blob: 731d3045b50a0fb9a89c887a154db9a3da8c7ddd [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0
/*
* INET An implementation of the TCP/IP protocol suite for the LINUX
* operating system. INET is implemented using the BSD Socket
* interface as the means of communication with the user level.
*
* Implementation of the Transmission Control Protocol(TCP).
*
* Authors: Ross Biro
* Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
* Mark Evans, <evansmp@uhura.aston.ac.uk>
* Corey Minyard <wf-rch!minyard@relay.EU.net>
* Florian La Roche, <flla@stud.uni-sb.de>
* Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
* Linus Torvalds, <torvalds@cs.helsinki.fi>
* Alan Cox, <gw4pts@gw4pts.ampr.org>
* Matthew Dillon, <dillon@apollo.west.oic.com>
* Arnt Gulbrandsen, <agulbra@nvg.unit.no>
* Jorge Cwik, <jorge@laser.satlink.net>
*/
/*
* Changes:
* Pedro Roque : Fast Retransmit/Recovery.
* Two receive queues.
* Retransmit queue handled by TCP.
* Better retransmit timer handling.
* New congestion avoidance.
* Header prediction.
* Variable renaming.
*
* Eric : Fast Retransmit.
* Randy Scott : MSS option defines.
* Eric Schenk : Fixes to slow start algorithm.
* Eric Schenk : Yet another double ACK bug.
* Eric Schenk : Delayed ACK bug fixes.
* Eric Schenk : Floyd style fast retrans war avoidance.
* David S. Miller : Don't allow zero congestion window.
* Eric Schenk : Fix retransmitter so that it sends
* next packet on ack of previous packet.
* Andi Kleen : Moved open_request checking here
* and process RSTs for open_requests.
* Andi Kleen : Better prune_queue, and other fixes.
* Andrey Savochkin: Fix RTT measurements in the presence of
* timestamps.
* Andrey Savochkin: Check sequence numbers correctly when
* removing SACKs due to in sequence incoming
* data segments.
* Andi Kleen: Make sure we never ack data there is not
* enough room for. Also make this condition
* a fatal error if it might still happen.
* Andi Kleen: Add tcp_measure_rcv_mss to make
* connections with MSS<min(MTU,ann. MSS)
* work without delayed acks.
* Andi Kleen: Process packets with PSH set in the
* fast path.
* J Hadi Salim: ECN support
* Andrei Gurtov,
* Pasi Sarolahti,
* Panu Kuhlberg: Experimental audit of TCP (re)transmission
* engine. Lots of bugs are found.
* Pasi Sarolahti: F-RTO for dealing with spurious RTOs
*/
#define pr_fmt(fmt) "TCP: " fmt
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/sysctl.h>
#include <linux/kernel.h>
#include <linux/prefetch.h>
#include <net/dst.h>
#include <net/tcp.h>
#include <net/inet_common.h>
#include <linux/ipsec.h>
#include <asm/unaligned.h>
#include <linux/errqueue.h>
#include <trace/events/tcp.h>
#include <linux/static_key.h>
#include <net/busy_poll.h>
int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
#define FLAG_DATA 0x01 /* Incoming frame contained data. */
#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */
#define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */
#define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */
#define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */
#define FLAG_DATA_SACKED 0x20 /* New SACK. */
#define FLAG_ECE 0x40 /* ECE in this ACK */
#define FLAG_LOST_RETRANS 0x80 /* This ACK marks some retransmission lost */
#define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/
#define FLAG_ORIG_SACK_ACKED 0x200 /* Never retransmitted data are (s)acked */
#define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
#define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */
#define FLAG_SET_XMIT_TIMER 0x1000 /* Set TLP or RTO timer */
#define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */
#define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */
#define FLAG_NO_CHALLENGE_ACK 0x8000 /* do not call tcp_send_challenge_ack() */
#define FLAG_ACK_MAYBE_DELAYED 0x10000 /* Likely a delayed ACK */
#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
#define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
#define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED)
#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
#define REXMIT_NONE 0 /* no loss recovery to do */
#define REXMIT_LOST 1 /* retransmit packets marked lost */
#define REXMIT_NEW 2 /* FRTO-style transmit of unsent/new packets */
#if IS_ENABLED(CONFIG_TLS_DEVICE)
static DEFINE_STATIC_KEY_FALSE(clean_acked_data_enabled);
void clean_acked_data_enable(struct inet_connection_sock *icsk,
void (*cad)(struct sock *sk, u32 ack_seq))
{
icsk->icsk_clean_acked = cad;
static_branch_inc(&clean_acked_data_enabled);
}
EXPORT_SYMBOL_GPL(clean_acked_data_enable);
void clean_acked_data_disable(struct inet_connection_sock *icsk)
{
static_branch_dec(&clean_acked_data_enabled);
icsk->icsk_clean_acked = NULL;
}
EXPORT_SYMBOL_GPL(clean_acked_data_disable);
#endif
static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
unsigned int len)
{
static bool __once __read_mostly;
if (!__once) {
struct net_device *dev;
__once = true;
rcu_read_lock();
dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
if (!dev || len >= dev->mtu)
pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
dev ? dev->name : "Unknown driver");
rcu_read_unlock();
}
}
/* Adapt the MSS value used to make delayed ack decision to the
* real world.
*/
static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
{
struct inet_connection_sock *icsk = inet_csk(sk);
const unsigned int lss = icsk->icsk_ack.last_seg_size;
unsigned int len;
icsk->icsk_ack.last_seg_size = 0;
/* skb->len may jitter because of SACKs, even if peer
* sends good full-sized frames.
*/
len = skb_shinfo(skb)->gso_size ? : skb->len;
if (len >= icsk->icsk_ack.rcv_mss) {
icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
tcp_sk(sk)->advmss);
/* Account for possibly-removed options */
if (unlikely(len > icsk->icsk_ack.rcv_mss +
MAX_TCP_OPTION_SPACE))
tcp_gro_dev_warn(sk, skb, len);
} else {
/* Otherwise, we make more careful check taking into account,
* that SACKs block is variable.
*
* "len" is invariant segment length, including TCP header.
*/
len += skb->data - skb_transport_header(skb);
if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
/* If PSH is not set, packet should be
* full sized, provided peer TCP is not badly broken.
* This observation (if it is correct 8)) allows
* to handle super-low mtu links fairly.
*/
(len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
!(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
/* Subtract also invariant (if peer is RFC compliant),
* tcp header plus fixed timestamp option length.
* Resulting "len" is MSS free of SACK jitter.
*/
len -= tcp_sk(sk)->tcp_header_len;
icsk->icsk_ack.last_seg_size = len;
if (len == lss) {
icsk->icsk_ack.rcv_mss = len;
return;
}
}
if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
}
}
static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks)
{
struct inet_connection_sock *icsk = inet_csk(sk);
unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
if (quickacks == 0)
quickacks = 2;
quickacks = min(quickacks, max_quickacks);
if (quickacks > icsk->icsk_ack.quick)
icsk->icsk_ack.quick = quickacks;
}
void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
{
struct inet_connection_sock *icsk = inet_csk(sk);
tcp_incr_quickack(sk, max_quickacks);
inet_csk_exit_pingpong_mode(sk);
icsk->icsk_ack.ato = TCP_ATO_MIN;
}
EXPORT_SYMBOL(tcp_enter_quickack_mode);
/* Send ACKs quickly, if "quick" count is not exhausted
* and the session is not interactive.
*/
static bool tcp_in_quickack_mode(struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
const struct dst_entry *dst = __sk_dst_get(sk);
return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
(icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk));
}
static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
{
if (tp->ecn_flags & TCP_ECN_OK)
tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
}
static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb)
{
if (tcp_hdr(skb)->cwr) {
tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
/* If the sender is telling us it has entered CWR, then its
* cwnd may be very low (even just 1 packet), so we should ACK
* immediately.
*/
inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
}
}
static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
{
tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
}
static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
case INET_ECN_NOT_ECT:
/* Funny extension: if ECT is not set on a segment,
* and we already seen ECT on a previous segment,
* it is probably a retransmit.
*/
if (tp->ecn_flags & TCP_ECN_SEEN)
tcp_enter_quickack_mode(sk, 2);
break;
case INET_ECN_CE:
if (tcp_ca_needs_ecn(sk))
tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
/* Better not delay acks, sender can have a very low cwnd */
tcp_enter_quickack_mode(sk, 2);
tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
}
tp->ecn_flags |= TCP_ECN_SEEN;
break;
default:
if (tcp_ca_needs_ecn(sk))
tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
tp->ecn_flags |= TCP_ECN_SEEN;
break;
}
}
static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
{
if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK)
__tcp_ecn_check_ce(sk, skb);
}
static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
{
if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
tp->ecn_flags &= ~TCP_ECN_OK;
}
static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
{
if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
tp->ecn_flags &= ~TCP_ECN_OK;
}
static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
{
if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
return true;
return false;
}
/* Buffer size and advertised window tuning.
*
* 1. Tuning sk->sk_sndbuf, when connection enters established state.
*/
static void tcp_sndbuf_expand(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
int sndmem, per_mss;
u32 nr_segs;
/* Worst case is non GSO/TSO : each frame consumes one skb
* and skb->head is kmalloced using power of two area of memory
*/
per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
MAX_TCP_HEADER +
SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
per_mss = roundup_pow_of_two(per_mss) +
SKB_DATA_ALIGN(sizeof(struct sk_buff));
nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
/* Fast Recovery (RFC 5681 3.2) :
* Cubic needs 1.7 factor, rounded to 2 to include
* extra cushion (application might react slowly to EPOLLOUT)
*/
sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
sndmem *= nr_segs * per_mss;
if (sk->sk_sndbuf < sndmem)
sk->sk_sndbuf = min(sndmem, sock_net(sk)->ipv4.sysctl_tcp_wmem[2]);
}
/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
*
* All tcp_full_space() is split to two parts: "network" buffer, allocated
* forward and advertised in receiver window (tp->rcv_wnd) and
* "application buffer", required to isolate scheduling/application
* latencies from network.
* window_clamp is maximal advertised window. It can be less than
* tcp_full_space(), in this case tcp_full_space() - window_clamp
* is reserved for "application" buffer. The less window_clamp is
* the smoother our behaviour from viewpoint of network, but the lower
* throughput and the higher sensitivity of the connection to losses. 8)
*
* rcv_ssthresh is more strict window_clamp used at "slow start"
* phase to predict further behaviour of this connection.
* It is used for two goals:
* - to enforce header prediction at sender, even when application
* requires some significant "application buffer". It is check #1.
* - to prevent pruning of receive queue because of misprediction
* of receiver window. Check #2.
*
* The scheme does not work when sender sends good segments opening
* window and then starts to feed us spaghetti. But it should work
* in common situations. Otherwise, we have to rely on queue collapsing.
*/
/* Slow part of check#2. */
static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
/* Optimize this! */
int truesize = tcp_win_from_space(sk, skb->truesize) >> 1;
int window = tcp_win_from_space(sk, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]) >> 1;
while (tp->rcv_ssthresh <= window) {
if (truesize <= skb->len)
return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
truesize >>= 1;
window >>= 1;
}
return 0;
}
static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
int room;
room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
/* Check #1 */
if (room > 0 && !tcp_under_memory_pressure(sk)) {
int incr;
/* Check #2. Increase window, if skb with such overhead
* will fit to rcvbuf in future.
*/
if (tcp_win_from_space(sk, skb->truesize) <= skb->len)
incr = 2 * tp->advmss;
else
incr = __tcp_grow_window(sk, skb);
if (incr) {
incr = max_t(int, incr, 2 * skb->len);
tp->rcv_ssthresh += min(room, incr);
inet_csk(sk)->icsk_ack.quick |= 1;
}
}
}
/* 3. Try to fixup all. It is made immediately after connection enters
* established state.
*/
void tcp_init_buffer_space(struct sock *sk)
{
int tcp_app_win = sock_net(sk)->ipv4.sysctl_tcp_app_win;
struct tcp_sock *tp = tcp_sk(sk);
int maxwin;
if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
tcp_sndbuf_expand(sk);
tp->rcvq_space.space = min_t(u32, tp->rcv_wnd, TCP_INIT_CWND * tp->advmss);
tcp_mstamp_refresh(tp);
tp->rcvq_space.time = tp->tcp_mstamp;
tp->rcvq_space.seq = tp->copied_seq;
maxwin = tcp_full_space(sk);
if (tp->window_clamp >= maxwin) {
tp->window_clamp = maxwin;
if (tcp_app_win && maxwin > 4 * tp->advmss)
tp->window_clamp = max(maxwin -
(maxwin >> tcp_app_win),
4 * tp->advmss);
}
/* Force reservation of one segment. */
if (tcp_app_win &&
tp->window_clamp > 2 * tp->advmss &&
tp->window_clamp + tp->advmss > maxwin)
tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
tp->snd_cwnd_stamp = tcp_jiffies32;
}
/* 4. Recalculate window clamp after socket hit its memory bounds. */
static void tcp_clamp_window(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
struct net *net = sock_net(sk);
icsk->icsk_ack.quick = 0;
if (sk->sk_rcvbuf < net->ipv4.sysctl_tcp_rmem[2] &&
!(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
!tcp_under_memory_pressure(sk) &&
sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
net->ipv4.sysctl_tcp_rmem[2]);
}
if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
}
/* Initialize RCV_MSS value.
* RCV_MSS is an our guess about MSS used by the peer.
* We haven't any direct information about the MSS.
* It's better to underestimate the RCV_MSS rather than overestimate.
* Overestimations make us ACKing less frequently than needed.
* Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
*/
void tcp_initialize_rcv_mss(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
hint = min(hint, tp->rcv_wnd / 2);
hint = min(hint, TCP_MSS_DEFAULT);
hint = max(hint, TCP_MIN_MSS);
inet_csk(sk)->icsk_ack.rcv_mss = hint;
}
EXPORT_SYMBOL(tcp_initialize_rcv_mss);
/* Receiver "autotuning" code.
*
* The algorithm for RTT estimation w/o timestamps is based on
* Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
* <http://public.lanl.gov/radiant/pubs.html#DRS>
*
* More detail on this code can be found at
* <http://staff.psc.edu/jheffner/>,
* though this reference is out of date. A new paper
* is pending.
*/
static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
{
u32 new_sample = tp->rcv_rtt_est.rtt_us;
long m = sample;
if (new_sample != 0) {
/* If we sample in larger samples in the non-timestamp
* case, we could grossly overestimate the RTT especially
* with chatty applications or bulk transfer apps which
* are stalled on filesystem I/O.
*
* Also, since we are only going for a minimum in the
* non-timestamp case, we do not smooth things out
* else with timestamps disabled convergence takes too
* long.
*/
if (!win_dep) {
m -= (new_sample >> 3);
new_sample += m;
} else {
m <<= 3;
if (m < new_sample)
new_sample = m;
}
} else {
/* No previous measure. */
new_sample = m << 3;
}
tp->rcv_rtt_est.rtt_us = new_sample;
}
static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
{
u32 delta_us;
if (tp->rcv_rtt_est.time == 0)
goto new_measure;
if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
return;
delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
if (!delta_us)
delta_us = 1;
tcp_rcv_rtt_update(tp, delta_us, 1);
new_measure:
tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
tp->rcv_rtt_est.time = tp->tcp_mstamp;
}
static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr)
return;
tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
if (TCP_SKB_CB(skb)->end_seq -
TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) {
u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
u32 delta_us;
if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
if (!delta)
delta = 1;
delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
tcp_rcv_rtt_update(tp, delta_us, 0);
}
}
}
/*
* This function should be called every time data is copied to user space.
* It calculates the appropriate TCP receive buffer space.
*/
void tcp_rcv_space_adjust(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 copied;
int time;
trace_tcp_rcv_space_adjust(sk);
tcp_mstamp_refresh(tp);
time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
return;
/* Number of bytes copied to user in last RTT */
copied = tp->copied_seq - tp->rcvq_space.seq;
if (copied <= tp->rcvq_space.space)
goto new_measure;
/* A bit of theory :
* copied = bytes received in previous RTT, our base window
* To cope with packet losses, we need a 2x factor
* To cope with slow start, and sender growing its cwin by 100 %
* every RTT, we need a 4x factor, because the ACK we are sending
* now is for the next RTT, not the current one :
* <prev RTT . ><current RTT .. ><next RTT .... >
*/
if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf &&
!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
int rcvmem, rcvbuf;
u64 rcvwin, grow;
/* minimal window to cope with packet losses, assuming
* steady state. Add some cushion because of small variations.
*/
rcvwin = ((u64)copied << 1) + 16 * tp->advmss;
/* Accommodate for sender rate increase (eg. slow start) */
grow = rcvwin * (copied - tp->rcvq_space.space);
do_div(grow, tp->rcvq_space.space);
rcvwin += (grow << 1);
rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
while (tcp_win_from_space(sk, rcvmem) < tp->advmss)
rcvmem += 128;
do_div(rcvwin, tp->advmss);
rcvbuf = min_t(u64, rcvwin * rcvmem,
sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
if (rcvbuf > sk->sk_rcvbuf) {
sk->sk_rcvbuf = rcvbuf;
/* Make the window clamp follow along. */
tp->window_clamp = tcp_win_from_space(sk, rcvbuf);
}
}
tp->rcvq_space.space = copied;
new_measure:
tp->rcvq_space.seq = tp->copied_seq;
tp->rcvq_space.time = tp->tcp_mstamp;
}
/* There is something which you must keep in mind when you analyze the
* behavior of the tp->ato delayed ack timeout interval. When a
* connection starts up, we want to ack as quickly as possible. The
* problem is that "good" TCP's do slow start at the beginning of data
* transmission. The means that until we send the first few ACK's the
* sender will sit on his end and only queue most of his data, because
* he can only send snd_cwnd unacked packets at any given time. For
* each ACK we send, he increments snd_cwnd and transmits more of his
* queue. -DaveM
*/
static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
u32 now;
inet_csk_schedule_ack(sk);
tcp_measure_rcv_mss(sk, skb);
tcp_rcv_rtt_measure(tp);
now = tcp_jiffies32;
if (!icsk->icsk_ack.ato) {
/* The _first_ data packet received, initialize
* delayed ACK engine.
*/
tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
icsk->icsk_ack.ato = TCP_ATO_MIN;
} else {
int m = now - icsk->icsk_ack.lrcvtime;
if (m <= TCP_ATO_MIN / 2) {
/* The fastest case is the first. */
icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
} else if (m < icsk->icsk_ack.ato) {
icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
if (icsk->icsk_ack.ato > icsk->icsk_rto)
icsk->icsk_ack.ato = icsk->icsk_rto;
} else if (m > icsk->icsk_rto) {
/* Too long gap. Apparently sender failed to
* restart window, so that we send ACKs quickly.
*/
tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
sk_mem_reclaim(sk);
}
}
icsk->icsk_ack.lrcvtime = now;
tcp_ecn_check_ce(sk, skb);
if (skb->len >= 128)
tcp_grow_window(sk, skb);
}
/* Called to compute a smoothed rtt estimate. The data fed to this
* routine either comes from timestamps, or from segments that were
* known _not_ to have been retransmitted [see Karn/Partridge
* Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
* piece by Van Jacobson.
* NOTE: the next three routines used to be one big routine.
* To save cycles in the RFC 1323 implementation it was better to break
* it up into three procedures. -- erics
*/
static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
{
struct tcp_sock *tp = tcp_sk(sk);
long m = mrtt_us; /* RTT */
u32 srtt = tp->srtt_us;
/* The following amusing code comes from Jacobson's
* article in SIGCOMM '88. Note that rtt and mdev
* are scaled versions of rtt and mean deviation.
* This is designed to be as fast as possible
* m stands for "measurement".
*
* On a 1990 paper the rto value is changed to:
* RTO = rtt + 4 * mdev
*
* Funny. This algorithm seems to be very broken.
* These formulae increase RTO, when it should be decreased, increase
* too slowly, when it should be increased quickly, decrease too quickly
* etc. I guess in BSD RTO takes ONE value, so that it is absolutely
* does not matter how to _calculate_ it. Seems, it was trap
* that VJ failed to avoid. 8)
*/
if (srtt != 0) {
m -= (srtt >> 3); /* m is now error in rtt est */
srtt += m; /* rtt = 7/8 rtt + 1/8 new */
if (m < 0) {
m = -m; /* m is now abs(error) */
m -= (tp->mdev_us >> 2); /* similar update on mdev */
/* This is similar to one of Eifel findings.
* Eifel blocks mdev updates when rtt decreases.
* This solution is a bit different: we use finer gain
* for mdev in this case (alpha*beta).
* Like Eifel it also prevents growth of rto,
* but also it limits too fast rto decreases,
* happening in pure Eifel.
*/
if (m > 0)
m >>= 3;
} else {
m -= (tp->mdev_us >> 2); /* similar update on mdev */
}
tp->mdev_us += m; /* mdev = 3/4 mdev + 1/4 new */
if (tp->mdev_us > tp->mdev_max_us) {
tp->mdev_max_us = tp->mdev_us;
if (tp->mdev_max_us > tp->rttvar_us)
tp->rttvar_us = tp->mdev_max_us;
}
if (after(tp->snd_una, tp->rtt_seq)) {
if (tp->mdev_max_us < tp->rttvar_us)
tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
tp->rtt_seq = tp->snd_nxt;
tp->mdev_max_us = tcp_rto_min_us(sk);
}
} else {
/* no previous measure. */
srtt = m << 3; /* take the measured time to be rtt */
tp->mdev_us = m << 1; /* make sure rto = 3*rtt */
tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
tp->mdev_max_us = tp->rttvar_us;
tp->rtt_seq = tp->snd_nxt;
}
tp->srtt_us = max(1U, srtt);
}
static void tcp_update_pacing_rate(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
u64 rate;
/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
/* current rate is (cwnd * mss) / srtt
* In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
* In Congestion Avoidance phase, set it to 120 % the current rate.
*
* [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
* If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
* end of slow start and should slow down.
*/
if (tp->snd_cwnd < tp->snd_ssthresh / 2)
rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio;
else
rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio;
rate *= max(tp->snd_cwnd, tp->packets_out);
if (likely(tp->srtt_us))
do_div(rate, tp->srtt_us);
/* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate
* without any lock. We want to make sure compiler wont store
* intermediate values in this location.
*/
WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate,
sk->sk_max_pacing_rate));
}
/* Calculate rto without backoff. This is the second half of Van Jacobson's
* routine referred to above.
*/
static void tcp_set_rto(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
/* Old crap is replaced with new one. 8)
*
* More seriously:
* 1. If rtt variance happened to be less 50msec, it is hallucination.
* It cannot be less due to utterly erratic ACK generation made
* at least by solaris and freebsd. "Erratic ACKs" has _nothing_
* to do with delayed acks, because at cwnd>2 true delack timeout
* is invisible. Actually, Linux-2.4 also generates erratic
* ACKs in some circumstances.
*/
inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
/* 2. Fixups made earlier cannot be right.
* If we do not estimate RTO correctly without them,
* all the algo is pure shit and should be replaced
* with correct one. It is exactly, which we pretend to do.
*/
/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
* guarantees that rto is higher.
*/
tcp_bound_rto(sk);
}
__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
{
__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
if (!cwnd)
cwnd = TCP_INIT_CWND;
return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
}
/* Take a notice that peer is sending D-SACKs */
static void tcp_dsack_seen(struct tcp_sock *tp)
{
tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
tp->rack.dsack_seen = 1;
tp->dsack_dups++;
}
/* It's reordering when higher sequence was delivered (i.e. sacked) before
* some lower never-retransmitted sequence ("low_seq"). The maximum reordering
* distance is approximated in full-mss packet distance ("reordering").
*/
static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
const int ts)
{
struct tcp_sock *tp = tcp_sk(sk);
const u32 mss = tp->mss_cache;
u32 fack, metric;
fack = tcp_highest_sack_seq(tp);
if (!before(low_seq, fack))
return;
metric = fack - low_seq;
if ((metric > tp->reordering * mss) && mss) {
#if FASTRETRANS_DEBUG > 1
pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
tp->reordering,
0,
tp->sacked_out,
tp->undo_marker ? tp->undo_retrans : 0);
#endif
tp->reordering = min_t(u32, (metric + mss - 1) / mss,
sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
}
/* This exciting event is worth to be remembered. 8) */
tp->reord_seen++;
NET_INC_STATS(sock_net(sk),
ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
}
/* This must be called before lost_out is incremented */
static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
{
if (!tp->retransmit_skb_hint ||
before(TCP_SKB_CB(skb)->seq,
TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
tp->retransmit_skb_hint = skb;
}
/* Sum the number of packets on the wire we have marked as lost.
* There are two cases we care about here:
* a) Packet hasn't been marked lost (nor retransmitted),
* and this is the first loss.
* b) Packet has been marked both lost and retransmitted,
* and this means we think it was lost again.
*/
static void tcp_sum_lost(struct tcp_sock *tp, struct sk_buff *skb)
{
__u8 sacked = TCP_SKB_CB(skb)->sacked;
if (!(sacked & TCPCB_LOST) ||
((sacked & TCPCB_LOST) && (sacked & TCPCB_SACKED_RETRANS)))
tp->lost += tcp_skb_pcount(skb);
}
static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
{
if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
tcp_verify_retransmit_hint(tp, skb);
tp->lost_out += tcp_skb_pcount(skb);
tcp_sum_lost(tp, skb);
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
}
}
void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
{
tcp_verify_retransmit_hint(tp, skb);
tcp_sum_lost(tp, skb);
if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
tp->lost_out += tcp_skb_pcount(skb);
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
}
}
/* This procedure tags the retransmission queue when SACKs arrive.
*
* We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
* Packets in queue with these bits set are counted in variables
* sacked_out, retrans_out and lost_out, correspondingly.
*
* Valid combinations are:
* Tag InFlight Description
* 0 1 - orig segment is in flight.
* S 0 - nothing flies, orig reached receiver.
* L 0 - nothing flies, orig lost by net.
* R 2 - both orig and retransmit are in flight.
* L|R 1 - orig is lost, retransmit is in flight.
* S|R 1 - orig reached receiver, retrans is still in flight.
* (L|S|R is logically valid, it could occur when L|R is sacked,
* but it is equivalent to plain S and code short-curcuits it to S.
* L|S is logically invalid, it would mean -1 packet in flight 8))
*
* These 6 states form finite state machine, controlled by the following events:
* 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
* 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
* 3. Loss detection event of two flavors:
* A. Scoreboard estimator decided the packet is lost.
* A'. Reno "three dupacks" marks head of queue lost.
* B. SACK arrives sacking SND.NXT at the moment, when the
* segment was retransmitted.
* 4. D-SACK added new rule: D-SACK changes any tag to S.
*
* It is pleasant to note, that state diagram turns out to be commutative,
* so that we are allowed not to be bothered by order of our actions,
* when multiple events arrive simultaneously. (see the function below).
*
* Reordering detection.
* --------------------
* Reordering metric is maximal distance, which a packet can be displaced
* in packet stream. With SACKs we can estimate it:
*
* 1. SACK fills old hole and the corresponding segment was not
* ever retransmitted -> reordering. Alas, we cannot use it
* when segment was retransmitted.
* 2. The last flaw is solved with D-SACK. D-SACK arrives
* for retransmitted and already SACKed segment -> reordering..
* Both of these heuristics are not used in Loss state, when we cannot
* account for retransmits accurately.
*
* SACK block validation.
* ----------------------
*
* SACK block range validation checks that the received SACK block fits to
* the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
* Note that SND.UNA is not included to the range though being valid because
* it means that the receiver is rather inconsistent with itself reporting
* SACK reneging when it should advance SND.UNA. Such SACK block this is
* perfectly valid, however, in light of RFC2018 which explicitly states
* that "SACK block MUST reflect the newest segment. Even if the newest
* segment is going to be discarded ...", not that it looks very clever
* in case of head skb. Due to potentional receiver driven attacks, we
* choose to avoid immediate execution of a walk in write queue due to
* reneging and defer head skb's loss recovery to standard loss recovery
* procedure that will eventually trigger (nothing forbids us doing this).
*
* Implements also blockage to start_seq wrap-around. Problem lies in the
* fact that though start_seq (s) is before end_seq (i.e., not reversed),
* there's no guarantee that it will be before snd_nxt (n). The problem
* happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
* wrap (s_w):
*
* <- outs wnd -> <- wrapzone ->
* u e n u_w e_w s n_w
* | | | | | | |
* |<------------+------+----- TCP seqno space --------------+---------->|
* ...-- <2^31 ->| |<--------...
* ...---- >2^31 ------>| |<--------...
*
* Current code wouldn't be vulnerable but it's better still to discard such
* crazy SACK blocks. Doing this check for start_seq alone closes somewhat
* similar case (end_seq after snd_nxt wrap) as earlier reversed check in
* snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
* equal to the ideal case (infinite seqno space without wrap caused issues).
*
* With D-SACK the lower bound is extended to cover sequence space below
* SND.UNA down to undo_marker, which is the last point of interest. Yet
* again, D-SACK block must not to go across snd_una (for the same reason as
* for the normal SACK blocks, explained above). But there all simplicity
* ends, TCP might receive valid D-SACKs below that. As long as they reside
* fully below undo_marker they do not affect behavior in anyway and can
* therefore be safely ignored. In rare cases (which are more or less
* theoretical ones), the D-SACK will nicely cross that boundary due to skb
* fragmentation and packet reordering past skb's retransmission. To consider
* them correctly, the acceptable range must be extended even more though
* the exact amount is rather hard to quantify. However, tp->max_window can
* be used as an exaggerated estimate.
*/
static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
u32 start_seq, u32 end_seq)
{
/* Too far in future, or reversed (interpretation is ambiguous) */
if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
return false;
/* Nasty start_seq wrap-around check (see comments above) */
if (!before(start_seq, tp->snd_nxt))
return false;
/* In outstanding window? ...This is valid exit for D-SACKs too.
* start_seq == snd_una is non-sensical (see comments above)
*/
if (after(start_seq, tp->snd_una))
return true;
if (!is_dsack || !tp->undo_marker)
return false;
/* ...Then it's D-SACK, and must reside below snd_una completely */
if (after(end_seq, tp->snd_una))
return false;
if (!before(start_seq, tp->undo_marker))
return true;
/* Too old */
if (!after(end_seq, tp->undo_marker))
return false;
/* Undo_marker boundary crossing (overestimates a lot). Known already:
* start_seq < undo_marker and end_seq >= undo_marker.
*/
return !before(start_seq, end_seq - tp->max_window);
}
static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
struct tcp_sack_block_wire *sp, int num_sacks,
u32 prior_snd_una)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
bool dup_sack = false;
if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
dup_sack = true;
tcp_dsack_seen(tp);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
} else if (num_sacks > 1) {
u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
if (!after(end_seq_0, end_seq_1) &&
!before(start_seq_0, start_seq_1)) {
dup_sack = true;
tcp_dsack_seen(tp);
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPDSACKOFORECV);
}
}
/* D-SACK for already forgotten data... Do dumb counting. */
if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
!after(end_seq_0, prior_snd_una) &&
after(end_seq_0, tp->undo_marker))
tp->undo_retrans--;
return dup_sack;
}
struct tcp_sacktag_state {
u32 reord;
/* Timestamps for earliest and latest never-retransmitted segment
* that was SACKed. RTO needs the earliest RTT to stay conservative,
* but congestion control should still get an accurate delay signal.
*/
u64 first_sackt;
u64 last_sackt;
struct rate_sample *rate;
int flag;
unsigned int mss_now;
};
/* Check if skb is fully within the SACK block. In presence of GSO skbs,
* the incoming SACK may not exactly match but we can find smaller MSS
* aligned portion of it that matches. Therefore we might need to fragment
* which may fail and creates some hassle (caller must handle error case
* returns).
*
* FIXME: this could be merged to shift decision code
*/
static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
u32 start_seq, u32 end_seq)
{
int err;
bool in_sack;
unsigned int pkt_len;
unsigned int mss;
in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
!before(end_seq, TCP_SKB_CB(skb)->end_seq);
if (tcp_skb_pcount(skb) > 1 && !in_sack &&
after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
mss = tcp_skb_mss(skb);
in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
if (!in_sack) {
pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
if (pkt_len < mss)
pkt_len = mss;
} else {
pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
if (pkt_len < mss)
return -EINVAL;
}
/* Round if necessary so that SACKs cover only full MSSes
* and/or the remaining small portion (if present)
*/
if (pkt_len > mss) {
unsigned int new_len = (pkt_len / mss) * mss;
if (!in_sack && new_len < pkt_len)
new_len += mss;
pkt_len = new_len;
}
if (pkt_len >= skb->len && !in_sack)
return 0;
err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
pkt_len, mss, GFP_ATOMIC);
if (err < 0)
return err;
}
return in_sack;
}
/* Mark the given newly-SACKed range as such, adjusting counters and hints. */
static u8 tcp_sacktag_one(struct sock *sk,
struct tcp_sacktag_state *state, u8 sacked,
u32 start_seq, u32 end_seq,
int dup_sack, int pcount,
u64 xmit_time)
{
struct tcp_sock *tp = tcp_sk(sk);
/* Account D-SACK for retransmitted packet. */
if (dup_sack && (sacked & TCPCB_RETRANS)) {
if (tp->undo_marker && tp->undo_retrans > 0 &&
after(end_seq, tp->undo_marker))
tp->undo_retrans--;
if ((sacked & TCPCB_SACKED_ACKED) &&
before(start_seq, state->reord))
state->reord = start_seq;
}
/* Nothing to do; acked frame is about to be dropped (was ACKed). */
if (!after(end_seq, tp->snd_una))
return sacked;
if (!(sacked & TCPCB_SACKED_ACKED)) {
tcp_rack_advance(tp, sacked, end_seq, xmit_time);
if (sacked & TCPCB_SACKED_RETRANS) {
/* If the segment is not tagged as lost,
* we do not clear RETRANS, believing
* that retransmission is still in flight.
*/
if (sacked & TCPCB_LOST) {
sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
tp->lost_out -= pcount;
tp->retrans_out -= pcount;
}
} else {
if (!(sacked & TCPCB_RETRANS)) {
/* New sack for not retransmitted frame,
* which was in hole. It is reordering.
*/
if (before(start_seq,
tcp_highest_sack_seq(tp)) &&
before(start_seq, state->reord))
state->reord = start_seq;
if (!after(end_seq, tp->high_seq))
state->flag |= FLAG_ORIG_SACK_ACKED;
if (state->first_sackt == 0)
state->first_sackt = xmit_time;
state->last_sackt = xmit_time;
}
if (sacked & TCPCB_LOST) {
sacked &= ~TCPCB_LOST;
tp->lost_out -= pcount;
}
}
sacked |= TCPCB_SACKED_ACKED;
state->flag |= FLAG_DATA_SACKED;
tp->sacked_out += pcount;
tp->delivered += pcount; /* Out-of-order packets delivered */
/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
if (tp->lost_skb_hint &&
before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
tp->lost_cnt_hint += pcount;
}
/* D-SACK. We can detect redundant retransmission in S|R and plain R
* frames and clear it. undo_retrans is decreased above, L|R frames
* are accounted above as well.
*/
if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
sacked &= ~TCPCB_SACKED_RETRANS;
tp->retrans_out -= pcount;
}
return sacked;
}
/* Shift newly-SACKed bytes from this skb to the immediately previous
* already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
*/
static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
struct sk_buff *skb,
struct tcp_sacktag_state *state,
unsigned int pcount, int shifted, int mss,
bool dup_sack)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 start_seq = TCP_SKB_CB(skb)->seq; /* start of newly-SACKed */
u32 end_seq = start_seq + shifted; /* end of newly-SACKed */
BUG_ON(!pcount);
/* Adjust counters and hints for the newly sacked sequence
* range but discard the return value since prev is already
* marked. We must tag the range first because the seq
* advancement below implicitly advances
* tcp_highest_sack_seq() when skb is highest_sack.
*/
tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
start_seq, end_seq, dup_sack, pcount,
tcp_skb_timestamp_us(skb));
tcp_rate_skb_delivered(sk, skb, state->rate);
if (skb == tp->lost_skb_hint)
tp->lost_cnt_hint += pcount;
TCP_SKB_CB(prev)->end_seq += shifted;
TCP_SKB_CB(skb)->seq += shifted;
tcp_skb_pcount_add(prev, pcount);
BUG_ON(tcp_skb_pcount(skb) < pcount);
tcp_skb_pcount_add(skb, -pcount);
/* When we're adding to gso_segs == 1, gso_size will be zero,
* in theory this shouldn't be necessary but as long as DSACK
* code can come after this skb later on it's better to keep
* setting gso_size to something.
*/
if (!TCP_SKB_CB(prev)->tcp_gso_size)
TCP_SKB_CB(prev)->tcp_gso_size = mss;
/* CHECKME: To clear or not to clear? Mimics normal skb currently */
if (tcp_skb_pcount(skb) <= 1)
TCP_SKB_CB(skb)->tcp_gso_size = 0;
/* Difference in this won't matter, both ACKed by the same cumul. ACK */
TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
if (skb->len > 0) {
BUG_ON(!tcp_skb_pcount(skb));
NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
return false;
}
/* Whole SKB was eaten :-) */
if (skb == tp->retransmit_skb_hint)
tp->retransmit_skb_hint = prev;
if (skb == tp->lost_skb_hint) {
tp->lost_skb_hint = prev;
tp->lost_cnt_hint -= tcp_skb_pcount(prev);
}
TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
TCP_SKB_CB(prev)->end_seq++;
if (skb == tcp_highest_sack(sk))
tcp_advance_highest_sack(sk, skb);
tcp_skb_collapse_tstamp(prev, skb);
if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
tcp_rtx_queue_unlink_and_free(skb, sk);
NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
return true;
}
/* I wish gso_size would have a bit more sane initialization than
* something-or-zero which complicates things
*/
static int tcp_skb_seglen(const struct sk_buff *skb)
{
return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
}
/* Shifting pages past head area doesn't work */
static int skb_can_shift(const struct sk_buff *skb)
{
return !skb_headlen(skb) && skb_is_nonlinear(skb);
}
/* Try collapsing SACK blocks spanning across multiple skbs to a single
* skb.
*/
static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
struct tcp_sacktag_state *state,
u32 start_seq, u32 end_seq,
bool dup_sack)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *prev;
int mss;
int pcount = 0;
int len;
int in_sack;
/* Normally R but no L won't result in plain S */
if (!dup_sack &&
(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
goto fallback;
if (!skb_can_shift(skb))
goto fallback;
/* This frame is about to be dropped (was ACKed). */
if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
goto fallback;
/* Can only happen with delayed DSACK + discard craziness */
prev = skb_rb_prev(skb);
if (!prev)
goto fallback;
if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
goto fallback;
if (!tcp_skb_can_collapse_to(prev))
goto fallback;
in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
!before(end_seq, TCP_SKB_CB(skb)->end_seq);
if (in_sack) {
len = skb->len;
pcount = tcp_skb_pcount(skb);
mss = tcp_skb_seglen(skb);
/* TODO: Fix DSACKs to not fragment already SACKed and we can
* drop this restriction as unnecessary
*/
if (mss != tcp_skb_seglen(prev))
goto fallback;
} else {
if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
goto noop;
/* CHECKME: This is non-MSS split case only?, this will
* cause skipped skbs due to advancing loop btw, original
* has that feature too
*/
if (tcp_skb_pcount(skb) <= 1)
goto noop;
in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
if (!in_sack) {
/* TODO: head merge to next could be attempted here
* if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
* though it might not be worth of the additional hassle
*
* ...we can probably just fallback to what was done
* previously. We could try merging non-SACKed ones
* as well but it probably isn't going to buy off
* because later SACKs might again split them, and
* it would make skb timestamp tracking considerably
* harder problem.
*/
goto fallback;
}
len = end_seq - TCP_SKB_CB(skb)->seq;
BUG_ON(len < 0);
BUG_ON(len > skb->len);
/* MSS boundaries should be honoured or else pcount will
* severely break even though it makes things bit trickier.
* Optimize common case to avoid most of the divides
*/
mss = tcp_skb_mss(skb);
/* TODO: Fix DSACKs to not fragment already SACKed and we can
* drop this restriction as unnecessary
*/
if (mss != tcp_skb_seglen(prev))
goto fallback;
if (len == mss) {
pcount = 1;
} else if (len < mss) {
goto noop;
} else {
pcount = len / mss;
len = pcount * mss;
}
}
/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
goto fallback;
if (!skb_shift(prev, skb, len))
goto fallback;
if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack))
goto out;
/* Hole filled allows collapsing with the next as well, this is very
* useful when hole on every nth skb pattern happens
*/
skb = skb_rb_next(prev);
if (!skb)
goto out;
if (!skb_can_shift(skb) ||
((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
(mss != tcp_skb_seglen(skb)))
goto out;
len = skb->len;
if (skb_shift(prev, skb, len)) {
pcount += tcp_skb_pcount(skb);
tcp_shifted_skb(sk, prev, skb, state, tcp_skb_pcount(skb),
len, mss, 0);
}
out:
return prev;
noop:
return skb;
fallback:
NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
return NULL;
}
static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
struct tcp_sack_block *next_dup,
struct tcp_sacktag_state *state,
u32 start_seq, u32 end_seq,
bool dup_sack_in)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *tmp;
skb_rbtree_walk_from(skb) {
int in_sack = 0;
bool dup_sack = dup_sack_in;
/* queue is in-order => we can short-circuit the walk early */
if (!before(TCP_SKB_CB(skb)->seq, end_seq))
break;
if (next_dup &&
before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
in_sack = tcp_match_skb_to_sack(sk, skb,
next_dup->start_seq,
next_dup->end_seq);
if (in_sack > 0)
dup_sack = true;
}
/* skb reference here is a bit tricky to get right, since
* shifting can eat and free both this skb and the next,
* so not even _safe variant of the loop is enough.
*/
if (in_sack <= 0) {
tmp = tcp_shift_skb_data(sk, skb, state,
start_seq, end_seq, dup_sack);
if (tmp) {
if (tmp != skb) {
skb = tmp;
continue;
}
in_sack = 0;
} else {
in_sack = tcp_match_skb_to_sack(sk, skb,
start_seq,
end_seq);
}
}
if (unlikely(in_sack < 0))
break;
if (in_sack) {
TCP_SKB_CB(skb)->sacked =
tcp_sacktag_one(sk,
state,
TCP_SKB_CB(skb)->sacked,
TCP_SKB_CB(skb)->seq,
TCP_SKB_CB(skb)->end_seq,
dup_sack,
tcp_skb_pcount(skb),
tcp_skb_timestamp_us(skb));
tcp_rate_skb_delivered(sk, skb, state->rate);
if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
list_del_init(&skb->tcp_tsorted_anchor);
if (!before(TCP_SKB_CB(skb)->seq,
tcp_highest_sack_seq(tp)))
tcp_advance_highest_sack(sk, skb);
}
}
return skb;
}
static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq)
{
struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
struct sk_buff *skb;
while (*p) {
parent = *p;
skb = rb_to_skb(parent);
if (before(seq, TCP_SKB_CB(skb)->seq)) {
p = &parent->rb_left;
continue;
}
if (!before(seq, TCP_SKB_CB(skb)->end_seq)) {
p = &parent->rb_right;
continue;
}
return skb;
}
return NULL;
}
static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
u32 skip_to_seq)
{
if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
return skb;
return tcp_sacktag_bsearch(sk, skip_to_seq);
}
static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
struct sock *sk,
struct tcp_sack_block *next_dup,
struct tcp_sacktag_state *state,
u32 skip_to_seq)
{
if (!next_dup)
return skb;
if (before(next_dup->start_seq, skip_to_seq)) {
skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq);
skb = tcp_sacktag_walk(skb, sk, NULL, state,
next_dup->start_seq, next_dup->end_seq,
1);
}
return skb;
}
static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
{
return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
}
static int
tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
u32 prior_snd_una, struct tcp_sacktag_state *state)
{
struct tcp_sock *tp = tcp_sk(sk);
const unsigned char *ptr = (skb_transport_header(ack_skb) +
TCP_SKB_CB(ack_skb)->sacked);
struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
struct tcp_sack_block sp[TCP_NUM_SACKS];
struct tcp_sack_block *cache;
struct sk_buff *skb;
int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
int used_sacks;
bool found_dup_sack = false;
int i, j;
int first_sack_index;
state->flag = 0;
state->reord = tp->snd_nxt;
if (!tp->sacked_out)
tcp_highest_sack_reset(sk);
found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
num_sacks, prior_snd_una);
if (found_dup_sack) {
state->flag |= FLAG_DSACKING_ACK;
tp->delivered++; /* A spurious retransmission is delivered */
}
/* Eliminate too old ACKs, but take into
* account more or less fresh ones, they can
* contain valid SACK info.
*/
if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
return 0;
if (!tp->packets_out)
goto out;
used_sacks = 0;
first_sack_index = 0;
for (i = 0; i < num_sacks; i++) {
bool dup_sack = !i && found_dup_sack;
sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
if (!tcp_is_sackblock_valid(tp, dup_sack,
sp[used_sacks].start_seq,
sp[used_sacks].end_seq)) {
int mib_idx;
if (dup_sack) {
if (!tp->undo_marker)
mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
else
mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
} else {
/* Don't count olds caused by ACK reordering */
if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
!after(sp[used_sacks].end_seq, tp->snd_una))
continue;
mib_idx = LINUX_MIB_TCPSACKDISCARD;
}
NET_INC_STATS(sock_net(sk), mib_idx);
if (i == 0)
first_sack_index = -1;
continue;
}
/* Ignore very old stuff early */
if (!after(sp[used_sacks].end_seq, prior_snd_una))
continue;
used_sacks++;
}
/* order SACK blocks to allow in order walk of the retrans queue */
for (i = used_sacks - 1; i > 0; i--) {
for (j = 0; j < i; j++) {
if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
swap(sp[j], sp[j + 1]);
/* Track where the first SACK block goes to */
if (j == first_sack_index)
first_sack_index = j + 1;
}
}
}
state->mss_now = tcp_current_mss(sk);
skb = NULL;
i = 0;
if (!tp->sacked_out) {
/* It's already past, so skip checking against it */
cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
} else {
cache = tp->recv_sack_cache;
/* Skip empty blocks in at head of the cache */
while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
!cache->end_seq)
cache++;
}
while (i < used_sacks) {
u32 start_seq = sp[i].start_seq;
u32 end_seq = sp[i].end_seq;
bool dup_sack = (found_dup_sack && (i == first_sack_index));
struct tcp_sack_block *next_dup = NULL;
if (found_dup_sack && ((i + 1) == first_sack_index))
next_dup = &sp[i + 1];
/* Skip too early cached blocks */
while (tcp_sack_cache_ok(tp, cache) &&
!before(start_seq, cache->end_seq))
cache++;
/* Can skip some work by looking recv_sack_cache? */
if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
after(end_seq, cache->start_seq)) {
/* Head todo? */
if (before(start_seq, cache->start_seq)) {
skb = tcp_sacktag_skip(skb, sk, start_seq);
skb = tcp_sacktag_walk(skb, sk, next_dup,
state,
start_seq,
cache->start_seq,
dup_sack);
}
/* Rest of the block already fully processed? */
if (!after(end_seq, cache->end_seq))
goto advance_sp;
skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
state,
cache->end_seq);
/* ...tail remains todo... */
if (tcp_highest_sack_seq(tp) == cache->end_seq) {
/* ...but better entrypoint exists! */
skb = tcp_highest_sack(sk);
if (!skb)
break;
cache++;
goto walk;
}
skb = tcp_sacktag_skip(skb, sk, cache->end_seq);
/* Check overlap against next cached too (past this one already) */
cache++;
continue;
}
if (!before(start_seq, tcp_highest_sack_seq(tp))) {
skb = tcp_highest_sack(sk);
if (!skb)
break;
}
skb = tcp_sacktag_skip(skb, sk, start_seq);
walk:
skb = tcp_sacktag_walk(skb, sk, next_dup, state,
start_seq, end_seq, dup_sack);
advance_sp:
i++;
}
/* Clear the head of the cache sack blocks so we can skip it next time */
for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
tp->recv_sack_cache[i].start_seq = 0;
tp->recv_sack_cache[i].end_seq = 0;
}
for (j = 0; j < used_sacks; j++)
tp->recv_sack_cache[i++] = sp[j];
if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
tcp_check_sack_reordering(sk, state->reord, 0);
tcp_verify_left_out(tp);
out:
#if FASTRETRANS_DEBUG > 0
WARN_ON((int)tp->sacked_out < 0);
WARN_ON((int)tp->lost_out < 0);
WARN_ON((int)tp->retrans_out < 0);
WARN_ON((int)tcp_packets_in_flight(tp) < 0);
#endif
return state->flag;
}
/* Limits sacked_out so that sum with lost_out isn't ever larger than
* packets_out. Returns false if sacked_out adjustement wasn't necessary.
*/
static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
{
u32 holes;
holes = max(tp->lost_out, 1U);
holes = min(holes, tp->packets_out);
if ((tp->sacked_out + holes) > tp->packets_out) {
tp->sacked_out = tp->packets_out - holes;
return true;
}
return false;
}
/* If we receive more dupacks than we expected counting segments
* in assumption of absent reordering, interpret this as reordering.
* The only another reason could be bug in receiver TCP.
*/
static void tcp_check_reno_reordering(struct sock *sk, const int addend)
{
struct tcp_sock *tp = tcp_sk(sk);
if (!tcp_limit_reno_sacked(tp))
return;
tp->reordering = min_t(u32, tp->packets_out + addend,
sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
tp->reord_seen++;
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
}
/* Emulate SACKs for SACKless connection: account for a new dupack. */
static void tcp_add_reno_sack(struct sock *sk, int num_dupack)
{
if (num_dupack) {
struct tcp_sock *tp = tcp_sk(sk);
u32 prior_sacked = tp->sacked_out;
s32 delivered;
tp->sacked_out += num_dupack;
tcp_check_reno_reordering(sk, 0);
delivered = tp->sacked_out - prior_sacked;
if (delivered > 0)
tp->delivered += delivered;
tcp_verify_left_out(tp);
}
}
/* Account for ACK, ACKing some data in Reno Recovery phase. */
static void tcp_remove_reno_sacks(struct sock *sk, int acked)
{
struct tcp_sock *tp = tcp_sk(sk);
if (acked > 0) {
/* One ACK acked hole. The rest eat duplicate ACKs. */
tp->delivered += max_t(int, acked - tp->sacked_out, 1);
if (acked - 1 >= tp->sacked_out)
tp->sacked_out = 0;
else
tp->sacked_out -= acked - 1;
}
tcp_check_reno_reordering(sk, acked);
tcp_verify_left_out(tp);
}
static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
{
tp->sacked_out = 0;
}
void tcp_clear_retrans(struct tcp_sock *tp)
{
tp->retrans_out = 0;
tp->lost_out = 0;
tp->undo_marker = 0;
tp->undo_retrans = -1;
tp->sacked_out = 0;
}
static inline void tcp_init_undo(struct tcp_sock *tp)
{
tp->undo_marker = tp->snd_una;
/* Retransmission still in flight may cause DSACKs later. */
tp->undo_retrans = tp->retrans_out ? : -1;
}
static bool tcp_is_rack(const struct sock *sk)
{
return sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_LOSS_DETECTION;
}
/* If we detect SACK reneging, forget all SACK information
* and reset tags completely, otherwise preserve SACKs. If receiver
* dropped its ofo queue, we will know this due to reneging detection.
*/
static void tcp_timeout_mark_lost(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb, *head;
bool is_reneg; /* is receiver reneging on SACKs? */
head = tcp_rtx_queue_head(sk);
is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED);
if (is_reneg) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
tp->sacked_out = 0;
/* Mark SACK reneging until we recover from this loss event. */
tp->is_sack_reneg = 1;
} else if (tcp_is_reno(tp)) {
tcp_reset_reno_sack(tp);
}
skb = head;
skb_rbtree_walk_from(skb) {
if (is_reneg)
TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
else if (tcp_is_rack(sk) && skb != head &&
tcp_rack_skb_timeout(tp, skb, 0) > 0)
continue; /* Don't mark recently sent ones lost yet */
tcp_mark_skb_lost(sk, skb);
}
tcp_verify_left_out(tp);
tcp_clear_all_retrans_hints(tp);
}
/* Enter Loss state. */
void tcp_enter_loss(struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct net *net = sock_net(sk);
bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
tcp_timeout_mark_lost(sk);
/* Reduce ssthresh if it has not yet been made inside this window. */
if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
!after(tp->high_seq, tp->snd_una) ||
(icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
tp->prior_ssthresh = tcp_current_ssthresh(sk);
tp->prior_cwnd = tp->snd_cwnd;
tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
tcp_ca_event(sk, CA_EVENT_LOSS);
tcp_init_undo(tp);
}
tp->snd_cwnd = tcp_packets_in_flight(tp) + 1;
tp->snd_cwnd_cnt = 0;
tp->snd_cwnd_stamp = tcp_jiffies32;
/* Timeout in disordered state after receiving substantial DUPACKs
* suggests that the degree of reordering is over-estimated.
*/
if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
tp->sacked_out >= net->ipv4.sysctl_tcp_reordering)
tp->reordering = min_t(unsigned int, tp->reordering,
net->ipv4.sysctl_tcp_reordering);
tcp_set_ca_state(sk, TCP_CA_Loss);
tp->high_seq = tp->snd_nxt;
tcp_ecn_queue_cwr(tp);
/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
* loss recovery is underway except recurring timeout(s) on
* the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
*/
tp->frto = net->ipv4.sysctl_tcp_frto &&
(new_recovery || icsk->icsk_retransmits) &&
!inet_csk(sk)->icsk_mtup.probe_size;
}
/* If ACK arrived pointing to a remembered SACK, it means that our
* remembered SACKs do not reflect real state of receiver i.e.
* receiver _host_ is heavily congested (or buggy).
*
* To avoid big spurious retransmission bursts due to transient SACK
* scoreboard oddities that look like reneging, we give the receiver a
* little time (max(RTT/2, 10ms)) to send us some more ACKs that will
* restore sanity to the SACK scoreboard. If the apparent reneging
* persists until this RTO then we'll clear the SACK scoreboard.
*/
static bool tcp_check_sack_reneging(struct sock *sk, int flag)
{
if (flag & FLAG_SACK_RENEGING) {
struct tcp_sock *tp = tcp_sk(sk);
unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
msecs_to_jiffies(10));
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
delay, TCP_RTO_MAX);
return true;
}
return false;
}
/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
* counter when SACK is enabled (without SACK, sacked_out is used for
* that purpose).
*
* With reordering, holes may still be in flight, so RFC3517 recovery
* uses pure sacked_out (total number of SACKed segments) even though
* it violates the RFC that uses duplicate ACKs, often these are equal
* but when e.g. out-of-window ACKs or packet duplication occurs,
* they differ. Since neither occurs due to loss, TCP should really
* ignore them.
*/
static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
{
return tp->sacked_out + 1;
}
/* Linux NewReno/SACK/ECN state machine.
* --------------------------------------
*
* "Open" Normal state, no dubious events, fast path.
* "Disorder" In all the respects it is "Open",
* but requires a bit more attention. It is entered when
* we see some SACKs or dupacks. It is split of "Open"
* mainly to move some processing from fast path to slow one.
* "CWR" CWND was reduced due to some Congestion Notification event.
* It can be ECN, ICMP source quench, local device congestion.
* "Recovery" CWND was reduced, we are fast-retransmitting.
* "Loss" CWND was reduced due to RTO timeout or SACK reneging.
*
* tcp_fastretrans_alert() is entered:
* - each incoming ACK, if state is not "Open"
* - when arrived ACK is unusual, namely:
* * SACK
* * Duplicate ACK.
* * ECN ECE.
*
* Counting packets in flight is pretty simple.
*
* in_flight = packets_out - left_out + retrans_out
*
* packets_out is SND.NXT-SND.UNA counted in packets.
*
* retrans_out is number of retransmitted segments.
*
* left_out is number of segments left network, but not ACKed yet.
*
* left_out = sacked_out + lost_out
*
* sacked_out: Packets, which arrived to receiver out of order
* and hence not ACKed. With SACKs this number is simply
* amount of SACKed data. Even without SACKs
* it is easy to give pretty reliable estimate of this number,
* counting duplicate ACKs.
*
* lost_out: Packets lost by network. TCP has no explicit
* "loss notification" feedback from network (for now).
* It means that this number can be only _guessed_.
* Actually, it is the heuristics to predict lossage that
* distinguishes different algorithms.
*
* F.e. after RTO, when all the queue is considered as lost,
* lost_out = packets_out and in_flight = retrans_out.
*
* Essentially, we have now a few algorithms detecting
* lost packets.
*
* If the receiver supports SACK:
*
* RFC6675/3517: It is the conventional algorithm. A packet is
* considered lost if the number of higher sequence packets
* SACKed is greater than or equal the DUPACK thoreshold
* (reordering). This is implemented in tcp_mark_head_lost and
* tcp_update_scoreboard.
*
* RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm
* (2017-) that checks timing instead of counting DUPACKs.
* Essentially a packet is considered lost if it's not S/ACKed
* after RTT + reordering_window, where both metrics are
* dynamically measured and adjusted. This is implemented in
* tcp_rack_mark_lost.
*
* If the receiver does not support SACK:
*
* NewReno (RFC6582): in Recovery we assume that one segment
* is lost (classic Reno). While we are in Recovery and
* a partial ACK arrives, we assume that one more packet
* is lost (NewReno). This heuristics are the same in NewReno
* and SACK.
*
* Really tricky (and requiring careful tuning) part of algorithm
* is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
* The first determines the moment _when_ we should reduce CWND and,
* hence, slow down forward transmission. In fact, it determines the moment
* when we decide that hole is caused by loss, rather than by a reorder.
*
* tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
* holes, caused by lost packets.
*
* And the most logically complicated part of algorithm is undo
* heuristics. We detect false retransmits due to both too early
* fast retransmit (reordering) and underestimated RTO, analyzing
* timestamps and D-SACKs. When we detect that some segments were
* retransmitted by mistake and CWND reduction was wrong, we undo
* window reduction and abort recovery phase. This logic is hidden
* inside several functions named tcp_try_undo_<something>.
*/
/* This function decides, when we should leave Disordered state
* and enter Recovery phase, reducing congestion window.
*
* Main question: may we further continue forward transmission
* with the same cwnd?
*/
static bool tcp_time_to_recover(struct sock *sk, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
/* Trick#1: The loss is proven. */
if (tp->lost_out)
return true;
/* Not-A-Trick#2 : Classic rule... */
if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering)
return true;
return false;
}
/* Detect loss in event "A" above by marking head of queue up as lost.
* For non-SACK(Reno) senders, the first "packets" number of segments
* are considered lost. For RFC3517 SACK, a segment is considered lost if it
* has at least tp->reordering SACKed seqments above it; "packets" refers to
* the maximum SACKed segments to pass before reaching this limit.
*/
static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
int cnt, oldcnt, lost;
unsigned int mss;
/* Use SACK to deduce losses of new sequences sent during recovery */
const u32 loss_high = tcp_is_sack(tp) ? tp->snd_nxt : tp->high_seq;
WARN_ON(packets > tp->packets_out);
skb = tp->lost_skb_hint;
if (skb) {
/* Head already handled? */
if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una))
return;
cnt = tp->lost_cnt_hint;
} else {
skb = tcp_rtx_queue_head(sk);
cnt = 0;
}
skb_rbtree_walk_from(skb) {
/* TODO: do this better */
/* this is not the most efficient way to do this... */
tp->lost_skb_hint = skb;
tp->lost_cnt_hint = cnt;
if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
break;
oldcnt = cnt;
if (tcp_is_reno(tp) ||
(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
cnt += tcp_skb_pcount(skb);
if (cnt > packets) {
if (tcp_is_sack(tp) ||
(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
(oldcnt >= packets))
break;
mss = tcp_skb_mss(skb);
/* If needed, chop off the prefix to mark as lost. */
lost = (packets - oldcnt) * mss;
if (lost < skb->len &&
tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
lost, mss, GFP_ATOMIC) < 0)
break;
cnt = packets;
}
tcp_skb_mark_lost(tp, skb);
if (mark_head)
break;
}
tcp_verify_left_out(tp);
}
/* Account newly detected lost packet(s) */
static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tcp_is_sack(tp)) {
int sacked_upto = tp->sacked_out - tp->reordering;
if (sacked_upto >= 0)
tcp_mark_head_lost(sk, sacked_upto, 0);
else if (fast_rexmit)
tcp_mark_head_lost(sk, 1, 1);
}
}
static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
{
return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
before(tp->rx_opt.rcv_tsecr, when);
}
/* skb is spurious retransmitted if the returned timestamp echo
* reply is prior to the skb transmission time
*/
static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
const struct sk_buff *skb)
{
return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
}
/* Nothing was retransmitted or returned timestamp is less
* than timestamp of the first retransmission.
*/
static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
{
return !tp->retrans_stamp ||
tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
}
/* Undo procedures. */
/* We can clear retrans_stamp when there are no retransmissions in the
* window. It would seem that it is trivially available for us in
* tp->retrans_out, however, that kind of assumptions doesn't consider
* what will happen if errors occur when sending retransmission for the
* second time. ...It could the that such segment has only
* TCPCB_EVER_RETRANS set at the present time. It seems that checking
* the head skb is enough except for some reneging corner cases that
* are not worth the effort.
*
* Main reason for all this complexity is the fact that connection dying
* time now depends on the validity of the retrans_stamp, in particular,
* that successive retransmissions of a segment must not advance
* retrans_stamp under any conditions.
*/
static bool tcp_any_retrans_done(const struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
if (tp->retrans_out)
return true;
skb = tcp_rtx_queue_head(sk);
if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
return true;
return false;
}
static void DBGUNDO(struct sock *sk, const char *msg)
{
#if FASTRETRANS_DEBUG > 1
struct tcp_sock *tp = tcp_sk(sk);
struct inet_sock *inet = inet_sk(sk);
if (sk->sk_family == AF_INET) {
pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
msg,
&inet->inet_daddr, ntohs(inet->inet_dport),
tp->snd_cwnd, tcp_left_out(tp),
tp->snd_ssthresh, tp->prior_ssthresh,
tp->packets_out);
}
#if IS_ENABLED(CONFIG_IPV6)
else if (sk->sk_family == AF_INET6) {
pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
msg,
&sk->sk_v6_daddr, ntohs(inet->inet_dport),
tp->snd_cwnd, tcp_left_out(tp),
tp->snd_ssthresh, tp->prior_ssthresh,
tp->packets_out);
}
#endif
#endif
}
static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
{
struct tcp_sock *tp = tcp_sk(sk);
if (unmark_loss) {
struct sk_buff *skb;
skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
}
tp->lost_out = 0;
tcp_clear_all_retrans_hints(tp);
}
if (tp->prior_ssthresh) {
const struct inet_connection_sock *icsk = inet_csk(sk);
tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
if (tp->prior_ssthresh > tp->snd_ssthresh) {
tp->snd_ssthresh = tp->prior_ssthresh;
tcp_ecn_withdraw_cwr(tp);
}
}
tp->snd_cwnd_stamp = tcp_jiffies32;
tp->undo_marker = 0;
tp->rack.advanced = 1; /* Force RACK to re-exam losses */
}
static inline bool tcp_may_undo(const struct tcp_sock *tp)
{
return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
}
/* People celebrate: "We love our President!" */
static bool tcp_try_undo_recovery(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tcp_may_undo(tp)) {
int mib_idx;
/* Happy end! We did not retransmit anything
* or our original transmission succeeded.
*/
DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
tcp_undo_cwnd_reduction(sk, false);
if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
mib_idx = LINUX_MIB_TCPLOSSUNDO;
else
mib_idx = LINUX_MIB_TCPFULLUNDO;
NET_INC_STATS(sock_net(sk), mib_idx);
} else if (tp->rack.reo_wnd_persist) {
tp->rack.reo_wnd_persist--;
}
if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
/* Hold old state until something *above* high_seq
* is ACKed. For Reno it is MUST to prevent false
* fast retransmits (RFC2582). SACK TCP is safe. */
if (!tcp_any_retrans_done(sk))
tp->retrans_stamp = 0;
return true;
}
tcp_set_ca_state(sk, TCP_CA_Open);
tp->is_sack_reneg = 0;
return false;
}
/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
static bool tcp_try_undo_dsack(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tp->undo_marker && !tp->undo_retrans) {
tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH,
tp->rack.reo_wnd_persist + 1);
DBGUNDO(sk, "D-SACK");
tcp_undo_cwnd_reduction(sk, false);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
return true;
}
return false;
}
/* Undo during loss recovery after partial ACK or using F-RTO. */
static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
{
struct tcp_sock *tp = tcp_sk(sk);
if (frto_undo || tcp_may_undo(tp)) {
tcp_undo_cwnd_reduction(sk, true);
DBGUNDO(sk, "partial loss");
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
if (frto_undo)
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPSPURIOUSRTOS);
inet_csk(sk)->icsk_retransmits = 0;
if (frto_undo || tcp_is_sack(tp)) {
tcp_set_ca_state(sk, TCP_CA_Open);
tp->is_sack_reneg = 0;
}
return true;
}
return false;
}
/* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
* It computes the number of packets to send (sndcnt) based on packets newly
* delivered:
* 1) If the packets in flight is larger than ssthresh, PRR spreads the
* cwnd reductions across a full RTT.
* 2) Otherwise PRR uses packet conservation to send as much as delivered.
* But when the retransmits are acked without further losses, PRR
* slow starts cwnd up to ssthresh to speed up the recovery.
*/
static void tcp_init_cwnd_reduction(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
tp->high_seq = tp->snd_nxt;
tp->tlp_high_seq = 0;
tp->snd_cwnd_cnt = 0;
tp->prior_cwnd = tp->snd_cwnd;
tp->prr_delivered = 0;
tp->prr_out = 0;
tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
tcp_ecn_queue_cwr(tp);
}
void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
int sndcnt = 0;
int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
return;
tp->prr_delivered += newly_acked_sacked;
if (delta < 0) {
u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
tp->prior_cwnd - 1;
sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
} else if ((flag & (FLAG_RETRANS_DATA_ACKED | FLAG_LOST_RETRANS)) ==
FLAG_RETRANS_DATA_ACKED) {
sndcnt = min_t(int, delta,
max_t(int, tp->prr_delivered - tp->prr_out,
newly_acked_sacked) + 1);
} else {
sndcnt = min(delta, newly_acked_sacked);
}
/* Force a fast retransmit upon entering fast recovery */
sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
}
static inline void tcp_end_cwnd_reduction(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
if (inet_csk(sk)->icsk_ca_ops->cong_control)
return;
/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
(inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
tp->snd_cwnd = tp->snd_ssthresh;
tp->snd_cwnd_stamp = tcp_jiffies32;
}
tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
}
/* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
void tcp_enter_cwr(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
tp->prior_ssthresh = 0;
if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
tp->undo_marker = 0;
tcp_init_cwnd_reduction(sk);
tcp_set_ca_state(sk, TCP_CA_CWR);
}
}
EXPORT_SYMBOL(tcp_enter_cwr);
static void tcp_try_keep_open(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
int state = TCP_CA_Open;
if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
state = TCP_CA_Disorder;
if (inet_csk(sk)->icsk_ca_state != state) {
tcp_set_ca_state(sk, state);
tp->high_seq = tp->snd_nxt;
}
}
static void tcp_try_to_open(struct sock *sk, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
tcp_verify_left_out(tp);
if (!tcp_any_retrans_done(sk))
tp->retrans_stamp = 0;
if (flag & FLAG_ECE)
tcp_enter_cwr(sk);
if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
tcp_try_keep_open(sk);
}
}
static void tcp_mtup_probe_failed(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
icsk->icsk_mtup.probe_size = 0;
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
}
static void tcp_mtup_probe_success(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
/* FIXME: breaks with very large cwnd */
tp->prior_ssthresh = tcp_current_ssthresh(sk);
tp->snd_cwnd = tp->snd_cwnd *
tcp_mss_to_mtu(sk, tp->mss_cache) /
icsk->icsk_mtup.probe_size;
tp->snd_cwnd_cnt = 0;
tp->snd_cwnd_stamp = tcp_jiffies32;
tp->snd_ssthresh = tcp_current_ssthresh(sk);
icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
icsk->icsk_mtup.probe_size = 0;
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
}
/* Do a simple retransmit without using the backoff mechanisms in
* tcp_timer. This is used for path mtu discovery.
* The socket is already locked here.
*/
void tcp_simple_retransmit(struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
unsigned int mss = tcp_current_mss(sk);
skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
if (tcp_skb_seglen(skb) > mss &&
!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
tp->retrans_out -= tcp_skb_pcount(skb);
}
tcp_skb_mark_lost_uncond_verify(tp, skb);
}
}
tcp_clear_retrans_hints_partial(tp);
if (!tp->lost_out)
return;
if (tcp_is_reno(tp))
tcp_limit_reno_sacked(tp);
tcp_verify_left_out(tp);
/* Don't muck with the congestion window here.
* Reason is that we do not increase amount of _data_
* in network, but units changed and effective
* cwnd/ssthresh really reduced now.
*/
if (icsk->icsk_ca_state != TCP_CA_Loss) {
tp->high_seq = tp->snd_nxt;
tp->snd_ssthresh = tcp_current_ssthresh(sk);
tp->prior_ssthresh = 0;
tp->undo_marker = 0;
tcp_set_ca_state(sk, TCP_CA_Loss);
}
tcp_xmit_retransmit_queue(sk);
}
EXPORT_SYMBOL(tcp_simple_retransmit);
void tcp_enter_recovery(struct sock *sk, bool ece_ack)
{
struct tcp_sock *tp = tcp_sk(sk);
int mib_idx;
if (tcp_is_reno(tp))
mib_idx = LINUX_MIB_TCPRENORECOVERY;
else
mib_idx = LINUX_MIB_TCPSACKRECOVERY;
NET_INC_STATS(sock_net(sk), mib_idx);
tp->prior_ssthresh = 0;
tcp_init_undo(tp);
if (!tcp_in_cwnd_reduction(sk)) {
if (!ece_ack)
tp->prior_ssthresh = tcp_current_ssthresh(sk);
tcp_init_cwnd_reduction(sk);
}
tcp_set_ca_state(sk, TCP_CA_Recovery);
}
/* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
* recovered or spurious. Otherwise retransmits more on partial ACKs.
*/
static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
int *rexmit)
{
struct tcp_sock *tp = tcp_sk(sk);
bool recovered = !before(tp->snd_una, tp->high_seq);
if ((flag & FLAG_SND_UNA_ADVANCED) &&
tcp_try_undo_loss(sk, false))
return;
if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
/* Step 3.b. A timeout is spurious if not all data are
* lost, i.e., never-retransmitted data are (s)acked.
*/
if ((flag & FLAG_ORIG_SACK_ACKED) &&
tcp_try_undo_loss(sk, true))
return;
if (after(tp->snd_nxt, tp->high_seq)) {
if (flag & FLAG_DATA_SACKED || num_dupack)
tp->frto = 0; /* Step 3.a. loss was real */
} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
tp->high_seq = tp->snd_nxt;
/* Step 2.b. Try send new data (but deferred until cwnd
* is updated in tcp_ack()). Otherwise fall back to
* the conventional recovery.
*/
if (!tcp_write_queue_empty(sk) &&
after(tcp_wnd_end(tp), tp->snd_nxt)) {
*rexmit = REXMIT_NEW;
return;
}
tp->frto = 0;
}
}
if (recovered) {
/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
tcp_try_undo_recovery(sk);
return;
}
if (tcp_is_reno(tp)) {
/* A Reno DUPACK means new data in F-RTO step 2.b above are
* delivered. Lower inflight to clock out (re)tranmissions.
*/
if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
tcp_add_reno_sack(sk, num_dupack);
else if (flag & FLAG_SND_UNA_ADVANCED)
tcp_reset_reno_sack(tp);
}
*rexmit = REXMIT_LOST;
}
/* Undo during fast recovery after partial ACK. */
static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tp->undo_marker && tcp_packet_delayed(tp)) {
/* Plain luck! Hole if filled with delayed
* packet, rather than with a retransmit. Check reordering.
*/
tcp_check_sack_reordering(sk, prior_snd_una, 1);
/* We are getting evidence that the reordering degree is higher
* than we realized. If there are no retransmits out then we
* can undo. Otherwise we clock out new packets but do not
* mark more packets lost or retransmit more.
*/
if (tp->retrans_out)
return true;
if (!tcp_any_retrans_done(sk))
tp->retrans_stamp = 0;
DBGUNDO(sk, "partial recovery");
tcp_undo_cwnd_reduction(sk, true);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
tcp_try_keep_open(sk);
return true;
}
return false;
}
static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tcp_rtx_queue_empty(sk))
return;
if (unlikely(tcp_is_reno(tp))) {
tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
} else if (tcp_is_rack(sk)) {
u32 prior_retrans = tp->retrans_out;
tcp_rack_mark_lost(sk);
if (prior_retrans > tp->retrans_out)
*ack_flag |= FLAG_LOST_RETRANS;
}
}
static bool tcp_force_fast_retransmit(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
return after(tcp_highest_sack_seq(tp),
tp->snd_una + tp->reordering * tp->mss_cache);
}
/* Process an event, which can update packets-in-flight not trivially.
* Main goal of this function is to calculate new estimate for left_out,
* taking into account both packets sitting in receiver's buffer and
* packets lost by network.
*
* Besides that it updates the congestion state when packet loss or ECN
* is detected. But it does not reduce the cwnd, it is done by the
* congestion control later.
*
* It does _not_ decide what to send, it is made in function
* tcp_xmit_retransmit_queue().
*/
static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
int num_dupack, int *ack_flag, int *rexmit)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int fast_rexmit = 0, flag = *ack_flag;
bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) &&
tcp_force_fast_retransmit(sk));
if (!tp->packets_out && tp->sacked_out)
tp->sacked_out = 0;
/* Now state machine starts.
* A. ECE, hence prohibit cwnd undoing, the reduction is required. */
if (flag & FLAG_ECE)
tp->prior_ssthresh = 0;
/* B. In all the states check for reneging SACKs. */
if (tcp_check_sack_reneging(sk, flag))
return;
/* C. Check consistency of the current state. */