct tcphdr);
5685 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5686 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5688 /* RFC1323: The window in SYN & SYN/ACK segments is
5691 tp->snd_wnd = ntohs(th->window);
5692 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
5693 tp->max_window = tp->snd_wnd;
5695 tcp_ecn_rcv_syn(tp, th);
5698 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5699 tcp_initialize_rcv_mss(sk);
5701 tcp_send_synack(sk);
5703 /* Note, we could accept data and URG from this segment.
5704 * There are no obstacles to make this (except that we must
5705 * either change tcp_recvmsg() to prevent it from returning data
5706 * before 3WHS completes per RFC793, or employ TCP Fast Open).
5708 * However, if we ignore data in ACKless segments sometimes,
5709 * we have no reasons to accept it sometimes.
5710 * Also, seems the code doing it in step6 of tcp_rcv_state_process
5711 * is not flawless. So, discard packet for sanity.
5712 * Uncomment this return to process the data.
5719 /* "fifth, if neither of the SYN or RST bits is set then
5720 * drop the segment and return."
5724 tcp_clear_options(&tp->rx_opt);
5725 tp->rx_opt.mss_clamp = saved_clamp;
5729 tcp_clear_options(&tp->rx_opt);
5730 tp->rx_opt.mss_clamp = saved_clamp;
5735 * This function implements the receiving procedure of RFC 793 for
5736 * all states except ESTABLISHED and TIME_WAIT.
5737 * It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5738 * address independent.
5741 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
5743 struct tcp_sock *tp = tcp_sk(sk);
5744 struct inet_connection_sock *icsk = inet_csk(sk);
5745 const struct tcphdr *th = tcp_hdr(skb);
5746 struct request_sock *req;
5750 tp->rx_opt.saw_tstamp = 0;
5752 switch (sk->sk_state) {
5766 if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
5769 /* Now we have several options: In theory there is
5770 * nothing else in the frame. KA9Q has an option to
5771 * send data with the syn, BSD accepts data with the
5772 * syn up to the [to be] advertised window and
5773 * Solaris 2.1 gives you a protocol error. For now
5774 * we just ignore it, that fits the spec precisely
5775 * and avoids incompatibilities. It would be nice in
5776 * future to drop through and process the data.
5778 * Now that TTCP is starting to be used we ought to
5780 * But, this leaves one open to an easy denial of
5781 * service attack, and SYN cookies can't defend
5782 * against this problem. So, we drop the data
5783 * in the interest of security over speed unless
5784 * it's still in use.
5792 queued = tcp_rcv_synsent_state_process(sk, skb, th);
5796 /* Do step6 onward by hand. */
5797 tcp_urg(sk, skb, th);
5799 tcp_data_snd_check(sk);
5803 req = tp->fastopen_rsk;
5805 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
5806 sk->sk_state != TCP_FIN_WAIT1);
5808 if (!tcp_check_req(sk, skb, req, true))
5812 if (!th->ack && !th->rst && !th->syn)
5815 if (!tcp_validate_incoming(sk, skb, th, 0))
5818 /* step 5: check the ACK field */
5819 acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
5820 FLAG_UPDATE_TS_RECENT) > 0;
5822 switch (sk->sk_state) {
5828 tcp_synack_rtt_meas(sk, req);
5830 /* Once we leave TCP_SYN_RECV, we no longer need req
5834 tp->total_retrans = req->num_retrans;
5835 reqsk_fastopen_remove(sk, req, false);
5837 /* Make sure socket is routed, for correct metrics. */
5838 icsk->icsk_af_ops->rebuild_header(sk);
5839 tcp_init_congestion_control(sk);
5842 tp->copied_seq = tp->rcv_nxt;
5843 tcp_init_buffer_space(sk);
5846 tcp_set_state(sk, TCP_ESTABLISHED);
5847 sk->sk_state_change(sk);
5849 /* Note, that this wakeup is only for marginal crossed SYN case.
5850 * Passively open sockets are not waked up, because
5851 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
5854 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5856 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5857 tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
5858 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5860 if (tp->rx_opt.tstamp_ok)
5861 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5864 /* Re-arm the timer because data may have been sent out.
5865 * This is similar to the regular data transmission case
5866 * when new data has just been ack'ed.
5868 * (TFO) - we could try to be more aggressive and
5869 * retransmitting any data sooner based on when they
5874 tcp_init_metrics(sk);
5876 tcp_update_pacing_rate(sk);
5878 /* Prevent spurious tcp_cwnd_restart() on first data packet */
5879 tp->lsndtime = tcp_time_stamp;
5881 tcp_initialize_rcv_mss(sk);
5882 tcp_fast_path_on(tp);
5885 case TCP_FIN_WAIT1: {
5886 struct dst_entry *dst;
5889 /* If we enter the TCP_FIN_WAIT1 state and we are a
5890 * Fast Open socket and this is the first acceptable
5891 * ACK we have received, this would have acknowledged
5892 * our SYNACK so stop the SYNACK timer.
5895 /* Return RST if ack_seq is invalid.
5896 * Note that RFC793 only says to generate a
5897 * DUPACK for it but for TCP Fast Open it seems
5898 * better to treat this case like TCP_SYN_RECV
5903 /* We no longer need the request sock. */
5904 reqsk_fastopen_remove(sk, req, false);
5907 if (tp->snd_una != tp->write_seq)
5910 tcp_set_state(sk, TCP_FIN_WAIT2);
5911 sk->sk_shutdown |= SEND_SHUTDOWN;
5913 dst = __sk_dst_get(sk);
5917 if (!sock_flag(sk, SOCK_DEAD)) {
5918 /* Wake up lingering close() */
5919 sk->sk_state_change(sk);
5923 if (tp->linger2 < 0 ||
5924 (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5925 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5927 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5931 tmo = tcp_fin_time(sk);
5932 if (tmo > TCP_TIMEWAIT_LEN) {
5933 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5934 } else if (th->fin || sock_owned_by_user(sk)) {
5935 /* Bad case. We could lose such FIN otherwise.
5936 * It is not a big problem, but it looks confusing
5937 * and not so rare event. We still can lose it now,
5938 * if it spins in bh_lock_sock(), but it is really
5941 inet_csk_reset_keepalive_timer(sk, tmo);
5943 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5950 if (tp->snd_una == tp->write_seq) {
5951 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
5957 if (tp->snd_una == tp->write_seq) {
5958 tcp_update_metrics(sk);
5965 /* step 6: check the URG bit */
5966 tcp_urg(sk, skb, th);
5968 /* step 7: process the segment text */
5969 switch (sk->sk_state) {
5970 case TCP_CLOSE_WAIT:
5973 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5977 /* RFC 793 says to queue data in these states,
5978 * RFC 1122 says we MUST send a reset.
5979 * BSD 4.4 also does reset.
5981 if (sk->sk_shutdown & RCV_SHUTDOWN) {
5982 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5983 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
5984 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5990 case TCP_ESTABLISHED:
5991 tcp_data_queue(sk, skb);
5996 /* tcp_data could move socket to TIME-WAIT */
5997 if (sk->sk_state != TCP_CLOSE) {
5998 tcp_data_snd_check(sk);
5999 tcp_ack_snd_check(sk);
6008 EXPORT_SYMBOL(tcp_rcv_state_process);
6010 static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
6012 struct inet_request_sock *ireq = inet_rsk(req);
6014 if (family == AF_INET)
6015 net_dbg_ratelimited("drop open request from %pI4/%u\n",
6016 &ireq->ir_rmt_addr, port);
6017 #if IS_ENABLED(CONFIG_IPV6)
6018 else if (family == AF_INET6)
6019 net_dbg_ratelimited("drop open request from %pI6/%u\n",
6020 &ireq->ir_v6_rmt_addr, port);
6024 /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
6026 * If we receive a SYN packet with these bits set, it means a
6027 * network is playing bad games with TOS bits. In order to
6028 * avoid possible false congestion notifications, we disable
6029 * TCP ECN negotiation.
6031 * Exception: tcp_ca wants ECN. This is required for DCTCP
6032 * congestion control: Linux DCTCP asserts ECT on all packets,
6033 * including SYN, which is most optimal solution; however,
6034 * others, such as FreeBSD do not.
6036 static void tcp_ecn_create_request(struct request_sock *req,
6037 const struct sk_buff *skb,
6038 const struct sock *listen_sk,
6039 const struct dst_entry *dst)
6041 const struct tcphdr *th = tcp_hdr(skb);
6042 const struct net *net = sock_net(listen_sk);
6043 bool th_ecn = th->ece && th->cwr;
6050 ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
6051 ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
6052 ecn_ok = net->ipv4.sysctl_tcp_ecn || ecn_ok_dst;
6054 if ((!ect && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
6055 (ecn_ok_dst & DST_FEATURE_ECN_CA))
6056 inet_rsk(req)->ecn_ok = 1;
6059 static void tcp_openreq_init(struct request_sock *req,
6060 const struct tcp_options_received *rx_opt,
6061 struct sk_buff *skb, const struct sock *sk)
6063 struct inet_request_sock *ireq = inet_rsk(req);
6065 req->rsk_rcv_wnd = 0; /* So that tcp_send_synack() knows! */
6067 tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
6068 tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
6069 skb_mstamp_get(&tcp_rsk(req)->snt_synack);
6070 tcp_rsk(req)->last_oow_ack_time = 0;
6071 req->mss = rx_opt->mss_clamp;
6072 req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
6073 ireq->tstamp_ok = rx_opt->tstamp_ok;
6074 ireq->sack_ok = rx_opt->sack_ok;
6075 ireq->snd_wscale = rx_opt->snd_wscale;
6076 ireq->wscale_ok = rx_opt->wscale_ok;
6079 ireq->ir_rmt_port = tcp_hdr(skb)->source;
6080 ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
6081 ireq->ir_mark = inet_request_mark(sk, skb);
6084 struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
6085 struct sock *sk_listener,
6086 bool attach_listener)
6088 struct request_sock *req = reqsk_alloc(ops, sk_listener,
6092 struct inet_request_sock *ireq = inet_rsk(req);
6094 kmemcheck_annotate_bitfield(ireq, flags);
6096 atomic64_set(&ireq->ir_cookie, 0);
6097 ireq->ireq_state = TCP_NEW_SYN_RECV;
6098 write_pnet(&ireq->ireq_net, sock_net(sk_listener));
6099 ireq->ireq_family = sk_listener->sk_family;
6104 EXPORT_SYMBOL(inet_reqsk_alloc);
6107 * Return true if a syncookie should be sent
6109 static bool tcp_syn_flood_action(const struct sock *sk,
6110 const struct sk_buff *skb,
6113 struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
6114 const char *msg = "Dropping request";
6115 bool want_cookie = false;
6117 #ifdef CONFIG_SYN_COOKIES
6118 if (sysctl_tcp_syncookies) {
6119 msg = "Sending cookies";
6121 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
6124 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
6126 if (!queue->synflood_warned &&
6127 sysctl_tcp_syncookies != 2 &&
6128 xchg(&queue->synflood_warned, 1) == 0)
6129 pr_info("%s: Possible SYN flooding on port %d. %s. Check SNMP counters.\n",
6130 proto, ntohs(tcp_hdr(skb)->dest), msg);
6135 static void tcp_reqsk_record_syn(const struct sock *sk,
6136 struct request_sock *req,
6137 const struct sk_buff *skb)
6139 if (tcp_sk(sk)->save_syn) {
6140 u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
6143 copy = kmalloc(len + sizeof(u32), GFP_ATOMIC);
6146 memcpy(©[1], skb_network_header(skb), len);
6147 req->saved_syn = copy;
6152 int tcp_conn_request(struct request_sock_ops *rsk_ops,
6153 const struct tcp_request_sock_ops *af_ops,
6154 struct sock *sk, struct sk_buff *skb)
6156 struct tcp_fastopen_cookie foc = { .len = -1 };
6157 __u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
6158 struct tcp_options_received tmp_opt;
6159 struct tcp_sock *tp = tcp_sk(sk);
6160 struct sock *fastopen_sk = NULL;
6161 struct dst_entry *dst = NULL;
6162 struct request_sock *req;
6163 bool want_cookie = false;
6166 /* TW buckets are converted to open requests without
6167 * limitations, they conserve resources and peer is
6168 * evidently real one.
6170 if ((sysctl_tcp_syncookies == 2 ||
6171 inet_csk_reqsk_queue_is_full(sk)) && !isn) {
6172 want_cookie = tcp_syn_flood_action(sk, skb, rsk_ops->slab_name);
6178 /* Accept backlog is full. If we have already queued enough
6179 * of warm entries in syn queue, drop request. It is better than
6180 * clogging syn queue with openreqs with exponentially increasing
6183 if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) {
6184 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6188 req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
6192 tcp_rsk(req)->af_specific = af_ops;
6194 tcp_clear_options(&tmp_opt);
6195 tmp_opt.mss_clamp = af_ops->mss_clamp;
6196 tmp_opt.user_mss = tp->rx_opt.user_mss;
6197 tcp_parse_options(skb, &tmp_opt, 0, want_cookie ? NULL : &foc);
6199 if (want_cookie && !tmp_opt.saw_tstamp)
6200 tcp_clear_options(&tmp_opt);
6202 tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
6203 tcp_openreq_init(req, &tmp_opt, skb, sk);
6205 /* Note: tcp_v6_init_req() might override ir_iif for link locals */
6206 inet_rsk(req)->ir_iif = sk->sk_bound_dev_if;
6208 af_ops->init_req(req, sk, skb);
6210 if (security_inet_conn_request(sk, skb, req))
6213 if (!want_cookie && !isn) {
6214 /* VJ's idea. We save last timestamp seen
6215 * from the destination in peer table, when entering
6216 * state TIME-WAIT, and check against it before
6217 * accepting new connection request.
6219 * If "isn" is not zero, this request hit alive
6220 * timewait bucket, so that all the necessary checks
6221 * are made in the function processing timewait state.
6223 if (tcp_death_row.sysctl_tw_recycle) {
6226 dst = af_ops->route_req(sk, &fl, req, &strict);
6228 if (dst && strict &&
6229 !tcp_peer_is_proven(req, dst, true,
6230 tmp_opt.saw_tstamp)) {
6231 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSPASSIVEREJECTED);
6232 goto drop_and_release;
6235 /* Kill the following clause, if you dislike this way. */
6236 else if (!sysctl_tcp_syncookies &&
6237 (sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
6238 (sysctl_max_syn_backlog >> 2)) &&
6239 !tcp_peer_is_proven(req, dst, false,
6240 tmp_opt.saw_tstamp)) {
6241 /* Without syncookies last quarter of
6242 * backlog is filled with destinations,
6243 * proven to be alive.
6244 * It means that we continue to communicate
6245 * to destinations, already remembered
6246 * to the moment of synflood.
6248 pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
6250 goto drop_and_release;
6253 isn = af_ops->init_seq(skb);
6256 dst = af_ops->route_req(sk, &fl, req, NULL);
6261 tcp_ecn_create_request(req, skb, sk, dst);
6264 isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
6265 req->cookie_ts = tmp_opt.tstamp_ok;
6266 if (!tmp_opt.tstamp_ok)
6267 inet_rsk(req)->ecn_ok = 0;
6270 tcp_rsk(req)->snt_isn = isn;
6271 tcp_rsk(req)->txhash = net_tx_rndhash();
6272 tcp_openreq_init_rwin(req, sk, dst);
6274 tcp_reqsk_record_syn(sk, req, skb);
6275 fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
6278 af_ops->send_synack(fastopen_sk, dst, &fl, req,
6280 /* Add the child socket directly into the accept queue */
6281 inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
6282 sk->sk_data_ready(sk);
6283 bh_unlock_sock(fastopen_sk);
6284 sock_put(fastopen_sk);
6286 tcp_rsk(req)->tfo_listener = false;
6288 inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
6289 af_ops->send_synack(sk, dst, &fl, req,
6290 &foc, !want_cookie);
6302 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
6305 EXPORT_SYMBOL(tcp_conn_request);