Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...
[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 #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