/*

   * Copyright (C) 2008-2014 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;

  #ifdef CONFIG_MODULES

  /*

   * Tracepoint module list mutex protects the local module list.

   */

  static DEFINE_MUTEX(tracepoint_module_list_mutex);

  /* Local list of struct tp_module */

  static LIST_HEAD(tracepoint_module_list);
  #endif /* CONFIG_MODULES */

  /*

   * tracepoints_mutex protects the builtin and module tracepoints.
   * tracepoints_mutex nests inside tracepoint_module_list_mutex.

   */

  static DEFINE_MUTEX(tracepoints_mutex);

  
  /*
   * Note about RCU :

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

   * state is reached.

   */

  struct tp_probes {

  	struct rcu_head rcu;

  	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, 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->rcu, rcu_free_old_probes);

  	}

  }

  static void debug_print_probes(struct tracepoint_func *funcs)

  {
  	int i;

  	if (!tracepoint_debug || !funcs)

  		return;

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

  }

  static struct tracepoint_func *func_add(struct tracepoint_func **funcs,
  		struct tracepoint_func *tp_func)

  {
  	int nr_probes = 0;

  	struct tracepoint_func *old, *new;

  	if (WARN_ON(!tp_func->func))

  		return ERR_PTR(-EINVAL);

  	debug_print_probes(*funcs);
  	old = *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 == tp_func->func &&
  			    old[nr_probes].data == tp_func->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] = *tp_func;

  	new[nr_probes + 1].func = NULL;

  	*funcs = new;
  	debug_print_probes(*funcs);

  	return old;
  }

  static void *func_remove(struct tracepoint_func **funcs,
  		struct tracepoint_func *tp_func)

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

  	struct tracepoint_func *old, *new;

  	old = *funcs;

  	if (!old)

  		return ERR_PTR(-ENOENT);

  	debug_print_probes(*funcs);

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

  	if (tp_func->func) {

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

  			if (old[nr_probes].func == tp_func->func &&
  			     old[nr_probes].data == tp_func->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) */

  		*funcs = NULL;
  		debug_print_probes(*funcs);

  		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 != tp_func->func
  					|| old[i].data != tp_func->data)

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

  		new[nr_probes - nr_del].func = NULL;

  		*funcs = new;

  	}

  	debug_print_probes(*funcs);

  	return old;
  }
  
  /*

   * Add the probe function to a tracepoint.

   */

  static int tracepoint_add_func(struct tracepoint *tp,
  		struct tracepoint_func *func)

  {

  	struct tracepoint_func *old, *tp_funcs;

  	if (tp->regfunc && !static_key_enabled(&tp->key))
  		tp->regfunc();

  	tp_funcs = rcu_dereference_protected(tp->funcs,
  			lockdep_is_held(&tracepoints_mutex));

  	old = func_add(&tp_funcs, func);
  	if (IS_ERR(old)) {
  		WARN_ON_ONCE(1);
  		return PTR_ERR(old);
  	}
  	release_probes(old);

  	/*
  	 * 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(tp->funcs, tp_funcs);
  	if (!static_key_enabled(&tp->key))
  		static_key_slow_inc(&tp->key);
  	return 0;

  }
  
  /*

   * Remove a probe function from a tracepoint.

   * 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 int tracepoint_remove_func(struct tracepoint *tp,
  		struct tracepoint_func *func)

  {

  	struct tracepoint_func *old, *tp_funcs;

  	tp_funcs = rcu_dereference_protected(tp->funcs,
  			lockdep_is_held(&tracepoints_mutex));

  	old = func_remove(&tp_funcs, func);
  	if (IS_ERR(old)) {
  		WARN_ON_ONCE(1);
  		return PTR_ERR(old);

  	}

  	release_probes(old);

  	if (!tp_funcs) {
  		/* Removed last function */
  		if (tp->unregfunc && static_key_enabled(&tp->key))
  			tp->unregfunc();

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

  	}

  	rcu_assign_pointer(tp->funcs, tp_funcs);
  	return 0;

  }

  /**
   * tracepoint_probe_register -  Connect a probe to a tracepoint

   * @tp: tracepoint

   * @probe: probe handler
   *

   * Returns 0 if ok, error value on error.
   * Note: if @tp is within a module, the caller is responsible for
   * unregistering the probe before the module is gone. This can be
   * performed either with a tracepoint module going notifier, or from
   * within module exit functions.

   */

  int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data)

  {

  	struct tracepoint_func tp_func;
  	int ret;

  
  	mutex_lock(&tracepoints_mutex);

  	tp_func.func = probe;
  	tp_func.data = data;
  	ret = tracepoint_add_func(tp, &tp_func);

  	mutex_unlock(&tracepoints_mutex);

  	return ret;

  }
  EXPORT_SYMBOL_GPL(tracepoint_probe_register);
  
  /**
   * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint

   * @tp: tracepoint

   * @probe: probe function pointer
   *

   * Returns 0 if ok, error value on error.

   */

  int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)

  {

  	struct tracepoint_func tp_func;
  	int ret;

  
  	mutex_lock(&tracepoints_mutex);

  	tp_func.func = probe;
  	tp_func.data = data;
  	ret = tracepoint_remove_func(tp, &tp_func);

  	mutex_unlock(&tracepoints_mutex);

  	return ret;

  }
  EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);

  #ifdef CONFIG_MODULES

  bool trace_module_has_bad_taint(struct module *mod)
  {

  	return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP) |
  			       (1 << TAINT_UNSIGNED_MODULE));

  }

  static BLOCKING_NOTIFIER_HEAD(tracepoint_notify_list);
  
  /**
   * register_tracepoint_notifier - register tracepoint coming/going notifier
   * @nb: notifier block
   *
   * Notifiers registered with this function are called on module
   * coming/going with the tracepoint_module_list_mutex held.
   * The notifier block callback should expect a "struct tp_module" data
   * pointer.
   */
  int register_tracepoint_module_notifier(struct notifier_block *nb)
  {
  	struct tp_module *tp_mod;
  	int ret;
  
  	mutex_lock(&tracepoint_module_list_mutex);
  	ret = blocking_notifier_chain_register(&tracepoint_notify_list, nb);
  	if (ret)
  		goto end;
  	list_for_each_entry(tp_mod, &tracepoint_module_list, list)
  		(void) nb->notifier_call(nb, MODULE_STATE_COMING, tp_mod);
  end:
  	mutex_unlock(&tracepoint_module_list_mutex);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(register_tracepoint_module_notifier);
  
  /**
   * unregister_tracepoint_notifier - unregister tracepoint coming/going notifier
   * @nb: notifier block
   *
   * The notifier block callback should expect a "struct tp_module" data
   * pointer.
   */
  int unregister_tracepoint_module_notifier(struct notifier_block *nb)
  {
  	struct tp_module *tp_mod;
  	int ret;
  
  	mutex_lock(&tracepoint_module_list_mutex);
  	ret = blocking_notifier_chain_unregister(&tracepoint_notify_list, nb);
  	if (ret)
  		goto end;
  	list_for_each_entry(tp_mod, &tracepoint_module_list, list)
  		(void) nb->notifier_call(nb, MODULE_STATE_GOING, tp_mod);
  end:
  	mutex_unlock(&tracepoint_module_list_mutex);
  	return ret;
  
  }
  EXPORT_SYMBOL_GPL(unregister_tracepoint_module_notifier);
  
  /*
   * Ensure the tracer unregistered the module's probes before the module
   * teardown is performed. Prevents leaks of probe and data pointers.
   */
  static void tp_module_going_check_quiescent(struct tracepoint * const *begin,
  		struct tracepoint * const *end)
  {
  	struct tracepoint * const *iter;
  
  	if (!begin)
  		return;
  	for (iter = begin; iter < end; iter++)
  		WARN_ON_ONCE((*iter)->funcs);
  }

  static int tracepoint_module_coming(struct module *mod)
  {

  	struct tp_module *tp_mod;

  	int ret = 0;

  	if (!mod->num_tracepoints)
  		return 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, out-of-tree, and unsigned GPL modules are fine.

  	 */

  	if (trace_module_has_bad_taint(mod))

  		return 0;

  	mutex_lock(&tracepoint_module_list_mutex);

  	tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);
  	if (!tp_mod) {
  		ret = -ENOMEM;
  		goto end;
  	}

  	tp_mod->mod = mod;

  	list_add_tail(&tp_mod->list, &tracepoint_module_list);

  	blocking_notifier_call_chain(&tracepoint_notify_list,
  			MODULE_STATE_COMING, tp_mod);

  end:

  	mutex_unlock(&tracepoint_module_list_mutex);

  	return ret;
  }

  static void tracepoint_module_going(struct module *mod)

  {

  	struct tp_module *tp_mod;

  	if (!mod->num_tracepoints)

  		return;

  	mutex_lock(&tracepoint_module_list_mutex);
  	list_for_each_entry(tp_mod, &tracepoint_module_list, list) {

  		if (tp_mod->mod == mod) {

  			blocking_notifier_call_chain(&tracepoint_notify_list,
  					MODULE_STATE_GOING, tp_mod);
  			list_del(&tp_mod->list);
  			kfree(tp_mod);
  			/*
  			 * Called the going notifier before checking for
  			 * quiescence.
  			 */
  			tp_module_going_check_quiescent(mod->tracepoints_ptrs,
  				mod->tracepoints_ptrs + mod->num_tracepoints);

  			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(&tracepoint_module_list_mutex);

  }

  static 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:

  		tracepoint_module_going(mod);
  		break;
  	case MODULE_STATE_UNFORMED:

  		break;
  	}

  	return ret;

  }

  static struct notifier_block tracepoint_module_nb = {

  	.notifier_call = tracepoint_module_notify,
  	.priority = 0,
  };

  static __init int init_tracepoints(void)

  {

  	int ret;
  
  	ret = register_module_notifier(&tracepoint_module_nb);

  	if (ret)

  		pr_warning("Failed to register tracepoint module enter notifier
  ");

  	return ret;

  }
  __initcall(init_tracepoints);

  #endif /* CONFIG_MODULES */

  static void for_each_tracepoint_range(struct tracepoint * const *begin,
  		struct tracepoint * const *end,
  		void (*fct)(struct tracepoint *tp, void *priv),
  		void *priv)
  {
  	struct tracepoint * const *iter;
  
  	if (!begin)
  		return;
  	for (iter = begin; iter < end; iter++)
  		fct(*iter, priv);
  }
  
  /**
   * for_each_kernel_tracepoint - iteration on all kernel tracepoints
   * @fct: callback
   * @priv: private data
   */
  void for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
  		void *priv)
  {
  	for_each_tracepoint_range(__start___tracepoints_ptrs,
  		__stop___tracepoints_ptrs, fct, priv);
  }
  EXPORT_SYMBOL_GPL(for_each_kernel_tracepoint);

  #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