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         debug_print_probes(entry);
 135         /* (N -> M), (N > 1, M >= 0) probes */
 136         for (nr_probes = 0; old[nr_probes]; nr_probes++) {
 137                 if ((!probe || old[nr_probes] == probe))
 138                         nr_del++;
 139         }
 140
 141         if (nr_probes - nr_del == 0) {
 142                 /* N -> 0, (N > 1) */
 143                 entry->funcs = NULL;
 144                 entry->refcount = 0;
 145                 debug_print_probes(entry);
 146                 return old;
 147         } else {
 148                 int j = 0;
 149                 /* N -> M, (N > 1, M > 0) */
 150                 /* + 1 for NULL */
 151                 new = kzalloc((nr_probes - nr_del + 1)
 152                         * sizeof(void *), GFP_KERNEL);
 153                 if (new == NULL)
 154                         return ERR_PTR(-ENOMEM);
 155                 for (i = 0; old[i]; i++)
 156                         if ((probe && old[i] != probe))
 157                                 new[j++] = old[i];
 158                 entry->refcount = nr_probes - nr_del;
 159                 entry->funcs = new;
 160         }
 161         debug_print_probes(entry);
 162         return old;
 163 }
 164
 165 /*
 166  * Get tracepoint if the tracepoint is present in the tracepoint hash table.
 167  * Must be called with tracepoints_mutex held.
 168  * Returns NULL if not present.
 169  */
 170 static struct tracepoint_entry *get_tracepoint(const char *name)
 171 {
 172         struct hlist_head *head;
 173         struct hlist_node *node;
 174         struct tracepoint_entry *e;
 175         u32 hash = jhash(name, strlen(name), 0);
 176
 177         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 178         hlist_for_each_entry(e, node, head, hlist) {
 179                 if (!strcmp(name, e->name))
 180                         return e;
 181         }
 182         return NULL;
 183 }
 184
 185 /*
 186  * Add the tracepoint to the tracepoint hash table. Must be called with
 187  * tracepoints_mutex held.
 188  */
 189 static struct tracepoint_entry *add_tracepoint(const char *name)
 190 {
 191         struct hlist_head *head;
 192         struct hlist_node *node;
 193         struct tracepoint_entry *e;
 194         size_t name_len = strlen(name) + 1;
 195         u32 hash = jhash(name, name_len-1, 0);
 196
 197         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 198         hlist_for_each_entry(e, node, head, hlist) {
 199                 if (!strcmp(name, e->name)) {
 200                         printk(KERN_NOTICE
 201                                 "tracepoint %s busy\n", name);
 202                         return ERR_PTR(-EEXIST);        /* Already there */
 203                 }
 204         }
 205         /*
 206          * Using kmalloc here to allocate a variable length element. Could
 207          * cause some memory fragmentation if overused.
 208          */
 209         e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
 210         if (!e)
 211                 return ERR_PTR(-ENOMEM);
 212         memcpy(&e->name[0], name, name_len);
 213         e->funcs = NULL;
 214         e->refcount = 0;
 215         e->rcu_pending = 0;
 216         hlist_add_head(&e->hlist, head);
 217         return e;
 218 }
 219
 220 /*
 221  * Remove the tracepoint from the tracepoint hash table. Must be called with
 222  * mutex_lock held.
 223  */
 224 static int remove_tracepoint(const char *name)
 225 {
 226         struct hlist_head *head;
 227         struct hlist_node *node;
 228         struct tracepoint_entry *e;
 229         int found = 0;
 230         size_t len = strlen(name) + 1;
 231         u32 hash = jhash(name, len-1, 0);
 232
 233         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 234         hlist_for_each_entry(e, node, head, hlist) {
 235                 if (!strcmp(name, e->name)) {
 236                         found = 1;
 237                         break;
 238                 }
 239         }
 240         if (!found)
 241                 return -ENOENT;
 242         if (e->refcount)
 243                 return -EBUSY;
 244         hlist_del(&e->hlist);
 245         /* Make sure the call_rcu_sched has been executed */
 246         if (e->rcu_pending)
 247                 rcu_barrier_sched();
 248         kfree(e);
 249         return 0;
 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 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 smp_read_barrier_depends()
 265          * is used.
 266          */
 267         rcu_assign_pointer(elem->funcs, (*entry)->funcs);
 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 }
 281
 282 /**
 283  * tracepoint_update_probe_range - Update a probe range
 284  * @begin: beginning of the range
 285  * @end: end of the range
 286  *
 287  * Updates the probe callback corresponding to a range of tracepoints.
 288  */
 289 void tracepoint_update_probe_range(struct tracepoint *begin,
 290         struct tracepoint *end)
 291 {
 292         struct tracepoint *iter;
 293         struct tracepoint_entry *mark_entry;
 294
 295         mutex_lock(&tracepoints_mutex);
 296         for (iter = begin; iter < end; iter++) {
 297                 mark_entry = get_tracepoint(iter->name);
 298                 if (mark_entry) {
 299                         set_tracepoint(&mark_entry, iter,
 300                                         !!mark_entry->refcount);
 301                 } else {
 302                         disable_tracepoint(iter);
 303                 }
 304         }
 305         mutex_unlock(&tracepoints_mutex);
 306 }
 307
 308 /*
 309  * Update probes, removing the faulty probes.
 310  */
 311 static void tracepoint_update_probes(void)
 312 {
 313         /* Core kernel tracepoints */
 314         tracepoint_update_probe_range(__start___tracepoints,
 315                 __stop___tracepoints);
 316         /* tracepoints in modules. */
 317         module_update_tracepoints();
 318 }
 319
 320 /**
 321  * tracepoint_probe_register -  Connect a probe to a tracepoint
 322  * @name: tracepoint name
 323  * @probe: probe handler
 324  *
 325  * Returns 0 if ok, error value on error.
 326  * The probe address must at least be aligned on the architecture pointer size.
 327  */
 328 int tracepoint_probe_register(const char *name, void *probe)
 329 {
 330         struct tracepoint_entry *entry;
 331         int ret = 0;
 332         void *old;
 333
 334         mutex_lock(&tracepoints_mutex);
 335         entry = get_tracepoint(name);
 336         if (!entry) {
 337                 entry = add_tracepoint(name);
 338                 if (IS_ERR(entry)) {
 339                         ret = PTR_ERR(entry);
 340                         goto end;
 341                 }
 342         }
 343         /*
 344          * If we detect that a call_rcu_sched is pending for this tracepoint,
 345          * make sure it's executed now.
 346          */
 347         if (entry->rcu_pending)
 348                 rcu_barrier_sched();
 349         old = tracepoint_entry_add_probe(entry, probe);
 350         if (IS_ERR(old)) {
 351                 ret = PTR_ERR(old);
 352                 goto end;
 353         }
 354         mutex_unlock(&tracepoints_mutex);
 355         tracepoint_update_probes();             /* may update entry */
 356         mutex_lock(&tracepoints_mutex);
 357         entry = get_tracepoint(name);
 358         WARN_ON(!entry);
 359         tracepoint_entry_free_old(entry, old);
 360 end:
 361         mutex_unlock(&tracepoints_mutex);
 362         return ret;
 363 }
 364 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
 365
 366 /**
 367  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
 368  * @name: tracepoint name
 369  * @probe: probe function pointer
 370  *
 371  * We do not need to call a synchronize_sched to make sure the probes have
 372  * finished running before doing a module unload, because the module unload
 373  * itself uses stop_machine(), which insures that every preempt disabled section
 374  * have finished.
 375  */
 376 int tracepoint_probe_unregister(const char *name, void *probe)
 377 {
 378         struct tracepoint_entry *entry;
 379         void *old;
 380         int ret = -ENOENT;
 381
 382         mutex_lock(&tracepoints_mutex);
 383         entry = get_tracepoint(name);
 384         if (!entry)
 385                 goto end;
 386         if (entry->rcu_pending)
 387                 rcu_barrier_sched();
 388         old = tracepoint_entry_remove_probe(entry, probe);
 389         mutex_unlock(&tracepoints_mutex);
 390         tracepoint_update_probes();             /* may update entry */
 391         mutex_lock(&tracepoints_mutex);
 392         entry = get_tracepoint(name);
 393         if (!entry)
 394                 goto end;
 395         tracepoint_entry_free_old(entry, old);
 396         remove_tracepoint(name);        /* Ignore busy error message */
 397         ret = 0;
 398 end:
 399         mutex_unlock(&tracepoints_mutex);
 400         return ret;
 401 }
 402 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
 403
 404 /**
 405  * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
 406  * @tracepoint: current tracepoints (in), next tracepoint (out)
 407  * @begin: beginning of the range
 408  * @end: end of the range
 409  *
 410  * Returns whether a next tracepoint has been found (1) or not (0).
 411  * Will return the first tracepoint in the range if the input tracepoint is
 412  * NULL.
 413  */
 414 int tracepoint_get_iter_range(struct tracepoint **tracepoint,
 415         struct tracepoint *begin, struct tracepoint *end)
 416 {
 417         if (!*tracepoint && begin != end) {
 418                 *tracepoint = begin;
 419                 return 1;
 420         }
 421         if (*tracepoint >= begin && *tracepoint < end)
 422                 return 1;
 423         return 0;
 424 }
 425 EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
 426
 427 static void tracepoint_get_iter(struct tracepoint_iter *iter)
 428 {
 429         int found = 0;
 430
 431         /* Core kernel tracepoints */
 432         if (!iter->module) {
 433                 found = tracepoint_get_iter_range(&iter->tracepoint,
 434                                 __start___tracepoints, __stop___tracepoints);
 435                 if (found)
 436                         goto end;
 437         }
 438         /* tracepoints in modules. */
 439         found = module_get_iter_tracepoints(iter);
 440 end:
 441         if (!found)
 442                 tracepoint_iter_reset(iter);
 443 }
 444
 445 void tracepoint_iter_start(struct tracepoint_iter *iter)
 446 {
 447         tracepoint_get_iter(iter);
 448 }
 449 EXPORT_SYMBOL_GPL(tracepoint_iter_start);
 450
 451 void tracepoint_iter_next(struct tracepoint_iter *iter)
 452 {
 453         iter->tracepoint++;
 454         /*
 455          * iter->tracepoint may be invalid because we blindly incremented it.
 456          * Make sure it is valid by marshalling on the tracepoints, getting the
 457          * tracepoints from following modules if necessary.
 458          */
 459         tracepoint_get_iter(iter);
 460 }
 461 EXPORT_SYMBOL_GPL(tracepoint_iter_next);
 462
 463 void tracepoint_iter_stop(struct tracepoint_iter *iter)
 464 {
 465 }
 466 EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
 467
 468 void tracepoint_iter_reset(struct tracepoint_iter *iter)
 469 {
 470         iter->module = NULL;
 471         iter->tracepoint = NULL;
 472 }
 473 EXPORT_SYMBOL_GPL(tracepoint_iter_reset);