kernel/tracepoint.c

   1 /*
   2  * Copyright (C) 2008 Mathieu Desnoyers
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17  */
  18 #include <linux/module.h>
  19 #include <linux/mutex.h>
  20 #include <linux/types.h>
  21 #include <linux/jhash.h>
  22 #include <linux/list.h>
  23 #include <linux/rcupdate.h>
  24 #include <linux/tracepoint.h>
  25 #include <linux/err.h>
  26 #include <linux/slab.h>
  27
  28 extern struct tracepoint __start___tracepoints[];
  29 extern struct tracepoint __stop___tracepoints[];
  30
  31 /* Set to 1 to enable tracepoint debug output */
  32 static const int tracepoint_debug;
  33
  34 /*
  35  * tracepoints_mutex nests inside module_mutex. Tracepoints mutex protects the
  36  * builtin and module tracepoints and the hash table.
  37  */
  38 static DEFINE_MUTEX(tracepoints_mutex);
  39
  40 /*
  41  * Tracepoint hash table, containing the active tracepoints.
  42  * Protected by tracepoints_mutex.
  43  */
  44 #define TRACEPOINT_HASH_BITS 6
  45 #define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
  46
  47 /*
  48  * Note about RCU :
  49  * It is used to to delay the free of multiple probes array until a quiescent
  50  * state is reached.
  51  * Tracepoint entries modifications are protected by the tracepoints_mutex.
  52  */
  53 struct tracepoint_entry {
  54         struct hlist_node hlist;
  55         void **funcs;
  56         int refcount;   /* Number of times armed. 0 if disarmed. */
  57         struct rcu_head rcu;
  58         void *oldptr;
  59         unsigned char rcu_pending:1;
  60         char name[0];
  61 };
  62
  63 static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
  64
  65 static void free_old_closure(struct rcu_head *head)
  66 {
  67         struct tracepoint_entry *entry = container_of(head,
  68                 struct tracepoint_entry, rcu);
  69         kfree(entry->oldptr);
  70         /* Make sure we free the data before setting the pending flag to 0 */
  71         smp_wmb();
  72         entry->rcu_pending = 0;
  73 }
  74
  75 static void tracepoint_entry_free_old(struct tracepoint_entry *entry, void *old)
  76 {
  77         if (!old)
  78                 return;
  79         entry->oldptr = old;
  80         entry->rcu_pending = 1;
  81         /* write rcu_pending before calling the RCU callback */
  82         smp_wmb();
  83         call_rcu_sched(&entry->rcu, free_old_closure);
  84 }
  85
  86 static void debug_print_probes(struct tracepoint_entry *entry)
  87 {
  88         int i;
  89
  90         if (!tracepoint_debug)
  91                 return;
  92
  93         for (i = 0; entry->funcs[i]; i++)
  94                 printk(KERN_DEBUG "Probe %d : %p\n", i, entry->funcs[i]);
  95 }
  96
  97 static void *
  98 tracepoint_entry_add_probe(struct tracepoint_entry *entry, void *probe)
  99 {
 100         int nr_probes = 0;
 101         void **old, **new;
 102
 103         WARN_ON(!probe);
 104
 105         debug_print_probes(entry);
 106         old = entry->funcs;
 107         if (old) {
 108                 /* (N -> N+1), (N != 0, 1) probes */
 109                 for (nr_probes = 0; old[nr_probes]; nr_probes++)
 110                         if (old[nr_probes] == probe)
 111                                 return ERR_PTR(-EEXIST);
 112         }
 113         /* + 2 : one for new probe, one for NULL func */
 114         new = kzalloc((nr_probes + 2) * sizeof(void *), GFP_KERNEL);
 115         if (new == NULL)
 116                 return ERR_PTR(-ENOMEM);
 117         if (old)
 118                 memcpy(new, old, nr_probes * sizeof(void *));
 119         new[nr_probes] = probe;
 120         entry->refcount = nr_probes + 1;
 121         entry->funcs = new;
 122         debug_print_probes(entry);
 123         return old;
 124 }
 125
 126 static void *
 127 tracepoint_entry_remove_probe(struct tracepoint_entry *entry, void *probe)
 128 {
 129         int nr_probes = 0, nr_del = 0, i;
 130         void **old, **new;
 131
 132         old = entry->funcs;
 133
 134         if (!old)
 135                 return NULL;
 136
 137         debug_print_probes(entry);
 138         /* (N -> M), (N > 1, M >= 0) probes */
 139         for (nr_probes = 0; old[nr_probes]; nr_probes++) {
 140                 if ((!probe || old[nr_probes] == probe))
 141                         nr_del++;
 142         }
 143
 144         if (nr_probes - nr_del == 0) {
 145                 /* N -> 0, (N > 1) */
 146                 entry->funcs = NULL;
 147                 entry->refcount = 0;
 148                 debug_print_probes(entry);
 149                 return old;
 150         } else {
 151                 int j = 0;
 152                 /* N -> M, (N > 1, M > 0) */
 153                 /* + 1 for NULL */
 154                 new = kzalloc((nr_probes - nr_del + 1)
 155                         * sizeof(void *), GFP_KERNEL);
 156                 if (new == NULL)
 157                         return ERR_PTR(-ENOMEM);
 158                 for (i = 0; old[i]; i++)
 159                         if ((probe && old[i] != probe))
 160                                 new[j++] = old[i];
 161                 entry->refcount = nr_probes - nr_del;
 162                 entry->funcs = new;
 163         }
 164         debug_print_probes(entry);
 165         return old;
 166 }
 167
 168 /*
 169  * Get tracepoint if the tracepoint is present in the tracepoint hash table.
 170  * Must be called with tracepoints_mutex held.
 171  * Returns NULL if not present.
 172  */
 173 static struct tracepoint_entry *get_tracepoint(const char *name)
 174 {
 175         struct hlist_head *head;
 176         struct hlist_node *node;
 177         struct tracepoint_entry *e;
 178         u32 hash = jhash(name, strlen(name), 0);
 179
 180         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 181         hlist_for_each_entry(e, node, head, hlist) {
 182                 if (!strcmp(name, e->name))
 183                         return e;
 184         }
 185         return NULL;
 186 }
 187
 188 /*
 189  * Add the tracepoint to the tracepoint hash table. Must be called with
 190  * tracepoints_mutex held.
 191  */
 192 static struct tracepoint_entry *add_tracepoint(const char *name)
 193 {
 194         struct hlist_head *head;
 195         struct hlist_node *node;
 196         struct tracepoint_entry *e;
 197         size_t name_len = strlen(name) + 1;
 198         u32 hash = jhash(name, name_len-1, 0);
 199
 200         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 201         hlist_for_each_entry(e, node, head, hlist) {
 202                 if (!strcmp(name, e->name)) {
 203                         printk(KERN_NOTICE
 204                                 "tracepoint %s busy\n", name);
 205                         return ERR_PTR(-EEXIST);        /* Already there */
 206                 }
 207         }
 208         /*
 209          * Using kmalloc here to allocate a variable length element. Could
 210          * cause some memory fragmentation if overused.
 211          */
 212         e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
 213         if (!e)
 214                 return ERR_PTR(-ENOMEM);
 215         memcpy(&e->name[0], name, name_len);
 216         e->funcs = NULL;
 217         e->refcount = 0;
 218         e->rcu_pending = 0;
 219         hlist_add_head(&e->hlist, head);
 220         return e;
 221 }
 222
 223 /*
 224  * Remove the tracepoint from the tracepoint hash table. Must be called with
 225  * mutex_lock held.
 226  */
 227 static int remove_tracepoint(const char *name)
 228 {
 229         struct hlist_head *head;
 230         struct hlist_node *node;
 231         struct tracepoint_entry *e;
 232         int found = 0;
 233         size_t len = strlen(name) + 1;
 234         u32 hash = jhash(name, len-1, 0);
 235
 236         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 237         hlist_for_each_entry(e, node, head, hlist) {
 238                 if (!strcmp(name, e->name)) {
 239                         found = 1;
 240                         break;
 241                 }
 242         }
 243         if (!found)
 244                 return -ENOENT;
 245         if (e->refcount)
 246                 return -EBUSY;
 247         hlist_del(&e->hlist);
 248         /* Make sure the call_rcu_sched has been executed */
 249         if (e->rcu_pending)
 250                 rcu_barrier_sched();
 251         kfree(e);
 252         return 0;
 253 }
 254
 255 /*
 256  * Sets the probe callback corresponding to one tracepoint.
 257  */
 258 static void set_tracepoint(struct tracepoint_entry **entry,
 259         struct tracepoint *elem, int active)
 260 {
 261         WARN_ON(strcmp((*entry)->name, elem->name) != 0);
 262
 263         /*
 264          * rcu_assign_pointer has a smp_wmb() which makes sure that the new
 265          * probe callbacks array is consistent before setting a pointer to it.
 266          * This array is referenced by __DO_TRACE from
 267          * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
 268          * is used.
 269          */
 270         rcu_assign_pointer(elem->funcs, (*entry)->funcs);
 271         elem->state = active;
 272 }
 273
 274 /*
 275  * Disable a tracepoint and its probe callback.
 276  * Note: only waiting an RCU period after setting elem->call to the empty
 277  * function insures that the original callback is not used anymore. This insured
 278  * by preempt_disable around the call site.
 279  */
 280 static void disable_tracepoint(struct tracepoint *elem)
 281 {
 282         elem->state = 0;
 283 }
 284
 285 /**
 286  * tracepoint_update_probe_range - Update a probe range
 287  * @begin: beginning of the range
 288  * @end: end of the range
 289  *
 290  * Updates the probe callback corresponding to a range of tracepoints.
 291  */
 292 void tracepoint_update_probe_range(struct tracepoint *begin,
 293         struct tracepoint *end)
 294 {
 295         struct tracepoint *iter;
 296         struct tracepoint_entry *mark_entry;
 297
 298         mutex_lock(&tracepoints_mutex);
 299         for (iter = begin; iter < end; iter++) {
 300                 mark_entry = get_tracepoint(iter->name);
 301                 if (mark_entry) {
 302                         set_tracepoint(&mark_entry, iter,
 303                                         !!mark_entry->refcount);
 304                 } else {
 305                         disable_tracepoint(iter);
 306                 }
 307         }
 308         mutex_unlock(&tracepoints_mutex);
 309 }
 310
 311 /*
 312  * Update probes, removing the faulty probes.
 313  */
 314 static void tracepoint_update_probes(void)
 315 {
 316         /* Core kernel tracepoints */
 317         tracepoint_update_probe_range(__start___tracepoints,
 318                 __stop___tracepoints);
 319         /* tracepoints in modules. */
 320         module_update_tracepoints();
 321 }
 322
 323 /**
 324  * tracepoint_probe_register -  Connect a probe to a tracepoint
 325  * @name: tracepoint name
 326  * @probe: probe handler
 327  *
 328  * Returns 0 if ok, error value on error.
 329  * The probe address must at least be aligned on the architecture pointer size.
 330  */
 331 int tracepoint_probe_register(const char *name, void *probe)
 332 {
 333         struct tracepoint_entry *entry;
 334         int ret = 0;
 335         void *old;
 336
 337         mutex_lock(&tracepoints_mutex);
 338         entry = get_tracepoint(name);
 339         if (!entry) {
 340                 entry = add_tracepoint(name);
 341                 if (IS_ERR(entry)) {
 342                         ret = PTR_ERR(entry);
 343                         goto end;
 344                 }
 345         }
 346         /*
 347          * If we detect that a call_rcu_sched is pending for this tracepoint,
 348          * make sure it's executed now.
 349          */
 350         if (entry->rcu_pending)
 351                 rcu_barrier_sched();
 352         old = tracepoint_entry_add_probe(entry, probe);
 353         if (IS_ERR(old)) {
 354                 ret = PTR_ERR(old);
 355                 goto end;
 356         }
 357         mutex_unlock(&tracepoints_mutex);
 358         tracepoint_update_probes();             /* may update entry */
 359         mutex_lock(&tracepoints_mutex);
 360         entry = get_tracepoint(name);
 361         WARN_ON(!entry);
 362         if (entry->rcu_pending)
 363                 rcu_barrier_sched();
 364         tracepoint_entry_free_old(entry, old);
 365 end:
 366         mutex_unlock(&tracepoints_mutex);
 367         return ret;
 368 }
 369 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
 370
 371 /**
 372  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
 373  * @name: tracepoint name
 374  * @probe: probe function pointer
 375  *
 376  * We do not need to call a synchronize_sched to make sure the probes have
 377  * finished running before doing a module unload, because the module unload
 378  * itself uses stop_machine(), which insures that every preempt disabled section
 379  * have finished.
 380  */
 381 int tracepoint_probe_unregister(const char *name, void *probe)
 382 {
 383         struct tracepoint_entry *entry;
 384         void *old;
 385         int ret = -ENOENT;
 386
 387         mutex_lock(&tracepoints_mutex);
 388         entry = get_tracepoint(name);
 389         if (!entry)
 390                 goto end;
 391         if (entry->rcu_pending)
 392                 rcu_barrier_sched();
 393         old = tracepoint_entry_remove_probe(entry, probe);
 394         if (!old) {
 395                 printk(KERN_WARNING "Warning: Trying to unregister a probe"
 396                                     "that doesn't exist\n");
 397                 goto end;
 398         }
 399         mutex_unlock(&tracepoints_mutex);
 400         tracepoint_update_probes();             /* may update entry */
 401         mutex_lock(&tracepoints_mutex);
 402         entry = get_tracepoint(name);
 403         if (!entry)
 404                 goto end;
 405         if (entry->rcu_pending)
 406                 rcu_barrier_sched();
 407         tracepoint_entry_free_old(entry, old);
 408         remove_tracepoint(name);        /* Ignore busy error message */
 409         ret = 0;
 410 end:
 411         mutex_unlock(&tracepoints_mutex);
 412         return ret;
 413 }
 414 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
 415
 416 /**
 417  * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
 418  * @tracepoint: current tracepoints (in), next tracepoint (out)
 419  * @begin: beginning of the range
 420  * @end: end of the range
 421  *
 422  * Returns whether a next tracepoint has been found (1) or not (0).
 423  * Will return the first tracepoint in the range if the input tracepoint is
 424  * NULL.
 425  */
 426 int tracepoint_get_iter_range(struct tracepoint **tracepoint,
 427         struct tracepoint *begin, struct tracepoint *end)
 428 {
 429         if (!*tracepoint && begin != end) {
 430                 *tracepoint = begin;
 431                 return 1;
 432         }
 433         if (*tracepoint >= begin && *tracepoint < end)
 434                 return 1;
 435         return 0;
 436 }
 437 EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
 438
 439 static void tracepoint_get_iter(struct tracepoint_iter *iter)
 440 {
 441         int found = 0;
 442
 443         /* Core kernel tracepoints */
 444         if (!iter->module) {
 445                 found = tracepoint_get_iter_range(&iter->tracepoint,
 446                                 __start___tracepoints, __stop___tracepoints);
 447                 if (found)
 448                         goto end;
 449         }
 450         /* tracepoints in modules. */
 451         found = module_get_iter_tracepoints(iter);
 452 end:
 453         if (!found)
 454                 tracepoint_iter_reset(iter);
 455 }
 456
 457 void tracepoint_iter_start(struct tracepoint_iter *iter)
 458 {
 459         tracepoint_get_iter(iter);
 460 }
 461 EXPORT_SYMBOL_GPL(tracepoint_iter_start);
 462
 463 void tracepoint_iter_next(struct tracepoint_iter *iter)
 464 {
 465         iter->tracepoint++;
 466         /*
 467          * iter->tracepoint may be invalid because we blindly incremented it.
 468          * Make sure it is valid by marshalling on the tracepoints, getting the
 469          * tracepoints from following modules if necessary.
 470          */
 471         tracepoint_get_iter(iter);
 472 }
 473 EXPORT_SYMBOL_GPL(tracepoint_iter_next);
 474
 475 void tracepoint_iter_stop(struct tracepoint_iter *iter)
 476 {
 477 }
 478 EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
 479
 480 void tracepoint_iter_reset(struct tracepoint_iter *iter)
 481 {
 482         iter->module = NULL;
 483         iter->tracepoint = NULL;
 484 }
 485 EXPORT_SYMBOL_GPL(tracepoint_iter_reset);