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