1/*
2 * Copyright (C) 2008 Mathieu Desnoyers
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17 */
18#include <linux/module.h>
19#include <linux/mutex.h>
20#include <linux/types.h>
21#include <linux/jhash.h>
22#include <linux/list.h>
23#include <linux/rcupdate.h>
24#include <linux/tracepoint.h>
25#include <linux/err.h>
26#include <linux/slab.h>
27#include <linux/sched.h>
28
29extern struct tracepoint __start___tracepoints[];
30extern struct tracepoint __stop___tracepoints[];
31
32/* Set to 1 to enable tracepoint debug output */
33static const int tracepoint_debug;
34
35/*
36 * tracepoints_mutex nests inside module_mutex. Tracepoints mutex protects the
37 * builtin and module tracepoints and the hash table.
38 */
39static DEFINE_MUTEX(tracepoints_mutex);
40
41/*
42 * Tracepoint hash table, containing the active tracepoints.
43 * Protected by tracepoints_mutex.
44 */
45#define TRACEPOINT_HASH_BITS 6
46#define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
47static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
48
49/*
50 * Note about RCU :
51 * It is used to delay the free of multiple probes array until a quiescent
52 * state is reached.
53 * Tracepoint entries modifications are protected by the tracepoints_mutex.
54 */
55struct tracepoint_entry {
56	struct hlist_node hlist;
57	struct tracepoint_func *funcs;
58	int refcount;	/* Number of times armed. 0 if disarmed. */
59	char name[0];
60};
61
62struct tp_probes {
63	union {
64		struct rcu_head rcu;
65		struct list_head list;
66	} u;
67	struct tracepoint_func probes[0];
68};
69
70static inline void *allocate_probes(int count)
71{
72	struct tp_probes *p  = kmalloc(count * sizeof(struct tracepoint_func)
73			+ sizeof(struct tp_probes), GFP_KERNEL);
74	return p == NULL ? NULL : p->probes;
75}
76
77static void rcu_free_old_probes(struct rcu_head *head)
78{
79	kfree(container_of(head, struct tp_probes, u.rcu));
80}
81
82static inline void release_probes(struct tracepoint_func *old)
83{
84	if (old) {
85		struct tp_probes *tp_probes = container_of(old,
86			struct tp_probes, probes[0]);
87		call_rcu_sched(&tp_probes->u.rcu, rcu_free_old_probes);
88	}
89}
90
91static void debug_print_probes(struct tracepoint_entry *entry)
92{
93	int i;
94
95	if (!tracepoint_debug || !entry->funcs)
96		return;
97
98	for (i = 0; entry->funcs[i].func; i++)
99		printk(KERN_DEBUG "Probe %d : %p\n", i, entry->funcs[i].func);
100}
101
102static struct tracepoint_func *
103tracepoint_entry_add_probe(struct tracepoint_entry *entry,
104			   void *probe, void *data)
105{
106	int nr_probes = 0;
107	struct tracepoint_func *old, *new;
108
109	WARN_ON(!probe);
110
111	debug_print_probes(entry);
112	old = entry->funcs;
113	if (old) {
114		/* (N -> N+1), (N != 0, 1) probes */
115		for (nr_probes = 0; old[nr_probes].func; nr_probes++)
116			if (old[nr_probes].func == probe &&
117			    old[nr_probes].data == data)
118				return ERR_PTR(-EEXIST);
119	}
120	/* + 2 : one for new probe, one for NULL func */
121	new = allocate_probes(nr_probes + 2);
122	if (new == NULL)
123		return ERR_PTR(-ENOMEM);
124	if (old)
125		memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));
126	new[nr_probes].func = probe;
127	new[nr_probes].data = data;
128	new[nr_probes + 1].func = NULL;
129	entry->refcount = nr_probes + 1;
130	entry->funcs = new;
131	debug_print_probes(entry);
132	return old;
133}
134
135static void *
136tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
137			      void *probe, void *data)
138{
139	int nr_probes = 0, nr_del = 0, i;
140	struct tracepoint_func *old, *new;
141
142	old = entry->funcs;
143
144	if (!old)
145		return ERR_PTR(-ENOENT);
146
147	debug_print_probes(entry);
148	/* (N -> M), (N > 1, M >= 0) probes */
149	for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
150		if (!probe ||
151		    (old[nr_probes].func == probe &&
152		     old[nr_probes].data == data))
153			nr_del++;
154	}
155
156	if (nr_probes - nr_del == 0) {
157		/* N -> 0, (N > 1) */
158		entry->funcs = NULL;
159		entry->refcount = 0;
160		debug_print_probes(entry);
161		return old;
162	} else {
163		int j = 0;
164		/* N -> M, (N > 1, M > 0) */
165		/* + 1 for NULL */
166		new = allocate_probes(nr_probes - nr_del + 1);
167		if (new == NULL)
168			return ERR_PTR(-ENOMEM);
169		for (i = 0; old[i].func; i++)
170			if (probe &&
171			    (old[i].func != probe || old[i].data != data))
172				new[j++] = old[i];
173		new[nr_probes - nr_del].func = NULL;
174		entry->refcount = nr_probes - nr_del;
175		entry->funcs = new;
176	}
177	debug_print_probes(entry);
178	return old;
179}
180
181/*
182 * Get tracepoint if the tracepoint is present in the tracepoint hash table.
183 * Must be called with tracepoints_mutex held.
184 * Returns NULL if not present.
185 */
186static struct tracepoint_entry *get_tracepoint(const char *name)
187{
188	struct hlist_head *head;
189	struct hlist_node *node;
190	struct tracepoint_entry *e;
191	u32 hash = jhash(name, strlen(name), 0);
192
193	head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
194	hlist_for_each_entry(e, node, head, hlist) {
195		if (!strcmp(name, e->name))
196			return e;
197	}
198	return NULL;
199}
200
201/*
202 * Add the tracepoint to the tracepoint hash table. Must be called with
203 * tracepoints_mutex held.
204 */
205static struct tracepoint_entry *add_tracepoint(const char *name)
206{
207	struct hlist_head *head;
208	struct hlist_node *node;
209	struct tracepoint_entry *e;
210	size_t name_len = strlen(name) + 1;
211	u32 hash = jhash(name, name_len-1, 0);
212
213	head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
214	hlist_for_each_entry(e, node, head, hlist) {
215		if (!strcmp(name, e->name)) {
216			printk(KERN_NOTICE
217				"tracepoint %s busy\n", name);
218			return ERR_PTR(-EEXIST);	/* Already there */
219		}
220	}
221	/*
222	 * Using kmalloc here to allocate a variable length element. Could
223	 * cause some memory fragmentation if overused.
224	 */
225	e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
226	if (!e)
227		return ERR_PTR(-ENOMEM);
228	memcpy(&e->name[0], name, name_len);
229	e->funcs = NULL;
230	e->refcount = 0;
231	hlist_add_head(&e->hlist, head);
232	return e;
233}
234
235/*
236 * Remove the tracepoint from the tracepoint hash table. Must be called with
237 * mutex_lock held.
238 */
239static inline void remove_tracepoint(struct tracepoint_entry *e)
240{
241	hlist_del(&e->hlist);
242	kfree(e);
243}
244
245/*
246 * Sets the probe callback corresponding to one tracepoint.
247 */
248static void set_tracepoint(struct tracepoint_entry **entry,
249	struct tracepoint *elem, int active)
250{
251	WARN_ON(strcmp((*entry)->name, elem->name) != 0);
252
253	if (elem->regfunc && !elem->state && active)
254		elem->regfunc();
255	else if (elem->unregfunc && elem->state && !active)
256		elem->unregfunc();
257
258	/*
259	 * rcu_assign_pointer has a smp_wmb() which makes sure that the new
260	 * probe callbacks array is consistent before setting a pointer to it.
261	 * This array is referenced by __DO_TRACE from
262	 * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
263	 * is used.
264	 */
265	rcu_assign_pointer(elem->funcs, (*entry)->funcs);
266	elem->state = active;
267}
268
269/*
270 * Disable a tracepoint and its probe callback.
271 * Note: only waiting an RCU period after setting elem->call to the empty
272 * function insures that the original callback is not used anymore. This insured
273 * by preempt_disable around the call site.
274 */
275static void disable_tracepoint(struct tracepoint *elem)
276{
277	if (elem->unregfunc && elem->state)
278		elem->unregfunc();
279
280	elem->state = 0;
281	rcu_assign_pointer(elem->funcs, NULL);
282}
283
284/**
285 * tracepoint_update_probe_range - Update a probe range
286 * @begin: beginning of the range
287 * @end: end of the range
288 *
289 * Updates the probe callback corresponding to a range of tracepoints.
290 */
291void
292tracepoint_update_probe_range(struct tracepoint *begin, struct tracepoint *end)
293{
294	struct tracepoint *iter;
295	struct tracepoint_entry *mark_entry;
296
297	if (!begin)
298		return;
299
300	mutex_lock(&tracepoints_mutex);
301	for (iter = begin; iter < end; iter++) {
302		mark_entry = get_tracepoint(iter->name);
303		if (mark_entry) {
304			set_tracepoint(&mark_entry, iter,
305					!!mark_entry->refcount);
306		} else {
307			disable_tracepoint(iter);
308		}
309	}
310	mutex_unlock(&tracepoints_mutex);
311}
312
313/*
314 * Update probes, removing the faulty probes.
315 */
316static void tracepoint_update_probes(void)
317{
318	/* Core kernel tracepoints */
319	tracepoint_update_probe_range(__start___tracepoints,
320		__stop___tracepoints);
321	/* tracepoints in modules. */
322	module_update_tracepoints();
323}
324
325static struct tracepoint_func *
326tracepoint_add_probe(const char *name, void *probe, void *data)
327{
328	struct tracepoint_entry *entry;
329	struct tracepoint_func *old;
330
331	entry = get_tracepoint(name);
332	if (!entry) {
333		entry = add_tracepoint(name);
334		if (IS_ERR(entry))
335			return (struct tracepoint_func *)entry;
336	}
337	old = tracepoint_entry_add_probe(entry, probe, data);
338	if (IS_ERR(old) && !entry->refcount)
339		remove_tracepoint(entry);
340	return old;
341}
342
343/**
344 * tracepoint_probe_register -  Connect a probe to a tracepoint
345 * @name: tracepoint name
346 * @probe: probe handler
347 *
348 * Returns 0 if ok, error value on error.
349 * The probe address must at least be aligned on the architecture pointer size.
350 */
351int tracepoint_probe_register(const char *name, void *probe, void *data)
352{
353	struct tracepoint_func *old;
354
355	mutex_lock(&tracepoints_mutex);
356	old = tracepoint_add_probe(name, probe, data);
357	mutex_unlock(&tracepoints_mutex);
358	if (IS_ERR(old))
359		return PTR_ERR(old);
360
361	tracepoint_update_probes();		/* may update entry */
362	release_probes(old);
363	return 0;
364}
365EXPORT_SYMBOL_GPL(tracepoint_probe_register);
366
367static struct tracepoint_func *
368tracepoint_remove_probe(const char *name, void *probe, void *data)
369{
370	struct tracepoint_entry *entry;
371	struct tracepoint_func *old;
372
373	entry = get_tracepoint(name);
374	if (!entry)
375		return ERR_PTR(-ENOENT);
376	old = tracepoint_entry_remove_probe(entry, probe, data);
377	if (IS_ERR(old))
378		return old;
379	if (!entry->refcount)
380		remove_tracepoint(entry);
381	return old;
382}
383
384/**
385 * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
386 * @name: tracepoint name
387 * @probe: probe function pointer
388 *
389 * We do not need to call a synchronize_sched to make sure the probes have
390 * finished running before doing a module unload, because the module unload
391 * itself uses stop_machine(), which insures that every preempt disabled section
392 * have finished.
393 */
394int tracepoint_probe_unregister(const char *name, void *probe, void *data)
395{
396	struct tracepoint_func *old;
397
398	mutex_lock(&tracepoints_mutex);
399	old = tracepoint_remove_probe(name, probe, data);
400	mutex_unlock(&tracepoints_mutex);
401	if (IS_ERR(old))
402		return PTR_ERR(old);
403
404	tracepoint_update_probes();		/* may update entry */
405	release_probes(old);
406	return 0;
407}
408EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
409
410static LIST_HEAD(old_probes);
411static int need_update;
412
413static void tracepoint_add_old_probes(void *old)
414{
415	need_update = 1;
416	if (old) {
417		struct tp_probes *tp_probes = container_of(old,
418			struct tp_probes, probes[0]);
419		list_add(&tp_probes->u.list, &old_probes);
420	}
421}
422
423/**
424 * tracepoint_probe_register_noupdate -  register a probe but not connect
425 * @name: tracepoint name
426 * @probe: probe handler
427 *
428 * caller must call tracepoint_probe_update_all()
429 */
430int tracepoint_probe_register_noupdate(const char *name, void *probe,
431				       void *data)
432{
433	struct tracepoint_func *old;
434
435	mutex_lock(&tracepoints_mutex);
436	old = tracepoint_add_probe(name, probe, data);
437	if (IS_ERR(old)) {
438		mutex_unlock(&tracepoints_mutex);
439		return PTR_ERR(old);
440	}
441	tracepoint_add_old_probes(old);
442	mutex_unlock(&tracepoints_mutex);
443	return 0;
444}
445EXPORT_SYMBOL_GPL(tracepoint_probe_register_noupdate);
446
447/**
448 * tracepoint_probe_unregister_noupdate -  remove a probe but not disconnect
449 * @name: tracepoint name
450 * @probe: probe function pointer
451 *
452 * caller must call tracepoint_probe_update_all()
453 */
454int tracepoint_probe_unregister_noupdate(const char *name, void *probe,
455					 void *data)
456{
457	struct tracepoint_func *old;
458
459	mutex_lock(&tracepoints_mutex);
460	old = tracepoint_remove_probe(name, probe, data);
461	if (IS_ERR(old)) {
462		mutex_unlock(&tracepoints_mutex);
463		return PTR_ERR(old);
464	}
465	tracepoint_add_old_probes(old);
466	mutex_unlock(&tracepoints_mutex);
467	return 0;
468}
469EXPORT_SYMBOL_GPL(tracepoint_probe_unregister_noupdate);
470
471/**
472 * tracepoint_probe_update_all -  update tracepoints
473 */
474void tracepoint_probe_update_all(void)
475{
476	LIST_HEAD(release_probes);
477	struct tp_probes *pos, *next;
478
479	mutex_lock(&tracepoints_mutex);
480	if (!need_update) {
481		mutex_unlock(&tracepoints_mutex);
482		return;
483	}
484	if (!list_empty(&old_probes))
485		list_replace_init(&old_probes, &release_probes);
486	need_update = 0;
487	mutex_unlock(&tracepoints_mutex);
488
489	tracepoint_update_probes();
490	list_for_each_entry_safe(pos, next, &release_probes, u.list) {
491		list_del(&pos->u.list);
492		call_rcu_sched(&pos->u.rcu, rcu_free_old_probes);
493	}
494}
495EXPORT_SYMBOL_GPL(tracepoint_probe_update_all);
496
497/**
498 * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
499 * @tracepoint: current tracepoints (in), next tracepoint (out)
500 * @begin: beginning of the range
501 * @end: end of the range
502 *
503 * Returns whether a next tracepoint has been found (1) or not (0).
504 * Will return the first tracepoint in the range if the input tracepoint is
505 * NULL.
506 */
507int tracepoint_get_iter_range(struct tracepoint **tracepoint,
508	struct tracepoint *begin, struct tracepoint *end)
509{
510	if (!*tracepoint && begin != end) {
511		*tracepoint = begin;
512		return 1;
513	}
514	if (*tracepoint >= begin && *tracepoint < end)
515		return 1;
516	return 0;
517}
518EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
519
520static void tracepoint_get_iter(struct tracepoint_iter *iter)
521{
522	int found = 0;
523
524	/* Core kernel tracepoints */
525	if (!iter->module) {
526		found = tracepoint_get_iter_range(&iter->tracepoint,
527				__start___tracepoints, __stop___tracepoints);
528		if (found)
529			goto end;
530	}
531	/* tracepoints in modules. */
532	found = module_get_iter_tracepoints(iter);
533end:
534	if (!found)
535		tracepoint_iter_reset(iter);
536}
537
538void tracepoint_iter_start(struct tracepoint_iter *iter)
539{
540	tracepoint_get_iter(iter);
541}
542EXPORT_SYMBOL_GPL(tracepoint_iter_start);
543
544void tracepoint_iter_next(struct tracepoint_iter *iter)
545{
546	iter->tracepoint++;
547	/*
548	 * iter->tracepoint may be invalid because we blindly incremented it.
549	 * Make sure it is valid by marshalling on the tracepoints, getting the
550	 * tracepoints from following modules if necessary.
551	 */
552	tracepoint_get_iter(iter);
553}
554EXPORT_SYMBOL_GPL(tracepoint_iter_next);
555
556void tracepoint_iter_stop(struct tracepoint_iter *iter)
557{
558}
559EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
560
561void tracepoint_iter_reset(struct tracepoint_iter *iter)
562{
563	iter->module = NULL;
564	iter->tracepoint = NULL;
565}
566EXPORT_SYMBOL_GPL(tracepoint_iter_reset);
567
568#ifdef CONFIG_MODULES
569
570int tracepoint_module_notify(struct notifier_block *self,
571			     unsigned long val, void *data)
572{
573	struct module *mod = data;
574
575	switch (val) {
576	case MODULE_STATE_COMING:
577	case MODULE_STATE_GOING:
578		tracepoint_update_probe_range(mod->tracepoints,
579			mod->tracepoints + mod->num_tracepoints);
580		break;
581	}
582	return 0;
583}
584
585struct notifier_block tracepoint_module_nb = {
586	.notifier_call = tracepoint_module_notify,
587	.priority = 0,
588};
589
590static int init_tracepoints(void)
591{
592	return register_module_notifier(&tracepoint_module_nb);
593}
594__initcall(init_tracepoints);
595
596#endif /* CONFIG_MODULES */
597
598#ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
599
600/* NB: reg/unreg are called while guarded with the tracepoints_mutex */
601static int sys_tracepoint_refcount;
602
603void syscall_regfunc(void)
604{
605	unsigned long flags;
606	struct task_struct *g, *t;
607
608	if (!sys_tracepoint_refcount) {
609		read_lock_irqsave(&tasklist_lock, flags);
610		do_each_thread(g, t) {
611			/* Skip kernel threads. */
612			if (t->mm)
613				set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
614		} while_each_thread(g, t);
615		read_unlock_irqrestore(&tasklist_lock, flags);
616	}
617	sys_tracepoint_refcount++;
618}
619
620void syscall_unregfunc(void)
621{
622	unsigned long flags;
623	struct task_struct *g, *t;
624
625	sys_tracepoint_refcount--;
626	if (!sys_tracepoint_refcount) {
627		read_lock_irqsave(&tasklist_lock, flags);
628		do_each_thread(g, t) {
629			clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
630		} while_each_thread(g, t);
631		read_unlock_irqrestore(&tasklist_lock, flags);
632	}
633}
634#endif
635