kernel/tracepoint.c

   1 /*
   2  * Copyright (C) 2008-2014 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/static_key.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 #ifdef CONFIG_MODULES
  37 /*
  38  * Tracepoint module list mutex protects the local module list.
  39  */
  40 static DEFINE_MUTEX(tracepoint_module_list_mutex);
  41
  42 /* Local list of struct tp_module */
  43 static LIST_HEAD(tracepoint_module_list);
  44 #endif /* CONFIG_MODULES */
  45
  46 /*
  47  * tracepoints_mutex protects the builtin and module tracepoints.
  48  * tracepoints_mutex nests inside tracepoint_module_list_mutex.
  49  */
  50 static DEFINE_MUTEX(tracepoints_mutex);
  51
  52 /*
  53  * Note about RCU :
  54  * It is used to delay the free of multiple probes array until a quiescent
  55  * state is reached.
  56  */
  57 struct tp_probes {
  58         struct rcu_head rcu;
  59         struct tracepoint_func probes[0];
  60 };
  61
  62 static inline void *allocate_probes(int count)
  63 {
  64         struct tp_probes *p  = kmalloc(count * sizeof(struct tracepoint_func)
  65                         + sizeof(struct tp_probes), GFP_KERNEL);
  66         return p == NULL ? NULL : p->probes;
  67 }
  68
  69 static void rcu_free_old_probes(struct rcu_head *head)
  70 {
  71         kfree(container_of(head, struct tp_probes, rcu));
  72 }
  73
  74 static inline void release_probes(struct tracepoint_func *old)
  75 {
  76         if (old) {
  77                 struct tp_probes *tp_probes = container_of(old,
  78                         struct tp_probes, probes[0]);
  79                 call_rcu_sched(&tp_probes->rcu, rcu_free_old_probes);
  80         }
  81 }
  82
  83 static void debug_print_probes(struct tracepoint_func *funcs)
  84 {
  85         int i;
  86
  87         if (!tracepoint_debug || !funcs)
  88                 return;
  89
  90         for (i = 0; funcs[i].func; i++)
  91                 printk(KERN_DEBUG "Probe %d : %p\n", i, funcs[i].func);
  92 }
  93
  94 static struct tracepoint_func *
  95 func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
  96          int prio)
  97 {
  98         struct tracepoint_func *old, *new;
  99         int nr_probes = 0;
 100         int pos = -1;
 101
 102         if (WARN_ON(!tp_func->func))
 103                 return ERR_PTR(-EINVAL);
 104
 105         debug_print_probes(*funcs);
 106         old = *funcs;
 107         if (old) {
 108                 /* (N -> N+1), (N != 0, 1) probes */
 109                 for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
 110                         /* Insert before probes of lower priority */
 111                         if (pos < 0 && old[nr_probes].prio < prio)
 112                                 pos = nr_probes;
 113                         if (old[nr_probes].func == tp_func->func &&
 114                             old[nr_probes].data == tp_func->data)
 115                                 return ERR_PTR(-EEXIST);
 116                 }
 117         }
 118         /* + 2 : one for new probe, one for NULL func */
 119         new = allocate_probes(nr_probes + 2);
 120         if (new == NULL)
 121                 return ERR_PTR(-ENOMEM);
 122         if (old) {
 123                 if (pos < 0) {
 124                         pos = nr_probes;
 125                         memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));
 126                 } else {
 127                         /* Copy higher priority probes ahead of the new probe */
 128                         memcpy(new, old, pos * sizeof(struct tracepoint_func));
 129                         /* Copy the rest after it. */
 130                         memcpy(new + pos + 1, old + pos,
 131                                (nr_probes - pos) * sizeof(struct tracepoint_func));
 132                 }
 133         } else
 134                 pos = 0;
 135         new[pos] = *tp_func;
 136         new[nr_probes + 1].func = NULL;
 137         *funcs = new;
 138         debug_print_probes(*funcs);
 139         return old;
 140 }
 141
 142 static void *func_remove(struct tracepoint_func **funcs,
 143                 struct tracepoint_func *tp_func)
 144 {
 145         int nr_probes = 0, nr_del = 0, i;
 146         struct tracepoint_func *old, *new;
 147
 148         old = *funcs;
 149
 150         if (!old)
 151                 return ERR_PTR(-ENOENT);
 152
 153         debug_print_probes(*funcs);
 154         /* (N -> M), (N > 1, M >= 0) probes */
 155         if (tp_func->func) {
 156                 for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
 157                         if (old[nr_probes].func == tp_func->func &&
 158                              old[nr_probes].data == tp_func->data)
 159                                 nr_del++;
 160                 }
 161         }
 162
 163         /*
 164          * If probe is NULL, then nr_probes = nr_del = 0, and then the
 165          * entire entry will be removed.
 166          */
 167         if (nr_probes - nr_del == 0) {
 168                 /* N -> 0, (N > 1) */
 169                 *funcs = NULL;
 170                 debug_print_probes(*funcs);
 171                 return old;
 172         } else {
 173                 int j = 0;
 174                 /* N -> M, (N > 1, M > 0) */
 175                 /* + 1 for NULL */
 176                 new = allocate_probes(nr_probes - nr_del + 1);
 177                 if (new == NULL)
 178                         return ERR_PTR(-ENOMEM);
 179                 for (i = 0; old[i].func; i++)
 180                         if (old[i].func != tp_func->func
 181                                         || old[i].data != tp_func->data)
 182                                 new[j++] = old[i];
 183                 new[nr_probes - nr_del].func = NULL;
 184                 *funcs = new;
 185         }
 186         debug_print_probes(*funcs);
 187         return old;
 188 }
 189
 190 /*
 191  * Add the probe function to a tracepoint.
 192  */
 193 static int tracepoint_add_func(struct tracepoint *tp,
 194                                struct tracepoint_func *func, int prio)
 195 {
 196         struct tracepoint_func *old, *tp_funcs;
 197         int ret;
 198
 199         if (tp->regfunc && !static_key_enabled(&tp->key)) {
 200                 ret = tp->regfunc();
 201                 if (ret < 0)
 202                         return ret;
 203         }
 204
 205         tp_funcs = rcu_dereference_protected(tp->funcs,
 206                         lockdep_is_held(&tracepoints_mutex));
 207         old = func_add(&tp_funcs, func, prio);
 208         if (IS_ERR(old)) {
 209                 WARN_ON_ONCE(1);
 210                 return PTR_ERR(old);
 211         }
 212
 213         /*
 214          * rcu_assign_pointer has a smp_wmb() which makes sure that the new
 215          * probe callbacks array is consistent before setting a pointer to it.
 216          * This array is referenced by __DO_TRACE from
 217          * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
 218          * is used.
 219          */
 220         rcu_assign_pointer(tp->funcs, tp_funcs);
 221         if (!static_key_enabled(&tp->key))
 222                 static_key_slow_inc(&tp->key);
 223         release_probes(old);
 224         return 0;
 225 }
 226
 227 /*
 228  * Remove a probe function from a tracepoint.
 229  * Note: only waiting an RCU period after setting elem->call to the empty
 230  * function insures that the original callback is not used anymore. This insured
 231  * by preempt_disable around the call site.
 232  */
 233 static int tracepoint_remove_func(struct tracepoint *tp,
 234                 struct tracepoint_func *func)
 235 {
 236         struct tracepoint_func *old, *tp_funcs;
 237
 238         tp_funcs = rcu_dereference_protected(tp->funcs,
 239                         lockdep_is_held(&tracepoints_mutex));
 240         old = func_remove(&tp_funcs, func);
 241         if (IS_ERR(old)) {
 242                 WARN_ON_ONCE(1);
 243                 return PTR_ERR(old);
 244         }
 245
 246         if (!tp_funcs) {
 247                 /* Removed last function */
 248                 if (tp->unregfunc && static_key_enabled(&tp->key))
 249                         tp->unregfunc();
 250
 251                 if (static_key_enabled(&tp->key))
 252                         static_key_slow_dec(&tp->key);
 253         }
 254         rcu_assign_pointer(tp->funcs, tp_funcs);
 255         release_probes(old);
 256         return 0;
 257 }
 258
 259 /**
 260  * tracepoint_probe_register -  Connect a probe to a tracepoint
 261  * @tp: tracepoint
 262  * @probe: probe handler
 263  * @data: tracepoint data
 264  * @prio: priority of this function over other registered functions
 265  *
 266  * Returns 0 if ok, error value on error.
 267  * Note: if @tp is within a module, the caller is responsible for
 268  * unregistering the probe before the module is gone. This can be
 269  * performed either with a tracepoint module going notifier, or from
 270  * within module exit functions.
 271  */
 272 int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,
 273                                    void *data, int prio)
 274 {
 275         struct tracepoint_func tp_func;
 276         int ret;
 277
 278         mutex_lock(&tracepoints_mutex);
 279         tp_func.func = probe;
 280         tp_func.data = data;
 281         tp_func.prio = prio;
 282         ret = tracepoint_add_func(tp, &tp_func, prio);
 283         mutex_unlock(&tracepoints_mutex);
 284         return ret;
 285 }
 286 EXPORT_SYMBOL_GPL(tracepoint_probe_register_prio);
 287
 288 /**
 289  * tracepoint_probe_register -  Connect a probe to a tracepoint
 290  * @tp: tracepoint
 291  * @probe: probe handler
 292  * @data: tracepoint data
 293  * @prio: priority of this function over other registered functions
 294  *
 295  * Returns 0 if ok, error value on error.
 296  * Note: if @tp is within a module, the caller is responsible for
 297  * unregistering the probe before the module is gone. This can be
 298  * performed either with a tracepoint module going notifier, or from
 299  * within module exit functions.
 300  */
 301 int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data)
 302 {
 303         return tracepoint_probe_register_prio(tp, probe, data, TRACEPOINT_DEFAULT_PRIO);
 304 }
 305 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
 306
 307 /**
 308  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
 309  * @tp: tracepoint
 310  * @probe: probe function pointer
 311  * @data: tracepoint data
 312  *
 313  * Returns 0 if ok, error value on error.
 314  */
 315 int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
 316 {
 317         struct tracepoint_func tp_func;
 318         int ret;
 319
 320         mutex_lock(&tracepoints_mutex);
 321         tp_func.func = probe;
 322         tp_func.data = data;
 323         ret = tracepoint_remove_func(tp, &tp_func);
 324         mutex_unlock(&tracepoints_mutex);
 325         return ret;
 326 }
 327 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
 328
 329 #ifdef CONFIG_MODULES
 330 bool trace_module_has_bad_taint(struct module *mod)
 331 {
 332         return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP) |
 333                                (1 << TAINT_UNSIGNED_MODULE));
 334 }
 335
 336 static BLOCKING_NOTIFIER_HEAD(tracepoint_notify_list);
 337
 338 /**
 339  * register_tracepoint_notifier - register tracepoint coming/going notifier
 340  * @nb: notifier block
 341  *
 342  * Notifiers registered with this function are called on module
 343  * coming/going with the tracepoint_module_list_mutex held.
 344  * The notifier block callback should expect a "struct tp_module" data
 345  * pointer.
 346  */
 347 int register_tracepoint_module_notifier(struct notifier_block *nb)
 348 {
 349         struct tp_module *tp_mod;
 350         int ret;
 351
 352         mutex_lock(&tracepoint_module_list_mutex);
 353         ret = blocking_notifier_chain_register(&tracepoint_notify_list, nb);
 354         if (ret)
 355                 goto end;
 356         list_for_each_entry(tp_mod, &tracepoint_module_list, list)
 357                 (void) nb->notifier_call(nb, MODULE_STATE_COMING, tp_mod);
 358 end:
 359         mutex_unlock(&tracepoint_module_list_mutex);
 360         return ret;
 361 }
 362 EXPORT_SYMBOL_GPL(register_tracepoint_module_notifier);
 363
 364 /**
 365  * unregister_tracepoint_notifier - unregister tracepoint coming/going notifier
 366  * @nb: notifier block
 367  *
 368  * The notifier block callback should expect a "struct tp_module" data
 369  * pointer.
 370  */
 371 int unregister_tracepoint_module_notifier(struct notifier_block *nb)
 372 {
 373         struct tp_module *tp_mod;
 374         int ret;
 375
 376         mutex_lock(&tracepoint_module_list_mutex);
 377         ret = blocking_notifier_chain_unregister(&tracepoint_notify_list, nb);
 378         if (ret)
 379                 goto end;
 380         list_for_each_entry(tp_mod, &tracepoint_module_list, list)
 381                 (void) nb->notifier_call(nb, MODULE_STATE_GOING, tp_mod);
 382 end:
 383         mutex_unlock(&tracepoint_module_list_mutex);
 384         return ret;
 385
 386 }
 387 EXPORT_SYMBOL_GPL(unregister_tracepoint_module_notifier);
 388
 389 /*
 390  * Ensure the tracer unregistered the module's probes before the module
 391  * teardown is performed. Prevents leaks of probe and data pointers.
 392  */
 393 static void tp_module_going_check_quiescent(struct tracepoint * const *begin,
 394                 struct tracepoint * const *end)
 395 {
 396         struct tracepoint * const *iter;
 397
 398         if (!begin)
 399                 return;
 400         for (iter = begin; iter < end; iter++)
 401                 WARN_ON_ONCE((*iter)->funcs);
 402 }
 403
 404 static int tracepoint_module_coming(struct module *mod)
 405 {
 406         struct tp_module *tp_mod;
 407         int ret = 0;
 408
 409         if (!mod->num_tracepoints)
 410                 return 0;
 411
 412         /*
 413          * We skip modules that taint the kernel, especially those with different
 414          * module headers (for forced load), to make sure we don't cause a crash.
 415          * Staging, out-of-tree, and unsigned GPL modules are fine.
 416          */
 417         if (trace_module_has_bad_taint(mod))
 418                 return 0;
 419         mutex_lock(&tracepoint_module_list_mutex);
 420         tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);
 421         if (!tp_mod) {
 422                 ret = -ENOMEM;
 423                 goto end;
 424         }
 425         tp_mod->mod = mod;
 426         list_add_tail(&tp_mod->list, &tracepoint_module_list);
 427         blocking_notifier_call_chain(&tracepoint_notify_list,
 428                         MODULE_STATE_COMING, tp_mod);
 429 end:
 430         mutex_unlock(&tracepoint_module_list_mutex);
 431         return ret;
 432 }
 433
 434 static void tracepoint_module_going(struct module *mod)
 435 {
 436         struct tp_module *tp_mod;
 437
 438         if (!mod->num_tracepoints)
 439                 return;
 440
 441         mutex_lock(&tracepoint_module_list_mutex);
 442         list_for_each_entry(tp_mod, &tracepoint_module_list, list) {
 443                 if (tp_mod->mod == mod) {
 444                         blocking_notifier_call_chain(&tracepoint_notify_list,
 445                                         MODULE_STATE_GOING, tp_mod);
 446                         list_del(&tp_mod->list);
 447                         kfree(tp_mod);
 448                         /*
 449                          * Called the going notifier before checking for
 450                          * quiescence.
 451                          */
 452                         tp_module_going_check_quiescent(mod->tracepoints_ptrs,
 453                                 mod->tracepoints_ptrs + mod->num_tracepoints);
 454                         break;
 455                 }
 456         }
 457         /*
 458          * In the case of modules that were tainted at "coming", we'll simply
 459          * walk through the list without finding it. We cannot use the "tainted"
 460          * flag on "going", in case a module taints the kernel only after being
 461          * loaded.
 462          */
 463         mutex_unlock(&tracepoint_module_list_mutex);
 464 }
 465
 466 static int tracepoint_module_notify(struct notifier_block *self,
 467                 unsigned long val, void *data)
 468 {
 469         struct module *mod = data;
 470         int ret = 0;
 471
 472         switch (val) {
 473         case MODULE_STATE_COMING:
 474                 ret = tracepoint_module_coming(mod);
 475                 break;
 476         case MODULE_STATE_LIVE:
 477                 break;
 478         case MODULE_STATE_GOING:
 479                 tracepoint_module_going(mod);
 480                 break;
 481         case MODULE_STATE_UNFORMED:
 482                 break;
 483         }
 484         return ret;
 485 }
 486
 487 static struct notifier_block tracepoint_module_nb = {
 488         .notifier_call = tracepoint_module_notify,
 489         .priority = 0,
 490 };
 491
 492 static __init int init_tracepoints(void)
 493 {
 494         int ret;
 495
 496         ret = register_module_notifier(&tracepoint_module_nb);
 497         if (ret)
 498                 pr_warn("Failed to register tracepoint module enter notifier\n");
 499
 500         return ret;
 501 }
 502 __initcall(init_tracepoints);
 503 #endif /* CONFIG_MODULES */
 504
 505 static void for_each_tracepoint_range(struct tracepoint * const *begin,
 506                 struct tracepoint * const *end,
 507                 void (*fct)(struct tracepoint *tp, void *priv),
 508                 void *priv)
 509 {
 510         struct tracepoint * const *iter;
 511
 512         if (!begin)
 513                 return;
 514         for (iter = begin; iter < end; iter++)
 515                 fct(*iter, priv);
 516 }
 517
 518 /**
 519  * for_each_kernel_tracepoint - iteration on all kernel tracepoints
 520  * @fct: callback
 521  * @priv: private data
 522  */
 523 void for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
 524                 void *priv)
 525 {
 526         for_each_tracepoint_range(__start___tracepoints_ptrs,
 527                 __stop___tracepoints_ptrs, fct, priv);
 528 }
 529 EXPORT_SYMBOL_GPL(for_each_kernel_tracepoint);
 530
 531 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
 532
 533 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
 534 static int sys_tracepoint_refcount;
 535
 536 int syscall_regfunc(void)
 537 {
 538         struct task_struct *p, *t;
 539
 540         if (!sys_tracepoint_refcount) {
 541                 read_lock(&tasklist_lock);
 542                 for_each_process_thread(p, t) {
 543                         set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
 544                 }
 545                 read_unlock(&tasklist_lock);
 546         }
 547         sys_tracepoint_refcount++;
 548
 549         return 0;
 550 }
 551
 552 void syscall_unregfunc(void)
 553 {
 554         struct task_struct *p, *t;
 555
 556         sys_tracepoint_refcount--;
 557         if (!sys_tracepoint_refcount) {
 558                 read_lock(&tasklist_lock);
 559                 for_each_process_thread(p, t) {
 560                         clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
 561                 }
 562                 read_unlock(&tasklist_lock);
 563         }
 564 }
 565 #endif