Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 907 insertions, 0 deletions

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
new file mode 100644
index 000000000..e56eae4bc
--- /dev/null
+++ b/net/ipv4/tcp_timer.c
@@ -0,0 +1,907 @@
+// 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>
+#include <net/tcp_ecn.h>
+#include <net/rstreason.h>
+
+static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
+{
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+	const struct tcp_sock *tp = tcp_sk(sk);
+	u32 elapsed, user_timeout;
+	s32 remaining;
+
+	user_timeout = READ_ONCE(icsk->icsk_user_timeout);
+	if (!user_timeout)
+		return icsk->icsk_rto;
+
+	elapsed = tcp_time_stamp_ts(tp) - tp->retrans_stamp;
+	if (tp->tcp_usec_ts)
+		elapsed /= USEC_PER_MSEC;
+
+	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)
+{
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+	u32 user_timeout;
+	s32 remaining;
+	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(int, 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)
+{
+	tcp_done_with_error(sk, READ_ONCE(sk->sk_err_soft) ? : ETIMEDOUT);
+	__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(sk) || !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,
+					      SK_RST_REASON_TCP_ABORT_ON_MEMORY);
+		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(sk) / 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(sk);
+	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)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	unsigned int start_ts, delta;
+
+	if (!inet_csk(sk)->icsk_retransmits)
+		return false;
+
+	start_ts = tp->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);
+	}
+
+	if (tp->tcp_usec_ts) {
+		/* delta maybe off up to a jiffy due to timer granularity. */
+		delta = tp->tcp_mstamp - start_ts + jiffies_to_usecs(1);
+		return (s32)(delta - timeout * USEC_PER_MSEC) >= 0;
+	}
+	return (s32)(tcp_time_stamp_ts(tp) - 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(sk);
+
+			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);
+	mptcp_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_reset_dst(sk)) {
+		WRITE_ONCE(tp->timeout_rehash, tp->timeout_rehash + 1);
+		__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_delack_timeout(icsk), jiffies)) {
+		sk_reset_timer(sk, &icsk->icsk_delack_timer,
+			       icsk_delack_timeout(icsk));
+		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 = min3((u32)icsk->icsk_ack.ato << 1,
+						  icsk->icsk_rto,
+						  (u32)TCP_DELACK_MAX);
+		} 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 =
+			timer_container_of(icsk, t, icsk_delack_timer);
+	struct sock *sk = &icsk->icsk_inet.sk;
+
+	/* Avoid taking socket spinlock if there is no ACK to send.
+	 * The compressed_ack check is racy, but a separate hrtimer
+	 * will take care of it eventually.
+	 */
+	if (!(smp_load_acquire(&icsk->icsk_ack.pending) & ICSK_ACK_TIMER) &&
+	    !READ_ONCE(tcp_sk(sk)->compressed_ack))
+		goto out;
+
+	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);
+out:
+	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) {
+		WRITE_ONCE(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)) {
+		unsigned int rto_max = tcp_rto_max(sk);
+		const bool alive = inet_csk_rto_backoff(icsk, rto_max) < 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);
+	}
+}
+
+static void tcp_update_rto_stats(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	if (!icsk->icsk_retransmits) {
+		tp->total_rto_recoveries++;
+		tp->rto_stamp = tcp_time_stamp_ms(tp);
+	}
+	WRITE_ONCE(icsk->icsk_retransmits, icsk->icsk_retransmits + 1);
+	tp->total_rto++;
+}
+
+/*
+ *	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;
+
+	tcp_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.
+	 */
+	tcp_rtx_synack(sk, req);
+	if (req->num_retrans > 1 && tcp_rsk(req)->accecn_ok)
+		tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_SEND;
+	req->num_timeout++;
+	tcp_update_rto_stats(sk);
+	if (!tp->retrans_stamp)
+		tp->retrans_stamp = tcp_time_stamp_ts(tp);
+	tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+			  req->timeout << req->num_timeout, false);
+}
+
+static bool tcp_rtx_probe0_timed_out(const struct sock *sk,
+				     const struct sk_buff *skb,
+				     u32 rtx_delta)
+{
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+	u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
+	const struct tcp_sock *tp = tcp_sk(sk);
+	int timeout = tcp_rto_max(sk) * 2;
+	s32 rcv_delta;
+
+	if (user_timeout) {
+		/* If user application specified a TCP_USER_TIMEOUT,
+		 * it does not want win 0 packets to 'reset the timer'
+		 * while retransmits are not making progress.
+		 */
+		if (rtx_delta > user_timeout)
+			return true;
+		timeout = min_t(u32, timeout, msecs_to_jiffies(user_timeout));
+	}
+	/* Note: timer interrupt might have been delayed by at least one jiffy,
+	 * and tp->rcv_tstamp might very well have been written recently.
+	 * rcv_delta can thus be negative.
+	 */
+	rcv_delta = tcp_timeout_expires(sk) - tp->rcv_tstamp;
+	if (rcv_delta <= timeout)
+		return false;
+
+	return msecs_to_jiffies(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;
+
+	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_ts(tp) - (tp->retrans_stamp ?: 
+				tcp_skb_timestamp_ts(tp->tcp_usec_ts, skb));
+		if (tp->tcp_usec_ts)
+			rtx_delta /= USEC_PER_MSEC;
+
+		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, rtx_delta)) {
+			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);
+
+	tcp_update_rto_stats(sk);
+	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.
+		 */
+		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+				     TCP_RESOURCE_PROBE_INTERVAL,
+				     false);
+		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!
+	 */
+
+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(sk));
+	} else if (sk->sk_state != TCP_SYN_SENT ||
+		   tp->total_rto >
+		   READ_ONCE(net->ipv4.sysctl_tcp_syn_linear_timeouts)) {
+		/* Use normal (exponential) backoff unless linear timeouts are
+		 * activated.
+		 */
+		icsk->icsk_backoff++;
+		icsk->icsk_rto = min(icsk->icsk_rto << 1, tcp_rto_max(sk));
+	}
+	tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+			     tcp_clamp_rto_to_user_timeout(sk), false);
+	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() and tcp_release_cb().
+ */
+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(tcp_timeout_expires(sk), jiffies)) {
+		sk_reset_timer(sk, &sk->tcp_retransmit_timer,
+			       tcp_timeout_expires(sk));
+		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:
+		smp_store_release(&icsk->icsk_pending, 0);
+		tcp_retransmit_timer(sk);
+		break;
+	case ICSK_TIME_PROBE0:
+		smp_store_release(&icsk->icsk_pending, 0);
+		tcp_probe_timer(sk);
+		break;
+	}
+}
+
+static void tcp_write_timer(struct timer_list *t)
+{
+	struct sock *sk = timer_container_of(sk, t, tcp_retransmit_timer);
+
+	/* Avoid locking the socket when there is no pending event. */
+	if (!smp_load_acquire(&inet_csk(sk)->icsk_pending))
+		goto out;
+
+	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);
+out:
+	sock_put(sk);
+}
+
+noinline_for_tracing 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);
+}
+
+void tcp_reset_keepalive_timer(struct sock *sk, unsigned long len)
+{
+	sk_reset_timer(sk, &inet_csk(sk)->icsk_keepalive_timer, jiffies + len);
+}
+
+static void tcp_delete_keepalive_timer(struct sock *sk)
+{
+	sk_stop_timer(sk, &inet_csk(sk)->icsk_keepalive_timer);
+}
+
+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))
+		tcp_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
+	else if (!val)
+		tcp_delete_keepalive_timer(sk);
+}
+
+static void tcp_keepalive_timer(struct timer_list *t)
+{
+	struct inet_connection_sock *icsk =
+		timer_container_of(icsk, t, icsk_keepalive_timer);
+	struct sock *sk = &icsk->icsk_inet.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. */
+		tcp_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, SK_RST_REASON_TCP_STATE);
+		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,
+					      SK_RST_REASON_TCP_KEEPALIVE_TIMEOUT);
+			tcp_write_err(sk);
+			goto out;
+		}
+		if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
+			WRITE_ONCE(icsk->icsk_probes_out, icsk->icsk_probes_out + 1);
+			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:
+	tcp_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_mstamp_refresh(tp);
+			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_setup(&tcp_sk(sk)->pacing_timer, tcp_pace_kick, CLOCK_MONOTONIC,
+		      HRTIMER_MODE_ABS_PINNED_SOFT);
+
+	hrtimer_setup(&tcp_sk(sk)->compressed_ack_timer, tcp_compressed_ack_kick, CLOCK_MONOTONIC,
+		      HRTIMER_MODE_REL_PINNED_SOFT);
+}