alistair23-linux/kernel/trace/trace_sched_wakeup.c

// SPDX-License-Identifier: GPL-2.0
/*
 * trace task wakeup timings
 *
 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
 * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
 *
 * Based on code from the latency_tracer, that is:
 *
 *  Copyright (C) 2004-2006 Ingo Molnar
 *  Copyright (C) 2004 Nadia Yvette Chambers
 */
#include <linux/module.h>
#include <linux/kallsyms.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/sched/rt.h>
#include <linux/sched/deadline.h>
#include <trace/events/sched.h>
#include "trace.h"

static struct trace_array	*wakeup_trace;
static int __read_mostly	tracer_enabled;

static struct task_struct	*wakeup_task;
static int			wakeup_cpu;
static int			wakeup_current_cpu;
static unsigned			wakeup_prio = -1;
static int			wakeup_rt;
static int			wakeup_dl;
static int			tracing_dl = 0;

static arch_spinlock_t wakeup_lock =
	(arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;

static void wakeup_reset(struct trace_array *tr);
static void __wakeup_reset(struct trace_array *tr);
static int start_func_tracer(struct trace_array *tr, int graph);
static void stop_func_tracer(struct trace_array *tr, int graph);

static int save_flags;

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
# define is_graph(tr) ((tr)->trace_flags & TRACE_ITER_DISPLAY_GRAPH)
#else
# define is_graph(tr) false
#endif

#ifdef CONFIG_FUNCTION_TRACER

static bool function_enabled;

/*
 * Prologue for the wakeup function tracers.
 *
 * Returns 1 if it is OK to continue, and preemption
 *            is disabled and data->disabled is incremented.
 *         0 if the trace is to be ignored, and preemption
 *            is not disabled and data->disabled is
 *            kept the same.
 *
 * Note, this function is also used outside this ifdef but
 *  inside the #ifdef of the function graph tracer below.
 *  This is OK, since the function graph tracer is
 *  dependent on the function tracer.
 */
static int
func_prolog_preempt_disable(struct trace_array *tr,
			    struct trace_array_cpu **data,
			    int *pc)
{
	long disabled;
	int cpu;

	if (likely(!wakeup_task))
		return 0;

	*pc = preempt_count();
	preempt_disable_notrace();

	cpu = raw_smp_processor_id();
	if (cpu != wakeup_current_cpu)
		goto out_enable;

	*data = per_cpu_ptr(tr->array_buffer.data, cpu);
	disabled = atomic_inc_return(&(*data)->disabled);
	if (unlikely(disabled != 1))
		goto out;

	return 1;

out:
	atomic_dec(&(*data)->disabled);

out_enable:
	preempt_enable_notrace();
	return 0;
}

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

static int wakeup_display_graph(struct trace_array *tr, int set)
{
	if (!(is_graph(tr) ^ set))
		return 0;

	stop_func_tracer(tr, !set);

	wakeup_reset(wakeup_trace);
	tr->max_latency = 0;

	return start_func_tracer(tr, set);
}

static int wakeup_graph_entry(struct ftrace_graph_ent *trace)
{
	struct trace_array *tr = wakeup_trace;
	struct trace_array_cpu *data;
	unsigned long flags;
	int pc, ret = 0;

	if (ftrace_graph_ignore_func(trace))
		return 0;
	/*
	 * Do not trace a function if it's filtered by set_graph_notrace.
	 * Make the index of ret stack negative to indicate that it should
	 * ignore further functions.  But it needs its own ret stack entry
	 * to recover the original index in order to continue tracing after
	 * returning from the function.
	 */
	if (ftrace_graph_notrace_addr(trace->func))
		return 1;

	if (!func_prolog_preempt_disable(tr, &data, &pc))
		return 0;

	local_save_flags(flags);
	ret = __trace_graph_entry(tr, trace, flags, pc);
	atomic_dec(&data->disabled);
	preempt_enable_notrace();

	return ret;
}

static void wakeup_graph_return(struct ftrace_graph_ret *trace)
{
	struct trace_array *tr = wakeup_trace;
	struct trace_array_cpu *data;
	unsigned long flags;
	int pc;

	ftrace_graph_addr_finish(trace);

	if (!func_prolog_preempt_disable(tr, &data, &pc))
		return;

	local_save_flags(flags);
	__trace_graph_return(tr, trace, flags, pc);
	atomic_dec(&data->disabled);

	preempt_enable_notrace();
	return;
}

static struct fgraph_ops fgraph_wakeup_ops = {
	.entryfunc = &wakeup_graph_entry,
	.retfunc = &wakeup_graph_return,
};

static void wakeup_trace_open(struct trace_iterator *iter)
{
	if (is_graph(iter->tr))
		graph_trace_open(iter);
}

static void wakeup_trace_close(struct trace_iterator *iter)
{
	if (iter->private)
		graph_trace_close(iter);
}

#define GRAPH_TRACER_FLAGS (TRACE_GRAPH_PRINT_PROC | \
			    TRACE_GRAPH_PRINT_CPU |  \
			    TRACE_GRAPH_PRINT_REL_TIME | \
			    TRACE_GRAPH_PRINT_DURATION | \
			    TRACE_GRAPH_PRINT_OVERHEAD | \
			    TRACE_GRAPH_PRINT_IRQS)

static enum print_line_t wakeup_print_line(struct trace_iterator *iter)
{
	/*
	 * In graph mode call the graph tracer output function,
	 * otherwise go with the TRACE_FN event handler
	 */
	if (is_graph(iter->tr))
		return print_graph_function_flags(iter, GRAPH_TRACER_FLAGS);

	return TRACE_TYPE_UNHANDLED;
}

static void wakeup_print_header(struct seq_file *s)
{
	if (is_graph(wakeup_trace))
		print_graph_headers_flags(s, GRAPH_TRACER_FLAGS);
	else
		trace_default_header(s);
}
#endif /* else CONFIG_FUNCTION_GRAPH_TRACER */

/*
 * wakeup uses its own tracer function to keep the overhead down:
 */
static void
wakeup_tracer_call(unsigned long ip, unsigned long parent_ip,
		   struct ftrace_ops *op, struct pt_regs *pt_regs)
{
	struct trace_array *tr = wakeup_trace;
	struct trace_array_cpu *data;
	unsigned long flags;
	int pc;

	if (!func_prolog_preempt_disable(tr, &data, &pc))
		return;

	local_irq_save(flags);
	trace_function(tr, ip, parent_ip, flags, pc);
	local_irq_restore(flags);

	atomic_dec(&data->disabled);
	preempt_enable_notrace();
}

static int register_wakeup_function(struct trace_array *tr, int graph, int set)
{
	int ret;

	/* 'set' is set if TRACE_ITER_FUNCTION is about to be set */
	if (function_enabled || (!set && !(tr->trace_flags & TRACE_ITER_FUNCTION)))
		return 0;

	if (graph)
		ret = register_ftrace_graph(&fgraph_wakeup_ops);
	else
		ret = register_ftrace_function(tr->ops);

	if (!ret)
		function_enabled = true;

	return ret;
}

static void unregister_wakeup_function(struct trace_array *tr, int graph)
{
	if (!function_enabled)
		return;

	if (graph)
		unregister_ftrace_graph(&fgraph_wakeup_ops);
	else
		unregister_ftrace_function(tr->ops);

	function_enabled = false;
}

static int wakeup_function_set(struct trace_array *tr, u32 mask, int set)
{
	if (!(mask & TRACE_ITER_FUNCTION))
		return 0;

	if (set)
		register_wakeup_function(tr, is_graph(tr), 1);
	else
		unregister_wakeup_function(tr, is_graph(tr));
	return 1;
}
#else /* CONFIG_FUNCTION_TRACER */
static int register_wakeup_function(struct trace_array *tr, int graph, int set)
{
	return 0;
}
static void unregister_wakeup_function(struct trace_array *tr, int graph) { }
static int wakeup_function_set(struct trace_array *tr, u32 mask, int set)
{
	return 0;
}
#endif /* else CONFIG_FUNCTION_TRACER */

#ifndef CONFIG_FUNCTION_GRAPH_TRACER
static enum print_line_t wakeup_print_line(struct trace_iterator *iter)
{
	return TRACE_TYPE_UNHANDLED;
}

static void wakeup_trace_open(struct trace_iterator *iter) { }
static void wakeup_trace_close(struct trace_iterator *iter) { }

static void wakeup_print_header(struct seq_file *s)
{
	trace_default_header(s);
}
#endif /* !CONFIG_FUNCTION_GRAPH_TRACER */

static void
__trace_function(struct trace_array *tr,
		 unsigned long ip, unsigned long parent_ip,
		 unsigned long flags, int pc)
{
	if (is_graph(tr))
		trace_graph_function(tr, ip, parent_ip, flags, pc);
	else
		trace_function(tr, ip, parent_ip, flags, pc);
}

static int wakeup_flag_changed(struct trace_array *tr, u32 mask, int set)
{
	struct tracer *tracer = tr->current_trace;

	if (wakeup_function_set(tr, mask, set))
		return 0;

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	if (mask & TRACE_ITER_DISPLAY_GRAPH)
		return wakeup_display_graph(tr, set);
#endif

	return trace_keep_overwrite(tracer, mask, set);
}

static int start_func_tracer(struct trace_array *tr, int graph)
{
	int ret;

	ret = register_wakeup_function(tr, graph, 0);

	if (!ret && tracing_is_enabled())
		tracer_enabled = 1;
	else
		tracer_enabled = 0;

	return ret;
}

static void stop_func_tracer(struct trace_array *tr, int graph)
{
	tracer_enabled = 0;

	unregister_wakeup_function(tr, graph);
}

/*
 * Should this new latency be reported/recorded?
 */
static bool report_latency(struct trace_array *tr, u64 delta)
{
	if (tracing_thresh) {
		if (delta < tracing_thresh)
			return false;
	} else {
		if (delta <= tr->max_latency)
			return false;
	}
	return true;
}

static void
probe_wakeup_migrate_task(void *ignore, struct task_struct *task, int cpu)
{
	if (task != wakeup_task)
		return;

	wakeup_current_cpu = cpu;
}

static void
tracing_sched_switch_trace(struct trace_array *tr,
			   struct task_struct *prev,
			   struct task_struct *next,
			   unsigned long flags, int pc)
{
	struct trace_event_call *call = &event_context_switch;
	struct trace_buffer *buffer = tr->array_buffer.buffer;
	struct ring_buffer_event *event;
	struct ctx_switch_entry *entry;

	event = trace_buffer_lock_reserve(buffer, TRACE_CTX,
					  sizeof(*entry), flags, pc);
	if (!event)
		return;
	entry	= ring_buffer_event_data(event);
	entry->prev_pid			= prev->pid;
	entry->prev_prio		= prev->prio;
	entry->prev_state		= task_state_index(prev);
	entry->next_pid			= next->pid;
	entry->next_prio		= next->prio;
	entry->next_state		= task_state_index(next);
	entry->next_cpu	= task_cpu(next);

	if (!call_filter_check_discard(call, entry, buffer, event))
		trace_buffer_unlock_commit(tr, buffer, event, flags, pc);
}

static void
tracing_sched_wakeup_trace(struct trace_array *tr,
			   struct task_struct *wakee,
			   struct task_struct *curr,
			   unsigned long flags, int pc)
{
	struct trace_event_call *call = &event_wakeup;
	struct ring_buffer_event *event;
	struct ctx_switch_entry *entry;
	struct trace_buffer *buffer = tr->array_buffer.buffer;

	event = trace_buffer_lock_reserve(buffer, TRACE_WAKE,
					  sizeof(*entry), flags, pc);
	if (!event)
		return;
	entry	= ring_buffer_event_data(event);
	entry->prev_pid			= curr->pid;
	entry->prev_prio		= curr->prio;
	entry->prev_state		= task_state_index(curr);
	entry->next_pid			= wakee->pid;
	entry->next_prio		= wakee->prio;
	entry->next_state		= task_state_index(wakee);
	entry->next_cpu			= task_cpu(wakee);

	if (!call_filter_check_discard(call, entry, buffer, event))
		trace_buffer_unlock_commit(tr, buffer, event, flags, pc);
}

static void notrace
probe_wakeup_sched_switch(void *ignore, bool preempt,
			  struct task_struct *prev, struct task_struct *next)
{
	struct trace_array_cpu *data;
	u64 T0, T1, delta;
	unsigned long flags;
	long disabled;
	int cpu;
	int pc;

	tracing_record_cmdline(prev);

	if (unlikely(!tracer_enabled))
		return;

	/*
	 * When we start a new trace, we set wakeup_task to NULL
	 * and then set tracer_enabled = 1. We want to make sure
	 * that another CPU does not see the tracer_enabled = 1
	 * and the wakeup_task with an older task, that might
	 * actually be the same as next.
	 */
	smp_rmb();

	if (next != wakeup_task)
		return;

	pc = preempt_count();

	/* disable local data, not wakeup_cpu data */
	cpu = raw_smp_processor_id();
	disabled = atomic_inc_return(&per_cpu_ptr(wakeup_trace->array_buffer.data, cpu)->disabled);
	if (likely(disabled != 1))
		goto out;

	local_irq_save(flags);
	arch_spin_lock(&wakeup_lock);

	/* We could race with grabbing wakeup_lock */
	if (unlikely(!tracer_enabled || next != wakeup_task))
		goto out_unlock;

	/* The task we are waiting for is waking up */
	data = per_cpu_ptr(wakeup_trace->array_buffer.data, wakeup_cpu);

	__trace_function(wakeup_trace, CALLER_ADDR0, CALLER_ADDR1, flags, pc);
	tracing_sched_switch_trace(wakeup_trace, prev, next, flags, pc);
	__trace_stack(wakeup_trace, flags, 0, pc);

	T0 = data->preempt_timestamp;
	T1 = ftrace_now(cpu);
	delta = T1-T0;

	if (!report_latency(wakeup_trace, delta))
		goto out_unlock;

	if (likely(!is_tracing_stopped())) {
		wakeup_trace->max_latency = delta;
		update_max_tr(wakeup_trace, wakeup_task, wakeup_cpu, NULL);
	}

out_unlock:
	__wakeup_reset(wakeup_trace);
	arch_spin_unlock(&wakeup_lock);
	local_irq_restore(flags);
out:
	atomic_dec(&per_cpu_ptr(wakeup_trace->array_buffer.data, cpu)->disabled);
}

static void __wakeup_reset(struct trace_array *tr)
{
	wakeup_cpu = -1;
	wakeup_prio = -1;
	tracing_dl = 0;

	if (wakeup_task)
		put_task_struct(wakeup_task);

	wakeup_task = NULL;
}

static void wakeup_reset(struct trace_array *tr)
{
	unsigned long flags;

	tracing_reset_online_cpus(&tr->array_buffer);

	local_irq_save(flags);
	arch_spin_lock(&wakeup_lock);
	__wakeup_reset(tr);
	arch_spin_unlock(&wakeup_lock);
	local_irq_restore(flags);
}

static void
probe_wakeup(void *ignore, struct task_struct *p)
{
	struct trace_array_cpu *data;
	int cpu = smp_processor_id();
	unsigned long flags;
	long disabled;
	int pc;

	if (likely(!tracer_enabled))
		return;

	tracing_record_cmdline(p);
	tracing_record_cmdline(current);

	/*
	 * Semantic is like this:
	 *  - wakeup tracer handles all tasks in the system, independently
	 *    from their scheduling class;
	 *  - wakeup_rt tracer handles tasks belonging to sched_dl and
	 *    sched_rt class;
	 *  - wakeup_dl handles tasks belonging to sched_dl class only.
	 */
	if (tracing_dl || (wakeup_dl && !dl_task(p)) ||
	    (wakeup_rt && !dl_task(p) && !rt_task(p)) ||
	    (!dl_task(p) && (p->prio >= wakeup_prio || p->prio >= current->prio)))
		return;

	pc = preempt_count();
	disabled = atomic_inc_return(&per_cpu_ptr(wakeup_trace->array_buffer.data, cpu)->disabled);
	if (unlikely(disabled != 1))
		goto out;

	/* interrupts should be off from try_to_wake_up */
	arch_spin_lock(&wakeup_lock);

	/* check for races. */
	if (!tracer_enabled || tracing_dl ||
	    (!dl_task(p) && p->prio >= wakeup_prio))
		goto out_locked;

	/* reset the trace */
	__wakeup_reset(wakeup_trace);

	wakeup_cpu = task_cpu(p);
	wakeup_current_cpu = wakeup_cpu;
	wakeup_prio = p->prio;

	/*
	 * Once you start tracing a -deadline task, don't bother tracing
	 * another task until the first one wakes up.
	 */
	if (dl_task(p))
		tracing_dl = 1;
	else
		tracing_dl = 0;

	wakeup_task = get_task_struct(p);

	local_save_flags(flags);

	data = per_cpu_ptr(wakeup_trace->array_buffer.data, wakeup_cpu);
	data->preempt_timestamp = ftrace_now(cpu);
	tracing_sched_wakeup_trace(wakeup_trace, p, current, flags, pc);
	__trace_stack(wakeup_trace, flags, 0, pc);

	/*
	 * We must be careful in using CALLER_ADDR2. But since wake_up
	 * is not called by an assembly function  (where as schedule is)
	 * it should be safe to use it here.
	 */
	__trace_function(wakeup_trace, CALLER_ADDR1, CALLER_ADDR2, flags, pc);

out_locked:
	arch_spin_unlock(&wakeup_lock);
out:
	atomic_dec(&per_cpu_ptr(wakeup_trace->array_buffer.data, cpu)->disabled);
}

static void start_wakeup_tracer(struct trace_array *tr)
{
	int ret;

	ret = register_trace_sched_wakeup(probe_wakeup, NULL);
	if (ret) {
		pr_info("wakeup trace: Couldn't activate tracepoint"
			" probe to kernel_sched_wakeup\n");
		return;
	}

	ret = register_trace_sched_wakeup_new(probe_wakeup, NULL);
	if (ret) {
		pr_info("wakeup trace: Couldn't activate tracepoint"
			" probe to kernel_sched_wakeup_new\n");
		goto fail_deprobe;
	}

	ret = register_trace_sched_switch(probe_wakeup_sched_switch, NULL);
	if (ret) {
		pr_info("sched trace: Couldn't activate tracepoint"
			" probe to kernel_sched_switch\n");
		goto fail_deprobe_wake_new;
	}

	ret = register_trace_sched_migrate_task(probe_wakeup_migrate_task, NULL);
	if (ret) {
		pr_info("wakeup trace: Couldn't activate tracepoint"
			" probe to kernel_sched_migrate_task\n");
		goto fail_deprobe_sched_switch;
	}

	wakeup_reset(tr);

	/*
	 * Don't let the tracer_enabled = 1 show up before
	 * the wakeup_task is reset. This may be overkill since
	 * wakeup_reset does a spin_unlock after setting the
	 * wakeup_task to NULL, but I want to be safe.
	 * This is a slow path anyway.
	 */
	smp_wmb();

	if (start_func_tracer(tr, is_graph(tr)))
		printk(KERN_ERR "failed to start wakeup tracer\n");

	return;
fail_deprobe_sched_switch:
	unregister_trace_sched_switch(probe_wakeup_sched_switch, NULL);
fail_deprobe_wake_new:
	unregister_trace_sched_wakeup_new(probe_wakeup, NULL);
fail_deprobe:
	unregister_trace_sched_wakeup(probe_wakeup, NULL);
}

static void stop_wakeup_tracer(struct trace_array *tr)
{
	tracer_enabled = 0;
	stop_func_tracer(tr, is_graph(tr));
	unregister_trace_sched_switch(probe_wakeup_sched_switch, NULL);
	unregister_trace_sched_wakeup_new(probe_wakeup, NULL);
	unregister_trace_sched_wakeup(probe_wakeup, NULL);
	unregister_trace_sched_migrate_task(probe_wakeup_migrate_task, NULL);
}

static bool wakeup_busy;

static int __wakeup_tracer_init(struct trace_array *tr)
{
	save_flags = tr->trace_flags;

	/* non overwrite screws up the latency tracers */
	set_tracer_flag(tr, TRACE_ITER_OVERWRITE, 1);
	set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, 1);

	tr->max_latency = 0;
	wakeup_trace = tr;
	ftrace_init_array_ops(tr, wakeup_tracer_call);
	start_wakeup_tracer(tr);

	wakeup_busy = true;
	return 0;
}

static int wakeup_tracer_init(struct trace_array *tr)
{
	if (wakeup_busy)
		return -EBUSY;

	wakeup_dl = 0;
	wakeup_rt = 0;
	return __wakeup_tracer_init(tr);
}

static int wakeup_rt_tracer_init(struct trace_array *tr)
{
	if (wakeup_busy)
		return -EBUSY;

	wakeup_dl = 0;
	wakeup_rt = 1;
	return __wakeup_tracer_init(tr);
}

static int wakeup_dl_tracer_init(struct trace_array *tr)
{
	if (wakeup_busy)
		return -EBUSY;

	wakeup_dl = 1;
	wakeup_rt = 0;
	return __wakeup_tracer_init(tr);
}

static void wakeup_tracer_reset(struct trace_array *tr)
{
	int lat_flag = save_flags & TRACE_ITER_LATENCY_FMT;
	int overwrite_flag = save_flags & TRACE_ITER_OVERWRITE;

	stop_wakeup_tracer(tr);
	/* make sure we put back any tasks we are tracing */
	wakeup_reset(tr);

	set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, lat_flag);
	set_tracer_flag(tr, TRACE_ITER_OVERWRITE, overwrite_flag);
	ftrace_reset_array_ops(tr);
	wakeup_busy = false;
}

static void wakeup_tracer_start(struct trace_array *tr)
{
	wakeup_reset(tr);
	tracer_enabled = 1;
}

static void wakeup_tracer_stop(struct trace_array *tr)
{
	tracer_enabled = 0;
}

static struct tracer wakeup_tracer __read_mostly =
{
	.name		= "wakeup",
	.init		= wakeup_tracer_init,
	.reset		= wakeup_tracer_reset,
	.start		= wakeup_tracer_start,
	.stop		= wakeup_tracer_stop,
	.print_max	= true,
	.print_header	= wakeup_print_header,
	.print_line	= wakeup_print_line,
	.flag_changed	= wakeup_flag_changed,
#ifdef CONFIG_FTRACE_SELFTEST
	.selftest    = trace_selftest_startup_wakeup,
#endif
	.open		= wakeup_trace_open,
	.close		= wakeup_trace_close,
	.allow_instances = true,
	.use_max_tr	= true,
};

static struct tracer wakeup_rt_tracer __read_mostly =
{
	.name		= "wakeup_rt",
	.init		= wakeup_rt_tracer_init,
	.reset		= wakeup_tracer_reset,
	.start		= wakeup_tracer_start,
	.stop		= wakeup_tracer_stop,
	.print_max	= true,
	.print_header	= wakeup_print_header,
	.print_line	= wakeup_print_line,
	.flag_changed	= wakeup_flag_changed,
#ifdef CONFIG_FTRACE_SELFTEST
	.selftest    = trace_selftest_startup_wakeup,
#endif
	.open		= wakeup_trace_open,
	.close		= wakeup_trace_close,
	.allow_instances = true,
	.use_max_tr	= true,
};

static struct tracer wakeup_dl_tracer __read_mostly =
{
	.name		= "wakeup_dl",
	.init		= wakeup_dl_tracer_init,
	.reset		= wakeup_tracer_reset,
	.start		= wakeup_tracer_start,
	.stop		= wakeup_tracer_stop,
	.print_max	= true,
	.print_header	= wakeup_print_header,
	.print_line	= wakeup_print_line,
	.flag_changed	= wakeup_flag_changed,
#ifdef CONFIG_FTRACE_SELFTEST
	.selftest    = trace_selftest_startup_wakeup,
#endif
	.open		= wakeup_trace_open,
	.close		= wakeup_trace_close,
	.allow_instances = true,
	.use_max_tr	= true,
};

__init static int init_wakeup_tracer(void)
{
	int ret;

	ret = register_tracer(&wakeup_tracer);
	if (ret)
		return ret;

	ret = register_tracer(&wakeup_rt_tracer);
	if (ret)
		return ret;

	ret = register_tracer(&wakeup_dl_tracer);
	if (ret)
		return ret;

	return 0;
}
core_initcall(init_wakeup_tracer);