libust/tracepoint.c

   1 /*
   2  * Copyright (C) 2008-2011 Mathieu Desnoyers
   3  * Copyright (C) 2009 Pierre-Marc Fournier
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation;
   8  * version 2.1 of the License.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public
  16  * License along with this library; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
  18  *
  19  * Ported to userspace by Pierre-Marc Fournier.
  20  */
  21
  22 #define _LGPL_SOURCE
  23 #include <errno.h>
  24 #include <ust/tracepoint.h>
  25 #include <ust/tracepoint-internal.h>
  26 #include <ust/core.h>
  27 #include <ust/kcompat/kcompat.h>
  28 #include <urcu-bp.h>
  29 #include <urcu/hlist.h>
  30
  31 #include "usterr_signal_safe.h"
  32
  33 extern struct tracepoint * const __start___tracepoints_ptrs[]
  34         __attribute__((visibility("hidden")));
  35 extern struct tracepoint * const __stop___tracepoints_ptrs[]
  36         __attribute__((visibility("hidden")));
  37
  38 static struct tracepoint * __tracepoint_ptr_dummy
  39         __attribute__((used, section("__tracepoints_ptrs")));
  40
  41 /* Set to 1 to enable tracepoint debug output */
  42 static const int tracepoint_debug;
  43 static int initialized;
  44 static void (*new_tracepoint_cb)(struct tracepoint *);
  45
  46 /* libraries that contain tracepoints (struct tracepoint_lib) */
  47 static CDS_LIST_HEAD(libs);
  48
  49 /*
  50  * Allow nested mutex for mutex listing and nested enable.
  51  */
  52 static __thread int nested_mutex;
  53
  54 /*
  55  * Tracepoints mutex protects the library tracepoints, the hash table,
  56  * and the library list.
  57  */
  58 static pthread_mutex_t tracepoints_mutex;
  59
  60 static
  61 void lock_tracepoints(void)
  62 {
  63         if (!(nested_mutex++))
  64                 pthread_mutex_lock(&tracepoints_mutex);
  65 }
  66
  67 static
  68 void unlock_tracepoints(void)
  69 {
  70         if (!(--nested_mutex))
  71                 pthread_mutex_unlock(&tracepoints_mutex);
  72 }
  73
  74 /*
  75  * Tracepoint hash table, containing the active tracepoints.
  76  * Protected by tracepoints_mutex.
  77  */
  78 #define TRACEPOINT_HASH_BITS 6
  79 #define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
  80 static struct cds_hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
  81
  82 static CDS_LIST_HEAD(old_probes);
  83 static int need_update;
  84
  85 /*
  86  * Note about RCU :
  87  * It is used to to delay the free of multiple probes array until a quiescent
  88  * state is reached.
  89  * Tracepoint entries modifications are protected by the tracepoints_mutex.
  90  */
  91 struct tracepoint_entry {
  92         struct cds_hlist_node hlist;
  93         struct tracepoint_probe *probes;
  94         int refcount;   /* Number of times armed. 0 if disarmed. */
  95         char name[0];
  96 };
  97
  98 struct tp_probes {
  99         union {
 100                 struct cds_list_head list;
 101         } u;
 102         struct tracepoint_probe probes[0];
 103 };
 104
 105 static inline void *allocate_probes(int count)
 106 {
 107         struct tp_probes *p  = zmalloc(count * sizeof(struct tracepoint_probe)
 108                         + sizeof(struct tp_probes));
 109         return p == NULL ? NULL : p->probes;
 110 }
 111
 112 static inline void release_probes(void *old)
 113 {
 114         if (old) {
 115                 struct tp_probes *tp_probes = _ust_container_of(old,
 116                         struct tp_probes, probes[0]);
 117                 synchronize_rcu();
 118                 free(tp_probes);
 119         }
 120 }
 121
 122 static void debug_print_probes(struct tracepoint_entry *entry)
 123 {
 124         int i;
 125
 126         if (!tracepoint_debug || !entry->probes)
 127                 return;
 128
 129         for (i = 0; entry->probes[i].func; i++)
 130                 DBG("Probe %d : %p", i, entry->probes[i].func);
 131 }
 132
 133 static void *
 134 tracepoint_entry_add_probe(struct tracepoint_entry *entry,
 135                            void *probe, void *data)
 136 {
 137         int nr_probes = 0;
 138         struct tracepoint_probe *old, *new;
 139
 140         WARN_ON(!probe);
 141
 142         debug_print_probes(entry);
 143         old = entry->probes;
 144         if (old) {
 145                 /* (N -> N+1), (N != 0, 1) probes */
 146                 for (nr_probes = 0; old[nr_probes].func; nr_probes++)
 147                         if (old[nr_probes].func == probe &&
 148                             old[nr_probes].data == data)
 149                                 return ERR_PTR(-EEXIST);
 150         }
 151         /* + 2 : one for new probe, one for NULL func */
 152         new = allocate_probes(nr_probes + 2);
 153         if (new == NULL)
 154                 return ERR_PTR(-ENOMEM);
 155         if (old)
 156                 memcpy(new, old, nr_probes * sizeof(struct tracepoint_probe));
 157         new[nr_probes].func = probe;
 158         new[nr_probes].data = data;
 159         new[nr_probes + 1].func = NULL;
 160         entry->refcount = nr_probes + 1;
 161         entry->probes = new;
 162         debug_print_probes(entry);
 163         return old;
 164 }
 165
 166 static void *
 167 tracepoint_entry_remove_probe(struct tracepoint_entry *entry, void *probe,
 168                               void *data)
 169 {
 170         int nr_probes = 0, nr_del = 0, i;
 171         struct tracepoint_probe *old, *new;
 172
 173         old = entry->probes;
 174
 175         if (!old)
 176                 return ERR_PTR(-ENOENT);
 177
 178         debug_print_probes(entry);
 179         /* (N -> M), (N > 1, M >= 0) probes */
 180         for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
 181                 if (!probe ||
 182                      (old[nr_probes].func == probe &&
 183                      old[nr_probes].data == data))
 184                         nr_del++;
 185         }
 186
 187         if (nr_probes - nr_del == 0) {
 188                 /* N -> 0, (N > 1) */
 189                 entry->probes = NULL;
 190                 entry->refcount = 0;
 191                 debug_print_probes(entry);
 192                 return old;
 193         } else {
 194                 int j = 0;
 195                 /* N -> M, (N > 1, M > 0) */
 196                 /* + 1 for NULL */
 197                 new = allocate_probes(nr_probes - nr_del + 1);
 198                 if (new == NULL)
 199                         return ERR_PTR(-ENOMEM);
 200                 for (i = 0; old[i].func; i++)
 201                         if (probe &&
 202                             (old[i].func != probe || old[i].data != data))
 203                                 new[j++] = old[i];
 204                 new[nr_probes - nr_del].func = NULL;
 205                 entry->refcount = nr_probes - nr_del;
 206                 entry->probes = new;
 207         }
 208         debug_print_probes(entry);
 209         return old;
 210 }
 211
 212 /*
 213  * Get tracepoint if the tracepoint is present in the tracepoint hash table.
 214  * Must be called with tracepoints_mutex held.
 215  * Returns NULL if not present.
 216  */
 217 static struct tracepoint_entry *get_tracepoint(const char *name)
 218 {
 219         struct cds_hlist_head *head;
 220         struct cds_hlist_node *node;
 221         struct tracepoint_entry *e;
 222         u32 hash = jhash(name, strlen(name), 0);
 223
 224         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 225         cds_hlist_for_each_entry(e, node, head, hlist) {
 226                 if (!strcmp(name, e->name))
 227                         return e;
 228         }
 229         return NULL;
 230 }
 231
 232 /*
 233  * Add the tracepoint to the tracepoint hash table. Must be called with
 234  * tracepoints_mutex held.
 235  */
 236 static struct tracepoint_entry *add_tracepoint(const char *name)
 237 {
 238         struct cds_hlist_head *head;
 239         struct cds_hlist_node *node;
 240         struct tracepoint_entry *e;
 241         size_t name_len = strlen(name) + 1;
 242         u32 hash = jhash(name, name_len-1, 0);
 243
 244         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 245         cds_hlist_for_each_entry(e, node, head, hlist) {
 246                 if (!strcmp(name, e->name)) {
 247                         DBG("tracepoint %s busy", name);
 248                         return ERR_PTR(-EEXIST);        /* Already there */
 249                 }
 250         }
 251         /*
 252          * Using zmalloc here to allocate a variable length element. Could
 253          * cause some memory fragmentation if overused.
 254          */
 255         e = zmalloc(sizeof(struct tracepoint_entry) + name_len);
 256         if (!e)
 257                 return ERR_PTR(-ENOMEM);
 258         memcpy(&e->name[0], name, name_len);
 259         e->probes = NULL;
 260         e->refcount = 0;
 261         cds_hlist_add_head(&e->hlist, head);
 262         return e;
 263 }
 264
 265 /*
 266  * Remove the tracepoint from the tracepoint hash table. Must be called with
 267  * mutex_lock held.
 268  */
 269 static inline void remove_tracepoint(struct tracepoint_entry *e)
 270 {
 271         cds_hlist_del(&e->hlist);
 272         free(e);
 273 }
 274
 275 /*
 276  * Sets the probe callback corresponding to one tracepoint.
 277  */
 278 static void set_tracepoint(struct tracepoint_entry **entry,
 279         struct tracepoint *elem, int active)
 280 {
 281         WARN_ON(strcmp((*entry)->name, elem->name) != 0);
 282
 283         /*
 284          * rcu_assign_pointer has a cmm_smp_wmb() which makes sure that the new
 285          * probe callbacks array is consistent before setting a pointer to it.
 286          * This array is referenced by __DO_TRACE from
 287          * include/linux/tracepoints.h. A matching cmm_smp_read_barrier_depends()
 288          * is used.
 289          */
 290         rcu_assign_pointer(elem->probes, (*entry)->probes);
 291         elem->state = active;
 292 }
 293
 294 /*
 295  * Disable a tracepoint and its probe callback.
 296  * Note: only waiting an RCU period after setting elem->call to the empty
 297  * function insures that the original callback is not used anymore. This insured
 298  * by preempt_disable around the call site.
 299  */
 300 static void disable_tracepoint(struct tracepoint *elem)
 301 {
 302         elem->state = 0;
 303         rcu_assign_pointer(elem->probes, NULL);
 304 }
 305
 306 /**
 307  * tracepoint_update_probe_range - Update a probe range
 308  * @begin: beginning of the range
 309  * @end: end of the range
 310  *
 311  * Updates the probe callback corresponding to a range of tracepoints.
 312  */
 313 static
 314 void tracepoint_update_probe_range(struct tracepoint * const *begin,
 315                                    struct tracepoint * const *end)
 316 {
 317         struct tracepoint * const *iter;
 318         struct tracepoint_entry *mark_entry;
 319
 320         for (iter = begin; iter < end; iter++) {
 321                 if (!*iter)
 322                         continue;       /* skip dummy */
 323                 if (!(*iter)->name) {
 324                         disable_tracepoint(*iter);
 325                         continue;
 326                 }
 327                 mark_entry = get_tracepoint((*iter)->name);
 328                 if (mark_entry) {
 329                         set_tracepoint(&mark_entry, *iter,
 330                                         !!mark_entry->refcount);
 331                 } else {
 332                         disable_tracepoint(*iter);
 333                 }
 334         }
 335 }
 336
 337 static void lib_update_tracepoints(void)
 338 {
 339         struct tracepoint_lib *lib;
 340
 341         lock_tracepoints();
 342         cds_list_for_each_entry(lib, &libs, list) {
 343                 tracepoint_update_probe_range(lib->tracepoints_start,
 344                                 lib->tracepoints_start + lib->tracepoints_count);
 345         }
 346         unlock_tracepoints();
 347 }
 348
 349 /*
 350  * Update probes, removing the faulty probes.
 351  */
 352 static void tracepoint_update_probes(void)
 353 {
 354         /* tracepoints registered from libraries and executable. */
 355         lib_update_tracepoints();
 356 }
 357
 358 static struct tracepoint_probe *
 359 tracepoint_add_probe(const char *name, void *probe, void *data)
 360 {
 361         struct tracepoint_entry *entry;
 362         struct tracepoint_probe *old;
 363
 364         entry = get_tracepoint(name);
 365         if (!entry) {
 366                 entry = add_tracepoint(name);
 367                 if (IS_ERR(entry))
 368                         return (struct tracepoint_probe *)entry;
 369         }
 370         old = tracepoint_entry_add_probe(entry, probe, data);
 371         if (IS_ERR(old) && !entry->refcount)
 372                 remove_tracepoint(entry);
 373         return old;
 374 }
 375
 376 /**
 377  * __tracepoint_probe_register -  Connect a probe to a tracepoint
 378  * @name: tracepoint name
 379  * @probe: probe handler
 380  *
 381  * Returns 0 if ok, error value on error.
 382  * The probe address must at least be aligned on the architecture pointer size.
 383  */
 384 int __tracepoint_probe_register(const char *name, void *probe, void *data)
 385 {
 386         void *old;
 387
 388         lock_tracepoints();
 389         old = tracepoint_add_probe(name, probe, data);
 390         unlock_tracepoints();
 391         if (IS_ERR(old))
 392                 return PTR_ERR(old);
 393
 394         tracepoint_update_probes();             /* may update entry */
 395         release_probes(old);
 396         return 0;
 397 }
 398
 399 static void *tracepoint_remove_probe(const char *name, void *probe, void *data)
 400 {
 401         struct tracepoint_entry *entry;
 402         void *old;
 403
 404         entry = get_tracepoint(name);
 405         if (!entry)
 406                 return ERR_PTR(-ENOENT);
 407         old = tracepoint_entry_remove_probe(entry, probe, data);
 408         if (IS_ERR(old))
 409                 return old;
 410         if (!entry->refcount)
 411                 remove_tracepoint(entry);
 412         return old;
 413 }
 414
 415 /**
 416  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
 417  * @name: tracepoint name
 418  * @probe: probe function pointer
 419  * @probe: probe data pointer
 420  *
 421  * We do not need to call a synchronize_sched to make sure the probes have
 422  * finished running before doing a module unload, because the module unload
 423  * itself uses stop_machine(), which insures that every preempt disabled section
 424  * have finished.
 425  */
 426 int __tracepoint_probe_unregister(const char *name, void *probe, void *data)
 427 {
 428         void *old;
 429
 430         lock_tracepoints();
 431         old = tracepoint_remove_probe(name, probe, data);
 432         unlock_tracepoints();
 433         if (IS_ERR(old))
 434                 return PTR_ERR(old);
 435
 436         tracepoint_update_probes();             /* may update entry */
 437         release_probes(old);
 438         return 0;
 439 }
 440
 441 static void tracepoint_add_old_probes(void *old)
 442 {
 443         need_update = 1;
 444         if (old) {
 445                 struct tp_probes *tp_probes = _ust_container_of(old,
 446                         struct tp_probes, probes[0]);
 447                 cds_list_add(&tp_probes->u.list, &old_probes);
 448         }
 449 }
 450
 451 /**
 452  * tracepoint_probe_register_noupdate -  register a probe but not connect
 453  * @name: tracepoint name
 454  * @probe: probe handler
 455  *
 456  * caller must call tracepoint_probe_update_all()
 457  */
 458 int tracepoint_probe_register_noupdate(const char *name, void *probe,
 459                                        void *data)
 460 {
 461         void *old;
 462
 463         lock_tracepoints();
 464         old = tracepoint_add_probe(name, probe, data);
 465         if (IS_ERR(old)) {
 466                 unlock_tracepoints();
 467                 return PTR_ERR(old);
 468         }
 469         tracepoint_add_old_probes(old);
 470         unlock_tracepoints();
 471         return 0;
 472 }
 473
 474 /**
 475  * tracepoint_probe_unregister_noupdate -  remove a probe but not disconnect
 476  * @name: tracepoint name
 477  * @probe: probe function pointer
 478  *
 479  * caller must call tracepoint_probe_update_all()
 480  */
 481 int tracepoint_probe_unregister_noupdate(const char *name, void *probe,
 482                                          void *data)
 483 {
 484         void *old;
 485
 486         lock_tracepoints();
 487         old = tracepoint_remove_probe(name, probe, data);
 488         if (IS_ERR(old)) {
 489                 unlock_tracepoints();
 490                 return PTR_ERR(old);
 491         }
 492         tracepoint_add_old_probes(old);
 493         unlock_tracepoints();
 494         return 0;
 495 }
 496
 497 /**
 498  * tracepoint_probe_update_all -  update tracepoints
 499  */
 500 void tracepoint_probe_update_all(void)
 501 {
 502         CDS_LIST_HEAD(release_probes);
 503         struct tp_probes *pos, *next;
 504
 505         lock_tracepoints();
 506         if (!need_update) {
 507                 unlock_tracepoints();
 508                 return;
 509         }
 510         if (!cds_list_empty(&old_probes))
 511                 cds_list_replace_init(&old_probes, &release_probes);
 512         need_update = 0;
 513         unlock_tracepoints();
 514
 515         tracepoint_update_probes();
 516         cds_list_for_each_entry_safe(pos, next, &release_probes, u.list) {
 517                 cds_list_del(&pos->u.list);
 518                 synchronize_rcu();
 519                 free(pos);
 520         }
 521 }
 522
 523 /*
 524  * Returns 0 if current not found.
 525  * Returns 1 if current found.
 526  *
 527  * Called with tracepoint mutex held
 528  */
 529 int lib_get_iter_tracepoints(struct tracepoint_iter *iter)
 530 {
 531         struct tracepoint_lib *iter_lib;
 532         int found = 0;
 533
 534         cds_list_for_each_entry(iter_lib, &libs, list) {
 535                 if (iter_lib < iter->lib)
 536                         continue;
 537                 else if (iter_lib > iter->lib)
 538                         iter->tracepoint = NULL;
 539                 found = tracepoint_get_iter_range(&iter->tracepoint,
 540                         iter_lib->tracepoints_start,
 541                         iter_lib->tracepoints_start + iter_lib->tracepoints_count);
 542                 if (found) {
 543                         iter->lib = iter_lib;
 544                         break;
 545                 }
 546         }
 547         return found;
 548 }
 549
 550 /**
 551  * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
 552  * @tracepoint: current tracepoints (in), next tracepoint (out)
 553  * @begin: beginning of the range
 554  * @end: end of the range
 555  *
 556  * Returns whether a next tracepoint has been found (1) or not (0).
 557  * Will return the first tracepoint in the range if the input tracepoint is
 558  * NULL.
 559  * Called with tracepoint mutex held.
 560  */
 561 int tracepoint_get_iter_range(struct tracepoint * const **tracepoint,
 562         struct tracepoint * const *begin, struct tracepoint * const *end)
 563 {
 564         if (!*tracepoint && begin != end)
 565                 *tracepoint = begin;
 566         while (*tracepoint >= begin && *tracepoint < end) {
 567                 if (!**tracepoint)
 568                         (*tracepoint)++;        /* skip dummy */
 569                 else
 570                         return 1;
 571         }
 572         return 0;
 573 }
 574
 575 /*
 576  * Called with tracepoint mutex held.
 577  */
 578 static void tracepoint_get_iter(struct tracepoint_iter *iter)
 579 {
 580         int found = 0;
 581
 582         /* tracepoints in libs. */
 583         found = lib_get_iter_tracepoints(iter);
 584         if (!found)
 585                 tracepoint_iter_reset(iter);
 586 }
 587
 588 void tracepoint_iter_start(struct tracepoint_iter *iter)
 589 {
 590         lock_tracepoints();
 591         tracepoint_get_iter(iter);
 592 }
 593
 594 /*
 595  * Called with tracepoint mutex held.
 596  */
 597 void tracepoint_iter_next(struct tracepoint_iter *iter)
 598 {
 599         iter->tracepoint++;
 600         /*
 601          * iter->tracepoint may be invalid because we blindly incremented it.
 602          * Make sure it is valid by marshalling on the tracepoints, getting the
 603          * tracepoints from following modules if necessary.
 604          */
 605         tracepoint_get_iter(iter);
 606 }
 607
 608 void tracepoint_iter_stop(struct tracepoint_iter *iter)
 609 {
 610         unlock_tracepoints();
 611 }
 612
 613 void tracepoint_iter_reset(struct tracepoint_iter *iter)
 614 {
 615         iter->tracepoint = NULL;
 616 }
 617
 618 void tracepoint_set_new_tracepoint_cb(void (*cb)(struct tracepoint *))
 619 {
 620         new_tracepoint_cb = cb;
 621 }
 622
 623 static void new_tracepoints(struct tracepoint * const *start, struct tracepoint * const *end)
 624 {
 625         if (new_tracepoint_cb) {
 626                 struct tracepoint * const *t;
 627
 628                 for (t = start; t < end; t++) {
 629                         if (*t)
 630                                 new_tracepoint_cb(*t);
 631                 }
 632         }
 633 }
 634
 635 int tracepoint_register_lib(struct tracepoint * const *tracepoints_start,
 636                             int tracepoints_count)
 637 {
 638         struct tracepoint_lib *pl, *iter;
 639
 640         pl = (struct tracepoint_lib *) zmalloc(sizeof(struct tracepoint_lib));
 641
 642         pl->tracepoints_start = tracepoints_start;
 643         pl->tracepoints_count = tracepoints_count;
 644
 645         lock_tracepoints();
 646         /*
 647          * We sort the libs by struct lib pointer address.
 648          */
 649         cds_list_for_each_entry_reverse(iter, &libs, list) {
 650                 BUG_ON(iter == pl);    /* Should never be in the list twice */
 651                 if (iter < pl) {
 652                         /* We belong to the location right after iter. */
 653                         cds_list_add(&pl->list, &iter->list);
 654                         goto lib_added;
 655                 }
 656         }
 657         /* We should be added at the head of the list */
 658         cds_list_add(&pl->list, &libs);
 659 lib_added:
 660         unlock_tracepoints();
 661
 662         new_tracepoints(tracepoints_start, tracepoints_start + tracepoints_count);
 663
 664         /* TODO: update just the loaded lib */
 665         lib_update_tracepoints();
 666
 667         /* tracepoints_count - 1: skip dummy */
 668         DBG("just registered a tracepoints section from %p and having %d tracepoints (minus dummy tracepoints)", tracepoints_start, tracepoints_count);
 669
 670         return 0;
 671 }
 672
 673 int tracepoint_unregister_lib(struct tracepoint * const *tracepoints_start)
 674 {
 675         struct tracepoint_lib *lib;
 676
 677         lock_tracepoints();
 678         cds_list_for_each_entry(lib, &libs, list) {
 679                 if (lib->tracepoints_start == tracepoints_start) {
 680                         struct tracepoint_lib *lib2free = lib;
 681                         cds_list_del(&lib->list);
 682                         free(lib2free);
 683                         break;
 684                 }
 685         }
 686         unlock_tracepoints();
 687
 688         return 0;
 689 }
 690
 691 void __attribute__((constructor)) init_tracepoint(void)
 692 {
 693         if (!initialized) {
 694                 tracepoint_register_lib(__start___tracepoints_ptrs,
 695                         __stop___tracepoints_ptrs
 696                         - __start___tracepoints_ptrs);
 697                 initialized = 1;
 698         }
 699 }
 700
 701 void __attribute__((destructor)) destroy_tracepoint(void)
 702 {
 703         tracepoint_unregister_lib(__start___tracepoints_ptrs);
 704 }