ftrace: latency tracer infrastructure

This patch adds the latency tracer infrastructure. This patch
does not add anything that will select and turn it on, but will
be used by later patches.

If it were to be compiled, it would add the following files
to the debugfs:

 The root tracing directory:

  /debugfs/tracing/

This patch also adds the following files:

  available_tracers
     list of available tracers. Currently no tracers are
     available. Looking into this file only shows
     "none" which is used to unregister all tracers.

  current_tracer
     The trace that is currently active. Empty on start up.
     To switch to a tracer simply echo one of the tracers that
     are listed in available_tracers:

   example: (used with later patches)

      echo function > /debugfs/tracing/current_tracer

     To disable the tracer:

       echo disable > /debugfs/tracing/current_tracer

  tracing_enabled
     echoing "1" into this file starts the ftrace function tracing
      (if sysctl kernel.ftrace_enabled=1)
     echoing "0" turns it off.

  latency_trace
      This file is readonly and holds the result of the trace.

  trace
      This file outputs a easier to read version of the trace.

  iter_ctrl
      Controls the way the output of traces look.
      So far there's two controls:
        echoing in "symonly" will only show the kallsyms variables
            without the addresses (if kallsyms was configured)
        echoing in "verbose" will change the output to show
            a lot more data, but not very easy to understand by
            humans.
        echoing in "nosymonly" turns off symonly.
        echoing in "noverbose" turns off verbose.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NArnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

kernel/Makefile

@@ -70,6 +70,7 @@ obj-$(CONFIG_TASKSTATS) += taskstats.o tsacct.o
 obj-$(CONFIG_MARKERS) += marker.o
 obj-$(CONFIG_LATENCYTOP) += latencytop.o
 obj-$(CONFIG_FTRACE) += trace/
+obj-$(CONFIG_TRACING) += trace/
 
 ifneq ($(CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER),y)
 # According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is

kernel/trace/Kconfig

@@ -3,3 +3,8 @@
 #
 config HAVE_FTRACE
 	bool
+
+config TRACING
+	bool
+	select DEBUG_FS
+

kernel/trace/Makefile

 obj-$(CONFIG_FTRACE) += libftrace.o
 
+obj-$(CONFIG_TRACING) += trace.o
+
 libftrace-y := ftrace.o

kernel/trace/trace.c

+/*
+ * ring buffer based function tracer
+ *
+ * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
+ * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
+ *
+ * Originally taken from the RT patch by:
+ *    Arnaldo Carvalho de Melo <acme@redhat.com>
+ *
+ * Based on code from the latency_tracer, that is:
+ *  Copyright (C) 2004-2006 Ingo Molnar
+ *  Copyright (C) 2004 William Lee Irwin III
+ */
+#include <linux/utsrelease.h>
+#include <linux/kallsyms.h>
+#include <linux/seq_file.h>
+#include <linux/debugfs.h>
+#include <linux/hardirq.h>
+#include <linux/linkage.h>
+#include <linux/uaccess.h>
+#include <linux/ftrace.h>
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/ctype.h>
+#include <linux/init.h>
+#include <linux/gfp.h>
+#include <linux/fs.h>
+
+#include "trace.h"
+
+unsigned long __read_mostly	tracing_max_latency = (cycle_t)ULONG_MAX;
+unsigned long __read_mostly	tracing_thresh;
+
+static long notrace
+ns2usecs(cycle_t nsec)
+{
+	nsec += 500;
+	do_div(nsec, 1000);
+	return nsec;
+}
+
+static atomic_t			tracer_counter;
+static struct trace_array	global_trace;
+
+static DEFINE_PER_CPU(struct trace_array_cpu, global_trace_cpu);
+
+static struct trace_array	max_tr;
+
+static DEFINE_PER_CPU(struct trace_array_cpu, max_data);
+
+static int			tracer_enabled;
+static unsigned long		trace_nr_entries = 4096UL;
+
+static struct tracer		*trace_types __read_mostly;
+static struct tracer		*current_trace __read_mostly;
+static int			max_tracer_type_len;
+
+static DEFINE_MUTEX(trace_types_lock);
+
+static int __init set_nr_entries(char *str)
+{
+	if (!str)
+		return 0;
+	trace_nr_entries = simple_strtoul(str, &str, 0);
+	return 1;
+}
+__setup("trace_entries=", set_nr_entries);
+
+enum trace_type {
+	__TRACE_FIRST_TYPE = 0,
+
+	TRACE_FN,
+	TRACE_CTX,
+
+	__TRACE_LAST_TYPE
+};
+
+enum trace_flag_type {
+	TRACE_FLAG_IRQS_OFF		= 0x01,
+	TRACE_FLAG_NEED_RESCHED		= 0x02,
+	TRACE_FLAG_HARDIRQ		= 0x04,
+	TRACE_FLAG_SOFTIRQ		= 0x08,
+};
+
+enum trace_iterator_flags {
+	TRACE_ITER_PRINT_PARENT		= 0x01,
+	TRACE_ITER_SYM_OFFSET		= 0x02,
+	TRACE_ITER_SYM_ADDR		= 0x04,
+	TRACE_ITER_VERBOSE		= 0x08,
+};
+
+#define TRACE_ITER_SYM_MASK \
+	(TRACE_ITER_PRINT_PARENT|TRACE_ITER_SYM_OFFSET|TRACE_ITER_SYM_ADDR)
+
+/* These must match the bit postions above */
+static const char *trace_options[] = {
+	"print-parent",
+	"sym-offset",
+	"sym-addr",
+	"verbose",
+	NULL
+};
+
+static unsigned trace_flags;
+
+
+/*
+ * Copy the new maximum trace into the separate maximum-trace
+ * structure. (this way the maximum trace is permanently saved,
+ * for later retrieval via /debugfs/tracing/latency_trace)
+ */
+static void notrace
+__update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
+{
+	struct trace_array_cpu *data = tr->data[cpu];
+
+	max_tr.cpu = cpu;
+	max_tr.time_start = data->preempt_timestamp;
+
+	data = max_tr.data[cpu];
+	data->saved_latency = tracing_max_latency;
+
+	memcpy(data->comm, tsk->comm, TASK_COMM_LEN);
+	data->pid = tsk->pid;
+	data->uid = tsk->uid;
+	data->nice = tsk->static_prio - 20 - MAX_RT_PRIO;
+	data->policy = tsk->policy;
+	data->rt_priority = tsk->rt_priority;
+
+	/* record this tasks comm */
+	tracing_record_cmdline(current);
+}
+
+notrace void
+update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
+{
+	struct trace_array_cpu *data;
+	void *save_trace;
+	int i;
+
+	/* clear out all the previous traces */
+	for_each_possible_cpu(i) {
+		data = tr->data[i];
+		save_trace = max_tr.data[i]->trace;
+		memcpy(max_tr.data[i], data, sizeof(*data));
+		data->trace = save_trace;
+	}
+
+	__update_max_tr(tr, tsk, cpu);
+}
+
+/**
+ * update_max_tr_single - only copy one trace over, and reset the rest
+ * @tr - tracer
+ * @tsk - task with the latency
+ * @cpu - the cpu of the buffer to copy.
+ */
+notrace void
+update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu)
+{
+	struct trace_array_cpu *data = tr->data[cpu];
+	void *save_trace;
+	int i;
+
+	for_each_possible_cpu(i)
+		tracing_reset(max_tr.data[i]);
+
+	save_trace = max_tr.data[cpu]->trace;
+	memcpy(max_tr.data[cpu], data, sizeof(*data));
+	data->trace = save_trace;
+
+	__update_max_tr(tr, tsk, cpu);
+}
+
+int register_tracer(struct tracer *type)
+{
+	struct tracer *t;
+	int len;
+	int ret = 0;
+
+	if (!type->name) {
+		pr_info("Tracer must have a name\n");
+		return -1;
+	}
+
+	mutex_lock(&trace_types_lock);
+	for (t = trace_types; t; t = t->next) {
+		if (strcmp(type->name, t->name) == 0) {
+			/* already found */
+			pr_info("Trace %s already registered\n",
+				type->name);
+			ret = -1;
+			goto out;
+		}
+	}
+
+	type->next = trace_types;
+	trace_types = type;
+	len = strlen(type->name);
+	if (len > max_tracer_type_len)
+		max_tracer_type_len = len;
+ out:
+	mutex_unlock(&trace_types_lock);
+
+	return ret;
+}
+
+void unregister_tracer(struct tracer *type)
+{
+	struct tracer **t;
+	int len;
+
+	mutex_lock(&trace_types_lock);
+	for (t = &trace_types; *t; t = &(*t)->next) {
+		if (*t == type)
+			goto found;
+	}
+	pr_info("Trace %s not registered\n", type->name);
+	goto out;
+
+ found:
+	*t = (*t)->next;
+	if (strlen(type->name) != max_tracer_type_len)
+		goto out;
+
+	max_tracer_type_len = 0;
+	for (t = &trace_types; *t; t = &(*t)->next) {
+		len = strlen((*t)->name);
+		if (len > max_tracer_type_len)
+			max_tracer_type_len = len;
+	}
+ out:
+	mutex_unlock(&trace_types_lock);
+}
+
+void notrace tracing_reset(struct trace_array_cpu *data)
+{
+	data->trace_idx = 0;
+	atomic_set(&data->underrun, 0);
+}
+
+#ifdef CONFIG_FTRACE
+static void notrace
+function_trace_call(unsigned long ip, unsigned long parent_ip)
+{
+	struct trace_array *tr = &global_trace;
+	struct trace_array_cpu *data;
+	unsigned long flags;
+	long disabled;
+	int cpu;
+
+	if (unlikely(!tracer_enabled))
+		return;
+
+	raw_local_irq_save(flags);
+	cpu = raw_smp_processor_id();
+	data = tr->data[cpu];
+	disabled = atomic_inc_return(&data->disabled);
+
+	if (likely(disabled == 1))
+		ftrace(tr, data, ip, parent_ip, flags);
+
+	atomic_dec(&data->disabled);
+	raw_local_irq_restore(flags);
+}
+
+static struct ftrace_ops trace_ops __read_mostly =
+{
+	.func = function_trace_call,
+};
+#endif
+
+notrace void tracing_start_function_trace(void)
+{
+	register_ftrace_function(&trace_ops);
+}
+
+notrace void tracing_stop_function_trace(void)
+{
+	unregister_ftrace_function(&trace_ops);
+}
+
+#define SAVED_CMDLINES 128
+static unsigned map_pid_to_cmdline[PID_MAX_DEFAULT+1];
+static unsigned map_cmdline_to_pid[SAVED_CMDLINES];
+static char saved_cmdlines[SAVED_CMDLINES][TASK_COMM_LEN];
+static int cmdline_idx;
+static DEFINE_SPINLOCK(trace_cmdline_lock);
+atomic_t trace_record_cmdline_disabled;
+
+static void trace_init_cmdlines(void)
+{
+	memset(&map_pid_to_cmdline, -1, sizeof(map_pid_to_cmdline));
+	memset(&map_cmdline_to_pid, -1, sizeof(map_cmdline_to_pid));
+	cmdline_idx = 0;
+}
+
+notrace void trace_stop_cmdline_recording(void);
+
+static void notrace trace_save_cmdline(struct task_struct *tsk)
+{
+	unsigned map;
+	unsigned idx;
+
+	if (!tsk->pid || unlikely(tsk->pid > PID_MAX_DEFAULT))
+		return;
+
+	/*
+	 * It's not the end of the world if we don't get
+	 * the lock, but we also don't want to spin
+	 * nor do we want to disable interrupts,
+	 * so if we miss here, then better luck next time.
+	 */
+	if (!spin_trylock(&trace_cmdline_lock))
+		return;
+
+	idx = map_pid_to_cmdline[tsk->pid];
+	if (idx >= SAVED_CMDLINES) {
+		idx = (cmdline_idx + 1) % SAVED_CMDLINES;
+
+		map = map_cmdline_to_pid[idx];
+		if (map <= PID_MAX_DEFAULT)
+			map_pid_to_cmdline[map] = (unsigned)-1;
+
+		map_pid_to_cmdline[tsk->pid] = idx;
+
+		cmdline_idx = idx;
+	}
+
+	memcpy(&saved_cmdlines[idx], tsk->comm, TASK_COMM_LEN);
+
+	spin_unlock(&trace_cmdline_lock);
+}
+
+static notrace char *trace_find_cmdline(int pid)
+{
+	char *cmdline = "<...>";
+	unsigned map;
+
+	if (!pid)
+		return "<idle>";
+
+	if (pid > PID_MAX_DEFAULT)
+		goto out;
+
+	map = map_pid_to_cmdline[pid];
+	if (map >= SAVED_CMDLINES)
+		goto out;
+
+	cmdline = saved_cmdlines[map];
+
+ out:
+	return cmdline;
+}
+
+notrace void tracing_record_cmdline(struct task_struct *tsk)
+{
+	if (atomic_read(&trace_record_cmdline_disabled))
+		return;
+
+	trace_save_cmdline(tsk);
+}
+
+static inline notrace struct trace_entry *
+tracing_get_trace_entry(struct trace_array *tr,
+			struct trace_array_cpu *data)
+{
+	unsigned long idx, idx_next;
+	struct trace_entry *entry;
+
+	idx = data->trace_idx;
+	idx_next = idx + 1;
+
+	if (unlikely(idx_next >= tr->entries)) {
+		atomic_inc(&data->underrun);
+		idx_next = 0;
+	}
+
+	data->trace_idx = idx_next;
+
+	if (unlikely(idx_next != 0 && atomic_read(&data->underrun)))
+		atomic_inc(&data->underrun);
+
+	entry = data->trace + idx * TRACE_ENTRY_SIZE;
+
+	return entry;
+}
+
+static inline notrace void
+tracing_generic_entry_update(struct trace_entry *entry,
+			     unsigned long flags)
+{
+	struct task_struct *tsk = current;
+	unsigned long pc;
+
+	pc = preempt_count();
+
+	entry->idx	= atomic_inc_return(&tracer_counter);
+	entry->preempt_count = pc & 0xff;
+	entry->pid	 = tsk->pid;
+	entry->t	 = now(raw_smp_processor_id());
+	entry->flags = (irqs_disabled_flags(flags) ? TRACE_FLAG_IRQS_OFF : 0) |
+		((pc & HARDIRQ_MASK) ? TRACE_FLAG_HARDIRQ : 0) |
+		((pc & SOFTIRQ_MASK) ? TRACE_FLAG_SOFTIRQ : 0) |
+		(need_resched() ? TRACE_FLAG_NEED_RESCHED : 0);
+}
+
+notrace void
+ftrace(struct trace_array *tr, struct trace_array_cpu *data,
+		       unsigned long ip, unsigned long parent_ip,
+		       unsigned long flags)
+{
+	struct trace_entry *entry;
+
+	entry = tracing_get_trace_entry(tr, data);
+	tracing_generic_entry_update(entry, flags);
+	entry->type	    = TRACE_FN;
+	entry->fn.ip	    = ip;
+	entry->fn.parent_ip = parent_ip;
+}
+
+notrace void
+tracing_sched_switch_trace(struct trace_array *tr,
+			   struct trace_array_cpu *data,
+			   struct task_struct *prev, struct task_struct *next,
+			   unsigned long flags)
+{
+	struct trace_entry *entry;
+
+	entry = tracing_get_trace_entry(tr, data);
+	tracing_generic_entry_update(entry, flags);
+	entry->type		= TRACE_CTX;
+	entry->ctx.prev_pid	= prev->pid;
+	entry->ctx.prev_prio	= prev->prio;
+	entry->ctx.prev_state	= prev->state;
+	entry->ctx.next_pid	= next->pid;
+	entry->ctx.next_prio	= next->prio;
+}
+
+enum trace_file_type {
+	TRACE_FILE_LAT_FMT	= 1,
+};
+
+static struct trace_entry *
+trace_entry_idx(struct trace_array *tr, unsigned long idx, int cpu)
+{
+	struct trace_entry *array = tr->data[cpu]->trace;
+	unsigned long underrun;
+
+	if (idx >= tr->entries)
+		return NULL;
+
+	underrun = atomic_read(&tr->data[cpu]->underrun);
+	if (underrun)
+		idx = ((underrun - 1) + idx) % tr->entries;
+	else if (idx >= tr->data[cpu]->trace_idx)
+		return NULL;
+
+	return &array[idx];
+}
+
+static struct notrace trace_entry *
+find_next_entry(struct trace_iterator *iter, int *ent_cpu)
+{
+	struct trace_array *tr = iter->tr;
+	struct trace_entry *ent, *next = NULL;
+	int next_cpu = -1;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		if (!tr->data[cpu]->trace)
+			continue;
+		ent = trace_entry_idx(tr, iter->next_idx[cpu], cpu);
+		if (ent &&
+		    (!next || (long)(next->idx - ent->idx) > 0)) {
+			next = ent;
+			next_cpu = cpu;
+		}
+	}
+
+	if (ent_cpu)
+		*ent_cpu = next_cpu;
+
+	return next;
+}
+
+static void *find_next_entry_inc(struct trace_iterator *iter)
+{
+	struct trace_entry *next;
+	int next_cpu = -1;
+
+	next = find_next_entry(iter, &next_cpu);
+
+	if (next) {
+		iter->next_idx[next_cpu]++;
+		iter->idx++;
+	}
+	iter->ent = next;
+	iter->cpu = next_cpu;
+
+	return next ? iter : NULL;
+}
+
+static void notrace *
+s_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	struct trace_iterator *iter = m->private;
+	void *ent;
+	void *last_ent = iter->ent;
+	int i = (int)*pos;
+
+	(*pos)++;
+
+	/* can't go backwards */
+	if (iter->idx > i)
+		return NULL;
+
+	if (iter->idx < 0)
+		ent = find_next_entry_inc(iter);
+	else
+		ent = iter;
+
+	while (ent && iter->idx < i)
+		ent = find_next_entry_inc(iter);
+
+	iter->pos = *pos;
+
+	if (last_ent && !ent)
+		seq_puts(m, "\n\nvim:ft=help\n");
+
+	return ent;
+}
+
+static void *s_start(struct seq_file *m, loff_t *pos)
+{
+	struct trace_iterator *iter = m->private;
+	void *p = NULL;
+	loff_t l = 0;
+	int i;
+
+	mutex_lock(&trace_types_lock);
+
+	if (!current_trace || current_trace != iter->trace)
+		return NULL;
+
+	atomic_inc(&trace_record_cmdline_disabled);
+
+	/* let the tracer grab locks here if needed */
+	if (current_trace->start)
+		current_trace->start(iter);
+
+	if (*pos != iter->pos) {
+		iter->ent = NULL;
+		iter->cpu = 0;
+		iter->idx = -1;
+
+		for (i = 0; i < NR_CPUS; i++)
+			iter->next_idx[i] = 0;
+
+		for (p = iter; p && l < *pos; p = s_next(m, p, &l))
+			;
+
+	} else {
+		l = *pos;
+		p = s_next(m, p, &l);
+	}
+
+	return p;
+}
+
+static void s_stop(struct seq_file *m, void *p)
+{
+	struct trace_iterator *iter = m->private;
+
+	atomic_dec(&trace_record_cmdline_disabled);
+
+	/* let the tracer release locks here if needed */
+	if (current_trace && current_trace == iter->trace && iter->trace->stop)
+		iter->trace->stop(iter);
+
+	mutex_unlock(&trace_types_lock);
+}
+
+static void
+seq_print_sym_short(struct seq_file *m, const char *fmt, unsigned long address)
+{
+#ifdef CONFIG_KALLSYMS
+	char str[KSYM_SYMBOL_LEN];
+
+	kallsyms_lookup(address, NULL, NULL, NULL, str);
+
+	seq_printf(m, fmt, str);
+#endif
+}
+
+static void
+seq_print_sym_offset(struct seq_file *m, const char *fmt, unsigned long address)
+{
+#ifdef CONFIG_KALLSYMS
+	char str[KSYM_SYMBOL_LEN];
+
+	sprint_symbol(str, address);
+	seq_printf(m, fmt, str);
+#endif
+}
+
+#ifndef CONFIG_64BIT
+# define IP_FMT "%08lx"
+#else
+# define IP_FMT "%016lx"
+#endif
+
+static void notrace
+seq_print_ip_sym(struct seq_file *m, unsigned long ip, unsigned long sym_flags)
+{
+	if (!ip) {
+		seq_printf(m, "0");
+		return;
+	}
+
+	if (sym_flags & TRACE_ITER_SYM_OFFSET)
+		seq_print_sym_offset(m, "%s", ip);
+	else
+		seq_print_sym_short(m, "%s", ip);
+
+	if (sym_flags & TRACE_ITER_SYM_ADDR)
+		seq_printf(m, " <" IP_FMT ">", ip);
+}
+
+static void notrace print_lat_help_header(struct seq_file *m)
+{
+	seq_puts(m, "#                _------=> CPU#            \n");
+	seq_puts(m, "#               / _-----=> irqs-off        \n");
+	seq_puts(m, "#              | / _----=> need-resched    \n");
+	seq_puts(m, "#              || / _---=> hardirq/softirq \n");
+	seq_puts(m, "#              ||| / _--=> preempt-depth   \n");
+	seq_puts(m, "#              |||| /                      \n");
+	seq_puts(m, "#              |||||     delay             \n");
+	seq_puts(m, "#  cmd     pid ||||| time  |   caller      \n");
+	seq_puts(m, "#     \\   /    |||||   \\   |   /           \n");
+}
+
+static void notrace print_func_help_header(struct seq_file *m)
+{
+	seq_puts(m, "#           TASK-PID   CPU#    TIMESTAMP  FUNCTION\n");
+	seq_puts(m, "#              | |      |          |         |\n");
+}
+
+
+static void notrace
+print_trace_header(struct seq_file *m, struct trace_iterator *iter)
+{
+	unsigned long sym_flags = (trace_flags & TRACE_ITER_SYM_MASK);
+	struct trace_array *tr = iter->tr;
+	struct trace_array_cpu *data = tr->data[tr->cpu];
+	struct tracer *type = current_trace;
+	unsigned long underruns = 0;
+	unsigned long underrun;
+	unsigned long entries   = 0;
+	int cpu;
+	const char *name = "preemption";
+
+	if (type)
+		name = type->name;
+
+	for_each_possible_cpu(cpu) {
+		if (tr->data[cpu]->trace) {
+			underrun = atomic_read(&tr->data[cpu]->underrun);
+			if (underrun) {
+				underruns += underrun;
+				entries += tr->entries;
+			} else
+				entries += tr->data[cpu]->trace_idx;
+		}
+	}
+
+	seq_printf(m, "%s latency trace v1.1.5 on %s\n",
+		   name, UTS_RELEASE);
+	seq_puts(m, "-----------------------------------"
+		 "---------------------------------\n");
+	seq_printf(m, " latency: %lu us, #%lu/%lu, CPU#%d |"
+		   " (M:%s VP:%d, KP:%d, SP:%d HP:%d",
+		   data->saved_latency,
+		   entries,
+		   (entries + underruns),
+		   tr->cpu,
+#if defined(CONFIG_PREEMPT_NONE)
+		   "server",
+#elif defined(CONFIG_PREEMPT_VOLUNTARY)
+		   "desktop",
+#elif defined(CONFIG_PREEMPT_DESKTOP)
+		   "preempt",
+#else
+		   "unknown",
+#endif
+		   /* These are reserved for later use */
+		   0, 0, 0, 0);
+#ifdef CONFIG_SMP
+	seq_printf(m, " #P:%d)\n", num_online_cpus());
+#else
+	seq_puts(m, ")\n");
+#endif
+	seq_puts(m, "    -----------------\n");
+	seq_printf(m, "    | task: %.16s-%d "
+		   "(uid:%d nice:%ld policy:%ld rt_prio:%ld)\n",
+		   data->comm, data->pid, data->uid, data->nice,
+		   data->policy, data->rt_priority);
+	seq_puts(m, "    -----------------\n");
+
+	if (data->critical_start) {
+		seq_puts(m, " => started at: ");
+		seq_print_ip_sym(m, data->critical_start, sym_flags);
+		seq_puts(m, "\n => ended at:   ");
+		seq_print_ip_sym(m, data->critical_end, sym_flags);
+		seq_puts(m, "\n");
+	}
+
+	seq_puts(m, "\n");
+}
+
+unsigned long nsecs_to_usecs(unsigned long nsecs)
+{
+	return nsecs / 1000;
+}
+
+static void notrace
+lat_print_generic(struct seq_file *m, struct trace_entry *entry, int cpu)
+{
+	int hardirq, softirq;
+	char *comm;
+
+	comm = trace_find_cmdline(entry->pid);
+
+	seq_printf(m, "%8.8s-%-5d ", comm, entry->pid);
+	seq_printf(m, "%d", cpu);
+	seq_printf(m, "%c%c",
+		   (entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' : '.',
+		   ((entry->flags & TRACE_FLAG_NEED_RESCHED) ? 'N' : '.'));
+
+	hardirq = entry->flags & TRACE_FLAG_HARDIRQ;
+	softirq = entry->flags & TRACE_FLAG_SOFTIRQ;
+	if (hardirq && softirq)
+		seq_putc(m, 'H');
+	else {
+		if (hardirq)
+			seq_putc(m, 'h');
+		else {
+			if (softirq)
+				seq_putc(m, 's');
+			else
+				seq_putc(m, '.');
+		}
+	}
+
+	if (entry->preempt_count)
+		seq_printf(m, "%x", entry->preempt_count);
+	else
+		seq_puts(m, ".");
+}
+
+unsigned long preempt_mark_thresh = 100;
+
+static void notrace
+lat_print_timestamp(struct seq_file *m, unsigned long long abs_usecs,
+		    unsigned long rel_usecs)
+{
+	seq_printf(m, " %4lldus", abs_usecs);
+	if (rel_usecs > preempt_mark_thresh)
+		seq_puts(m, "!: ");
+	else if (rel_usecs > 1)
+		seq_puts(m, "+: ");
+	else
+		seq_puts(m, " : ");
+}
+
+static const char state_to_char[] = TASK_STATE_TO_CHAR_STR;
+
+static void notrace
+print_lat_fmt(struct seq_file *m, struct trace_iterator *iter,
+	      unsigned int trace_idx, int cpu)
+{
+	unsigned long sym_flags = (trace_flags & TRACE_ITER_SYM_MASK);
+	struct trace_entry *next_entry = find_next_entry(iter, NULL);
+	unsigned long verbose = (trace_flags & TRACE_ITER_VERBOSE);
+	struct trace_entry *entry = iter->ent;
+	unsigned long abs_usecs;
+	unsigned long rel_usecs;
+	char *comm;
+	int S;
+
+	if (!next_entry)
+		next_entry = entry;
+	rel_usecs = ns2usecs(next_entry->t - entry->t);
+	abs_usecs = ns2usecs(entry->t - iter->tr->time_start);
+
+	if (verbose) {
+		comm = trace_find_cmdline(entry->pid);
+		seq_printf(m, "%16s %5d %d %d %08x %08x [%08lx]"
+			   " %ld.%03ldms (+%ld.%03ldms): ",
+			   comm,
+			   entry->pid, cpu, entry->flags,
+			   entry->preempt_count, trace_idx,
+			   ns2usecs(entry->t),
+			   abs_usecs/1000,
+			   abs_usecs % 1000, rel_usecs/1000, rel_usecs % 1000);
+	} else {
+		lat_print_generic(m, entry, cpu);
+		lat_print_timestamp(m, abs_usecs, rel_usecs);
+	}
+	switch (entry->type) {
+	case TRACE_FN:
+		seq_print_ip_sym(m, entry->fn.ip, sym_flags);
+		seq_puts(m, " (");
+		seq_print_ip_sym(m, entry->fn.parent_ip, sym_flags);
+		seq_puts(m, ")\n");
+		break;
+	case TRACE_CTX:
+		S = entry->ctx.prev_state < sizeof(state_to_char) ?
+			state_to_char[entry->ctx.prev_state] : 'X';
+		comm = trace_find_cmdline(entry->ctx.next_pid);
+		seq_printf(m, " %d:%d:%c --> %d:%d %s\n",
+			   entry->ctx.prev_pid,
+			   entry->ctx.prev_prio,
+			   S,
+			   entry->ctx.next_pid,
+			   entry->ctx.next_prio,
+			   comm);
+		break;
+	}
+}
+
+static void notrace
+print_trace_fmt(struct seq_file *m, struct trace_iterator *iter)
+{
+	unsigned long sym_flags = (trace_flags & TRACE_ITER_SYM_MASK);
+	struct trace_entry *entry = iter->ent;
+	unsigned long usec_rem;
+	unsigned long long t;
+	unsigned long secs;
+	char *comm;
+	int S;
+
+	comm = trace_find_cmdline(iter->ent->pid);
+
+	t = ns2usecs(entry->t);
+	usec_rem = do_div(t, 1000000ULL);
+	secs = (unsigned long)t;
+
+	seq_printf(m, "%16s-%-5d ", comm, entry->pid);
+	seq_printf(m, "[%02d] ", iter->cpu);
+	seq_printf(m, "%5lu.%06lu: ", secs, usec_rem);
+
+	switch (entry->type) {
+	case TRACE_FN:
+		seq_print_ip_sym(m, entry->fn.ip, sym_flags);
+		if ((sym_flags & TRACE_ITER_PRINT_PARENT) &&
+						entry->fn.parent_ip) {
+			seq_printf(m, " <-");
+			seq_print_ip_sym(m, entry->fn.parent_ip, sym_flags);
+		}
+		break;
+	case TRACE_CTX:
+		S = entry->ctx.prev_state < sizeof(state_to_char) ?
+			state_to_char[entry->ctx.prev_state] : 'X';
+		seq_printf(m, " %d:%d:%c ==> %d:%d\n",
+			   entry->ctx.prev_pid,
+			   entry->ctx.prev_prio,
+			   S,
+			   entry->ctx.next_pid,
+			   entry->ctx.next_prio);
+		break;
+	}
+	seq_printf(m, "\n");
+}
+
+static int trace_empty(struct trace_iterator *iter)
+{
+	struct trace_array_cpu *data;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		data = iter->tr->data[cpu];
+
+		if (data->trace &&
+		    (data->trace_idx ||
+		     atomic_read(&data->underrun)))
+			return 0;
+	}
+	return 1;
+}
+
+static int s_show(struct seq_file *m, void *v)
+{
+	struct trace_iterator *iter = v;
+
+	if (iter->ent == NULL) {
+		if (iter->tr) {
+			seq_printf(m, "# tracer: %s\n", iter->trace->name);
+			seq_puts(m, "#\n");
+		}
+		if (iter->iter_flags & TRACE_FILE_LAT_FMT) {
+			/* print nothing if the buffers are empty */
+			if (trace_empty(iter))
+				return 0;
+			print_trace_header(m, iter);
+			if (!(trace_flags & TRACE_ITER_VERBOSE))
+				print_lat_help_header(m);
+		} else {
+			if (!(trace_flags & TRACE_ITER_VERBOSE))
+				print_func_help_header(m);
+		}
+	} else {
+		if (iter->iter_flags & TRACE_FILE_LAT_FMT)
+			print_lat_fmt(m, iter, iter->idx, iter->cpu);
+		else
+			print_trace_fmt(m, iter);
+	}
+
+	return 0;
+}
+
+static struct seq_operations tracer_seq_ops = {
+	.start = s_start,
+	.next = s_next,
+	.stop = s_stop,
+	.show = s_show,
+};
+
+static struct trace_iterator notrace *
+__tracing_open(struct inode *inode, struct file *file, int *ret)
+{
+	struct trace_iterator *iter;
+
+	iter = kzalloc(sizeof(*iter), GFP_KERNEL);
+	if (!iter) {
+		*ret = -ENOMEM;
+		goto out;
+	}
+
+	mutex_lock(&trace_types_lock);
+	if (current_trace && current_trace->print_max)
+		iter->tr = &max_tr;
+	else
+		iter->tr = inode->i_private;
+	iter->trace = current_trace;
+	iter->pos = -1;
+
+	/* TODO stop tracer */
+	*ret = seq_open(file, &tracer_seq_ops);
+	if (!*ret) {
+		struct seq_file *m = file->private_data;
+		m->private = iter;
+
+		/* stop the trace while dumping */
+		if (iter->tr->ctrl)
+			tracer_enabled = 0;
+
+		if (iter->trace && iter->trace->open)
+			iter->trace->open(iter);
+	} else {
+		kfree(iter);
+		iter = NULL;
+	}
+	mutex_unlock(&trace_types_lock);
+
+ out:
+	return iter;
+}
+
+int tracing_open_generic(struct inode *inode, struct file *filp)
+{
+	filp->private_data = inode->i_private;
+	return 0;
+}
+
+int tracing_release(struct inode *inode, struct file *file)
+{
+	struct seq_file *m = (struct seq_file *)file->private_data;
+	struct trace_iterator *iter = m->private;
+
+	mutex_lock(&trace_types_lock);
+	if (iter->trace && iter->trace->close)
+		iter->trace->close(iter);
+
+	/* reenable tracing if it was previously enabled */
+	if (iter->tr->ctrl)
+		tracer_enabled = 1;
+	mutex_unlock(&trace_types_lock);
+
+	seq_release(inode, file);
+	kfree(iter);
+	return 0;
+}
+
+static int tracing_open(struct inode *inode, struct file *file)
+{
+	int ret;
+
+	__tracing_open(inode, file, &ret);
+
+	return ret;
+}
+
+static int tracing_lt_open(struct inode *inode, struct file *file)
+{
+	struct trace_iterator *iter;
+	int ret;
+
+	iter = __tracing_open(inode, file, &ret);
+
+	if (!ret)
+		iter->iter_flags |= TRACE_FILE_LAT_FMT;
+
+	return ret;
+}
+
+
+static void notrace *
+t_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	struct tracer *t = m->private;
+
+	(*pos)++;
+
+	if (t)
+		t = t->next;
+
+	m->private = t;
+
+	return t;
+}
+
+static void *t_start(struct seq_file *m, loff_t *pos)
+{
+	struct tracer *t = m->private;
+	loff_t l = 0;
+
+	mutex_lock(&trace_types_lock);
+	for (; t && l < *pos; t = t_next(m, t, &l))
+		;
+
+	return t;
+}
+
+static void t_stop(struct seq_file *m, void *p)
+{
+	mutex_unlock(&trace_types_lock);
+}
+
+static int t_show(struct seq_file *m, void *v)
+{
+	struct tracer *t = v;
+
+	if (!t)
+		return 0;
+
+	seq_printf(m, "%s", t->name);
+	if (t->next)
+		seq_putc(m, ' ');
+	else
+		seq_putc(m, '\n');
+
+	return 0;
+}
+
+static struct seq_operations show_traces_seq_ops = {
+	.start = t_start,
+	.next = t_next,
+	.stop = t_stop,
+	.show = t_show,
+};
+
+static int show_traces_open(struct inode *inode, struct file *file)
+{
+	int ret;
+
+	ret = seq_open(file, &show_traces_seq_ops);
+	if (!ret) {
+		struct seq_file *m = file->private_data;
+		m->private = trace_types;
+	}
+
+	return ret;
+}
+
+static struct file_operations tracing_fops = {
+	.open = tracing_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = tracing_release,
+};
+
+static struct file_operations tracing_lt_fops = {
+	.open = tracing_lt_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = tracing_release,
+};
+
+static struct file_operations show_traces_fops = {
+	.open = show_traces_open,
+	.read = seq_read,
+	.release = seq_release,
+};
+
+static ssize_t
+tracing_iter_ctrl_read(struct file *filp, char __user *ubuf,
+		       size_t cnt, loff_t *ppos)
+{
+	char *buf;
+	int r = 0;
+	int len = 0;
+	int i;
+
+	/* calulate max size */
+	for (i = 0; trace_options[i]; i++) {
+		len += strlen(trace_options[i]);
+		len += 3; /* "no" and space */
+	}
+
+	/* +2 for \n and \0 */
+	buf = kmalloc(len + 2, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	for (i = 0; trace_options[i]; i++) {
+		if (trace_flags & (1 << i))
+			r += sprintf(buf + r, "%s ", trace_options[i]);
+		else
+			r += sprintf(buf + r, "no%s ", trace_options[i]);
+	}
+
+	r += sprintf(buf + r, "\n");
+	WARN_ON(r >= len + 2);
+
+	r = simple_read_from_buffer(ubuf, cnt, ppos,
+				    buf, r);
+
+	kfree(buf);
+
+	return r;
+}
+
+static ssize_t
+tracing_iter_ctrl_write(struct file *filp, const char __user *ubuf,
+			size_t cnt, loff_t *ppos)
+{
+	char buf[64];
+	char *cmp = buf;
+	int neg = 0;
+	int i;
+
+	if (cnt > 63)
+		cnt = 63;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+
+	if (strncmp(buf, "no", 2) == 0) {
+		neg = 1;
+		cmp += 2;
+	}
+
+	for (i = 0; trace_options[i]; i++) {
+		int len = strlen(trace_options[i]);
+
+		if (strncmp(cmp, trace_options[i], len) == 0) {
+			if (neg)
+				trace_flags &= ~(1 << i);
+			else
+				trace_flags |= (1 << i);
+			break;
+		}
+	}
+
+	filp->f_pos += cnt;
+
+	return cnt;
+}
+
+static struct file_operations tracing_iter_fops = {
+	.open = tracing_open_generic,
+	.read = tracing_iter_ctrl_read,
+	.write = tracing_iter_ctrl_write,
+};
+
+static ssize_t
+tracing_ctrl_read(struct file *filp, char __user *ubuf,
+		  size_t cnt, loff_t *ppos)
+{
+	struct trace_array *tr = filp->private_data;
+	char buf[64];
+	int r;
+
+	r = sprintf(buf, "%ld\n", tr->ctrl);
+	return simple_read_from_buffer(ubuf, cnt, ppos,
+				       buf, r);
+}
+
+static ssize_t
+tracing_ctrl_write(struct file *filp, const char __user *ubuf,
+		   size_t cnt, loff_t *ppos)
+{
+	struct trace_array *tr = filp->private_data;
+	long val;
+	char buf[64];
+
+	if (cnt > 63)
+		cnt = 63;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+
+	val = simple_strtoul(buf, NULL, 10);
+
+	val = !!val;
+
+	mutex_lock(&trace_types_lock);
+	if (tr->ctrl ^ val) {
+		if (val)
+			tracer_enabled = 1;
+		else
+			tracer_enabled = 0;
+
+		tr->ctrl = val;
+
+		if (current_trace && current_trace->ctrl_update)
+			current_trace->ctrl_update(tr);
+	}
+	mutex_unlock(&trace_types_lock);
+
+	filp->f_pos += cnt;
+
+	return cnt;
+}
+
+static ssize_t
+tracing_set_trace_read(struct file *filp, char __user *ubuf,
+		       size_t cnt, loff_t *ppos)
+{
+	char buf[max_tracer_type_len+2];
+	int r;
+
+	mutex_lock(&trace_types_lock);
+	if (current_trace)
+		r = sprintf(buf, "%s\n", current_trace->name);
+	else
+		r = sprintf(buf, "\n");
+	mutex_unlock(&trace_types_lock);
+
+	return simple_read_from_buffer(ubuf, cnt, ppos,
+				       buf, r);
+}
+
+static ssize_t
+tracing_set_trace_write(struct file *filp, const char __user *ubuf,
+			size_t cnt, loff_t *ppos)
+{
+	struct trace_array *tr = &global_trace;
+	struct tracer *t;
+	char buf[max_tracer_type_len+1];
+	int i;
+
+	if (cnt > max_tracer_type_len)
+		cnt = max_tracer_type_len;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+
+	/* strip ending whitespace. */
+	for (i = cnt - 1; i > 0 && isspace(buf[i]); i--)
+		buf[i] = 0;
+
+	mutex_lock(&trace_types_lock);
+	for (t = trace_types; t; t = t->next) {
+		if (strcmp(t->name, buf) == 0)
+			break;
+	}
+	if (!t || t == current_trace)
+		goto out;
+
+	if (current_trace && current_trace->reset)
+		current_trace->reset(tr);
+
+	current_trace = t;
+	if (t->init)
+		t->init(tr);
+
+ out:
+	mutex_unlock(&trace_types_lock);
+
+	filp->f_pos += cnt;
+
+	return cnt;
+}
+
+static ssize_t
+tracing_max_lat_read(struct file *filp, char __user *ubuf,
+		     size_t cnt, loff_t *ppos)
+{
+	unsigned long *ptr = filp->private_data;
+	char buf[64];
+	int r;
+
+	r = snprintf(buf, 64, "%ld\n",
+		     *ptr == (unsigned long)-1 ? -1 : nsecs_to_usecs(*ptr));
+	if (r > 64)
+		r = 64;
+	return simple_read_from_buffer(ubuf, cnt, ppos,
+				       buf, r);
+}
+
+static ssize_t
+tracing_max_lat_write(struct file *filp, const char __user *ubuf,
+		      size_t cnt, loff_t *ppos)
+{
+	long *ptr = filp->private_data;
+	long val;
+	char buf[64];
+
+	if (cnt > 63)
+		cnt = 63;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+
+	val = simple_strtoul(buf, NULL, 10);
+
+	*ptr = val * 1000;
+
+	return cnt;
+}
+
+static struct file_operations tracing_max_lat_fops = {
+	.open = tracing_open_generic,
+	.read = tracing_max_lat_read,
+	.write = tracing_max_lat_write,
+};
+
+static struct file_operations tracing_ctrl_fops = {
+	.open = tracing_open_generic,
+	.read = tracing_ctrl_read,
+	.write = tracing_ctrl_write,
+};
+
+static struct file_operations set_tracer_fops = {
+	.open = tracing_open_generic,
+	.read = tracing_set_trace_read,
+	.write = tracing_set_trace_write,
+};
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+
+static ssize_t
+tracing_read_long(struct file *filp, char __user *ubuf,
+		  size_t cnt, loff_t *ppos)
+{
+	unsigned long *p = filp->private_data;
+	char buf[64];
+	int r;
+
+	r = sprintf(buf, "%ld\n", *p);
+	return simple_read_from_buffer(ubuf, cnt, ppos,
+				       buf, r);
+}
+
+static struct file_operations tracing_read_long_fops = {
+	.open = tracing_open_generic,
+	.read = tracing_read_long,
+};
+#endif
+
+static struct dentry *d_tracer;
+
+struct dentry *tracing_init_dentry(void)
+{
+	static int once;
+
+	if (d_tracer)
+		return d_tracer;
+
+	d_tracer = debugfs_create_dir("tracing", NULL);
+
+	if (!d_tracer && !once) {
+		once = 1;
+		pr_warning("Could not create debugfs directory 'tracing'\n");
+		return NULL;
+	}
+
+	return d_tracer;
+}
+
+static __init void tracer_init_debugfs(void)
+{
+	struct dentry *d_tracer;
+	struct dentry *entry;
+
+	d_tracer = tracing_init_dentry();
+
+	entry = debugfs_create_file("tracing_enabled", 0644, d_tracer,
+				    &global_trace, &tracing_ctrl_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs 'tracing_enabled' entry\n");
+
+	entry = debugfs_create_file("iter_ctrl", 0644, d_tracer,
+				    NULL, &tracing_iter_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs 'iter_ctrl' entry\n");
+
+	entry = debugfs_create_file("latency_trace", 0444, d_tracer,
+				    &global_trace, &tracing_lt_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs 'latency_trace' entry\n");
+
+	entry = debugfs_create_file("trace", 0444, d_tracer,
+				    &global_trace, &tracing_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs 'trace' entry\n");
+
+	entry = debugfs_create_file("available_tracers", 0444, d_tracer,
+				    &global_trace, &show_traces_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs 'trace' entry\n");
+
+	entry = debugfs_create_file("current_tracer", 0444, d_tracer,
+				    &global_trace, &set_tracer_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs 'trace' entry\n");
+
+	entry = debugfs_create_file("tracing_max_latency", 0644, d_tracer,
+				    &tracing_max_latency,
+				    &tracing_max_lat_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs "
+			   "'tracing_max_latency' entry\n");
+
+	entry = debugfs_create_file("tracing_thresh", 0644, d_tracer,
+				    &tracing_thresh, &tracing_max_lat_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs "
+			   "'tracing_threash' entry\n");
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+	entry = debugfs_create_file("dyn_ftrace_total_info", 0444, d_tracer,
+				    &ftrace_update_tot_cnt,
+				    &tracing_read_long_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs "
+			   "'dyn_ftrace_total_info' entry\n");
+#endif
+}
+
+/* dummy trace to disable tracing */
+static struct tracer no_tracer __read_mostly =
+{
+	.name = "none",
+};
+
+static inline notrace int page_order(const unsigned long size)
+{
+	const unsigned long nr_pages = DIV_ROUND_UP(size, PAGE_SIZE);
+	return ilog2(roundup_pow_of_two(nr_pages));
+}
+
+__init static int tracer_alloc_buffers(void)
+{
+	const int order = page_order(trace_nr_entries * TRACE_ENTRY_SIZE);
+	const unsigned long size = (1UL << order) << PAGE_SHIFT;
+	struct trace_entry *array;
+	int i;
+
+	for_each_possible_cpu(i) {
+		global_trace.data[i] = &per_cpu(global_trace_cpu, i);
+		max_tr.data[i] = &per_cpu(max_data, i);
+
+		array = (struct trace_entry *)
+			  __get_free_pages(GFP_KERNEL, order);
+		if (array == NULL) {
+			printk(KERN_ERR "tracer: failed to allocate"
+			       " %ld bytes for trace buffer!\n", size);
+			goto free_buffers;
+		}
+		global_trace.data[i]->trace = array;
+
+/* Only allocate if we are actually using the max trace */
+#ifdef CONFIG_TRACER_MAX_TRACE
+		array = (struct trace_entry *)
+			  __get_free_pages(GFP_KERNEL, order);
+		if (array == NULL) {
+			printk(KERN_ERR "wakeup tracer: failed to allocate"
+			       " %ld bytes for trace buffer!\n", size);
+			goto free_buffers;
+		}
+		max_tr.data[i]->trace = array;
+#endif
+	}
+
+	/*
+	 * Since we allocate by orders of pages, we may be able to
+	 * round up a bit.
+	 */
+	global_trace.entries = size / TRACE_ENTRY_SIZE;
+	max_tr.entries = global_trace.entries;
+
+	pr_info("tracer: %ld bytes allocated for %ld",
+		size, trace_nr_entries);
+	pr_info(" entries of %ld bytes\n", (long)TRACE_ENTRY_SIZE);
+	pr_info("   actual entries %ld\n", global_trace.entries);
+
+	tracer_init_debugfs();
+
+	trace_init_cmdlines();
+
+	register_tracer(&no_tracer);
+	current_trace = &no_tracer;
+
+	return 0;
+
+ free_buffers:
+	for (i-- ; i >= 0; i--) {
+		struct trace_array_cpu *data = global_trace.data[i];
+
+		if (data && data->trace) {
+			free_pages((unsigned long)data->trace, order);
+			data->trace = NULL;
+		}
+
+#ifdef CONFIG_TRACER_MAX_TRACE
+		data = max_tr.data[i];
+		if (data && data->trace) {
+			free_pages((unsigned long)data->trace, order);
+			data->trace = NULL;
+		}
+#endif
+	}
+	return -ENOMEM;
+}
+
+device_initcall(tracer_alloc_buffers);

kernel/trace/trace.h

+#ifndef _LINUX_KERNEL_TRACE_H
+#define _LINUX_KERNEL_TRACE_H
+
+#include <linux/fs.h>
+#include <asm/atomic.h>
+#include <linux/sched.h>
+#include <linux/clocksource.h>
+
+/*
+ * Function trace entry - function address and parent function addres:
+ */
+struct ftrace_entry {
+	unsigned long		ip;
+	unsigned long		parent_ip;
+};
+
+/*
+ * Context switch trace entry - which task (and prio) we switched from/to:
+ */
+struct ctx_switch_entry {
+	unsigned int		prev_pid;
+	unsigned char		prev_prio;
+	unsigned char		prev_state;
+	unsigned int		next_pid;
+	unsigned char		next_prio;
+};
+
+/*
+ * The trace entry - the most basic unit of tracing. This is what
+ * is printed in the end as a single line in the trace output, such as:
+ *
+ *     bash-15816 [01]   235.197585: idle_cpu <- irq_enter
+ */
+struct trace_entry {
+	char			type;
+	char			cpu;
+	char			flags;
+	char			preempt_count;
+	int			pid;
+	cycle_t			t;
+	unsigned long		idx;
+	union {
+		struct ftrace_entry		fn;
+		struct ctx_switch_entry		ctx;
+	};
+};
+
+#define TRACE_ENTRY_SIZE	sizeof(struct trace_entry)
+
+/*
+ * The CPU trace array - it consists of thousands of trace entries
+ * plus some other descriptor data: (for example which task started
+ * the trace, etc.)
+ */
+struct trace_array_cpu {
+	void			*trace;
+	unsigned long		trace_idx;
+	atomic_t		disabled;
+	atomic_t		underrun;
+	unsigned long		saved_latency;
+	unsigned long		critical_start;
+	unsigned long		critical_end;
+	unsigned long		critical_sequence;
+	unsigned long		nice;
+	unsigned long		policy;
+	unsigned long		rt_priority;
+	cycle_t			preempt_timestamp;
+	pid_t			pid;
+	uid_t			uid;
+	char			comm[TASK_COMM_LEN];
+};
+
+struct trace_iterator;
+
+/*
+ * The trace array - an array of per-CPU trace arrays. This is the
+ * highest level data structure that individual tracers deal with.
+ * They have on/off state as well:
+ */
+struct trace_array {
+	unsigned long		entries;
+	long			ctrl;
+	int			cpu;
+	cycle_t			time_start;
+	struct trace_array_cpu	*data[NR_CPUS];
+};
+
+/*
+ * A specific tracer, represented by methods that operate on a trace array:
+ */
+struct tracer {
+	const char		*name;
+	void			(*init)(struct trace_array *tr);
+	void			(*reset)(struct trace_array *tr);
+	void			(*open)(struct trace_iterator *iter);
+	void			(*close)(struct trace_iterator *iter);
+	void			(*start)(struct trace_iterator *iter);
+	void			(*stop)(struct trace_iterator *iter);
+	void			(*ctrl_update)(struct trace_array *tr);
+	struct tracer		*next;
+	int			print_max;
+};
+
+/*
+ * Trace iterator - used by printout routines who present trace
+ * results to users and which routines might sleep, etc:
+ */
+struct trace_iterator {
+	struct trace_array	*tr;
+	struct tracer		*trace;
+	struct trace_entry	*ent;
+	unsigned long		iter_flags;
+	loff_t			pos;
+	unsigned long		next_idx[NR_CPUS];
+	int			cpu;
+	int			idx;
+};
+
+void notrace tracing_reset(struct trace_array_cpu *data);
+int tracing_open_generic(struct inode *inode, struct file *filp);
+struct dentry *tracing_init_dentry(void);
+void ftrace(struct trace_array *tr,
+			    struct trace_array_cpu *data,
+			    unsigned long ip,
+			    unsigned long parent_ip,
+			    unsigned long flags);
+void tracing_sched_switch_trace(struct trace_array *tr,
+				struct trace_array_cpu *data,
+				struct task_struct *prev,
+				struct task_struct *next,
+				unsigned long flags);
+void tracing_record_cmdline(struct task_struct *tsk);
+
+void tracing_start_function_trace(void);
+void tracing_stop_function_trace(void);
+int register_tracer(struct tracer *type);
+void unregister_tracer(struct tracer *type);
+
+extern unsigned long nsecs_to_usecs(unsigned long nsecs);
+
+extern unsigned long tracing_max_latency;
+extern unsigned long tracing_thresh;
+
+void update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu);
+void update_max_tr_single(struct trace_array *tr,
+			  struct task_struct *tsk, int cpu);
+
+static inline notrace cycle_t now(int cpu)
+{
+	return cpu_clock(cpu);
+}
+
+#ifdef CONFIG_SCHED_TRACER
+extern void notrace
+wakeup_sched_switch(struct task_struct *prev, struct task_struct *next);
+#else
+static inline void
+wakeup_sched_switch(struct task_struct *prev, struct task_struct *next)
+{
+}
+#endif
+
+#ifdef CONFIG_CONTEXT_SWITCH_TRACER
+typedef void
+(*tracer_switch_func_t)(void *private,
+			struct task_struct *prev,
+			struct task_struct *next);
+
+struct tracer_switch_ops {
+	tracer_switch_func_t		func;
+	void				*private;
+	struct tracer_switch_ops	*next;
+};
+
+extern int register_tracer_switch(struct tracer_switch_ops *ops);
+extern int unregister_tracer_switch(struct tracer_switch_ops *ops);
+
+#endif /* CONFIG_CONTEXT_SWITCH_TRACER */
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+extern unsigned long ftrace_update_tot_cnt;
+#endif
+
+#endif /* _LINUX_KERNEL_TRACE_H */