kernel/marker.c

   1 /*
   2  * Copyright (C) 2007 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/marker.h>
  25 #include <linux/err.h>
  26
  27 extern struct marker __start___markers[];
  28 extern struct marker __stop___markers[];
  29
  30 /*
  31  * markers_mutex nests inside module_mutex. Markers mutex protects the builtin
  32  * and module markers, the hash table and deferred_sync.
  33  */
  34 static DEFINE_MUTEX(markers_mutex);
  35
  36 /*
  37  * Marker deferred synchronization.
  38  * Upon marker probe_unregister, we delay call to synchronize_sched() to
  39  * accelerate mass unregistration (only when there is no more reference to a
  40  * given module do we call synchronize_sched()). However, we need to make sure
  41  * every critical region has ended before we re-arm a marker that has been
  42  * unregistered and then registered back with a different probe data.
  43  */
  44 static int deferred_sync;
  45
  46 /*
  47  * Marker hash table, containing the active markers.
  48  * Protected by module_mutex.
  49  */
  50 #define MARKER_HASH_BITS 6
  51 #define MARKER_TABLE_SIZE (1 << MARKER_HASH_BITS)
  52
  53 struct marker_entry {
  54         struct hlist_node hlist;
  55         char *format;
  56         marker_probe_func *probe;
  57         void *private;
  58         int refcount;   /* Number of times armed. 0 if disarmed. */
  59         char name[0];   /* Contains name'\0'format'\0' */
  60 };
  61
  62 static struct hlist_head marker_table[MARKER_TABLE_SIZE];
  63
  64 /**
  65  * __mark_empty_function - Empty probe callback
  66  * @mdata: pointer of type const struct marker
  67  * @fmt: format string
  68  * @...: variable argument list
  69  *
  70  * Empty callback provided as a probe to the markers. By providing this to a
  71  * disabled marker, we make sure the  execution flow is always valid even
  72  * though the function pointer change and the marker enabling are two distinct
  73  * operations that modifies the execution flow of preemptible code.
  74  */
  75 void __mark_empty_function(const struct marker *mdata, void *private,
  76         const char *fmt, ...)
  77 {
  78 }
  79 EXPORT_SYMBOL_GPL(__mark_empty_function);
  80
  81 /*
  82  * Get marker if the marker is present in the marker hash table.
  83  * Must be called with markers_mutex held.
  84  * Returns NULL if not present.
  85  */
  86 static struct marker_entry *get_marker(const char *name)
  87 {
  88         struct hlist_head *head;
  89         struct hlist_node *node;
  90         struct marker_entry *e;
  91         u32 hash = jhash(name, strlen(name), 0);
  92
  93         head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
  94         hlist_for_each_entry(e, node, head, hlist) {
  95                 if (!strcmp(name, e->name))
  96                         return e;
  97         }
  98         return NULL;
  99 }
 100
 101 /*
 102  * Add the marker to the marker hash table. Must be called with markers_mutex
 103  * held.
 104  */
 105 static int add_marker(const char *name, const char *format,
 106         marker_probe_func *probe, void *private)
 107 {
 108         struct hlist_head *head;
 109         struct hlist_node *node;
 110         struct marker_entry *e;
 111         size_t name_len = strlen(name) + 1;
 112         size_t format_len = 0;
 113         u32 hash = jhash(name, name_len-1, 0);
 114
 115         if (format)
 116                 format_len = strlen(format) + 1;
 117         head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
 118         hlist_for_each_entry(e, node, head, hlist) {
 119                 if (!strcmp(name, e->name)) {
 120                         printk(KERN_NOTICE
 121                                 "Marker %s busy, probe %p already installed\n",
 122                                 name, e->probe);
 123                         return -EBUSY;  /* Already there */
 124                 }
 125         }
 126         /*
 127          * Using kmalloc here to allocate a variable length element. Could
 128          * cause some memory fragmentation if overused.
 129          */
 130         e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
 131                         GFP_KERNEL);
 132         if (!e)
 133                 return -ENOMEM;
 134         memcpy(&e->name[0], name, name_len);
 135         if (format) {
 136                 e->format = &e->name[name_len];
 137                 memcpy(e->format, format, format_len);
 138                 trace_mark(core_marker_format, "name %s format %s",
 139                                 e->name, e->format);
 140         } else
 141                 e->format = NULL;
 142         e->probe = probe;
 143         e->private = private;
 144         e->refcount = 0;
 145         hlist_add_head(&e->hlist, head);
 146         return 0;
 147 }
 148
 149 /*
 150  * Remove the marker from the marker hash table. Must be called with mutex_lock
 151  * held.
 152  */
 153 static void *remove_marker(const char *name)
 154 {
 155         struct hlist_head *head;
 156         struct hlist_node *node;
 157         struct marker_entry *e;
 158         int found = 0;
 159         size_t len = strlen(name) + 1;
 160         void *private = NULL;
 161         u32 hash = jhash(name, len-1, 0);
 162
 163         head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
 164         hlist_for_each_entry(e, node, head, hlist) {
 165                 if (!strcmp(name, e->name)) {
 166                         found = 1;
 167                         break;
 168                 }
 169         }
 170         if (found) {
 171                 private = e->private;
 172                 hlist_del(&e->hlist);
 173                 kfree(e);
 174         }
 175         return private;
 176 }
 177
 178 /*
 179  * Set the mark_entry format to the format found in the element.
 180  */
 181 static int marker_set_format(struct marker_entry **entry, const char *format)
 182 {
 183         struct marker_entry *e;
 184         size_t name_len = strlen((*entry)->name) + 1;
 185         size_t format_len = strlen(format) + 1;
 186
 187         e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
 188                         GFP_KERNEL);
 189         if (!e)
 190                 return -ENOMEM;
 191         memcpy(&e->name[0], (*entry)->name, name_len);
 192         e->format = &e->name[name_len];
 193         memcpy(e->format, format, format_len);
 194         e->probe = (*entry)->probe;
 195         e->private = (*entry)->private;
 196         e->refcount = (*entry)->refcount;
 197         hlist_add_before(&e->hlist, &(*entry)->hlist);
 198         hlist_del(&(*entry)->hlist);
 199         kfree(*entry);
 200         *entry = e;
 201         trace_mark(core_marker_format, "name %s format %s",
 202                         e->name, e->format);
 203         return 0;
 204 }
 205
 206 /*
 207  * Sets the probe callback corresponding to one marker.
 208  */
 209 static int set_marker(struct marker_entry **entry, struct marker *elem)
 210 {
 211         int ret;
 212         WARN_ON(strcmp((*entry)->name, elem->name) != 0);
 213
 214         if ((*entry)->format) {
 215                 if (strcmp((*entry)->format, elem->format) != 0) {
 216                         printk(KERN_NOTICE
 217                                 "Format mismatch for probe %s "
 218                                 "(%s), marker (%s)\n",
 219                                 (*entry)->name,
 220                                 (*entry)->format,
 221                                 elem->format);
 222                         return -EPERM;
 223                 }
 224         } else {
 225                 ret = marker_set_format(entry, elem->format);
 226                 if (ret)
 227                         return ret;
 228         }
 229         elem->call = (*entry)->probe;
 230         elem->private = (*entry)->private;
 231         elem->state = 1;
 232         return 0;
 233 }
 234
 235 /*
 236  * Disable a marker and its probe callback.
 237  * Note: only after a synchronize_sched() issued after setting elem->call to the
 238  * empty function insures that the original callback is not used anymore. This
 239  * insured by preemption disabling around the call site.
 240  */
 241 static void disable_marker(struct marker *elem)
 242 {
 243         elem->state = 0;
 244         elem->call = __mark_empty_function;
 245         /*
 246          * Leave the private data and id there, because removal is racy and
 247          * should be done only after a synchronize_sched(). These are never used
 248          * until the next initialization anyway.
 249          */
 250 }
 251
 252 /**
 253  * marker_update_probe_range - Update a probe range
 254  * @begin: beginning of the range
 255  * @end: end of the range
 256  * @probe_module: module address of the probe being updated
 257  * @refcount: number of references left to the given probe_module (out)
 258  *
 259  * Updates the probe callback corresponding to a range of markers.
 260  */
 261 void marker_update_probe_range(struct marker *begin,
 262         struct marker *end, struct module *probe_module,
 263         int *refcount)
 264 {
 265         struct marker *iter;
 266         struct marker_entry *mark_entry;
 267
 268         mutex_lock(&markers_mutex);
 269         for (iter = begin; iter < end; iter++) {
 270                 mark_entry = get_marker(iter->name);
 271                 if (mark_entry && mark_entry->refcount) {
 272                         set_marker(&mark_entry, iter);
 273                         /*
 274                          * ignore error, continue
 275                          */
 276                         if (probe_module)
 277                                 if (probe_module ==
 278                         __module_text_address((unsigned long)mark_entry->probe))
 279                                         (*refcount)++;
 280                 } else {
 281                         disable_marker(iter);
 282                 }
 283         }
 284         mutex_unlock(&markers_mutex);
 285 }
 286
 287 /*
 288  * Update probes, removing the faulty probes.
 289  * Issues a synchronize_sched() when no reference to the module passed
 290  * as parameter is found in the probes so the probe module can be
 291  * safely unloaded from now on.
 292  */
 293 static void marker_update_probes(struct module *probe_module)
 294 {
 295         int refcount = 0;
 296
 297         /* Core kernel markers */
 298         marker_update_probe_range(__start___markers,
 299                         __stop___markers, probe_module, &refcount);
 300         /* Markers in modules. */
 301         module_update_markers(probe_module, &refcount);
 302         if (probe_module && refcount == 0) {
 303                 synchronize_sched();
 304                 deferred_sync = 0;
 305         }
 306 }
 307
 308 /**
 309  * marker_probe_register -  Connect a probe to a marker
 310  * @name: marker name
 311  * @format: format string
 312  * @probe: probe handler
 313  * @private: probe private data
 314  *
 315  * private data must be a valid allocated memory address, or NULL.
 316  * Returns 0 if ok, error value on error.
 317  */
 318 int marker_probe_register(const char *name, const char *format,
 319                         marker_probe_func *probe, void *private)
 320 {
 321         struct marker_entry *entry;
 322         int ret = 0;
 323
 324         mutex_lock(&markers_mutex);
 325         entry = get_marker(name);
 326         if (entry && entry->refcount) {
 327                 ret = -EBUSY;
 328                 goto end;
 329         }
 330         if (deferred_sync) {
 331                 synchronize_sched();
 332                 deferred_sync = 0;
 333         }
 334         ret = add_marker(name, format, probe, private);
 335         if (ret)
 336                 goto end;
 337         mutex_unlock(&markers_mutex);
 338         marker_update_probes(NULL);
 339         return ret;
 340 end:
 341         mutex_unlock(&markers_mutex);
 342         return ret;
 343 }
 344 EXPORT_SYMBOL_GPL(marker_probe_register);
 345
 346 /**
 347  * marker_probe_unregister -  Disconnect a probe from a marker
 348  * @name: marker name
 349  *
 350  * Returns the private data given to marker_probe_register, or an ERR_PTR().
 351  */
 352 void *marker_probe_unregister(const char *name)
 353 {
 354         struct module *probe_module;
 355         struct marker_entry *entry;
 356         void *private;
 357
 358         mutex_lock(&markers_mutex);
 359         entry = get_marker(name);
 360         if (!entry) {
 361                 private = ERR_PTR(-ENOENT);
 362                 goto end;
 363         }
 364         entry->refcount = 0;
 365         /* In what module is the probe handler ? */
 366         probe_module = __module_text_address((unsigned long)entry->probe);
 367         private = remove_marker(name);
 368         deferred_sync = 1;
 369         mutex_unlock(&markers_mutex);
 370         marker_update_probes(probe_module);
 371         return private;
 372 end:
 373         mutex_unlock(&markers_mutex);
 374         return private;
 375 }
 376 EXPORT_SYMBOL_GPL(marker_probe_unregister);
 377
 378 /**
 379  * marker_probe_unregister_private_data -  Disconnect a probe from a marker
 380  * @private: probe private data
 381  *
 382  * Unregister a marker by providing the registered private data.
 383  * Returns the private data given to marker_probe_register, or an ERR_PTR().
 384  */
 385 void *marker_probe_unregister_private_data(void *private)
 386 {
 387         struct module *probe_module;
 388         struct hlist_head *head;
 389         struct hlist_node *node;
 390         struct marker_entry *entry;
 391         int found = 0;
 392         unsigned int i;
 393
 394         mutex_lock(&markers_mutex);
 395         for (i = 0; i < MARKER_TABLE_SIZE; i++) {
 396                 head = &marker_table[i];
 397                 hlist_for_each_entry(entry, node, head, hlist) {
 398                         if (entry->private == private) {
 399                                 found = 1;
 400                                 goto iter_end;
 401                         }
 402                 }
 403         }
 404 iter_end:
 405         if (!found) {
 406                 private = ERR_PTR(-ENOENT);
 407                 goto end;
 408         }
 409         entry->refcount = 0;
 410         /* In what module is the probe handler ? */
 411         probe_module = __module_text_address((unsigned long)entry->probe);
 412         private = remove_marker(entry->name);
 413         deferred_sync = 1;
 414         mutex_unlock(&markers_mutex);
 415         marker_update_probes(probe_module);
 416         return private;
 417 end:
 418         mutex_unlock(&markers_mutex);
 419         return private;
 420 }
 421 EXPORT_SYMBOL_GPL(marker_probe_unregister_private_data);
 422
 423 /**
 424  * marker_arm - Arm a marker
 425  * @name: marker name
 426  *
 427  * Activate a marker. It keeps a reference count of the number of
 428  * arming/disarming done.
 429  * Returns 0 if ok, error value on error.
 430  */
 431 int marker_arm(const char *name)
 432 {
 433         struct marker_entry *entry;
 434         int ret = 0;
 435
 436         mutex_lock(&markers_mutex);
 437         entry = get_marker(name);
 438         if (!entry) {
 439                 ret = -ENOENT;
 440                 goto end;
 441         }
 442         /*
 443          * Only need to update probes when refcount passes from 0 to 1.
 444          */
 445         if (entry->refcount++)
 446                 goto end;
 447 end:
 448         mutex_unlock(&markers_mutex);
 449         marker_update_probes(NULL);
 450         return ret;
 451 }
 452 EXPORT_SYMBOL_GPL(marker_arm);
 453
 454 /**
 455  * marker_disarm - Disarm a marker
 456  * @name: marker name
 457  *
 458  * Disarm a marker. It keeps a reference count of the number of arming/disarming
 459  * done.
 460  * Returns 0 if ok, error value on error.
 461  */
 462 int marker_disarm(const char *name)
 463 {
 464         struct marker_entry *entry;
 465         int ret = 0;
 466
 467         mutex_lock(&markers_mutex);
 468         entry = get_marker(name);
 469         if (!entry) {
 470                 ret = -ENOENT;
 471                 goto end;
 472         }
 473         /*
 474          * Only permit decrement refcount if higher than 0.
 475          * Do probe update only on 1 -> 0 transition.
 476          */
 477         if (entry->refcount) {
 478                 if (--entry->refcount)
 479                         goto end;
 480         } else {
 481                 ret = -EPERM;
 482                 goto end;
 483         }
 484 end:
 485         mutex_unlock(&markers_mutex);
 486         marker_update_probes(NULL);
 487         return ret;
 488 }
 489 EXPORT_SYMBOL_GPL(marker_disarm);
 490
 491 /**
 492  * marker_get_private_data - Get a marker's probe private data
 493  * @name: marker name
 494  *
 495  * Returns the private data pointer, or an ERR_PTR.
 496  * The private data pointer should _only_ be dereferenced if the caller is the
 497  * owner of the data, or its content could vanish. This is mostly used to
 498  * confirm that a caller is the owner of a registered probe.
 499  */
 500 void *marker_get_private_data(const char *name)
 501 {
 502         struct hlist_head *head;
 503         struct hlist_node *node;
 504         struct marker_entry *e;
 505         size_t name_len = strlen(name) + 1;
 506         u32 hash = jhash(name, name_len-1, 0);
 507         int found = 0;
 508
 509         head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
 510         hlist_for_each_entry(e, node, head, hlist) {
 511                 if (!strcmp(name, e->name)) {
 512                         found = 1;
 513                         return e->private;
 514                 }
 515         }
 516         return ERR_PTR(-ENOENT);
 517 }
 518 EXPORT_SYMBOL_GPL(marker_get_private_data);