Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 841 insertions, 0 deletions

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
new file mode 100644
index 0000000000..984ab4a042
--- /dev/null
+++ b/net/ipv4/tcp_timer.c
@@ -0,0 +1,841 @@
+// 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, user_timeout;
+	s32 remaining;
+
+	start_ts = tcp_sk(sk)->retrans_stamp;
+	user_timeout = READ_ONCE(icsk->icsk_user_timeout);
+	if (!user_timeout)
+		return icsk->icsk_rto;
+	elapsed = tcp_time_stamp(tcp_sk(sk)) - start_ts;
+	remaining = 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));
+}
+
+u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	u32 remaining, user_timeout;
+	s32 elapsed;
+
+	user_timeout = READ_ONCE(icsk->icsk_user_timeout);
+	if (!user_timeout || !icsk->icsk_probes_tstamp)
+		return when;
+
+	elapsed = tcp_jiffies32 - icsk->icsk_probes_tstamp;
+	if (unlikely(elapsed < 0))
+		elapsed = 0;
+	remaining = msecs_to_jiffies(user_timeout) - elapsed;
+	remaining = max_t(u32, remaining, TCP_TIMEOUT_MIN);
+
+	return min_t(u32, remaining, when);
+}
+
+/**
+ *  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)
+{
+	WRITE_ONCE(sk->sk_err, READ_ONCE(sk->sk_err_soft) ? : ETIMEDOUT);
+	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 (READ_ONCE(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 = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_orphan_retries); /* May be zero. */
+
+	/* We know from an ICMP that something is wrong. */
+	if (READ_ONCE(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 (!READ_ONCE(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(READ_ONCE(net->ipv4.sysctl_tcp_base_mss), mss);
+		mss = max(mss, READ_ONCE(net->ipv4.sysctl_tcp_mtu_probe_floor));
+		mss = max(mss, READ_ONCE(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, max_retransmits;
+
+	if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
+		if (icsk->icsk_retransmits)
+			__dst_negative_advice(sk);
+		/* Paired with WRITE_ONCE() in tcp_sock_set_syncnt() */
+		retry_until = READ_ONCE(icsk->icsk_syn_retries) ? :
+			READ_ONCE(net->ipv4.sysctl_tcp_syn_retries);
+
+		max_retransmits = retry_until;
+		if (sk->sk_state == TCP_SYN_SENT)
+			max_retransmits += READ_ONCE(net->ipv4.sysctl_tcp_syn_linear_timeouts);
+
+		expired = icsk->icsk_retransmits >= max_retransmits;
+	} else {
+		if (retransmits_timed_out(sk, READ_ONCE(net->ipv4.sysctl_tcp_retries1), 0)) {
+			/* Black hole detection */
+			tcp_mtu_probing(icsk, sk);
+
+			__dst_negative_advice(sk);
+		}
+
+		retry_until = READ_ONCE(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,
+						READ_ONCE(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;
+	}
+
+	if (sk_rethink_txhash(sk)) {
+		tp->timeout_rehash++;
+		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTREHASH);
+	}
+
+	return 0;
+}
+
+/* Called with BH disabled */
+void tcp_delack_timer_handler(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
+		return;
+
+	/* Handling the sack compression case */
+	if (tp->compressed_ack) {
+		tcp_mstamp_refresh(tp);
+		tcp_sack_compress_send_ack(sk);
+		return;
+	}
+
+	if (!(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
+		return;
+
+	if (time_after(icsk->icsk_ack.timeout, jiffies)) {
+		sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
+		return;
+	}
+	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(tp);
+		tcp_send_ack(sk);
+		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
+	}
+}
+
+
+/**
+ *  tcp_delack_timer() - The TCP delayed ACK timeout handler
+ *  @t:  Pointer to the timer. (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 {
+		__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;
+		icsk->icsk_probes_tstamp = 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_probes_tstamp) {
+		icsk->icsk_probes_tstamp = tcp_jiffies32;
+	} else {
+		u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
+
+		if (user_timeout &&
+		    (s32)(tcp_jiffies32 - icsk->icsk_probes_tstamp) >=
+		     msecs_to_jiffies(user_timeout))
+		goto abort;
+	}
+	max_probes = READ_ONCE(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);
+	struct tcp_sock *tp = tcp_sk(sk);
+	int max_retries;
+
+	req->rsk_ops->syn_ack_timeout(req);
+
+	/* Add one more retry for fastopen.
+	 * Paired with WRITE_ONCE() in tcp_sock_set_syncnt()
+	 */
+	max_retries = READ_ONCE(icsk->icsk_syn_retries) ? :
+		READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_synack_retries) + 1;
+
+	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,
+			  req->timeout << req->num_timeout, TCP_RTO_MAX);
+}
+
+static bool tcp_rtx_probe0_timed_out(const struct sock *sk,
+				     const struct sk_buff *skb)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+	const int timeout = TCP_RTO_MAX * 2;
+	u32 rcv_delta, rtx_delta;
+
+	rcv_delta = inet_csk(sk)->icsk_timeout - tp->rcv_tstamp;
+	if (rcv_delta <= timeout)
+		return false;
+
+	rtx_delta = (u32)msecs_to_jiffies(tcp_time_stamp(tp) -
+			(tp->retrans_stamp ?: tcp_skb_timestamp(skb)));
+
+	return rtx_delta > timeout;
+}
+
+/**
+ *  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 necessary 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;
+	struct sk_buff *skb;
+
+	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)
+		return;
+
+	skb = tcp_rtx_queue_head(sk);
+	if (WARN_ON_ONCE(!skb))
+		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);
+		u32 rtx_delta;
+
+		rtx_delta = tcp_time_stamp(tp) - (tp->retrans_stamp ?: tcp_skb_timestamp(skb));
+		if (sk->sk_family == AF_INET) {
+			net_dbg_ratelimited("Probing zero-window on %pI4:%u/%u, seq=%u:%u, recv %ums ago, lasting %ums\n",
+				&inet->inet_daddr, ntohs(inet->inet_dport),
+				inet->inet_num, tp->snd_una, tp->snd_nxt,
+				jiffies_to_msecs(jiffies - tp->rcv_tstamp),
+				rtx_delta);
+		}
+#if IS_ENABLED(CONFIG_IPV6)
+		else if (sk->sk_family == AF_INET6) {
+			net_dbg_ratelimited("Probing zero-window on %pI6:%u/%u, seq=%u:%u, recv %ums ago, lasting %ums\n",
+				&sk->sk_v6_daddr, ntohs(inet->inet_dport),
+				inet->inet_num, tp->snd_una, tp->snd_nxt,
+				jiffies_to_msecs(jiffies - tp->rcv_tstamp),
+				rtx_delta);
+		}
+#endif
+		if (tcp_rtx_probe0_timed_out(sk, skb)) {
+			tcp_write_err(sk);
+			goto out;
+		}
+		tcp_enter_loss(sk);
+		tcp_retransmit_skb(sk, skb, 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 || READ_ONCE(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 = clamp(__tcp_set_rto(tp),
+				       tcp_rto_min(sk),
+				       TCP_RTO_MAX);
+	} else if (sk->sk_state != TCP_SYN_SENT ||
+		   icsk->icsk_backoff >
+		   READ_ONCE(net->ipv4.sysctl_tcp_syn_linear_timeouts)) {
+		/* Use normal (exponential) backoff unless linear timeouts are
+		 * activated.
+		 */
+		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, READ_ONCE(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)
+		return;
+
+	if (time_after(icsk->icsk_timeout, jiffies)) {
+		sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
+		return;
+	}
+
+	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;
+	}
+}
+
+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 ???\n");
+		goto out;
+	}
+
+	tcp_mstamp_refresh(tp);
+	if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
+		if (READ_ONCE(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)) {
+		u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
+
+		/* If the TCP_USER_TIMEOUT option is enabled, use that
+		 * to determine when to timeout instead.
+		 */
+		if ((user_timeout != 0 &&
+		    elapsed >= msecs_to_jiffies(user_timeout) &&
+		    icsk->icsk_probes_out > 0) ||
+		    (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;
+	}
+
+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) {
+			/* Since we have to send one ack finally,
+			 * subtract one from tp->compressed_ack to keep
+			 * LINUX_MIB_TCPACKCOMPRESSED accurate.
+			 */
+			tp->compressed_ack--;
+			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;
+}