xref: /openbmc/linux/kernel/tracepoint.c (revision 4800cd83)
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 #include <linux/jump_label.h>
29 
30 extern struct tracepoint * const __start___tracepoints_ptrs[];
31 extern struct tracepoint * const __stop___tracepoints_ptrs[];
32 
33 /* Set to 1 to enable tracepoint debug output */
34 static const int tracepoint_debug;
35 
36 /*
37  * tracepoints_mutex nests inside module_mutex. Tracepoints mutex protects the
38  * builtin and module tracepoints and the hash table.
39  */
40 static DEFINE_MUTEX(tracepoints_mutex);
41 
42 /*
43  * Tracepoint hash table, containing the active tracepoints.
44  * Protected by tracepoints_mutex.
45  */
46 #define TRACEPOINT_HASH_BITS 6
47 #define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
48 static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
49 
50 /*
51  * Note about RCU :
52  * It is used to delay the free of multiple probes array until a quiescent
53  * state is reached.
54  * Tracepoint entries modifications are protected by the tracepoints_mutex.
55  */
56 struct tracepoint_entry {
57 	struct hlist_node hlist;
58 	struct tracepoint_func *funcs;
59 	int refcount;	/* Number of times armed. 0 if disarmed. */
60 	char name[0];
61 };
62 
63 struct tp_probes {
64 	union {
65 		struct rcu_head rcu;
66 		struct list_head list;
67 	} u;
68 	struct tracepoint_func probes[0];
69 };
70 
71 static inline void *allocate_probes(int count)
72 {
73 	struct tp_probes *p  = kmalloc(count * sizeof(struct tracepoint_func)
74 			+ sizeof(struct tp_probes), GFP_KERNEL);
75 	return p == NULL ? NULL : p->probes;
76 }
77 
78 static void rcu_free_old_probes(struct rcu_head *head)
79 {
80 	kfree(container_of(head, struct tp_probes, u.rcu));
81 }
82 
83 static inline void release_probes(struct tracepoint_func *old)
84 {
85 	if (old) {
86 		struct tp_probes *tp_probes = container_of(old,
87 			struct tp_probes, probes[0]);
88 		call_rcu_sched(&tp_probes->u.rcu, rcu_free_old_probes);
89 	}
90 }
91 
92 static void debug_print_probes(struct tracepoint_entry *entry)
93 {
94 	int i;
95 
96 	if (!tracepoint_debug || !entry->funcs)
97 		return;
98 
99 	for (i = 0; entry->funcs[i].func; i++)
100 		printk(KERN_DEBUG "Probe %d : %p\n", i, entry->funcs[i].func);
101 }
102 
103 static struct tracepoint_func *
104 tracepoint_entry_add_probe(struct tracepoint_entry *entry,
105 			   void *probe, void *data)
106 {
107 	int nr_probes = 0;
108 	struct tracepoint_func *old, *new;
109 
110 	WARN_ON(!probe);
111 
112 	debug_print_probes(entry);
113 	old = entry->funcs;
114 	if (old) {
115 		/* (N -> N+1), (N != 0, 1) probes */
116 		for (nr_probes = 0; old[nr_probes].func; nr_probes++)
117 			if (old[nr_probes].func == probe &&
118 			    old[nr_probes].data == data)
119 				return ERR_PTR(-EEXIST);
120 	}
121 	/* + 2 : one for new probe, one for NULL func */
122 	new = allocate_probes(nr_probes + 2);
123 	if (new == NULL)
124 		return ERR_PTR(-ENOMEM);
125 	if (old)
126 		memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));
127 	new[nr_probes].func = probe;
128 	new[nr_probes].data = data;
129 	new[nr_probes + 1].func = NULL;
130 	entry->refcount = nr_probes + 1;
131 	entry->funcs = new;
132 	debug_print_probes(entry);
133 	return old;
134 }
135 
136 static void *
137 tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
138 			      void *probe, void *data)
139 {
140 	int nr_probes = 0, nr_del = 0, i;
141 	struct tracepoint_func *old, *new;
142 
143 	old = entry->funcs;
144 
145 	if (!old)
146 		return ERR_PTR(-ENOENT);
147 
148 	debug_print_probes(entry);
149 	/* (N -> M), (N > 1, M >= 0) probes */
150 	for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
151 		if (!probe ||
152 		    (old[nr_probes].func == probe &&
153 		     old[nr_probes].data == data))
154 			nr_del++;
155 	}
156 
157 	if (nr_probes - nr_del == 0) {
158 		/* N -> 0, (N > 1) */
159 		entry->funcs = NULL;
160 		entry->refcount = 0;
161 		debug_print_probes(entry);
162 		return old;
163 	} else {
164 		int j = 0;
165 		/* N -> M, (N > 1, M > 0) */
166 		/* + 1 for NULL */
167 		new = allocate_probes(nr_probes - nr_del + 1);
168 		if (new == NULL)
169 			return ERR_PTR(-ENOMEM);
170 		for (i = 0; old[i].func; i++)
171 			if (probe &&
172 			    (old[i].func != probe || old[i].data != data))
173 				new[j++] = old[i];
174 		new[nr_probes - nr_del].func = NULL;
175 		entry->refcount = nr_probes - nr_del;
176 		entry->funcs = new;
177 	}
178 	debug_print_probes(entry);
179 	return old;
180 }
181 
182 /*
183  * Get tracepoint if the tracepoint is present in the tracepoint hash table.
184  * Must be called with tracepoints_mutex held.
185  * Returns NULL if not present.
186  */
187 static struct tracepoint_entry *get_tracepoint(const char *name)
188 {
189 	struct hlist_head *head;
190 	struct hlist_node *node;
191 	struct tracepoint_entry *e;
192 	u32 hash = jhash(name, strlen(name), 0);
193 
194 	head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
195 	hlist_for_each_entry(e, node, head, hlist) {
196 		if (!strcmp(name, e->name))
197 			return e;
198 	}
199 	return NULL;
200 }
201 
202 /*
203  * Add the tracepoint to the tracepoint hash table. Must be called with
204  * tracepoints_mutex held.
205  */
206 static struct tracepoint_entry *add_tracepoint(const char *name)
207 {
208 	struct hlist_head *head;
209 	struct hlist_node *node;
210 	struct tracepoint_entry *e;
211 	size_t name_len = strlen(name) + 1;
212 	u32 hash = jhash(name, name_len-1, 0);
213 
214 	head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
215 	hlist_for_each_entry(e, node, head, hlist) {
216 		if (!strcmp(name, e->name)) {
217 			printk(KERN_NOTICE
218 				"tracepoint %s busy\n", name);
219 			return ERR_PTR(-EEXIST);	/* Already there */
220 		}
221 	}
222 	/*
223 	 * Using kmalloc here to allocate a variable length element. Could
224 	 * cause some memory fragmentation if overused.
225 	 */
226 	e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
227 	if (!e)
228 		return ERR_PTR(-ENOMEM);
229 	memcpy(&e->name[0], name, name_len);
230 	e->funcs = NULL;
231 	e->refcount = 0;
232 	hlist_add_head(&e->hlist, head);
233 	return e;
234 }
235 
236 /*
237  * Remove the tracepoint from the tracepoint hash table. Must be called with
238  * mutex_lock held.
239  */
240 static inline void remove_tracepoint(struct tracepoint_entry *e)
241 {
242 	hlist_del(&e->hlist);
243 	kfree(e);
244 }
245 
246 /*
247  * Sets the probe callback corresponding to one tracepoint.
248  */
249 static void set_tracepoint(struct tracepoint_entry **entry,
250 	struct tracepoint *elem, int active)
251 {
252 	WARN_ON(strcmp((*entry)->name, elem->name) != 0);
253 
254 	if (elem->regfunc && !elem->state && active)
255 		elem->regfunc();
256 	else if (elem->unregfunc && elem->state && !active)
257 		elem->unregfunc();
258 
259 	/*
260 	 * rcu_assign_pointer has a smp_wmb() which makes sure that the new
261 	 * probe callbacks array is consistent before setting a pointer to it.
262 	 * This array is referenced by __DO_TRACE from
263 	 * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
264 	 * is used.
265 	 */
266 	rcu_assign_pointer(elem->funcs, (*entry)->funcs);
267 	if (!elem->state && active) {
268 		jump_label_enable(&elem->state);
269 		elem->state = active;
270 	} else if (elem->state && !active) {
271 		jump_label_disable(&elem->state);
272 		elem->state = active;
273 	}
274 }
275 
276 /*
277  * Disable a tracepoint and its probe callback.
278  * Note: only waiting an RCU period after setting elem->call to the empty
279  * function insures that the original callback is not used anymore. This insured
280  * by preempt_disable around the call site.
281  */
282 static void disable_tracepoint(struct tracepoint *elem)
283 {
284 	if (elem->unregfunc && elem->state)
285 		elem->unregfunc();
286 
287 	if (elem->state) {
288 		jump_label_disable(&elem->state);
289 		elem->state = 0;
290 	}
291 	rcu_assign_pointer(elem->funcs, NULL);
292 }
293 
294 /**
295  * tracepoint_update_probe_range - Update a probe range
296  * @begin: beginning of the range
297  * @end: end of the range
298  *
299  * Updates the probe callback corresponding to a range of tracepoints.
300  */
301 void tracepoint_update_probe_range(struct tracepoint * const *begin,
302 				   struct tracepoint * const *end)
303 {
304 	struct tracepoint * const *iter;
305 	struct tracepoint_entry *mark_entry;
306 
307 	if (!begin)
308 		return;
309 
310 	mutex_lock(&tracepoints_mutex);
311 	for (iter = begin; iter < end; iter++) {
312 		mark_entry = get_tracepoint((*iter)->name);
313 		if (mark_entry) {
314 			set_tracepoint(&mark_entry, *iter,
315 					!!mark_entry->refcount);
316 		} else {
317 			disable_tracepoint(*iter);
318 		}
319 	}
320 	mutex_unlock(&tracepoints_mutex);
321 }
322 
323 /*
324  * Update probes, removing the faulty probes.
325  */
326 static void tracepoint_update_probes(void)
327 {
328 	/* Core kernel tracepoints */
329 	tracepoint_update_probe_range(__start___tracepoints_ptrs,
330 		__stop___tracepoints_ptrs);
331 	/* tracepoints in modules. */
332 	module_update_tracepoints();
333 }
334 
335 static struct tracepoint_func *
336 tracepoint_add_probe(const char *name, void *probe, void *data)
337 {
338 	struct tracepoint_entry *entry;
339 	struct tracepoint_func *old;
340 
341 	entry = get_tracepoint(name);
342 	if (!entry) {
343 		entry = add_tracepoint(name);
344 		if (IS_ERR(entry))
345 			return (struct tracepoint_func *)entry;
346 	}
347 	old = tracepoint_entry_add_probe(entry, probe, data);
348 	if (IS_ERR(old) && !entry->refcount)
349 		remove_tracepoint(entry);
350 	return old;
351 }
352 
353 /**
354  * tracepoint_probe_register -  Connect a probe to a tracepoint
355  * @name: tracepoint name
356  * @probe: probe handler
357  *
358  * Returns 0 if ok, error value on error.
359  * The probe address must at least be aligned on the architecture pointer size.
360  */
361 int tracepoint_probe_register(const char *name, void *probe, void *data)
362 {
363 	struct tracepoint_func *old;
364 
365 	mutex_lock(&tracepoints_mutex);
366 	old = tracepoint_add_probe(name, probe, data);
367 	mutex_unlock(&tracepoints_mutex);
368 	if (IS_ERR(old))
369 		return PTR_ERR(old);
370 
371 	tracepoint_update_probes();		/* may update entry */
372 	release_probes(old);
373 	return 0;
374 }
375 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
376 
377 static struct tracepoint_func *
378 tracepoint_remove_probe(const char *name, void *probe, void *data)
379 {
380 	struct tracepoint_entry *entry;
381 	struct tracepoint_func *old;
382 
383 	entry = get_tracepoint(name);
384 	if (!entry)
385 		return ERR_PTR(-ENOENT);
386 	old = tracepoint_entry_remove_probe(entry, probe, data);
387 	if (IS_ERR(old))
388 		return old;
389 	if (!entry->refcount)
390 		remove_tracepoint(entry);
391 	return old;
392 }
393 
394 /**
395  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
396  * @name: tracepoint name
397  * @probe: probe function pointer
398  *
399  * We do not need to call a synchronize_sched to make sure the probes have
400  * finished running before doing a module unload, because the module unload
401  * itself uses stop_machine(), which insures that every preempt disabled section
402  * have finished.
403  */
404 int tracepoint_probe_unregister(const char *name, void *probe, void *data)
405 {
406 	struct tracepoint_func *old;
407 
408 	mutex_lock(&tracepoints_mutex);
409 	old = tracepoint_remove_probe(name, probe, data);
410 	mutex_unlock(&tracepoints_mutex);
411 	if (IS_ERR(old))
412 		return PTR_ERR(old);
413 
414 	tracepoint_update_probes();		/* may update entry */
415 	release_probes(old);
416 	return 0;
417 }
418 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
419 
420 static LIST_HEAD(old_probes);
421 static int need_update;
422 
423 static void tracepoint_add_old_probes(void *old)
424 {
425 	need_update = 1;
426 	if (old) {
427 		struct tp_probes *tp_probes = container_of(old,
428 			struct tp_probes, probes[0]);
429 		list_add(&tp_probes->u.list, &old_probes);
430 	}
431 }
432 
433 /**
434  * tracepoint_probe_register_noupdate -  register a probe but not connect
435  * @name: tracepoint name
436  * @probe: probe handler
437  *
438  * caller must call tracepoint_probe_update_all()
439  */
440 int tracepoint_probe_register_noupdate(const char *name, void *probe,
441 				       void *data)
442 {
443 	struct tracepoint_func *old;
444 
445 	mutex_lock(&tracepoints_mutex);
446 	old = tracepoint_add_probe(name, probe, data);
447 	if (IS_ERR(old)) {
448 		mutex_unlock(&tracepoints_mutex);
449 		return PTR_ERR(old);
450 	}
451 	tracepoint_add_old_probes(old);
452 	mutex_unlock(&tracepoints_mutex);
453 	return 0;
454 }
455 EXPORT_SYMBOL_GPL(tracepoint_probe_register_noupdate);
456 
457 /**
458  * tracepoint_probe_unregister_noupdate -  remove a probe but not disconnect
459  * @name: tracepoint name
460  * @probe: probe function pointer
461  *
462  * caller must call tracepoint_probe_update_all()
463  */
464 int tracepoint_probe_unregister_noupdate(const char *name, void *probe,
465 					 void *data)
466 {
467 	struct tracepoint_func *old;
468 
469 	mutex_lock(&tracepoints_mutex);
470 	old = tracepoint_remove_probe(name, probe, data);
471 	if (IS_ERR(old)) {
472 		mutex_unlock(&tracepoints_mutex);
473 		return PTR_ERR(old);
474 	}
475 	tracepoint_add_old_probes(old);
476 	mutex_unlock(&tracepoints_mutex);
477 	return 0;
478 }
479 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister_noupdate);
480 
481 /**
482  * tracepoint_probe_update_all -  update tracepoints
483  */
484 void tracepoint_probe_update_all(void)
485 {
486 	LIST_HEAD(release_probes);
487 	struct tp_probes *pos, *next;
488 
489 	mutex_lock(&tracepoints_mutex);
490 	if (!need_update) {
491 		mutex_unlock(&tracepoints_mutex);
492 		return;
493 	}
494 	if (!list_empty(&old_probes))
495 		list_replace_init(&old_probes, &release_probes);
496 	need_update = 0;
497 	mutex_unlock(&tracepoints_mutex);
498 
499 	tracepoint_update_probes();
500 	list_for_each_entry_safe(pos, next, &release_probes, u.list) {
501 		list_del(&pos->u.list);
502 		call_rcu_sched(&pos->u.rcu, rcu_free_old_probes);
503 	}
504 }
505 EXPORT_SYMBOL_GPL(tracepoint_probe_update_all);
506 
507 /**
508  * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
509  * @tracepoint: current tracepoints (in), next tracepoint (out)
510  * @begin: beginning of the range
511  * @end: end of the range
512  *
513  * Returns whether a next tracepoint has been found (1) or not (0).
514  * Will return the first tracepoint in the range if the input tracepoint is
515  * NULL.
516  */
517 int tracepoint_get_iter_range(struct tracepoint * const **tracepoint,
518 	struct tracepoint * const *begin, struct tracepoint * const *end)
519 {
520 	if (!*tracepoint && begin != end) {
521 		*tracepoint = begin;
522 		return 1;
523 	}
524 	if (*tracepoint >= begin && *tracepoint < end)
525 		return 1;
526 	return 0;
527 }
528 EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
529 
530 static void tracepoint_get_iter(struct tracepoint_iter *iter)
531 {
532 	int found = 0;
533 
534 	/* Core kernel tracepoints */
535 	if (!iter->module) {
536 		found = tracepoint_get_iter_range(&iter->tracepoint,
537 				__start___tracepoints_ptrs,
538 				__stop___tracepoints_ptrs);
539 		if (found)
540 			goto end;
541 	}
542 	/* tracepoints in modules. */
543 	found = module_get_iter_tracepoints(iter);
544 end:
545 	if (!found)
546 		tracepoint_iter_reset(iter);
547 }
548 
549 void tracepoint_iter_start(struct tracepoint_iter *iter)
550 {
551 	tracepoint_get_iter(iter);
552 }
553 EXPORT_SYMBOL_GPL(tracepoint_iter_start);
554 
555 void tracepoint_iter_next(struct tracepoint_iter *iter)
556 {
557 	iter->tracepoint++;
558 	/*
559 	 * iter->tracepoint may be invalid because we blindly incremented it.
560 	 * Make sure it is valid by marshalling on the tracepoints, getting the
561 	 * tracepoints from following modules if necessary.
562 	 */
563 	tracepoint_get_iter(iter);
564 }
565 EXPORT_SYMBOL_GPL(tracepoint_iter_next);
566 
567 void tracepoint_iter_stop(struct tracepoint_iter *iter)
568 {
569 }
570 EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
571 
572 void tracepoint_iter_reset(struct tracepoint_iter *iter)
573 {
574 	iter->module = NULL;
575 	iter->tracepoint = NULL;
576 }
577 EXPORT_SYMBOL_GPL(tracepoint_iter_reset);
578 
579 #ifdef CONFIG_MODULES
580 
581 int tracepoint_module_notify(struct notifier_block *self,
582 			     unsigned long val, void *data)
583 {
584 	struct module *mod = data;
585 
586 	switch (val) {
587 	case MODULE_STATE_COMING:
588 	case MODULE_STATE_GOING:
589 		tracepoint_update_probe_range(mod->tracepoints_ptrs,
590 			mod->tracepoints_ptrs + mod->num_tracepoints);
591 		break;
592 	}
593 	return 0;
594 }
595 
596 struct notifier_block tracepoint_module_nb = {
597 	.notifier_call = tracepoint_module_notify,
598 	.priority = 0,
599 };
600 
601 static int init_tracepoints(void)
602 {
603 	return register_module_notifier(&tracepoint_module_nb);
604 }
605 __initcall(init_tracepoints);
606 
607 #endif /* CONFIG_MODULES */
608 
609 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
610 
611 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
612 static int sys_tracepoint_refcount;
613 
614 void syscall_regfunc(void)
615 {
616 	unsigned long flags;
617 	struct task_struct *g, *t;
618 
619 	if (!sys_tracepoint_refcount) {
620 		read_lock_irqsave(&tasklist_lock, flags);
621 		do_each_thread(g, t) {
622 			/* Skip kernel threads. */
623 			if (t->mm)
624 				set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
625 		} while_each_thread(g, t);
626 		read_unlock_irqrestore(&tasklist_lock, flags);
627 	}
628 	sys_tracepoint_refcount++;
629 }
630 
631 void syscall_unregfunc(void)
632 {
633 	unsigned long flags;
634 	struct task_struct *g, *t;
635 
636 	sys_tracepoint_refcount--;
637 	if (!sys_tracepoint_refcount) {
638 		read_lock_irqsave(&tasklist_lock, flags);
639 		do_each_thread(g, t) {
640 			clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
641 		} while_each_thread(g, t);
642 		read_unlock_irqrestore(&tasklist_lock, flags);
643 	}
644 }
645 #endif
646