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/core.h>
  26 #include <stdint.h>
  27 #include <stddef.h>
  28 #include <urcu/arch.h>
  29 #include <urcu-bp.h>
  30 #include <urcu/hlist.h>
  31 #include <urcu/uatomic.h>
  32 #include <urcu/compiler.h>
  33
  34 #include <lttng/usterr-signal-safe.h>
  35 #include "tracepoint-internal.h"
  36 #include "ltt-tracer-core.h"
  37 #include "jhash.h"
  38
  39 /* Set to 1 to enable tracepoint debug output */
  40 static const int tracepoint_debug;
  41 static int initialized;
  42 static void (*new_tracepoint_cb)(struct tracepoint *);
  43
  44 /* libraries that contain tracepoints (struct tracepoint_lib) */
  45 static CDS_LIST_HEAD(libs);
  46
  47 /*
  48  * The UST lock protects the library tracepoints, the hash table, and
  49  * the library list.
  50  * All calls to the tracepoint API must be protected by the UST lock,
  51  * excepts calls to tracepoint_register_lib and
  52  * tracepoint_unregister_lib, which take the UST lock themselves.
  53  */
  54
  55 /*
  56  * Tracepoint hash table, containing the active tracepoints.
  57  * Protected by tracepoints_mutex.
  58  */
  59 #define TRACEPOINT_HASH_BITS 6
  60 #define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
  61 static struct cds_hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
  62
  63 static CDS_LIST_HEAD(old_probes);
  64 static int need_update;
  65
  66 /*
  67  * Note about RCU :
  68  * It is used to to delay the free of multiple probes array until a quiescent
  69  * state is reached.
  70  * Tracepoint entries modifications are protected by the tracepoints_mutex.
  71  */
  72 struct tracepoint_entry {
  73         struct cds_hlist_node hlist;
  74         struct tracepoint_probe *probes;
  75         int refcount;   /* Number of times armed. 0 if disarmed. */
  76         char name[0];
  77 };
  78
  79 struct tp_probes {
  80         union {
  81                 struct cds_list_head list;
  82         } u;
  83         struct tracepoint_probe probes[0];
  84 };
  85
  86 static inline void *allocate_probes(int count)
  87 {
  88         struct tp_probes *p  = zmalloc(count * sizeof(struct tracepoint_probe)
  89                         + sizeof(struct tp_probes));
  90         return p == NULL ? NULL : p->probes;
  91 }
  92
  93 static inline void release_probes(void *old)
  94 {
  95         if (old) {
  96                 struct tp_probes *tp_probes = caa_container_of(old,
  97                         struct tp_probes, probes[0]);
  98                 synchronize_rcu();
  99                 free(tp_probes);
 100         }
 101 }
 102
 103 static void debug_print_probes(struct tracepoint_entry *entry)
 104 {
 105         int i;
 106
 107         if (!tracepoint_debug || !entry->probes)
 108                 return;
 109
 110         for (i = 0; entry->probes[i].func; i++)
 111                 DBG("Probe %d : %p", i, entry->probes[i].func);
 112 }
 113
 114 static void *
 115 tracepoint_entry_add_probe(struct tracepoint_entry *entry,
 116                            void *probe, void *data)
 117 {
 118         int nr_probes = 0;
 119         struct tracepoint_probe *old, *new;
 120
 121         WARN_ON(!probe);
 122
 123         debug_print_probes(entry);
 124         old = entry->probes;
 125         if (old) {
 126                 /* (N -> N+1), (N != 0, 1) probes */
 127                 for (nr_probes = 0; old[nr_probes].func; nr_probes++)
 128                         if (old[nr_probes].func == probe &&
 129                             old[nr_probes].data == data)
 130                                 return ERR_PTR(-EEXIST);
 131         }
 132         /* + 2 : one for new probe, one for NULL func */
 133         new = allocate_probes(nr_probes + 2);
 134         if (new == NULL)
 135                 return ERR_PTR(-ENOMEM);
 136         if (old)
 137                 memcpy(new, old, nr_probes * sizeof(struct tracepoint_probe));
 138         new[nr_probes].func = probe;
 139         new[nr_probes].data = data;
 140         new[nr_probes + 1].func = NULL;
 141         entry->refcount = nr_probes + 1;
 142         entry->probes = new;
 143         debug_print_probes(entry);
 144         return old;
 145 }
 146
 147 static void *
 148 tracepoint_entry_remove_probe(struct tracepoint_entry *entry, void *probe,
 149                               void *data)
 150 {
 151         int nr_probes = 0, nr_del = 0, i;
 152         struct tracepoint_probe *old, *new;
 153
 154         old = entry->probes;
 155
 156         if (!old)
 157                 return ERR_PTR(-ENOENT);
 158
 159         debug_print_probes(entry);
 160         /* (N -> M), (N > 1, M >= 0) probes */
 161         for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
 162                 if (!probe ||
 163                      (old[nr_probes].func == probe &&
 164                      old[nr_probes].data == data))
 165                         nr_del++;
 166         }
 167
 168         if (nr_probes - nr_del == 0) {
 169                 /* N -> 0, (N > 1) */
 170                 entry->probes = NULL;
 171                 entry->refcount = 0;
 172                 debug_print_probes(entry);
 173                 return old;
 174         } else {
 175                 int j = 0;
 176                 /* N -> M, (N > 1, M > 0) */
 177                 /* + 1 for NULL */
 178                 new = allocate_probes(nr_probes - nr_del + 1);
 179                 if (new == NULL)
 180                         return ERR_PTR(-ENOMEM);
 181                 for (i = 0; old[i].func; i++)
 182                         if (probe &&
 183                             (old[i].func != probe || old[i].data != data))
 184                                 new[j++] = old[i];
 185                 new[nr_probes - nr_del].func = NULL;
 186                 entry->refcount = nr_probes - nr_del;
 187                 entry->probes = new;
 188         }
 189         debug_print_probes(entry);
 190         return old;
 191 }
 192
 193 /*
 194  * Get tracepoint if the tracepoint is present in the tracepoint hash table.
 195  * Must be called with tracepoints_mutex held.
 196  * Returns NULL if not present.
 197  */
 198 static struct tracepoint_entry *get_tracepoint(const char *name)
 199 {
 200         struct cds_hlist_head *head;
 201         struct cds_hlist_node *node;
 202         struct tracepoint_entry *e;
 203         uint32_t hash = jhash(name, strlen(name), 0);
 204
 205         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 206         cds_hlist_for_each_entry(e, node, head, hlist) {
 207                 if (!strcmp(name, e->name))
 208                         return e;
 209         }
 210         return NULL;
 211 }
 212
 213 /*
 214  * Add the tracepoint to the tracepoint hash table. Must be called with
 215  * tracepoints_mutex held.
 216  */
 217 static struct tracepoint_entry *add_tracepoint(const char *name)
 218 {
 219         struct cds_hlist_head *head;
 220         struct cds_hlist_node *node;
 221         struct tracepoint_entry *e;
 222         size_t name_len = strlen(name) + 1;
 223         uint32_t hash = jhash(name, name_len-1, 0);
 224
 225         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 226         cds_hlist_for_each_entry(e, node, head, hlist) {
 227                 if (!strcmp(name, e->name)) {
 228                         DBG("tracepoint %s busy", name);
 229                         return ERR_PTR(-EEXIST);        /* Already there */
 230                 }
 231         }
 232         /*
 233          * Using zmalloc here to allocate a variable length element. Could
 234          * cause some memory fragmentation if overused.
 235          */
 236         e = zmalloc(sizeof(struct tracepoint_entry) + name_len);
 237         if (!e)
 238                 return ERR_PTR(-ENOMEM);
 239         memcpy(&e->name[0], name, name_len);
 240         e->probes = NULL;
 241         e->refcount = 0;
 242         cds_hlist_add_head(&e->hlist, head);
 243         return e;
 244 }
 245
 246 /*
 247  * Remove the tracepoint from the tracepoint hash table. Must be called with
 248  * ust_lock held.
 249  */
 250 static inline void remove_tracepoint(struct tracepoint_entry *e)
 251 {
 252         cds_hlist_del(&e->hlist);
 253         free(e);
 254 }
 255
 256 /*
 257  * Sets the probe callback corresponding to one tracepoint.
 258  */
 259 static void set_tracepoint(struct tracepoint_entry **entry,
 260         struct tracepoint *elem, int active)
 261 {
 262         WARN_ON(strcmp((*entry)->name, elem->name) != 0);
 263
 264         /*
 265          * rcu_assign_pointer has a cmm_smp_wmb() which makes sure that the new
 266          * probe callbacks array is consistent before setting a pointer to it.
 267          * This array is referenced by __DO_TRACE from
 268          * include/linux/tracepoints.h. A matching cmm_smp_read_barrier_depends()
 269          * is used.
 270          */
 271         rcu_assign_pointer(elem->probes, (*entry)->probes);
 272         elem->state = active;
 273 }
 274
 275 /*
 276  * Disable a tracepoint and its probe callback.
 277  * Note: only waiting an RCU period after setting elem->call to the empty
 278  * function insures that the original callback is not used anymore. This insured
 279  * by preempt_disable around the call site.
 280  */
 281 static void disable_tracepoint(struct tracepoint *elem)
 282 {
 283         elem->state = 0;
 284         rcu_assign_pointer(elem->probes, NULL);
 285 }
 286
 287 /**
 288  * tracepoint_update_probe_range - Update a probe range
 289  * @begin: beginning of the range
 290  * @end: end of the range
 291  *
 292  * Updates the probe callback corresponding to a range of tracepoints.
 293  */
 294 static
 295 void tracepoint_update_probe_range(struct tracepoint * const *begin,
 296                                    struct tracepoint * const *end)
 297 {
 298         struct tracepoint * const *iter;
 299         struct tracepoint_entry *mark_entry;
 300
 301         for (iter = begin; iter < end; iter++) {
 302                 if (!*iter)
 303                         continue;       /* skip dummy */
 304                 if (!(*iter)->name) {
 305                         disable_tracepoint(*iter);
 306                         continue;
 307                 }
 308                 mark_entry = get_tracepoint((*iter)->name);
 309                 if (mark_entry) {
 310                         set_tracepoint(&mark_entry, *iter,
 311                                         !!mark_entry->refcount);
 312                 } else {
 313                         disable_tracepoint(*iter);
 314                 }
 315         }
 316 }
 317
 318 static void lib_update_tracepoints(void)
 319 {
 320         struct tracepoint_lib *lib;
 321
 322         cds_list_for_each_entry(lib, &libs, list) {
 323                 tracepoint_update_probe_range(lib->tracepoints_start,
 324                                 lib->tracepoints_start + lib->tracepoints_count);
 325         }
 326 }
 327
 328 /*
 329  * Update probes, removing the faulty probes.
 330  */
 331 static void tracepoint_update_probes(void)
 332 {
 333         /* tracepoints registered from libraries and executable. */
 334         lib_update_tracepoints();
 335 }
 336
 337 static struct tracepoint_probe *
 338 tracepoint_add_probe(const char *name, void *probe, void *data)
 339 {
 340         struct tracepoint_entry *entry;
 341         struct tracepoint_probe *old;
 342
 343         entry = get_tracepoint(name);
 344         if (!entry) {
 345                 entry = add_tracepoint(name);
 346                 if (IS_ERR(entry))
 347                         return (struct tracepoint_probe *)entry;
 348         }
 349         old = tracepoint_entry_add_probe(entry, probe, data);
 350         if (IS_ERR(old) && !entry->refcount)
 351                 remove_tracepoint(entry);
 352         return old;
 353 }
 354
 355 /**
 356  * __tracepoint_probe_register -  Connect a probe to a tracepoint
 357  * @name: tracepoint name
 358  * @probe: probe handler
 359  *
 360  * Returns 0 if ok, error value on error.
 361  * The probe address must at least be aligned on the architecture pointer size.
 362  * Called with the UST lock held.
 363  */
 364 int __tracepoint_probe_register(const char *name, void *probe, void *data)
 365 {
 366         void *old;
 367
 368         old = tracepoint_add_probe(name, probe, data);
 369         if (IS_ERR(old))
 370                 return PTR_ERR(old);
 371
 372         tracepoint_update_probes();             /* may update entry */
 373         release_probes(old);
 374         return 0;
 375 }
 376
 377 static void *tracepoint_remove_probe(const char *name, void *probe, void *data)
 378 {
 379         struct tracepoint_entry *entry;
 380         void *old;
 381
 382         entry = get_tracepoint(name);
 383         if (!entry)
 384                 return ERR_PTR(-ENOENT);
 385         old = tracepoint_entry_remove_probe(entry, probe, data);
 386         if (IS_ERR(old))
 387                 return old;
 388         if (!entry->refcount)
 389                 remove_tracepoint(entry);
 390         return old;
 391 }
 392
 393 /**
 394  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
 395  * @name: tracepoint name
 396  * @probe: probe function pointer
 397  * @probe: probe data pointer
 398  *
 399  * Called with the UST lock held.
 400  */
 401 int __tracepoint_probe_unregister(const char *name, void *probe, void *data)
 402 {
 403         void *old;
 404
 405         old = tracepoint_remove_probe(name, probe, data);
 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
 414 static void tracepoint_add_old_probes(void *old)
 415 {
 416         need_update = 1;
 417         if (old) {
 418                 struct tp_probes *tp_probes = caa_container_of(old,
 419                         struct tp_probes, probes[0]);
 420                 cds_list_add(&tp_probes->u.list, &old_probes);
 421         }
 422 }
 423
 424 /**
 425  * tracepoint_probe_register_noupdate -  register a probe but not connect
 426  * @name: tracepoint name
 427  * @probe: probe handler
 428  *
 429  * caller must call tracepoint_probe_update_all()
 430  * Called with the UST lock held.
 431  */
 432 int tracepoint_probe_register_noupdate(const char *name, void *probe,
 433                                        void *data)
 434 {
 435         void *old;
 436
 437         old = tracepoint_add_probe(name, probe, data);
 438         if (IS_ERR(old)) {
 439                 return PTR_ERR(old);
 440         }
 441         tracepoint_add_old_probes(old);
 442         return 0;
 443 }
 444
 445 /**
 446  * tracepoint_probe_unregister_noupdate -  remove a probe but not disconnect
 447  * @name: tracepoint name
 448  * @probe: probe function pointer
 449  *
 450  * caller must call tracepoint_probe_update_all()
 451  * Called with the UST lock held.
 452  */
 453 int tracepoint_probe_unregister_noupdate(const char *name, void *probe,
 454                                          void *data)
 455 {
 456         void *old;
 457
 458         old = tracepoint_remove_probe(name, probe, data);
 459         if (IS_ERR(old)) {
 460                 return PTR_ERR(old);
 461         }
 462         tracepoint_add_old_probes(old);
 463         return 0;
 464 }
 465
 466 /**
 467  * tracepoint_probe_update_all -  update tracepoints
 468  * Called with the UST lock held.
 469  */
 470 void tracepoint_probe_update_all(void)
 471 {
 472         CDS_LIST_HEAD(release_probes);
 473         struct tp_probes *pos, *next;
 474
 475         if (!need_update) {
 476                 return;
 477         }
 478         if (!cds_list_empty(&old_probes))
 479                 cds_list_replace_init(&old_probes, &release_probes);
 480         need_update = 0;
 481
 482         tracepoint_update_probes();
 483         cds_list_for_each_entry_safe(pos, next, &release_probes, u.list) {
 484                 cds_list_del(&pos->u.list);
 485                 synchronize_rcu();
 486                 free(pos);
 487         }
 488 }
 489
 490 /*
 491  * Returns 0 if current not found.
 492  * Returns 1 if current found.
 493  *
 494  * Called with tracepoint mutex held
 495  */
 496 int lib_get_iter_tracepoints(struct tracepoint_iter *iter)
 497 {
 498         struct tracepoint_lib *iter_lib;
 499         int found = 0;
 500
 501         cds_list_for_each_entry(iter_lib, &libs, list) {
 502                 if (iter_lib < iter->lib)
 503                         continue;
 504                 else if (iter_lib > iter->lib)
 505                         iter->tracepoint = NULL;
 506                 found = tracepoint_get_iter_range(&iter->tracepoint,
 507                         iter_lib->tracepoints_start,
 508                         iter_lib->tracepoints_start + iter_lib->tracepoints_count);
 509                 if (found) {
 510                         iter->lib = iter_lib;
 511                         break;
 512                 }
 513         }
 514         return found;
 515 }
 516
 517 /**
 518  * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
 519  * @tracepoint: current tracepoints (in), next tracepoint (out)
 520  * @begin: beginning of the range
 521  * @end: end of the range
 522  *
 523  * Returns whether a next tracepoint has been found (1) or not (0).
 524  * Will return the first tracepoint in the range if the input tracepoint is
 525  * NULL.
 526  * Called with tracepoint mutex held.
 527  */
 528 int tracepoint_get_iter_range(struct tracepoint * const **tracepoint,
 529         struct tracepoint * const *begin, struct tracepoint * const *end)
 530 {
 531         if (!*tracepoint && begin != end)
 532                 *tracepoint = begin;
 533         while (*tracepoint >= begin && *tracepoint < end) {
 534                 if (!**tracepoint)
 535                         (*tracepoint)++;        /* skip dummy */
 536                 else
 537                         return 1;
 538         }
 539         return 0;
 540 }
 541
 542 /*
 543  * Called with tracepoint mutex held.
 544  */
 545 static void tracepoint_get_iter(struct tracepoint_iter *iter)
 546 {
 547         int found = 0;
 548
 549         /* tracepoints in libs. */
 550         found = lib_get_iter_tracepoints(iter);
 551         if (!found)
 552                 tracepoint_iter_reset(iter);
 553 }
 554
 555 /*
 556  * Called with UST lock held.
 557  */
 558 void tracepoint_iter_start(struct tracepoint_iter *iter)
 559 {
 560         tracepoint_get_iter(iter);
 561 }
 562
 563 /*
 564  * Called with UST lock held.
 565  */
 566 void tracepoint_iter_next(struct tracepoint_iter *iter)
 567 {
 568         iter->tracepoint++;
 569         /*
 570          * iter->tracepoint may be invalid because we blindly incremented it.
 571          * Make sure it is valid by marshalling on the tracepoints, getting the
 572          * tracepoints from following modules if necessary.
 573          */
 574         tracepoint_get_iter(iter);
 575 }
 576
 577 /*
 578  * Called with UST lock held.
 579  */
 580 void tracepoint_iter_stop(struct tracepoint_iter *iter)
 581 {
 582 }
 583
 584 void tracepoint_iter_reset(struct tracepoint_iter *iter)
 585 {
 586         iter->tracepoint = NULL;
 587 }
 588
 589 void tracepoint_set_new_tracepoint_cb(void (*cb)(struct tracepoint *))
 590 {
 591         new_tracepoint_cb = cb;
 592 }
 593
 594 static void new_tracepoints(struct tracepoint * const *start, struct tracepoint * const *end)
 595 {
 596         if (new_tracepoint_cb) {
 597                 struct tracepoint * const *t;
 598
 599                 for (t = start; t < end; t++) {
 600                         if (*t)
 601                                 new_tracepoint_cb(*t);
 602                 }
 603         }
 604 }
 605
 606 int tracepoint_register_lib(struct tracepoint * const *tracepoints_start,
 607                             int tracepoints_count)
 608 {
 609         struct tracepoint_lib *pl, *iter;
 610
 611         init_tracepoint();
 612
 613         pl = (struct tracepoint_lib *) zmalloc(sizeof(struct tracepoint_lib));
 614
 615         pl->tracepoints_start = tracepoints_start;
 616         pl->tracepoints_count = tracepoints_count;
 617
 618         ust_lock();
 619         /*
 620          * We sort the libs by struct lib pointer address.
 621          */
 622         cds_list_for_each_entry_reverse(iter, &libs, list) {
 623                 BUG_ON(iter == pl);    /* Should never be in the list twice */
 624                 if (iter < pl) {
 625                         /* We belong to the location right after iter. */
 626                         cds_list_add(&pl->list, &iter->list);
 627                         goto lib_added;
 628                 }
 629         }
 630         /* We should be added at the head of the list */
 631         cds_list_add(&pl->list, &libs);
 632 lib_added:
 633         new_tracepoints(tracepoints_start, tracepoints_start + tracepoints_count);
 634
 635         /* TODO: update just the loaded lib */
 636         lib_update_tracepoints();
 637         ust_unlock();
 638
 639         DBG("just registered a tracepoints section from %p and having %d tracepoints",
 640                 tracepoints_start, tracepoints_count);
 641
 642         return 0;
 643 }
 644
 645 int tracepoint_unregister_lib(struct tracepoint * const *tracepoints_start)
 646 {
 647         struct tracepoint_lib *lib;
 648
 649         ust_lock();
 650         cds_list_for_each_entry(lib, &libs, list) {
 651                 if (lib->tracepoints_start == tracepoints_start) {
 652                         struct tracepoint_lib *lib2free = lib;
 653                         cds_list_del(&lib->list);
 654                         free(lib2free);
 655                         break;
 656                 }
 657         }
 658         ust_unlock();
 659
 660         return 0;
 661 }
 662
 663 void init_tracepoint(void)
 664 {
 665         if (uatomic_xchg(&initialized, 1) == 1)
 666                 return;
 667         init_usterr();
 668 }
 669
 670 void exit_tracepoint(void)
 671 {
 672         initialized = 0;
 673 }