// SPDX-License-Identifier: GPL-2.0-only

  /*
   * INET		An implementation of the TCP/IP protocol suite for the LINUX
   *		operating system.  INET is implemented using the  BSD Socket
   *		interface as the means of communication with the user level.
   *
   *		Implementation of the Transmission Control Protocol(TCP).
   *

   * Authors:	Ross Biro

   *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
   *		Mark Evans, <evansmp@uhura.aston.ac.uk>
   *		Corey Minyard <wf-rch!minyard@relay.EU.net>
   *		Florian La Roche, <flla@stud.uni-sb.de>
   *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
   *		Linus Torvalds, <torvalds@cs.helsinki.fi>
   *		Alan Cox, <gw4pts@gw4pts.ampr.org>
   *		Matthew Dillon, <dillon@apollo.west.oic.com>
   *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
   *		Jorge Cwik, <jorge@laser.satlink.net>
   */
  
  #include <linux/module.h>

  #include <linux/gfp.h>

  #include <net/tcp.h>

  static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	u32 elapsed, start_ts;

  	s32 remaining;

  	start_ts = tcp_sk(sk)->retrans_stamp;
  	if (!icsk->icsk_user_timeout)

  		return icsk->icsk_rto;
  	elapsed = tcp_time_stamp(tcp_sk(sk)) - start_ts;

  	remaining = icsk->icsk_user_timeout - elapsed;
  	if (remaining <= 0)

  		return 1; /* user timeout has passed; fire ASAP */

  
  	return min_t(u32, icsk->icsk_rto, msecs_to_jiffies(remaining));

  }

  /**
   *  tcp_write_err() - close socket and save error info
   *  @sk:  The socket the error has appeared on.
   *
   *  Returns: Nothing (void)
   */

  static void tcp_write_err(struct sock *sk)
  {
  	sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  	sk->sk_error_report(sk);

  	tcp_write_queue_purge(sk);

  	tcp_done(sk);

  	__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);

  }

  /**
   *  tcp_out_of_resources() - Close socket if out of resources
   *  @sk:        pointer to current socket
   *  @do_reset:  send a last packet with reset flag

   *

   *  Do not allow orphaned sockets to eat all our resources.
   *  This is direct violation of TCP specs, but it is required
   *  to prevent DoS attacks. It is called when a retransmission timeout
   *  or zero probe timeout occurs on orphaned socket.
   *

   *  Also close if our net namespace is exiting; in that case there is no
   *  hope of ever communicating again since all netns interfaces are already
   *  down (or about to be down), and we need to release our dst references,
   *  which have been moved to the netns loopback interface, so the namespace
   *  can finish exiting.  This condition is only possible if we are a kernel
   *  socket, as those do not hold references to the namespace.
   *

   *  Criteria is still not confirmed experimentally and may change.
   *  We kill the socket, if:
   *  1. If number of orphaned sockets exceeds an administratively configured
   *     limit.
   *  2. If we have strong memory pressure.

   *  3. If our net namespace is exiting.

   */

  static int tcp_out_of_resources(struct sock *sk, bool do_reset)

  {
  	struct tcp_sock *tp = tcp_sk(sk);

  	int shift = 0;

  	/* If peer does not open window for long time, or did not transmit

  	 * anything for long time, penalize it. */

  	if ((s32)(tcp_jiffies32 - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)

  		shift++;

  
  	/* If some dubious ICMP arrived, penalize even more. */
  	if (sk->sk_err_soft)

  		shift++;

  	if (tcp_check_oom(sk, shift)) {

  		/* Catch exceptional cases, when connection requires reset.
  		 *      1. Last segment was sent recently. */

  		if ((s32)(tcp_jiffies32 - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||

  		    /*  2. Window is closed. */
  		    (!tp->snd_wnd && !tp->packets_out))

  			do_reset = true;

  		if (do_reset)
  			tcp_send_active_reset(sk, GFP_ATOMIC);
  		tcp_done(sk);

  		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);

  		return 1;
  	}

  
  	if (!check_net(sock_net(sk))) {
  		/* Not possible to send reset; just close */
  		tcp_done(sk);
  		return 1;
  	}

  	return 0;
  }

  /**
   *  tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket
   *  @sk:    Pointer to the current socket.
   *  @alive: bool, socket alive state
   */

  static int tcp_orphan_retries(struct sock *sk, bool alive)

  {

  	int retries = sock_net(sk)->ipv4.sysctl_tcp_orphan_retries; /* May be zero. */

  
  	/* We know from an ICMP that something is wrong. */
  	if (sk->sk_err_soft && !alive)
  		retries = 0;
  
  	/* However, if socket sent something recently, select some safe
  	 * number of retries. 8 corresponds to >100 seconds with minimal
  	 * RTO of 200msec. */
  	if (retries == 0 && alive)
  		retries = 8;
  	return retries;
  }

  static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
  {

  	const struct net *net = sock_net(sk);
  	int mss;

  	/* Black hole detection */

  	if (!net->ipv4.sysctl_tcp_mtu_probing)
  		return;
  
  	if (!icsk->icsk_mtup.enabled) {
  		icsk->icsk_mtup.enabled = 1;
  		icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
  	} else {
  		mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
  		mss = min(net->ipv4.sysctl_tcp_base_mss, mss);

  		mss = max(mss, net->ipv4.sysctl_tcp_mtu_probe_floor);

  		mss = max(mss, net->ipv4.sysctl_tcp_min_snd_mss);

  		icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);

  	}

  	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);

  }

  static unsigned int tcp_model_timeout(struct sock *sk,
  				      unsigned int boundary,
  				      unsigned int rto_base)
  {
  	unsigned int linear_backoff_thresh, timeout;
  
  	linear_backoff_thresh = ilog2(TCP_RTO_MAX / rto_base);
  	if (boundary <= linear_backoff_thresh)
  		timeout = ((2 << boundary) - 1) * rto_base;
  	else
  		timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
  			(boundary - linear_backoff_thresh) * TCP_RTO_MAX;
  	return jiffies_to_msecs(timeout);
  }

  /**
   *  retransmits_timed_out() - returns true if this connection has timed out
   *  @sk:       The current socket
   *  @boundary: max number of retransmissions
   *  @timeout:  A custom timeout value.
   *             If set to 0 the default timeout is calculated and used.
   *             Using TCP_RTO_MIN and the number of unsuccessful retransmits.

   *
   * The default "timeout" value this function can calculate and use
   * is equivalent to the timeout of a TCP Connection
   * after "boundary" unsuccessful, exponentially backed-off

   * retransmissions with an initial RTO of TCP_RTO_MIN.

   */
  static bool retransmits_timed_out(struct sock *sk,

  				  unsigned int boundary,

  				  unsigned int timeout)

  {

  	unsigned int start_ts;

  
  	if (!inet_csk(sk)->icsk_retransmits)
  		return false;

  	start_ts = tcp_sk(sk)->retrans_stamp;

  	if (likely(timeout == 0)) {
  		unsigned int rto_base = TCP_RTO_MIN;
  
  		if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))
  			rto_base = tcp_timeout_init(sk);
  		timeout = tcp_model_timeout(sk, boundary, rto_base);
  	}

  	return (s32)(tcp_time_stamp(tcp_sk(sk)) - start_ts - timeout) >= 0;

  }

  /* A write timeout has occurred. Process the after effects. */
  static int tcp_write_timeout(struct sock *sk)
  {

  	struct inet_connection_sock *icsk = inet_csk(sk);

  	struct tcp_sock *tp = tcp_sk(sk);

  	struct net *net = sock_net(sk);

  	bool expired = false, do_reset;

  	int retry_until;
  
  	if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {

  		if (icsk->icsk_retransmits) {

  			dst_negative_advice(sk);

  		} else {

  			sk_rethink_txhash(sk);

  		}

  		retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;

  		expired = icsk->icsk_retransmits >= retry_until;

  	} else {

  		if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0)) {

  			/* Black hole detection */

  			tcp_mtu_probing(icsk, sk);

  			dst_negative_advice(sk);

  		} else {
  			sk_rethink_txhash(sk);

  		}

  		retry_until = net->ipv4.sysctl_tcp_retries2;

  		if (sock_flag(sk, SOCK_DEAD)) {

  			const bool alive = icsk->icsk_rto < TCP_RTO_MAX;

  			retry_until = tcp_orphan_retries(sk, alive);

  			do_reset = alive ||

  				!retransmits_timed_out(sk, retry_until, 0);

  			if (tcp_out_of_resources(sk, do_reset))

  				return 1;
  		}

  	}
  	if (!expired)

  		expired = retransmits_timed_out(sk, retry_until,
  						icsk->icsk_user_timeout);

  	tcp_fastopen_active_detect_blackhole(sk, expired);

  
  	if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RTO_CB_FLAG))
  		tcp_call_bpf_3arg(sk, BPF_SOCK_OPS_RTO_CB,
  				  icsk->icsk_retransmits,
  				  icsk->icsk_rto, (int)expired);

  	if (expired) {

  		/* Has it gone just too far? */
  		tcp_write_err(sk);
  		return 1;
  	}

  	return 0;
  }

  /* Called with BH disabled */

  void tcp_delack_timer_handler(struct sock *sk)

  {

  	struct inet_connection_sock *icsk = inet_csk(sk);

  	sk_mem_reclaim_partial(sk);

  	if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
  	    !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))

  		goto out;

  	if (time_after(icsk->icsk_ack.timeout, jiffies)) {
  		sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);

  		goto out;
  	}

  	icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;

  	if (inet_csk_ack_scheduled(sk)) {

  		if (!inet_csk_in_pingpong_mode(sk)) {

  			/* Delayed ACK missed: inflate ATO. */

  			icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);

  		} else {
  			/* Delayed ACK missed: leave pingpong mode and
  			 * deflate ATO.
  			 */

  			inet_csk_exit_pingpong_mode(sk);

  			icsk->icsk_ack.ato      = TCP_ATO_MIN;

  		}

  		tcp_mstamp_refresh(tcp_sk(sk));

  		tcp_send_ack(sk);

  		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);

  	}

  
  out:

  	if (tcp_under_memory_pressure(sk))

  		sk_mem_reclaim(sk);

  }

  
  /**
   *  tcp_delack_timer() - The TCP delayed ACK timeout handler
   *  @data:  Pointer to the current socket. (gets casted to struct sock *)
   *
   *  This function gets (indirectly) called when the kernel timer for a TCP packet
   *  of this socket expires. Calls tcp_delack_timer_handler() to do the actual work.
   *
   *  Returns: Nothing (void)
   */

  static void tcp_delack_timer(struct timer_list *t)

  {

  	struct inet_connection_sock *icsk =
  			from_timer(icsk, t, icsk_delack_timer);
  	struct sock *sk = &icsk->icsk_inet.sk;

  
  	bh_lock_sock(sk);
  	if (!sock_owned_by_user(sk)) {
  		tcp_delack_timer_handler(sk);
  	} else {

  		icsk->icsk_ack.blocked = 1;

  		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);

  		/* deleguate our work to tcp_release_cb() */

  		if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &sk->sk_tsq_flags))

  			sock_hold(sk);

  	}

  	bh_unlock_sock(sk);
  	sock_put(sk);
  }
  
  static void tcp_probe_timer(struct sock *sk)
  {

  	struct inet_connection_sock *icsk = inet_csk(sk);

  	struct sk_buff *skb = tcp_send_head(sk);

  	struct tcp_sock *tp = tcp_sk(sk);
  	int max_probes;

  	if (tp->packets_out || !skb) {

  		icsk->icsk_probes_out = 0;

  		return;
  	}

  	/* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
  	 * long as the receiver continues to respond probes. We support this by
  	 * default and reset icsk_probes_out with incoming ACKs. But if the
  	 * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
  	 * kill the socket when the retry count and the time exceeds the
  	 * corresponding system limit. We also implement similar policy when
  	 * we use RTO to probe window in tcp_retransmit_timer().

  	 */

  	if (icsk->icsk_user_timeout) {
  		u32 elapsed = tcp_model_timeout(sk, icsk->icsk_probes_out,
  						tcp_probe0_base(sk));
  
  		if (elapsed >= icsk->icsk_user_timeout)
  			goto abort;
  	}

  	max_probes = sock_net(sk)->ipv4.sysctl_tcp_retries2;

  	if (sock_flag(sk, SOCK_DEAD)) {

  		const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX;

  		max_probes = tcp_orphan_retries(sk, alive);

  		if (!alive && icsk->icsk_backoff >= max_probes)
  			goto abort;
  		if (tcp_out_of_resources(sk, true))

  			return;
  	}

  	if (icsk->icsk_probes_out >= max_probes) {

  abort:		tcp_write_err(sk);

  	} else {
  		/* Only send another probe if we didn't close things up. */
  		tcp_send_probe0(sk);
  	}
  }
  
  /*

   *	Timer for Fast Open socket to retransmit SYNACK. Note that the
   *	sk here is the child socket, not the parent (listener) socket.
   */

  static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)

  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	int max_retries = icsk->icsk_syn_retries ? :

  	    sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */

  	struct tcp_sock *tp = tcp_sk(sk);

  	req->rsk_ops->syn_ack_timeout(req);

  	if (req->num_timeout >= max_retries) {

  		tcp_write_err(sk);
  		return;
  	}

  	/* Lower cwnd after certain SYNACK timeout like tcp_init_transfer() */
  	if (icsk->icsk_retransmits == 1)
  		tcp_enter_loss(sk);

  	/* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
  	 * returned from rtx_syn_ack() to make it more persistent like
  	 * regular retransmit because if the child socket has been accepted
  	 * it's not good to give up too easily.
  	 */

  	inet_rtx_syn_ack(sk, req);
  	req->num_timeout++;

  	icsk->icsk_retransmits++;

  	if (!tp->retrans_stamp)
  		tp->retrans_stamp = tcp_time_stamp(tp);

  	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,

  			  TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);

  }

  /**
   *  tcp_retransmit_timer() - The TCP retransmit timeout handler
   *  @sk:  Pointer to the current socket.
   *
   *  This function gets called when the kernel timer for a TCP packet
   *  of this socket expires.
   *
   *  It handles retransmission, timer adjustment and other necesarry measures.
   *
   *  Returns: Nothing (void)
   */

  void tcp_retransmit_timer(struct sock *sk)

  {
  	struct tcp_sock *tp = tcp_sk(sk);

  	struct net *net = sock_net(sk);

  	struct inet_connection_sock *icsk = inet_csk(sk);

  	struct request_sock *req;

  	req = rcu_dereference_protected(tp->fastopen_rsk,
  					lockdep_sock_is_held(sk));
  	if (req) {

  		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
  			     sk->sk_state != TCP_FIN_WAIT1);

  		tcp_fastopen_synack_timer(sk, req);

  		/* Before we receive ACK to our SYN-ACK don't retransmit
  		 * anything else (e.g., data or FIN segments).
  		 */
  		return;
  	}

  	if (!tp->packets_out || WARN_ON_ONCE(tcp_rtx_queue_empty(sk)))
  		return;

  	tp->tlp_high_seq = 0;

  	if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
  	    !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
  		/* Receiver dastardly shrinks window. Our retransmits
  		 * become zero probes, but we should not timeout this
  		 * connection. If the socket is an orphan, time it out,
  		 * we cannot allow such beasts to hang infinitely.
  		 */

  		struct inet_sock *inet = inet_sk(sk);
  		if (sk->sk_family == AF_INET) {

  			net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)
  ",
  					    &inet->inet_daddr,
  					    ntohs(inet->inet_dport),
  					    inet->inet_num,
  					    tp->snd_una, tp->snd_nxt);

  		}

  #if IS_ENABLED(CONFIG_IPV6)

  		else if (sk->sk_family == AF_INET6) {

  			net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)
  ",
  					    &sk->sk_v6_daddr,
  					    ntohs(inet->inet_dport),
  					    inet->inet_num,
  					    tp->snd_una, tp->snd_nxt);

  		}
  #endif

  		if (tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX) {

  			tcp_write_err(sk);
  			goto out;
  		}

  		tcp_enter_loss(sk);

  		tcp_retransmit_skb(sk, tcp_rtx_queue_head(sk), 1);

  		__sk_dst_reset(sk);
  		goto out_reset_timer;
  	}

  	__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);

  	if (tcp_write_timeout(sk))
  		goto out;

  	if (icsk->icsk_retransmits == 0) {

  		int mib_idx = 0;

  		if (icsk->icsk_ca_state == TCP_CA_Recovery) {

  			if (tcp_is_sack(tp))
  				mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
  			else
  				mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;

  		} else if (icsk->icsk_ca_state == TCP_CA_Loss) {

  			mib_idx = LINUX_MIB_TCPLOSSFAILURES;

  		} else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
  			   tp->sacked_out) {
  			if (tcp_is_sack(tp))
  				mib_idx = LINUX_MIB_TCPSACKFAILURES;
  			else
  				mib_idx = LINUX_MIB_TCPRENOFAILURES;

  		}

  		if (mib_idx)
  			__NET_INC_STATS(sock_net(sk), mib_idx);

  	}

  	tcp_enter_loss(sk);

  	icsk->icsk_retransmits++;

  	if (tcp_retransmit_skb(sk, tcp_rtx_queue_head(sk), 1) > 0) {

  		/* Retransmission failed because of local congestion,

  		 * Let senders fight for local resources conservatively.

  		 */

  		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,

  					  TCP_RESOURCE_PROBE_INTERVAL,

  					  TCP_RTO_MAX);

  		goto out;
  	}
  
  	/* Increase the timeout each time we retransmit.  Note that
  	 * we do not increase the rtt estimate.  rto is initialized
  	 * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
  	 * that doubling rto each time is the least we can get away with.
  	 * In KA9Q, Karn uses this for the first few times, and then
  	 * goes to quadratic.  netBSD doubles, but only goes up to *64,
  	 * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
  	 * defined in the protocol as the maximum possible RTT.  I guess
  	 * we'll have to use something other than TCP to talk to the
  	 * University of Mars.
  	 *
  	 * PAWS allows us longer timeouts and large windows, so once
  	 * implemented ftp to mars will work nicely. We will have to fix
  	 * the 120 second clamps though!
  	 */

  	icsk->icsk_backoff++;

  
  out_reset_timer:

  	/* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
  	 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
  	 * might be increased if the stream oscillates between thin and thick,
  	 * thus the old value might already be too high compared to the value
  	 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
  	 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
  	 * exponential backoff behaviour to avoid continue hammering
  	 * linear-timeout retransmissions into a black hole
  	 */
  	if (sk->sk_state == TCP_ESTABLISHED &&

  	    (tp->thin_lto || net->ipv4.sysctl_tcp_thin_linear_timeouts) &&

  	    tcp_stream_is_thin(tp) &&
  	    icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
  		icsk->icsk_backoff = 0;
  		icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
  	} else {
  		/* Use normal (exponential) backoff */
  		icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
  	}

  	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
  				  tcp_clamp_rto_to_user_timeout(sk), TCP_RTO_MAX);

  	if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1 + 1, 0))

  		__sk_dst_reset(sk);
  
  out:;
  }

  /* Called with bottom-half processing disabled.
     Called by tcp_write_timer() */

  void tcp_write_timer_handler(struct sock *sk)

  {

  	struct inet_connection_sock *icsk = inet_csk(sk);

  	int event;

  	if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
  	    !icsk->icsk_pending)

  		goto out;

  	if (time_after(icsk->icsk_timeout, jiffies)) {
  		sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);

  		goto out;
  	}

  	tcp_mstamp_refresh(tcp_sk(sk));

  	event = icsk->icsk_pending;

  
  	switch (event) {

  	case ICSK_TIME_REO_TIMEOUT:
  		tcp_rack_reo_timeout(sk);
  		break;

  	case ICSK_TIME_LOSS_PROBE:
  		tcp_send_loss_probe(sk);
  		break;

  	case ICSK_TIME_RETRANS:

  		icsk->icsk_pending = 0;

  		tcp_retransmit_timer(sk);
  		break;

  	case ICSK_TIME_PROBE0:

  		icsk->icsk_pending = 0;

  		tcp_probe_timer(sk);
  		break;
  	}

  
  out:

  	sk_mem_reclaim(sk);

  }

  static void tcp_write_timer(struct timer_list *t)

  {

  	struct inet_connection_sock *icsk =
  			from_timer(icsk, t, icsk_retransmit_timer);
  	struct sock *sk = &icsk->icsk_inet.sk;

  
  	bh_lock_sock(sk);
  	if (!sock_owned_by_user(sk)) {
  		tcp_write_timer_handler(sk);
  	} else {

  		/* delegate our work to tcp_release_cb() */

  		if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &sk->sk_tsq_flags))

  			sock_hold(sk);

  	}

  	bh_unlock_sock(sk);
  	sock_put(sk);
  }

  void tcp_syn_ack_timeout(const struct request_sock *req)

  {

  	struct net *net = read_pnet(&inet_rsk(req)->ireq_net);

  	__NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS);

  }
  EXPORT_SYMBOL(tcp_syn_ack_timeout);

  void tcp_set_keepalive(struct sock *sk, int val)
  {
  	if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
  		return;
  
  	if (val && !sock_flag(sk, SOCK_KEEPOPEN))

  		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));

  	else if (!val)

  		inet_csk_delete_keepalive_timer(sk);

  }

  EXPORT_SYMBOL_GPL(tcp_set_keepalive);

  static void tcp_keepalive_timer (struct timer_list *t)

  {

  	struct sock *sk = from_timer(sk, t, sk_timer);

  	struct inet_connection_sock *icsk = inet_csk(sk);

  	struct tcp_sock *tp = tcp_sk(sk);

  	u32 elapsed;

  
  	/* Only process if socket is not in use. */
  	bh_lock_sock(sk);
  	if (sock_owned_by_user(sk)) {

  		/* Try again later. */

  		inet_csk_reset_keepalive_timer (sk, HZ/20);

  		goto out;
  	}
  
  	if (sk->sk_state == TCP_LISTEN) {

  		pr_err("Hmm... keepalive on a LISTEN ???
  ");

  		goto out;
  	}

  	tcp_mstamp_refresh(tp);

  	if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
  		if (tp->linger2 >= 0) {

  			const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;

  
  			if (tmo > 0) {
  				tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
  				goto out;
  			}
  		}
  		tcp_send_active_reset(sk, GFP_ATOMIC);
  		goto death;
  	}

  	if (!sock_flag(sk, SOCK_KEEPOPEN) ||
  	    ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT)))

  		goto out;
  
  	elapsed = keepalive_time_when(tp);
  
  	/* It is alive without keepalive 8) */

  	if (tp->packets_out || !tcp_write_queue_empty(sk))

  		goto resched;

  	elapsed = keepalive_time_elapsed(tp);

  
  	if (elapsed >= keepalive_time_when(tp)) {

  		/* If the TCP_USER_TIMEOUT option is enabled, use that
  		 * to determine when to timeout instead.
  		 */
  		if ((icsk->icsk_user_timeout != 0 &&

  		    elapsed >= msecs_to_jiffies(icsk->icsk_user_timeout) &&

  		    icsk->icsk_probes_out > 0) ||
  		    (icsk->icsk_user_timeout == 0 &&
  		    icsk->icsk_probes_out >= keepalive_probes(tp))) {

  			tcp_send_active_reset(sk, GFP_ATOMIC);
  			tcp_write_err(sk);
  			goto out;
  		}

  		if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {

  			icsk->icsk_probes_out++;

  			elapsed = keepalive_intvl_when(tp);
  		} else {
  			/* If keepalive was lost due to local congestion,
  			 * try harder.
  			 */
  			elapsed = TCP_RESOURCE_PROBE_INTERVAL;
  		}
  	} else {
  		/* It is tp->rcv_tstamp + keepalive_time_when(tp) */
  		elapsed = keepalive_time_when(tp) - elapsed;
  	}

  	sk_mem_reclaim(sk);

  
  resched:

  	inet_csk_reset_keepalive_timer (sk, elapsed);

  	goto out;

  death:

  	tcp_done(sk);
  
  out:
  	bh_unlock_sock(sk);
  	sock_put(sk);
  }

  static enum hrtimer_restart tcp_compressed_ack_kick(struct hrtimer *timer)
  {
  	struct tcp_sock *tp = container_of(timer, struct tcp_sock, compressed_ack_timer);
  	struct sock *sk = (struct sock *)tp;
  
  	bh_lock_sock(sk);
  	if (!sock_owned_by_user(sk)) {

  		if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)

  			tcp_send_ack(sk);
  	} else {
  		if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED,
  				      &sk->sk_tsq_flags))
  			sock_hold(sk);
  	}
  	bh_unlock_sock(sk);
  
  	sock_put(sk);
  
  	return HRTIMER_NORESTART;
  }

  void tcp_init_xmit_timers(struct sock *sk)
  {
  	inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
  				  &tcp_keepalive_timer);

  	hrtimer_init(&tcp_sk(sk)->pacing_timer, CLOCK_MONOTONIC,

  		     HRTIMER_MODE_ABS_PINNED_SOFT);

  	tcp_sk(sk)->pacing_timer.function = tcp_pace_kick;

  
  	hrtimer_init(&tcp_sk(sk)->compressed_ack_timer, CLOCK_MONOTONIC,
  		     HRTIMER_MODE_REL_PINNED_SOFT);
  	tcp_sk(sk)->compressed_ack_timer.function = tcp_compressed_ack_kick;

  }