tracing: Let tracepoints have data passed to tracepoint callbacks
[linux-2.6.git] / kernel / tracepoint.c
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
29 extern struct tracepoint __start___tracepoints[];
30 extern struct tracepoint __stop___tracepoints[];
31
32 /* Set to 1 to enable tracepoint debug output */
33 static 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  */
39 static 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)
47 static 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  */
55 struct 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
62 struct tp_probes {
63         union {
64                 struct rcu_head rcu;
65                 struct list_head list;
66         } u;
67         struct tracepoint_func probes[0];
68 };
69
70 static 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
77 static void rcu_free_old_probes(struct rcu_head *head)
78 {
79         kfree(container_of(head, struct tp_probes, u.rcu));
80 }
81
82 static 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
91 static 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
102 static struct tracepoint_func *
103 tracepoint_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
135 static void *
136 tracepoint_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  */
186 static 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  */
205 static 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  */
239 static 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  */
248 static 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  */
275 static 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  */
291 void
292 tracepoint_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  */
316 static 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
325 static struct tracepoint_func *
326 tracepoint_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  */
351 int 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 }
365 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
366
367 static struct tracepoint_func *
368 tracepoint_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  */
394 int 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 }
408 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
409
410 static LIST_HEAD(old_probes);
411 static int need_update;
412
413 static 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  */
430 int 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 }
445 EXPORT_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  */
454 int 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 }
469 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister_noupdate);
470
471 /**
472  * tracepoint_probe_update_all -  update tracepoints
473  */
474 void 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 }
495 EXPORT_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  */
507 int 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 }
518 EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
519
520 static 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);
533 end:
534         if (!found)
535                 tracepoint_iter_reset(iter);
536 }
537
538 void tracepoint_iter_start(struct tracepoint_iter *iter)
539 {
540         tracepoint_get_iter(iter);
541 }
542 EXPORT_SYMBOL_GPL(tracepoint_iter_start);
543
544 void 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 }
554 EXPORT_SYMBOL_GPL(tracepoint_iter_next);
555
556 void tracepoint_iter_stop(struct tracepoint_iter *iter)
557 {
558 }
559 EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
560
561 void tracepoint_iter_reset(struct tracepoint_iter *iter)
562 {
563         iter->module = NULL;
564         iter->tracepoint = NULL;
565 }
566 EXPORT_SYMBOL_GPL(tracepoint_iter_reset);
567
568 #ifdef CONFIG_MODULES
569
570 int 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
585 struct notifier_block tracepoint_module_nb = {
586         .notifier_call = tracepoint_module_notify,
587         .priority = 0,
588 };
589
590 static 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 */
601 static int sys_tracepoint_refcount;
602
603 void 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
620 void 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