/*
   * Copyright (C) 2008 Mathieu Desnoyers
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
   */
  #include <linux/module.h>
  #include <linux/mutex.h>
  #include <linux/types.h>
  #include <linux/jhash.h>
  #include <linux/list.h>
  #include <linux/rcupdate.h>
  #include <linux/tracepoint.h>
  #include <linux/err.h>
  #include <linux/slab.h>

  #include <linux/sched.h>

  #include <linux/static_key.h>

  extern struct tracepoint * const __start___tracepoints_ptrs[];
  extern struct tracepoint * const __stop___tracepoints_ptrs[];

  
  /* Set to 1 to enable tracepoint debug output */
  static const int tracepoint_debug;
  
  /*

   * Tracepoints mutex protects the builtin and module tracepoints and the hash
   * table, as well as the local module list.

   */
  static DEFINE_MUTEX(tracepoints_mutex);

  #ifdef CONFIG_MODULES
  /* Local list of struct module */
  static LIST_HEAD(tracepoint_module_list);
  #endif /* CONFIG_MODULES */

  /*
   * Tracepoint hash table, containing the active tracepoints.
   * Protected by tracepoints_mutex.
   */
  #define TRACEPOINT_HASH_BITS 6
  #define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)

  static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];

  
  /*
   * Note about RCU :

   * It is used to delay the free of multiple probes array until a quiescent

   * state is reached.
   * Tracepoint entries modifications are protected by the tracepoints_mutex.
   */
  struct tracepoint_entry {
  	struct hlist_node hlist;

  	struct tracepoint_func *funcs;

  	int refcount;	/* Number of times armed. 0 if disarmed. */

  	char name[0];
  };

  struct tp_probes {

  	union {
  		struct rcu_head rcu;
  		struct list_head list;
  	} u;

  	struct tracepoint_func probes[0];

  };

  static inline void *allocate_probes(int count)

  {

  	struct tp_probes *p  = kmalloc(count * sizeof(struct tracepoint_func)

  			+ sizeof(struct tp_probes), GFP_KERNEL);
  	return p == NULL ? NULL : p->probes;

  }

  static void rcu_free_old_probes(struct rcu_head *head)

  {

  	kfree(container_of(head, struct tp_probes, u.rcu));

  }

  static inline void release_probes(struct tracepoint_func *old)

  {
  	if (old) {
  		struct tp_probes *tp_probes = container_of(old,
  			struct tp_probes, probes[0]);

  		call_rcu_sched(&tp_probes->u.rcu, rcu_free_old_probes);

  	}

  }
  
  static void debug_print_probes(struct tracepoint_entry *entry)
  {
  	int i;

  	if (!tracepoint_debug || !entry->funcs)

  		return;

  	for (i = 0; entry->funcs[i].func; i++)
  		printk(KERN_DEBUG "Probe %d : %p
  ", i, entry->funcs[i].func);

  }

  static struct tracepoint_func *
  tracepoint_entry_add_probe(struct tracepoint_entry *entry,
  			   void *probe, void *data)

  {
  	int nr_probes = 0;

  	struct tracepoint_func *old, *new;

  	if (WARN_ON(!probe))
  		return ERR_PTR(-EINVAL);

  
  	debug_print_probes(entry);
  	old = entry->funcs;
  	if (old) {
  		/* (N -> N+1), (N != 0, 1) probes */

  		for (nr_probes = 0; old[nr_probes].func; nr_probes++)
  			if (old[nr_probes].func == probe &&
  			    old[nr_probes].data == data)

  				return ERR_PTR(-EEXIST);
  	}
  	/* + 2 : one for new probe, one for NULL func */

  	new = allocate_probes(nr_probes + 2);

  	if (new == NULL)
  		return ERR_PTR(-ENOMEM);
  	if (old)

  		memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));
  	new[nr_probes].func = probe;
  	new[nr_probes].data = data;
  	new[nr_probes + 1].func = NULL;

  	entry->refcount = nr_probes + 1;
  	entry->funcs = new;
  	debug_print_probes(entry);
  	return old;
  }
  
  static void *

  tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
  			      void *probe, void *data)

  {
  	int nr_probes = 0, nr_del = 0, i;

  	struct tracepoint_func *old, *new;

  
  	old = entry->funcs;

  	if (!old)

  		return ERR_PTR(-ENOENT);

  	debug_print_probes(entry);
  	/* (N -> M), (N > 1, M >= 0) probes */

  	if (probe) {
  		for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
  			if (old[nr_probes].func == probe &&
  			     old[nr_probes].data == data)
  				nr_del++;
  		}

  	}

  	/*
  	 * If probe is NULL, then nr_probes = nr_del = 0, and then the
  	 * entire entry will be removed.
  	 */

  	if (nr_probes - nr_del == 0) {
  		/* N -> 0, (N > 1) */
  		entry->funcs = NULL;
  		entry->refcount = 0;
  		debug_print_probes(entry);
  		return old;
  	} else {
  		int j = 0;
  		/* N -> M, (N > 1, M > 0) */
  		/* + 1 for NULL */

  		new = allocate_probes(nr_probes - nr_del + 1);

  		if (new == NULL)
  			return ERR_PTR(-ENOMEM);

  		for (i = 0; old[i].func; i++)

  			if (old[i].func != probe || old[i].data != data)

  				new[j++] = old[i];

  		new[nr_probes - nr_del].func = NULL;

  		entry->refcount = nr_probes - nr_del;
  		entry->funcs = new;
  	}
  	debug_print_probes(entry);
  	return old;
  }
  
  /*
   * Get tracepoint if the tracepoint is present in the tracepoint hash table.
   * Must be called with tracepoints_mutex held.
   * Returns NULL if not present.
   */
  static struct tracepoint_entry *get_tracepoint(const char *name)
  {
  	struct hlist_head *head;

  	struct tracepoint_entry *e;
  	u32 hash = jhash(name, strlen(name), 0);

  	head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];

  	hlist_for_each_entry(e, head, hlist) {

  		if (!strcmp(name, e->name))
  			return e;
  	}
  	return NULL;
  }
  
  /*
   * Add the tracepoint to the tracepoint hash table. Must be called with
   * tracepoints_mutex held.
   */
  static struct tracepoint_entry *add_tracepoint(const char *name)
  {
  	struct hlist_head *head;

  	struct tracepoint_entry *e;
  	size_t name_len = strlen(name) + 1;
  	u32 hash = jhash(name, name_len-1, 0);

  	head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];

  	hlist_for_each_entry(e, head, hlist) {

  		if (!strcmp(name, e->name)) {
  			printk(KERN_NOTICE
  				"tracepoint %s busy
  ", name);
  			return ERR_PTR(-EEXIST);	/* Already there */
  		}
  	}
  	/*
  	 * Using kmalloc here to allocate a variable length element. Could
  	 * cause some memory fragmentation if overused.
  	 */
  	e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
  	if (!e)
  		return ERR_PTR(-ENOMEM);
  	memcpy(&e->name[0], name, name_len);
  	e->funcs = NULL;
  	e->refcount = 0;

  	hlist_add_head(&e->hlist, head);
  	return e;
  }
  
  /*
   * Remove the tracepoint from the tracepoint hash table. Must be called with
   * mutex_lock held.
   */

  static inline void remove_tracepoint(struct tracepoint_entry *e)

  {

  	hlist_del(&e->hlist);

  	kfree(e);

  }
  
  /*
   * Sets the probe callback corresponding to one tracepoint.
   */
  static void set_tracepoint(struct tracepoint_entry **entry,
  	struct tracepoint *elem, int active)
  {
  	WARN_ON(strcmp((*entry)->name, elem->name) != 0);

  	if (elem->regfunc && !static_key_enabled(&elem->key) && active)

  		elem->regfunc();

  	else if (elem->unregfunc && static_key_enabled(&elem->key) && !active)

  		elem->unregfunc();

  	/*
  	 * rcu_assign_pointer has a smp_wmb() which makes sure that the new
  	 * probe callbacks array is consistent before setting a pointer to it.
  	 * This array is referenced by __DO_TRACE from
  	 * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
  	 * is used.
  	 */
  	rcu_assign_pointer(elem->funcs, (*entry)->funcs);

  	if (active && !static_key_enabled(&elem->key))
  		static_key_slow_inc(&elem->key);
  	else if (!active && static_key_enabled(&elem->key))
  		static_key_slow_dec(&elem->key);

  }
  
  /*
   * Disable a tracepoint and its probe callback.
   * Note: only waiting an RCU period after setting elem->call to the empty
   * function insures that the original callback is not used anymore. This insured
   * by preempt_disable around the call site.
   */
  static void disable_tracepoint(struct tracepoint *elem)
  {

  	if (elem->unregfunc && static_key_enabled(&elem->key))

  		elem->unregfunc();

  	if (static_key_enabled(&elem->key))
  		static_key_slow_dec(&elem->key);

  	rcu_assign_pointer(elem->funcs, NULL);

  }
  
  /**
   * tracepoint_update_probe_range - Update a probe range
   * @begin: beginning of the range
   * @end: end of the range
   *
   * Updates the probe callback corresponding to a range of tracepoints.

   * Called with tracepoints_mutex held.

   */

  static void tracepoint_update_probe_range(struct tracepoint * const *begin,
  					  struct tracepoint * const *end)

  {

  	struct tracepoint * const *iter;

  	struct tracepoint_entry *mark_entry;

  	if (!begin)

  		return;

  	for (iter = begin; iter < end; iter++) {

  		mark_entry = get_tracepoint((*iter)->name);

  		if (mark_entry) {

  			set_tracepoint(&mark_entry, *iter,

  					!!mark_entry->refcount);
  		} else {

  			disable_tracepoint(*iter);

  		}
  	}

  }

  #ifdef CONFIG_MODULES
  void module_update_tracepoints(void)
  {
  	struct tp_module *tp_mod;
  
  	list_for_each_entry(tp_mod, &tracepoint_module_list, list)
  		tracepoint_update_probe_range(tp_mod->tracepoints_ptrs,
  			tp_mod->tracepoints_ptrs + tp_mod->num_tracepoints);
  }
  #else /* CONFIG_MODULES */
  void module_update_tracepoints(void)
  {
  }
  #endif /* CONFIG_MODULES */

  /*
   * Update probes, removing the faulty probes.

   * Called with tracepoints_mutex held.

   */
  static void tracepoint_update_probes(void)
  {
  	/* Core kernel tracepoints */

  	tracepoint_update_probe_range(__start___tracepoints_ptrs,
  		__stop___tracepoints_ptrs);

  	/* tracepoints in modules. */
  	module_update_tracepoints();
  }

  static struct tracepoint_func *
  tracepoint_add_probe(const char *name, void *probe, void *data)

  {
  	struct tracepoint_entry *entry;

  	struct tracepoint_func *old;

  
  	entry = get_tracepoint(name);
  	if (!entry) {
  		entry = add_tracepoint(name);
  		if (IS_ERR(entry))

  			return (struct tracepoint_func *)entry;

  	}

  	old = tracepoint_entry_add_probe(entry, probe, data);

  	if (IS_ERR(old) && !entry->refcount)
  		remove_tracepoint(entry);
  	return old;
  }

  /**
   * tracepoint_probe_register -  Connect a probe to a tracepoint
   * @name: tracepoint name
   * @probe: probe handler
   *
   * Returns 0 if ok, error value on error.
   * The probe address must at least be aligned on the architecture pointer size.
   */

  int tracepoint_probe_register(const char *name, void *probe, void *data)

  {

  	struct tracepoint_func *old;

  
  	mutex_lock(&tracepoints_mutex);

  	old = tracepoint_add_probe(name, probe, data);

  	if (IS_ERR(old)) {
  		mutex_unlock(&tracepoints_mutex);

  		return PTR_ERR(old);

  	}

  	tracepoint_update_probes();		/* may update entry */

  	mutex_unlock(&tracepoints_mutex);

  	release_probes(old);
  	return 0;

  }
  EXPORT_SYMBOL_GPL(tracepoint_probe_register);

  static struct tracepoint_func *
  tracepoint_remove_probe(const char *name, void *probe, void *data)

  {
  	struct tracepoint_entry *entry;

  	struct tracepoint_func *old;

  
  	entry = get_tracepoint(name);
  	if (!entry)
  		return ERR_PTR(-ENOENT);

  	old = tracepoint_entry_remove_probe(entry, probe, data);

  	if (IS_ERR(old))
  		return old;
  	if (!entry->refcount)
  		remove_tracepoint(entry);
  	return old;
  }

  /**
   * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
   * @name: tracepoint name
   * @probe: probe function pointer
   *
   * We do not need to call a synchronize_sched to make sure the probes have
   * finished running before doing a module unload, because the module unload
   * itself uses stop_machine(), which insures that every preempt disabled section
   * have finished.
   */

  int tracepoint_probe_unregister(const char *name, void *probe, void *data)

  {

  	struct tracepoint_func *old;

  
  	mutex_lock(&tracepoints_mutex);

  	old = tracepoint_remove_probe(name, probe, data);

  	if (IS_ERR(old)) {
  		mutex_unlock(&tracepoints_mutex);

  		return PTR_ERR(old);

  	}

  	tracepoint_update_probes();		/* may update entry */

  	mutex_unlock(&tracepoints_mutex);

  	release_probes(old);
  	return 0;

  }
  EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);

  static LIST_HEAD(old_probes);
  static int need_update;
  
  static void tracepoint_add_old_probes(void *old)
  {
  	need_update = 1;
  	if (old) {
  		struct tp_probes *tp_probes = container_of(old,
  			struct tp_probes, probes[0]);
  		list_add(&tp_probes->u.list, &old_probes);
  	}
  }
  
  /**
   * tracepoint_probe_register_noupdate -  register a probe but not connect
   * @name: tracepoint name
   * @probe: probe handler
   *
   * caller must call tracepoint_probe_update_all()
   */

  int tracepoint_probe_register_noupdate(const char *name, void *probe,
  				       void *data)

  {

  	struct tracepoint_func *old;

  
  	mutex_lock(&tracepoints_mutex);

  	old = tracepoint_add_probe(name, probe, data);

  	if (IS_ERR(old)) {
  		mutex_unlock(&tracepoints_mutex);
  		return PTR_ERR(old);
  	}
  	tracepoint_add_old_probes(old);
  	mutex_unlock(&tracepoints_mutex);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(tracepoint_probe_register_noupdate);
  
  /**
   * tracepoint_probe_unregister_noupdate -  remove a probe but not disconnect
   * @name: tracepoint name
   * @probe: probe function pointer
   *
   * caller must call tracepoint_probe_update_all()
   */

  int tracepoint_probe_unregister_noupdate(const char *name, void *probe,
  					 void *data)

  {

  	struct tracepoint_func *old;

  
  	mutex_lock(&tracepoints_mutex);

  	old = tracepoint_remove_probe(name, probe, data);

  	if (IS_ERR(old)) {
  		mutex_unlock(&tracepoints_mutex);
  		return PTR_ERR(old);
  	}
  	tracepoint_add_old_probes(old);
  	mutex_unlock(&tracepoints_mutex);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(tracepoint_probe_unregister_noupdate);
  
  /**
   * tracepoint_probe_update_all -  update tracepoints
   */
  void tracepoint_probe_update_all(void)
  {
  	LIST_HEAD(release_probes);
  	struct tp_probes *pos, *next;
  
  	mutex_lock(&tracepoints_mutex);
  	if (!need_update) {
  		mutex_unlock(&tracepoints_mutex);
  		return;
  	}
  	if (!list_empty(&old_probes))
  		list_replace_init(&old_probes, &release_probes);
  	need_update = 0;

  	tracepoint_update_probes();

  	mutex_unlock(&tracepoints_mutex);

  	list_for_each_entry_safe(pos, next, &release_probes, u.list) {
  		list_del(&pos->u.list);
  		call_rcu_sched(&pos->u.rcu, rcu_free_old_probes);
  	}
  }
  EXPORT_SYMBOL_GPL(tracepoint_probe_update_all);

  /**
   * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
   * @tracepoint: current tracepoints (in), next tracepoint (out)
   * @begin: beginning of the range
   * @end: end of the range
   *
   * Returns whether a next tracepoint has been found (1) or not (0).
   * Will return the first tracepoint in the range if the input tracepoint is
   * NULL.
   */

  static int tracepoint_get_iter_range(struct tracepoint * const **tracepoint,

  	struct tracepoint * const *begin, struct tracepoint * const *end)

  {
  	if (!*tracepoint && begin != end) {
  		*tracepoint = begin;
  		return 1;
  	}
  	if (*tracepoint >= begin && *tracepoint < end)
  		return 1;
  	return 0;
  }

  #ifdef CONFIG_MODULES

  static void tracepoint_get_iter(struct tracepoint_iter *iter)
  {
  	int found = 0;

  	struct tp_module *iter_mod;

  
  	/* Core kernel tracepoints */
  	if (!iter->module) {
  		found = tracepoint_get_iter_range(&iter->tracepoint,

  				__start___tracepoints_ptrs,
  				__stop___tracepoints_ptrs);

  		if (found)
  			goto end;
  	}

  	/* Tracepoints in modules */
  	mutex_lock(&tracepoints_mutex);
  	list_for_each_entry(iter_mod, &tracepoint_module_list, list) {
  		/*
  		 * Sorted module list
  		 */
  		if (iter_mod < iter->module)
  			continue;
  		else if (iter_mod > iter->module)
  			iter->tracepoint = NULL;
  		found = tracepoint_get_iter_range(&iter->tracepoint,
  			iter_mod->tracepoints_ptrs,
  			iter_mod->tracepoints_ptrs
  				+ iter_mod->num_tracepoints);
  		if (found) {
  			iter->module = iter_mod;
  			break;
  		}
  	}
  	mutex_unlock(&tracepoints_mutex);

  end:
  	if (!found)
  		tracepoint_iter_reset(iter);
  }

  #else /* CONFIG_MODULES */
  static void tracepoint_get_iter(struct tracepoint_iter *iter)
  {
  	int found = 0;
  
  	/* Core kernel tracepoints */
  	found = tracepoint_get_iter_range(&iter->tracepoint,
  			__start___tracepoints_ptrs,
  			__stop___tracepoints_ptrs);
  	if (!found)
  		tracepoint_iter_reset(iter);
  }
  #endif /* CONFIG_MODULES */

  
  void tracepoint_iter_start(struct tracepoint_iter *iter)
  {
  	tracepoint_get_iter(iter);
  }
  EXPORT_SYMBOL_GPL(tracepoint_iter_start);
  
  void tracepoint_iter_next(struct tracepoint_iter *iter)
  {
  	iter->tracepoint++;
  	/*
  	 * iter->tracepoint may be invalid because we blindly incremented it.
  	 * Make sure it is valid by marshalling on the tracepoints, getting the
  	 * tracepoints from following modules if necessary.
  	 */
  	tracepoint_get_iter(iter);
  }
  EXPORT_SYMBOL_GPL(tracepoint_iter_next);
  
  void tracepoint_iter_stop(struct tracepoint_iter *iter)
  {
  }
  EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
  
  void tracepoint_iter_reset(struct tracepoint_iter *iter)
  {

  #ifdef CONFIG_MODULES

  	iter->module = NULL;

  #endif /* CONFIG_MODULES */

  	iter->tracepoint = NULL;
  }
  EXPORT_SYMBOL_GPL(tracepoint_iter_reset);

  #ifdef CONFIG_MODULES

  static int tracepoint_module_coming(struct module *mod)
  {
  	struct tp_module *tp_mod, *iter;
  	int ret = 0;
  
  	/*

  	 * We skip modules that taint the kernel, especially those with different
  	 * module headers (for forced load), to make sure we don't cause a crash.
  	 * Staging and out-of-tree GPL modules are fine.

  	 */

  	if (mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP)))

  		return 0;
  	mutex_lock(&tracepoints_mutex);
  	tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);
  	if (!tp_mod) {
  		ret = -ENOMEM;
  		goto end;
  	}
  	tp_mod->num_tracepoints = mod->num_tracepoints;
  	tp_mod->tracepoints_ptrs = mod->tracepoints_ptrs;
  
  	/*
  	 * tracepoint_module_list is kept sorted by struct module pointer
  	 * address for iteration on tracepoints from a seq_file that can release
  	 * the mutex between calls.
  	 */
  	list_for_each_entry_reverse(iter, &tracepoint_module_list, list) {
  		BUG_ON(iter == tp_mod);	/* Should never be in the list twice */
  		if (iter < tp_mod) {
  			/* We belong to the location right after iter. */
  			list_add(&tp_mod->list, &iter->list);
  			goto module_added;
  		}
  	}
  	/* We belong to the beginning of the list */
  	list_add(&tp_mod->list, &tracepoint_module_list);
  module_added:
  	tracepoint_update_probe_range(mod->tracepoints_ptrs,
  		mod->tracepoints_ptrs + mod->num_tracepoints);
  end:
  	mutex_unlock(&tracepoints_mutex);
  	return ret;
  }
  
  static int tracepoint_module_going(struct module *mod)
  {
  	struct tp_module *pos;
  
  	mutex_lock(&tracepoints_mutex);
  	tracepoint_update_probe_range(mod->tracepoints_ptrs,
  		mod->tracepoints_ptrs + mod->num_tracepoints);
  	list_for_each_entry(pos, &tracepoint_module_list, list) {
  		if (pos->tracepoints_ptrs == mod->tracepoints_ptrs) {
  			list_del(&pos->list);
  			kfree(pos);
  			break;
  		}
  	}
  	/*
  	 * In the case of modules that were tainted at "coming", we'll simply
  	 * walk through the list without finding it. We cannot use the "tainted"
  	 * flag on "going", in case a module taints the kernel only after being
  	 * loaded.
  	 */
  	mutex_unlock(&tracepoints_mutex);
  	return 0;
  }

  int tracepoint_module_notify(struct notifier_block *self,
  			     unsigned long val, void *data)
  {
  	struct module *mod = data;

  	int ret = 0;

  
  	switch (val) {
  	case MODULE_STATE_COMING:

  		ret = tracepoint_module_coming(mod);
  		break;
  	case MODULE_STATE_LIVE:
  		break;

  	case MODULE_STATE_GOING:

  		ret = tracepoint_module_going(mod);

  		break;
  	}

  	return ret;

  }
  
  struct notifier_block tracepoint_module_nb = {
  	.notifier_call = tracepoint_module_notify,
  	.priority = 0,
  };
  
  static int init_tracepoints(void)
  {
  	return register_module_notifier(&tracepoint_module_nb);
  }
  __initcall(init_tracepoints);

  #endif /* CONFIG_MODULES */

  #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS

  /* NB: reg/unreg are called while guarded with the tracepoints_mutex */

  static int sys_tracepoint_refcount;
  
  void syscall_regfunc(void)
  {
  	unsigned long flags;
  	struct task_struct *g, *t;

  	if (!sys_tracepoint_refcount) {
  		read_lock_irqsave(&tasklist_lock, flags);
  		do_each_thread(g, t) {

  			/* Skip kernel threads. */
  			if (t->mm)
  				set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);

  		} while_each_thread(g, t);
  		read_unlock_irqrestore(&tasklist_lock, flags);
  	}
  	sys_tracepoint_refcount++;

  }
  
  void syscall_unregfunc(void)
  {
  	unsigned long flags;
  	struct task_struct *g, *t;

  	sys_tracepoint_refcount--;
  	if (!sys_tracepoint_refcount) {
  		read_lock_irqsave(&tasklist_lock, flags);
  		do_each_thread(g, t) {

  			clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);

  		} while_each_thread(g, t);
  		read_unlock_irqrestore(&tasklist_lock, flags);
  	}

  }

  #endif