tcp_output.c 105.8 KB
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/*
 * 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).
 *
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 * Authors:	Ross Biro
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 *		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	:	Retransmit queue handled by TCP.
 *				:	Fragmentation on mtu decrease
 *				:	Segment collapse on retransmit
 *				:	AF independence
 *
 *		Linus Torvalds	:	send_delayed_ack
 *		David S. Miller	:	Charge memory using the right skb
 *					during syn/ack processing.
 *		David S. Miller :	Output engine completely rewritten.
 *		Andrea Arcangeli:	SYNACK carry ts_recent in tsecr.
 *		Cacophonix Gaul :	draft-minshall-nagle-01
 *		J Hadi Salim	:	ECN support
 *
 */

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#define pr_fmt(fmt) "TCP: " fmt

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#include <net/tcp.h>

#include <linux/compiler.h>
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#include <linux/gfp.h>
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#include <linux/module.h>

/* People can turn this off for buggy TCP's found in printers etc. */
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int sysctl_tcp_retrans_collapse __read_mostly = 1;
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/* People can turn this on to work with those rare, broken TCPs that
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 * interpret the window field as a signed quantity.
 */
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int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
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/* Default TSQ limit of four TSO segments */
int sysctl_tcp_limit_output_bytes __read_mostly = 262144;
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/* This limits the percentage of the congestion window which we
 * will allow a single TSO frame to consume.  Building TSO frames
 * which are too large can cause TCP streams to be bursty.
 */
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int sysctl_tcp_tso_win_divisor __read_mostly = 3;
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/* By default, RFC2861 behavior.  */
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int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
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static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
			   int push_one, gfp_t gfp);
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/* Account for new data that has been sent to the network. */
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static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
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{
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	struct inet_connection_sock *icsk = inet_csk(sk);
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	struct tcp_sock *tp = tcp_sk(sk);
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	unsigned int prior_packets = tp->packets_out;
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	tcp_advance_send_head(sk, skb);
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	tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
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	tp->packets_out += tcp_skb_pcount(skb);
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	if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
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	    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
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		tcp_rearm_rto(sk);
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	}
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	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
		      tcp_skb_pcount(skb));
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}

/* SND.NXT, if window was not shrunk.
 * If window has been shrunk, what should we make? It is not clear at all.
 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
 * invalid. OK, let's make this for now:
 */
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static inline __u32 tcp_acceptable_seq(const struct sock *sk)
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{
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	const struct tcp_sock *tp = tcp_sk(sk);
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	if (!before(tcp_wnd_end(tp), tp->snd_nxt))
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		return tp->snd_nxt;
	else
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		return tcp_wnd_end(tp);
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}

/* Calculate mss to advertise in SYN segment.
 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
 *
 * 1. It is independent of path mtu.
 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
 *    attached devices, because some buggy hosts are confused by
 *    large MSS.
 * 4. We do not make 3, we advertise MSS, calculated from first
 *    hop device mtu, but allow to raise it to ip_rt_min_advmss.
 *    This may be overridden via information stored in routing table.
 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
 *    probably even Jumbo".
 */
static __u16 tcp_advertise_mss(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
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	const struct dst_entry *dst = __sk_dst_get(sk);
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	int mss = tp->advmss;

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	if (dst) {
		unsigned int metric = dst_metric_advmss(dst);

		if (metric < mss) {
			mss = metric;
			tp->advmss = mss;
		}
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	}

	return (__u16)mss;
}

/* RFC2861. Reset CWND after idle period longer RTO to "restart window".
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 * This is the first part of cwnd validation mechanism.
 */
void tcp_cwnd_restart(struct sock *sk, s32 delta)
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{
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	struct tcp_sock *tp = tcp_sk(sk);
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	u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
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	u32 cwnd = tp->snd_cwnd;

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	tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
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	tp->snd_ssthresh = tcp_current_ssthresh(sk);
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	restart_cwnd = min(restart_cwnd, cwnd);

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	while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
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		cwnd >>= 1;
	tp->snd_cwnd = max(cwnd, restart_cwnd);
	tp->snd_cwnd_stamp = tcp_time_stamp;
	tp->snd_cwnd_used = 0;
}

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/* Congestion state accounting after a packet has been sent. */
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static void tcp_event_data_sent(struct tcp_sock *tp,
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				struct sock *sk)
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{
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	struct inet_connection_sock *icsk = inet_csk(sk);
	const u32 now = tcp_time_stamp;
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	if (tcp_packets_in_flight(tp) == 0)
		tcp_ca_event(sk, CA_EVENT_TX_START);

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	tp->lsndtime = now;

	/* If it is a reply for ato after last received
	 * packet, enter pingpong mode.
	 */
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	if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
		icsk->icsk_ack.pingpong = 1;
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}

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/* Account for an ACK we sent. */
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static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
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{
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	tcp_dec_quickack_mode(sk, pkts);
	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
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}

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u32 tcp_default_init_rwnd(u32 mss)
{
	/* Initial receive window should be twice of TCP_INIT_CWND to
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	 * enable proper sending of new unsent data during fast recovery
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	 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
	 * limit when mss is larger than 1460.
	 */
	u32 init_rwnd = TCP_INIT_CWND * 2;

	if (mss > 1460)
		init_rwnd = max((1460 * init_rwnd) / mss, 2U);
	return init_rwnd;
}

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/* Determine a window scaling and initial window to offer.
 * Based on the assumption that the given amount of space
 * will be offered. Store the results in the tp structure.
 * NOTE: for smooth operation initial space offering should
 * be a multiple of mss if possible. We assume here that mss >= 1.
 * This MUST be enforced by all callers.
 */
void tcp_select_initial_window(int __space, __u32 mss,
			       __u32 *rcv_wnd, __u32 *window_clamp,
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			       int wscale_ok, __u8 *rcv_wscale,
			       __u32 init_rcv_wnd)
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{
	unsigned int space = (__space < 0 ? 0 : __space);

	/* If no clamp set the clamp to the max possible scaled window */
	if (*window_clamp == 0)
		(*window_clamp) = (65535 << 14);
	space = min(*window_clamp, space);

	/* Quantize space offering to a multiple of mss if possible. */
	if (space > mss)
		space = (space / mss) * mss;

	/* NOTE: offering an initial window larger than 32767
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	 * will break some buggy TCP stacks. If the admin tells us
	 * it is likely we could be speaking with such a buggy stack
	 * we will truncate our initial window offering to 32K-1
	 * unless the remote has sent us a window scaling option,
	 * which we interpret as a sign the remote TCP is not
	 * misinterpreting the window field as a signed quantity.
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	 */
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	if (sysctl_tcp_workaround_signed_windows)
		(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
	else
		(*rcv_wnd) = space;

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	(*rcv_wscale) = 0;
	if (wscale_ok) {
		/* Set window scaling on max possible window
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		 * See RFC1323 for an explanation of the limit to 14
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		 */
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		space = max_t(u32, space, sysctl_tcp_rmem[2]);
		space = max_t(u32, space, sysctl_rmem_max);
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		space = min_t(u32, space, *window_clamp);
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		while (space > 65535 && (*rcv_wscale) < 14) {
			space >>= 1;
			(*rcv_wscale)++;
		}
	}

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	if (mss > (1 << *rcv_wscale)) {
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		if (!init_rcv_wnd) /* Use default unless specified otherwise */
			init_rcv_wnd = tcp_default_init_rwnd(mss);
		*rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
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	}

	/* Set the clamp no higher than max representable value */
	(*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
}
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EXPORT_SYMBOL(tcp_select_initial_window);
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/* Chose a new window to advertise, update state in tcp_sock for the
 * socket, and return result with RFC1323 scaling applied.  The return
 * value can be stuffed directly into th->window for an outgoing
 * frame.
 */
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static u16 tcp_select_window(struct sock *sk)
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{
	struct tcp_sock *tp = tcp_sk(sk);
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	u32 old_win = tp->rcv_wnd;
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	u32 cur_win = tcp_receive_window(tp);
	u32 new_win = __tcp_select_window(sk);

	/* Never shrink the offered window */
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	if (new_win < cur_win) {
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		/* Danger Will Robinson!
		 * Don't update rcv_wup/rcv_wnd here or else
		 * we will not be able to advertise a zero
		 * window in time.  --DaveM
		 *
		 * Relax Will Robinson.
		 */
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		if (new_win == 0)
			NET_INC_STATS(sock_net(sk),
				      LINUX_MIB_TCPWANTZEROWINDOWADV);
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		new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
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	}
	tp->rcv_wnd = new_win;
	tp->rcv_wup = tp->rcv_nxt;

	/* Make sure we do not exceed the maximum possible
	 * scaled window.
	 */
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	if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
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		new_win = min(new_win, MAX_TCP_WINDOW);
	else
		new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));

	/* RFC1323 scaling applied */
	new_win >>= tp->rx_opt.rcv_wscale;

	/* If we advertise zero window, disable fast path. */
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	if (new_win == 0) {
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		tp->pred_flags = 0;
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		if (old_win)
			NET_INC_STATS(sock_net(sk),
				      LINUX_MIB_TCPTOZEROWINDOWADV);
	} else if (old_win == 0) {
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
	}
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	return new_win;
}

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/* Packet ECN state for a SYN-ACK */
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static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
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{
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	const struct tcp_sock *tp = tcp_sk(sk);

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	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
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	if (!(tp->ecn_flags & TCP_ECN_OK))
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		TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
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	else if (tcp_ca_needs_ecn(sk))
		INET_ECN_xmit(sk);
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}

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/* Packet ECN state for a SYN.  */
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static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
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{
	struct tcp_sock *tp = tcp_sk(sk);
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	bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
		       tcp_ca_needs_ecn(sk);

	if (!use_ecn) {
		const struct dst_entry *dst = __sk_dst_get(sk);

		if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
			use_ecn = true;
	}
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	tp->ecn_flags = 0;
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	if (use_ecn) {
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		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
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		tp->ecn_flags = TCP_ECN_OK;
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		if (tcp_ca_needs_ecn(sk))
			INET_ECN_xmit(sk);
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	}
}

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static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
{
	if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
		/* tp->ecn_flags are cleared at a later point in time when
		 * SYN ACK is ultimatively being received.
		 */
		TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
}

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static void
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tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
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{
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	if (inet_rsk(req)->ecn_ok)
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		th->ece = 1;
}

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/* Set up ECN state for a packet on a ESTABLISHED socket that is about to
 * be sent.
 */
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static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
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			 struct tcphdr *th, int tcp_header_len)
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{
	struct tcp_sock *tp = tcp_sk(sk);

	if (tp->ecn_flags & TCP_ECN_OK) {
		/* Not-retransmitted data segment: set ECT and inject CWR. */
		if (skb->len != tcp_header_len &&
		    !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
			INET_ECN_xmit(sk);
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			if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
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				tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
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				th->cwr = 1;
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				skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
			}
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		} else if (!tcp_ca_needs_ecn(sk)) {
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			/* ACK or retransmitted segment: clear ECT|CE */
			INET_ECN_dontxmit(sk);
		}
		if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
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			th->ece = 1;
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	}
}

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/* Constructs common control bits of non-data skb. If SYN/FIN is present,
 * auto increment end seqno.
 */
static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
{
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	skb->ip_summed = CHECKSUM_PARTIAL;
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	skb->csum = 0;

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	TCP_SKB_CB(skb)->tcp_flags = flags;
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	TCP_SKB_CB(skb)->sacked = 0;

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	tcp_skb_pcount_set(skb, 1);
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	TCP_SKB_CB(skb)->seq = seq;
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	if (flags & (TCPHDR_SYN | TCPHDR_FIN))
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		seq++;
	TCP_SKB_CB(skb)->end_seq = seq;
}

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static inline bool tcp_urg_mode(const struct tcp_sock *tp)
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{
	return tp->snd_una != tp->snd_up;
}

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#define OPTION_SACK_ADVERTISE	(1 << 0)
#define OPTION_TS		(1 << 1)
#define OPTION_MD5		(1 << 2)
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#define OPTION_WSCALE		(1 << 3)
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#define OPTION_FAST_OPEN_COOKIE	(1 << 8)
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struct tcp_out_options {
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	u16 options;		/* bit field of OPTION_* */
	u16 mss;		/* 0 to disable */
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	u8 ws;			/* window scale, 0 to disable */
	u8 num_sack_blocks;	/* number of SACK blocks to include */
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	u8 hash_size;		/* bytes in hash_location */
	__u8 *hash_location;	/* temporary pointer, overloaded */
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	__u32 tsval, tsecr;	/* need to include OPTION_TS */
	struct tcp_fastopen_cookie *fastopen_cookie;	/* Fast open cookie */
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};

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/* Write previously computed TCP options to the packet.
 *
 * Beware: Something in the Internet is very sensitive to the ordering of
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 * TCP options, we learned this through the hard way, so be careful here.
 * Luckily we can at least blame others for their non-compliance but from
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 * inter-operability perspective it seems that we're somewhat stuck with
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 * the ordering which we have been using if we want to keep working with
 * those broken things (not that it currently hurts anybody as there isn't
 * particular reason why the ordering would need to be changed).
 *
 * At least SACK_PERM as the first option is known to lead to a disaster
 * (but it may well be that other scenarios fail similarly).
 */
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static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
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			      struct tcp_out_options *opts)
{
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	u16 options = opts->options;	/* mungable copy */
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	if (unlikely(OPTION_MD5 & options)) {
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		*ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
			       (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
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		/* overload cookie hash location */
		opts->hash_location = (__u8 *)ptr;
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		ptr += 4;
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	}
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	if (unlikely(opts->mss)) {
		*ptr++ = htonl((TCPOPT_MSS << 24) |
			       (TCPOLEN_MSS << 16) |
			       opts->mss);
	}

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	if (likely(OPTION_TS & options)) {
		if (unlikely(OPTION_SACK_ADVERTISE & options)) {
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			*ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
				       (TCPOLEN_SACK_PERM << 16) |
				       (TCPOPT_TIMESTAMP << 8) |
				       TCPOLEN_TIMESTAMP);
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			options &= ~OPTION_SACK_ADVERTISE;
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		} else {
			*ptr++ = htonl((TCPOPT_NOP << 24) |
				       (TCPOPT_NOP << 16) |
				       (TCPOPT_TIMESTAMP << 8) |
				       TCPOLEN_TIMESTAMP);
		}
		*ptr++ = htonl(opts->tsval);
		*ptr++ = htonl(opts->tsecr);
	}

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	if (unlikely(OPTION_SACK_ADVERTISE & options)) {
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		*ptr++ = htonl((TCPOPT_NOP << 24) |
			       (TCPOPT_NOP << 16) |
			       (TCPOPT_SACK_PERM << 8) |
			       TCPOLEN_SACK_PERM);
	}

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	if (unlikely(OPTION_WSCALE & options)) {
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		*ptr++ = htonl((TCPOPT_NOP << 24) |
			       (TCPOPT_WINDOW << 16) |
			       (TCPOLEN_WINDOW << 8) |
			       opts->ws);
	}

	if (unlikely(opts->num_sack_blocks)) {
		struct tcp_sack_block *sp = tp->rx_opt.dsack ?
			tp->duplicate_sack : tp->selective_acks;
S
Stephen Hemminger 已提交
498 499 500 501 502
		int this_sack;

		*ptr++ = htonl((TCPOPT_NOP  << 24) |
			       (TCPOPT_NOP  << 16) |
			       (TCPOPT_SACK <<  8) |
A
Adam Langley 已提交
503
			       (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
S
Stephen Hemminger 已提交
504
						     TCPOLEN_SACK_PERBLOCK)));
S
Stephen Hemminger 已提交
505

A
Adam Langley 已提交
506 507
		for (this_sack = 0; this_sack < opts->num_sack_blocks;
		     ++this_sack) {
S
Stephen Hemminger 已提交
508 509 510
			*ptr++ = htonl(sp[this_sack].start_seq);
			*ptr++ = htonl(sp[this_sack].end_seq);
		}
S
Stephen Hemminger 已提交
511

512
		tp->rx_opt.dsack = 0;
S
Stephen Hemminger 已提交
513
	}
Y
Yuchung Cheng 已提交
514 515 516

	if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
		struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
517 518 519 520 521 522 523 524 525 526 527 528 529
		u8 *p = (u8 *)ptr;
		u32 len; /* Fast Open option length */

		if (foc->exp) {
			len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
			*ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
				     TCPOPT_FASTOPEN_MAGIC);
			p += TCPOLEN_EXP_FASTOPEN_BASE;
		} else {
			len = TCPOLEN_FASTOPEN_BASE + foc->len;
			*p++ = TCPOPT_FASTOPEN;
			*p++ = len;
		}
Y
Yuchung Cheng 已提交
530

531 532 533 534
		memcpy(p, foc->val, foc->len);
		if ((len & 3) == 2) {
			p[foc->len] = TCPOPT_NOP;
			p[foc->len + 1] = TCPOPT_NOP;
Y
Yuchung Cheng 已提交
535
		}
536
		ptr += (len + 3) >> 2;
Y
Yuchung Cheng 已提交
537
	}
A
Adam Langley 已提交
538 539
}

540 541 542
/* Compute TCP options for SYN packets. This is not the final
 * network wire format yet.
 */
543
static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
A
Adam Langley 已提交
544
				struct tcp_out_options *opts,
545 546
				struct tcp_md5sig_key **md5)
{
A
Adam Langley 已提交
547
	struct tcp_sock *tp = tcp_sk(sk);
548
	unsigned int remaining = MAX_TCP_OPTION_SPACE;
549
	struct tcp_fastopen_request *fastopen = tp->fastopen_req;
A
Adam Langley 已提交
550

551
#ifdef CONFIG_TCP_MD5SIG
A
Adam Langley 已提交
552 553 554
	*md5 = tp->af_specific->md5_lookup(sk, sk);
	if (*md5) {
		opts->options |= OPTION_MD5;
555
		remaining -= TCPOLEN_MD5SIG_ALIGNED;
556
	}
A
Adam Langley 已提交
557 558
#else
	*md5 = NULL;
559
#endif
A
Adam Langley 已提交
560 561 562 563 564 565 566 567 568 569 570

	/* We always get an MSS option.  The option bytes which will be seen in
	 * normal data packets should timestamps be used, must be in the MSS
	 * advertised.  But we subtract them from tp->mss_cache so that
	 * calculations in tcp_sendmsg are simpler etc.  So account for this
	 * fact here if necessary.  If we don't do this correctly, as a
	 * receiver we won't recognize data packets as being full sized when we
	 * should, and thus we won't abide by the delayed ACK rules correctly.
	 * SACKs don't matter, we never delay an ACK when we have any of those
	 * going out.  */
	opts->mss = tcp_advertise_mss(sk);
571
	remaining -= TCPOLEN_MSS_ALIGNED;
A
Adam Langley 已提交
572

573
	if (likely(sysctl_tcp_timestamps && !*md5)) {
A
Adam Langley 已提交
574
		opts->options |= OPTION_TS;
E
Eric Dumazet 已提交
575
		opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
A
Adam Langley 已提交
576
		opts->tsecr = tp->rx_opt.ts_recent;
577
		remaining -= TCPOLEN_TSTAMP_ALIGNED;
A
Adam Langley 已提交
578
	}
579
	if (likely(sysctl_tcp_window_scaling)) {
A
Adam Langley 已提交
580
		opts->ws = tp->rx_opt.rcv_wscale;
581
		opts->options |= OPTION_WSCALE;
582
		remaining -= TCPOLEN_WSCALE_ALIGNED;
A
Adam Langley 已提交
583
	}
584
	if (likely(sysctl_tcp_sack)) {
A
Adam Langley 已提交
585
		opts->options |= OPTION_SACK_ADVERTISE;
586
		if (unlikely(!(OPTION_TS & opts->options)))
587
			remaining -= TCPOLEN_SACKPERM_ALIGNED;
A
Adam Langley 已提交
588 589
	}

590
	if (fastopen && fastopen->cookie.len >= 0) {
591 592 593 594
		u32 need = fastopen->cookie.len;

		need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
					       TCPOLEN_FASTOPEN_BASE;
595 596 597 598 599 600
		need = (need + 3) & ~3U;  /* Align to 32 bits */
		if (remaining >= need) {
			opts->options |= OPTION_FAST_OPEN_COOKIE;
			opts->fastopen_cookie = &fastopen->cookie;
			remaining -= need;
			tp->syn_fastopen = 1;
601
			tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
602 603
		}
	}
604 605

	return MAX_TCP_OPTION_SPACE - remaining;
S
Stephen Hemminger 已提交
606 607
}

608
/* Set up TCP options for SYN-ACKs. */
609 610 611 612 613
static unsigned int tcp_synack_options(struct request_sock *req,
				       unsigned int mss, struct sk_buff *skb,
				       struct tcp_out_options *opts,
				       const struct tcp_md5sig_key *md5,
				       struct tcp_fastopen_cookie *foc)
614
{
A
Adam Langley 已提交
615
	struct inet_request_sock *ireq = inet_rsk(req);
616
	unsigned int remaining = MAX_TCP_OPTION_SPACE;
A
Adam Langley 已提交
617

618
#ifdef CONFIG_TCP_MD5SIG
E
Eric Dumazet 已提交
619
	if (md5) {
A
Adam Langley 已提交
620
		opts->options |= OPTION_MD5;
621 622 623 624 625 626 627
		remaining -= TCPOLEN_MD5SIG_ALIGNED;

		/* We can't fit any SACK blocks in a packet with MD5 + TS
		 * options. There was discussion about disabling SACK
		 * rather than TS in order to fit in better with old,
		 * buggy kernels, but that was deemed to be unnecessary.
		 */
E
Eric Dumazet 已提交
628
		ireq->tstamp_ok &= !ireq->sack_ok;
629 630
	}
#endif
A
Adam Langley 已提交
631

632
	/* We always send an MSS option. */
A
Adam Langley 已提交
633
	opts->mss = mss;
634
	remaining -= TCPOLEN_MSS_ALIGNED;
A
Adam Langley 已提交
635 636 637

	if (likely(ireq->wscale_ok)) {
		opts->ws = ireq->rcv_wscale;
638
		opts->options |= OPTION_WSCALE;
639
		remaining -= TCPOLEN_WSCALE_ALIGNED;
A
Adam Langley 已提交
640
	}
E
Eric Dumazet 已提交
641
	if (likely(ireq->tstamp_ok)) {
A
Adam Langley 已提交
642
		opts->options |= OPTION_TS;
643
		opts->tsval = tcp_skb_timestamp(skb) + tcp_rsk(req)->ts_off;
A
Adam Langley 已提交
644
		opts->tsecr = req->ts_recent;
645
		remaining -= TCPOLEN_TSTAMP_ALIGNED;
A
Adam Langley 已提交
646 647 648
	}
	if (likely(ireq->sack_ok)) {
		opts->options |= OPTION_SACK_ADVERTISE;
E
Eric Dumazet 已提交
649
		if (unlikely(!ireq->tstamp_ok))
650
			remaining -= TCPOLEN_SACKPERM_ALIGNED;
A
Adam Langley 已提交
651
	}
652 653 654 655 656
	if (foc != NULL && foc->len >= 0) {
		u32 need = foc->len;

		need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
				   TCPOLEN_FASTOPEN_BASE;
657 658 659 660 661 662 663
		need = (need + 3) & ~3U;  /* Align to 32 bits */
		if (remaining >= need) {
			opts->options |= OPTION_FAST_OPEN_COOKIE;
			opts->fastopen_cookie = foc;
			remaining -= need;
		}
	}
C
Christoph Paasch 已提交
664

665
	return MAX_TCP_OPTION_SPACE - remaining;
A
Adam Langley 已提交
666 667
}

668 669 670
/* Compute TCP options for ESTABLISHED sockets. This is not the
 * final wire format yet.
 */
671
static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
A
Adam Langley 已提交
672
					struct tcp_out_options *opts,
673 674
					struct tcp_md5sig_key **md5)
{
A
Adam Langley 已提交
675
	struct tcp_sock *tp = tcp_sk(sk);
676
	unsigned int size = 0;
677
	unsigned int eff_sacks;
A
Adam Langley 已提交
678

679 680
	opts->options = 0;

A
Adam Langley 已提交
681 682 683 684 685 686 687 688 689 690 691 692
#ifdef CONFIG_TCP_MD5SIG
	*md5 = tp->af_specific->md5_lookup(sk, sk);
	if (unlikely(*md5)) {
		opts->options |= OPTION_MD5;
		size += TCPOLEN_MD5SIG_ALIGNED;
	}
#else
	*md5 = NULL;
#endif

	if (likely(tp->rx_opt.tstamp_ok)) {
		opts->options |= OPTION_TS;
E
Eric Dumazet 已提交
693
		opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
A
Adam Langley 已提交
694 695 696 697
		opts->tsecr = tp->rx_opt.ts_recent;
		size += TCPOLEN_TSTAMP_ALIGNED;
	}

698 699
	eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
	if (unlikely(eff_sacks)) {
700
		const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
A
Adam Langley 已提交
701
		opts->num_sack_blocks =
702
			min_t(unsigned int, eff_sacks,
A
Adam Langley 已提交
703 704 705 706 707 708 709
			      (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
			      TCPOLEN_SACK_PERBLOCK);
		size += TCPOLEN_SACK_BASE_ALIGNED +
			opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
	}

	return size;
S
Stephen Hemminger 已提交
710
}
L
Linus Torvalds 已提交
711

E
Eric Dumazet 已提交
712 713 714 715 716 717 718 719 720

/* TCP SMALL QUEUES (TSQ)
 *
 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
 * to reduce RTT and bufferbloat.
 * We do this using a special skb destructor (tcp_wfree).
 *
 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
 * needs to be reallocated in a driver.
S
stephen hemminger 已提交
721
 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
E
Eric Dumazet 已提交
722 723 724 725 726 727 728 729 730 731 732
 *
 * Since transmit from skb destructor is forbidden, we use a tasklet
 * to process all sockets that eventually need to send more skbs.
 * We use one tasklet per cpu, with its own queue of sockets.
 */
struct tsq_tasklet {
	struct tasklet_struct	tasklet;
	struct list_head	head; /* queue of tcp sockets */
};
static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);

733 734 735 736
static void tcp_tsq_handler(struct sock *sk)
{
	if ((1 << sk->sk_state) &
	    (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
737 738 739 740 741 742 743 744
	     TCPF_CLOSE_WAIT  | TCPF_LAST_ACK)) {
		struct tcp_sock *tp = tcp_sk(sk);

		if (tp->lost_out > tp->retrans_out &&
		    tp->snd_cwnd > tcp_packets_in_flight(tp))
			tcp_xmit_retransmit_queue(sk);

		tcp_write_xmit(sk, tcp_current_mss(sk), tp->nonagle,
J
John Ogness 已提交
745
			       0, GFP_ATOMIC);
746
	}
747
}
E
Eric Dumazet 已提交
748
/*
S
stephen hemminger 已提交
749
 * One tasklet per cpu tries to send more skbs.
E
Eric Dumazet 已提交
750
 * We run in tasklet context but need to disable irqs when
S
stephen hemminger 已提交
751
 * transferring tsq->head because tcp_wfree() might
E
Eric Dumazet 已提交
752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774
 * interrupt us (non NAPI drivers)
 */
static void tcp_tasklet_func(unsigned long data)
{
	struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
	LIST_HEAD(list);
	unsigned long flags;
	struct list_head *q, *n;
	struct tcp_sock *tp;
	struct sock *sk;

	local_irq_save(flags);
	list_splice_init(&tsq->head, &list);
	local_irq_restore(flags);

	list_for_each_safe(q, n, &list) {
		tp = list_entry(q, struct tcp_sock, tsq_node);
		list_del(&tp->tsq_node);

		sk = (struct sock *)tp;
		bh_lock_sock(sk);

		if (!sock_owned_by_user(sk)) {
775
			tcp_tsq_handler(sk);
E
Eric Dumazet 已提交
776 777
		} else {
			/* defer the work to tcp_release_cb() */
778
			set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
E
Eric Dumazet 已提交
779 780 781 782 783 784 785 786
		}
		bh_unlock_sock(sk);

		clear_bit(TSQ_QUEUED, &tp->tsq_flags);
		sk_free(sk);
	}
}

E
Eric Dumazet 已提交
787 788 789 790
#define TCP_DEFERRED_ALL (TCPF_TSQ_DEFERRED |		\
			  TCPF_WRITE_TIMER_DEFERRED |	\
			  TCPF_DELACK_TIMER_DEFERRED |	\
			  TCPF_MTU_REDUCED_DEFERRED)
E
Eric Dumazet 已提交
791 792 793 794 795 796 797 798 799 800
/**
 * tcp_release_cb - tcp release_sock() callback
 * @sk: socket
 *
 * called from release_sock() to perform protocol dependent
 * actions before socket release.
 */
void tcp_release_cb(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
801
	unsigned long flags, nflags;
E
Eric Dumazet 已提交
802

803 804 805 806 807 808 809 810
	/* perform an atomic operation only if at least one flag is set */
	do {
		flags = tp->tsq_flags;
		if (!(flags & TCP_DEFERRED_ALL))
			return;
		nflags = flags & ~TCP_DEFERRED_ALL;
	} while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);

E
Eric Dumazet 已提交
811
	if (flags & TCPF_TSQ_DEFERRED)
812 813
		tcp_tsq_handler(sk);

814 815 816 817 818 819 820 821 822 823 824
	/* Here begins the tricky part :
	 * We are called from release_sock() with :
	 * 1) BH disabled
	 * 2) sk_lock.slock spinlock held
	 * 3) socket owned by us (sk->sk_lock.owned == 1)
	 *
	 * But following code is meant to be called from BH handlers,
	 * so we should keep BH disabled, but early release socket ownership
	 */
	sock_release_ownership(sk);

E
Eric Dumazet 已提交
825
	if (flags & TCPF_WRITE_TIMER_DEFERRED) {
826
		tcp_write_timer_handler(sk);
827 828
		__sock_put(sk);
	}
E
Eric Dumazet 已提交
829
	if (flags & TCPF_DELACK_TIMER_DEFERRED) {
830
		tcp_delack_timer_handler(sk);
831 832
		__sock_put(sk);
	}
E
Eric Dumazet 已提交
833
	if (flags & TCPF_MTU_REDUCED_DEFERRED) {
834
		inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
835 836
		__sock_put(sk);
	}
E
Eric Dumazet 已提交
837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855
}
EXPORT_SYMBOL(tcp_release_cb);

void __init tcp_tasklet_init(void)
{
	int i;

	for_each_possible_cpu(i) {
		struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);

		INIT_LIST_HEAD(&tsq->head);
		tasklet_init(&tsq->tasklet,
			     tcp_tasklet_func,
			     (unsigned long)tsq);
	}
}

/*
 * Write buffer destructor automatically called from kfree_skb.
S
stephen hemminger 已提交
856
 * We can't xmit new skbs from this context, as we might already
E
Eric Dumazet 已提交
857 858
 * hold qdisc lock.
 */
E
Eric Dumazet 已提交
859
void tcp_wfree(struct sk_buff *skb)
E
Eric Dumazet 已提交
860 861 862
{
	struct sock *sk = skb->sk;
	struct tcp_sock *tp = tcp_sk(sk);
863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878
	int wmem;

	/* Keep one reference on sk_wmem_alloc.
	 * Will be released by sk_free() from here or tcp_tasklet_func()
	 */
	wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);

	/* If this softirq is serviced by ksoftirqd, we are likely under stress.
	 * Wait until our queues (qdisc + devices) are drained.
	 * This gives :
	 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
	 * - chance for incoming ACK (processed by another cpu maybe)
	 *   to migrate this flow (skb->ooo_okay will be eventually set)
	 */
	if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
		goto out;
E
Eric Dumazet 已提交
879 880 881 882 883 884 885 886

	if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
	    !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
		unsigned long flags;
		struct tsq_tasklet *tsq;

		/* queue this socket to tasklet queue */
		local_irq_save(flags);
887
		tsq = this_cpu_ptr(&tsq_tasklet);
E
Eric Dumazet 已提交
888 889 890
		list_add(&tp->tsq_node, &tsq->head);
		tasklet_schedule(&tsq->tasklet);
		local_irq_restore(flags);
891
		return;
E
Eric Dumazet 已提交
892
	}
893 894
out:
	sk_free(sk);
E
Eric Dumazet 已提交
895 896
}

L
Linus Torvalds 已提交
897 898 899 900 901 902 903 904 905 906 907
/* This routine actually transmits TCP packets queued in by
 * tcp_do_sendmsg().  This is used by both the initial
 * transmission and possible later retransmissions.
 * All SKB's seen here are completely headerless.  It is our
 * job to build the TCP header, and pass the packet down to
 * IP so it can do the same plus pass the packet off to the
 * device.
 *
 * We are working here with either a clone of the original
 * SKB, or a fresh unique copy made by the retransmit engine.
 */
908 909
static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
			    gfp_t gfp_mask)
L
Linus Torvalds 已提交
910
{
911 912 913 914
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct inet_sock *inet;
	struct tcp_sock *tp;
	struct tcp_skb_cb *tcb;
A
Adam Langley 已提交
915
	struct tcp_out_options opts;
916
	unsigned int tcp_options_size, tcp_header_size;
917
	struct tcp_md5sig_key *md5;
918 919 920 921
	struct tcphdr *th;
	int err;

	BUG_ON(!skb || !tcp_skb_pcount(skb));
922
	tp = tcp_sk(sk);
923

924
	if (clone_it) {
925
		skb_mstamp_get(&skb->skb_mstamp);
926 927
		TCP_SKB_CB(skb)->tx.in_flight = TCP_SKB_CB(skb)->end_seq
			- tp->snd_una;
928
		tcp_rate_skb_sent(sk, skb);
929

930 931 932 933 934 935 936
		if (unlikely(skb_cloned(skb)))
			skb = pskb_copy(skb, gfp_mask);
		else
			skb = skb_clone(skb, gfp_mask);
		if (unlikely(!skb))
			return -ENOBUFS;
	}
L
Linus Torvalds 已提交
937

938 939
	inet = inet_sk(sk);
	tcb = TCP_SKB_CB(skb);
A
Adam Langley 已提交
940
	memset(&opts, 0, sizeof(opts));
L
Linus Torvalds 已提交
941

E
Eric Dumazet 已提交
942
	if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
A
Adam Langley 已提交
943 944 945 946 947
		tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
	else
		tcp_options_size = tcp_established_options(sk, skb, &opts,
							   &md5);
	tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
948

E
Eric Dumazet 已提交
949
	/* if no packet is in qdisc/device queue, then allow XPS to select
950 951 952 953 954
	 * another queue. We can be called from tcp_tsq_handler()
	 * which holds one reference to sk_wmem_alloc.
	 *
	 * TODO: Ideally, in-flight pure ACK packets should not matter here.
	 * One way to get this would be to set skb->truesize = 2 on them.
E
Eric Dumazet 已提交
955
	 */
956
	skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
957

958 959
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
E
Eric Dumazet 已提交
960 961 962

	skb_orphan(skb);
	skb->sk = sk;
E
Eric Dumazet 已提交
963
	skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree;
964
	skb_set_hash_from_sk(skb, sk);
E
Eric Dumazet 已提交
965
	atomic_add(skb->truesize, &sk->sk_wmem_alloc);
966 967

	/* Build TCP header and checksum it. */
968
	th = (struct tcphdr *)skb->data;
E
Eric Dumazet 已提交
969 970
	th->source		= inet->inet_sport;
	th->dest		= inet->inet_dport;
971 972
	th->seq			= htonl(tcb->seq);
	th->ack_seq		= htonl(tp->rcv_nxt);
973
	*(((__be16 *)th) + 6)	= htons(((tcp_header_size >> 2) << 12) |
E
Eric Dumazet 已提交
974
					tcb->tcp_flags);
975 976 977

	th->check		= 0;
	th->urg_ptr		= 0;
L
Linus Torvalds 已提交
978

I
Ilpo Järvinen 已提交
979
	/* The urg_mode check is necessary during a below snd_una win probe */
980 981 982 983 984
	if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
		if (before(tp->snd_up, tcb->seq + 0x10000)) {
			th->urg_ptr = htons(tp->snd_up - tcb->seq);
			th->urg = 1;
		} else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
985
			th->urg_ptr = htons(0xFFFF);
986 987
			th->urg = 1;
		}
988
	}
L
Linus Torvalds 已提交
989

990
	tcp_options_write((__be32 *)(th + 1), tp, &opts);
991
	skb_shinfo(skb)->gso_type = sk->sk_gso_type;
992 993 994 995 996 997 998 999 1000
	if (likely(!(tcb->tcp_flags & TCPHDR_SYN))) {
		th->window      = htons(tcp_select_window(sk));
		tcp_ecn_send(sk, skb, th, tcp_header_size);
	} else {
		/* RFC1323: The window in SYN & SYN/ACK segments
		 * is never scaled.
		 */
		th->window	= htons(min(tp->rcv_wnd, 65535U));
	}
1001 1002 1003
#ifdef CONFIG_TCP_MD5SIG
	/* Calculate the MD5 hash, as we have all we need now */
	if (md5) {
E
Eric Dumazet 已提交
1004
		sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1005
		tp->af_specific->calc_md5_hash(opts.hash_location,
1006
					       md5, sk, skb);
1007 1008 1009
	}
#endif

1010
	icsk->icsk_af_ops->send_check(sk, skb);
L
Linus Torvalds 已提交
1011

E
Eric Dumazet 已提交
1012
	if (likely(tcb->tcp_flags & TCPHDR_ACK))
1013
		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
L
Linus Torvalds 已提交
1014

1015
	if (skb->len != tcp_header_size) {
1016
		tcp_event_data_sent(tp, sk);
1017 1018
		tp->data_segs_out += tcp_skb_pcount(skb);
	}
L
Linus Torvalds 已提交
1019

1020
	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1021 1022
		TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
			      tcp_skb_pcount(skb));
L
Linus Torvalds 已提交
1023

1024
	tp->segs_out += tcp_skb_pcount(skb);
1025
	/* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1026
	skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1027
	skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1028

E
Eric Dumazet 已提交
1029 1030
	/* Our usage of tstamp should remain private */
	skb->tstamp.tv64 = 0;
1031 1032 1033 1034 1035

	/* Cleanup our debris for IP stacks */
	memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
			       sizeof(struct inet6_skb_parm)));

1036
	err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
E
Eric Dumazet 已提交
1037

1038
	if (likely(err <= 0))
1039 1040
		return err;

1041
	tcp_enter_cwr(sk);
1042

1043
	return net_xmit_eval(err);
L
Linus Torvalds 已提交
1044 1045
}

1046
/* This routine just queues the buffer for sending.
L
Linus Torvalds 已提交
1047 1048 1049 1050 1051 1052 1053 1054 1055 1056
 *
 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
 * otherwise socket can stall.
 */
static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);

	/* Advance write_seq and place onto the write_queue. */
	tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1057
	__skb_header_release(skb);
1058
	tcp_add_write_queue_tail(sk, skb);
1059 1060
	sk->sk_wmem_queued += skb->truesize;
	sk_mem_charge(sk, skb->truesize);
L
Linus Torvalds 已提交
1061 1062
}

1063
/* Initialize TSO segments for a packet. */
1064
static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1065
{
1066
	if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1067 1068 1069
		/* Avoid the costly divide in the normal
		 * non-TSO case.
		 */
1070
		tcp_skb_pcount_set(skb, 1);
1071
		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1072
	} else {
1073
		tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1074
		TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
L
Linus Torvalds 已提交
1075 1076 1077
	}
}

I
Ilpo Järvinen 已提交
1078
/* When a modification to fackets out becomes necessary, we need to check
1079
 * skb is counted to fackets_out or not.
I
Ilpo Järvinen 已提交
1080
 */
1081
static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
I
Ilpo Järvinen 已提交
1082 1083
				   int decr)
{
1084 1085
	struct tcp_sock *tp = tcp_sk(sk);

1086
	if (!tp->sacked_out || tcp_is_reno(tp))
I
Ilpo Järvinen 已提交
1087 1088
		return;

1089
	if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
I
Ilpo Järvinen 已提交
1090 1091 1092
		tp->fackets_out -= decr;
}

1093 1094 1095
/* Pcount in the middle of the write queue got changed, we need to do various
 * tweaks to fix counters
 */
1096
static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116
{
	struct tcp_sock *tp = tcp_sk(sk);

	tp->packets_out -= decr;

	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
		tp->sacked_out -= decr;
	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
		tp->retrans_out -= decr;
	if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
		tp->lost_out -= decr;

	/* Reno case is special. Sigh... */
	if (tcp_is_reno(tp) && decr > 0)
		tp->sacked_out -= min_t(u32, tp->sacked_out, decr);

	tcp_adjust_fackets_out(sk, skb, decr);

	if (tp->lost_skb_hint &&
	    before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1117
	    (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1118 1119 1120 1121 1122
		tp->lost_cnt_hint -= decr;

	tcp_verify_left_out(tp);
}

1123 1124 1125 1126 1127 1128
static bool tcp_has_tx_tstamp(const struct sk_buff *skb)
{
	return TCP_SKB_CB(skb)->txstamp_ack ||
		(skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP);
}

1129 1130 1131 1132
static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
{
	struct skb_shared_info *shinfo = skb_shinfo(skb);

1133
	if (unlikely(tcp_has_tx_tstamp(skb)) &&
1134 1135 1136 1137 1138 1139 1140
	    !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
		struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
		u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;

		shinfo->tx_flags &= ~tsflags;
		shinfo2->tx_flags |= tsflags;
		swap(shinfo->tskey, shinfo2->tskey);
1141 1142
		TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack;
		TCP_SKB_CB(skb)->txstamp_ack = 0;
1143 1144 1145
	}
}

1146 1147 1148 1149 1150 1151
static void tcp_skb_fragment_eor(struct sk_buff *skb, struct sk_buff *skb2)
{
	TCP_SKB_CB(skb2)->eor = TCP_SKB_CB(skb)->eor;
	TCP_SKB_CB(skb)->eor = 0;
}

L
Linus Torvalds 已提交
1152 1153
/* Function to create two new TCP segments.  Shrinks the given segment
 * to the specified size and appends a new segment with the rest of the
1154
 * packet to the list.  This won't be called frequently, I hope.
L
Linus Torvalds 已提交
1155 1156
 * Remember, these are still headerless SKBs at this point.
 */
1157
int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1158
		 unsigned int mss_now, gfp_t gfp)
L
Linus Torvalds 已提交
1159 1160 1161
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;
1162
	int nsize, old_factor;
1163
	int nlen;
1164
	u8 flags;
L
Linus Torvalds 已提交
1165

1166 1167
	if (WARN_ON(len > skb->len))
		return -EINVAL;
1168

L
Linus Torvalds 已提交
1169 1170 1171 1172
	nsize = skb_headlen(skb) - len;
	if (nsize < 0)
		nsize = 0;

1173
	if (skb_unclone(skb, gfp))
L
Linus Torvalds 已提交
1174 1175 1176
		return -ENOMEM;

	/* Get a new skb... force flag on. */
1177
	buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1178
	if (!buff)
L
Linus Torvalds 已提交
1179
		return -ENOMEM; /* We'll just try again later. */
H
Herbert Xu 已提交
1180

1181 1182
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
1183 1184 1185
	nlen = skb->len - len - nsize;
	buff->truesize += nlen;
	skb->truesize -= nlen;
L
Linus Torvalds 已提交
1186 1187 1188 1189 1190 1191 1192

	/* Correct the sequence numbers. */
	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;

	/* PSH and FIN should only be set in the second packet. */
E
Eric Dumazet 已提交
1193 1194 1195
	flags = TCP_SKB_CB(skb)->tcp_flags;
	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
	TCP_SKB_CB(buff)->tcp_flags = flags;
1196
	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1197
	tcp_skb_fragment_eor(skb, buff);
L
Linus Torvalds 已提交
1198

1199
	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
L
Linus Torvalds 已提交
1200
		/* Copy and checksum data tail into the new buffer. */
1201 1202
		buff->csum = csum_partial_copy_nocheck(skb->data + len,
						       skb_put(buff, nsize),
L
Linus Torvalds 已提交
1203 1204 1205 1206 1207 1208
						       nsize, 0);

		skb_trim(skb, len);

		skb->csum = csum_block_sub(skb->csum, buff->csum, len);
	} else {
1209
		skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
1210 1211 1212 1213 1214
		skb_split(skb, buff, len);
	}

	buff->ip_summed = skb->ip_summed;

1215
	buff->tstamp = skb->tstamp;
1216
	tcp_fragment_tstamp(skb, buff);
L
Linus Torvalds 已提交
1217

1218 1219
	old_factor = tcp_skb_pcount(skb);

L
Linus Torvalds 已提交
1220
	/* Fix up tso_factor for both original and new SKB.  */
1221 1222
	tcp_set_skb_tso_segs(skb, mss_now);
	tcp_set_skb_tso_segs(buff, mss_now);
L
Linus Torvalds 已提交
1223

1224 1225 1226
	/* Update delivered info for the new segment */
	TCP_SKB_CB(buff)->tx = TCP_SKB_CB(skb)->tx;

1227 1228 1229
	/* If this packet has been sent out already, we must
	 * adjust the various packet counters.
	 */
1230
	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1231 1232
		int diff = old_factor - tcp_skb_pcount(skb) -
			tcp_skb_pcount(buff);
L
Linus Torvalds 已提交
1233

1234 1235
		if (diff)
			tcp_adjust_pcount(sk, skb, diff);
L
Linus Torvalds 已提交
1236 1237 1238
	}

	/* Link BUFF into the send queue. */
1239
	__skb_header_release(buff);
1240
	tcp_insert_write_queue_after(skb, buff, sk);
L
Linus Torvalds 已提交
1241 1242 1243 1244 1245 1246 1247 1248

	return 0;
}

/* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
 * eventually). The difference is that pulled data not copied, but
 * immediately discarded.
 */
1249
static void __pskb_trim_head(struct sk_buff *skb, int len)
L
Linus Torvalds 已提交
1250
{
1251
	struct skb_shared_info *shinfo;
L
Linus Torvalds 已提交
1252 1253
	int i, k, eat;

E
Eric Dumazet 已提交
1254 1255 1256 1257 1258 1259 1260
	eat = min_t(int, len, skb_headlen(skb));
	if (eat) {
		__skb_pull(skb, eat);
		len -= eat;
		if (!len)
			return;
	}
L
Linus Torvalds 已提交
1261 1262
	eat = len;
	k = 0;
1263 1264 1265
	shinfo = skb_shinfo(skb);
	for (i = 0; i < shinfo->nr_frags; i++) {
		int size = skb_frag_size(&shinfo->frags[i]);
E
Eric Dumazet 已提交
1266 1267

		if (size <= eat) {
1268
			skb_frag_unref(skb, i);
E
Eric Dumazet 已提交
1269
			eat -= size;
L
Linus Torvalds 已提交
1270
		} else {
1271
			shinfo->frags[k] = shinfo->frags[i];
L
Linus Torvalds 已提交
1272
			if (eat) {
1273 1274
				shinfo->frags[k].page_offset += eat;
				skb_frag_size_sub(&shinfo->frags[k], eat);
L
Linus Torvalds 已提交
1275 1276 1277 1278 1279
				eat = 0;
			}
			k++;
		}
	}
1280
	shinfo->nr_frags = k;
L
Linus Torvalds 已提交
1281

1282
	skb_reset_tail_pointer(skb);
L
Linus Torvalds 已提交
1283 1284 1285 1286
	skb->data_len -= len;
	skb->len = skb->data_len;
}

1287
/* Remove acked data from a packet in the transmit queue. */
L
Linus Torvalds 已提交
1288 1289
int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
{
1290
	if (skb_unclone(skb, GFP_ATOMIC))
L
Linus Torvalds 已提交
1291 1292
		return -ENOMEM;

E
Eric Dumazet 已提交
1293
	__pskb_trim_head(skb, len);
L
Linus Torvalds 已提交
1294 1295

	TCP_SKB_CB(skb)->seq += len;
1296
	skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
1297 1298 1299

	skb->truesize	     -= len;
	sk->sk_wmem_queued   -= len;
1300
	sk_mem_uncharge(sk, len);
L
Linus Torvalds 已提交
1301 1302
	sock_set_flag(sk, SOCK_QUEUE_SHRUNK);

1303
	/* Any change of skb->len requires recalculation of tso factor. */
L
Linus Torvalds 已提交
1304
	if (tcp_skb_pcount(skb) > 1)
1305
		tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
L
Linus Torvalds 已提交
1306 1307 1308 1309

	return 0;
}

1310 1311
/* Calculate MSS not accounting any TCP options.  */
static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
J
John Heffner 已提交
1312
{
1313 1314
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1315 1316 1317 1318 1319 1320 1321
	int mss_now;

	/* Calculate base mss without TCP options:
	   It is MMS_S - sizeof(tcphdr) of rfc1122
	 */
	mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);

1322 1323 1324 1325 1326 1327 1328 1329
	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
	if (icsk->icsk_af_ops->net_frag_header_len) {
		const struct dst_entry *dst = __sk_dst_get(sk);

		if (dst && dst_allfrag(dst))
			mss_now -= icsk->icsk_af_ops->net_frag_header_len;
	}

J
John Heffner 已提交
1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342
	/* Clamp it (mss_clamp does not include tcp options) */
	if (mss_now > tp->rx_opt.mss_clamp)
		mss_now = tp->rx_opt.mss_clamp;

	/* Now subtract optional transport overhead */
	mss_now -= icsk->icsk_ext_hdr_len;

	/* Then reserve room for full set of TCP options and 8 bytes of data */
	if (mss_now < 48)
		mss_now = 48;
	return mss_now;
}

1343 1344 1345 1346 1347 1348 1349 1350
/* Calculate MSS. Not accounting for SACKs here.  */
int tcp_mtu_to_mss(struct sock *sk, int pmtu)
{
	/* Subtract TCP options size, not including SACKs */
	return __tcp_mtu_to_mss(sk, pmtu) -
	       (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
}

J
John Heffner 已提交
1351
/* Inverse of above */
1352
int tcp_mss_to_mtu(struct sock *sk, int mss)
J
John Heffner 已提交
1353
{
1354 1355
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1356 1357 1358 1359 1360 1361 1362
	int mtu;

	mtu = mss +
	      tp->tcp_header_len +
	      icsk->icsk_ext_hdr_len +
	      icsk->icsk_af_ops->net_header_len;

1363 1364 1365 1366 1367 1368 1369
	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
	if (icsk->icsk_af_ops->net_frag_header_len) {
		const struct dst_entry *dst = __sk_dst_get(sk);

		if (dst && dst_allfrag(dst))
			mtu += icsk->icsk_af_ops->net_frag_header_len;
	}
J
John Heffner 已提交
1370 1371
	return mtu;
}
1372
EXPORT_SYMBOL(tcp_mss_to_mtu);
J
John Heffner 已提交
1373

1374
/* MTU probing init per socket */
J
John Heffner 已提交
1375 1376 1377 1378
void tcp_mtup_init(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);
F
Fan Du 已提交
1379
	struct net *net = sock_net(sk);
J
John Heffner 已提交
1380

F
Fan Du 已提交
1381
	icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
J
John Heffner 已提交
1382
	icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1383
			       icsk->icsk_af_ops->net_header_len;
F
Fan Du 已提交
1384
	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
J
John Heffner 已提交
1385
	icsk->icsk_mtup.probe_size = 0;
1386 1387
	if (icsk->icsk_mtup.enabled)
		icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
J
John Heffner 已提交
1388
}
E
Eric Dumazet 已提交
1389
EXPORT_SYMBOL(tcp_mtup_init);
J
John Heffner 已提交
1390

L
Linus Torvalds 已提交
1391 1392 1393 1394 1395 1396
/* This function synchronize snd mss to current pmtu/exthdr set.

   tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
   for TCP options, but includes only bare TCP header.

   tp->rx_opt.mss_clamp is mss negotiated at connection setup.
S
Stephen Hemminger 已提交
1397
   It is minimum of user_mss and mss received with SYN.
L
Linus Torvalds 已提交
1398 1399
   It also does not include TCP options.

1400
   inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
L
Linus Torvalds 已提交
1401 1402 1403 1404 1405 1406 1407 1408 1409

   tp->mss_cache is current effective sending mss, including
   all tcp options except for SACKs. It is evaluated,
   taking into account current pmtu, but never exceeds
   tp->rx_opt.mss_clamp.

   NOTE1. rfc1122 clearly states that advertised MSS
   DOES NOT include either tcp or ip options.

1410 1411
   NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
   are READ ONLY outside this function.		--ANK (980731)
L
Linus Torvalds 已提交
1412 1413 1414 1415
 */
unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
{
	struct tcp_sock *tp = tcp_sk(sk);
1416
	struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1417
	int mss_now;
L
Linus Torvalds 已提交
1418

J
John Heffner 已提交
1419 1420
	if (icsk->icsk_mtup.search_high > pmtu)
		icsk->icsk_mtup.search_high = pmtu;
L
Linus Torvalds 已提交
1421

J
John Heffner 已提交
1422
	mss_now = tcp_mtu_to_mss(sk, pmtu);
1423
	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
L
Linus Torvalds 已提交
1424 1425

	/* And store cached results */
1426
	icsk->icsk_pmtu_cookie = pmtu;
J
John Heffner 已提交
1427 1428
	if (icsk->icsk_mtup.enabled)
		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1429
	tp->mss_cache = mss_now;
L
Linus Torvalds 已提交
1430 1431 1432

	return mss_now;
}
E
Eric Dumazet 已提交
1433
EXPORT_SYMBOL(tcp_sync_mss);
L
Linus Torvalds 已提交
1434 1435 1436 1437

/* Compute the current effective MSS, taking SACKs and IP options,
 * and even PMTU discovery events into account.
 */
I
Ilpo Järvinen 已提交
1438
unsigned int tcp_current_mss(struct sock *sk)
L
Linus Torvalds 已提交
1439
{
1440 1441
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct dst_entry *dst = __sk_dst_get(sk);
1442
	u32 mss_now;
1443
	unsigned int header_len;
A
Adam Langley 已提交
1444 1445
	struct tcp_out_options opts;
	struct tcp_md5sig_key *md5;
1446 1447 1448

	mss_now = tp->mss_cache;

L
Linus Torvalds 已提交
1449 1450
	if (dst) {
		u32 mtu = dst_mtu(dst);
1451
		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
L
Linus Torvalds 已提交
1452 1453 1454
			mss_now = tcp_sync_mss(sk, mtu);
	}

A
Adam Langley 已提交
1455 1456 1457 1458 1459 1460 1461 1462 1463 1464
	header_len = tcp_established_options(sk, NULL, &opts, &md5) +
		     sizeof(struct tcphdr);
	/* The mss_cache is sized based on tp->tcp_header_len, which assumes
	 * some common options. If this is an odd packet (because we have SACK
	 * blocks etc) then our calculated header_len will be different, and
	 * we have to adjust mss_now correspondingly */
	if (header_len != tp->tcp_header_len) {
		int delta = (int) header_len - tp->tcp_header_len;
		mss_now -= delta;
	}
1465

L
Linus Torvalds 已提交
1466 1467 1468
	return mss_now;
}

1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490
/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
 * As additional protections, we do not touch cwnd in retransmission phases,
 * and if application hit its sndbuf limit recently.
 */
static void tcp_cwnd_application_limited(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
	    sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
		/* Limited by application or receiver window. */
		u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
		u32 win_used = max(tp->snd_cwnd_used, init_win);
		if (win_used < tp->snd_cwnd) {
			tp->snd_ssthresh = tcp_current_ssthresh(sk);
			tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
		}
		tp->snd_cwnd_used = 0;
	}
	tp->snd_cwnd_stamp = tcp_time_stamp;
}

1491
static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1492
{
1493
	struct tcp_sock *tp = tcp_sk(sk);
1494

1495 1496 1497 1498 1499 1500 1501 1502 1503
	/* Track the maximum number of outstanding packets in each
	 * window, and remember whether we were cwnd-limited then.
	 */
	if (!before(tp->snd_una, tp->max_packets_seq) ||
	    tp->packets_out > tp->max_packets_out) {
		tp->max_packets_out = tp->packets_out;
		tp->max_packets_seq = tp->snd_nxt;
		tp->is_cwnd_limited = is_cwnd_limited;
	}
1504

1505
	if (tcp_is_cwnd_limited(sk)) {
1506 1507 1508 1509 1510 1511 1512 1513
		/* Network is feed fully. */
		tp->snd_cwnd_used = 0;
		tp->snd_cwnd_stamp = tcp_time_stamp;
	} else {
		/* Network starves. */
		if (tp->packets_out > tp->snd_cwnd_used)
			tp->snd_cwnd_used = tp->packets_out;

1514 1515
		if (sysctl_tcp_slow_start_after_idle &&
		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1516
			tcp_cwnd_application_limited(sk);
1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528

		/* The following conditions together indicate the starvation
		 * is caused by insufficient sender buffer:
		 * 1) just sent some data (see tcp_write_xmit)
		 * 2) not cwnd limited (this else condition)
		 * 3) no more data to send (null tcp_send_head )
		 * 4) application is hitting buffer limit (SOCK_NOSPACE)
		 */
		if (!tcp_send_head(sk) && sk->sk_socket &&
		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags) &&
		    (1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT))
			tcp_chrono_start(sk, TCP_CHRONO_SNDBUF_LIMITED);
1529 1530 1531
	}
}

E
Eric Dumazet 已提交
1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545
/* Minshall's variant of the Nagle send check. */
static bool tcp_minshall_check(const struct tcp_sock *tp)
{
	return after(tp->snd_sml, tp->snd_una) &&
		!after(tp->snd_sml, tp->snd_nxt);
}

/* Update snd_sml if this skb is under mss
 * Note that a TSO packet might end with a sub-mss segment
 * The test is really :
 * if ((skb->len % mss) != 0)
 *        tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
 * But we can avoid doing the divide again given we already have
 *  skb_pcount = skb->len / mss_now
1546
 */
E
Eric Dumazet 已提交
1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561
static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
				const struct sk_buff *skb)
{
	if (skb->len < tcp_skb_pcount(skb) * mss_now)
		tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
}

/* Return false, if packet can be sent now without violation Nagle's rules:
 * 1. It is full sized. (provided by caller in %partial bool)
 * 2. Or it contains FIN. (already checked by caller)
 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
 *    With Minshall's modification: all sent small packets are ACKed.
 */
static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1562
			    int nonagle)
E
Eric Dumazet 已提交
1563 1564 1565 1566 1567
{
	return partial &&
		((nonagle & TCP_NAGLE_CORK) ||
		 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
}
E
Eric Dumazet 已提交
1568 1569 1570 1571

/* Return how many segs we'd like on a TSO packet,
 * to send one TSO packet per ms
 */
1572 1573
u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
		     int min_tso_segs)
E
Eric Dumazet 已提交
1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584
{
	u32 bytes, segs;

	bytes = min(sk->sk_pacing_rate >> 10,
		    sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);

	/* Goal is to send at least one packet per ms,
	 * not one big TSO packet every 100 ms.
	 * This preserves ACK clocking and is consistent
	 * with tcp_tso_should_defer() heuristic.
	 */
1585
	segs = max_t(u32, bytes / mss_now, min_tso_segs);
E
Eric Dumazet 已提交
1586 1587 1588

	return min_t(u32, segs, sk->sk_gso_max_segs);
}
1589
EXPORT_SYMBOL(tcp_tso_autosize);
E
Eric Dumazet 已提交
1590

1591 1592 1593 1594 1595 1596 1597 1598
/* Return the number of segments we want in the skb we are transmitting.
 * See if congestion control module wants to decide; otherwise, autosize.
 */
static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
{
	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
	u32 tso_segs = ca_ops->tso_segs_goal ? ca_ops->tso_segs_goal(sk) : 0;

1599 1600
	return tso_segs ? :
		tcp_tso_autosize(sk, mss_now, sysctl_tcp_min_tso_segs);
1601 1602
}

E
Eric Dumazet 已提交
1603 1604 1605 1606 1607 1608
/* Returns the portion of skb which can be sent right away */
static unsigned int tcp_mss_split_point(const struct sock *sk,
					const struct sk_buff *skb,
					unsigned int mss_now,
					unsigned int max_segs,
					int nonagle)
1609
{
1610
	const struct tcp_sock *tp = tcp_sk(sk);
E
Eric Dumazet 已提交
1611
	u32 partial, needed, window, max_len;
1612

1613
	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1614
	max_len = mss_now * max_segs;
1615

1616 1617
	if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
		return max_len;
1618

1619 1620
	needed = min(skb->len, window);

1621 1622
	if (max_len <= needed)
		return max_len;
1623

E
Eric Dumazet 已提交
1624 1625 1626 1627 1628
	partial = needed % mss_now;
	/* If last segment is not a full MSS, check if Nagle rules allow us
	 * to include this last segment in this skb.
	 * Otherwise, we'll split the skb at last MSS boundary
	 */
1629
	if (tcp_nagle_check(partial != 0, tp, nonagle))
E
Eric Dumazet 已提交
1630 1631 1632
		return needed - partial;

	return needed;
1633 1634 1635 1636 1637
}

/* Can at least one segment of SKB be sent right now, according to the
 * congestion window rules?  If so, return how many segments are allowed.
 */
1638 1639
static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
					 const struct sk_buff *skb)
1640
{
E
Eric Dumazet 已提交
1641
	u32 in_flight, cwnd, halfcwnd;
1642 1643

	/* Don't be strict about the congestion window for the final FIN.  */
E
Eric Dumazet 已提交
1644 1645
	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
	    tcp_skb_pcount(skb) == 1)
1646 1647 1648 1649
		return 1;

	in_flight = tcp_packets_in_flight(tp);
	cwnd = tp->snd_cwnd;
E
Eric Dumazet 已提交
1650 1651
	if (in_flight >= cwnd)
		return 0;
1652

E
Eric Dumazet 已提交
1653 1654 1655 1656 1657
	/* For better scheduling, ensure we have at least
	 * 2 GSO packets in flight.
	 */
	halfcwnd = max(cwnd >> 1, 1U);
	return min(halfcwnd, cwnd - in_flight);
1658 1659
}

1660
/* Initialize TSO state of a skb.
1661
 * This must be invoked the first time we consider transmitting
1662 1663
 * SKB onto the wire.
 */
1664
static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1665 1666 1667
{
	int tso_segs = tcp_skb_pcount(skb);

1668
	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1669
		tcp_set_skb_tso_segs(skb, mss_now);
1670 1671 1672 1673 1674 1675
		tso_segs = tcp_skb_pcount(skb);
	}
	return tso_segs;
}


E
Eric Dumazet 已提交
1676
/* Return true if the Nagle test allows this packet to be
1677 1678
 * sent now.
 */
E
Eric Dumazet 已提交
1679 1680
static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
				  unsigned int cur_mss, int nonagle)
1681 1682 1683 1684 1685 1686 1687 1688
{
	/* Nagle rule does not apply to frames, which sit in the middle of the
	 * write_queue (they have no chances to get new data).
	 *
	 * This is implemented in the callers, where they modify the 'nonagle'
	 * argument based upon the location of SKB in the send queue.
	 */
	if (nonagle & TCP_NAGLE_PUSH)
E
Eric Dumazet 已提交
1689
		return true;
1690

Y
Yuchung Cheng 已提交
1691 1692
	/* Don't use the nagle rule for urgent data (or for the final FIN). */
	if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
E
Eric Dumazet 已提交
1693
		return true;
1694

1695
	if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
E
Eric Dumazet 已提交
1696
		return true;
1697

E
Eric Dumazet 已提交
1698
	return false;
1699 1700 1701
}

/* Does at least the first segment of SKB fit into the send window? */
E
Eric Dumazet 已提交
1702 1703 1704
static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
			     const struct sk_buff *skb,
			     unsigned int cur_mss)
1705 1706 1707 1708 1709 1710
{
	u32 end_seq = TCP_SKB_CB(skb)->end_seq;

	if (skb->len > cur_mss)
		end_seq = TCP_SKB_CB(skb)->seq + cur_mss;

1711
	return !after(end_seq, tcp_wnd_end(tp));
1712 1713
}

1714
/* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1715 1716 1717
 * should be put on the wire right now.  If so, it returns the number of
 * packets allowed by the congestion window.
 */
1718
static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1719 1720
				 unsigned int cur_mss, int nonagle)
{
1721
	const struct tcp_sock *tp = tcp_sk(sk);
1722 1723
	unsigned int cwnd_quota;

1724
	tcp_init_tso_segs(skb, cur_mss);
1725 1726 1727 1728 1729

	if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
		return 0;

	cwnd_quota = tcp_cwnd_test(tp, skb);
1730
	if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1731 1732 1733 1734 1735
		cwnd_quota = 0;

	return cwnd_quota;
}

1736
/* Test if sending is allowed right now. */
E
Eric Dumazet 已提交
1737
bool tcp_may_send_now(struct sock *sk)
1738
{
1739
	const struct tcp_sock *tp = tcp_sk(sk);
1740
	struct sk_buff *skb = tcp_send_head(sk);
1741

E
Eric Dumazet 已提交
1742
	return skb &&
I
Ilpo Järvinen 已提交
1743
		tcp_snd_test(sk, skb, tcp_current_mss(sk),
1744
			     (tcp_skb_is_last(sk, skb) ?
E
Eric Dumazet 已提交
1745
			      tp->nonagle : TCP_NAGLE_PUSH));
1746 1747 1748 1749 1750 1751 1752 1753 1754
}

/* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
 * which is put after SKB on the list.  It is very much like
 * tcp_fragment() except that it may make several kinds of assumptions
 * in order to speed up the splitting operation.  In particular, we
 * know that all the data is in scatter-gather pages, and that the
 * packet has never been sent out before (and thus is not cloned).
 */
1755
static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1756
			unsigned int mss_now, gfp_t gfp)
1757 1758 1759
{
	struct sk_buff *buff;
	int nlen = skb->len - len;
1760
	u8 flags;
1761 1762

	/* All of a TSO frame must be composed of paged data.  */
1763
	if (skb->len != skb->data_len)
1764
		return tcp_fragment(sk, skb, len, mss_now, gfp);
1765

1766
	buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1767
	if (unlikely(!buff))
1768 1769
		return -ENOMEM;

1770 1771
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
1772
	buff->truesize += nlen;
1773 1774 1775 1776 1777 1778 1779 1780
	skb->truesize -= nlen;

	/* Correct the sequence numbers. */
	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;

	/* PSH and FIN should only be set in the second packet. */
E
Eric Dumazet 已提交
1781 1782 1783
	flags = TCP_SKB_CB(skb)->tcp_flags;
	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
	TCP_SKB_CB(buff)->tcp_flags = flags;
1784 1785 1786 1787

	/* This packet was never sent out yet, so no SACK bits. */
	TCP_SKB_CB(buff)->sacked = 0;

1788 1789
	tcp_skb_fragment_eor(skb, buff);

1790
	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1791
	skb_split(skb, buff, len);
1792
	tcp_fragment_tstamp(skb, buff);
1793 1794

	/* Fix up tso_factor for both original and new SKB.  */
1795 1796
	tcp_set_skb_tso_segs(skb, mss_now);
	tcp_set_skb_tso_segs(buff, mss_now);
1797 1798

	/* Link BUFF into the send queue. */
1799
	__skb_header_release(buff);
1800
	tcp_insert_write_queue_after(skb, buff, sk);
1801 1802 1803 1804 1805 1806 1807 1808 1809

	return 0;
}

/* Try to defer sending, if possible, in order to minimize the amount
 * of TSO splitting we do.  View it as a kind of TSO Nagle test.
 *
 * This algorithm is from John Heffner.
 */
1810
static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
E
Eric Dumazet 已提交
1811
				 bool *is_cwnd_limited, u32 max_segs)
1812
{
1813
	const struct inet_connection_sock *icsk = inet_csk(sk);
1814 1815 1816 1817
	u32 age, send_win, cong_win, limit, in_flight;
	struct tcp_sock *tp = tcp_sk(sk);
	struct skb_mstamp now;
	struct sk_buff *head;
1818
	int win_divisor;
1819

E
Eric Dumazet 已提交
1820
	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
J
John Heffner 已提交
1821
		goto send_now;
1822

1823
	if (icsk->icsk_ca_state >= TCP_CA_Recovery)
J
John Heffner 已提交
1824 1825
		goto send_now;

E
Eric Dumazet 已提交
1826 1827 1828 1829
	/* Avoid bursty behavior by allowing defer
	 * only if the last write was recent.
	 */
	if ((s32)(tcp_time_stamp - tp->lsndtime) > 0)
J
John Heffner 已提交
1830
		goto send_now;
1831

1832 1833
	in_flight = tcp_packets_in_flight(tp);

1834
	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1835

1836
	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1837 1838 1839 1840 1841 1842

	/* From in_flight test above, we know that cwnd > in_flight.  */
	cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;

	limit = min(send_win, cong_win);

1843
	/* If a full-sized TSO skb can be sent, do it. */
E
Eric Dumazet 已提交
1844
	if (limit >= max_segs * tp->mss_cache)
J
John Heffner 已提交
1845
		goto send_now;
1846

1847 1848 1849 1850
	/* Middle in queue won't get any more data, full sendable already? */
	if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
		goto send_now;

1851 1852
	win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
	if (win_divisor) {
1853 1854 1855 1856 1857
		u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);

		/* If at least some fraction of a window is available,
		 * just use it.
		 */
1858
		chunk /= win_divisor;
1859
		if (limit >= chunk)
J
John Heffner 已提交
1860
			goto send_now;
1861 1862 1863 1864 1865 1866
	} else {
		/* Different approach, try not to defer past a single
		 * ACK.  Receiver should ACK every other full sized
		 * frame, so if we have space for more than 3 frames
		 * then send now.
		 */
1867
		if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
J
John Heffner 已提交
1868
			goto send_now;
1869 1870
	}

1871 1872 1873 1874 1875 1876 1877
	head = tcp_write_queue_head(sk);
	skb_mstamp_get(&now);
	age = skb_mstamp_us_delta(&now, &head->skb_mstamp);
	/* If next ACK is likely to come too late (half srtt), do not defer */
	if (age < (tp->srtt_us >> 4))
		goto send_now;

E
Eric Dumazet 已提交
1878
	/* Ok, it looks like it is advisable to defer. */
J
John Heffner 已提交
1879

1880
	if (cong_win < send_win && cong_win <= skb->len)
1881 1882
		*is_cwnd_limited = true;

E
Eric Dumazet 已提交
1883
	return true;
J
John Heffner 已提交
1884 1885

send_now:
E
Eric Dumazet 已提交
1886
	return false;
1887 1888
}

1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913
static inline void tcp_mtu_check_reprobe(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	struct net *net = sock_net(sk);
	u32 interval;
	s32 delta;

	interval = net->ipv4.sysctl_tcp_probe_interval;
	delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp;
	if (unlikely(delta >= interval * HZ)) {
		int mss = tcp_current_mss(sk);

		/* Update current search range */
		icsk->icsk_mtup.probe_size = 0;
		icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
			sizeof(struct tcphdr) +
			icsk->icsk_af_ops->net_header_len;
		icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);

		/* Update probe time stamp */
		icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
	}
}

J
John Heffner 已提交
1914
/* Create a new MTU probe if we are ready.
1915 1916 1917 1918
 * MTU probe is regularly attempting to increase the path MTU by
 * deliberately sending larger packets.  This discovers routing
 * changes resulting in larger path MTUs.
 *
J
John Heffner 已提交
1919 1920
 * Returns 0 if we should wait to probe (no cwnd available),
 *         1 if a probe was sent,
1921 1922
 *         -1 otherwise
 */
J
John Heffner 已提交
1923 1924 1925 1926 1927
static int tcp_mtu_probe(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct sk_buff *skb, *nskb, *next;
1928
	struct net *net = sock_net(sk);
J
John Heffner 已提交
1929 1930
	int len;
	int probe_size;
1931
	int size_needed;
J
John Heffner 已提交
1932 1933
	int copy;
	int mss_now;
1934
	int interval;
J
John Heffner 已提交
1935 1936 1937 1938 1939 1940 1941 1942 1943

	/* Not currently probing/verifying,
	 * not in recovery,
	 * have enough cwnd, and
	 * not SACKing (the variable headers throw things off) */
	if (!icsk->icsk_mtup.enabled ||
	    icsk->icsk_mtup.probe_size ||
	    inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
	    tp->snd_cwnd < 11 ||
1944
	    tp->rx_opt.num_sacks || tp->rx_opt.dsack)
J
John Heffner 已提交
1945 1946
		return -1;

1947 1948 1949 1950
	/* Use binary search for probe_size between tcp_mss_base,
	 * and current mss_clamp. if (search_high - search_low)
	 * smaller than a threshold, backoff from probing.
	 */
I
Ilpo Järvinen 已提交
1951
	mss_now = tcp_current_mss(sk);
1952 1953
	probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
				    icsk->icsk_mtup.search_low) >> 1);
1954
	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1955
	interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1956 1957 1958 1959
	/* When misfortune happens, we are reprobing actively,
	 * and then reprobe timer has expired. We stick with current
	 * probing process by not resetting search range to its orignal.
	 */
1960
	if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1961 1962 1963 1964 1965
		interval < net->ipv4.sysctl_tcp_probe_threshold) {
		/* Check whether enough time has elaplased for
		 * another round of probing.
		 */
		tcp_mtu_check_reprobe(sk);
J
John Heffner 已提交
1966 1967 1968 1969
		return -1;
	}

	/* Have enough data in the send queue to probe? */
1970
	if (tp->write_seq - tp->snd_nxt < size_needed)
J
John Heffner 已提交
1971 1972
		return -1;

1973 1974
	if (tp->snd_wnd < size_needed)
		return -1;
1975
	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1976
		return 0;
J
John Heffner 已提交
1977

1978 1979 1980
	/* Do we need to wait to drain cwnd? With none in flight, don't stall */
	if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
		if (!tcp_packets_in_flight(tp))
J
John Heffner 已提交
1981 1982 1983 1984 1985 1986
			return -1;
		else
			return 0;
	}

	/* We're allowed to probe.  Build it now. */
1987
	nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1988
	if (!nskb)
J
John Heffner 已提交
1989
		return -1;
1990 1991
	sk->sk_wmem_queued += nskb->truesize;
	sk_mem_charge(sk, nskb->truesize);
J
John Heffner 已提交
1992

1993
	skb = tcp_send_head(sk);
J
John Heffner 已提交
1994 1995 1996

	TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
	TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
E
Eric Dumazet 已提交
1997
	TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
J
John Heffner 已提交
1998 1999
	TCP_SKB_CB(nskb)->sacked = 0;
	nskb->csum = 0;
2000
	nskb->ip_summed = skb->ip_summed;
J
John Heffner 已提交
2001

2002 2003
	tcp_insert_write_queue_before(nskb, skb, sk);

J
John Heffner 已提交
2004
	len = 0;
2005
	tcp_for_write_queue_from_safe(skb, next, sk) {
J
John Heffner 已提交
2006
		copy = min_t(int, skb->len, probe_size - len);
2007
		if (nskb->ip_summed) {
J
John Heffner 已提交
2008
			skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
2009 2010 2011 2012 2013 2014
		} else {
			__wsum csum = skb_copy_and_csum_bits(skb, 0,
							     skb_put(nskb, copy),
							     copy, 0);
			nskb->csum = csum_block_add(nskb->csum, csum, len);
		}
J
John Heffner 已提交
2015 2016 2017 2018

		if (skb->len <= copy) {
			/* We've eaten all the data from this skb.
			 * Throw it away. */
E
Eric Dumazet 已提交
2019
			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
2020
			tcp_unlink_write_queue(skb, sk);
2021
			sk_wmem_free_skb(sk, skb);
J
John Heffner 已提交
2022
		} else {
E
Eric Dumazet 已提交
2023
			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
C
Changli Gao 已提交
2024
						   ~(TCPHDR_FIN|TCPHDR_PSH);
J
John Heffner 已提交
2025 2026
			if (!skb_shinfo(skb)->nr_frags) {
				skb_pull(skb, copy);
2027
				if (skb->ip_summed != CHECKSUM_PARTIAL)
2028 2029
					skb->csum = csum_partial(skb->data,
								 skb->len, 0);
J
John Heffner 已提交
2030 2031
			} else {
				__pskb_trim_head(skb, copy);
2032
				tcp_set_skb_tso_segs(skb, mss_now);
J
John Heffner 已提交
2033 2034 2035 2036 2037
			}
			TCP_SKB_CB(skb)->seq += copy;
		}

		len += copy;
2038 2039 2040

		if (len >= probe_size)
			break;
J
John Heffner 已提交
2041
	}
2042
	tcp_init_tso_segs(nskb, nskb->len);
J
John Heffner 已提交
2043 2044

	/* We're ready to send.  If this fails, the probe will
E
Eric Dumazet 已提交
2045 2046
	 * be resegmented into mss-sized pieces by tcp_write_xmit().
	 */
J
John Heffner 已提交
2047 2048
	if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
		/* Decrement cwnd here because we are sending
2049
		 * effectively two packets. */
J
John Heffner 已提交
2050
		tp->snd_cwnd--;
2051
		tcp_event_new_data_sent(sk, nskb);
J
John Heffner 已提交
2052 2053

		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2054 2055
		tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
		tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
J
John Heffner 已提交
2056 2057 2058 2059 2060 2061 2062

		return 1;
	}

	return -1;
}

2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095
/* TCP Small Queues :
 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
 * (These limits are doubled for retransmits)
 * This allows for :
 *  - better RTT estimation and ACK scheduling
 *  - faster recovery
 *  - high rates
 * Alas, some drivers / subsystems require a fair amount
 * of queued bytes to ensure line rate.
 * One example is wifi aggregation (802.11 AMPDU)
 */
static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
				  unsigned int factor)
{
	unsigned int limit;

	limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
	limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
	limit <<= factor;

	if (atomic_read(&sk->sk_wmem_alloc) > limit) {
		set_bit(TSQ_THROTTLED, &tcp_sk(sk)->tsq_flags);
		/* It is possible TX completion already happened
		 * before we set TSQ_THROTTLED, so we must
		 * test again the condition.
		 */
		smp_mb__after_atomic();
		if (atomic_read(&sk->sk_wmem_alloc) > limit)
			return true;
	}
	return false;
}

2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110
static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new)
{
	const u32 now = tcp_time_stamp;

	if (tp->chrono_type > TCP_CHRONO_UNSPEC)
		tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start;
	tp->chrono_start = now;
	tp->chrono_type = new;
}

void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type)
{
	struct tcp_sock *tp = tcp_sk(sk);

	/* If there are multiple conditions worthy of tracking in a
2111 2112
	 * chronograph then the highest priority enum takes precedence
	 * over the other conditions. So that if something "more interesting"
2113 2114 2115 2116 2117 2118 2119 2120 2121 2122
	 * starts happening, stop the previous chrono and start a new one.
	 */
	if (type > tp->chrono_type)
		tcp_chrono_set(tp, type);
}

void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type)
{
	struct tcp_sock *tp = tcp_sk(sk);

2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133 2134

	/* There are multiple conditions worthy of tracking in a
	 * chronograph, so that the highest priority enum takes
	 * precedence over the other conditions (see tcp_chrono_start).
	 * If a condition stops, we only stop chrono tracking if
	 * it's the "most interesting" or current chrono we are
	 * tracking and starts busy chrono if we have pending data.
	 */
	if (tcp_write_queue_empty(sk))
		tcp_chrono_set(tp, TCP_CHRONO_UNSPEC);
	else if (type == tp->chrono_type)
		tcp_chrono_set(tp, TCP_CHRONO_BUSY);
2135 2136
}

L
Linus Torvalds 已提交
2137 2138 2139 2140
/* This routine writes packets to the network.  It advances the
 * send_head.  This happens as incoming acks open up the remote
 * window for us.
 *
2141 2142 2143 2144
 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
 * account rare use of URG, this is not a big flaw.
 *
N
Nandita Dukkipati 已提交
2145 2146 2147
 * Send at most one packet when push_one > 0. Temporarily ignore
 * cwnd limit to force at most one packet out when push_one == 2.

E
Eric Dumazet 已提交
2148 2149
 * Returns true, if no segments are in flight and we have queued segments,
 * but cannot send anything now because of SWS or another problem.
L
Linus Torvalds 已提交
2150
 */
E
Eric Dumazet 已提交
2151 2152
static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
			   int push_one, gfp_t gfp)
L
Linus Torvalds 已提交
2153 2154
{
	struct tcp_sock *tp = tcp_sk(sk);
2155
	struct sk_buff *skb;
2156 2157
	unsigned int tso_segs, sent_pkts;
	int cwnd_quota;
J
John Heffner 已提交
2158
	int result;
2159
	bool is_cwnd_limited = false, is_rwnd_limited = false;
E
Eric Dumazet 已提交
2160
	u32 max_segs;
L
Linus Torvalds 已提交
2161

2162
	sent_pkts = 0;
J
John Heffner 已提交
2163

2164 2165 2166 2167
	if (!push_one) {
		/* Do MTU probing. */
		result = tcp_mtu_probe(sk);
		if (!result) {
E
Eric Dumazet 已提交
2168
			return false;
2169 2170 2171
		} else if (result > 0) {
			sent_pkts = 1;
		}
J
John Heffner 已提交
2172 2173
	}

2174
	max_segs = tcp_tso_segs(sk, mss_now);
2175
	while ((skb = tcp_send_head(sk))) {
2176 2177
		unsigned int limit;

2178
		tso_segs = tcp_init_tso_segs(skb, mss_now);
2179
		BUG_ON(!tso_segs);
2180

2181
		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
E
Eric Dumazet 已提交
2182 2183
			/* "skb_mstamp" is used as a start point for the retransmit timer */
			skb_mstamp_get(&skb->skb_mstamp);
2184
			goto repair; /* Skip network transmission */
2185
		}
2186

2187
		cwnd_quota = tcp_cwnd_test(tp, skb);
N
Nandita Dukkipati 已提交
2188 2189 2190 2191 2192 2193 2194
		if (!cwnd_quota) {
			if (push_one == 2)
				/* Force out a loss probe pkt. */
				cwnd_quota = 1;
			else
				break;
		}
2195

2196 2197
		if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) {
			is_rwnd_limited = true;
2198
			break;
2199
		}
2200

2201
		if (tso_segs == 1) {
2202 2203 2204 2205 2206
			if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
						     (tcp_skb_is_last(sk, skb) ?
						      nonagle : TCP_NAGLE_PUSH))))
				break;
		} else {
2207
			if (!push_one &&
E
Eric Dumazet 已提交
2208 2209
			    tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
						 max_segs))
2210 2211
				break;
		}
2212

E
Eric Dumazet 已提交
2213
		limit = mss_now;
2214
		if (tso_segs > 1 && !tcp_urg_mode(tp))
E
Eric Dumazet 已提交
2215 2216 2217 2218 2219 2220 2221 2222 2223 2224
			limit = tcp_mss_split_point(sk, skb, mss_now,
						    min_t(unsigned int,
							  cwnd_quota,
							  max_segs),
						    nonagle);

		if (skb->len > limit &&
		    unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
			break;

2225 2226
		if (tcp_small_queue_check(sk, skb, 0))
			break;
E
Eric Dumazet 已提交
2227

2228
		if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2229
			break;
L
Linus Torvalds 已提交
2230

2231
repair:
2232 2233 2234
		/* Advance the send_head.  This one is sent out.
		 * This call will increment packets_out.
		 */
2235
		tcp_event_new_data_sent(sk, skb);
L
Linus Torvalds 已提交
2236

2237
		tcp_minshall_update(tp, mss_now, skb);
2238
		sent_pkts += tcp_skb_pcount(skb);
2239 2240 2241

		if (push_one)
			break;
2242
	}
L
Linus Torvalds 已提交
2243

2244 2245 2246 2247 2248
	if (is_rwnd_limited)
		tcp_chrono_start(sk, TCP_CHRONO_RWND_LIMITED);
	else
		tcp_chrono_stop(sk, TCP_CHRONO_RWND_LIMITED);

2249
	if (likely(sent_pkts)) {
2250 2251
		if (tcp_in_cwnd_reduction(sk))
			tp->prr_out += sent_pkts;
N
Nandita Dukkipati 已提交
2252 2253 2254 2255

		/* Send one loss probe per tail loss episode. */
		if (push_one != 2)
			tcp_schedule_loss_probe(sk);
2256
		is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
2257
		tcp_cwnd_validate(sk, is_cwnd_limited);
E
Eric Dumazet 已提交
2258
		return false;
L
Linus Torvalds 已提交
2259
	}
2260
	return !tp->packets_out && tcp_send_head(sk);
N
Nandita Dukkipati 已提交
2261 2262 2263 2264 2265 2266 2267
}

bool tcp_schedule_loss_probe(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	u32 timeout, tlp_time_stamp, rto_time_stamp;
2268
	u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
N
Nandita Dukkipati 已提交
2269 2270 2271 2272 2273 2274 2275 2276 2277 2278 2279

	if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
		return false;
	/* No consecutive loss probes. */
	if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
		tcp_rearm_rto(sk);
		return false;
	}
	/* Don't do any loss probe on a Fast Open connection before 3WHS
	 * finishes.
	 */
2280
	if (tp->fastopen_rsk)
N
Nandita Dukkipati 已提交
2281 2282 2283 2284 2285 2286 2287 2288 2289
		return false;

	/* TLP is only scheduled when next timer event is RTO. */
	if (icsk->icsk_pending != ICSK_TIME_RETRANS)
		return false;

	/* Schedule a loss probe in 2*RTT for SACK capable connections
	 * in Open state, that are either limited by cwnd or application.
	 */
2290
	if (sysctl_tcp_early_retrans < 3 || !tp->packets_out ||
N
Nandita Dukkipati 已提交
2291 2292 2293 2294 2295 2296 2297 2298
	    !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
		return false;

	if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
	     tcp_send_head(sk))
		return false;

	/* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2299 2300
	 * for delayed ack when there's one outstanding packet. If no RTT
	 * sample is available then probe after TCP_TIMEOUT_INIT.
N
Nandita Dukkipati 已提交
2301
	 */
2302
	timeout = rtt << 1 ? : TCP_TIMEOUT_INIT;
N
Nandita Dukkipati 已提交
2303 2304 2305 2306 2307 2308 2309 2310 2311 2312 2313 2314 2315 2316 2317 2318 2319 2320 2321
	if (tp->packets_out == 1)
		timeout = max_t(u32, timeout,
				(rtt + (rtt >> 1) + TCP_DELACK_MAX));
	timeout = max_t(u32, timeout, msecs_to_jiffies(10));

	/* If RTO is shorter, just schedule TLP in its place. */
	tlp_time_stamp = tcp_time_stamp + timeout;
	rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
	if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
		s32 delta = rto_time_stamp - tcp_time_stamp;
		if (delta > 0)
			timeout = delta;
	}

	inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
				  TCP_RTO_MAX);
	return true;
}

2322 2323 2324 2325 2326 2327 2328
/* Thanks to skb fast clones, we can detect if a prior transmit of
 * a packet is still in a qdisc or driver queue.
 * In this case, there is very little point doing a retransmit !
 */
static bool skb_still_in_host_queue(const struct sock *sk,
				    const struct sk_buff *skb)
{
2329
	if (unlikely(skb_fclone_busy(sk, skb))) {
2330 2331
		NET_INC_STATS(sock_net(sk),
			      LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2332 2333 2334 2335 2336
		return true;
	}
	return false;
}

2337
/* When probe timeout (PTO) fires, try send a new segment if possible, else
N
Nandita Dukkipati 已提交
2338 2339 2340 2341
 * retransmit the last segment.
 */
void tcp_send_loss_probe(struct sock *sk)
{
N
Nandita Dukkipati 已提交
2342
	struct tcp_sock *tp = tcp_sk(sk);
N
Nandita Dukkipati 已提交
2343 2344 2345 2346
	struct sk_buff *skb;
	int pcount;
	int mss = tcp_current_mss(sk);

2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358
	skb = tcp_send_head(sk);
	if (skb) {
		if (tcp_snd_wnd_test(tp, skb, mss)) {
			pcount = tp->packets_out;
			tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
			if (tp->packets_out > pcount)
				goto probe_sent;
			goto rearm_timer;
		}
		skb = tcp_write_queue_prev(sk, skb);
	} else {
		skb = tcp_write_queue_tail(sk);
N
Nandita Dukkipati 已提交
2359 2360
	}

N
Nandita Dukkipati 已提交
2361 2362 2363 2364
	/* At most one outstanding TLP retransmission. */
	if (tp->tlp_high_seq)
		goto rearm_timer;

N
Nandita Dukkipati 已提交
2365 2366 2367 2368
	/* Retransmit last segment. */
	if (WARN_ON(!skb))
		goto rearm_timer;

2369 2370 2371
	if (skb_still_in_host_queue(sk, skb))
		goto rearm_timer;

N
Nandita Dukkipati 已提交
2372 2373 2374 2375 2376
	pcount = tcp_skb_pcount(skb);
	if (WARN_ON(!pcount))
		goto rearm_timer;

	if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2377 2378
		if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
					  GFP_ATOMIC)))
N
Nandita Dukkipati 已提交
2379
			goto rearm_timer;
2380
		skb = tcp_write_queue_next(sk, skb);
N
Nandita Dukkipati 已提交
2381 2382 2383 2384 2385
	}

	if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
		goto rearm_timer;

2386
	if (__tcp_retransmit_skb(sk, skb, 1))
2387
		goto rearm_timer;
N
Nandita Dukkipati 已提交
2388

N
Nandita Dukkipati 已提交
2389
	/* Record snd_nxt for loss detection. */
2390
	tp->tlp_high_seq = tp->snd_nxt;
N
Nandita Dukkipati 已提交
2391

2392
probe_sent:
2393
	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2394 2395
	/* Reset s.t. tcp_rearm_rto will restart timer from now */
	inet_csk(sk)->icsk_pending = 0;
N
Nandita Dukkipati 已提交
2396
rearm_timer:
2397
	tcp_rearm_rto(sk);
L
Linus Torvalds 已提交
2398 2399
}

2400 2401 2402 2403
/* Push out any pending frames which were held back due to
 * TCP_CORK or attempt at coalescing tiny packets.
 * The socket must be locked by the caller.
 */
2404 2405
void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
			       int nonagle)
2406
{
2407 2408 2409 2410 2411 2412 2413
	/* If we are closed, the bytes will have to remain here.
	 * In time closedown will finish, we empty the write queue and
	 * all will be happy.
	 */
	if (unlikely(sk->sk_state == TCP_CLOSE))
		return;

2414
	if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2415
			   sk_gfp_mask(sk, GFP_ATOMIC)))
2416
		tcp_check_probe_timer(sk);
2417 2418
}

2419 2420 2421 2422 2423
/* Send _single_ skb sitting at the send head. This function requires
 * true push pending frames to setup probe timer etc.
 */
void tcp_push_one(struct sock *sk, unsigned int mss_now)
{
2424
	struct sk_buff *skb = tcp_send_head(sk);
2425 2426 2427

	BUG_ON(!skb || skb->len < mss_now);

2428
	tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2429 2430
}

L
Linus Torvalds 已提交
2431 2432
/* This function returns the amount that we can raise the
 * usable window based on the following constraints
2433
 *
L
Linus Torvalds 已提交
2434 2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448 2449 2450 2451
 * 1. The window can never be shrunk once it is offered (RFC 793)
 * 2. We limit memory per socket
 *
 * RFC 1122:
 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
 *  RECV.NEXT + RCV.WIN fixed until:
 *  RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
 *
 * i.e. don't raise the right edge of the window until you can raise
 * it at least MSS bytes.
 *
 * Unfortunately, the recommended algorithm breaks header prediction,
 * since header prediction assumes th->window stays fixed.
 *
 * Strictly speaking, keeping th->window fixed violates the receiver
 * side SWS prevention criteria. The problem is that under this rule
 * a stream of single byte packets will cause the right side of the
 * window to always advance by a single byte.
2452
 *
L
Linus Torvalds 已提交
2453 2454
 * Of course, if the sender implements sender side SWS prevention
 * then this will not be a problem.
2455
 *
L
Linus Torvalds 已提交
2456
 * BSD seems to make the following compromise:
2457
 *
L
Linus Torvalds 已提交
2458 2459 2460 2461 2462 2463 2464 2465 2466 2467 2468 2469 2470 2471 2472 2473 2474 2475 2476 2477 2478 2479 2480 2481 2482 2483 2484
 *	If the free space is less than the 1/4 of the maximum
 *	space available and the free space is less than 1/2 mss,
 *	then set the window to 0.
 *	[ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
 *	Otherwise, just prevent the window from shrinking
 *	and from being larger than the largest representable value.
 *
 * This prevents incremental opening of the window in the regime
 * where TCP is limited by the speed of the reader side taking
 * data out of the TCP receive queue. It does nothing about
 * those cases where the window is constrained on the sender side
 * because the pipeline is full.
 *
 * BSD also seems to "accidentally" limit itself to windows that are a
 * multiple of MSS, at least until the free space gets quite small.
 * This would appear to be a side effect of the mbuf implementation.
 * Combining these two algorithms results in the observed behavior
 * of having a fixed window size at almost all times.
 *
 * Below we obtain similar behavior by forcing the offered window to
 * a multiple of the mss when it is feasible to do so.
 *
 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
 * Regular options like TIMESTAMP are taken into account.
 */
u32 __tcp_select_window(struct sock *sk)
{
2485
	struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
2486
	struct tcp_sock *tp = tcp_sk(sk);
S
Stephen Hemminger 已提交
2487
	/* MSS for the peer's data.  Previous versions used mss_clamp
L
Linus Torvalds 已提交
2488 2489 2490 2491 2492
	 * here.  I don't know if the value based on our guesses
	 * of peer's MSS is better for the performance.  It's more correct
	 * but may be worse for the performance because of rcv_mss
	 * fluctuations.  --SAW  1998/11/1
	 */
2493
	int mss = icsk->icsk_ack.rcv_mss;
L
Linus Torvalds 已提交
2494
	int free_space = tcp_space(sk);
2495 2496
	int allowed_space = tcp_full_space(sk);
	int full_space = min_t(int, tp->window_clamp, allowed_space);
L
Linus Torvalds 已提交
2497 2498 2499
	int window;

	if (mss > full_space)
2500
		mss = full_space;
L
Linus Torvalds 已提交
2501

2502
	if (free_space < (full_space >> 1)) {
2503
		icsk->icsk_ack.quick = 0;
L
Linus Torvalds 已提交
2504

2505
		if (tcp_under_memory_pressure(sk))
2506 2507
			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
					       4U * tp->advmss);
L
Linus Torvalds 已提交
2508

2509 2510 2511 2512 2513 2514 2515 2516 2517 2518 2519 2520 2521
		/* free_space might become our new window, make sure we don't
		 * increase it due to wscale.
		 */
		free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);

		/* if free space is less than mss estimate, or is below 1/16th
		 * of the maximum allowed, try to move to zero-window, else
		 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
		 * new incoming data is dropped due to memory limits.
		 * With large window, mss test triggers way too late in order
		 * to announce zero window in time before rmem limit kicks in.
		 */
		if (free_space < (allowed_space >> 4) || free_space < mss)
L
Linus Torvalds 已提交
2522 2523 2524 2525 2526 2527 2528 2529 2530 2531 2532 2533 2534 2535 2536 2537 2538 2539 2540 2541 2542 2543 2544 2545 2546 2547 2548 2549 2550 2551
			return 0;
	}

	if (free_space > tp->rcv_ssthresh)
		free_space = tp->rcv_ssthresh;

	/* Don't do rounding if we are using window scaling, since the
	 * scaled window will not line up with the MSS boundary anyway.
	 */
	window = tp->rcv_wnd;
	if (tp->rx_opt.rcv_wscale) {
		window = free_space;

		/* Advertise enough space so that it won't get scaled away.
		 * Import case: prevent zero window announcement if
		 * 1<<rcv_wscale > mss.
		 */
		if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
			window = (((window >> tp->rx_opt.rcv_wscale) + 1)
				  << tp->rx_opt.rcv_wscale);
	} else {
		/* Get the largest window that is a nice multiple of mss.
		 * Window clamp already applied above.
		 * If our current window offering is within 1 mss of the
		 * free space we just keep it. This prevents the divide
		 * and multiply from happening most of the time.
		 * We also don't do any window rounding when the free space
		 * is too small.
		 */
		if (window <= free_space - mss || window > free_space)
2552
			window = (free_space / mss) * mss;
2553
		else if (mss == full_space &&
2554
			 free_space > window + (full_space >> 1))
2555
			window = free_space;
L
Linus Torvalds 已提交
2556 2557 2558 2559 2560
	}

	return window;
}

2561 2562
void tcp_skb_collapse_tstamp(struct sk_buff *skb,
			     const struct sk_buff *next_skb)
2563
{
2564 2565 2566
	if (unlikely(tcp_has_tx_tstamp(next_skb))) {
		const struct skb_shared_info *next_shinfo =
			skb_shinfo(next_skb);
2567 2568
		struct skb_shared_info *shinfo = skb_shinfo(skb);

2569
		shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
2570
		shinfo->tskey = next_shinfo->tskey;
2571 2572
		TCP_SKB_CB(skb)->txstamp_ack |=
			TCP_SKB_CB(next_skb)->txstamp_ack;
2573 2574 2575
	}
}

2576
/* Collapses two adjacent SKB's during retransmission. */
2577
static bool tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
L
Linus Torvalds 已提交
2578 2579
{
	struct tcp_sock *tp = tcp_sk(sk);
2580
	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2581
	int skb_size, next_skb_size;
L
Linus Torvalds 已提交
2582

2583 2584
	skb_size = skb->len;
	next_skb_size = next_skb->len;
L
Linus Torvalds 已提交
2585

2586
	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2587

2588 2589 2590 2591 2592 2593 2594
	if (next_skb_size) {
		if (next_skb_size <= skb_availroom(skb))
			skb_copy_bits(next_skb, 0, skb_put(skb, next_skb_size),
				      next_skb_size);
		else if (!skb_shift(skb, next_skb, next_skb_size))
			return false;
	}
2595
	tcp_highest_sack_combine(sk, next_skb, skb);
L
Linus Torvalds 已提交
2596

2597
	tcp_unlink_write_queue(next_skb, sk);
L
Linus Torvalds 已提交
2598

2599 2600
	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
		skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
2601

2602 2603
	if (skb->ip_summed != CHECKSUM_PARTIAL)
		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
L
Linus Torvalds 已提交
2604

2605 2606
	/* Update sequence range on original skb. */
	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
L
Linus Torvalds 已提交
2607

2608
	/* Merge over control information. This moves PSH/FIN etc. over */
E
Eric Dumazet 已提交
2609
	TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2610 2611 2612 2613 2614

	/* All done, get rid of second SKB and account for it so
	 * packet counting does not break.
	 */
	TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2615
	TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor;
2616 2617

	/* changed transmit queue under us so clear hints */
2618 2619 2620
	tcp_clear_retrans_hints_partial(tp);
	if (next_skb == tp->retransmit_skb_hint)
		tp->retransmit_skb_hint = skb;
2621

2622 2623
	tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));

2624 2625
	tcp_skb_collapse_tstamp(skb, next_skb);

2626
	sk_wmem_free_skb(sk, next_skb);
2627
	return true;
L
Linus Torvalds 已提交
2628 2629
}

2630
/* Check if coalescing SKBs is legal. */
E
Eric Dumazet 已提交
2631
static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2632 2633
{
	if (tcp_skb_pcount(skb) > 1)
E
Eric Dumazet 已提交
2634
		return false;
2635
	if (skb_cloned(skb))
E
Eric Dumazet 已提交
2636
		return false;
2637
	if (skb == tcp_send_head(sk))
E
Eric Dumazet 已提交
2638
		return false;
E
Eric Dumazet 已提交
2639
	/* Some heuristics for collapsing over SACK'd could be invented */
2640
	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
E
Eric Dumazet 已提交
2641
		return false;
2642

E
Eric Dumazet 已提交
2643
	return true;
2644 2645
}

2646 2647 2648
/* Collapse packets in the retransmit queue to make to create
 * less packets on the wire. This is only done on retransmission.
 */
2649 2650 2651 2652 2653
static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
				     int space)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb = to, *tmp;
E
Eric Dumazet 已提交
2654
	bool first = true;
2655 2656 2657

	if (!sysctl_tcp_retrans_collapse)
		return;
E
Eric Dumazet 已提交
2658
	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2659 2660 2661 2662 2663 2664
		return;

	tcp_for_write_queue_from_safe(skb, tmp, sk) {
		if (!tcp_can_collapse(sk, skb))
			break;

2665 2666 2667
		if (!tcp_skb_can_collapse_to(to))
			break;

2668 2669 2670
		space -= skb->len;

		if (first) {
E
Eric Dumazet 已提交
2671
			first = false;
2672 2673 2674 2675 2676 2677 2678 2679 2680
			continue;
		}

		if (space < 0)
			break;

		if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
			break;

2681 2682
		if (!tcp_collapse_retrans(sk, to))
			break;
2683 2684 2685
	}
}

L
Linus Torvalds 已提交
2686 2687 2688 2689
/* This retransmits one SKB.  Policy decisions and retransmit queue
 * state updates are done by the caller.  Returns non-zero if an
 * error occurred which prevented the send.
 */
2690
int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
L
Linus Torvalds 已提交
2691
{
J
John Heffner 已提交
2692
	struct inet_connection_sock *icsk = inet_csk(sk);
2693
	struct tcp_sock *tp = tcp_sk(sk);
2694
	unsigned int cur_mss;
2695 2696
	int diff, len, err;

L
Linus Torvalds 已提交
2697

2698 2699
	/* Inconclusive MTU probe */
	if (icsk->icsk_mtup.probe_size)
J
John Heffner 已提交
2700 2701
		icsk->icsk_mtup.probe_size = 0;

L
Linus Torvalds 已提交
2702
	/* Do not sent more than we queued. 1/4 is reserved for possible
S
Stephen Hemminger 已提交
2703
	 * copying overhead: fragmentation, tunneling, mangling etc.
L
Linus Torvalds 已提交
2704 2705
	 */
	if (atomic_read(&sk->sk_wmem_alloc) >
2706 2707
	    min_t(u32, sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2),
		  sk->sk_sndbuf))
L
Linus Torvalds 已提交
2708 2709
		return -EAGAIN;

2710 2711 2712
	if (skb_still_in_host_queue(sk, skb))
		return -EBUSY;

L
Linus Torvalds 已提交
2713 2714 2715 2716 2717 2718 2719
	if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
		if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
			BUG();
		if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
			return -ENOMEM;
	}

2720 2721 2722
	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
		return -EHOSTUNREACH; /* Routing failure or similar. */

I
Ilpo Järvinen 已提交
2723
	cur_mss = tcp_current_mss(sk);
2724

L
Linus Torvalds 已提交
2725 2726 2727 2728 2729
	/* If receiver has shrunk his window, and skb is out of
	 * new window, do not retransmit it. The exception is the
	 * case, when window is shrunk to zero. In this case
	 * our retransmit serves as a zero window probe.
	 */
2730 2731
	if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
	    TCP_SKB_CB(skb)->seq != tp->snd_una)
L
Linus Torvalds 已提交
2732 2733
		return -EAGAIN;

2734 2735 2736
	len = cur_mss * segs;
	if (skb->len > len) {
		if (tcp_fragment(sk, skb, len, cur_mss, GFP_ATOMIC))
L
Linus Torvalds 已提交
2737
			return -ENOMEM; /* We'll try again later. */
2738
	} else {
2739 2740
		if (skb_unclone(skb, GFP_ATOMIC))
			return -ENOMEM;
2741

2742 2743 2744 2745 2746 2747 2748
		diff = tcp_skb_pcount(skb);
		tcp_set_skb_tso_segs(skb, cur_mss);
		diff -= tcp_skb_pcount(skb);
		if (diff)
			tcp_adjust_pcount(sk, skb, diff);
		if (skb->len < cur_mss)
			tcp_retrans_try_collapse(sk, skb, cur_mss);
L
Linus Torvalds 已提交
2749 2750
	}

2751 2752 2753 2754
	/* RFC3168, section 6.1.1.1. ECN fallback */
	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
		tcp_ecn_clear_syn(sk, skb);

2755 2756 2757 2758 2759 2760
	/* make sure skb->data is aligned on arches that require it
	 * and check if ack-trimming & collapsing extended the headroom
	 * beyond what csum_start can cover.
	 */
	if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
		     skb_headroom(skb) >= 0xFFFF)) {
2761 2762 2763 2764
		struct sk_buff *nskb;

		skb_mstamp_get(&skb->skb_mstamp);
		nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
2765 2766
		err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
			     -ENOBUFS;
E
Eric Dumazet 已提交
2767
	} else {
2768
		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
E
Eric Dumazet 已提交
2769
	}
2770

2771
	if (likely(!err)) {
2772 2773
		segs = tcp_skb_pcount(skb);

2774
		TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2775
		/* Update global TCP statistics. */
2776
		TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
2777
		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2778
			__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2779
		tp->total_retrans += segs;
2780
	}
2781
	return err;
2782 2783
}

2784
int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2785 2786
{
	struct tcp_sock *tp = tcp_sk(sk);
2787
	int err = __tcp_retransmit_skb(sk, skb, segs);
L
Linus Torvalds 已提交
2788 2789 2790

	if (err == 0) {
#if FASTRETRANS_DEBUG > 0
2791
		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2792
			net_dbg_ratelimited("retrans_out leaked\n");
L
Linus Torvalds 已提交
2793 2794 2795 2796 2797 2798 2799
		}
#endif
		TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
		tp->retrans_out += tcp_skb_pcount(skb);

		/* Save stamp of the first retransmit. */
		if (!tp->retrans_stamp)
E
Eric Dumazet 已提交
2800
			tp->retrans_stamp = tcp_skb_timestamp(skb);
L
Linus Torvalds 已提交
2801

2802
	} else if (err != -EBUSY) {
2803
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
L
Linus Torvalds 已提交
2804
	}
Y
Yuchung Cheng 已提交
2805 2806 2807 2808

	if (tp->undo_retrans < 0)
		tp->undo_retrans = 0;
	tp->undo_retrans += tcp_skb_pcount(skb);
L
Linus Torvalds 已提交
2809 2810 2811
	return err;
}

2812 2813 2814
/* Check if we forward retransmits are possible in the current
 * window/congestion state.
 */
E
Eric Dumazet 已提交
2815
static bool tcp_can_forward_retransmit(struct sock *sk)
2816 2817
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
2818
	const struct tcp_sock *tp = tcp_sk(sk);
2819 2820 2821

	/* Forward retransmissions are possible only during Recovery. */
	if (icsk->icsk_ca_state != TCP_CA_Recovery)
E
Eric Dumazet 已提交
2822
		return false;
2823 2824 2825

	/* No forward retransmissions in Reno are possible. */
	if (tcp_is_reno(tp))
E
Eric Dumazet 已提交
2826
		return false;
2827 2828 2829 2830 2831 2832 2833 2834 2835 2836

	/* Yeah, we have to make difficult choice between forward transmission
	 * and retransmission... Both ways have their merits...
	 *
	 * For now we do not retransmit anything, while we have some new
	 * segments to send. In the other cases, follow rule 3 for
	 * NextSeg() specified in RFC3517.
	 */

	if (tcp_may_send_now(sk))
E
Eric Dumazet 已提交
2837
		return false;
2838

E
Eric Dumazet 已提交
2839
	return true;
2840 2841
}

L
Linus Torvalds 已提交
2842 2843 2844 2845 2846 2847 2848 2849 2850 2851
/* This gets called after a retransmit timeout, and the initially
 * retransmitted data is acknowledged.  It tries to continue
 * resending the rest of the retransmit queue, until either
 * we've sent it all or the congestion window limit is reached.
 * If doing SACK, the first ACK which comes back for a timeout
 * based retransmit packet might feed us FACK information again.
 * If so, we use it to avoid unnecessarily retransmissions.
 */
void tcp_xmit_retransmit_queue(struct sock *sk)
{
2852
	const struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
2853 2854
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
2855
	struct sk_buff *hole = NULL;
2856
	u32 max_segs, last_lost;
2857
	int mib_idx;
2858
	int fwd_rexmitting = 0;
2859

2860 2861 2862
	if (!tp->packets_out)
		return;

2863 2864 2865
	if (!tp->lost_out)
		tp->retransmit_high = tp->snd_una;

2866
	if (tp->retransmit_skb_hint) {
2867
		skb = tp->retransmit_skb_hint;
2868 2869 2870 2871
		last_lost = TCP_SKB_CB(skb)->end_seq;
		if (after(last_lost, tp->retransmit_high))
			last_lost = tp->retransmit_high;
	} else {
2872
		skb = tcp_write_queue_head(sk);
2873 2874
		last_lost = tp->snd_una;
	}
L
Linus Torvalds 已提交
2875

2876
	max_segs = tcp_tso_segs(sk, tcp_current_mss(sk));
2877
	tcp_for_write_queue_from(skb, sk) {
E
Eric Dumazet 已提交
2878
		__u8 sacked;
2879
		int segs;
L
Linus Torvalds 已提交
2880

2881 2882 2883
		if (skb == tcp_send_head(sk))
			break;
		/* we could do better than to assign each time */
2884
		if (!hole)
2885
			tp->retransmit_skb_hint = skb;
2886

2887 2888
		segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
		if (segs <= 0)
2889
			return;
E
Eric Dumazet 已提交
2890
		sacked = TCP_SKB_CB(skb)->sacked;
2891 2892 2893 2894
		/* In case tcp_shift_skb_data() have aggregated large skbs,
		 * we need to make sure not sending too bigs TSO packets
		 */
		segs = min_t(int, segs, max_segs);
L
Linus Torvalds 已提交
2895

2896 2897 2898 2899 2900
		if (fwd_rexmitting) {
begin_fwd:
			if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
				break;
			mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2901

2902
		} else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2903
			tp->retransmit_high = last_lost;
2904 2905 2906
			if (!tcp_can_forward_retransmit(sk))
				break;
			/* Backtrack if necessary to non-L'ed skb */
2907
			if (hole) {
2908 2909 2910 2911 2912
				skb = hole;
				hole = NULL;
			}
			fwd_rexmitting = 1;
			goto begin_fwd;
L
Linus Torvalds 已提交
2913

2914
		} else if (!(sacked & TCPCB_LOST)) {
2915
			if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2916 2917
				hole = skb;
			continue;
L
Linus Torvalds 已提交
2918

2919
		} else {
2920
			last_lost = TCP_SKB_CB(skb)->end_seq;
2921 2922 2923 2924 2925
			if (icsk->icsk_ca_state != TCP_CA_Loss)
				mib_idx = LINUX_MIB_TCPFASTRETRANS;
			else
				mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
		}
L
Linus Torvalds 已提交
2926

2927
		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
L
Linus Torvalds 已提交
2928 2929
			continue;

2930 2931 2932
		if (tcp_small_queue_check(sk, skb, 1))
			return;

2933
		if (tcp_retransmit_skb(sk, skb, segs))
2934
			return;
2935

2936
		NET_ADD_STATS(sock_net(sk), mib_idx, tcp_skb_pcount(skb));
L
Linus Torvalds 已提交
2937

2938
		if (tcp_in_cwnd_reduction(sk))
2939 2940
			tp->prr_out += tcp_skb_pcount(skb);

2941
		if (skb == tcp_write_queue_head(sk))
2942 2943 2944
			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
						  inet_csk(sk)->icsk_rto,
						  TCP_RTO_MAX);
L
Linus Torvalds 已提交
2945 2946 2947
	}
}

2948 2949
/* We allow to exceed memory limits for FIN packets to expedite
 * connection tear down and (memory) recovery.
2950 2951
 * Otherwise tcp_send_fin() could be tempted to either delay FIN
 * or even be forced to close flow without any FIN.
2952 2953
 * In general, we want to allow one skb per socket to avoid hangs
 * with edge trigger epoll()
2954
 */
2955
void sk_forced_mem_schedule(struct sock *sk, int size)
2956
{
2957
	int amt;
2958 2959 2960 2961 2962

	if (size <= sk->sk_forward_alloc)
		return;
	amt = sk_mem_pages(size);
	sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2963 2964
	sk_memory_allocated_add(sk, amt);

2965 2966
	if (mem_cgroup_sockets_enabled && sk->sk_memcg)
		mem_cgroup_charge_skmem(sk->sk_memcg, amt);
2967 2968
}

2969 2970
/* Send a FIN. The caller locks the socket for us.
 * We should try to send a FIN packet really hard, but eventually give up.
L
Linus Torvalds 已提交
2971 2972 2973
 */
void tcp_send_fin(struct sock *sk)
{
2974
	struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2975 2976
	struct tcp_sock *tp = tcp_sk(sk);

2977 2978 2979 2980
	/* Optimization, tack on the FIN if we have one skb in write queue and
	 * this skb was not yet sent, or we are under memory pressure.
	 * Note: in the latter case, FIN packet will be sent after a timeout,
	 * as TCP stack thinks it has already been transmitted.
L
Linus Torvalds 已提交
2981
	 */
2982
	if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
2983 2984 2985
coalesce:
		TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
		TCP_SKB_CB(tskb)->end_seq++;
L
Linus Torvalds 已提交
2986
		tp->write_seq++;
2987 2988 2989 2990 2991 2992 2993 2994 2995 2996
		if (!tcp_send_head(sk)) {
			/* This means tskb was already sent.
			 * Pretend we included the FIN on previous transmit.
			 * We need to set tp->snd_nxt to the value it would have
			 * if FIN had been sent. This is because retransmit path
			 * does not change tp->snd_nxt.
			 */
			tp->snd_nxt++;
			return;
		}
L
Linus Torvalds 已提交
2997
	} else {
2998 2999 3000 3001 3002
		skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
		if (unlikely(!skb)) {
			if (tskb)
				goto coalesce;
			return;
L
Linus Torvalds 已提交
3003
		}
3004
		skb_reserve(skb, MAX_TCP_HEADER);
3005
		sk_forced_mem_schedule(sk, skb->truesize);
L
Linus Torvalds 已提交
3006
		/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
3007
		tcp_init_nondata_skb(skb, tp->write_seq,
C
Changli Gao 已提交
3008
				     TCPHDR_ACK | TCPHDR_FIN);
L
Linus Torvalds 已提交
3009 3010
		tcp_queue_skb(sk, skb);
	}
3011
	__tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
L
Linus Torvalds 已提交
3012 3013 3014 3015 3016
}

/* We get here when a process closes a file descriptor (either due to
 * an explicit close() or as a byproduct of exit()'ing) and there
 * was unread data in the receive queue.  This behavior is recommended
3017
 * by RFC 2525, section 2.17.  -DaveM
L
Linus Torvalds 已提交
3018
 */
A
Al Viro 已提交
3019
void tcp_send_active_reset(struct sock *sk, gfp_t priority)
L
Linus Torvalds 已提交
3020 3021 3022 3023 3024 3025
{
	struct sk_buff *skb;

	/* NOTE: No TCP options attached and we never retransmit this. */
	skb = alloc_skb(MAX_TCP_HEADER, priority);
	if (!skb) {
P
Pavel Emelyanov 已提交
3026
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
L
Linus Torvalds 已提交
3027 3028 3029 3030 3031
		return;
	}

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, MAX_TCP_HEADER);
3032
	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
C
Changli Gao 已提交
3033
			     TCPHDR_ACK | TCPHDR_RST);
3034
	skb_mstamp_get(&skb->skb_mstamp);
L
Linus Torvalds 已提交
3035
	/* Send it off. */
3036
	if (tcp_transmit_skb(sk, skb, 0, priority))
P
Pavel Emelyanov 已提交
3037
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3038

P
Pavel Emelyanov 已提交
3039
	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
L
Linus Torvalds 已提交
3040 3041
}

3042 3043
/* Send a crossed SYN-ACK during socket establishment.
 * WARNING: This routine must only be called when we have already sent
L
Linus Torvalds 已提交
3044 3045 3046 3047 3048 3049
 * a SYN packet that crossed the incoming SYN that caused this routine
 * to get called. If this assumption fails then the initial rcv_wnd
 * and rcv_wscale values will not be correct.
 */
int tcp_send_synack(struct sock *sk)
{
3050
	struct sk_buff *skb;
L
Linus Torvalds 已提交
3051

3052
	skb = tcp_write_queue_head(sk);
3053
	if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
3054
		pr_debug("%s: wrong queue state\n", __func__);
L
Linus Torvalds 已提交
3055 3056
		return -EFAULT;
	}
E
Eric Dumazet 已提交
3057
	if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
L
Linus Torvalds 已提交
3058 3059
		if (skb_cloned(skb)) {
			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
3060
			if (!nskb)
L
Linus Torvalds 已提交
3061
				return -ENOMEM;
3062
			tcp_unlink_write_queue(skb, sk);
3063
			__skb_header_release(nskb);
3064
			__tcp_add_write_queue_head(sk, nskb);
3065 3066 3067
			sk_wmem_free_skb(sk, skb);
			sk->sk_wmem_queued += nskb->truesize;
			sk_mem_charge(sk, nskb->truesize);
L
Linus Torvalds 已提交
3068 3069 3070
			skb = nskb;
		}

E
Eric Dumazet 已提交
3071
		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
3072
		tcp_ecn_send_synack(sk, skb);
L
Linus Torvalds 已提交
3073
	}
3074
	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
L
Linus Torvalds 已提交
3075 3076
}

3077 3078 3079 3080 3081 3082 3083 3084 3085
/**
 * tcp_make_synack - Prepare a SYN-ACK.
 * sk: listener socket
 * dst: dst entry attached to the SYNACK
 * req: request_sock pointer
 *
 * Allocate one skb and build a SYNACK packet.
 * @dst is consumed : Caller should not use it again.
 */
3086
struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
3087
				struct request_sock *req,
3088
				struct tcp_fastopen_cookie *foc,
3089
				enum tcp_synack_type synack_type)
L
Linus Torvalds 已提交
3090
{
3091
	struct inet_request_sock *ireq = inet_rsk(req);
3092
	const struct tcp_sock *tp = tcp_sk(sk);
E
Eric Dumazet 已提交
3093
	struct tcp_md5sig_key *md5 = NULL;
3094 3095
	struct tcp_out_options opts;
	struct sk_buff *skb;
3096
	int tcp_header_size;
3097 3098
	struct tcphdr *th;
	u16 user_mss;
3099
	int mss;
L
Linus Torvalds 已提交
3100

3101
	skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
3102 3103
	if (unlikely(!skb)) {
		dst_release(dst);
L
Linus Torvalds 已提交
3104
		return NULL;
3105
	}
L
Linus Torvalds 已提交
3106 3107 3108
	/* Reserve space for headers. */
	skb_reserve(skb, MAX_TCP_HEADER);

3109 3110
	switch (synack_type) {
	case TCP_SYNACK_NORMAL:
3111
		skb_set_owner_w(skb, req_to_sk(req));
3112 3113 3114 3115 3116 3117 3118
		break;
	case TCP_SYNACK_COOKIE:
		/* Under synflood, we do not attach skb to a socket,
		 * to avoid false sharing.
		 */
		break;
	case TCP_SYNACK_FASTOPEN:
3119 3120 3121 3122 3123
		/* sk is a const pointer, because we want to express multiple
		 * cpu might call us concurrently.
		 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
		 */
		skb_set_owner_w(skb, (struct sock *)sk);
3124
		break;
3125
	}
3126
	skb_dst_set(skb, dst);
L
Linus Torvalds 已提交
3127

3128
	mss = dst_metric_advmss(dst);
3129 3130 3131
	user_mss = READ_ONCE(tp->rx_opt.user_mss);
	if (user_mss && user_mss < mss)
		mss = user_mss;
3132

A
Adam Langley 已提交
3133
	memset(&opts, 0, sizeof(opts));
3134 3135
#ifdef CONFIG_SYN_COOKIES
	if (unlikely(req->cookie_ts))
E
Eric Dumazet 已提交
3136
		skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
3137 3138
	else
#endif
E
Eric Dumazet 已提交
3139
	skb_mstamp_get(&skb->skb_mstamp);
E
Eric Dumazet 已提交
3140 3141 3142

#ifdef CONFIG_TCP_MD5SIG
	rcu_read_lock();
3143
	md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
E
Eric Dumazet 已提交
3144
#endif
3145
	skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
3146 3147
	tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
			  sizeof(*th);
3148

3149 3150
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
L
Linus Torvalds 已提交
3151

3152
	th = (struct tcphdr *)skb->data;
L
Linus Torvalds 已提交
3153 3154 3155
	memset(th, 0, sizeof(struct tcphdr));
	th->syn = 1;
	th->ack = 1;
3156
	tcp_ecn_make_synack(req, th);
E
Eric Dumazet 已提交
3157
	th->source = htons(ireq->ir_num);
3158
	th->dest = ireq->ir_rmt_port;
3159 3160 3161 3162
	/* Setting of flags are superfluous here for callers (and ECE is
	 * not even correctly set)
	 */
	tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
C
Changli Gao 已提交
3163
			     TCPHDR_SYN | TCPHDR_ACK);
3164

L
Linus Torvalds 已提交
3165
	th->seq = htonl(TCP_SKB_CB(skb)->seq);
3166 3167
	/* XXX data is queued and acked as is. No buffer/window check */
	th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
L
Linus Torvalds 已提交
3168 3169

	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3170
	th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3171
	tcp_options_write((__be32 *)(th + 1), NULL, &opts);
L
Linus Torvalds 已提交
3172
	th->doff = (tcp_header_size >> 2);
E
Eric Dumazet 已提交
3173
	__TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
3174 3175 3176

#ifdef CONFIG_TCP_MD5SIG
	/* Okay, we have all we need - do the md5 hash if needed */
E
Eric Dumazet 已提交
3177
	if (md5)
3178
		tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3179
					       md5, req_to_sk(req), skb);
E
Eric Dumazet 已提交
3180
	rcu_read_unlock();
3181 3182
#endif

3183 3184
	/* Do not fool tcpdump (if any), clean our debris */
	skb->tstamp.tv64 = 0;
L
Linus Torvalds 已提交
3185 3186
	return skb;
}
E
Eric Dumazet 已提交
3187
EXPORT_SYMBOL(tcp_make_synack);
L
Linus Torvalds 已提交
3188

3189 3190 3191 3192 3193 3194 3195 3196 3197 3198 3199 3200 3201 3202 3203 3204 3205 3206 3207
static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	const struct tcp_congestion_ops *ca;
	u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);

	if (ca_key == TCP_CA_UNSPEC)
		return;

	rcu_read_lock();
	ca = tcp_ca_find_key(ca_key);
	if (likely(ca && try_module_get(ca->owner))) {
		module_put(icsk->icsk_ca_ops->owner);
		icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
		icsk->icsk_ca_ops = ca;
	}
	rcu_read_unlock();
}

3208
/* Do all connect socket setups that can be done AF independent. */
3209
static void tcp_connect_init(struct sock *sk)
L
Linus Torvalds 已提交
3210
{
3211
	const struct dst_entry *dst = __sk_dst_get(sk);
L
Linus Torvalds 已提交
3212 3213 3214 3215 3216 3217 3218
	struct tcp_sock *tp = tcp_sk(sk);
	__u8 rcv_wscale;

	/* We'll fix this up when we get a response from the other end.
	 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
	 */
	tp->tcp_header_len = sizeof(struct tcphdr) +
3219
		(sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
L
Linus Torvalds 已提交
3220

3221
#ifdef CONFIG_TCP_MD5SIG
3222
	if (tp->af_specific->md5_lookup(sk, sk))
3223 3224 3225
		tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
#endif

L
Linus Torvalds 已提交
3226 3227 3228 3229
	/* If user gave his TCP_MAXSEG, record it to clamp */
	if (tp->rx_opt.user_mss)
		tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
	tp->max_window = 0;
J
John Heffner 已提交
3230
	tcp_mtup_init(sk);
L
Linus Torvalds 已提交
3231 3232
	tcp_sync_mss(sk, dst_mtu(dst));

3233 3234
	tcp_ca_dst_init(sk, dst);

L
Linus Torvalds 已提交
3235 3236
	if (!tp->window_clamp)
		tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3237
	tp->advmss = dst_metric_advmss(dst);
3238 3239 3240
	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
		tp->advmss = tp->rx_opt.user_mss;

L
Linus Torvalds 已提交
3241 3242
	tcp_initialize_rcv_mss(sk);

3243 3244 3245 3246 3247
	/* limit the window selection if the user enforce a smaller rx buffer */
	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
	    (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
		tp->window_clamp = tcp_full_space(sk);

L
Linus Torvalds 已提交
3248 3249 3250 3251
	tcp_select_initial_window(tcp_full_space(sk),
				  tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
				  &tp->rcv_wnd,
				  &tp->window_clamp,
3252
				  sysctl_tcp_window_scaling,
3253 3254
				  &rcv_wscale,
				  dst_metric(dst, RTAX_INITRWND));
L
Linus Torvalds 已提交
3255 3256 3257 3258 3259 3260 3261

	tp->rx_opt.rcv_wscale = rcv_wscale;
	tp->rcv_ssthresh = tp->rcv_wnd;

	sk->sk_err = 0;
	sock_reset_flag(sk, SOCK_DONE);
	tp->snd_wnd = 0;
3262
	tcp_init_wl(tp, 0);
L
Linus Torvalds 已提交
3263 3264
	tp->snd_una = tp->write_seq;
	tp->snd_sml = tp->write_seq;
I
Ilpo Järvinen 已提交
3265
	tp->snd_up = tp->write_seq;
P
Pavel Emelyanov 已提交
3266
	tp->snd_nxt = tp->write_seq;
P
Pavel Emelyanov 已提交
3267 3268 3269

	if (likely(!tp->repair))
		tp->rcv_nxt = 0;
3270 3271
	else
		tp->rcv_tstamp = tcp_time_stamp;
P
Pavel Emelyanov 已提交
3272 3273
	tp->rcv_wup = tp->rcv_nxt;
	tp->copied_seq = tp->rcv_nxt;
L
Linus Torvalds 已提交
3274

3275 3276
	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
	inet_csk(sk)->icsk_retransmits = 0;
L
Linus Torvalds 已提交
3277 3278 3279
	tcp_clear_retrans(tp);
}

3280 3281 3282 3283 3284 3285
static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);

	tcb->end_seq += skb->len;
3286
	__skb_header_release(skb);
3287 3288 3289 3290 3291 3292 3293 3294 3295 3296 3297 3298 3299 3300 3301 3302 3303 3304
	__tcp_add_write_queue_tail(sk, skb);
	sk->sk_wmem_queued += skb->truesize;
	sk_mem_charge(sk, skb->truesize);
	tp->write_seq = tcb->end_seq;
	tp->packets_out += tcp_skb_pcount(skb);
}

/* Build and send a SYN with data and (cached) Fast Open cookie. However,
 * queue a data-only packet after the regular SYN, such that regular SYNs
 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
 * only the SYN sequence, the data are retransmitted in the first ACK.
 * If cookie is not cached or other error occurs, falls back to send a
 * regular SYN with Fast Open cookie request option.
 */
static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcp_fastopen_request *fo = tp->fastopen_req;
3305
	int syn_loss = 0, space, err = 0;
3306
	unsigned long last_syn_loss = 0;
3307
	struct sk_buff *syn_data;
3308

3309
	tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
3310 3311 3312 3313 3314 3315 3316 3317
	tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
			       &syn_loss, &last_syn_loss);
	/* Recurring FO SYN losses: revert to regular handshake temporarily */
	if (syn_loss > 1 &&
	    time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
		fo->cookie.len = -1;
		goto fallback;
	}
3318

3319 3320 3321
	if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
		fo->cookie.len = -1;
	else if (fo->cookie.len <= 0)
3322 3323 3324 3325 3326 3327 3328 3329
		goto fallback;

	/* MSS for SYN-data is based on cached MSS and bounded by PMTU and
	 * user-MSS. Reserve maximum option space for middleboxes that add
	 * private TCP options. The cost is reduced data space in SYN :(
	 */
	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
		tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3330
	space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3331 3332
		MAX_TCP_OPTION_SPACE;

3333 3334 3335 3336 3337
	space = min_t(size_t, space, fo->size);

	/* limit to order-0 allocations */
	space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));

3338
	syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3339
	if (!syn_data)
3340
		goto fallback;
3341 3342
	syn_data->ip_summed = CHECKSUM_PARTIAL;
	memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3343 3344 3345 3346 3347 3348 3349 3350 3351 3352 3353
	if (space) {
		int copied = copy_from_iter(skb_put(syn_data, space), space,
					    &fo->data->msg_iter);
		if (unlikely(!copied)) {
			kfree_skb(syn_data);
			goto fallback;
		}
		if (copied != space) {
			skb_trim(syn_data, copied);
			space = copied;
		}
3354
	}
3355 3356 3357 3358
	/* No more data pending in inet_wait_for_connect() */
	if (space == fo->size)
		fo->data = NULL;
	fo->copied = space;
3359

3360
	tcp_connect_queue_skb(sk, syn_data);
3361 3362
	if (syn_data->len)
		tcp_chrono_start(sk, TCP_CHRONO_BUSY);
3363

3364
	err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3365

3366
	syn->skb_mstamp = syn_data->skb_mstamp;
E
Eric Dumazet 已提交
3367

3368 3369 3370 3371 3372 3373 3374 3375
	/* Now full SYN+DATA was cloned and sent (or not),
	 * remove the SYN from the original skb (syn_data)
	 * we keep in write queue in case of a retransmit, as we
	 * also have the SYN packet (with no data) in the same queue.
	 */
	TCP_SKB_CB(syn_data)->seq++;
	TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
	if (!err) {
3376
		tp->syn_data = (fo->copied > 0);
3377
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3378 3379 3380 3381 3382 3383 3384 3385 3386 3387 3388 3389 3390 3391 3392
		goto done;
	}

fallback:
	/* Send a regular SYN with Fast Open cookie request option */
	if (fo->cookie.len > 0)
		fo->cookie.len = 0;
	err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
	if (err)
		tp->syn_fastopen = 0;
done:
	fo->cookie.len = -1;  /* Exclude Fast Open option for SYN retries */
	return err;
}

3393
/* Build a SYN and send it off. */
L
Linus Torvalds 已提交
3394 3395 3396 3397
int tcp_connect(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;
3398
	int err;
L
Linus Torvalds 已提交
3399 3400 3401

	tcp_connect_init(sk);

A
Andrey Vagin 已提交
3402 3403 3404 3405 3406
	if (unlikely(tp->repair)) {
		tcp_finish_connect(sk, NULL);
		return 0;
	}

3407
	buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3408
	if (unlikely(!buff))
L
Linus Torvalds 已提交
3409 3410
		return -ENOBUFS;

C
Changli Gao 已提交
3411
	tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
E
Eric Dumazet 已提交
3412
	tp->retrans_stamp = tcp_time_stamp;
3413
	tcp_connect_queue_skb(sk, buff);
3414
	tcp_ecn_send_syn(sk, buff);
L
Linus Torvalds 已提交
3415

3416 3417 3418
	/* Send off SYN; include data in Fast Open. */
	err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
	      tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3419 3420
	if (err == -ECONNREFUSED)
		return err;
3421 3422 3423 3424 3425 3426

	/* We change tp->snd_nxt after the tcp_transmit_skb() call
	 * in order to make this packet get counted in tcpOutSegs.
	 */
	tp->snd_nxt = tp->write_seq;
	tp->pushed_seq = tp->write_seq;
P
Pavel Emelyanov 已提交
3427
	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
L
Linus Torvalds 已提交
3428 3429

	/* Timer for repeating the SYN until an answer. */
3430 3431
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
L
Linus Torvalds 已提交
3432 3433
	return 0;
}
E
Eric Dumazet 已提交
3434
EXPORT_SYMBOL(tcp_connect);
L
Linus Torvalds 已提交
3435 3436 3437 3438 3439 3440 3441

/* Send out a delayed ack, the caller does the policy checking
 * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
 * for details.
 */
void tcp_send_delayed_ack(struct sock *sk)
{
3442 3443
	struct inet_connection_sock *icsk = inet_csk(sk);
	int ato = icsk->icsk_ack.ato;
L
Linus Torvalds 已提交
3444 3445
	unsigned long timeout;

3446 3447
	tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);

L
Linus Torvalds 已提交
3448
	if (ato > TCP_DELACK_MIN) {
3449
		const struct tcp_sock *tp = tcp_sk(sk);
3450
		int max_ato = HZ / 2;
L
Linus Torvalds 已提交
3451

3452 3453
		if (icsk->icsk_ack.pingpong ||
		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
L
Linus Torvalds 已提交
3454 3455 3456 3457 3458
			max_ato = TCP_DELACK_MAX;

		/* Slow path, intersegment interval is "high". */

		/* If some rtt estimate is known, use it to bound delayed ack.
3459
		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
L
Linus Torvalds 已提交
3460 3461
		 * directly.
		 */
3462 3463 3464
		if (tp->srtt_us) {
			int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
					TCP_DELACK_MIN);
L
Linus Torvalds 已提交
3465 3466 3467 3468 3469 3470 3471 3472 3473 3474 3475 3476

			if (rtt < max_ato)
				max_ato = rtt;
		}

		ato = min(ato, max_ato);
	}

	/* Stay within the limit we were given */
	timeout = jiffies + ato;

	/* Use new timeout only if there wasn't a older one earlier. */
3477
	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
L
Linus Torvalds 已提交
3478 3479 3480
		/* If delack timer was blocked or is about to expire,
		 * send ACK now.
		 */
3481 3482
		if (icsk->icsk_ack.blocked ||
		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
L
Linus Torvalds 已提交
3483 3484 3485 3486
			tcp_send_ack(sk);
			return;
		}

3487 3488
		if (!time_before(timeout, icsk->icsk_ack.timeout))
			timeout = icsk->icsk_ack.timeout;
L
Linus Torvalds 已提交
3489
	}
3490 3491 3492
	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
	icsk->icsk_ack.timeout = timeout;
	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
L
Linus Torvalds 已提交
3493 3494 3495 3496 3497
}

/* This routine sends an ack and also updates the window. */
void tcp_send_ack(struct sock *sk)
{
3498
	struct sk_buff *buff;
L
Linus Torvalds 已提交
3499

3500 3501 3502
	/* If we have been reset, we may not send again. */
	if (sk->sk_state == TCP_CLOSE)
		return;
L
Linus Torvalds 已提交
3503

3504 3505
	tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);

3506 3507 3508 3509
	/* We are not putting this on the write queue, so
	 * tcp_transmit_skb() will set the ownership to this
	 * sock.
	 */
3510 3511 3512
	buff = alloc_skb(MAX_TCP_HEADER,
			 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
	if (unlikely(!buff)) {
3513 3514 3515 3516 3517
		inet_csk_schedule_ack(sk);
		inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
					  TCP_DELACK_MAX, TCP_RTO_MAX);
		return;
L
Linus Torvalds 已提交
3518
	}
3519 3520 3521

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(buff, MAX_TCP_HEADER);
C
Changli Gao 已提交
3522
	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3523

E
Eric Dumazet 已提交
3524 3525 3526 3527 3528 3529 3530 3531
	/* We do not want pure acks influencing TCP Small Queues or fq/pacing
	 * too much.
	 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
	 * We also avoid tcp_wfree() overhead (cache line miss accessing
	 * tp->tsq_flags) by using regular sock_wfree()
	 */
	skb_set_tcp_pure_ack(buff);

3532
	/* Send it off, this clears delayed acks for us. */
E
Eric Dumazet 已提交
3533
	skb_mstamp_get(&buff->skb_mstamp);
3534
	tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0);
L
Linus Torvalds 已提交
3535
}
3536
EXPORT_SYMBOL_GPL(tcp_send_ack);
L
Linus Torvalds 已提交
3537 3538 3539 3540 3541 3542 3543 3544 3545 3546 3547 3548

/* This routine sends a packet with an out of date sequence
 * number. It assumes the other end will try to ack it.
 *
 * Question: what should we make while urgent mode?
 * 4.4BSD forces sending single byte of data. We cannot send
 * out of window data, because we have SND.NXT==SND.MAX...
 *
 * Current solution: to send TWO zero-length segments in urgent mode:
 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
 * out-of-date with SND.UNA-1 to probe window.
 */
3549
static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
L
Linus Torvalds 已提交
3550 3551 3552 3553 3554
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;

	/* We don't queue it, tcp_transmit_skb() sets ownership. */
3555 3556
	skb = alloc_skb(MAX_TCP_HEADER,
			sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3557
	if (!skb)
L
Linus Torvalds 已提交
3558 3559 3560 3561 3562 3563 3564 3565
		return -1;

	/* Reserve space for headers and set control bits. */
	skb_reserve(skb, MAX_TCP_HEADER);
	/* Use a previous sequence.  This should cause the other
	 * end to send an ack.  Don't queue or clone SKB, just
	 * send it.
	 */
C
Changli Gao 已提交
3566
	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
E
Eric Dumazet 已提交
3567
	skb_mstamp_get(&skb->skb_mstamp);
3568
	NET_INC_STATS(sock_net(sk), mib);
3569
	return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0);
L
Linus Torvalds 已提交
3570 3571
}

P
Pavel Emelyanov 已提交
3572 3573 3574 3575
void tcp_send_window_probe(struct sock *sk)
{
	if (sk->sk_state == TCP_ESTABLISHED) {
		tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3576
		tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
P
Pavel Emelyanov 已提交
3577 3578 3579
	}
}

3580
/* Initiate keepalive or window probe from timer. */
3581
int tcp_write_wakeup(struct sock *sk, int mib)
L
Linus Torvalds 已提交
3582
{
3583 3584
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
L
Linus Torvalds 已提交
3585

3586 3587 3588
	if (sk->sk_state == TCP_CLOSE)
		return -1;

3589 3590
	skb = tcp_send_head(sk);
	if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3591
		int err;
I
Ilpo Järvinen 已提交
3592
		unsigned int mss = tcp_current_mss(sk);
3593 3594 3595 3596 3597 3598 3599 3600 3601 3602 3603 3604
		unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;

		if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
			tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;

		/* We are probing the opening of a window
		 * but the window size is != 0
		 * must have been a result SWS avoidance ( sender )
		 */
		if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
		    skb->len > mss) {
			seg_size = min(seg_size, mss);
E
Eric Dumazet 已提交
3605
			TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3606
			if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3607 3608
				return -1;
		} else if (!tcp_skb_pcount(skb))
3609
			tcp_set_skb_tso_segs(skb, mss);
3610

E
Eric Dumazet 已提交
3611
		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3612 3613 3614 3615 3616
		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
		if (!err)
			tcp_event_new_data_sent(sk, skb);
		return err;
	} else {
I
Ilpo Järvinen 已提交
3617
		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3618 3619
			tcp_xmit_probe_skb(sk, 1, mib);
		return tcp_xmit_probe_skb(sk, 0, mib);
L
Linus Torvalds 已提交
3620 3621 3622 3623 3624 3625 3626 3627
	}
}

/* A window probe timeout has occurred.  If window is not closed send
 * a partial packet else a zero probe.
 */
void tcp_send_probe0(struct sock *sk)
{
3628
	struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
3629
	struct tcp_sock *tp = tcp_sk(sk);
3630
	struct net *net = sock_net(sk);
3631
	unsigned long probe_max;
L
Linus Torvalds 已提交
3632 3633
	int err;

3634
	err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
L
Linus Torvalds 已提交
3635

3636
	if (tp->packets_out || !tcp_send_head(sk)) {
L
Linus Torvalds 已提交
3637
		/* Cancel probe timer, if it is not required. */
3638
		icsk->icsk_probes_out = 0;
3639
		icsk->icsk_backoff = 0;
L
Linus Torvalds 已提交
3640 3641 3642 3643
		return;
	}

	if (err <= 0) {
3644
		if (icsk->icsk_backoff < net->ipv4.sysctl_tcp_retries2)
3645
			icsk->icsk_backoff++;
3646
		icsk->icsk_probes_out++;
3647
		probe_max = TCP_RTO_MAX;
L
Linus Torvalds 已提交
3648 3649
	} else {
		/* If packet was not sent due to local congestion,
3650
		 * do not backoff and do not remember icsk_probes_out.
L
Linus Torvalds 已提交
3651 3652 3653 3654
		 * Let local senders to fight for local resources.
		 *
		 * Use accumulated backoff yet.
		 */
3655 3656
		if (!icsk->icsk_probes_out)
			icsk->icsk_probes_out = 1;
3657
		probe_max = TCP_RESOURCE_PROBE_INTERVAL;
L
Linus Torvalds 已提交
3658
	}
3659
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3660
				  tcp_probe0_when(sk, probe_max),
3661
				  TCP_RTO_MAX);
L
Linus Torvalds 已提交
3662
}
3663

3664
int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
3665 3666 3667 3668 3669
{
	const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
	struct flowi fl;
	int res;

3670
	tcp_rsk(req)->txhash = net_tx_rndhash();
3671
	res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL);
3672
	if (!res) {
E
Eric Dumazet 已提交
3673
		__TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
3674
		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3675 3676
		if (unlikely(tcp_passive_fastopen(sk)))
			tcp_sk(sk)->total_retrans++;
3677 3678 3679 3680
	}
	return res;
}
EXPORT_SYMBOL(tcp_rtx_synack);