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