tcp_output.c 102.3 KB
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/*
 * INET		An implementation of the TCP/IP protocol suite for the LINUX
 *		operating system.  INET is implemented using the  BSD Socket
 *		interface as the means of communication with the user level.
 *
 *		Implementation of the Transmission Control Protocol(TCP).
 *
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 * Authors:	Ross Biro
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 *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 *		Mark Evans, <evansmp@uhura.aston.ac.uk>
 *		Corey Minyard <wf-rch!minyard@relay.EU.net>
 *		Florian La Roche, <flla@stud.uni-sb.de>
 *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
 *		Linus Torvalds, <torvalds@cs.helsinki.fi>
 *		Alan Cox, <gw4pts@gw4pts.ampr.org>
 *		Matthew Dillon, <dillon@apollo.west.oic.com>
 *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 *		Jorge Cwik, <jorge@laser.satlink.net>
 */

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

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#define pr_fmt(fmt) "TCP: " fmt

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#include <net/tcp.h>

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

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

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

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

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

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

	return (__u16)mss;
}

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

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

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

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

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	tp->lsndtime = now;

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

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

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

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

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

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

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

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

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	(*rcv_wscale) = 0;
	if (wscale_ok) {
		/* Set window scaling on max possible window
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		 * See RFC1323 for an explanation of the limit to 14
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		 */
		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
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tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
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{
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	if (inet_rsk(req)->ecn_ok)
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		th->ece = 1;
}

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

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

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

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

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

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

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

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

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

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

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

	if (unlikely(opts->num_sack_blocks)) {
		struct tcp_sack_block *sp = tp->rx_opt.dsack ?
			tp->duplicate_sack : tp->selective_acks;
S
Stephen Hemminger 已提交
497 498 499 500 501
		int this_sack;

		*ptr++ = htonl((TCPOPT_NOP  << 24) |
			       (TCPOPT_NOP  << 16) |
			       (TCPOPT_SACK <<  8) |
A
Adam Langley 已提交
502
			       (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
S
Stephen Hemminger 已提交
503
						     TCPOLEN_SACK_PERBLOCK)));
S
Stephen Hemminger 已提交
504

A
Adam Langley 已提交
505 506
		for (this_sack = 0; this_sack < opts->num_sack_blocks;
		     ++this_sack) {
S
Stephen Hemminger 已提交
507 508 509
			*ptr++ = htonl(sp[this_sack].start_seq);
			*ptr++ = htonl(sp[this_sack].end_seq);
		}
S
Stephen Hemminger 已提交
510

511
		tp->rx_opt.dsack = 0;
S
Stephen Hemminger 已提交
512
	}
Y
Yuchung Cheng 已提交
513 514 515

	if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
		struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
516 517 518 519 520 521 522 523 524 525 526 527 528
		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
529

530 531 532 533
		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
534
		}
535
		ptr += (len + 3) >> 2;
Y
Yuchung Cheng 已提交
536
	}
A
Adam Langley 已提交
537 538
}

539 540 541
/* Compute TCP options for SYN packets. This is not the final
 * network wire format yet.
 */
542
static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
A
Adam Langley 已提交
543
				struct tcp_out_options *opts,
544 545
				struct tcp_md5sig_key **md5)
{
A
Adam Langley 已提交
546
	struct tcp_sock *tp = tcp_sk(sk);
547
	unsigned int remaining = MAX_TCP_OPTION_SPACE;
548
	struct tcp_fastopen_request *fastopen = tp->fastopen_req;
A
Adam Langley 已提交
549

550
#ifdef CONFIG_TCP_MD5SIG
A
Adam Langley 已提交
551 552 553
	*md5 = tp->af_specific->md5_lookup(sk, sk);
	if (*md5) {
		opts->options |= OPTION_MD5;
554
		remaining -= TCPOLEN_MD5SIG_ALIGNED;
555
	}
A
Adam Langley 已提交
556 557
#else
	*md5 = NULL;
558
#endif
A
Adam Langley 已提交
559 560 561 562 563 564 565 566 567 568 569

	/* 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);
570
	remaining -= TCPOLEN_MSS_ALIGNED;
A
Adam Langley 已提交
571

572
	if (likely(sysctl_tcp_timestamps && !*md5)) {
A
Adam Langley 已提交
573
		opts->options |= OPTION_TS;
E
Eric Dumazet 已提交
574
		opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
A
Adam Langley 已提交
575
		opts->tsecr = tp->rx_opt.ts_recent;
576
		remaining -= TCPOLEN_TSTAMP_ALIGNED;
A
Adam Langley 已提交
577
	}
578
	if (likely(sysctl_tcp_window_scaling)) {
A
Adam Langley 已提交
579
		opts->ws = tp->rx_opt.rcv_wscale;
580
		opts->options |= OPTION_WSCALE;
581
		remaining -= TCPOLEN_WSCALE_ALIGNED;
A
Adam Langley 已提交
582
	}
583
	if (likely(sysctl_tcp_sack)) {
A
Adam Langley 已提交
584
		opts->options |= OPTION_SACK_ADVERTISE;
585
		if (unlikely(!(OPTION_TS & opts->options)))
586
			remaining -= TCPOLEN_SACKPERM_ALIGNED;
A
Adam Langley 已提交
587 588
	}

589
	if (fastopen && fastopen->cookie.len >= 0) {
590 591 592 593
		u32 need = fastopen->cookie.len;

		need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
					       TCPOLEN_FASTOPEN_BASE;
594 595 596 597 598 599
		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;
600
			tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
601 602
		}
	}
603 604

	return MAX_TCP_OPTION_SPACE - remaining;
S
Stephen Hemminger 已提交
605 606
}

607
/* Set up TCP options for SYN-ACKs. */
608 609 610 611 612
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)
613
{
A
Adam Langley 已提交
614
	struct inet_request_sock *ireq = inet_rsk(req);
615
	unsigned int remaining = MAX_TCP_OPTION_SPACE;
A
Adam Langley 已提交
616

617
#ifdef CONFIG_TCP_MD5SIG
E
Eric Dumazet 已提交
618
	if (md5) {
A
Adam Langley 已提交
619
		opts->options |= OPTION_MD5;
620 621 622 623 624 625 626
		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
627
		ireq->tstamp_ok &= !ireq->sack_ok;
628 629
	}
#endif
A
Adam Langley 已提交
630

631
	/* We always send an MSS option. */
A
Adam Langley 已提交
632
	opts->mss = mss;
633
	remaining -= TCPOLEN_MSS_ALIGNED;
A
Adam Langley 已提交
634 635 636

	if (likely(ireq->wscale_ok)) {
		opts->ws = ireq->rcv_wscale;
637
		opts->options |= OPTION_WSCALE;
638
		remaining -= TCPOLEN_WSCALE_ALIGNED;
A
Adam Langley 已提交
639
	}
E
Eric Dumazet 已提交
640
	if (likely(ireq->tstamp_ok)) {
A
Adam Langley 已提交
641
		opts->options |= OPTION_TS;
E
Eric Dumazet 已提交
642
		opts->tsval = tcp_skb_timestamp(skb);
A
Adam Langley 已提交
643
		opts->tsecr = req->ts_recent;
644
		remaining -= TCPOLEN_TSTAMP_ALIGNED;
A
Adam Langley 已提交
645 646 647
	}
	if (likely(ireq->sack_ok)) {
		opts->options |= OPTION_SACK_ADVERTISE;
E
Eric Dumazet 已提交
648
		if (unlikely(!ireq->tstamp_ok))
649
			remaining -= TCPOLEN_SACKPERM_ALIGNED;
A
Adam Langley 已提交
650
	}
651 652 653 654 655
	if (foc != NULL && foc->len >= 0) {
		u32 need = foc->len;

		need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
				   TCPOLEN_FASTOPEN_BASE;
656 657 658 659 660 661 662
		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
663

664
	return MAX_TCP_OPTION_SPACE - remaining;
A
Adam Langley 已提交
665 666
}

667 668 669
/* Compute TCP options for ESTABLISHED sockets. This is not the
 * final wire format yet.
 */
670
static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
A
Adam Langley 已提交
671
					struct tcp_out_options *opts,
672 673
					struct tcp_md5sig_key **md5)
{
A
Adam Langley 已提交
674
	struct tcp_sock *tp = tcp_sk(sk);
675
	unsigned int size = 0;
676
	unsigned int eff_sacks;
A
Adam Langley 已提交
677

678 679
	opts->options = 0;

A
Adam Langley 已提交
680 681 682 683 684 685 686 687 688 689 690 691
#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
692
		opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
A
Adam Langley 已提交
693 694 695 696
		opts->tsecr = tp->rx_opt.ts_recent;
		size += TCPOLEN_TSTAMP_ALIGNED;
	}

697 698
	eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
	if (unlikely(eff_sacks)) {
699
		const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
A
Adam Langley 已提交
700
		opts->num_sack_blocks =
701
			min_t(unsigned int, eff_sacks,
A
Adam Langley 已提交
702 703 704 705 706 707 708
			      (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
709
}
L
Linus Torvalds 已提交
710

E
Eric Dumazet 已提交
711 712 713 714 715 716 717 718 719

/* 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
720
 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
E
Eric Dumazet 已提交
721 722 723 724 725 726 727 728 729 730 731
 *
 * 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);

732 733 734 735 736
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
737 738
		tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
			       0, GFP_ATOMIC);
739
}
E
Eric Dumazet 已提交
740
/*
S
stephen hemminger 已提交
741
 * One tasklet per cpu tries to send more skbs.
E
Eric Dumazet 已提交
742
 * We run in tasklet context but need to disable irqs when
S
stephen hemminger 已提交
743
 * transferring tsq->head because tcp_wfree() might
E
Eric Dumazet 已提交
744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766
 * 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)) {
767
			tcp_tsq_handler(sk);
E
Eric Dumazet 已提交
768 769
		} else {
			/* defer the work to tcp_release_cb() */
770
			set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
E
Eric Dumazet 已提交
771 772 773 774 775 776 777 778
		}
		bh_unlock_sock(sk);

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

779 780
#define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) |		\
			  (1UL << TCP_WRITE_TIMER_DEFERRED) |	\
781 782
			  (1UL << TCP_DELACK_TIMER_DEFERRED) |	\
			  (1UL << TCP_MTU_REDUCED_DEFERRED))
E
Eric Dumazet 已提交
783 784 785 786 787 788 789 790 791 792
/**
 * 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);
793
	unsigned long flags, nflags;
E
Eric Dumazet 已提交
794

795 796 797 798 799 800 801 802 803 804 805
	/* 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);

806 807 808 809 810 811 812 813 814 815 816
	/* 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);

817
	if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
818
		tcp_write_timer_handler(sk);
819 820 821
		__sock_put(sk);
	}
	if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
822
		tcp_delack_timer_handler(sk);
823 824 825
		__sock_put(sk);
	}
	if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
826
		inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
827 828
		__sock_put(sk);
	}
E
Eric Dumazet 已提交
829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847
}
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
848
 * We can't xmit new skbs from this context, as we might already
E
Eric Dumazet 已提交
849 850
 * hold qdisc lock.
 */
E
Eric Dumazet 已提交
851
void tcp_wfree(struct sk_buff *skb)
E
Eric Dumazet 已提交
852 853 854
{
	struct sock *sk = skb->sk;
	struct tcp_sock *tp = tcp_sk(sk);
855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870
	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
871 872 873 874 875 876 877 878

	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);
879
		tsq = this_cpu_ptr(&tsq_tasklet);
E
Eric Dumazet 已提交
880 881 882
		list_add(&tp->tsq_node, &tsq->head);
		tasklet_schedule(&tsq->tasklet);
		local_irq_restore(flags);
883
		return;
E
Eric Dumazet 已提交
884
	}
885 886
out:
	sk_free(sk);
E
Eric Dumazet 已提交
887 888
}

L
Linus Torvalds 已提交
889 890 891 892 893 894 895 896 897 898 899
/* 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.
 */
900 901
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
902
{
903 904 905 906
	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
907
	struct tcp_out_options opts;
908
	unsigned int tcp_options_size, tcp_header_size;
909
	struct tcp_md5sig_key *md5;
910 911 912 913 914
	struct tcphdr *th;
	int err;

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

915
	if (clone_it) {
916
		skb_mstamp_get(&skb->skb_mstamp);
917

918 919 920 921 922 923 924
		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
925

926 927 928
	inet = inet_sk(sk);
	tp = tcp_sk(sk);
	tcb = TCP_SKB_CB(skb);
A
Adam Langley 已提交
929
	memset(&opts, 0, sizeof(opts));
L
Linus Torvalds 已提交
930

E
Eric Dumazet 已提交
931
	if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
A
Adam Langley 已提交
932 933 934 935 936
		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);
937

E
Eric Dumazet 已提交
938
	/* if no packet is in qdisc/device queue, then allow XPS to select
939 940 941 942 943
	 * 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
944
	 */
945
	skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
946

947 948
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
E
Eric Dumazet 已提交
949 950 951

	skb_orphan(skb);
	skb->sk = sk;
E
Eric Dumazet 已提交
952
	skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree;
953
	skb_set_hash_from_sk(skb, sk);
E
Eric Dumazet 已提交
954
	atomic_add(skb->truesize, &sk->sk_wmem_alloc);
955 956

	/* Build TCP header and checksum it. */
957
	th = (struct tcphdr *)skb->data;
E
Eric Dumazet 已提交
958 959
	th->source		= inet->inet_sport;
	th->dest		= inet->inet_dport;
960 961
	th->seq			= htonl(tcb->seq);
	th->ack_seq		= htonl(tp->rcv_nxt);
962
	*(((__be16 *)th) + 6)	= htons(((tcp_header_size >> 2) << 12) |
E
Eric Dumazet 已提交
963
					tcb->tcp_flags);
964 965 966

	th->check		= 0;
	th->urg_ptr		= 0;
L
Linus Torvalds 已提交
967

I
Ilpo Järvinen 已提交
968
	/* The urg_mode check is necessary during a below snd_una win probe */
969 970 971 972 973
	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)) {
974
			th->urg_ptr = htons(0xFFFF);
975 976
			th->urg = 1;
		}
977
	}
L
Linus Torvalds 已提交
978

979
	tcp_options_write((__be32 *)(th + 1), tp, &opts);
980
	skb_shinfo(skb)->gso_type = sk->sk_gso_type;
981 982 983 984 985 986 987 988 989
	if (likely(!(tcb->tcp_flags & TCPHDR_SYN))) {
		th->window      = htons(tcp_select_window(sk));
		tcp_ecn_send(sk, skb, th, tcp_header_size);
	} else {
		/* RFC1323: The window in SYN & SYN/ACK segments
		 * is never scaled.
		 */
		th->window	= htons(min(tp->rcv_wnd, 65535U));
	}
990 991 992
#ifdef CONFIG_TCP_MD5SIG
	/* Calculate the MD5 hash, as we have all we need now */
	if (md5) {
E
Eric Dumazet 已提交
993
		sk_nocaps_add(sk, NETIF_F_GSO_MASK);
994
		tp->af_specific->calc_md5_hash(opts.hash_location,
995
					       md5, sk, skb);
996 997 998
	}
#endif

999
	icsk->icsk_af_ops->send_check(sk, skb);
L
Linus Torvalds 已提交
1000

E
Eric Dumazet 已提交
1001
	if (likely(tcb->tcp_flags & TCPHDR_ACK))
1002
		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
L
Linus Torvalds 已提交
1003

1004
	if (skb->len != tcp_header_size) {
1005
		tcp_event_data_sent(tp, sk);
1006 1007
		tp->data_segs_out += tcp_skb_pcount(skb);
	}
L
Linus Torvalds 已提交
1008

1009
	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1010 1011
		TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
			      tcp_skb_pcount(skb));
L
Linus Torvalds 已提交
1012

1013
	tp->segs_out += tcp_skb_pcount(skb);
1014
	/* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1015
	skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1016
	skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1017

E
Eric Dumazet 已提交
1018 1019
	/* Our usage of tstamp should remain private */
	skb->tstamp.tv64 = 0;
1020 1021 1022 1023 1024

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

1025
	err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
E
Eric Dumazet 已提交
1026

1027
	if (likely(err <= 0))
1028 1029
		return err;

1030
	tcp_enter_cwr(sk);
1031

1032
	return net_xmit_eval(err);
L
Linus Torvalds 已提交
1033 1034
}

1035
/* This routine just queues the buffer for sending.
L
Linus Torvalds 已提交
1036 1037 1038 1039 1040 1041 1042 1043 1044 1045
 *
 * 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;
1046
	__skb_header_release(skb);
1047
	tcp_add_write_queue_tail(sk, skb);
1048 1049
	sk->sk_wmem_queued += skb->truesize;
	sk_mem_charge(sk, skb->truesize);
L
Linus Torvalds 已提交
1050 1051
}

1052
/* Initialize TSO segments for a packet. */
1053
static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1054
{
1055
	if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1056 1057 1058
		/* Avoid the costly divide in the normal
		 * non-TSO case.
		 */
1059
		tcp_skb_pcount_set(skb, 1);
1060
		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1061
	} else {
1062
		tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1063
		TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
L
Linus Torvalds 已提交
1064 1065 1066
	}
}

I
Ilpo Järvinen 已提交
1067
/* When a modification to fackets out becomes necessary, we need to check
1068
 * skb is counted to fackets_out or not.
I
Ilpo Järvinen 已提交
1069
 */
1070
static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
I
Ilpo Järvinen 已提交
1071 1072
				   int decr)
{
1073 1074
	struct tcp_sock *tp = tcp_sk(sk);

1075
	if (!tp->sacked_out || tcp_is_reno(tp))
I
Ilpo Järvinen 已提交
1076 1077
		return;

1078
	if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
I
Ilpo Järvinen 已提交
1079 1080 1081
		tp->fackets_out -= decr;
}

1082 1083 1084
/* Pcount in the middle of the write queue got changed, we need to do various
 * tweaks to fix counters
 */
1085
static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105
{
	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) &&
1106
	    (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1107 1108 1109 1110 1111
		tp->lost_cnt_hint -= decr;

	tcp_verify_left_out(tp);
}

1112 1113 1114 1115 1116 1117
static bool tcp_has_tx_tstamp(const struct sk_buff *skb)
{
	return TCP_SKB_CB(skb)->txstamp_ack ||
		(skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP);
}

1118 1119 1120 1121
static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
{
	struct skb_shared_info *shinfo = skb_shinfo(skb);

1122
	if (unlikely(tcp_has_tx_tstamp(skb)) &&
1123 1124 1125 1126 1127 1128 1129
	    !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);
1130 1131
		TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack;
		TCP_SKB_CB(skb)->txstamp_ack = 0;
1132 1133 1134
	}
}

1135 1136 1137 1138 1139 1140
static void tcp_skb_fragment_eor(struct sk_buff *skb, struct sk_buff *skb2)
{
	TCP_SKB_CB(skb2)->eor = TCP_SKB_CB(skb)->eor;
	TCP_SKB_CB(skb)->eor = 0;
}

L
Linus Torvalds 已提交
1141 1142
/* 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
1143
 * packet to the list.  This won't be called frequently, I hope.
L
Linus Torvalds 已提交
1144 1145
 * Remember, these are still headerless SKBs at this point.
 */
1146
int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1147
		 unsigned int mss_now, gfp_t gfp)
L
Linus Torvalds 已提交
1148 1149 1150
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;
1151
	int nsize, old_factor;
1152
	int nlen;
1153
	u8 flags;
L
Linus Torvalds 已提交
1154

1155 1156
	if (WARN_ON(len > skb->len))
		return -EINVAL;
1157

L
Linus Torvalds 已提交
1158 1159 1160 1161
	nsize = skb_headlen(skb) - len;
	if (nsize < 0)
		nsize = 0;

1162
	if (skb_unclone(skb, gfp))
L
Linus Torvalds 已提交
1163 1164 1165
		return -ENOMEM;

	/* Get a new skb... force flag on. */
1166
	buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1167
	if (!buff)
L
Linus Torvalds 已提交
1168
		return -ENOMEM; /* We'll just try again later. */
H
Herbert Xu 已提交
1169

1170 1171
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
1172 1173 1174
	nlen = skb->len - len - nsize;
	buff->truesize += nlen;
	skb->truesize -= nlen;
L
Linus Torvalds 已提交
1175 1176 1177 1178 1179 1180 1181

	/* 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
1182 1183 1184
	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;
1185
	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1186
	tcp_skb_fragment_eor(skb, buff);
L
Linus Torvalds 已提交
1187

1188
	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
L
Linus Torvalds 已提交
1189
		/* Copy and checksum data tail into the new buffer. */
1190 1191
		buff->csum = csum_partial_copy_nocheck(skb->data + len,
						       skb_put(buff, nsize),
L
Linus Torvalds 已提交
1192 1193 1194 1195 1196 1197
						       nsize, 0);

		skb_trim(skb, len);

		skb->csum = csum_block_sub(skb->csum, buff->csum, len);
	} else {
1198
		skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
1199 1200 1201 1202 1203
		skb_split(skb, buff, len);
	}

	buff->ip_summed = skb->ip_summed;

1204
	buff->tstamp = skb->tstamp;
1205
	tcp_fragment_tstamp(skb, buff);
L
Linus Torvalds 已提交
1206

1207 1208
	old_factor = tcp_skb_pcount(skb);

L
Linus Torvalds 已提交
1209
	/* Fix up tso_factor for both original and new SKB.  */
1210 1211
	tcp_set_skb_tso_segs(skb, mss_now);
	tcp_set_skb_tso_segs(buff, mss_now);
L
Linus Torvalds 已提交
1212

1213 1214 1215
	/* If this packet has been sent out already, we must
	 * adjust the various packet counters.
	 */
1216
	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1217 1218
		int diff = old_factor - tcp_skb_pcount(skb) -
			tcp_skb_pcount(buff);
L
Linus Torvalds 已提交
1219

1220 1221
		if (diff)
			tcp_adjust_pcount(sk, skb, diff);
L
Linus Torvalds 已提交
1222 1223 1224
	}

	/* Link BUFF into the send queue. */
1225
	__skb_header_release(buff);
1226
	tcp_insert_write_queue_after(skb, buff, sk);
L
Linus Torvalds 已提交
1227 1228 1229 1230 1231 1232 1233 1234

	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.
 */
1235
static void __pskb_trim_head(struct sk_buff *skb, int len)
L
Linus Torvalds 已提交
1236
{
1237
	struct skb_shared_info *shinfo;
L
Linus Torvalds 已提交
1238 1239
	int i, k, eat;

E
Eric Dumazet 已提交
1240 1241 1242 1243 1244 1245 1246
	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
1247 1248
	eat = len;
	k = 0;
1249 1250 1251
	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
1252 1253

		if (size <= eat) {
1254
			skb_frag_unref(skb, i);
E
Eric Dumazet 已提交
1255
			eat -= size;
L
Linus Torvalds 已提交
1256
		} else {
1257
			shinfo->frags[k] = shinfo->frags[i];
L
Linus Torvalds 已提交
1258
			if (eat) {
1259 1260
				shinfo->frags[k].page_offset += eat;
				skb_frag_size_sub(&shinfo->frags[k], eat);
L
Linus Torvalds 已提交
1261 1262 1263 1264 1265
				eat = 0;
			}
			k++;
		}
	}
1266
	shinfo->nr_frags = k;
L
Linus Torvalds 已提交
1267

1268
	skb_reset_tail_pointer(skb);
L
Linus Torvalds 已提交
1269 1270 1271 1272
	skb->data_len -= len;
	skb->len = skb->data_len;
}

1273
/* Remove acked data from a packet in the transmit queue. */
L
Linus Torvalds 已提交
1274 1275
int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
{
1276
	if (skb_unclone(skb, GFP_ATOMIC))
L
Linus Torvalds 已提交
1277 1278
		return -ENOMEM;

E
Eric Dumazet 已提交
1279
	__pskb_trim_head(skb, len);
L
Linus Torvalds 已提交
1280 1281

	TCP_SKB_CB(skb)->seq += len;
1282
	skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
1283 1284 1285

	skb->truesize	     -= len;
	sk->sk_wmem_queued   -= len;
1286
	sk_mem_uncharge(sk, len);
L
Linus Torvalds 已提交
1287 1288
	sock_set_flag(sk, SOCK_QUEUE_SHRUNK);

1289
	/* Any change of skb->len requires recalculation of tso factor. */
L
Linus Torvalds 已提交
1290
	if (tcp_skb_pcount(skb) > 1)
1291
		tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
L
Linus Torvalds 已提交
1292 1293 1294 1295

	return 0;
}

1296 1297
/* 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
1298
{
1299 1300
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1301 1302 1303 1304 1305 1306 1307
	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);

1308 1309 1310 1311 1312 1313 1314 1315
	/* 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
1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328
	/* 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;
}

1329 1330 1331 1332 1333 1334 1335 1336
/* 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
1337
/* Inverse of above */
1338
int tcp_mss_to_mtu(struct sock *sk, int mss)
J
John Heffner 已提交
1339
{
1340 1341
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1342 1343 1344 1345 1346 1347 1348
	int mtu;

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

1349 1350 1351 1352 1353 1354 1355
	/* 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
1356 1357 1358
	return mtu;
}

1359
/* MTU probing init per socket */
J
John Heffner 已提交
1360 1361 1362 1363
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
1364
	struct net *net = sock_net(sk);
J
John Heffner 已提交
1365

F
Fan Du 已提交
1366
	icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
J
John Heffner 已提交
1367
	icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1368
			       icsk->icsk_af_ops->net_header_len;
F
Fan Du 已提交
1369
	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
J
John Heffner 已提交
1370
	icsk->icsk_mtup.probe_size = 0;
1371 1372
	if (icsk->icsk_mtup.enabled)
		icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
J
John Heffner 已提交
1373
}
E
Eric Dumazet 已提交
1374
EXPORT_SYMBOL(tcp_mtup_init);
J
John Heffner 已提交
1375

L
Linus Torvalds 已提交
1376 1377 1378 1379 1380 1381
/* 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
1382
   It is minimum of user_mss and mss received with SYN.
L
Linus Torvalds 已提交
1383 1384
   It also does not include TCP options.

1385
   inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
L
Linus Torvalds 已提交
1386 1387 1388 1389 1390 1391 1392 1393 1394

   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.

1395 1396
   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
1397 1398 1399 1400
 */
unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
{
	struct tcp_sock *tp = tcp_sk(sk);
1401
	struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1402
	int mss_now;
L
Linus Torvalds 已提交
1403

J
John Heffner 已提交
1404 1405
	if (icsk->icsk_mtup.search_high > pmtu)
		icsk->icsk_mtup.search_high = pmtu;
L
Linus Torvalds 已提交
1406

J
John Heffner 已提交
1407
	mss_now = tcp_mtu_to_mss(sk, pmtu);
1408
	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
L
Linus Torvalds 已提交
1409 1410

	/* And store cached results */
1411
	icsk->icsk_pmtu_cookie = pmtu;
J
John Heffner 已提交
1412 1413
	if (icsk->icsk_mtup.enabled)
		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1414
	tp->mss_cache = mss_now;
L
Linus Torvalds 已提交
1415 1416 1417

	return mss_now;
}
E
Eric Dumazet 已提交
1418
EXPORT_SYMBOL(tcp_sync_mss);
L
Linus Torvalds 已提交
1419 1420 1421 1422

/* Compute the current effective MSS, taking SACKs and IP options,
 * and even PMTU discovery events into account.
 */
I
Ilpo Järvinen 已提交
1423
unsigned int tcp_current_mss(struct sock *sk)
L
Linus Torvalds 已提交
1424
{
1425 1426
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct dst_entry *dst = __sk_dst_get(sk);
1427
	u32 mss_now;
1428
	unsigned int header_len;
A
Adam Langley 已提交
1429 1430
	struct tcp_out_options opts;
	struct tcp_md5sig_key *md5;
1431 1432 1433

	mss_now = tp->mss_cache;

L
Linus Torvalds 已提交
1434 1435
	if (dst) {
		u32 mtu = dst_mtu(dst);
1436
		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
L
Linus Torvalds 已提交
1437 1438 1439
			mss_now = tcp_sync_mss(sk, mtu);
	}

A
Adam Langley 已提交
1440 1441 1442 1443 1444 1445 1446 1447 1448 1449
	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;
	}
1450

L
Linus Torvalds 已提交
1451 1452 1453
	return mss_now;
}

1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475
/* 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;
}

1476
static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1477
{
1478
	struct tcp_sock *tp = tcp_sk(sk);
1479

1480 1481 1482 1483 1484 1485 1486 1487 1488
	/* 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;
	}
1489

1490
	if (tcp_is_cwnd_limited(sk)) {
1491 1492 1493 1494 1495 1496 1497 1498
		/* 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;

1499 1500
		if (sysctl_tcp_slow_start_after_idle &&
		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1501 1502 1503 1504
			tcp_cwnd_application_limited(sk);
	}
}

E
Eric Dumazet 已提交
1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518
/* 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
1519
 */
E
Eric Dumazet 已提交
1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534
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,
1535
			    int nonagle)
E
Eric Dumazet 已提交
1536 1537 1538 1539 1540
{
	return partial &&
		((nonagle & TCP_NAGLE_CORK) ||
		 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
}
E
Eric Dumazet 已提交
1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561

/* 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
1562 1563 1564 1565 1566 1567
/* 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)
1568
{
1569
	const struct tcp_sock *tp = tcp_sk(sk);
E
Eric Dumazet 已提交
1570
	u32 partial, needed, window, max_len;
1571

1572
	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1573
	max_len = mss_now * max_segs;
1574

1575 1576
	if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
		return max_len;
1577

1578 1579
	needed = min(skb->len, window);

1580 1581
	if (max_len <= needed)
		return max_len;
1582

E
Eric Dumazet 已提交
1583 1584 1585 1586 1587
	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
	 */
1588
	if (tcp_nagle_check(partial != 0, tp, nonagle))
E
Eric Dumazet 已提交
1589 1590 1591
		return needed - partial;

	return needed;
1592 1593 1594 1595 1596
}

/* 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.
 */
1597 1598
static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
					 const struct sk_buff *skb)
1599
{
E
Eric Dumazet 已提交
1600
	u32 in_flight, cwnd, halfcwnd;
1601 1602

	/* Don't be strict about the congestion window for the final FIN.  */
E
Eric Dumazet 已提交
1603 1604
	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
	    tcp_skb_pcount(skb) == 1)
1605 1606 1607 1608
		return 1;

	in_flight = tcp_packets_in_flight(tp);
	cwnd = tp->snd_cwnd;
E
Eric Dumazet 已提交
1609 1610
	if (in_flight >= cwnd)
		return 0;
1611

E
Eric Dumazet 已提交
1612 1613 1614 1615 1616
	/* For better scheduling, ensure we have at least
	 * 2 GSO packets in flight.
	 */
	halfcwnd = max(cwnd >> 1, 1U);
	return min(halfcwnd, cwnd - in_flight);
1617 1618
}

1619
/* Initialize TSO state of a skb.
1620
 * This must be invoked the first time we consider transmitting
1621 1622
 * SKB onto the wire.
 */
1623
static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1624 1625 1626
{
	int tso_segs = tcp_skb_pcount(skb);

1627
	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1628
		tcp_set_skb_tso_segs(skb, mss_now);
1629 1630 1631 1632 1633 1634
		tso_segs = tcp_skb_pcount(skb);
	}
	return tso_segs;
}


E
Eric Dumazet 已提交
1635
/* Return true if the Nagle test allows this packet to be
1636 1637
 * sent now.
 */
E
Eric Dumazet 已提交
1638 1639
static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
				  unsigned int cur_mss, int nonagle)
1640 1641 1642 1643 1644 1645 1646 1647
{
	/* 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
1648
		return true;
1649

Y
Yuchung Cheng 已提交
1650 1651
	/* 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
1652
		return true;
1653

1654
	if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
E
Eric Dumazet 已提交
1655
		return true;
1656

E
Eric Dumazet 已提交
1657
	return false;
1658 1659 1660
}

/* Does at least the first segment of SKB fit into the send window? */
E
Eric Dumazet 已提交
1661 1662 1663
static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
			     const struct sk_buff *skb,
			     unsigned int cur_mss)
1664 1665 1666 1667 1668 1669
{
	u32 end_seq = TCP_SKB_CB(skb)->end_seq;

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

1670
	return !after(end_seq, tcp_wnd_end(tp));
1671 1672
}

1673
/* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1674 1675 1676
 * should be put on the wire right now.  If so, it returns the number of
 * packets allowed by the congestion window.
 */
1677
static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1678 1679
				 unsigned int cur_mss, int nonagle)
{
1680
	const struct tcp_sock *tp = tcp_sk(sk);
1681 1682
	unsigned int cwnd_quota;

1683
	tcp_init_tso_segs(skb, cur_mss);
1684 1685 1686 1687 1688

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

	cwnd_quota = tcp_cwnd_test(tp, skb);
1689
	if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1690 1691 1692 1693 1694
		cwnd_quota = 0;

	return cwnd_quota;
}

1695
/* Test if sending is allowed right now. */
E
Eric Dumazet 已提交
1696
bool tcp_may_send_now(struct sock *sk)
1697
{
1698
	const struct tcp_sock *tp = tcp_sk(sk);
1699
	struct sk_buff *skb = tcp_send_head(sk);
1700

E
Eric Dumazet 已提交
1701
	return skb &&
I
Ilpo Järvinen 已提交
1702
		tcp_snd_test(sk, skb, tcp_current_mss(sk),
1703
			     (tcp_skb_is_last(sk, skb) ?
E
Eric Dumazet 已提交
1704
			      tp->nonagle : TCP_NAGLE_PUSH));
1705 1706 1707 1708 1709 1710 1711 1712 1713
}

/* 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).
 */
1714
static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1715
			unsigned int mss_now, gfp_t gfp)
1716 1717 1718
{
	struct sk_buff *buff;
	int nlen = skb->len - len;
1719
	u8 flags;
1720 1721

	/* All of a TSO frame must be composed of paged data.  */
1722
	if (skb->len != skb->data_len)
1723
		return tcp_fragment(sk, skb, len, mss_now, gfp);
1724

1725
	buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1726
	if (unlikely(!buff))
1727 1728
		return -ENOMEM;

1729 1730
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
1731
	buff->truesize += nlen;
1732 1733 1734 1735 1736 1737 1738 1739
	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
1740 1741 1742
	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;
1743 1744 1745 1746

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

1747 1748
	tcp_skb_fragment_eor(skb, buff);

1749
	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1750
	skb_split(skb, buff, len);
1751
	tcp_fragment_tstamp(skb, buff);
1752 1753

	/* Fix up tso_factor for both original and new SKB.  */
1754 1755
	tcp_set_skb_tso_segs(skb, mss_now);
	tcp_set_skb_tso_segs(buff, mss_now);
1756 1757

	/* Link BUFF into the send queue. */
1758
	__skb_header_release(buff);
1759
	tcp_insert_write_queue_after(skb, buff, sk);
1760 1761 1762 1763 1764 1765 1766 1767 1768

	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.
 */
1769
static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
E
Eric Dumazet 已提交
1770
				 bool *is_cwnd_limited, u32 max_segs)
1771
{
1772
	const struct inet_connection_sock *icsk = inet_csk(sk);
1773 1774 1775 1776
	u32 age, send_win, cong_win, limit, in_flight;
	struct tcp_sock *tp = tcp_sk(sk);
	struct skb_mstamp now;
	struct sk_buff *head;
1777
	int win_divisor;
1778

E
Eric Dumazet 已提交
1779
	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
J
John Heffner 已提交
1780
		goto send_now;
1781

1782
	if (icsk->icsk_ca_state >= TCP_CA_Recovery)
J
John Heffner 已提交
1783 1784
		goto send_now;

E
Eric Dumazet 已提交
1785 1786 1787 1788
	/* 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
1789
		goto send_now;
1790

1791 1792
	in_flight = tcp_packets_in_flight(tp);

1793
	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1794

1795
	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1796 1797 1798 1799 1800 1801

	/* 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);

1802
	/* If a full-sized TSO skb can be sent, do it. */
E
Eric Dumazet 已提交
1803
	if (limit >= max_segs * tp->mss_cache)
J
John Heffner 已提交
1804
		goto send_now;
1805

1806 1807 1808 1809
	/* 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;

1810 1811
	win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
	if (win_divisor) {
1812 1813 1814 1815 1816
		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.
		 */
1817
		chunk /= win_divisor;
1818
		if (limit >= chunk)
J
John Heffner 已提交
1819
			goto send_now;
1820 1821 1822 1823 1824 1825
	} 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.
		 */
1826
		if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
J
John Heffner 已提交
1827
			goto send_now;
1828 1829
	}

1830 1831 1832 1833 1834 1835 1836
	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
1837
	/* Ok, it looks like it is advisable to defer. */
J
John Heffner 已提交
1838

1839
	if (cong_win < send_win && cong_win <= skb->len)
1840 1841
		*is_cwnd_limited = true;

E
Eric Dumazet 已提交
1842
	return true;
J
John Heffner 已提交
1843 1844

send_now:
E
Eric Dumazet 已提交
1845
	return false;
1846 1847
}

1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872
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
1873
/* Create a new MTU probe if we are ready.
1874 1875 1876 1877
 * 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
1878 1879
 * Returns 0 if we should wait to probe (no cwnd available),
 *         1 if a probe was sent,
1880 1881
 *         -1 otherwise
 */
J
John Heffner 已提交
1882 1883 1884 1885 1886
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;
1887
	struct net *net = sock_net(sk);
J
John Heffner 已提交
1888 1889
	int len;
	int probe_size;
1890
	int size_needed;
J
John Heffner 已提交
1891 1892
	int copy;
	int mss_now;
1893
	int interval;
J
John Heffner 已提交
1894 1895 1896 1897 1898 1899 1900 1901 1902

	/* 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 ||
1903
	    tp->rx_opt.num_sacks || tp->rx_opt.dsack)
J
John Heffner 已提交
1904 1905
		return -1;

1906 1907 1908 1909
	/* 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
1910
	mss_now = tcp_current_mss(sk);
1911 1912
	probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
				    icsk->icsk_mtup.search_low) >> 1);
1913
	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1914
	interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1915 1916 1917 1918
	/* 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.
	 */
1919
	if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1920 1921 1922 1923 1924
		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
1925 1926 1927 1928
		return -1;
	}

	/* Have enough data in the send queue to probe? */
1929
	if (tp->write_seq - tp->snd_nxt < size_needed)
J
John Heffner 已提交
1930 1931
		return -1;

1932 1933
	if (tp->snd_wnd < size_needed)
		return -1;
1934
	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1935
		return 0;
J
John Heffner 已提交
1936

1937 1938 1939
	/* 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
1940 1941 1942 1943 1944 1945
			return -1;
		else
			return 0;
	}

	/* We're allowed to probe.  Build it now. */
1946
	nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1947
	if (!nskb)
J
John Heffner 已提交
1948
		return -1;
1949 1950
	sk->sk_wmem_queued += nskb->truesize;
	sk_mem_charge(sk, nskb->truesize);
J
John Heffner 已提交
1951

1952
	skb = tcp_send_head(sk);
J
John Heffner 已提交
1953 1954 1955

	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
1956
	TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
J
John Heffner 已提交
1957 1958
	TCP_SKB_CB(nskb)->sacked = 0;
	nskb->csum = 0;
1959
	nskb->ip_summed = skb->ip_summed;
J
John Heffner 已提交
1960

1961 1962
	tcp_insert_write_queue_before(nskb, skb, sk);

J
John Heffner 已提交
1963
	len = 0;
1964
	tcp_for_write_queue_from_safe(skb, next, sk) {
J
John Heffner 已提交
1965 1966 1967 1968 1969
		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,
1970 1971
							    skb_put(nskb, copy),
							    copy, nskb->csum);
J
John Heffner 已提交
1972 1973 1974 1975

		if (skb->len <= copy) {
			/* We've eaten all the data from this skb.
			 * Throw it away. */
E
Eric Dumazet 已提交
1976
			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1977
			tcp_unlink_write_queue(skb, sk);
1978
			sk_wmem_free_skb(sk, skb);
J
John Heffner 已提交
1979
		} else {
E
Eric Dumazet 已提交
1980
			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
C
Changli Gao 已提交
1981
						   ~(TCPHDR_FIN|TCPHDR_PSH);
J
John Heffner 已提交
1982 1983
			if (!skb_shinfo(skb)->nr_frags) {
				skb_pull(skb, copy);
1984
				if (skb->ip_summed != CHECKSUM_PARTIAL)
1985 1986
					skb->csum = csum_partial(skb->data,
								 skb->len, 0);
J
John Heffner 已提交
1987 1988
			} else {
				__pskb_trim_head(skb, copy);
1989
				tcp_set_skb_tso_segs(skb, mss_now);
J
John Heffner 已提交
1990 1991 1992 1993 1994
			}
			TCP_SKB_CB(skb)->seq += copy;
		}

		len += copy;
1995 1996 1997

		if (len >= probe_size)
			break;
J
John Heffner 已提交
1998
	}
1999
	tcp_init_tso_segs(nskb, nskb->len);
J
John Heffner 已提交
2000 2001

	/* We're ready to send.  If this fails, the probe will
E
Eric Dumazet 已提交
2002 2003
	 * be resegmented into mss-sized pieces by tcp_write_xmit().
	 */
J
John Heffner 已提交
2004 2005
	if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
		/* Decrement cwnd here because we are sending
2006
		 * effectively two packets. */
J
John Heffner 已提交
2007
		tp->snd_cwnd--;
2008
		tcp_event_new_data_sent(sk, nskb);
J
John Heffner 已提交
2009 2010

		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2011 2012
		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
2013 2014 2015 2016 2017 2018 2019

		return 1;
	}

	return -1;
}

L
Linus Torvalds 已提交
2020 2021 2022 2023
/* This routine writes packets to the network.  It advances the
 * send_head.  This happens as incoming acks open up the remote
 * window for us.
 *
2024 2025 2026 2027
 * 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
2028 2029 2030
 * 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
2031 2032
 * 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
2033
 */
E
Eric Dumazet 已提交
2034 2035
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
2036 2037
{
	struct tcp_sock *tp = tcp_sk(sk);
2038
	struct sk_buff *skb;
2039 2040
	unsigned int tso_segs, sent_pkts;
	int cwnd_quota;
J
John Heffner 已提交
2041
	int result;
2042
	bool is_cwnd_limited = false;
E
Eric Dumazet 已提交
2043
	u32 max_segs;
L
Linus Torvalds 已提交
2044

2045
	sent_pkts = 0;
J
John Heffner 已提交
2046

2047 2048 2049 2050
	if (!push_one) {
		/* Do MTU probing. */
		result = tcp_mtu_probe(sk);
		if (!result) {
E
Eric Dumazet 已提交
2051
			return false;
2052 2053 2054
		} else if (result > 0) {
			sent_pkts = 1;
		}
J
John Heffner 已提交
2055 2056
	}

E
Eric Dumazet 已提交
2057
	max_segs = tcp_tso_autosize(sk, mss_now);
2058
	while ((skb = tcp_send_head(sk))) {
2059 2060
		unsigned int limit;

2061
		tso_segs = tcp_init_tso_segs(skb, mss_now);
2062
		BUG_ON(!tso_segs);
2063

2064
		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
E
Eric Dumazet 已提交
2065 2066
			/* "skb_mstamp" is used as a start point for the retransmit timer */
			skb_mstamp_get(&skb->skb_mstamp);
2067
			goto repair; /* Skip network transmission */
2068
		}
2069

2070
		cwnd_quota = tcp_cwnd_test(tp, skb);
N
Nandita Dukkipati 已提交
2071 2072 2073 2074 2075 2076 2077
		if (!cwnd_quota) {
			if (push_one == 2)
				/* Force out a loss probe pkt. */
				cwnd_quota = 1;
			else
				break;
		}
2078 2079 2080 2081

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

2082
		if (tso_segs == 1) {
2083 2084 2085 2086 2087
			if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
						     (tcp_skb_is_last(sk, skb) ?
						      nonagle : TCP_NAGLE_PUSH))))
				break;
		} else {
2088
			if (!push_one &&
E
Eric Dumazet 已提交
2089 2090
			    tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
						 max_segs))
2091 2092
				break;
		}
2093

E
Eric Dumazet 已提交
2094
		limit = mss_now;
2095
		if (tso_segs > 1 && !tcp_urg_mode(tp))
E
Eric Dumazet 已提交
2096 2097 2098 2099 2100 2101 2102 2103 2104 2105
			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
2106 2107 2108 2109 2110 2111
		/* 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
2112 2113 2114
		 * 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
2115
		 */
E
Eric Dumazet 已提交
2116 2117
		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
2118 2119

		if (atomic_read(&sk->sk_wmem_alloc) > limit) {
E
Eric Dumazet 已提交
2120
			set_bit(TSQ_THROTTLED, &tp->tsq_flags);
J
John Ogness 已提交
2121 2122 2123 2124
			/* It is possible TX completion already happened
			 * before we set TSQ_THROTTLED, so we must
			 * test again the condition.
			 */
2125
			smp_mb__after_atomic();
J
John Ogness 已提交
2126 2127
			if (atomic_read(&sk->sk_wmem_alloc) > limit)
				break;
E
Eric Dumazet 已提交
2128
		}
E
Eric Dumazet 已提交
2129

2130
		if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2131
			break;
L
Linus Torvalds 已提交
2132

2133
repair:
2134 2135 2136
		/* Advance the send_head.  This one is sent out.
		 * This call will increment packets_out.
		 */
2137
		tcp_event_new_data_sent(sk, skb);
L
Linus Torvalds 已提交
2138

2139
		tcp_minshall_update(tp, mss_now, skb);
2140
		sent_pkts += tcp_skb_pcount(skb);
2141 2142 2143

		if (push_one)
			break;
2144
	}
L
Linus Torvalds 已提交
2145

2146
	if (likely(sent_pkts)) {
2147 2148
		if (tcp_in_cwnd_reduction(sk))
			tp->prr_out += sent_pkts;
N
Nandita Dukkipati 已提交
2149 2150 2151 2152

		/* Send one loss probe per tail loss episode. */
		if (push_one != 2)
			tcp_schedule_loss_probe(sk);
2153
		is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
2154
		tcp_cwnd_validate(sk, is_cwnd_limited);
E
Eric Dumazet 已提交
2155
		return false;
L
Linus Torvalds 已提交
2156
	}
2157
	return !tp->packets_out && tcp_send_head(sk);
N
Nandita Dukkipati 已提交
2158 2159 2160 2161 2162 2163 2164
}

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;
2165
	u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
N
Nandita Dukkipati 已提交
2166 2167 2168 2169 2170 2171 2172 2173 2174 2175 2176

	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.
	 */
2177
	if (tp->fastopen_rsk)
N
Nandita Dukkipati 已提交
2178 2179 2180 2181 2182 2183 2184 2185 2186
		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.
	 */
2187
	if (sysctl_tcp_early_retrans < 3 || !tp->packets_out ||
N
Nandita Dukkipati 已提交
2188 2189 2190 2191 2192 2193 2194 2195
	    !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
2196 2197
	 * 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
2198
	 */
2199
	timeout = rtt << 1 ? : TCP_TIMEOUT_INIT;
N
Nandita Dukkipati 已提交
2200 2201 2202 2203 2204 2205 2206 2207 2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218
	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;
}

2219 2220 2221 2222 2223 2224 2225
/* Thanks to skb fast clones, we can detect if a prior transmit of
 * a packet is still in a qdisc or driver queue.
 * In this case, there is very little point doing a retransmit !
 */
static bool skb_still_in_host_queue(const struct sock *sk,
				    const struct sk_buff *skb)
{
2226
	if (unlikely(skb_fclone_busy(sk, skb))) {
2227 2228
		NET_INC_STATS(sock_net(sk),
			      LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2229 2230 2231 2232 2233
		return true;
	}
	return false;
}

2234
/* When probe timeout (PTO) fires, try send a new segment if possible, else
N
Nandita Dukkipati 已提交
2235 2236 2237 2238
 * retransmit the last segment.
 */
void tcp_send_loss_probe(struct sock *sk)
{
N
Nandita Dukkipati 已提交
2239
	struct tcp_sock *tp = tcp_sk(sk);
N
Nandita Dukkipati 已提交
2240 2241 2242 2243
	struct sk_buff *skb;
	int pcount;
	int mss = tcp_current_mss(sk);

2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255
	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
2256 2257
	}

N
Nandita Dukkipati 已提交
2258 2259 2260 2261
	/* At most one outstanding TLP retransmission. */
	if (tp->tlp_high_seq)
		goto rearm_timer;

N
Nandita Dukkipati 已提交
2262 2263 2264 2265
	/* Retransmit last segment. */
	if (WARN_ON(!skb))
		goto rearm_timer;

2266 2267 2268
	if (skb_still_in_host_queue(sk, skb))
		goto rearm_timer;

N
Nandita Dukkipati 已提交
2269 2270 2271 2272 2273
	pcount = tcp_skb_pcount(skb);
	if (WARN_ON(!pcount))
		goto rearm_timer;

	if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2274 2275
		if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
					  GFP_ATOMIC)))
N
Nandita Dukkipati 已提交
2276
			goto rearm_timer;
2277
		skb = tcp_write_queue_next(sk, skb);
N
Nandita Dukkipati 已提交
2278 2279 2280 2281 2282
	}

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

2283
	if (__tcp_retransmit_skb(sk, skb, 1))
2284
		goto rearm_timer;
N
Nandita Dukkipati 已提交
2285

N
Nandita Dukkipati 已提交
2286
	/* Record snd_nxt for loss detection. */
2287
	tp->tlp_high_seq = tp->snd_nxt;
N
Nandita Dukkipati 已提交
2288

2289
probe_sent:
2290
	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2291 2292
	/* Reset s.t. tcp_rearm_rto will restart timer from now */
	inet_csk(sk)->icsk_pending = 0;
N
Nandita Dukkipati 已提交
2293
rearm_timer:
2294
	tcp_rearm_rto(sk);
L
Linus Torvalds 已提交
2295 2296
}

2297 2298 2299 2300
/* 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.
 */
2301 2302
void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
			       int nonagle)
2303
{
2304 2305 2306 2307 2308 2309 2310
	/* 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;

2311
	if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2312
			   sk_gfp_mask(sk, GFP_ATOMIC)))
2313
		tcp_check_probe_timer(sk);
2314 2315
}

2316 2317 2318 2319 2320
/* 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)
{
2321
	struct sk_buff *skb = tcp_send_head(sk);
2322 2323 2324

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

2325
	tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2326 2327
}

L
Linus Torvalds 已提交
2328 2329
/* This function returns the amount that we can raise the
 * usable window based on the following constraints
2330
 *
L
Linus Torvalds 已提交
2331 2332 2333 2334 2335 2336 2337 2338 2339 2340 2341 2342 2343 2344 2345 2346 2347 2348
 * 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.
2349
 *
L
Linus Torvalds 已提交
2350 2351
 * Of course, if the sender implements sender side SWS prevention
 * then this will not be a problem.
2352
 *
L
Linus Torvalds 已提交
2353
 * BSD seems to make the following compromise:
2354
 *
L
Linus Torvalds 已提交
2355 2356 2357 2358 2359 2360 2361 2362 2363 2364 2365 2366 2367 2368 2369 2370 2371 2372 2373 2374 2375 2376 2377 2378 2379 2380 2381
 *	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)
{
2382
	struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
2383
	struct tcp_sock *tp = tcp_sk(sk);
S
Stephen Hemminger 已提交
2384
	/* MSS for the peer's data.  Previous versions used mss_clamp
L
Linus Torvalds 已提交
2385 2386 2387 2388 2389
	 * 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
	 */
2390
	int mss = icsk->icsk_ack.rcv_mss;
L
Linus Torvalds 已提交
2391
	int free_space = tcp_space(sk);
2392 2393
	int allowed_space = tcp_full_space(sk);
	int full_space = min_t(int, tp->window_clamp, allowed_space);
L
Linus Torvalds 已提交
2394 2395 2396
	int window;

	if (mss > full_space)
2397
		mss = full_space;
L
Linus Torvalds 已提交
2398

2399
	if (free_space < (full_space >> 1)) {
2400
		icsk->icsk_ack.quick = 0;
L
Linus Torvalds 已提交
2401

2402
		if (tcp_under_memory_pressure(sk))
2403 2404
			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
					       4U * tp->advmss);
L
Linus Torvalds 已提交
2405

2406 2407 2408 2409 2410 2411 2412 2413 2414 2415 2416 2417 2418
		/* 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
2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431 2432 2433 2434 2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448
			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)
2449
			window = (free_space / mss) * mss;
2450
		else if (mss == full_space &&
2451
			 free_space > window + (full_space >> 1))
2452
			window = free_space;
L
Linus Torvalds 已提交
2453 2454 2455 2456 2457
	}

	return window;
}

2458 2459
void tcp_skb_collapse_tstamp(struct sk_buff *skb,
			     const struct sk_buff *next_skb)
2460
{
2461 2462 2463
	if (unlikely(tcp_has_tx_tstamp(next_skb))) {
		const struct skb_shared_info *next_shinfo =
			skb_shinfo(next_skb);
2464 2465
		struct skb_shared_info *shinfo = skb_shinfo(skb);

2466
		shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
2467
		shinfo->tskey = next_shinfo->tskey;
2468 2469
		TCP_SKB_CB(skb)->txstamp_ack |=
			TCP_SKB_CB(next_skb)->txstamp_ack;
2470 2471 2472
	}
}

2473 2474
/* 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
2475 2476
{
	struct tcp_sock *tp = tcp_sk(sk);
2477
	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2478
	int skb_size, next_skb_size;
L
Linus Torvalds 已提交
2479

2480 2481
	skb_size = skb->len;
	next_skb_size = next_skb->len;
L
Linus Torvalds 已提交
2482

2483
	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2484

2485
	tcp_highest_sack_combine(sk, next_skb, skb);
L
Linus Torvalds 已提交
2486

2487
	tcp_unlink_write_queue(next_skb, sk);
L
Linus Torvalds 已提交
2488

2489 2490
	skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
				  next_skb_size);
L
Linus Torvalds 已提交
2491

2492 2493
	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
		skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
2494

2495 2496
	if (skb->ip_summed != CHECKSUM_PARTIAL)
		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
L
Linus Torvalds 已提交
2497

2498 2499
	/* 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
2500

2501
	/* Merge over control information. This moves PSH/FIN etc. over */
E
Eric Dumazet 已提交
2502
	TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2503 2504 2505 2506 2507

	/* 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;
2508
	TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor;
2509 2510

	/* changed transmit queue under us so clear hints */
2511 2512 2513
	tcp_clear_retrans_hints_partial(tp);
	if (next_skb == tp->retransmit_skb_hint)
		tp->retransmit_skb_hint = skb;
2514

2515 2516
	tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));

2517 2518
	tcp_skb_collapse_tstamp(skb, next_skb);

2519
	sk_wmem_free_skb(sk, next_skb);
L
Linus Torvalds 已提交
2520 2521
}

2522
/* Check if coalescing SKBs is legal. */
E
Eric Dumazet 已提交
2523
static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2524 2525
{
	if (tcp_skb_pcount(skb) > 1)
E
Eric Dumazet 已提交
2526
		return false;
2527 2528
	/* TODO: SACK collapsing could be used to remove this condition */
	if (skb_shinfo(skb)->nr_frags != 0)
E
Eric Dumazet 已提交
2529
		return false;
2530
	if (skb_cloned(skb))
E
Eric Dumazet 已提交
2531
		return false;
2532
	if (skb == tcp_send_head(sk))
E
Eric Dumazet 已提交
2533
		return false;
2534 2535
	/* 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
2536
		return false;
2537

E
Eric Dumazet 已提交
2538
	return true;
2539 2540
}

2541 2542 2543
/* Collapse packets in the retransmit queue to make to create
 * less packets on the wire. This is only done on retransmission.
 */
2544 2545 2546 2547 2548
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
2549
	bool first = true;
2550 2551 2552

	if (!sysctl_tcp_retrans_collapse)
		return;
E
Eric Dumazet 已提交
2553
	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2554 2555 2556 2557 2558 2559
		return;

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

2560 2561 2562
		if (!tcp_skb_can_collapse_to(to))
			break;

2563 2564 2565
		space -= skb->len;

		if (first) {
E
Eric Dumazet 已提交
2566
			first = false;
2567 2568 2569 2570 2571 2572 2573 2574
			continue;
		}

		if (space < 0)
			break;
		/* Punt if not enough space exists in the first SKB for
		 * the data in the second
		 */
2575
		if (skb->len > skb_availroom(to))
2576 2577 2578 2579 2580 2581 2582 2583 2584
			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
2585 2586 2587 2588
/* 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.
 */
2589
int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
L
Linus Torvalds 已提交
2590
{
J
John Heffner 已提交
2591
	struct inet_connection_sock *icsk = inet_csk(sk);
2592
	struct tcp_sock *tp = tcp_sk(sk);
2593
	unsigned int cur_mss;
2594 2595
	int diff, len, err;

L
Linus Torvalds 已提交
2596

2597 2598
	/* Inconclusive MTU probe */
	if (icsk->icsk_mtup.probe_size)
J
John Heffner 已提交
2599 2600
		icsk->icsk_mtup.probe_size = 0;

L
Linus Torvalds 已提交
2601
	/* Do not sent more than we queued. 1/4 is reserved for possible
S
Stephen Hemminger 已提交
2602
	 * copying overhead: fragmentation, tunneling, mangling etc.
L
Linus Torvalds 已提交
2603 2604 2605 2606 2607
	 */
	if (atomic_read(&sk->sk_wmem_alloc) >
	    min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
		return -EAGAIN;

2608 2609 2610
	if (skb_still_in_host_queue(sk, skb))
		return -EBUSY;

L
Linus Torvalds 已提交
2611 2612 2613 2614 2615 2616 2617
	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;
	}

2618 2619 2620
	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
		return -EHOSTUNREACH; /* Routing failure or similar. */

I
Ilpo Järvinen 已提交
2621
	cur_mss = tcp_current_mss(sk);
2622

L
Linus Torvalds 已提交
2623 2624 2625 2626 2627
	/* 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.
	 */
2628 2629
	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
2630 2631
		return -EAGAIN;

2632 2633 2634
	len = cur_mss * segs;
	if (skb->len > len) {
		if (tcp_fragment(sk, skb, len, cur_mss, GFP_ATOMIC))
L
Linus Torvalds 已提交
2635
			return -ENOMEM; /* We'll try again later. */
2636
	} else {
2637 2638
		if (skb_unclone(skb, GFP_ATOMIC))
			return -ENOMEM;
2639

2640 2641 2642 2643 2644 2645 2646
		diff = tcp_skb_pcount(skb);
		tcp_set_skb_tso_segs(skb, cur_mss);
		diff -= tcp_skb_pcount(skb);
		if (diff)
			tcp_adjust_pcount(sk, skb, diff);
		if (skb->len < cur_mss)
			tcp_retrans_try_collapse(sk, skb, cur_mss);
L
Linus Torvalds 已提交
2647 2648
	}

2649 2650 2651 2652
	/* 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);

2653 2654 2655 2656 2657 2658
	/* 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)) {
2659 2660 2661 2662
		struct sk_buff *nskb;

		skb_mstamp_get(&skb->skb_mstamp);
		nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
2663 2664
		err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
			     -ENOBUFS;
E
Eric Dumazet 已提交
2665
	} else {
2666
		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
E
Eric Dumazet 已提交
2667
	}
2668

2669
	if (likely(!err)) {
2670 2671
		segs = tcp_skb_pcount(skb);

2672
		TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2673
		/* Update global TCP statistics. */
2674
		TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
2675
		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2676
			__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2677
		tp->total_retrans += segs;
2678
	}
2679
	return err;
2680 2681
}

2682
int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2683 2684
{
	struct tcp_sock *tp = tcp_sk(sk);
2685
	int err = __tcp_retransmit_skb(sk, skb, segs);
L
Linus Torvalds 已提交
2686 2687 2688

	if (err == 0) {
#if FASTRETRANS_DEBUG > 0
2689
		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2690
			net_dbg_ratelimited("retrans_out leaked\n");
L
Linus Torvalds 已提交
2691 2692 2693 2694 2695 2696 2697
		}
#endif
		TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
		tp->retrans_out += tcp_skb_pcount(skb);

		/* Save stamp of the first retransmit. */
		if (!tp->retrans_stamp)
E
Eric Dumazet 已提交
2698
			tp->retrans_stamp = tcp_skb_timestamp(skb);
L
Linus Torvalds 已提交
2699

2700
	} else if (err != -EBUSY) {
2701
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
L
Linus Torvalds 已提交
2702
	}
Y
Yuchung Cheng 已提交
2703 2704 2705 2706

	if (tp->undo_retrans < 0)
		tp->undo_retrans = 0;
	tp->undo_retrans += tcp_skb_pcount(skb);
L
Linus Torvalds 已提交
2707 2708 2709
	return err;
}

2710 2711 2712
/* Check if we forward retransmits are possible in the current
 * window/congestion state.
 */
E
Eric Dumazet 已提交
2713
static bool tcp_can_forward_retransmit(struct sock *sk)
2714 2715
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
2716
	const struct tcp_sock *tp = tcp_sk(sk);
2717 2718 2719

	/* Forward retransmissions are possible only during Recovery. */
	if (icsk->icsk_ca_state != TCP_CA_Recovery)
E
Eric Dumazet 已提交
2720
		return false;
2721 2722 2723

	/* No forward retransmissions in Reno are possible. */
	if (tcp_is_reno(tp))
E
Eric Dumazet 已提交
2724
		return false;
2725 2726 2727 2728 2729 2730 2731 2732 2733 2734

	/* 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
2735
		return false;
2736

E
Eric Dumazet 已提交
2737
	return true;
2738 2739
}

L
Linus Torvalds 已提交
2740 2741 2742 2743 2744 2745 2746 2747 2748 2749
/* 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)
{
2750
	const struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
2751 2752
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
2753
	struct sk_buff *hole = NULL;
2754
	u32 last_lost;
2755
	int mib_idx;
2756
	int fwd_rexmitting = 0;
2757

2758 2759 2760
	if (!tp->packets_out)
		return;

2761 2762 2763
	if (!tp->lost_out)
		tp->retransmit_high = tp->snd_una;

2764
	if (tp->retransmit_skb_hint) {
2765
		skb = tp->retransmit_skb_hint;
2766 2767 2768 2769
		last_lost = TCP_SKB_CB(skb)->end_seq;
		if (after(last_lost, tp->retransmit_high))
			last_lost = tp->retransmit_high;
	} else {
2770
		skb = tcp_write_queue_head(sk);
2771 2772
		last_lost = tp->snd_una;
	}
L
Linus Torvalds 已提交
2773

2774 2775
	tcp_for_write_queue_from(skb, sk) {
		__u8 sacked = TCP_SKB_CB(skb)->sacked;
2776
		int segs;
L
Linus Torvalds 已提交
2777

2778 2779 2780
		if (skb == tcp_send_head(sk))
			break;
		/* we could do better than to assign each time */
2781
		if (!hole)
2782
			tp->retransmit_skb_hint = skb;
2783

2784 2785
		segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
		if (segs <= 0)
2786
			return;
L
Linus Torvalds 已提交
2787

2788 2789 2790 2791 2792
		if (fwd_rexmitting) {
begin_fwd:
			if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
				break;
			mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2793

2794
		} else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2795
			tp->retransmit_high = last_lost;
2796 2797 2798
			if (!tcp_can_forward_retransmit(sk))
				break;
			/* Backtrack if necessary to non-L'ed skb */
2799
			if (hole) {
2800 2801 2802 2803 2804
				skb = hole;
				hole = NULL;
			}
			fwd_rexmitting = 1;
			goto begin_fwd;
L
Linus Torvalds 已提交
2805

2806
		} else if (!(sacked & TCPCB_LOST)) {
2807
			if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2808 2809
				hole = skb;
			continue;
L
Linus Torvalds 已提交
2810

2811
		} else {
2812
			last_lost = TCP_SKB_CB(skb)->end_seq;
2813 2814 2815 2816 2817
			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
2818

2819
		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
L
Linus Torvalds 已提交
2820 2821
			continue;

2822
		if (tcp_retransmit_skb(sk, skb, segs))
2823
			return;
2824

2825
		NET_INC_STATS(sock_net(sk), mib_idx);
L
Linus Torvalds 已提交
2826

2827
		if (tcp_in_cwnd_reduction(sk))
2828 2829
			tp->prr_out += tcp_skb_pcount(skb);

2830
		if (skb == tcp_write_queue_head(sk))
2831 2832 2833
			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
						  inet_csk(sk)->icsk_rto,
						  TCP_RTO_MAX);
L
Linus Torvalds 已提交
2834 2835 2836
	}
}

2837 2838
/* We allow to exceed memory limits for FIN packets to expedite
 * connection tear down and (memory) recovery.
2839 2840
 * Otherwise tcp_send_fin() could be tempted to either delay FIN
 * or even be forced to close flow without any FIN.
2841 2842
 * In general, we want to allow one skb per socket to avoid hangs
 * with edge trigger epoll()
2843
 */
2844
void sk_forced_mem_schedule(struct sock *sk, int size)
2845
{
2846
	int amt;
2847 2848 2849 2850 2851

	if (size <= sk->sk_forward_alloc)
		return;
	amt = sk_mem_pages(size);
	sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2852 2853
	sk_memory_allocated_add(sk, amt);

2854 2855
	if (mem_cgroup_sockets_enabled && sk->sk_memcg)
		mem_cgroup_charge_skmem(sk->sk_memcg, amt);
2856 2857
}

2858 2859
/* 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
2860 2861 2862
 */
void tcp_send_fin(struct sock *sk)
{
2863
	struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2864 2865
	struct tcp_sock *tp = tcp_sk(sk);

2866 2867 2868 2869
	/* 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
2870
	 */
2871
	if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
2872 2873 2874
coalesce:
		TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
		TCP_SKB_CB(tskb)->end_seq++;
L
Linus Torvalds 已提交
2875
		tp->write_seq++;
2876 2877 2878 2879 2880 2881 2882 2883 2884 2885
		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
2886
	} else {
2887 2888 2889 2890 2891
		skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
		if (unlikely(!skb)) {
			if (tskb)
				goto coalesce;
			return;
L
Linus Torvalds 已提交
2892
		}
2893
		skb_reserve(skb, MAX_TCP_HEADER);
2894
		sk_forced_mem_schedule(sk, skb->truesize);
L
Linus Torvalds 已提交
2895
		/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2896
		tcp_init_nondata_skb(skb, tp->write_seq,
C
Changli Gao 已提交
2897
				     TCPHDR_ACK | TCPHDR_FIN);
L
Linus Torvalds 已提交
2898 2899
		tcp_queue_skb(sk, skb);
	}
2900
	__tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
L
Linus Torvalds 已提交
2901 2902 2903 2904 2905
}

/* 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
2906
 * by RFC 2525, section 2.17.  -DaveM
L
Linus Torvalds 已提交
2907
 */
A
Al Viro 已提交
2908
void tcp_send_active_reset(struct sock *sk, gfp_t priority)
L
Linus Torvalds 已提交
2909 2910 2911 2912 2913 2914
{
	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
2915
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
L
Linus Torvalds 已提交
2916 2917 2918 2919 2920
		return;
	}

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, MAX_TCP_HEADER);
2921
	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
C
Changli Gao 已提交
2922
			     TCPHDR_ACK | TCPHDR_RST);
2923
	skb_mstamp_get(&skb->skb_mstamp);
L
Linus Torvalds 已提交
2924
	/* Send it off. */
2925
	if (tcp_transmit_skb(sk, skb, 0, priority))
P
Pavel Emelyanov 已提交
2926
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2927

P
Pavel Emelyanov 已提交
2928
	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
L
Linus Torvalds 已提交
2929 2930
}

2931 2932
/* 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
2933 2934 2935 2936 2937 2938
 * 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)
{
2939
	struct sk_buff *skb;
L
Linus Torvalds 已提交
2940

2941
	skb = tcp_write_queue_head(sk);
2942
	if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2943
		pr_debug("%s: wrong queue state\n", __func__);
L
Linus Torvalds 已提交
2944 2945
		return -EFAULT;
	}
E
Eric Dumazet 已提交
2946
	if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
L
Linus Torvalds 已提交
2947 2948
		if (skb_cloned(skb)) {
			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2949
			if (!nskb)
L
Linus Torvalds 已提交
2950
				return -ENOMEM;
2951
			tcp_unlink_write_queue(skb, sk);
2952
			__skb_header_release(nskb);
2953
			__tcp_add_write_queue_head(sk, nskb);
2954 2955 2956
			sk_wmem_free_skb(sk, skb);
			sk->sk_wmem_queued += nskb->truesize;
			sk_mem_charge(sk, nskb->truesize);
L
Linus Torvalds 已提交
2957 2958 2959
			skb = nskb;
		}

E
Eric Dumazet 已提交
2960
		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2961
		tcp_ecn_send_synack(sk, skb);
L
Linus Torvalds 已提交
2962
	}
2963
	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
L
Linus Torvalds 已提交
2964 2965
}

2966 2967 2968 2969 2970 2971 2972 2973 2974
/**
 * 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.
 */
2975
struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
2976
				struct request_sock *req,
2977
				struct tcp_fastopen_cookie *foc,
2978
				enum tcp_synack_type synack_type)
L
Linus Torvalds 已提交
2979
{
2980
	struct inet_request_sock *ireq = inet_rsk(req);
2981
	const struct tcp_sock *tp = tcp_sk(sk);
E
Eric Dumazet 已提交
2982
	struct tcp_md5sig_key *md5 = NULL;
2983 2984
	struct tcp_out_options opts;
	struct sk_buff *skb;
2985
	int tcp_header_size;
2986 2987
	struct tcphdr *th;
	u16 user_mss;
2988
	int mss;
L
Linus Torvalds 已提交
2989

2990
	skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
2991 2992
	if (unlikely(!skb)) {
		dst_release(dst);
L
Linus Torvalds 已提交
2993
		return NULL;
2994
	}
L
Linus Torvalds 已提交
2995 2996 2997
	/* Reserve space for headers. */
	skb_reserve(skb, MAX_TCP_HEADER);

2998 2999
	switch (synack_type) {
	case TCP_SYNACK_NORMAL:
3000
		skb_set_owner_w(skb, req_to_sk(req));
3001 3002 3003 3004 3005 3006 3007
		break;
	case TCP_SYNACK_COOKIE:
		/* Under synflood, we do not attach skb to a socket,
		 * to avoid false sharing.
		 */
		break;
	case TCP_SYNACK_FASTOPEN:
3008 3009 3010 3011 3012
		/* sk is a const pointer, because we want to express multiple
		 * cpu might call us concurrently.
		 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
		 */
		skb_set_owner_w(skb, (struct sock *)sk);
3013
		break;
3014
	}
3015
	skb_dst_set(skb, dst);
L
Linus Torvalds 已提交
3016

3017
	mss = dst_metric_advmss(dst);
3018 3019 3020
	user_mss = READ_ONCE(tp->rx_opt.user_mss);
	if (user_mss && user_mss < mss)
		mss = user_mss;
3021

A
Adam Langley 已提交
3022
	memset(&opts, 0, sizeof(opts));
3023 3024
#ifdef CONFIG_SYN_COOKIES
	if (unlikely(req->cookie_ts))
E
Eric Dumazet 已提交
3025
		skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
3026 3027
	else
#endif
E
Eric Dumazet 已提交
3028
	skb_mstamp_get(&skb->skb_mstamp);
E
Eric Dumazet 已提交
3029 3030 3031

#ifdef CONFIG_TCP_MD5SIG
	rcu_read_lock();
3032
	md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
E
Eric Dumazet 已提交
3033
#endif
3034
	skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
3035 3036
	tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
			  sizeof(*th);
3037

3038 3039
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
L
Linus Torvalds 已提交
3040

3041
	th = (struct tcphdr *)skb->data;
L
Linus Torvalds 已提交
3042 3043 3044
	memset(th, 0, sizeof(struct tcphdr));
	th->syn = 1;
	th->ack = 1;
3045
	tcp_ecn_make_synack(req, th);
E
Eric Dumazet 已提交
3046
	th->source = htons(ireq->ir_num);
3047
	th->dest = ireq->ir_rmt_port;
3048 3049 3050 3051
	/* 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
3052
			     TCPHDR_SYN | TCPHDR_ACK);
3053

L
Linus Torvalds 已提交
3054
	th->seq = htonl(TCP_SKB_CB(skb)->seq);
3055 3056
	/* 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
3057 3058

	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3059
	th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3060
	tcp_options_write((__be32 *)(th + 1), NULL, &opts);
L
Linus Torvalds 已提交
3061
	th->doff = (tcp_header_size >> 2);
E
Eric Dumazet 已提交
3062
	__TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
3063 3064 3065

#ifdef CONFIG_TCP_MD5SIG
	/* Okay, we have all we need - do the md5 hash if needed */
E
Eric Dumazet 已提交
3066
	if (md5)
3067
		tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3068
					       md5, req_to_sk(req), skb);
E
Eric Dumazet 已提交
3069
	rcu_read_unlock();
3070 3071
#endif

3072 3073
	/* Do not fool tcpdump (if any), clean our debris */
	skb->tstamp.tv64 = 0;
L
Linus Torvalds 已提交
3074 3075
	return skb;
}
E
Eric Dumazet 已提交
3076
EXPORT_SYMBOL(tcp_make_synack);
L
Linus Torvalds 已提交
3077

3078 3079 3080 3081 3082 3083 3084 3085 3086 3087 3088 3089 3090 3091 3092 3093 3094 3095 3096
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();
}

3097
/* Do all connect socket setups that can be done AF independent. */
3098
static void tcp_connect_init(struct sock *sk)
L
Linus Torvalds 已提交
3099
{
3100
	const struct dst_entry *dst = __sk_dst_get(sk);
L
Linus Torvalds 已提交
3101 3102 3103 3104 3105 3106 3107
	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) +
3108
		(sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
L
Linus Torvalds 已提交
3109

3110
#ifdef CONFIG_TCP_MD5SIG
3111
	if (tp->af_specific->md5_lookup(sk, sk))
3112 3113 3114
		tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
#endif

L
Linus Torvalds 已提交
3115 3116 3117 3118
	/* 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
3119
	tcp_mtup_init(sk);
L
Linus Torvalds 已提交
3120 3121
	tcp_sync_mss(sk, dst_mtu(dst));

3122 3123
	tcp_ca_dst_init(sk, dst);

L
Linus Torvalds 已提交
3124 3125
	if (!tp->window_clamp)
		tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3126
	tp->advmss = dst_metric_advmss(dst);
3127 3128 3129
	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
3130 3131
	tcp_initialize_rcv_mss(sk);

3132 3133 3134 3135 3136
	/* 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
3137 3138 3139 3140
	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,
3141
				  sysctl_tcp_window_scaling,
3142 3143
				  &rcv_wscale,
				  dst_metric(dst, RTAX_INITRWND));
L
Linus Torvalds 已提交
3144 3145 3146 3147 3148 3149 3150

	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;
3151
	tcp_init_wl(tp, 0);
L
Linus Torvalds 已提交
3152 3153
	tp->snd_una = tp->write_seq;
	tp->snd_sml = tp->write_seq;
I
Ilpo Järvinen 已提交
3154
	tp->snd_up = tp->write_seq;
P
Pavel Emelyanov 已提交
3155
	tp->snd_nxt = tp->write_seq;
P
Pavel Emelyanov 已提交
3156 3157 3158

	if (likely(!tp->repair))
		tp->rcv_nxt = 0;
3159 3160
	else
		tp->rcv_tstamp = tcp_time_stamp;
P
Pavel Emelyanov 已提交
3161 3162
	tp->rcv_wup = tp->rcv_nxt;
	tp->copied_seq = tp->rcv_nxt;
L
Linus Torvalds 已提交
3163

3164 3165
	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
	inet_csk(sk)->icsk_retransmits = 0;
L
Linus Torvalds 已提交
3166 3167 3168
	tcp_clear_retrans(tp);
}

3169 3170 3171 3172 3173 3174
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;
3175
	__skb_header_release(skb);
3176 3177 3178 3179 3180 3181 3182 3183 3184 3185 3186 3187 3188 3189 3190 3191 3192 3193
	__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;
3194
	int syn_loss = 0, space, err = 0;
3195
	unsigned long last_syn_loss = 0;
3196
	struct sk_buff *syn_data;
3197

3198
	tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
3199 3200 3201 3202 3203 3204 3205 3206
	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;
	}
3207

3208 3209 3210
	if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
		fo->cookie.len = -1;
	else if (fo->cookie.len <= 0)
3211 3212 3213 3214 3215 3216 3217 3218
		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;
3219
	space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3220 3221
		MAX_TCP_OPTION_SPACE;

3222 3223 3224 3225 3226
	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));

3227
	syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3228
	if (!syn_data)
3229
		goto fallback;
3230 3231
	syn_data->ip_summed = CHECKSUM_PARTIAL;
	memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3232 3233 3234 3235 3236 3237 3238 3239 3240 3241 3242
	if (space) {
		int copied = copy_from_iter(skb_put(syn_data, space), space,
					    &fo->data->msg_iter);
		if (unlikely(!copied)) {
			kfree_skb(syn_data);
			goto fallback;
		}
		if (copied != space) {
			skb_trim(syn_data, copied);
			space = copied;
		}
3243
	}
3244 3245 3246 3247
	/* No more data pending in inet_wait_for_connect() */
	if (space == fo->size)
		fo->data = NULL;
	fo->copied = space;
3248

3249
	tcp_connect_queue_skb(sk, syn_data);
3250

3251
	err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3252

3253
	syn->skb_mstamp = syn_data->skb_mstamp;
E
Eric Dumazet 已提交
3254

3255 3256 3257 3258 3259 3260 3261 3262
	/* 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) {
3263
		tp->syn_data = (fo->copied > 0);
3264
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3265 3266 3267 3268 3269 3270 3271 3272 3273 3274 3275 3276 3277 3278 3279
		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;
}

3280
/* Build a SYN and send it off. */
L
Linus Torvalds 已提交
3281 3282 3283 3284
int tcp_connect(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;
3285
	int err;
L
Linus Torvalds 已提交
3286 3287 3288

	tcp_connect_init(sk);

A
Andrey Vagin 已提交
3289 3290 3291 3292 3293
	if (unlikely(tp->repair)) {
		tcp_finish_connect(sk, NULL);
		return 0;
	}

3294
	buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3295
	if (unlikely(!buff))
L
Linus Torvalds 已提交
3296 3297
		return -ENOBUFS;

C
Changli Gao 已提交
3298
	tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
E
Eric Dumazet 已提交
3299
	tp->retrans_stamp = tcp_time_stamp;
3300
	tcp_connect_queue_skb(sk, buff);
3301
	tcp_ecn_send_syn(sk, buff);
L
Linus Torvalds 已提交
3302

3303 3304 3305
	/* 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);
3306 3307
	if (err == -ECONNREFUSED)
		return err;
3308 3309 3310 3311 3312 3313

	/* 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
3314
	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
L
Linus Torvalds 已提交
3315 3316

	/* Timer for repeating the SYN until an answer. */
3317 3318
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
L
Linus Torvalds 已提交
3319 3320
	return 0;
}
E
Eric Dumazet 已提交
3321
EXPORT_SYMBOL(tcp_connect);
L
Linus Torvalds 已提交
3322 3323 3324 3325 3326 3327 3328

/* 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)
{
3329 3330
	struct inet_connection_sock *icsk = inet_csk(sk);
	int ato = icsk->icsk_ack.ato;
L
Linus Torvalds 已提交
3331 3332
	unsigned long timeout;

3333 3334
	tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);

L
Linus Torvalds 已提交
3335
	if (ato > TCP_DELACK_MIN) {
3336
		const struct tcp_sock *tp = tcp_sk(sk);
3337
		int max_ato = HZ / 2;
L
Linus Torvalds 已提交
3338

3339 3340
		if (icsk->icsk_ack.pingpong ||
		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
L
Linus Torvalds 已提交
3341 3342 3343 3344 3345
			max_ato = TCP_DELACK_MAX;

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

		/* If some rtt estimate is known, use it to bound delayed ack.
3346
		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
L
Linus Torvalds 已提交
3347 3348
		 * directly.
		 */
3349 3350 3351
		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
3352 3353 3354 3355 3356 3357 3358 3359 3360 3361 3362 3363

			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. */
3364
	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
L
Linus Torvalds 已提交
3365 3366 3367
		/* If delack timer was blocked or is about to expire,
		 * send ACK now.
		 */
3368 3369
		if (icsk->icsk_ack.blocked ||
		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
L
Linus Torvalds 已提交
3370 3371 3372 3373
			tcp_send_ack(sk);
			return;
		}

3374 3375
		if (!time_before(timeout, icsk->icsk_ack.timeout))
			timeout = icsk->icsk_ack.timeout;
L
Linus Torvalds 已提交
3376
	}
3377 3378 3379
	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
3380 3381 3382 3383 3384
}

/* This routine sends an ack and also updates the window. */
void tcp_send_ack(struct sock *sk)
{
3385
	struct sk_buff *buff;
L
Linus Torvalds 已提交
3386

3387 3388 3389
	/* If we have been reset, we may not send again. */
	if (sk->sk_state == TCP_CLOSE)
		return;
L
Linus Torvalds 已提交
3390

3391 3392
	tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);

3393 3394 3395 3396
	/* We are not putting this on the write queue, so
	 * tcp_transmit_skb() will set the ownership to this
	 * sock.
	 */
3397 3398 3399
	buff = alloc_skb(MAX_TCP_HEADER,
			 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
	if (unlikely(!buff)) {
3400 3401 3402 3403 3404
		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
3405
	}
3406 3407 3408

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(buff, MAX_TCP_HEADER);
C
Changli Gao 已提交
3409
	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3410

E
Eric Dumazet 已提交
3411 3412 3413 3414 3415 3416 3417 3418
	/* 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);

3419
	/* Send it off, this clears delayed acks for us. */
E
Eric Dumazet 已提交
3420
	skb_mstamp_get(&buff->skb_mstamp);
3421
	tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0);
L
Linus Torvalds 已提交
3422
}
3423
EXPORT_SYMBOL_GPL(tcp_send_ack);
L
Linus Torvalds 已提交
3424 3425 3426 3427 3428 3429 3430 3431 3432 3433 3434 3435

/* 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.
 */
3436
static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
L
Linus Torvalds 已提交
3437 3438 3439 3440 3441
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;

	/* We don't queue it, tcp_transmit_skb() sets ownership. */
3442 3443
	skb = alloc_skb(MAX_TCP_HEADER,
			sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3444
	if (!skb)
L
Linus Torvalds 已提交
3445 3446 3447 3448 3449 3450 3451 3452
		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
3453
	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
E
Eric Dumazet 已提交
3454
	skb_mstamp_get(&skb->skb_mstamp);
3455
	NET_INC_STATS(sock_net(sk), mib);
3456
	return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0);
L
Linus Torvalds 已提交
3457 3458
}

P
Pavel Emelyanov 已提交
3459 3460 3461 3462
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;
3463
		tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
P
Pavel Emelyanov 已提交
3464 3465 3466
	}
}

3467
/* Initiate keepalive or window probe from timer. */
3468
int tcp_write_wakeup(struct sock *sk, int mib)
L
Linus Torvalds 已提交
3469
{
3470 3471
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
L
Linus Torvalds 已提交
3472

3473 3474 3475
	if (sk->sk_state == TCP_CLOSE)
		return -1;

3476 3477
	skb = tcp_send_head(sk);
	if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3478
		int err;
I
Ilpo Järvinen 已提交
3479
		unsigned int mss = tcp_current_mss(sk);
3480 3481 3482 3483 3484 3485 3486 3487 3488 3489 3490 3491
		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
3492
			TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3493
			if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3494 3495
				return -1;
		} else if (!tcp_skb_pcount(skb))
3496
			tcp_set_skb_tso_segs(skb, mss);
3497

E
Eric Dumazet 已提交
3498
		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3499 3500 3501 3502 3503
		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
3504
		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3505 3506
			tcp_xmit_probe_skb(sk, 1, mib);
		return tcp_xmit_probe_skb(sk, 0, mib);
L
Linus Torvalds 已提交
3507 3508 3509 3510 3511 3512 3513 3514
	}
}

/* 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)
{
3515
	struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
3516
	struct tcp_sock *tp = tcp_sk(sk);
3517
	struct net *net = sock_net(sk);
3518
	unsigned long probe_max;
L
Linus Torvalds 已提交
3519 3520
	int err;

3521
	err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
L
Linus Torvalds 已提交
3522

3523
	if (tp->packets_out || !tcp_send_head(sk)) {
L
Linus Torvalds 已提交
3524
		/* Cancel probe timer, if it is not required. */
3525
		icsk->icsk_probes_out = 0;
3526
		icsk->icsk_backoff = 0;
L
Linus Torvalds 已提交
3527 3528 3529 3530
		return;
	}

	if (err <= 0) {
3531
		if (icsk->icsk_backoff < net->ipv4.sysctl_tcp_retries2)
3532
			icsk->icsk_backoff++;
3533
		icsk->icsk_probes_out++;
3534
		probe_max = TCP_RTO_MAX;
L
Linus Torvalds 已提交
3535 3536
	} else {
		/* If packet was not sent due to local congestion,
3537
		 * do not backoff and do not remember icsk_probes_out.
L
Linus Torvalds 已提交
3538 3539 3540 3541
		 * Let local senders to fight for local resources.
		 *
		 * Use accumulated backoff yet.
		 */
3542 3543
		if (!icsk->icsk_probes_out)
			icsk->icsk_probes_out = 1;
3544
		probe_max = TCP_RESOURCE_PROBE_INTERVAL;
L
Linus Torvalds 已提交
3545
	}
3546
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3547
				  tcp_probe0_when(sk, probe_max),
3548
				  TCP_RTO_MAX);
L
Linus Torvalds 已提交
3549
}
3550

3551
int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
3552 3553 3554 3555 3556
{
	const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
	struct flowi fl;
	int res;

3557
	tcp_rsk(req)->txhash = net_tx_rndhash();
3558
	res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL);
3559
	if (!res) {
E
Eric Dumazet 已提交
3560
		__TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
3561
		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3562 3563 3564 3565
	}
	return res;
}
EXPORT_SYMBOL(tcp_rtx_synack);