tcp_output.c 101.1 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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unsigned int sysctl_tcp_notsent_lowat __read_mostly = UINT_MAX;
EXPORT_SYMBOL(sysctl_tcp_notsent_lowat);

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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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		 */
		space = max_t(u32, sysctl_tcp_rmem[2], 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
tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th,
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		    struct sock *sk)
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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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		if (tcp_ca_needs_ecn(sk))
			INET_ECN_xmit(sk);
	}
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}

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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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				int tcp_header_len)
{
	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;
				tcp_hdr(skb)->cwr = 1;
				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)
			tcp_hdr(skb)->ece = 1;
	}
}

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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);
	}

494
	if (unlikely(OPTION_WSCALE & options)) {
A
Adam Langley 已提交
495 496 497 498 499 500 501 502 503
		*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
504 505 506 507 508
		int this_sack;

		*ptr++ = htonl((TCPOPT_NOP  << 24) |
			       (TCPOPT_NOP  << 16) |
			       (TCPOPT_SACK <<  8) |
A
Adam Langley 已提交
509
			       (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
S
Stephen Hemminger 已提交
510
						     TCPOLEN_SACK_PERBLOCK)));
S
Stephen Hemminger 已提交
511

A
Adam Langley 已提交
512 513
		for (this_sack = 0; this_sack < opts->num_sack_blocks;
		     ++this_sack) {
S
Stephen Hemminger 已提交
514 515 516
			*ptr++ = htonl(sp[this_sack].start_seq);
			*ptr++ = htonl(sp[this_sack].end_seq);
		}
S
Stephen Hemminger 已提交
517

518
		tp->rx_opt.dsack = 0;
S
Stephen Hemminger 已提交
519
	}
Y
Yuchung Cheng 已提交
520 521 522

	if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
		struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
523 524 525 526 527 528 529 530 531 532 533 534 535
		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
536

537 538 539 540
		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
541
		}
542
		ptr += (len + 3) >> 2;
Y
Yuchung Cheng 已提交
543
	}
A
Adam Langley 已提交
544 545
}

546 547 548
/* Compute TCP options for SYN packets. This is not the final
 * network wire format yet.
 */
549
static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
A
Adam Langley 已提交
550
				struct tcp_out_options *opts,
551 552
				struct tcp_md5sig_key **md5)
{
A
Adam Langley 已提交
553
	struct tcp_sock *tp = tcp_sk(sk);
554
	unsigned int remaining = MAX_TCP_OPTION_SPACE;
555
	struct tcp_fastopen_request *fastopen = tp->fastopen_req;
A
Adam Langley 已提交
556

557
#ifdef CONFIG_TCP_MD5SIG
A
Adam Langley 已提交
558 559 560
	*md5 = tp->af_specific->md5_lookup(sk, sk);
	if (*md5) {
		opts->options |= OPTION_MD5;
561
		remaining -= TCPOLEN_MD5SIG_ALIGNED;
562
	}
A
Adam Langley 已提交
563 564
#else
	*md5 = NULL;
565
#endif
A
Adam Langley 已提交
566 567 568 569 570 571 572 573 574 575 576

	/* 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);
577
	remaining -= TCPOLEN_MSS_ALIGNED;
A
Adam Langley 已提交
578

579
	if (likely(sysctl_tcp_timestamps && !*md5)) {
A
Adam Langley 已提交
580
		opts->options |= OPTION_TS;
E
Eric Dumazet 已提交
581
		opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
A
Adam Langley 已提交
582
		opts->tsecr = tp->rx_opt.ts_recent;
583
		remaining -= TCPOLEN_TSTAMP_ALIGNED;
A
Adam Langley 已提交
584
	}
585
	if (likely(sysctl_tcp_window_scaling)) {
A
Adam Langley 已提交
586
		opts->ws = tp->rx_opt.rcv_wscale;
587
		opts->options |= OPTION_WSCALE;
588
		remaining -= TCPOLEN_WSCALE_ALIGNED;
A
Adam Langley 已提交
589
	}
590
	if (likely(sysctl_tcp_sack)) {
A
Adam Langley 已提交
591
		opts->options |= OPTION_SACK_ADVERTISE;
592
		if (unlikely(!(OPTION_TS & opts->options)))
593
			remaining -= TCPOLEN_SACKPERM_ALIGNED;
A
Adam Langley 已提交
594 595
	}

596
	if (fastopen && fastopen->cookie.len >= 0) {
597 598 599 600
		u32 need = fastopen->cookie.len;

		need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
					       TCPOLEN_FASTOPEN_BASE;
601 602 603 604 605 606
		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;
607
			tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
608 609
		}
	}
610 611

	return MAX_TCP_OPTION_SPACE - remaining;
S
Stephen Hemminger 已提交
612 613
}

614
/* Set up TCP options for SYN-ACKs. */
615 616 617 618 619
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)
620
{
A
Adam Langley 已提交
621
	struct inet_request_sock *ireq = inet_rsk(req);
622
	unsigned int remaining = MAX_TCP_OPTION_SPACE;
A
Adam Langley 已提交
623

624
#ifdef CONFIG_TCP_MD5SIG
E
Eric Dumazet 已提交
625
	if (md5) {
A
Adam Langley 已提交
626
		opts->options |= OPTION_MD5;
627 628 629 630 631 632 633
		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
634
		ireq->tstamp_ok &= !ireq->sack_ok;
635 636
	}
#endif
A
Adam Langley 已提交
637

638
	/* We always send an MSS option. */
A
Adam Langley 已提交
639
	opts->mss = mss;
640
	remaining -= TCPOLEN_MSS_ALIGNED;
A
Adam Langley 已提交
641 642 643

	if (likely(ireq->wscale_ok)) {
		opts->ws = ireq->rcv_wscale;
644
		opts->options |= OPTION_WSCALE;
645
		remaining -= TCPOLEN_WSCALE_ALIGNED;
A
Adam Langley 已提交
646
	}
E
Eric Dumazet 已提交
647
	if (likely(ireq->tstamp_ok)) {
A
Adam Langley 已提交
648
		opts->options |= OPTION_TS;
E
Eric Dumazet 已提交
649
		opts->tsval = tcp_skb_timestamp(skb);
A
Adam Langley 已提交
650
		opts->tsecr = req->ts_recent;
651
		remaining -= TCPOLEN_TSTAMP_ALIGNED;
A
Adam Langley 已提交
652 653 654
	}
	if (likely(ireq->sack_ok)) {
		opts->options |= OPTION_SACK_ADVERTISE;
E
Eric Dumazet 已提交
655
		if (unlikely(!ireq->tstamp_ok))
656
			remaining -= TCPOLEN_SACKPERM_ALIGNED;
A
Adam Langley 已提交
657
	}
658 659 660 661 662
	if (foc != NULL && foc->len >= 0) {
		u32 need = foc->len;

		need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
				   TCPOLEN_FASTOPEN_BASE;
663 664 665 666 667 668 669
		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
670

671
	return MAX_TCP_OPTION_SPACE - remaining;
A
Adam Langley 已提交
672 673
}

674 675 676
/* Compute TCP options for ESTABLISHED sockets. This is not the
 * final wire format yet.
 */
677
static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
A
Adam Langley 已提交
678
					struct tcp_out_options *opts,
679 680
					struct tcp_md5sig_key **md5)
{
A
Adam Langley 已提交
681
	struct tcp_sock *tp = tcp_sk(sk);
682
	unsigned int size = 0;
683
	unsigned int eff_sacks;
A
Adam Langley 已提交
684

685 686
	opts->options = 0;

A
Adam Langley 已提交
687 688 689 690 691 692 693 694 695 696 697 698
#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
699
		opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
A
Adam Langley 已提交
700 701 702 703
		opts->tsecr = tp->rx_opt.ts_recent;
		size += TCPOLEN_TSTAMP_ALIGNED;
	}

704 705
	eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
	if (unlikely(eff_sacks)) {
706
		const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
A
Adam Langley 已提交
707
		opts->num_sack_blocks =
708
			min_t(unsigned int, eff_sacks,
A
Adam Langley 已提交
709 710 711 712 713 714 715
			      (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
716
}
L
Linus Torvalds 已提交
717

E
Eric Dumazet 已提交
718 719 720 721 722 723 724 725 726

/* 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
727
 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
E
Eric Dumazet 已提交
728 729 730 731 732 733 734 735 736 737 738
 *
 * 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);

739 740 741 742 743
static void tcp_tsq_handler(struct sock *sk)
{
	if ((1 << sk->sk_state) &
	    (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
	     TCPF_CLOSE_WAIT  | TCPF_LAST_ACK))
J
John Ogness 已提交
744 745
		tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
			       0, GFP_ATOMIC);
746
}
E
Eric Dumazet 已提交
747
/*
S
stephen hemminger 已提交
748
 * One tasklet per cpu tries to send more skbs.
E
Eric Dumazet 已提交
749
 * We run in tasklet context but need to disable irqs when
S
stephen hemminger 已提交
750
 * transferring tsq->head because tcp_wfree() might
E
Eric Dumazet 已提交
751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773
 * 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)) {
774
			tcp_tsq_handler(sk);
E
Eric Dumazet 已提交
775 776
		} else {
			/* defer the work to tcp_release_cb() */
777
			set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
E
Eric Dumazet 已提交
778 779 780 781 782 783 784 785
		}
		bh_unlock_sock(sk);

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

786 787
#define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) |		\
			  (1UL << TCP_WRITE_TIMER_DEFERRED) |	\
788 789
			  (1UL << TCP_DELACK_TIMER_DEFERRED) |	\
			  (1UL << TCP_MTU_REDUCED_DEFERRED))
E
Eric Dumazet 已提交
790 791 792 793 794 795 796 797 798 799
/**
 * 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);
800
	unsigned long flags, nflags;
E
Eric Dumazet 已提交
801

802 803 804 805 806 807 808 809 810 811 812
	/* 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);

	if (flags & (1UL << TCP_TSQ_DEFERRED))
		tcp_tsq_handler(sk);

813 814 815 816 817 818 819 820 821 822 823
	/* 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);

824
	if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
825
		tcp_write_timer_handler(sk);
826 827 828
		__sock_put(sk);
	}
	if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
829
		tcp_delack_timer_handler(sk);
830 831 832
		__sock_put(sk);
	}
	if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
833
		inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
834 835
		__sock_put(sk);
	}
E
Eric Dumazet 已提交
836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854
}
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
855
 * We can't xmit new skbs from this context, as we might already
E
Eric Dumazet 已提交
856 857
 * hold qdisc lock.
 */
E
Eric Dumazet 已提交
858
void tcp_wfree(struct sk_buff *skb)
E
Eric Dumazet 已提交
859 860 861
{
	struct sock *sk = skb->sk;
	struct tcp_sock *tp = tcp_sk(sk);
862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877
	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
878 879 880 881 882 883 884 885

	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);
886
		tsq = this_cpu_ptr(&tsq_tasklet);
E
Eric Dumazet 已提交
887 888 889
		list_add(&tp->tsq_node, &tsq->head);
		tasklet_schedule(&tsq->tasklet);
		local_irq_restore(flags);
890
		return;
E
Eric Dumazet 已提交
891
	}
892 893
out:
	sk_free(sk);
E
Eric Dumazet 已提交
894 895
}

L
Linus Torvalds 已提交
896 897 898 899 900 901 902 903 904 905 906
/* 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.
 */
907 908
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
909
{
910 911 912 913
	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
914
	struct tcp_out_options opts;
915
	unsigned int tcp_options_size, tcp_header_size;
916
	struct tcp_md5sig_key *md5;
917 918 919 920 921
	struct tcphdr *th;
	int err;

	BUG_ON(!skb || !tcp_skb_pcount(skb));

922
	if (clone_it) {
923
		skb_mstamp_get(&skb->skb_mstamp);
924

925 926 927 928 929 930 931
		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
932

933 934 935
	inet = inet_sk(sk);
	tp = tcp_sk(sk);
	tcb = TCP_SKB_CB(skb);
A
Adam Langley 已提交
936
	memset(&opts, 0, sizeof(opts));
L
Linus Torvalds 已提交
937

E
Eric Dumazet 已提交
938
	if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
A
Adam Langley 已提交
939 940 941 942 943
		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);
944

E
Eric Dumazet 已提交
945
	/* if no packet is in qdisc/device queue, then allow XPS to select
946 947 948 949 950
	 * 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
951
	 */
952
	skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
953

954 955
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
E
Eric Dumazet 已提交
956 957 958

	skb_orphan(skb);
	skb->sk = sk;
E
Eric Dumazet 已提交
959
	skb->destructor = skb_is_tcp_pure_ack(skb) ? sock_wfree : tcp_wfree;
960
	skb_set_hash_from_sk(skb, sk);
E
Eric Dumazet 已提交
961
	atomic_add(skb->truesize, &sk->sk_wmem_alloc);
962 963

	/* Build TCP header and checksum it. */
964
	th = tcp_hdr(skb);
E
Eric Dumazet 已提交
965 966
	th->source		= inet->inet_sport;
	th->dest		= inet->inet_dport;
967 968
	th->seq			= htonl(tcb->seq);
	th->ack_seq		= htonl(tp->rcv_nxt);
969
	*(((__be16 *)th) + 6)	= htons(((tcp_header_size >> 2) << 12) |
E
Eric Dumazet 已提交
970
					tcb->tcp_flags);
971

E
Eric Dumazet 已提交
972
	if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
973 974 975
		/* RFC1323: The window in SYN & SYN/ACK segments
		 * is never scaled.
		 */
976
		th->window	= htons(min(tp->rcv_wnd, 65535U));
977 978 979 980 981
	} else {
		th->window	= htons(tcp_select_window(sk));
	}
	th->check		= 0;
	th->urg_ptr		= 0;
L
Linus Torvalds 已提交
982

I
Ilpo Järvinen 已提交
983
	/* The urg_mode check is necessary during a below snd_una win probe */
984 985 986 987 988
	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)) {
989
			th->urg_ptr = htons(0xFFFF);
990 991
			th->urg = 1;
		}
992
	}
L
Linus Torvalds 已提交
993

994
	tcp_options_write((__be32 *)(th + 1), tp, &opts);
995
	skb_shinfo(skb)->gso_type = sk->sk_gso_type;
E
Eric Dumazet 已提交
996
	if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
997
		tcp_ecn_send(sk, skb, tcp_header_size);
L
Linus Torvalds 已提交
998

999 1000 1001
#ifdef CONFIG_TCP_MD5SIG
	/* Calculate the MD5 hash, as we have all we need now */
	if (md5) {
E
Eric Dumazet 已提交
1002
		sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1003
		tp->af_specific->calc_md5_hash(opts.hash_location,
1004
					       md5, sk, skb);
1005 1006 1007
	}
#endif

1008
	icsk->icsk_af_ops->send_check(sk, skb);
L
Linus Torvalds 已提交
1009

E
Eric Dumazet 已提交
1010
	if (likely(tcb->tcp_flags & TCPHDR_ACK))
1011
		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
L
Linus Torvalds 已提交
1012

1013
	if (skb->len != tcp_header_size)
1014
		tcp_event_data_sent(tp, sk);
L
Linus Torvalds 已提交
1015

1016
	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1017 1018
		TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
			      tcp_skb_pcount(skb));
L
Linus Torvalds 已提交
1019

1020
	tp->segs_out += tcp_skb_pcount(skb);
1021
	/* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1022
	skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1023
	skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1024

E
Eric Dumazet 已提交
1025 1026
	/* Our usage of tstamp should remain private */
	skb->tstamp.tv64 = 0;
1027 1028 1029 1030 1031

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

1032
	err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
E
Eric Dumazet 已提交
1033

1034
	if (likely(err <= 0))
1035 1036
		return err;

1037
	tcp_enter_cwr(sk);
1038

1039
	return net_xmit_eval(err);
L
Linus Torvalds 已提交
1040 1041
}

1042
/* This routine just queues the buffer for sending.
L
Linus Torvalds 已提交
1043 1044 1045 1046 1047 1048 1049 1050 1051 1052
 *
 * 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;
1053
	__skb_header_release(skb);
1054
	tcp_add_write_queue_tail(sk, skb);
1055 1056
	sk->sk_wmem_queued += skb->truesize;
	sk_mem_charge(sk, skb->truesize);
L
Linus Torvalds 已提交
1057 1058
}

1059
/* Initialize TSO segments for a packet. */
1060
static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1061
{
1062
	if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1063 1064 1065
		/* Avoid the costly divide in the normal
		 * non-TSO case.
		 */
1066
		tcp_skb_pcount_set(skb, 1);
1067
		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1068
	} else {
1069
		tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1070
		TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
L
Linus Torvalds 已提交
1071 1072 1073
	}
}

I
Ilpo Järvinen 已提交
1074
/* When a modification to fackets out becomes necessary, we need to check
1075
 * skb is counted to fackets_out or not.
I
Ilpo Järvinen 已提交
1076
 */
1077
static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
I
Ilpo Järvinen 已提交
1078 1079
				   int decr)
{
1080 1081
	struct tcp_sock *tp = tcp_sk(sk);

1082
	if (!tp->sacked_out || tcp_is_reno(tp))
I
Ilpo Järvinen 已提交
1083 1084
		return;

1085
	if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
I
Ilpo Järvinen 已提交
1086 1087 1088
		tp->fackets_out -= decr;
}

1089 1090 1091
/* Pcount in the middle of the write queue got changed, we need to do various
 * tweaks to fix counters
 */
1092
static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112
{
	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) &&
1113
	    (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1114 1115 1116 1117 1118
		tp->lost_cnt_hint -= decr;

	tcp_verify_left_out(tp);
}

1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133
static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
{
	struct skb_shared_info *shinfo = skb_shinfo(skb);

	if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
	    !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);
	}
}

L
Linus Torvalds 已提交
1134 1135
/* 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
1136
 * packet to the list.  This won't be called frequently, I hope.
L
Linus Torvalds 已提交
1137 1138
 * Remember, these are still headerless SKBs at this point.
 */
1139
int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1140
		 unsigned int mss_now, gfp_t gfp)
L
Linus Torvalds 已提交
1141 1142 1143
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;
1144
	int nsize, old_factor;
1145
	int nlen;
1146
	u8 flags;
L
Linus Torvalds 已提交
1147

1148 1149
	if (WARN_ON(len > skb->len))
		return -EINVAL;
1150

L
Linus Torvalds 已提交
1151 1152 1153 1154
	nsize = skb_headlen(skb) - len;
	if (nsize < 0)
		nsize = 0;

1155
	if (skb_unclone(skb, gfp))
L
Linus Torvalds 已提交
1156 1157 1158
		return -ENOMEM;

	/* Get a new skb... force flag on. */
1159
	buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1160
	if (!buff)
L
Linus Torvalds 已提交
1161
		return -ENOMEM; /* We'll just try again later. */
H
Herbert Xu 已提交
1162

1163 1164
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
1165 1166 1167
	nlen = skb->len - len - nsize;
	buff->truesize += nlen;
	skb->truesize -= nlen;
L
Linus Torvalds 已提交
1168 1169 1170 1171 1172 1173 1174

	/* 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
1175 1176 1177
	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;
1178
	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
L
Linus Torvalds 已提交
1179

1180
	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
L
Linus Torvalds 已提交
1181
		/* Copy and checksum data tail into the new buffer. */
1182 1183
		buff->csum = csum_partial_copy_nocheck(skb->data + len,
						       skb_put(buff, nsize),
L
Linus Torvalds 已提交
1184 1185 1186 1187 1188 1189
						       nsize, 0);

		skb_trim(skb, len);

		skb->csum = csum_block_sub(skb->csum, buff->csum, len);
	} else {
1190
		skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
1191 1192 1193 1194 1195
		skb_split(skb, buff, len);
	}

	buff->ip_summed = skb->ip_summed;

1196
	buff->tstamp = skb->tstamp;
1197
	tcp_fragment_tstamp(skb, buff);
L
Linus Torvalds 已提交
1198

1199 1200
	old_factor = tcp_skb_pcount(skb);

L
Linus Torvalds 已提交
1201
	/* Fix up tso_factor for both original and new SKB.  */
1202 1203
	tcp_set_skb_tso_segs(skb, mss_now);
	tcp_set_skb_tso_segs(buff, mss_now);
L
Linus Torvalds 已提交
1204

1205 1206 1207
	/* If this packet has been sent out already, we must
	 * adjust the various packet counters.
	 */
1208
	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1209 1210
		int diff = old_factor - tcp_skb_pcount(skb) -
			tcp_skb_pcount(buff);
L
Linus Torvalds 已提交
1211

1212 1213
		if (diff)
			tcp_adjust_pcount(sk, skb, diff);
L
Linus Torvalds 已提交
1214 1215 1216
	}

	/* Link BUFF into the send queue. */
1217
	__skb_header_release(buff);
1218
	tcp_insert_write_queue_after(skb, buff, sk);
L
Linus Torvalds 已提交
1219 1220 1221 1222 1223 1224 1225 1226

	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.
 */
1227
static void __pskb_trim_head(struct sk_buff *skb, int len)
L
Linus Torvalds 已提交
1228
{
1229
	struct skb_shared_info *shinfo;
L
Linus Torvalds 已提交
1230 1231
	int i, k, eat;

E
Eric Dumazet 已提交
1232 1233 1234 1235 1236 1237 1238
	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
1239 1240
	eat = len;
	k = 0;
1241 1242 1243
	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
1244 1245

		if (size <= eat) {
1246
			skb_frag_unref(skb, i);
E
Eric Dumazet 已提交
1247
			eat -= size;
L
Linus Torvalds 已提交
1248
		} else {
1249
			shinfo->frags[k] = shinfo->frags[i];
L
Linus Torvalds 已提交
1250
			if (eat) {
1251 1252
				shinfo->frags[k].page_offset += eat;
				skb_frag_size_sub(&shinfo->frags[k], eat);
L
Linus Torvalds 已提交
1253 1254 1255 1256 1257
				eat = 0;
			}
			k++;
		}
	}
1258
	shinfo->nr_frags = k;
L
Linus Torvalds 已提交
1259

1260
	skb_reset_tail_pointer(skb);
L
Linus Torvalds 已提交
1261 1262 1263 1264
	skb->data_len -= len;
	skb->len = skb->data_len;
}

1265
/* Remove acked data from a packet in the transmit queue. */
L
Linus Torvalds 已提交
1266 1267
int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
{
1268
	if (skb_unclone(skb, GFP_ATOMIC))
L
Linus Torvalds 已提交
1269 1270
		return -ENOMEM;

E
Eric Dumazet 已提交
1271
	__pskb_trim_head(skb, len);
L
Linus Torvalds 已提交
1272 1273

	TCP_SKB_CB(skb)->seq += len;
1274
	skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
1275 1276 1277

	skb->truesize	     -= len;
	sk->sk_wmem_queued   -= len;
1278
	sk_mem_uncharge(sk, len);
L
Linus Torvalds 已提交
1279 1280
	sock_set_flag(sk, SOCK_QUEUE_SHRUNK);

1281
	/* Any change of skb->len requires recalculation of tso factor. */
L
Linus Torvalds 已提交
1282
	if (tcp_skb_pcount(skb) > 1)
1283
		tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
L
Linus Torvalds 已提交
1284 1285 1286 1287

	return 0;
}

1288 1289
/* 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
1290
{
1291 1292
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1293 1294 1295 1296 1297 1298 1299
	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);

1300 1301 1302 1303 1304 1305 1306 1307
	/* 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
1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320
	/* 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;
}

1321 1322 1323 1324 1325 1326 1327 1328
/* 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
1329
/* Inverse of above */
1330
int tcp_mss_to_mtu(struct sock *sk, int mss)
J
John Heffner 已提交
1331
{
1332 1333
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1334 1335 1336 1337 1338 1339 1340
	int mtu;

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

1341 1342 1343 1344 1345 1346 1347
	/* 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
1348 1349 1350
	return mtu;
}

1351
/* MTU probing init per socket */
J
John Heffner 已提交
1352 1353 1354 1355
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
1356
	struct net *net = sock_net(sk);
J
John Heffner 已提交
1357

F
Fan Du 已提交
1358
	icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
J
John Heffner 已提交
1359
	icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1360
			       icsk->icsk_af_ops->net_header_len;
F
Fan Du 已提交
1361
	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
J
John Heffner 已提交
1362
	icsk->icsk_mtup.probe_size = 0;
1363 1364
	if (icsk->icsk_mtup.enabled)
		icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
J
John Heffner 已提交
1365
}
E
Eric Dumazet 已提交
1366
EXPORT_SYMBOL(tcp_mtup_init);
J
John Heffner 已提交
1367

L
Linus Torvalds 已提交
1368 1369 1370 1371 1372 1373
/* 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
1374
   It is minimum of user_mss and mss received with SYN.
L
Linus Torvalds 已提交
1375 1376
   It also does not include TCP options.

1377
   inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
L
Linus Torvalds 已提交
1378 1379 1380 1381 1382 1383 1384 1385 1386

   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.

1387 1388
   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
1389 1390 1391 1392
 */
unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
{
	struct tcp_sock *tp = tcp_sk(sk);
1393
	struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1394
	int mss_now;
L
Linus Torvalds 已提交
1395

J
John Heffner 已提交
1396 1397
	if (icsk->icsk_mtup.search_high > pmtu)
		icsk->icsk_mtup.search_high = pmtu;
L
Linus Torvalds 已提交
1398

J
John Heffner 已提交
1399
	mss_now = tcp_mtu_to_mss(sk, pmtu);
1400
	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
L
Linus Torvalds 已提交
1401 1402

	/* And store cached results */
1403
	icsk->icsk_pmtu_cookie = pmtu;
J
John Heffner 已提交
1404 1405
	if (icsk->icsk_mtup.enabled)
		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1406
	tp->mss_cache = mss_now;
L
Linus Torvalds 已提交
1407 1408 1409

	return mss_now;
}
E
Eric Dumazet 已提交
1410
EXPORT_SYMBOL(tcp_sync_mss);
L
Linus Torvalds 已提交
1411 1412 1413 1414

/* Compute the current effective MSS, taking SACKs and IP options,
 * and even PMTU discovery events into account.
 */
I
Ilpo Järvinen 已提交
1415
unsigned int tcp_current_mss(struct sock *sk)
L
Linus Torvalds 已提交
1416
{
1417 1418
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct dst_entry *dst = __sk_dst_get(sk);
1419
	u32 mss_now;
1420
	unsigned int header_len;
A
Adam Langley 已提交
1421 1422
	struct tcp_out_options opts;
	struct tcp_md5sig_key *md5;
1423 1424 1425

	mss_now = tp->mss_cache;

L
Linus Torvalds 已提交
1426 1427
	if (dst) {
		u32 mtu = dst_mtu(dst);
1428
		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
L
Linus Torvalds 已提交
1429 1430 1431
			mss_now = tcp_sync_mss(sk, mtu);
	}

A
Adam Langley 已提交
1432 1433 1434 1435 1436 1437 1438 1439 1440 1441
	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;
	}
1442

L
Linus Torvalds 已提交
1443 1444 1445
	return mss_now;
}

1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467
/* 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;
}

1468
static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1469
{
1470
	struct tcp_sock *tp = tcp_sk(sk);
1471

1472 1473 1474 1475 1476 1477 1478 1479 1480
	/* 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;
	}
1481

1482
	if (tcp_is_cwnd_limited(sk)) {
1483 1484 1485 1486 1487 1488 1489 1490
		/* 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;

1491 1492
		if (sysctl_tcp_slow_start_after_idle &&
		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1493 1494 1495 1496
			tcp_cwnd_application_limited(sk);
	}
}

E
Eric Dumazet 已提交
1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510
/* 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
1511
 */
E
Eric Dumazet 已提交
1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526
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,
1527
			    int nonagle)
E
Eric Dumazet 已提交
1528 1529 1530 1531 1532
{
	return partial &&
		((nonagle & TCP_NAGLE_CORK) ||
		 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
}
E
Eric Dumazet 已提交
1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553

/* Return how many segs we'd like on a TSO packet,
 * to send one TSO packet per ms
 */
static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now)
{
	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.
	 */
	segs = max_t(u32, bytes / mss_now, sysctl_tcp_min_tso_segs);

	return min_t(u32, segs, sk->sk_gso_max_segs);
}

E
Eric Dumazet 已提交
1554 1555 1556 1557 1558 1559
/* 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)
1560
{
1561
	const struct tcp_sock *tp = tcp_sk(sk);
E
Eric Dumazet 已提交
1562
	u32 partial, needed, window, max_len;
1563

1564
	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1565
	max_len = mss_now * max_segs;
1566

1567 1568
	if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
		return max_len;
1569

1570 1571
	needed = min(skb->len, window);

1572 1573
	if (max_len <= needed)
		return max_len;
1574

E
Eric Dumazet 已提交
1575 1576 1577 1578 1579
	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
	 */
1580
	if (tcp_nagle_check(partial != 0, tp, nonagle))
E
Eric Dumazet 已提交
1581 1582 1583
		return needed - partial;

	return needed;
1584 1585 1586 1587 1588
}

/* 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.
 */
1589 1590
static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
					 const struct sk_buff *skb)
1591
{
E
Eric Dumazet 已提交
1592
	u32 in_flight, cwnd, halfcwnd;
1593 1594

	/* Don't be strict about the congestion window for the final FIN.  */
E
Eric Dumazet 已提交
1595 1596
	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
	    tcp_skb_pcount(skb) == 1)
1597 1598 1599 1600
		return 1;

	in_flight = tcp_packets_in_flight(tp);
	cwnd = tp->snd_cwnd;
E
Eric Dumazet 已提交
1601 1602
	if (in_flight >= cwnd)
		return 0;
1603

E
Eric Dumazet 已提交
1604 1605 1606 1607 1608
	/* For better scheduling, ensure we have at least
	 * 2 GSO packets in flight.
	 */
	halfcwnd = max(cwnd >> 1, 1U);
	return min(halfcwnd, cwnd - in_flight);
1609 1610
}

1611
/* Initialize TSO state of a skb.
1612
 * This must be invoked the first time we consider transmitting
1613 1614
 * SKB onto the wire.
 */
1615
static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1616 1617 1618
{
	int tso_segs = tcp_skb_pcount(skb);

1619
	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1620
		tcp_set_skb_tso_segs(skb, mss_now);
1621 1622 1623 1624 1625 1626
		tso_segs = tcp_skb_pcount(skb);
	}
	return tso_segs;
}


E
Eric Dumazet 已提交
1627
/* Return true if the Nagle test allows this packet to be
1628 1629
 * sent now.
 */
E
Eric Dumazet 已提交
1630 1631
static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
				  unsigned int cur_mss, int nonagle)
1632 1633 1634 1635 1636 1637 1638 1639
{
	/* 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
1640
		return true;
1641

Y
Yuchung Cheng 已提交
1642 1643
	/* 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
1644
		return true;
1645

1646
	if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
E
Eric Dumazet 已提交
1647
		return true;
1648

E
Eric Dumazet 已提交
1649
	return false;
1650 1651 1652
}

/* Does at least the first segment of SKB fit into the send window? */
E
Eric Dumazet 已提交
1653 1654 1655
static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
			     const struct sk_buff *skb,
			     unsigned int cur_mss)
1656 1657 1658 1659 1660 1661
{
	u32 end_seq = TCP_SKB_CB(skb)->end_seq;

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

1662
	return !after(end_seq, tcp_wnd_end(tp));
1663 1664
}

1665
/* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1666 1667 1668
 * should be put on the wire right now.  If so, it returns the number of
 * packets allowed by the congestion window.
 */
1669
static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1670 1671
				 unsigned int cur_mss, int nonagle)
{
1672
	const struct tcp_sock *tp = tcp_sk(sk);
1673 1674
	unsigned int cwnd_quota;

1675
	tcp_init_tso_segs(skb, cur_mss);
1676 1677 1678 1679 1680

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

	cwnd_quota = tcp_cwnd_test(tp, skb);
1681
	if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1682 1683 1684 1685 1686
		cwnd_quota = 0;

	return cwnd_quota;
}

1687
/* Test if sending is allowed right now. */
E
Eric Dumazet 已提交
1688
bool tcp_may_send_now(struct sock *sk)
1689
{
1690
	const struct tcp_sock *tp = tcp_sk(sk);
1691
	struct sk_buff *skb = tcp_send_head(sk);
1692

E
Eric Dumazet 已提交
1693
	return skb &&
I
Ilpo Järvinen 已提交
1694
		tcp_snd_test(sk, skb, tcp_current_mss(sk),
1695
			     (tcp_skb_is_last(sk, skb) ?
E
Eric Dumazet 已提交
1696
			      tp->nonagle : TCP_NAGLE_PUSH));
1697 1698 1699 1700 1701 1702 1703 1704 1705
}

/* 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).
 */
1706
static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1707
			unsigned int mss_now, gfp_t gfp)
1708 1709 1710
{
	struct sk_buff *buff;
	int nlen = skb->len - len;
1711
	u8 flags;
1712 1713

	/* All of a TSO frame must be composed of paged data.  */
1714
	if (skb->len != skb->data_len)
1715
		return tcp_fragment(sk, skb, len, mss_now, gfp);
1716

1717
	buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1718
	if (unlikely(!buff))
1719 1720
		return -ENOMEM;

1721 1722
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
1723
	buff->truesize += nlen;
1724 1725 1726 1727 1728 1729 1730 1731
	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
1732 1733 1734
	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;
1735 1736 1737 1738

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

1739
	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1740
	skb_split(skb, buff, len);
1741
	tcp_fragment_tstamp(skb, buff);
1742 1743

	/* Fix up tso_factor for both original and new SKB.  */
1744 1745
	tcp_set_skb_tso_segs(skb, mss_now);
	tcp_set_skb_tso_segs(buff, mss_now);
1746 1747

	/* Link BUFF into the send queue. */
1748
	__skb_header_release(buff);
1749
	tcp_insert_write_queue_after(skb, buff, sk);
1750 1751 1752 1753 1754 1755 1756 1757 1758

	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.
 */
1759
static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
E
Eric Dumazet 已提交
1760
				 bool *is_cwnd_limited, u32 max_segs)
1761
{
1762
	const struct inet_connection_sock *icsk = inet_csk(sk);
1763 1764 1765 1766
	u32 age, send_win, cong_win, limit, in_flight;
	struct tcp_sock *tp = tcp_sk(sk);
	struct skb_mstamp now;
	struct sk_buff *head;
1767
	int win_divisor;
1768

E
Eric Dumazet 已提交
1769
	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
J
John Heffner 已提交
1770
		goto send_now;
1771

1772
	if (icsk->icsk_ca_state >= TCP_CA_Recovery)
J
John Heffner 已提交
1773 1774
		goto send_now;

E
Eric Dumazet 已提交
1775 1776 1777 1778
	/* 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
1779
		goto send_now;
1780

1781 1782
	in_flight = tcp_packets_in_flight(tp);

1783
	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1784

1785
	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1786 1787 1788 1789 1790 1791

	/* 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);

1792
	/* If a full-sized TSO skb can be sent, do it. */
E
Eric Dumazet 已提交
1793
	if (limit >= max_segs * tp->mss_cache)
J
John Heffner 已提交
1794
		goto send_now;
1795

1796 1797 1798 1799
	/* 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;

1800 1801
	win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
	if (win_divisor) {
1802 1803 1804 1805 1806
		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.
		 */
1807
		chunk /= win_divisor;
1808
		if (limit >= chunk)
J
John Heffner 已提交
1809
			goto send_now;
1810 1811 1812 1813 1814 1815
	} 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.
		 */
1816
		if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
J
John Heffner 已提交
1817
			goto send_now;
1818 1819
	}

1820 1821 1822 1823 1824 1825 1826
	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
1827
	/* Ok, it looks like it is advisable to defer. */
J
John Heffner 已提交
1828

1829 1830 1831
	if (cong_win < send_win && cong_win < skb->len)
		*is_cwnd_limited = true;

E
Eric Dumazet 已提交
1832
	return true;
J
John Heffner 已提交
1833 1834

send_now:
E
Eric Dumazet 已提交
1835
	return false;
1836 1837
}

1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862
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
1863
/* Create a new MTU probe if we are ready.
1864 1865 1866 1867
 * 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
1868 1869
 * Returns 0 if we should wait to probe (no cwnd available),
 *         1 if a probe was sent,
1870 1871
 *         -1 otherwise
 */
J
John Heffner 已提交
1872 1873 1874 1875 1876
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;
1877
	struct net *net = sock_net(sk);
J
John Heffner 已提交
1878 1879
	int len;
	int probe_size;
1880
	int size_needed;
J
John Heffner 已提交
1881 1882
	int copy;
	int mss_now;
1883
	int interval;
J
John Heffner 已提交
1884 1885 1886 1887 1888 1889 1890 1891 1892

	/* 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 ||
1893
	    tp->rx_opt.num_sacks || tp->rx_opt.dsack)
J
John Heffner 已提交
1894 1895
		return -1;

1896 1897 1898 1899
	/* 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
1900
	mss_now = tcp_current_mss(sk);
1901 1902
	probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
				    icsk->icsk_mtup.search_low) >> 1);
1903
	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1904
	interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1905 1906 1907 1908
	/* 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.
	 */
1909
	if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1910 1911 1912 1913 1914
		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
1915 1916 1917 1918
		return -1;
	}

	/* Have enough data in the send queue to probe? */
1919
	if (tp->write_seq - tp->snd_nxt < size_needed)
J
John Heffner 已提交
1920 1921
		return -1;

1922 1923
	if (tp->snd_wnd < size_needed)
		return -1;
1924
	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1925
		return 0;
J
John Heffner 已提交
1926

1927 1928 1929
	/* 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
1930 1931 1932 1933 1934 1935
			return -1;
		else
			return 0;
	}

	/* We're allowed to probe.  Build it now. */
1936
	nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1937
	if (!nskb)
J
John Heffner 已提交
1938
		return -1;
1939 1940
	sk->sk_wmem_queued += nskb->truesize;
	sk_mem_charge(sk, nskb->truesize);
J
John Heffner 已提交
1941

1942
	skb = tcp_send_head(sk);
J
John Heffner 已提交
1943 1944 1945

	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
1946
	TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
J
John Heffner 已提交
1947 1948
	TCP_SKB_CB(nskb)->sacked = 0;
	nskb->csum = 0;
1949
	nskb->ip_summed = skb->ip_summed;
J
John Heffner 已提交
1950

1951 1952
	tcp_insert_write_queue_before(nskb, skb, sk);

J
John Heffner 已提交
1953
	len = 0;
1954
	tcp_for_write_queue_from_safe(skb, next, sk) {
J
John Heffner 已提交
1955 1956 1957 1958 1959
		copy = min_t(int, skb->len, probe_size - len);
		if (nskb->ip_summed)
			skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
		else
			nskb->csum = skb_copy_and_csum_bits(skb, 0,
1960 1961
							    skb_put(nskb, copy),
							    copy, nskb->csum);
J
John Heffner 已提交
1962 1963 1964 1965

		if (skb->len <= copy) {
			/* We've eaten all the data from this skb.
			 * Throw it away. */
E
Eric Dumazet 已提交
1966
			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1967
			tcp_unlink_write_queue(skb, sk);
1968
			sk_wmem_free_skb(sk, skb);
J
John Heffner 已提交
1969
		} else {
E
Eric Dumazet 已提交
1970
			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
C
Changli Gao 已提交
1971
						   ~(TCPHDR_FIN|TCPHDR_PSH);
J
John Heffner 已提交
1972 1973
			if (!skb_shinfo(skb)->nr_frags) {
				skb_pull(skb, copy);
1974
				if (skb->ip_summed != CHECKSUM_PARTIAL)
1975 1976
					skb->csum = csum_partial(skb->data,
								 skb->len, 0);
J
John Heffner 已提交
1977 1978
			} else {
				__pskb_trim_head(skb, copy);
1979
				tcp_set_skb_tso_segs(skb, mss_now);
J
John Heffner 已提交
1980 1981 1982 1983 1984
			}
			TCP_SKB_CB(skb)->seq += copy;
		}

		len += copy;
1985 1986 1987

		if (len >= probe_size)
			break;
J
John Heffner 已提交
1988
	}
1989
	tcp_init_tso_segs(nskb, nskb->len);
J
John Heffner 已提交
1990 1991

	/* We're ready to send.  If this fails, the probe will
E
Eric Dumazet 已提交
1992 1993
	 * be resegmented into mss-sized pieces by tcp_write_xmit().
	 */
J
John Heffner 已提交
1994 1995
	if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
		/* Decrement cwnd here because we are sending
1996
		 * effectively two packets. */
J
John Heffner 已提交
1997
		tp->snd_cwnd--;
1998
		tcp_event_new_data_sent(sk, nskb);
J
John Heffner 已提交
1999 2000

		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2001 2002
		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
2003 2004 2005 2006 2007 2008 2009

		return 1;
	}

	return -1;
}

L
Linus Torvalds 已提交
2010 2011 2012 2013
/* This routine writes packets to the network.  It advances the
 * send_head.  This happens as incoming acks open up the remote
 * window for us.
 *
2014 2015 2016 2017
 * 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
2018 2019 2020
 * 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
2021 2022
 * 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
2023
 */
E
Eric Dumazet 已提交
2024 2025
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
2026 2027
{
	struct tcp_sock *tp = tcp_sk(sk);
2028
	struct sk_buff *skb;
2029 2030
	unsigned int tso_segs, sent_pkts;
	int cwnd_quota;
J
John Heffner 已提交
2031
	int result;
2032
	bool is_cwnd_limited = false;
E
Eric Dumazet 已提交
2033
	u32 max_segs;
L
Linus Torvalds 已提交
2034

2035
	sent_pkts = 0;
J
John Heffner 已提交
2036

2037 2038 2039 2040
	if (!push_one) {
		/* Do MTU probing. */
		result = tcp_mtu_probe(sk);
		if (!result) {
E
Eric Dumazet 已提交
2041
			return false;
2042 2043 2044
		} else if (result > 0) {
			sent_pkts = 1;
		}
J
John Heffner 已提交
2045 2046
	}

E
Eric Dumazet 已提交
2047
	max_segs = tcp_tso_autosize(sk, mss_now);
2048
	while ((skb = tcp_send_head(sk))) {
2049 2050
		unsigned int limit;

2051
		tso_segs = tcp_init_tso_segs(skb, mss_now);
2052
		BUG_ON(!tso_segs);
2053

2054
		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
E
Eric Dumazet 已提交
2055 2056
			/* "skb_mstamp" is used as a start point for the retransmit timer */
			skb_mstamp_get(&skb->skb_mstamp);
2057
			goto repair; /* Skip network transmission */
2058
		}
2059

2060
		cwnd_quota = tcp_cwnd_test(tp, skb);
N
Nandita Dukkipati 已提交
2061
		if (!cwnd_quota) {
2062
			is_cwnd_limited = true;
N
Nandita Dukkipati 已提交
2063 2064 2065 2066 2067 2068
			if (push_one == 2)
				/* Force out a loss probe pkt. */
				cwnd_quota = 1;
			else
				break;
		}
2069 2070 2071 2072

		if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
			break;

2073
		if (tso_segs == 1) {
2074 2075 2076 2077 2078
			if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
						     (tcp_skb_is_last(sk, skb) ?
						      nonagle : TCP_NAGLE_PUSH))))
				break;
		} else {
2079
			if (!push_one &&
E
Eric Dumazet 已提交
2080 2081
			    tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
						 max_segs))
2082 2083
				break;
		}
2084

E
Eric Dumazet 已提交
2085
		limit = mss_now;
2086
		if (tso_segs > 1 && !tcp_urg_mode(tp))
E
Eric Dumazet 已提交
2087 2088 2089 2090 2091 2092 2093 2094 2095 2096
			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;

E
Eric Dumazet 已提交
2097 2098 2099 2100 2101 2102
		/* TCP Small Queues :
		 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
		 * This allows for :
		 *  - better RTT estimation and ACK scheduling
		 *  - faster recovery
		 *  - high rates
2103 2104 2105
		 * Alas, some drivers / subsystems require a fair amount
		 * of queued bytes to ensure line rate.
		 * One example is wifi aggregation (802.11 AMPDU)
E
Eric Dumazet 已提交
2106
		 */
E
Eric Dumazet 已提交
2107 2108
		limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
		limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
E
Eric Dumazet 已提交
2109 2110

		if (atomic_read(&sk->sk_wmem_alloc) > limit) {
E
Eric Dumazet 已提交
2111
			set_bit(TSQ_THROTTLED, &tp->tsq_flags);
J
John Ogness 已提交
2112 2113 2114 2115
			/* It is possible TX completion already happened
			 * before we set TSQ_THROTTLED, so we must
			 * test again the condition.
			 */
2116
			smp_mb__after_atomic();
J
John Ogness 已提交
2117 2118
			if (atomic_read(&sk->sk_wmem_alloc) > limit)
				break;
E
Eric Dumazet 已提交
2119
		}
E
Eric Dumazet 已提交
2120

2121
		if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2122
			break;
L
Linus Torvalds 已提交
2123

2124
repair:
2125 2126 2127
		/* Advance the send_head.  This one is sent out.
		 * This call will increment packets_out.
		 */
2128
		tcp_event_new_data_sent(sk, skb);
L
Linus Torvalds 已提交
2129

2130
		tcp_minshall_update(tp, mss_now, skb);
2131
		sent_pkts += tcp_skb_pcount(skb);
2132 2133 2134

		if (push_one)
			break;
2135
	}
L
Linus Torvalds 已提交
2136

2137
	if (likely(sent_pkts)) {
2138 2139
		if (tcp_in_cwnd_reduction(sk))
			tp->prr_out += sent_pkts;
N
Nandita Dukkipati 已提交
2140 2141 2142 2143

		/* Send one loss probe per tail loss episode. */
		if (push_one != 2)
			tcp_schedule_loss_probe(sk);
2144
		tcp_cwnd_validate(sk, is_cwnd_limited);
E
Eric Dumazet 已提交
2145
		return false;
L
Linus Torvalds 已提交
2146
	}
2147
	return !tp->packets_out && tcp_send_head(sk);
N
Nandita Dukkipati 已提交
2148 2149 2150 2151 2152 2153 2154
}

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;
2155
	u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
N
Nandita Dukkipati 已提交
2156 2157 2158 2159 2160 2161 2162 2163 2164 2165 2166

	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.
	 */
2167
	if (tp->fastopen_rsk)
N
Nandita Dukkipati 已提交
2168 2169 2170 2171 2172 2173 2174 2175 2176
		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.
	 */
2177
	if (sysctl_tcp_early_retrans < 3 || !tp->packets_out ||
N
Nandita Dukkipati 已提交
2178 2179 2180 2181 2182 2183 2184 2185
	    !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
2186 2187
	 * 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
2188
	 */
2189
	timeout = rtt << 1 ? : TCP_TIMEOUT_INIT;
N
Nandita Dukkipati 已提交
2190 2191 2192 2193 2194 2195 2196 2197 2198 2199 2200 2201 2202 2203 2204 2205 2206 2207 2208
	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;
}

2209 2210 2211 2212 2213 2214 2215 2216
/* 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 !
 * Note: This is called from BH context only.
 */
static bool skb_still_in_host_queue(const struct sock *sk,
				    const struct sk_buff *skb)
{
2217
	if (unlikely(skb_fclone_busy(sk, skb))) {
2218 2219 2220 2221 2222 2223 2224
		NET_INC_STATS_BH(sock_net(sk),
				 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
		return true;
	}
	return false;
}

2225
/* When probe timeout (PTO) fires, try send a new segment if possible, else
N
Nandita Dukkipati 已提交
2226 2227 2228 2229
 * retransmit the last segment.
 */
void tcp_send_loss_probe(struct sock *sk)
{
N
Nandita Dukkipati 已提交
2230
	struct tcp_sock *tp = tcp_sk(sk);
N
Nandita Dukkipati 已提交
2231 2232 2233 2234
	struct sk_buff *skb;
	int pcount;
	int mss = tcp_current_mss(sk);

2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246
	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
2247 2248
	}

N
Nandita Dukkipati 已提交
2249 2250 2251 2252
	/* At most one outstanding TLP retransmission. */
	if (tp->tlp_high_seq)
		goto rearm_timer;

N
Nandita Dukkipati 已提交
2253 2254 2255 2256
	/* Retransmit last segment. */
	if (WARN_ON(!skb))
		goto rearm_timer;

2257 2258 2259
	if (skb_still_in_host_queue(sk, skb))
		goto rearm_timer;

N
Nandita Dukkipati 已提交
2260 2261 2262 2263 2264
	pcount = tcp_skb_pcount(skb);
	if (WARN_ON(!pcount))
		goto rearm_timer;

	if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2265 2266
		if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
					  GFP_ATOMIC)))
N
Nandita Dukkipati 已提交
2267
			goto rearm_timer;
2268
		skb = tcp_write_queue_next(sk, skb);
N
Nandita Dukkipati 已提交
2269 2270 2271 2272 2273
	}

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

2274 2275
	if (__tcp_retransmit_skb(sk, skb))
		goto rearm_timer;
N
Nandita Dukkipati 已提交
2276

N
Nandita Dukkipati 已提交
2277
	/* Record snd_nxt for loss detection. */
2278
	tp->tlp_high_seq = tp->snd_nxt;
N
Nandita Dukkipati 已提交
2279

2280 2281 2282 2283
probe_sent:
	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
	/* Reset s.t. tcp_rearm_rto will restart timer from now */
	inet_csk(sk)->icsk_pending = 0;
N
Nandita Dukkipati 已提交
2284
rearm_timer:
2285
	tcp_rearm_rto(sk);
L
Linus Torvalds 已提交
2286 2287
}

2288 2289 2290 2291
/* 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.
 */
2292 2293
void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
			       int nonagle)
2294
{
2295 2296 2297 2298 2299 2300 2301
	/* 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;

2302 2303
	if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
			   sk_gfp_atomic(sk, GFP_ATOMIC)))
2304
		tcp_check_probe_timer(sk);
2305 2306
}

2307 2308 2309 2310 2311
/* 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)
{
2312
	struct sk_buff *skb = tcp_send_head(sk);
2313 2314 2315

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

2316
	tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2317 2318
}

L
Linus Torvalds 已提交
2319 2320
/* This function returns the amount that we can raise the
 * usable window based on the following constraints
2321
 *
L
Linus Torvalds 已提交
2322 2323 2324 2325 2326 2327 2328 2329 2330 2331 2332 2333 2334 2335 2336 2337 2338 2339
 * 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.
2340
 *
L
Linus Torvalds 已提交
2341 2342
 * Of course, if the sender implements sender side SWS prevention
 * then this will not be a problem.
2343
 *
L
Linus Torvalds 已提交
2344
 * BSD seems to make the following compromise:
2345
 *
L
Linus Torvalds 已提交
2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361 2362 2363 2364 2365 2366 2367 2368 2369 2370 2371 2372
 *	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)
{
2373
	struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
2374
	struct tcp_sock *tp = tcp_sk(sk);
S
Stephen Hemminger 已提交
2375
	/* MSS for the peer's data.  Previous versions used mss_clamp
L
Linus Torvalds 已提交
2376 2377 2378 2379 2380
	 * 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
	 */
2381
	int mss = icsk->icsk_ack.rcv_mss;
L
Linus Torvalds 已提交
2382
	int free_space = tcp_space(sk);
2383 2384
	int allowed_space = tcp_full_space(sk);
	int full_space = min_t(int, tp->window_clamp, allowed_space);
L
Linus Torvalds 已提交
2385 2386 2387
	int window;

	if (mss > full_space)
2388
		mss = full_space;
L
Linus Torvalds 已提交
2389

2390
	if (free_space < (full_space >> 1)) {
2391
		icsk->icsk_ack.quick = 0;
L
Linus Torvalds 已提交
2392

2393
		if (tcp_under_memory_pressure(sk))
2394 2395
			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
					       4U * tp->advmss);
L
Linus Torvalds 已提交
2396

2397 2398 2399 2400 2401 2402 2403 2404 2405 2406 2407 2408 2409
		/* 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
2410 2411 2412 2413 2414 2415 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431 2432 2433 2434 2435 2436 2437 2438 2439
			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)
2440
			window = (free_space / mss) * mss;
2441
		else if (mss == full_space &&
2442
			 free_space > window + (full_space >> 1))
2443
			window = free_space;
L
Linus Torvalds 已提交
2444 2445 2446 2447 2448
	}

	return window;
}

2449 2450
/* Collapses two adjacent SKB's during retransmission. */
static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
L
Linus Torvalds 已提交
2451 2452
{
	struct tcp_sock *tp = tcp_sk(sk);
2453
	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2454
	int skb_size, next_skb_size;
L
Linus Torvalds 已提交
2455

2456 2457
	skb_size = skb->len;
	next_skb_size = next_skb->len;
L
Linus Torvalds 已提交
2458

2459
	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2460

2461
	tcp_highest_sack_combine(sk, next_skb, skb);
L
Linus Torvalds 已提交
2462

2463
	tcp_unlink_write_queue(next_skb, sk);
L
Linus Torvalds 已提交
2464

2465 2466
	skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
				  next_skb_size);
L
Linus Torvalds 已提交
2467

2468 2469
	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
		skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
2470

2471 2472
	if (skb->ip_summed != CHECKSUM_PARTIAL)
		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
L
Linus Torvalds 已提交
2473

2474 2475
	/* 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
2476

2477
	/* Merge over control information. This moves PSH/FIN etc. over */
E
Eric Dumazet 已提交
2478
	TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2479 2480 2481 2482 2483 2484 2485

	/* 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;

	/* changed transmit queue under us so clear hints */
2486 2487 2488
	tcp_clear_retrans_hints_partial(tp);
	if (next_skb == tp->retransmit_skb_hint)
		tp->retransmit_skb_hint = skb;
2489

2490 2491
	tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));

2492
	sk_wmem_free_skb(sk, next_skb);
L
Linus Torvalds 已提交
2493 2494
}

2495
/* Check if coalescing SKBs is legal. */
E
Eric Dumazet 已提交
2496
static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2497 2498
{
	if (tcp_skb_pcount(skb) > 1)
E
Eric Dumazet 已提交
2499
		return false;
2500 2501
	/* TODO: SACK collapsing could be used to remove this condition */
	if (skb_shinfo(skb)->nr_frags != 0)
E
Eric Dumazet 已提交
2502
		return false;
2503
	if (skb_cloned(skb))
E
Eric Dumazet 已提交
2504
		return false;
2505
	if (skb == tcp_send_head(sk))
E
Eric Dumazet 已提交
2506
		return false;
2507 2508
	/* Some heurestics for collapsing over SACK'd could be invented */
	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
E
Eric Dumazet 已提交
2509
		return false;
2510

E
Eric Dumazet 已提交
2511
	return true;
2512 2513
}

2514 2515 2516
/* Collapse packets in the retransmit queue to make to create
 * less packets on the wire. This is only done on retransmission.
 */
2517 2518 2519 2520 2521
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
2522
	bool first = true;
2523 2524 2525

	if (!sysctl_tcp_retrans_collapse)
		return;
E
Eric Dumazet 已提交
2526
	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2527 2528 2529 2530 2531 2532 2533 2534 2535
		return;

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

		space -= skb->len;

		if (first) {
E
Eric Dumazet 已提交
2536
			first = false;
2537 2538 2539 2540 2541 2542 2543 2544
			continue;
		}

		if (space < 0)
			break;
		/* Punt if not enough space exists in the first SKB for
		 * the data in the second
		 */
2545
		if (skb->len > skb_availroom(to))
2546 2547 2548 2549 2550 2551 2552 2553 2554
			break;

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

		tcp_collapse_retrans(sk, to);
	}
}

L
Linus Torvalds 已提交
2555 2556 2557 2558
/* 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.
 */
2559
int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
L
Linus Torvalds 已提交
2560 2561
{
	struct tcp_sock *tp = tcp_sk(sk);
J
John Heffner 已提交
2562
	struct inet_connection_sock *icsk = inet_csk(sk);
2563
	unsigned int cur_mss;
2564
	int err;
L
Linus Torvalds 已提交
2565

J
John Heffner 已提交
2566 2567 2568 2569 2570
	/* Inconslusive MTU probe */
	if (icsk->icsk_mtup.probe_size) {
		icsk->icsk_mtup.probe_size = 0;
	}

L
Linus Torvalds 已提交
2571
	/* Do not sent more than we queued. 1/4 is reserved for possible
S
Stephen Hemminger 已提交
2572
	 * copying overhead: fragmentation, tunneling, mangling etc.
L
Linus Torvalds 已提交
2573 2574 2575 2576 2577
	 */
	if (atomic_read(&sk->sk_wmem_alloc) >
	    min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
		return -EAGAIN;

2578 2579 2580
	if (skb_still_in_host_queue(sk, skb))
		return -EBUSY;

L
Linus Torvalds 已提交
2581 2582 2583 2584 2585 2586 2587
	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;
	}

2588 2589 2590
	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
		return -EHOSTUNREACH; /* Routing failure or similar. */

I
Ilpo Järvinen 已提交
2591
	cur_mss = tcp_current_mss(sk);
2592

L
Linus Torvalds 已提交
2593 2594 2595 2596 2597
	/* 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.
	 */
2598 2599
	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
2600 2601 2602
		return -EAGAIN;

	if (skb->len > cur_mss) {
2603
		if (tcp_fragment(sk, skb, cur_mss, cur_mss, GFP_ATOMIC))
L
Linus Torvalds 已提交
2604
			return -ENOMEM; /* We'll try again later. */
2605
	} else {
2606 2607 2608
		int oldpcount = tcp_skb_pcount(skb);

		if (unlikely(oldpcount > 1)) {
2609 2610
			if (skb_unclone(skb, GFP_ATOMIC))
				return -ENOMEM;
2611
			tcp_init_tso_segs(skb, cur_mss);
2612 2613
			tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
		}
L
Linus Torvalds 已提交
2614 2615
	}

2616 2617 2618 2619
	/* 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);

2620
	tcp_retrans_try_collapse(sk, skb, cur_mss);
L
Linus Torvalds 已提交
2621 2622 2623 2624 2625

	/* Make a copy, if the first transmission SKB clone we made
	 * is still in somebody's hands, else make a clone.
	 */

2626 2627 2628 2629 2630 2631
	/* 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)) {
E
Eric Dumazet 已提交
2632 2633
		struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
						   GFP_ATOMIC);
2634 2635
		err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
			     -ENOBUFS;
E
Eric Dumazet 已提交
2636
	} else {
2637
		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
E
Eric Dumazet 已提交
2638
	}
2639

2640
	if (likely(!err)) {
2641
		TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2642 2643 2644 2645 2646 2647
		/* Update global TCP statistics. */
		TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
		tp->total_retrans++;
	}
2648
	return err;
2649 2650 2651 2652 2653 2654
}

int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int err = __tcp_retransmit_skb(sk, skb);
L
Linus Torvalds 已提交
2655 2656 2657

	if (err == 0) {
#if FASTRETRANS_DEBUG > 0
2658
		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2659
			net_dbg_ratelimited("retrans_out leaked\n");
L
Linus Torvalds 已提交
2660 2661
		}
#endif
2662 2663
		if (!tp->retrans_out)
			tp->lost_retrans_low = tp->snd_nxt;
L
Linus Torvalds 已提交
2664 2665 2666 2667 2668
		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
2669
			tp->retrans_stamp = tcp_skb_timestamp(skb);
L
Linus Torvalds 已提交
2670 2671 2672 2673 2674

		/* snd_nxt is stored to detect loss of retransmitted segment,
		 * see tcp_input.c tcp_sacktag_write_queue().
		 */
		TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
2675
	} else if (err != -EBUSY) {
2676
		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
L
Linus Torvalds 已提交
2677
	}
Y
Yuchung Cheng 已提交
2678 2679 2680 2681

	if (tp->undo_retrans < 0)
		tp->undo_retrans = 0;
	tp->undo_retrans += tcp_skb_pcount(skb);
L
Linus Torvalds 已提交
2682 2683 2684
	return err;
}

2685 2686 2687
/* Check if we forward retransmits are possible in the current
 * window/congestion state.
 */
E
Eric Dumazet 已提交
2688
static bool tcp_can_forward_retransmit(struct sock *sk)
2689 2690
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
2691
	const struct tcp_sock *tp = tcp_sk(sk);
2692 2693 2694

	/* Forward retransmissions are possible only during Recovery. */
	if (icsk->icsk_ca_state != TCP_CA_Recovery)
E
Eric Dumazet 已提交
2695
		return false;
2696 2697 2698

	/* No forward retransmissions in Reno are possible. */
	if (tcp_is_reno(tp))
E
Eric Dumazet 已提交
2699
		return false;
2700 2701 2702 2703 2704 2705 2706 2707 2708 2709

	/* 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
2710
		return false;
2711

E
Eric Dumazet 已提交
2712
	return true;
2713 2714
}

L
Linus Torvalds 已提交
2715 2716 2717 2718 2719 2720 2721 2722 2723 2724
/* 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)
{
2725
	const struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
2726 2727
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
2728
	struct sk_buff *hole = NULL;
2729
	u32 last_lost;
2730
	int mib_idx;
2731
	int fwd_rexmitting = 0;
2732

2733 2734 2735
	if (!tp->packets_out)
		return;

2736 2737 2738
	if (!tp->lost_out)
		tp->retransmit_high = tp->snd_una;

2739
	if (tp->retransmit_skb_hint) {
2740
		skb = tp->retransmit_skb_hint;
2741 2742 2743 2744
		last_lost = TCP_SKB_CB(skb)->end_seq;
		if (after(last_lost, tp->retransmit_high))
			last_lost = tp->retransmit_high;
	} else {
2745
		skb = tcp_write_queue_head(sk);
2746 2747
		last_lost = tp->snd_una;
	}
L
Linus Torvalds 已提交
2748

2749 2750
	tcp_for_write_queue_from(skb, sk) {
		__u8 sacked = TCP_SKB_CB(skb)->sacked;
L
Linus Torvalds 已提交
2751

2752 2753 2754
		if (skb == tcp_send_head(sk))
			break;
		/* we could do better than to assign each time */
2755
		if (!hole)
2756
			tp->retransmit_skb_hint = skb;
2757 2758 2759 2760 2761 2762 2763 2764 2765 2766

		/* Assume this retransmit will generate
		 * only one packet for congestion window
		 * calculation purposes.  This works because
		 * tcp_retransmit_skb() will chop up the
		 * packet to be MSS sized and all the
		 * packet counting works out.
		 */
		if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
			return;
L
Linus Torvalds 已提交
2767

2768 2769 2770 2771 2772
		if (fwd_rexmitting) {
begin_fwd:
			if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
				break;
			mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2773

2774
		} else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2775
			tp->retransmit_high = last_lost;
2776 2777 2778
			if (!tcp_can_forward_retransmit(sk))
				break;
			/* Backtrack if necessary to non-L'ed skb */
2779
			if (hole) {
2780 2781 2782 2783 2784
				skb = hole;
				hole = NULL;
			}
			fwd_rexmitting = 1;
			goto begin_fwd;
L
Linus Torvalds 已提交
2785

2786
		} else if (!(sacked & TCPCB_LOST)) {
2787
			if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2788 2789
				hole = skb;
			continue;
L
Linus Torvalds 已提交
2790

2791
		} else {
2792
			last_lost = TCP_SKB_CB(skb)->end_seq;
2793 2794 2795 2796 2797
			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
2798

2799
		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
L
Linus Torvalds 已提交
2800 2801
			continue;

2802
		if (tcp_retransmit_skb(sk, skb))
2803
			return;
2804

2805
		NET_INC_STATS_BH(sock_net(sk), mib_idx);
L
Linus Torvalds 已提交
2806

2807
		if (tcp_in_cwnd_reduction(sk))
2808 2809
			tp->prr_out += tcp_skb_pcount(skb);

2810
		if (skb == tcp_write_queue_head(sk))
2811 2812 2813
			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
						  inet_csk(sk)->icsk_rto,
						  TCP_RTO_MAX);
L
Linus Torvalds 已提交
2814 2815 2816
	}
}

2817 2818
/* We allow to exceed memory limits for FIN packets to expedite
 * connection tear down and (memory) recovery.
2819 2820
 * Otherwise tcp_send_fin() could be tempted to either delay FIN
 * or even be forced to close flow without any FIN.
2821 2822
 * In general, we want to allow one skb per socket to avoid hangs
 * with edge trigger epoll()
2823
 */
2824
void sk_forced_mem_schedule(struct sock *sk, int size)
2825 2826 2827 2828 2829 2830 2831 2832 2833 2834
{
	int amt, status;

	if (size <= sk->sk_forward_alloc)
		return;
	amt = sk_mem_pages(size);
	sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
	sk_memory_allocated_add(sk, amt, &status);
}

2835 2836
/* 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
2837 2838 2839
 */
void tcp_send_fin(struct sock *sk)
{
2840
	struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2841 2842
	struct tcp_sock *tp = tcp_sk(sk);

2843 2844 2845 2846
	/* 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
2847
	 */
2848
	if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
2849 2850 2851
coalesce:
		TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
		TCP_SKB_CB(tskb)->end_seq++;
L
Linus Torvalds 已提交
2852
		tp->write_seq++;
2853 2854 2855 2856 2857 2858 2859 2860 2861 2862
		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
2863
	} else {
2864 2865 2866 2867 2868
		skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
		if (unlikely(!skb)) {
			if (tskb)
				goto coalesce;
			return;
L
Linus Torvalds 已提交
2869
		}
2870
		skb_reserve(skb, MAX_TCP_HEADER);
2871
		sk_forced_mem_schedule(sk, skb->truesize);
L
Linus Torvalds 已提交
2872
		/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2873
		tcp_init_nondata_skb(skb, tp->write_seq,
C
Changli Gao 已提交
2874
				     TCPHDR_ACK | TCPHDR_FIN);
L
Linus Torvalds 已提交
2875 2876
		tcp_queue_skb(sk, skb);
	}
2877
	__tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
L
Linus Torvalds 已提交
2878 2879 2880 2881 2882
}

/* 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
2883
 * by RFC 2525, section 2.17.  -DaveM
L
Linus Torvalds 已提交
2884
 */
A
Al Viro 已提交
2885
void tcp_send_active_reset(struct sock *sk, gfp_t priority)
L
Linus Torvalds 已提交
2886 2887 2888 2889 2890 2891
{
	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
2892
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
L
Linus Torvalds 已提交
2893 2894 2895 2896 2897
		return;
	}

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, MAX_TCP_HEADER);
2898
	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
C
Changli Gao 已提交
2899
			     TCPHDR_ACK | TCPHDR_RST);
L
Linus Torvalds 已提交
2900
	/* Send it off. */
2901
	if (tcp_transmit_skb(sk, skb, 0, priority))
P
Pavel Emelyanov 已提交
2902
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2903

P
Pavel Emelyanov 已提交
2904
	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
L
Linus Torvalds 已提交
2905 2906
}

2907 2908
/* 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
2909 2910 2911 2912 2913 2914
 * 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)
{
2915
	struct sk_buff *skb;
L
Linus Torvalds 已提交
2916

2917
	skb = tcp_write_queue_head(sk);
2918
	if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2919
		pr_debug("%s: wrong queue state\n", __func__);
L
Linus Torvalds 已提交
2920 2921
		return -EFAULT;
	}
E
Eric Dumazet 已提交
2922
	if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
L
Linus Torvalds 已提交
2923 2924
		if (skb_cloned(skb)) {
			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2925
			if (!nskb)
L
Linus Torvalds 已提交
2926
				return -ENOMEM;
2927
			tcp_unlink_write_queue(skb, sk);
2928
			__skb_header_release(nskb);
2929
			__tcp_add_write_queue_head(sk, nskb);
2930 2931 2932
			sk_wmem_free_skb(sk, skb);
			sk->sk_wmem_queued += nskb->truesize;
			sk_mem_charge(sk, nskb->truesize);
L
Linus Torvalds 已提交
2933 2934 2935
			skb = nskb;
		}

E
Eric Dumazet 已提交
2936
		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2937
		tcp_ecn_send_synack(sk, skb);
L
Linus Torvalds 已提交
2938
	}
2939
	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
L
Linus Torvalds 已提交
2940 2941
}

2942 2943 2944 2945 2946 2947 2948 2949 2950
/**
 * 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.
 */
2951
struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
2952
				struct request_sock *req,
2953
				struct tcp_fastopen_cookie *foc)
L
Linus Torvalds 已提交
2954
{
2955
	struct tcp_out_options opts;
2956
	struct inet_request_sock *ireq = inet_rsk(req);
L
Linus Torvalds 已提交
2957 2958 2959
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcphdr *th;
	struct sk_buff *skb;
E
Eric Dumazet 已提交
2960
	struct tcp_md5sig_key *md5 = NULL;
2961
	int tcp_header_size;
2962
	int mss;
L
Linus Torvalds 已提交
2963

2964
	skb = sock_wmalloc(sk, MAX_TCP_HEADER, 1, GFP_ATOMIC);
2965 2966
	if (unlikely(!skb)) {
		dst_release(dst);
L
Linus Torvalds 已提交
2967
		return NULL;
2968
	}
L
Linus Torvalds 已提交
2969 2970 2971
	/* Reserve space for headers. */
	skb_reserve(skb, MAX_TCP_HEADER);

2972
	skb_dst_set(skb, dst);
L
Linus Torvalds 已提交
2973

2974
	mss = dst_metric_advmss(dst);
2975 2976 2977
	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
		mss = tp->rx_opt.user_mss;

A
Adam Langley 已提交
2978
	memset(&opts, 0, sizeof(opts));
2979 2980
#ifdef CONFIG_SYN_COOKIES
	if (unlikely(req->cookie_ts))
E
Eric Dumazet 已提交
2981
		skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
2982 2983
	else
#endif
E
Eric Dumazet 已提交
2984
	skb_mstamp_get(&skb->skb_mstamp);
E
Eric Dumazet 已提交
2985 2986 2987

#ifdef CONFIG_TCP_MD5SIG
	rcu_read_lock();
2988
	md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
E
Eric Dumazet 已提交
2989
#endif
2990
	skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
2991 2992
	tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
			  sizeof(*th);
2993

2994 2995
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
L
Linus Torvalds 已提交
2996

2997
	th = tcp_hdr(skb);
L
Linus Torvalds 已提交
2998 2999 3000
	memset(th, 0, sizeof(struct tcphdr));
	th->syn = 1;
	th->ack = 1;
3001
	tcp_ecn_make_synack(req, th, sk);
E
Eric Dumazet 已提交
3002
	th->source = htons(ireq->ir_num);
3003
	th->dest = ireq->ir_rmt_port;
3004 3005 3006 3007
	/* 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
3008
			     TCPHDR_SYN | TCPHDR_ACK);
3009

L
Linus Torvalds 已提交
3010
	th->seq = htonl(TCP_SKB_CB(skb)->seq);
3011 3012
	/* 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
3013 3014

	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3015
	th->window = htons(min(req->rcv_wnd, 65535U));
3016
	tcp_options_write((__be32 *)(th + 1), tp, &opts);
L
Linus Torvalds 已提交
3017
	th->doff = (tcp_header_size >> 2);
3018
	TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_OUTSEGS);
3019 3020 3021

#ifdef CONFIG_TCP_MD5SIG
	/* Okay, we have all we need - do the md5 hash if needed */
E
Eric Dumazet 已提交
3022
	if (md5)
3023
		tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3024
					       md5, req_to_sk(req), skb);
E
Eric Dumazet 已提交
3025
	rcu_read_unlock();
3026 3027
#endif

3028 3029
	/* Do not fool tcpdump (if any), clean our debris */
	skb->tstamp.tv64 = 0;
L
Linus Torvalds 已提交
3030 3031
	return skb;
}
E
Eric Dumazet 已提交
3032
EXPORT_SYMBOL(tcp_make_synack);
L
Linus Torvalds 已提交
3033

3034 3035 3036 3037 3038 3039 3040 3041 3042 3043 3044 3045 3046 3047 3048 3049 3050 3051 3052
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();
}

3053
/* Do all connect socket setups that can be done AF independent. */
3054
static void tcp_connect_init(struct sock *sk)
L
Linus Torvalds 已提交
3055
{
3056
	const struct dst_entry *dst = __sk_dst_get(sk);
L
Linus Torvalds 已提交
3057 3058 3059 3060 3061 3062 3063
	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) +
3064
		(sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
L
Linus Torvalds 已提交
3065

3066
#ifdef CONFIG_TCP_MD5SIG
3067
	if (tp->af_specific->md5_lookup(sk, sk))
3068 3069 3070
		tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
#endif

L
Linus Torvalds 已提交
3071 3072 3073 3074
	/* 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
3075
	tcp_mtup_init(sk);
L
Linus Torvalds 已提交
3076 3077
	tcp_sync_mss(sk, dst_mtu(dst));

3078 3079
	tcp_ca_dst_init(sk, dst);

L
Linus Torvalds 已提交
3080 3081
	if (!tp->window_clamp)
		tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3082
	tp->advmss = dst_metric_advmss(dst);
3083 3084 3085
	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
3086 3087
	tcp_initialize_rcv_mss(sk);

3088 3089 3090 3091 3092
	/* 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
3093 3094 3095 3096
	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,
3097
				  sysctl_tcp_window_scaling,
3098 3099
				  &rcv_wscale,
				  dst_metric(dst, RTAX_INITRWND));
L
Linus Torvalds 已提交
3100 3101 3102 3103 3104 3105 3106

	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;
3107
	tcp_init_wl(tp, 0);
L
Linus Torvalds 已提交
3108 3109
	tp->snd_una = tp->write_seq;
	tp->snd_sml = tp->write_seq;
I
Ilpo Järvinen 已提交
3110
	tp->snd_up = tp->write_seq;
P
Pavel Emelyanov 已提交
3111
	tp->snd_nxt = tp->write_seq;
P
Pavel Emelyanov 已提交
3112 3113 3114

	if (likely(!tp->repair))
		tp->rcv_nxt = 0;
3115 3116
	else
		tp->rcv_tstamp = tcp_time_stamp;
P
Pavel Emelyanov 已提交
3117 3118
	tp->rcv_wup = tp->rcv_nxt;
	tp->copied_seq = tp->rcv_nxt;
L
Linus Torvalds 已提交
3119

3120 3121
	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
	inet_csk(sk)->icsk_retransmits = 0;
L
Linus Torvalds 已提交
3122 3123 3124
	tcp_clear_retrans(tp);
}

3125 3126 3127 3128 3129 3130
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;
3131
	__skb_header_release(skb);
3132 3133 3134 3135 3136 3137 3138 3139 3140 3141 3142 3143 3144 3145 3146 3147 3148 3149
	__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;
3150
	int syn_loss = 0, space, err = 0, copied;
3151
	unsigned long last_syn_loss = 0;
3152
	struct sk_buff *syn_data;
3153

3154
	tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
3155 3156 3157 3158 3159 3160 3161 3162
	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;
	}
3163

3164 3165 3166
	if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
		fo->cookie.len = -1;
	else if (fo->cookie.len <= 0)
3167 3168 3169 3170 3171 3172 3173 3174
		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;
3175
	space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3176 3177
		MAX_TCP_OPTION_SPACE;

3178 3179 3180 3181 3182
	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));

3183
	syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3184
	if (!syn_data)
3185
		goto fallback;
3186 3187
	syn_data->ip_summed = CHECKSUM_PARTIAL;
	memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3188 3189 3190
	copied = copy_from_iter(skb_put(syn_data, space), space,
				&fo->data->msg_iter);
	if (unlikely(!copied)) {
3191 3192 3193
		kfree_skb(syn_data);
		goto fallback;
	}
3194 3195 3196 3197
	if (copied != space) {
		skb_trim(syn_data, copied);
		space = copied;
	}
3198

3199 3200 3201 3202
	/* No more data pending in inet_wait_for_connect() */
	if (space == fo->size)
		fo->data = NULL;
	fo->copied = space;
3203

3204
	tcp_connect_queue_skb(sk, syn_data);
3205

3206
	err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3207

3208
	syn->skb_mstamp = syn_data->skb_mstamp;
E
Eric Dumazet 已提交
3209

3210 3211 3212 3213 3214 3215 3216 3217
	/* 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) {
3218
		tp->syn_data = (fo->copied > 0);
3219
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3220 3221 3222 3223 3224 3225 3226 3227 3228 3229 3230 3231 3232 3233 3234
		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;
}

3235
/* Build a SYN and send it off. */
L
Linus Torvalds 已提交
3236 3237 3238 3239
int tcp_connect(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;
3240
	int err;
L
Linus Torvalds 已提交
3241 3242 3243

	tcp_connect_init(sk);

A
Andrey Vagin 已提交
3244 3245 3246 3247 3248
	if (unlikely(tp->repair)) {
		tcp_finish_connect(sk, NULL);
		return 0;
	}

3249
	buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3250
	if (unlikely(!buff))
L
Linus Torvalds 已提交
3251 3252
		return -ENOBUFS;

C
Changli Gao 已提交
3253
	tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
E
Eric Dumazet 已提交
3254
	tp->retrans_stamp = tcp_time_stamp;
3255
	tcp_connect_queue_skb(sk, buff);
3256
	tcp_ecn_send_syn(sk, buff);
L
Linus Torvalds 已提交
3257

3258 3259 3260
	/* 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);
3261 3262
	if (err == -ECONNREFUSED)
		return err;
3263 3264 3265 3266 3267 3268

	/* 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
3269
	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
L
Linus Torvalds 已提交
3270 3271

	/* Timer for repeating the SYN until an answer. */
3272 3273
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
L
Linus Torvalds 已提交
3274 3275
	return 0;
}
E
Eric Dumazet 已提交
3276
EXPORT_SYMBOL(tcp_connect);
L
Linus Torvalds 已提交
3277 3278 3279 3280 3281 3282 3283

/* 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)
{
3284 3285
	struct inet_connection_sock *icsk = inet_csk(sk);
	int ato = icsk->icsk_ack.ato;
L
Linus Torvalds 已提交
3286 3287
	unsigned long timeout;

3288 3289
	tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);

L
Linus Torvalds 已提交
3290
	if (ato > TCP_DELACK_MIN) {
3291
		const struct tcp_sock *tp = tcp_sk(sk);
3292
		int max_ato = HZ / 2;
L
Linus Torvalds 已提交
3293

3294 3295
		if (icsk->icsk_ack.pingpong ||
		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
L
Linus Torvalds 已提交
3296 3297 3298 3299 3300
			max_ato = TCP_DELACK_MAX;

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

		/* If some rtt estimate is known, use it to bound delayed ack.
3301
		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
L
Linus Torvalds 已提交
3302 3303
		 * directly.
		 */
3304 3305 3306
		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
3307 3308 3309 3310 3311 3312 3313 3314 3315 3316 3317 3318

			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. */
3319
	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
L
Linus Torvalds 已提交
3320 3321 3322
		/* If delack timer was blocked or is about to expire,
		 * send ACK now.
		 */
3323 3324
		if (icsk->icsk_ack.blocked ||
		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
L
Linus Torvalds 已提交
3325 3326 3327 3328
			tcp_send_ack(sk);
			return;
		}

3329 3330
		if (!time_before(timeout, icsk->icsk_ack.timeout))
			timeout = icsk->icsk_ack.timeout;
L
Linus Torvalds 已提交
3331
	}
3332 3333 3334
	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
3335 3336 3337 3338 3339
}

/* This routine sends an ack and also updates the window. */
void tcp_send_ack(struct sock *sk)
{
3340
	struct sk_buff *buff;
L
Linus Torvalds 已提交
3341

3342 3343 3344
	/* If we have been reset, we may not send again. */
	if (sk->sk_state == TCP_CLOSE)
		return;
L
Linus Torvalds 已提交
3345

3346 3347
	tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);

3348 3349 3350 3351
	/* We are not putting this on the write queue, so
	 * tcp_transmit_skb() will set the ownership to this
	 * sock.
	 */
3352
	buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3353
	if (!buff) {
3354 3355 3356 3357 3358
		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
3359
	}
3360 3361 3362

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(buff, MAX_TCP_HEADER);
C
Changli Gao 已提交
3363
	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3364

E
Eric Dumazet 已提交
3365 3366 3367 3368 3369 3370 3371 3372
	/* 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);

3373
	/* Send it off, this clears delayed acks for us. */
E
Eric Dumazet 已提交
3374
	skb_mstamp_get(&buff->skb_mstamp);
3375
	tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC));
L
Linus Torvalds 已提交
3376
}
3377
EXPORT_SYMBOL_GPL(tcp_send_ack);
L
Linus Torvalds 已提交
3378 3379 3380 3381 3382 3383 3384 3385 3386 3387 3388 3389

/* 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.
 */
3390
static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
L
Linus Torvalds 已提交
3391 3392 3393 3394 3395
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;

	/* We don't queue it, tcp_transmit_skb() sets ownership. */
3396
	skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3397
	if (!skb)
L
Linus Torvalds 已提交
3398 3399 3400 3401 3402 3403 3404 3405
		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
3406
	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
E
Eric Dumazet 已提交
3407
	skb_mstamp_get(&skb->skb_mstamp);
3408
	NET_INC_STATS_BH(sock_net(sk), mib);
3409
	return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
L
Linus Torvalds 已提交
3410 3411
}

P
Pavel Emelyanov 已提交
3412 3413 3414 3415
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;
3416
		tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
P
Pavel Emelyanov 已提交
3417 3418 3419
	}
}

3420
/* Initiate keepalive or window probe from timer. */
3421
int tcp_write_wakeup(struct sock *sk, int mib)
L
Linus Torvalds 已提交
3422
{
3423 3424
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
L
Linus Torvalds 已提交
3425

3426 3427 3428
	if (sk->sk_state == TCP_CLOSE)
		return -1;

3429 3430
	skb = tcp_send_head(sk);
	if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3431
		int err;
I
Ilpo Järvinen 已提交
3432
		unsigned int mss = tcp_current_mss(sk);
3433 3434 3435 3436 3437 3438 3439 3440 3441 3442 3443 3444
		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
3445
			TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3446
			if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3447 3448
				return -1;
		} else if (!tcp_skb_pcount(skb))
3449
			tcp_set_skb_tso_segs(skb, mss);
3450

E
Eric Dumazet 已提交
3451
		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3452 3453 3454 3455 3456
		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
3457
		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3458 3459
			tcp_xmit_probe_skb(sk, 1, mib);
		return tcp_xmit_probe_skb(sk, 0, mib);
L
Linus Torvalds 已提交
3460 3461 3462 3463 3464 3465 3466 3467
	}
}

/* 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)
{
3468
	struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
3469
	struct tcp_sock *tp = tcp_sk(sk);
3470
	unsigned long probe_max;
L
Linus Torvalds 已提交
3471 3472
	int err;

3473
	err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
L
Linus Torvalds 已提交
3474

3475
	if (tp->packets_out || !tcp_send_head(sk)) {
L
Linus Torvalds 已提交
3476
		/* Cancel probe timer, if it is not required. */
3477
		icsk->icsk_probes_out = 0;
3478
		icsk->icsk_backoff = 0;
L
Linus Torvalds 已提交
3479 3480 3481 3482
		return;
	}

	if (err <= 0) {
3483 3484
		if (icsk->icsk_backoff < sysctl_tcp_retries2)
			icsk->icsk_backoff++;
3485
		icsk->icsk_probes_out++;
3486
		probe_max = TCP_RTO_MAX;
L
Linus Torvalds 已提交
3487 3488
	} else {
		/* If packet was not sent due to local congestion,
3489
		 * do not backoff and do not remember icsk_probes_out.
L
Linus Torvalds 已提交
3490 3491 3492 3493
		 * Let local senders to fight for local resources.
		 *
		 * Use accumulated backoff yet.
		 */
3494 3495
		if (!icsk->icsk_probes_out)
			icsk->icsk_probes_out = 1;
3496
		probe_max = TCP_RESOURCE_PROBE_INTERVAL;
L
Linus Torvalds 已提交
3497
	}
3498
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3499
				  tcp_probe0_when(sk, probe_max),
3500
				  TCP_RTO_MAX);
L
Linus Torvalds 已提交
3501
}
3502 3503 3504 3505 3506 3507 3508

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

3509
	tcp_rsk(req)->txhash = net_tx_rndhash();
3510 3511 3512 3513 3514 3515 3516 3517
	res = af_ops->send_synack(sk, NULL, &fl, req, 0, NULL);
	if (!res) {
		TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
	}
	return res;
}
EXPORT_SYMBOL(tcp_rtx_synack);