kernel/trace/trace_stack.c - arm/linux-arm64-legacy - Git at Google

 /*
  * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
  *
  */
 #include <linux/stacktrace.h>
 #include <linux/kallsyms.h>
 #include <linux/seq_file.h>
 #include <linux/spinlock.h>
 #include <linux/uaccess.h>
 #include <linux/debugfs.h>
 #include <linux/ftrace.h>
 #include <linux/module.h>
 #include <linux/sysctl.h>
 #include <linux/init.h>
 #include <linux/fs.h>
 #include <linux/magic.h>

 #include <asm/setup.h>

 #include "trace.h"

 #define STACK_TRACE_ENTRIES 500

 #ifdef CC_USING_FENTRY
 # define fentry		1
 #else
 # define fentry		0
 #endif

 static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] =
 	 { [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX };
 static unsigned stack_dump_index[STACK_TRACE_ENTRIES];

 /*
  * Reserve one entry for the passed in ip. This will allow
  * us to remove most or all of the stack size overhead
  * added by the stack tracer itself.
  */
 static struct stack_trace max_stack_trace = {
 	.max_entries		= STACK_TRACE_ENTRIES - 1,
 	.entries		= &stack_dump_trace[1],
 };

 static unsigned long max_stack_size;
 static arch_spinlock_t max_stack_lock =
 	(arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;

 static DEFINE_PER_CPU(int, trace_active);
 static DEFINE_MUTEX(stack_sysctl_mutex);

 int stack_tracer_enabled;
 static int last_stack_tracer_enabled;

 static inline void
 check_stack(unsigned long ip, unsigned long *stack)
 {
 	unsigned long this_size, flags;
 	unsigned long *p, *top, *start;
 	static int tracer_frame;
 	int frame_size = ACCESS_ONCE(tracer_frame);
 	int i;

 	this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
 	this_size = THREAD_SIZE - this_size;
 	/* Remove the frame of the tracer */
 	this_size -= frame_size;

 	if (this_size <= max_stack_size)
 		return;

 	/* we do not handle interrupt stacks yet */
 	if (!object_is_on_stack(stack))
 		return;

 	local_irq_save(flags);
 	arch_spin_lock(&max_stack_lock);

 	/* In case another CPU set the tracer_frame on us */
 	if (unlikely(!frame_size))
 		this_size -= tracer_frame;

 	/* a race could have already updated it */
 	if (this_size <= max_stack_size)
 		goto out;

 	max_stack_size = this_size;

 	max_stack_trace.nr_entries	= 0;
 	max_stack_trace.skip		= 3;

 	save_stack_trace(&max_stack_trace);

 	/*
 	 * Add the passed in ip from the function tracer.
 	 * Searching for this on the stack will skip over
 	 * most of the overhead from the stack tracer itself.
 	 */
 	stack_dump_trace[0] = ip;
 	max_stack_trace.nr_entries++;

 	/*
 	 * Now find where in the stack these are.
 	 */
 	i = 0;
 	start = stack;
 	top = (unsigned long *)
 		(((unsigned long)start & ~(THREAD_SIZE-1)) + THREAD_SIZE);

 	/*
 	 * Loop through all the entries. One of the entries may
 	 * for some reason be missed on the stack, so we may
 	 * have to account for them. If they are all there, this
 	 * loop will only happen once. This code only takes place
 	 * on a new max, so it is far from a fast path.
 	 */
 	while (i < max_stack_trace.nr_entries) {
 		int found = 0;

 		stack_dump_index[i] = this_size;
 		p = start;

 		for (; p < top && i < max_stack_trace.nr_entries; p++) {
 			if (*p == stack_dump_trace[i]) {
 				this_size = stack_dump_index[i++] =
 					(top - p) * sizeof(unsigned long);
 				found = 1;
 				/* Start the search from here */
 				start = p + 1;
 				/*
 				 * We do not want to show the overhead
 				 * of the stack tracer stack in the
 				 * max stack. If we haven't figured
 				 * out what that is, then figure it out
 				 * now.
 				 */
 				if (unlikely(!tracer_frame) && i == 1) {
 					tracer_frame = (p - stack) *
 						sizeof(unsigned long);
 					max_stack_size -= tracer_frame;
 				}
 			}
 		}

 		if (!found)
 			i++;
 	}

 	BUG_ON(current != &init_task &&
 		*(end_of_stack(current)) != STACK_END_MAGIC);
  out:
 	arch_spin_unlock(&max_stack_lock);
 	local_irq_restore(flags);
 }

 static void
 stack_trace_call(unsigned long ip, unsigned long parent_ip,
 		 struct ftrace_ops *op, struct pt_regs *pt_regs)
 {
 	unsigned long stack;
 	int cpu;

 	preempt_disable_notrace();

 	cpu = raw_smp_processor_id();
 	/* no atomic needed, we only modify this variable by this cpu */
 	if (per_cpu(trace_active, cpu)++ != 0)
 		goto out;

 	/*
 	 * When fentry is used, the traced function does not get
 	 * its stack frame set up, and we lose the parent.
 	 * The ip is pretty useless because the function tracer
 	 * was called before that function set up its stack frame.
 	 * In this case, we use the parent ip.
 	 *
 	 * By adding the return address of either the parent ip
 	 * or the current ip we can disregard most of the stack usage
 	 * caused by the stack tracer itself.
 	 *
 	 * The function tracer always reports the address of where the
 	 * mcount call was, but the stack will hold the return address.
 	 */
 	if (fentry)
 		ip = parent_ip;
 	else
 		ip += MCOUNT_INSN_SIZE;

 	check_stack(ip, &stack);

  out:
 	per_cpu(trace_active, cpu)--;
 	/* prevent recursion in schedule */
 	preempt_enable_notrace();
 }

 static struct ftrace_ops trace_ops __read_mostly =
 {
 	.func = stack_trace_call,
 	.flags = FTRACE_OPS_FL_RECURSION_SAFE,
 };

 static ssize_t
 stack_max_size_read(struct file *filp, char __user *ubuf,
 		    size_t count, loff_t *ppos)
 {
 	unsigned long *ptr = filp->private_data;
 	char buf[64];
 	int r;

 	r = snprintf(buf, sizeof(buf), "%ld\n", *ptr);
 	if (r > sizeof(buf))
 		r = sizeof(buf);
 	return simple_read_from_buffer(ubuf, count, ppos, buf, r);
 }

 static ssize_t
 stack_max_size_write(struct file *filp, const char __user *ubuf,
 		     size_t count, loff_t *ppos)
 {
 	long *ptr = filp->private_data;
 	unsigned long val, flags;
 	int ret;
 	int cpu;

 	ret = kstrtoul_from_user(ubuf, count, 10, &val);
 	if (ret)
 		return ret;

 	local_irq_save(flags);

 	/*
 	 * In case we trace inside arch_spin_lock() or after (NMI),
 	 * we will cause circular lock, so we also need to increase
 	 * the percpu trace_active here.
 	 */
 	cpu = smp_processor_id();
 	per_cpu(trace_active, cpu)++;

 	arch_spin_lock(&max_stack_lock);
 	*ptr = val;
 	arch_spin_unlock(&max_stack_lock);

 	per_cpu(trace_active, cpu)--;
 	local_irq_restore(flags);

 	return count;
 }

 static const struct file_operations stack_max_size_fops = {
 	.open		= tracing_open_generic,
 	.read		= stack_max_size_read,
 	.write		= stack_max_size_write,
 	.llseek		= default_llseek,
 };

 static void *
 __next(struct seq_file *m, loff_t *pos)
 {
 	long n = *pos - 1;

 	if (n >= max_stack_trace.nr_entries || stack_dump_trace[n] == ULONG_MAX)
 		return NULL;

 	m->private = (void *)n;
 	return &m->private;
 }

 static void *
 t_next(struct seq_file *m, void *v, loff_t *pos)
 {
 	(*pos)++;
 	return __next(m, pos);
 }

 static void *t_start(struct seq_file *m, loff_t *pos)
 {
 	int cpu;

 	local_irq_disable();

 	cpu = smp_processor_id();
 	per_cpu(trace_active, cpu)++;

 	arch_spin_lock(&max_stack_lock);

 	if (*pos == 0)
 		return SEQ_START_TOKEN;

 	return __next(m, pos);
 }

 static void t_stop(struct seq_file *m, void *p)
 {
 	int cpu;

 	arch_spin_unlock(&max_stack_lock);

 	cpu = smp_processor_id();
 	per_cpu(trace_active, cpu)--;

 	local_irq_enable();
 }

 static int trace_lookup_stack(struct seq_file *m, long i)
 {
 	unsigned long addr = stack_dump_trace[i];

 	return seq_printf(m, "%pS\n", (void *)addr);
 }

 static void print_disabled(struct seq_file *m)
 {
 	seq_puts(m, "#\n"
 		 "#  Stack tracer disabled\n"
 		 "#\n"
 		 "# To enable the stack tracer, either add 'stacktrace' to the\n"
 		 "# kernel command line\n"
 		 "# or 'echo 1 > /proc/sys/kernel/stack_tracer_enabled'\n"
 		 "#\n");
 }

 static int t_show(struct seq_file *m, void *v)
 {
 	long i;
 	int size;

 	if (v == SEQ_START_TOKEN) {
 		seq_printf(m, "        Depth    Size   Location"
 			   "    (%d entries)\n"
 			   "        -----    ----   --------\n",
 			   max_stack_trace.nr_entries - 1);

 		if (!stack_tracer_enabled && !max_stack_size)
 			print_disabled(m);

 		return 0;
 	}

 	i = *(long *)v;

 	if (i >= max_stack_trace.nr_entries ||
 	    stack_dump_trace[i] == ULONG_MAX)
 		return 0;

 	if (i+1 == max_stack_trace.nr_entries ||
 	    stack_dump_trace[i+1] == ULONG_MAX)
 		size = stack_dump_index[i];
 	else
 		size = stack_dump_index[i] - stack_dump_index[i+1];

 	seq_printf(m, "%3ld) %8d   %5d   ", i, stack_dump_index[i], size);

 	trace_lookup_stack(m, i);

 	return 0;
 }

 static const struct seq_operations stack_trace_seq_ops = {
 	.start		= t_start,
 	.next		= t_next,
 	.stop		= t_stop,
 	.show		= t_show,
 };

 static int stack_trace_open(struct inode *inode, struct file *file)
 {
 	return seq_open(file, &stack_trace_seq_ops);
 }

 static const struct file_operations stack_trace_fops = {
 	.open		= stack_trace_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
 	.release	= seq_release,
 };

 static int
 stack_trace_filter_open(struct inode *inode, struct file *file)
 {
 	return ftrace_regex_open(&trace_ops, FTRACE_ITER_FILTER,
 				 inode, file);
 }

 static const struct file_operations stack_trace_filter_fops = {
 	.open = stack_trace_filter_open,
 	.read = seq_read,
 	.write = ftrace_filter_write,
 	.llseek = tracing_lseek,
 	.release = ftrace_regex_release,
 };

 int
 stack_trace_sysctl(struct ctl_table *table, int write,
 		   void __user *buffer, size_t *lenp,
 		   loff_t *ppos)
 {
 	int ret;

 	mutex_lock(&stack_sysctl_mutex);

 	ret = proc_dointvec(table, write, buffer, lenp, ppos);

 	if (ret || !write ||
 	    (last_stack_tracer_enabled == !!stack_tracer_enabled))
 		goto out;

 	last_stack_tracer_enabled = !!stack_tracer_enabled;

 	if (stack_tracer_enabled)
 		register_ftrace_function(&trace_ops);
 	else
 		unregister_ftrace_function(&trace_ops);

  out:
 	mutex_unlock(&stack_sysctl_mutex);
 	return ret;
 }

 static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;

 static __init int enable_stacktrace(char *str)
 {
 	if (strncmp(str, "_filter=", 8) == 0)
 		strncpy(stack_trace_filter_buf, str+8, COMMAND_LINE_SIZE);

 	stack_tracer_enabled = 1;
 	last_stack_tracer_enabled = 1;
 	return 1;
 }
 __setup("stacktrace", enable_stacktrace);

 static __init int stack_trace_init(void)
 {
 	struct dentry *d_tracer;

 	d_tracer = tracing_init_dentry();
 	if (!d_tracer)
 		return 0;

 	trace_create_file("stack_max_size", 0644, d_tracer,
 			&max_stack_size, &stack_max_size_fops);

 	trace_create_file("stack_trace", 0444, d_tracer,
 			NULL, &stack_trace_fops);

 	trace_create_file("stack_trace_filter", 0444, d_tracer,
 			NULL, &stack_trace_filter_fops);

 	if (stack_trace_filter_buf[0])
 		ftrace_set_early_filter(&trace_ops, stack_trace_filter_buf, 1);

 	if (stack_tracer_enabled)
 		register_ftrace_function(&trace_ops);

 	return 0;
 }

 device_initcall(stack_trace_init);
	/*
	* Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
	*
	*/
	#include <linux/stacktrace.h>
	#include <linux/kallsyms.h>
	#include <linux/seq_file.h>
	#include <linux/spinlock.h>
	#include <linux/uaccess.h>
	#include <linux/debugfs.h>
	#include <linux/ftrace.h>
	#include <linux/module.h>
	#include <linux/sysctl.h>
	#include <linux/init.h>
	#include <linux/fs.h>
	#include <linux/magic.h>

	#include <asm/setup.h>

	#include "trace.h"

	#define STACK_TRACE_ENTRIES 500

	#ifdef CC_USING_FENTRY
	# define fentry 1
	#else
	# define fentry 0
	#endif

	static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] =
	{ [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX };
	static unsigned stack_dump_index[STACK_TRACE_ENTRIES];

	/*
	* Reserve one entry for the passed in ip. This will allow
	* us to remove most or all of the stack size overhead
	* added by the stack tracer itself.
	*/
	static struct stack_trace max_stack_trace = {
	.max_entries = STACK_TRACE_ENTRIES - 1,
	.entries = &stack_dump_trace[1],
	};

	static unsigned long max_stack_size;
	static arch_spinlock_t max_stack_lock =
	(arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;

	static DEFINE_PER_CPU(int, trace_active);
	static DEFINE_MUTEX(stack_sysctl_mutex);

	int stack_tracer_enabled;
	static int last_stack_tracer_enabled;

	static inline void
	check_stack(unsigned long ip, unsigned long *stack)
	{
	unsigned long this_size, flags;
	unsigned long p, top, *start;
	static int tracer_frame;
	int frame_size = ACCESS_ONCE(tracer_frame);
	int i;

	this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
	this_size = THREAD_SIZE - this_size;
	/* Remove the frame of the tracer */
	this_size -= frame_size;

	if (this_size <= max_stack_size)
	return;

	/* we do not handle interrupt stacks yet */
	if (!object_is_on_stack(stack))
	return;

	local_irq_save(flags);
	arch_spin_lock(&max_stack_lock);

	/* In case another CPU set the tracer_frame on us */
	if (unlikely(!frame_size))
	this_size -= tracer_frame;

	/* a race could have already updated it */
	if (this_size <= max_stack_size)
	goto out;

	max_stack_size = this_size;

	max_stack_trace.nr_entries = 0;
	max_stack_trace.skip = 3;

	save_stack_trace(&max_stack_trace);

	/*
	* Add the passed in ip from the function tracer.
	* Searching for this on the stack will skip over
	* most of the overhead from the stack tracer itself.
	*/
	stack_dump_trace[0] = ip;
	max_stack_trace.nr_entries++;

	/*
	* Now find where in the stack these are.
	*/
	i = 0;
	start = stack;
	top = (unsigned long *)
	(((unsigned long)start & ~(THREAD_SIZE-1)) + THREAD_SIZE);

	/*
	* Loop through all the entries. One of the entries may
	* for some reason be missed on the stack, so we may
	* have to account for them. If they are all there, this
	* loop will only happen once. This code only takes place
	* on a new max, so it is far from a fast path.
	*/
	while (i < max_stack_trace.nr_entries) {
	int found = 0;

	stack_dump_index[i] = this_size;
	p = start;

	for (; p < top && i < max_stack_trace.nr_entries; p++) {
	if (*p == stack_dump_trace[i]) {
	this_size = stack_dump_index[i++] =
	(top - p) * sizeof(unsigned long);
	found = 1;
	/* Start the search from here */
	start = p + 1;
	/*
	* We do not want to show the overhead
	* of the stack tracer stack in the
	* max stack. If we haven't figured
	* out what that is, then figure it out
	* now.
	*/
	if (unlikely(!tracer_frame) && i == 1) {
	tracer_frame = (p - stack) *
	sizeof(unsigned long);
	max_stack_size -= tracer_frame;
	}
	}
	}

	if (!found)
	i++;
	}

	BUG_ON(current != &init_task &&
	*(end_of_stack(current)) != STACK_END_MAGIC);
	out:
	arch_spin_unlock(&max_stack_lock);
	local_irq_restore(flags);
	}

	static void
	stack_trace_call(unsigned long ip, unsigned long parent_ip,
	struct ftrace_ops op, struct pt_regs pt_regs)
	{
	unsigned long stack;
	int cpu;

	preempt_disable_notrace();

	cpu = raw_smp_processor_id();
	/* no atomic needed, we only modify this variable by this cpu */
	if (per_cpu(trace_active, cpu)++ != 0)
	goto out;

	/*
	* When fentry is used, the traced function does not get
	* its stack frame set up, and we lose the parent.
	* The ip is pretty useless because the function tracer
	* was called before that function set up its stack frame.
	* In this case, we use the parent ip.
	*
	* By adding the return address of either the parent ip
	* or the current ip we can disregard most of the stack usage
	* caused by the stack tracer itself.
	*
	* The function tracer always reports the address of where the
	* mcount call was, but the stack will hold the return address.
	*/
	if (fentry)
	ip = parent_ip;
	else
	ip += MCOUNT_INSN_SIZE;

	check_stack(ip, &stack);

	out:
	per_cpu(trace_active, cpu)--;
	/* prevent recursion in schedule */
	preempt_enable_notrace();
	}

	static struct ftrace_ops trace_ops __read_mostly =
	{
	.func = stack_trace_call,
	.flags = FTRACE_OPS_FL_RECURSION_SAFE,
	};

	static ssize_t
	stack_max_size_read(struct file filp, char __user ubuf,
	size_t count, loff_t *ppos)
	{
	unsigned long *ptr = filp->private_data;
	char buf[64];
	int r;

	r = snprintf(buf, sizeof(buf), "%ld\n", *ptr);
	if (r > sizeof(buf))
	r = sizeof(buf);
	return simple_read_from_buffer(ubuf, count, ppos, buf, r);
	}

	static ssize_t
	stack_max_size_write(struct file filp, const char __user ubuf,
	size_t count, loff_t *ppos)
	{
	long *ptr = filp->private_data;
	unsigned long val, flags;
	int ret;
	int cpu;

	ret = kstrtoul_from_user(ubuf, count, 10, &val);
	if (ret)
	return ret;

	local_irq_save(flags);

	/*
	* In case we trace inside arch_spin_lock() or after (NMI),
	* we will cause circular lock, so we also need to increase
	* the percpu trace_active here.
	*/
	cpu = smp_processor_id();
	per_cpu(trace_active, cpu)++;

	arch_spin_lock(&max_stack_lock);
	*ptr = val;
	arch_spin_unlock(&max_stack_lock);

	per_cpu(trace_active, cpu)--;
	local_irq_restore(flags);

	return count;
	}

	static const struct file_operations stack_max_size_fops = {
	.open = tracing_open_generic,
	.read = stack_max_size_read,
	.write = stack_max_size_write,
	.llseek = default_llseek,
	};

	static void *
	__next(struct seq_file m, loff_t pos)
	{
	long n = *pos - 1;

	if (n >= max_stack_trace.nr_entries \|\| stack_dump_trace[n] == ULONG_MAX)
	return NULL;

	m->private = (void *)n;
	return &m->private;
	}

	static void *
	t_next(struct seq_file m, void v, loff_t *pos)
	{
	(*pos)++;
	return __next(m, pos);
	}

	static void t_start(struct seq_file m, loff_t *pos)
	{
	int cpu;

	local_irq_disable();

	cpu = smp_processor_id();
	per_cpu(trace_active, cpu)++;

	arch_spin_lock(&max_stack_lock);

	if (*pos == 0)
	return SEQ_START_TOKEN;

	return __next(m, pos);
	}

	static void t_stop(struct seq_file m, void p)
	{
	int cpu;

	arch_spin_unlock(&max_stack_lock);

	cpu = smp_processor_id();
	per_cpu(trace_active, cpu)--;

	local_irq_enable();
	}

	static int trace_lookup_stack(struct seq_file *m, long i)
	{
	unsigned long addr = stack_dump_trace[i];

	return seq_printf(m, "%pS\n", (void *)addr);
	}

	static void print_disabled(struct seq_file *m)
	{
	seq_puts(m, "#\n"
	"# Stack tracer disabled\n"
	"#\n"
	"# To enable the stack tracer, either add 'stacktrace' to the\n"
	"# kernel command line\n"
	"# or 'echo 1 > /proc/sys/kernel/stack_tracer_enabled'\n"
	"#\n");
	}

	static int t_show(struct seq_file m, void v)
	{
	long i;
	int size;

	if (v == SEQ_START_TOKEN) {
	seq_printf(m, " Depth Size Location"
	" (%d entries)\n"
	" ----- ---- --------\n",
	max_stack_trace.nr_entries - 1);

	if (!stack_tracer_enabled && !max_stack_size)
	print_disabled(m);

	return 0;
	}

	i = (long )v;

	if (i >= max_stack_trace.nr_entries \|\|
	stack_dump_trace[i] == ULONG_MAX)
	return 0;

	if (i+1 == max_stack_trace.nr_entries \|\|
	stack_dump_trace[i+1] == ULONG_MAX)
	size = stack_dump_index[i];
	else
	size = stack_dump_index[i] - stack_dump_index[i+1];

	seq_printf(m, "%3ld) %8d %5d ", i, stack_dump_index[i], size);

	trace_lookup_stack(m, i);

	return 0;
	}

	static const struct seq_operations stack_trace_seq_ops = {
	.start = t_start,
	.next = t_next,
	.stop = t_stop,
	.show = t_show,
	};

	static int stack_trace_open(struct inode inode, struct file file)
	{
	return seq_open(file, &stack_trace_seq_ops);
	}

	static const struct file_operations stack_trace_fops = {
	.open = stack_trace_open,
	.read = seq_read,
	.llseek = seq_lseek,
	.release = seq_release,
	};

	static int
	stack_trace_filter_open(struct inode inode, struct file file)
	{
	return ftrace_regex_open(&trace_ops, FTRACE_ITER_FILTER,
	inode, file);
	}

	static const struct file_operations stack_trace_filter_fops = {
	.open = stack_trace_filter_open,
	.read = seq_read,
	.write = ftrace_filter_write,
	.llseek = tracing_lseek,
	.release = ftrace_regex_release,
	};

	int
	stack_trace_sysctl(struct ctl_table *table, int write,
	void __user buffer, size_t lenp,
	loff_t *ppos)
	{
	int ret;

	mutex_lock(&stack_sysctl_mutex);

	ret = proc_dointvec(table, write, buffer, lenp, ppos);

	if (ret \|\| !write \|\|
	(last_stack_tracer_enabled == !!stack_tracer_enabled))
	goto out;

	last_stack_tracer_enabled = !!stack_tracer_enabled;

	if (stack_tracer_enabled)
	register_ftrace_function(&trace_ops);
	else
	unregister_ftrace_function(&trace_ops);

	out:
	mutex_unlock(&stack_sysctl_mutex);
	return ret;
	}

	static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;

	static __init int enable_stacktrace(char *str)
	{
	if (strncmp(str, "_filter=", 8) == 0)
	strncpy(stack_trace_filter_buf, str+8, COMMAND_LINE_SIZE);

	stack_tracer_enabled = 1;
	last_stack_tracer_enabled = 1;
	return 1;
	}
	__setup("stacktrace", enable_stacktrace);

	static __init int stack_trace_init(void)
	{
	struct dentry *d_tracer;

	d_tracer = tracing_init_dentry();
	if (!d_tracer)
	return 0;

	trace_create_file("stack_max_size", 0644, d_tracer,
	&max_stack_size, &stack_max_size_fops);

	trace_create_file("stack_trace", 0444, d_tracer,
	NULL, &stack_trace_fops);

	trace_create_file("stack_trace_filter", 0444, d_tracer,
	NULL, &stack_trace_filter_fops);

	if (stack_trace_filter_buf[0])
	ftrace_set_early_filter(&trace_ops, stack_trace_filter_buf, 1);

	if (stack_tracer_enabled)
	register_ftrace_function(&trace_ops);

	return 0;
	}

	device_initcall(stack_trace_init);