cgroups: fix a css_set not found bug in cgroup_attach_proc
[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 && !jump_label_enabled(&elem->key) && active)
255                 elem->regfunc();
256         else if (elem->unregfunc && jump_label_enabled(&elem->key) && !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 (active && !jump_label_enabled(&elem->key))
268                 jump_label_inc(&elem->key);
269         else if (!active && jump_label_enabled(&elem->key))
270                 jump_label_dec(&elem->key);
271 }
272
273 /*
274  * Disable a tracepoint and its probe callback.
275  * Note: only waiting an RCU period after setting elem->call to the empty
276  * function insures that the original callback is not used anymore. This insured
277  * by preempt_disable around the call site.
278  */
279 static void disable_tracepoint(struct tracepoint *elem)
280 {
281         if (elem->unregfunc && jump_label_enabled(&elem->key))
282                 elem->unregfunc();
283
284         if (jump_label_enabled(&elem->key))
285                 jump_label_dec(&elem->key);
286         rcu_assign_pointer(elem->funcs, NULL);
287 }
288
289 /**
290  * tracepoint_update_probe_range - Update a probe range
291  * @begin: beginning of the range
292  * @end: end of the range
293  *
294  * Updates the probe callback corresponding to a range of tracepoints.
295  */
296 void tracepoint_update_probe_range(struct tracepoint * const *begin,
297                                    struct tracepoint * const *end)
298 {
299         struct tracepoint * const *iter;
300         struct tracepoint_entry *mark_entry;
301
302         if (!begin)
303                 return;
304
305         mutex_lock(&tracepoints_mutex);
306         for (iter = begin; iter < end; iter++) {
307                 mark_entry = get_tracepoint((*iter)->name);
308                 if (mark_entry) {
309                         set_tracepoint(&mark_entry, *iter,
310                                         !!mark_entry->refcount);
311                 } else {
312                         disable_tracepoint(*iter);
313                 }
314         }
315         mutex_unlock(&tracepoints_mutex);
316 }
317
318 /*
319  * Update probes, removing the faulty probes.
320  */
321 static void tracepoint_update_probes(void)
322 {
323         /* Core kernel tracepoints */
324         tracepoint_update_probe_range(__start___tracepoints_ptrs,
325                 __stop___tracepoints_ptrs);
326         /* tracepoints in modules. */
327         module_update_tracepoints();
328 }
329
330 static struct tracepoint_func *
331 tracepoint_add_probe(const char *name, void *probe, void *data)
332 {
333         struct tracepoint_entry *entry;
334         struct tracepoint_func *old;
335
336         entry = get_tracepoint(name);
337         if (!entry) {
338                 entry = add_tracepoint(name);
339                 if (IS_ERR(entry))
340                         return (struct tracepoint_func *)entry;
341         }
342         old = tracepoint_entry_add_probe(entry, probe, data);
343         if (IS_ERR(old) && !entry->refcount)
344                 remove_tracepoint(entry);
345         return old;
346 }
347
348 /**
349  * tracepoint_probe_register -  Connect a probe to a tracepoint
350  * @name: tracepoint name
351  * @probe: probe handler
352  *
353  * Returns 0 if ok, error value on error.
354  * The probe address must at least be aligned on the architecture pointer size.
355  */
356 int tracepoint_probe_register(const char *name, void *probe, void *data)
357 {
358         struct tracepoint_func *old;
359
360         mutex_lock(&tracepoints_mutex);
361         old = tracepoint_add_probe(name, probe, data);
362         mutex_unlock(&tracepoints_mutex);
363         if (IS_ERR(old))
364                 return PTR_ERR(old);
365
366         tracepoint_update_probes();             /* may update entry */
367         release_probes(old);
368         return 0;
369 }
370 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
371
372 static struct tracepoint_func *
373 tracepoint_remove_probe(const char *name, void *probe, void *data)
374 {
375         struct tracepoint_entry *entry;
376         struct tracepoint_func *old;
377
378         entry = get_tracepoint(name);
379         if (!entry)
380                 return ERR_PTR(-ENOENT);
381         old = tracepoint_entry_remove_probe(entry, probe, data);
382         if (IS_ERR(old))
383                 return old;
384         if (!entry->refcount)
385                 remove_tracepoint(entry);
386         return old;
387 }
388
389 /**
390  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
391  * @name: tracepoint name
392  * @probe: probe function pointer
393  *
394  * We do not need to call a synchronize_sched to make sure the probes have
395  * finished running before doing a module unload, because the module unload
396  * itself uses stop_machine(), which insures that every preempt disabled section
397  * have finished.
398  */
399 int tracepoint_probe_unregister(const char *name, void *probe, void *data)
400 {
401         struct tracepoint_func *old;
402
403         mutex_lock(&tracepoints_mutex);
404         old = tracepoint_remove_probe(name, probe, data);
405         mutex_unlock(&tracepoints_mutex);
406         if (IS_ERR(old))
407                 return PTR_ERR(old);
408
409         tracepoint_update_probes();             /* may update entry */
410         release_probes(old);
411         return 0;
412 }
413 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
414
415 static LIST_HEAD(old_probes);
416 static int need_update;
417
418 static void tracepoint_add_old_probes(void *old)
419 {
420         need_update = 1;
421         if (old) {
422                 struct tp_probes *tp_probes = container_of(old,
423                         struct tp_probes, probes[0]);
424                 list_add(&tp_probes->u.list, &old_probes);
425         }
426 }
427
428 /**
429  * tracepoint_probe_register_noupdate -  register a probe but not connect
430  * @name: tracepoint name
431  * @probe: probe handler
432  *
433  * caller must call tracepoint_probe_update_all()
434  */
435 int tracepoint_probe_register_noupdate(const char *name, void *probe,
436                                        void *data)
437 {
438         struct tracepoint_func *old;
439
440         mutex_lock(&tracepoints_mutex);
441         old = tracepoint_add_probe(name, probe, data);
442         if (IS_ERR(old)) {
443                 mutex_unlock(&tracepoints_mutex);
444                 return PTR_ERR(old);
445         }
446         tracepoint_add_old_probes(old);
447         mutex_unlock(&tracepoints_mutex);
448         return 0;
449 }
450 EXPORT_SYMBOL_GPL(tracepoint_probe_register_noupdate);
451
452 /**
453  * tracepoint_probe_unregister_noupdate -  remove a probe but not disconnect
454  * @name: tracepoint name
455  * @probe: probe function pointer
456  *
457  * caller must call tracepoint_probe_update_all()
458  */
459 int tracepoint_probe_unregister_noupdate(const char *name, void *probe,
460                                          void *data)
461 {
462         struct tracepoint_func *old;
463
464         mutex_lock(&tracepoints_mutex);
465         old = tracepoint_remove_probe(name, probe, data);
466         if (IS_ERR(old)) {
467                 mutex_unlock(&tracepoints_mutex);
468                 return PTR_ERR(old);
469         }
470         tracepoint_add_old_probes(old);
471         mutex_unlock(&tracepoints_mutex);
472         return 0;
473 }
474 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister_noupdate);
475
476 /**
477  * tracepoint_probe_update_all -  update tracepoints
478  */
479 void tracepoint_probe_update_all(void)
480 {
481         LIST_HEAD(release_probes);
482         struct tp_probes *pos, *next;
483
484         mutex_lock(&tracepoints_mutex);
485         if (!need_update) {
486                 mutex_unlock(&tracepoints_mutex);
487                 return;
488         }
489         if (!list_empty(&old_probes))
490                 list_replace_init(&old_probes, &release_probes);
491         need_update = 0;
492         mutex_unlock(&tracepoints_mutex);
493
494         tracepoint_update_probes();
495         list_for_each_entry_safe(pos, next, &release_probes, u.list) {
496                 list_del(&pos->u.list);
497                 call_rcu_sched(&pos->u.rcu, rcu_free_old_probes);
498         }
499 }
500 EXPORT_SYMBOL_GPL(tracepoint_probe_update_all);
501
502 /**
503  * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
504  * @tracepoint: current tracepoints (in), next tracepoint (out)
505  * @begin: beginning of the range
506  * @end: end of the range
507  *
508  * Returns whether a next tracepoint has been found (1) or not (0).
509  * Will return the first tracepoint in the range if the input tracepoint is
510  * NULL.
511  */
512 int tracepoint_get_iter_range(struct tracepoint * const **tracepoint,
513         struct tracepoint * const *begin, struct tracepoint * const *end)
514 {
515         if (!*tracepoint && begin != end) {
516                 *tracepoint = begin;
517                 return 1;
518         }
519         if (*tracepoint >= begin && *tracepoint < end)
520                 return 1;
521         return 0;
522 }
523 EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
524
525 static void tracepoint_get_iter(struct tracepoint_iter *iter)
526 {
527         int found = 0;
528
529         /* Core kernel tracepoints */
530         if (!iter->module) {
531                 found = tracepoint_get_iter_range(&iter->tracepoint,
532                                 __start___tracepoints_ptrs,
533                                 __stop___tracepoints_ptrs);
534                 if (found)
535                         goto end;
536         }
537         /* tracepoints in modules. */
538         found = module_get_iter_tracepoints(iter);
539 end:
540         if (!found)
541                 tracepoint_iter_reset(iter);
542 }
543
544 void tracepoint_iter_start(struct tracepoint_iter *iter)
545 {
546         tracepoint_get_iter(iter);
547 }
548 EXPORT_SYMBOL_GPL(tracepoint_iter_start);
549
550 void tracepoint_iter_next(struct tracepoint_iter *iter)
551 {
552         iter->tracepoint++;
553         /*
554          * iter->tracepoint may be invalid because we blindly incremented it.
555          * Make sure it is valid by marshalling on the tracepoints, getting the
556          * tracepoints from following modules if necessary.
557          */
558         tracepoint_get_iter(iter);
559 }
560 EXPORT_SYMBOL_GPL(tracepoint_iter_next);
561
562 void tracepoint_iter_stop(struct tracepoint_iter *iter)
563 {
564 }
565 EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
566
567 void tracepoint_iter_reset(struct tracepoint_iter *iter)
568 {
569         iter->module = NULL;
570         iter->tracepoint = NULL;
571 }
572 EXPORT_SYMBOL_GPL(tracepoint_iter_reset);
573
574 #ifdef CONFIG_MODULES
575
576 int tracepoint_module_notify(struct notifier_block *self,
577                              unsigned long val, void *data)
578 {
579         struct module *mod = data;
580
581         switch (val) {
582         case MODULE_STATE_COMING:
583         case MODULE_STATE_GOING:
584                 tracepoint_update_probe_range(mod->tracepoints_ptrs,
585                         mod->tracepoints_ptrs + mod->num_tracepoints);
586                 break;
587         }
588         return 0;
589 }
590
591 struct notifier_block tracepoint_module_nb = {
592         .notifier_call = tracepoint_module_notify,
593         .priority = 0,
594 };
595
596 static int init_tracepoints(void)
597 {
598         return register_module_notifier(&tracepoint_module_nb);
599 }
600 __initcall(init_tracepoints);
601
602 #endif /* CONFIG_MODULES */
603
604 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
605
606 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
607 static int sys_tracepoint_refcount;
608
609 void syscall_regfunc(void)
610 {
611         unsigned long flags;
612         struct task_struct *g, *t;
613
614         if (!sys_tracepoint_refcount) {
615                 read_lock_irqsave(&tasklist_lock, flags);
616                 do_each_thread(g, t) {
617                         /* Skip kernel threads. */
618                         if (t->mm)
619                                 set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
620                 } while_each_thread(g, t);
621                 read_unlock_irqrestore(&tasklist_lock, flags);
622         }
623         sys_tracepoint_refcount++;
624 }
625
626 void syscall_unregfunc(void)
627 {
628         unsigned long flags;
629         struct task_struct *g, *t;
630
631         sys_tracepoint_refcount--;
632         if (!sys_tracepoint_refcount) {
633                 read_lock_irqsave(&tasklist_lock, flags);
634                 do_each_thread(g, t) {
635                         clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
636                 } while_each_thread(g, t);
637                 read_unlock_irqrestore(&tasklist_lock, flags);
638         }
639 }
640 #endif