git.oblomov.eu Git - linux-2.6/blob - 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 static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
  47
  48 /*
  49  * Note about RCU :
  50  * It is used to to delay the free of multiple probes array until a quiescent
  51  * state is reached.
  52  * Tracepoint entries modifications are protected by the tracepoints_mutex.
  53  */
  54 struct tracepoint_entry {
  55         struct hlist_node hlist;
  56         void **funcs;
  57         int refcount;   /* Number of times armed. 0 if disarmed. */
  58         char name[0];
  59 };
  60
  61 struct tp_probes {
  62         struct rcu_head rcu;
  63         void *probes[0];
  64 };
  65
  66 static inline void *allocate_probes(int count)
  67 {
  68         struct tp_probes *p  = kmalloc(count * sizeof(void *)
  69                         + sizeof(struct tp_probes), GFP_KERNEL);
  70         return p == NULL ? NULL : p->probes;
  71 }
  72
  73 static void rcu_free_old_probes(struct rcu_head *head)
  74 {
  75         kfree(container_of(head, struct tp_probes, rcu));
  76 }
  77
  78 static inline void release_probes(void *old)
  79 {
  80         if (old) {
  81                 struct tp_probes *tp_probes = container_of(old,
  82                         struct tp_probes, probes[0]);
  83                 call_rcu(&tp_probes->rcu, rcu_free_old_probes);
  84         }
  85 }
  86
  87 static void debug_print_probes(struct tracepoint_entry *entry)
  88 {
  89         int i;
  90
  91         if (!tracepoint_debug || !entry->funcs)
  92                 return;
  93
  94         for (i = 0; entry->funcs[i]; i++)
  95                 printk(KERN_DEBUG "Probe %d : %p\n", i, entry->funcs[i]);
  96 }
  97
  98 static void *
  99 tracepoint_entry_add_probe(struct tracepoint_entry *entry, void *probe)
 100 {
 101         int nr_probes = 0;
 102         void **old, **new;
 103
 104         WARN_ON(!probe);
 105
 106         debug_print_probes(entry);
 107         old = entry->funcs;
 108         if (old) {
 109                 /* (N -> N+1), (N != 0, 1) probes */
 110                 for (nr_probes = 0; old[nr_probes]; nr_probes++)
 111                         if (old[nr_probes] == probe)
 112                                 return ERR_PTR(-EEXIST);
 113         }
 114         /* + 2 : one for new probe, one for NULL func */
 115         new = allocate_probes(nr_probes + 2);
 116         if (new == NULL)
 117                 return ERR_PTR(-ENOMEM);
 118         if (old)
 119                 memcpy(new, old, nr_probes * sizeof(void *));
 120         new[nr_probes] = probe;
 121         new[nr_probes + 1] = NULL;
 122         entry->refcount = nr_probes + 1;
 123         entry->funcs = new;
 124         debug_print_probes(entry);
 125         return old;
 126 }
 127
 128 static void *
 129 tracepoint_entry_remove_probe(struct tracepoint_entry *entry, void *probe)
 130 {
 131         int nr_probes = 0, nr_del = 0, i;
 132         void **old, **new;
 133
 134         old = entry->funcs;
 135
 136         if (!old)
 137                 return ERR_PTR(-ENOENT);
 138
 139         debug_print_probes(entry);
 140         /* (N -> M), (N > 1, M >= 0) probes */
 141         for (nr_probes = 0; old[nr_probes]; nr_probes++) {
 142                 if ((!probe || old[nr_probes] == probe))
 143                         nr_del++;
 144         }
 145
 146         if (nr_probes - nr_del == 0) {
 147                 /* N -> 0, (N > 1) */
 148                 entry->funcs = NULL;
 149                 entry->refcount = 0;
 150                 debug_print_probes(entry);
 151                 return old;
 152         } else {
 153                 int j = 0;
 154                 /* N -> M, (N > 1, M > 0) */
 155                 /* + 1 for NULL */
 156                 new = allocate_probes(nr_probes - nr_del + 1);
 157                 if (new == NULL)
 158                         return ERR_PTR(-ENOMEM);
 159                 for (i = 0; old[i]; i++)
 160                         if ((probe && old[i] != probe))
 161                                 new[j++] = old[i];
 162                 new[nr_probes - nr_del] = NULL;
 163                 entry->refcount = nr_probes - nr_del;
 164                 entry->funcs = new;
 165         }
 166         debug_print_probes(entry);
 167         return old;
 168 }
 169
 170 /*
 171  * Get tracepoint if the tracepoint is present in the tracepoint hash table.
 172  * Must be called with tracepoints_mutex held.
 173  * Returns NULL if not present.
 174  */
 175 static struct tracepoint_entry *get_tracepoint(const char *name)
 176 {
 177         struct hlist_head *head;
 178         struct hlist_node *node;
 179         struct tracepoint_entry *e;
 180         u32 hash = jhash(name, strlen(name), 0);
 181
 182         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 183         hlist_for_each_entry(e, node, head, hlist) {
 184                 if (!strcmp(name, e->name))
 185                         return e;
 186         }
 187         return NULL;
 188 }
 189
 190 /*
 191  * Add the tracepoint to the tracepoint hash table. Must be called with
 192  * tracepoints_mutex held.
 193  */
 194 static struct tracepoint_entry *add_tracepoint(const char *name)
 195 {
 196         struct hlist_head *head;
 197         struct hlist_node *node;
 198         struct tracepoint_entry *e;
 199         size_t name_len = strlen(name) + 1;
 200         u32 hash = jhash(name, name_len-1, 0);
 201
 202         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 203         hlist_for_each_entry(e, node, head, hlist) {
 204                 if (!strcmp(name, e->name)) {
 205                         printk(KERN_NOTICE
 206                                 "tracepoint %s busy\n", name);
 207                         return ERR_PTR(-EEXIST);        /* Already there */
 208                 }
 209         }
 210         /*
 211          * Using kmalloc here to allocate a variable length element. Could
 212          * cause some memory fragmentation if overused.
 213          */
 214         e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
 215         if (!e)
 216                 return ERR_PTR(-ENOMEM);
 217         memcpy(&e->name[0], name, name_len);
 218         e->funcs = NULL;
 219         e->refcount = 0;
 220         hlist_add_head(&e->hlist, head);
 221         return e;
 222 }
 223
 224 /*
 225  * Remove the tracepoint from the tracepoint hash table. Must be called with
 226  * mutex_lock held.
 227  */
 228 static inline void remove_tracepoint(struct tracepoint_entry *e)
 229 {
 230         hlist_del(&e->hlist);
 231         kfree(e);
 232 }
 233
 234 /*
 235  * Sets the probe callback corresponding to one tracepoint.
 236  */
 237 static void set_tracepoint(struct tracepoint_entry **entry,
 238         struct tracepoint *elem, int active)
 239 {
 240         WARN_ON(strcmp((*entry)->name, elem->name) != 0);
 241
 242         /*
 243          * rcu_assign_pointer has a smp_wmb() which makes sure that the new
 244          * probe callbacks array is consistent before setting a pointer to it.
 245          * This array is referenced by __DO_TRACE from
 246          * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
 247          * is used.
 248          */
 249         rcu_assign_pointer(elem->funcs, (*entry)->funcs);
 250         elem->state = active;
 251 }
 252
 253 /*
 254  * Disable a tracepoint and its probe callback.
 255  * Note: only waiting an RCU period after setting elem->call to the empty
 256  * function insures that the original callback is not used anymore. This insured
 257  * by preempt_disable around the call site.
 258  */
 259 static void disable_tracepoint(struct tracepoint *elem)
 260 {
 261         elem->state = 0;
 262 }
 263
 264 /**
 265  * tracepoint_update_probe_range - Update a probe range
 266  * @begin: beginning of the range
 267  * @end: end of the range
 268  *
 269  * Updates the probe callback corresponding to a range of tracepoints.
 270  */
 271 void tracepoint_update_probe_range(struct tracepoint *begin,
 272         struct tracepoint *end)
 273 {
 274         struct tracepoint *iter;
 275         struct tracepoint_entry *mark_entry;
 276
 277         mutex_lock(&tracepoints_mutex);
 278         for (iter = begin; iter < end; iter++) {
 279                 mark_entry = get_tracepoint(iter->name);
 280                 if (mark_entry) {
 281                         set_tracepoint(&mark_entry, iter,
 282                                         !!mark_entry->refcount);
 283                 } else {
 284                         disable_tracepoint(iter);
 285                 }
 286         }
 287         mutex_unlock(&tracepoints_mutex);
 288 }
 289
 290 /*
 291  * Update probes, removing the faulty probes.
 292  */
 293 static void tracepoint_update_probes(void)
 294 {
 295         /* Core kernel tracepoints */
 296         tracepoint_update_probe_range(__start___tracepoints,
 297                 __stop___tracepoints);
 298         /* tracepoints in modules. */
 299         module_update_tracepoints();
 300 }
 301
 302 /**
 303  * tracepoint_probe_register -  Connect a probe to a tracepoint
 304  * @name: tracepoint name
 305  * @probe: probe handler
 306  *
 307  * Returns 0 if ok, error value on error.
 308  * The probe address must at least be aligned on the architecture pointer size.
 309  */
 310 int tracepoint_probe_register(const char *name, void *probe)
 311 {
 312         struct tracepoint_entry *entry;
 313         int ret = 0;
 314         void *old;
 315
 316         mutex_lock(&tracepoints_mutex);
 317         entry = get_tracepoint(name);
 318         if (!entry) {
 319                 entry = add_tracepoint(name);
 320                 if (IS_ERR(entry)) {
 321                         ret = PTR_ERR(entry);
 322                         goto end;
 323                 }
 324         }
 325         old = tracepoint_entry_add_probe(entry, probe);
 326         if (IS_ERR(old)) {
 327                 if (!entry->refcount)
 328                         remove_tracepoint(entry);
 329                 ret = PTR_ERR(old);
 330                 goto end;
 331         }
 332         mutex_unlock(&tracepoints_mutex);
 333         tracepoint_update_probes();             /* may update entry */
 334         release_probes(old);
 335         return 0;
 336 end:
 337         mutex_unlock(&tracepoints_mutex);
 338         return ret;
 339 }
 340 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
 341
 342 /**
 343  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
 344  * @name: tracepoint name
 345  * @probe: probe function pointer
 346  *
 347  * We do not need to call a synchronize_sched to make sure the probes have
 348  * finished running before doing a module unload, because the module unload
 349  * itself uses stop_machine(), which insures that every preempt disabled section
 350  * have finished.
 351  */
 352 int tracepoint_probe_unregister(const char *name, void *probe)
 353 {
 354         struct tracepoint_entry *entry;
 355         void *old;
 356         int ret = -ENOENT;
 357
 358         mutex_lock(&tracepoints_mutex);
 359         entry = get_tracepoint(name);
 360         if (!entry)
 361                 goto end;
 362         old = tracepoint_entry_remove_probe(entry, probe);
 363         if (IS_ERR(old)) {
 364                 ret = PTR_ERR(old);
 365                 goto end;
 366         }
 367         if (!entry->refcount)
 368                 remove_tracepoint(entry);
 369         mutex_unlock(&tracepoints_mutex);
 370         tracepoint_update_probes();             /* may update entry */
 371         release_probes(old);
 372         return 0;
 373 end:
 374         mutex_unlock(&tracepoints_mutex);
 375         return ret;
 376 }
 377 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
 378
 379 /**
 380  * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
 381  * @tracepoint: current tracepoints (in), next tracepoint (out)
 382  * @begin: beginning of the range
 383  * @end: end of the range
 384  *
 385  * Returns whether a next tracepoint has been found (1) or not (0).
 386  * Will return the first tracepoint in the range if the input tracepoint is
 387  * NULL.
 388  */
 389 int tracepoint_get_iter_range(struct tracepoint **tracepoint,
 390         struct tracepoint *begin, struct tracepoint *end)
 391 {
 392         if (!*tracepoint && begin != end) {
 393                 *tracepoint = begin;
 394                 return 1;
 395         }
 396         if (*tracepoint >= begin && *tracepoint < end)
 397                 return 1;
 398         return 0;
 399 }
 400 EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
 401
 402 static void tracepoint_get_iter(struct tracepoint_iter *iter)
 403 {
 404         int found = 0;
 405
 406         /* Core kernel tracepoints */
 407         if (!iter->module) {
 408                 found = tracepoint_get_iter_range(&iter->tracepoint,
 409                                 __start___tracepoints, __stop___tracepoints);
 410                 if (found)
 411                         goto end;
 412         }
 413         /* tracepoints in modules. */
 414         found = module_get_iter_tracepoints(iter);
 415 end:
 416         if (!found)
 417                 tracepoint_iter_reset(iter);
 418 }
 419
 420 void tracepoint_iter_start(struct tracepoint_iter *iter)
 421 {
 422         tracepoint_get_iter(iter);
 423 }
 424 EXPORT_SYMBOL_GPL(tracepoint_iter_start);
 425
 426 void tracepoint_iter_next(struct tracepoint_iter *iter)
 427 {
 428         iter->tracepoint++;
 429         /*
 430          * iter->tracepoint may be invalid because we blindly incremented it.
 431          * Make sure it is valid by marshalling on the tracepoints, getting the
 432          * tracepoints from following modules if necessary.
 433          */
 434         tracepoint_get_iter(iter);
 435 }
 436 EXPORT_SYMBOL_GPL(tracepoint_iter_next);
 437
 438 void tracepoint_iter_stop(struct tracepoint_iter *iter)
 439 {
 440 }
 441 EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
 442
 443 void tracepoint_iter_reset(struct tracepoint_iter *iter)
 444 {
 445         iter->module = NULL;
 446         iter->tracepoint = NULL;
 447 }
 448 EXPORT_SYMBOL_GPL(tracepoint_iter_reset);