lttng-tracepoint.c

   1 /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1)
   2  *
   3  * lttng-tracepoint.c
   4  *
   5  * LTTng adaptation layer for Linux kernel 3.15+ tracepoints.
   6  *
   7  * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  */
   9
  10 #include <linux/mutex.h>
  11 #include <linux/err.h>
  12 #include <linux/notifier.h>
  13 #include <linux/tracepoint.h>
  14 #include <linux/slab.h>
  15 #include <linux/jhash.h>
  16 #include <linux/module.h>
  17
  18 #include <lttng-tracepoint.h>
  19 #include <wrapper/list.h>
  20 #include <wrapper/tracepoint.h>
  21
  22 /*
  23  * Protect the tracepoint table. lttng_tracepoint_mutex nests within
  24  * kernel/tracepoint.c tp_modlist_mutex. kernel/tracepoint.c
  25  * tracepoint_mutex nests within lttng_tracepoint_mutex.
  26  */
  27 static
  28 DEFINE_MUTEX(lttng_tracepoint_mutex);
  29
  30 #define TRACEPOINT_HASH_BITS 6
  31 #define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
  32 static
  33 struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
  34
  35 /*
  36  * The tracepoint entry is the node contained within the hash table. It
  37  * is a mapping from the "string" key to the struct tracepoint pointer.
  38  */
  39 struct tracepoint_entry {
  40         struct hlist_node hlist;
  41         struct tracepoint *tp;
  42         int refcount;
  43         struct list_head probes;
  44         char name[0];
  45 };
  46
  47 struct lttng_tp_probe {
  48         struct tracepoint_func tp_func;
  49         struct list_head list;
  50 };
  51
  52 static
  53 int add_probe(struct tracepoint_entry *e, void *probe, void *data)
  54 {
  55         struct lttng_tp_probe *p;
  56         int found = 0;
  57
  58         list_for_each_entry(p, &e->probes, list) {
  59                 if (p->tp_func.func == probe && p->tp_func.data == data) {
  60                         found = 1;
  61                         break;
  62                 }
  63         }
  64         if (found)
  65                 return -EEXIST;
  66         p = kmalloc(sizeof(struct lttng_tp_probe), GFP_KERNEL);
  67         if (!p)
  68                 return -ENOMEM;
  69         p->tp_func.func = probe;
  70         p->tp_func.data = data;
  71         list_add(&p->list, &e->probes);
  72         return 0;
  73 }
  74
  75 static
  76 int remove_probe(struct tracepoint_entry *e, void *probe, void *data)
  77 {
  78         struct lttng_tp_probe *p;
  79         int found = 0;
  80
  81         list_for_each_entry(p, &e->probes, list) {
  82                 if (p->tp_func.func == probe && p->tp_func.data == data) {
  83                         found = 1;
  84                         break;
  85                 }
  86         }
  87         if (found) {
  88                 list_del(&p->list);
  89                 kfree(p);
  90                 return 0;
  91         } else {
  92                 WARN_ON(1);
  93                 return -ENOENT;
  94         }
  95 }
  96
  97 /*
  98  * Get tracepoint if the tracepoint is present in the tracepoint hash table.
  99  * Must be called with lttng_tracepoint_mutex held.
 100  * Returns NULL if not present.
 101  */
 102 static
 103 struct tracepoint_entry *get_tracepoint(const char *name)
 104 {
 105         struct hlist_head *head;
 106         struct tracepoint_entry *e;
 107         u32 hash = jhash(name, strlen(name), 0);
 108
 109         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 110         lttng_hlist_for_each_entry(e, head, hlist) {
 111                 if (!strcmp(name, e->name))
 112                         return e;
 113         }
 114         return NULL;
 115 }
 116
 117 /*
 118  * Add the tracepoint to the tracepoint hash table. Must be called with
 119  * lttng_tracepoint_mutex held.
 120  */
 121 static
 122 struct tracepoint_entry *add_tracepoint(const char *name)
 123 {
 124         struct hlist_head *head;
 125         struct tracepoint_entry *e;
 126         size_t name_len = strlen(name) + 1;
 127         u32 hash = jhash(name, name_len - 1, 0);
 128
 129         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
 130         lttng_hlist_for_each_entry(e, head, hlist) {
 131                 if (!strcmp(name, e->name)) {
 132                         printk(KERN_NOTICE
 133                                 "tracepoint %s busy\n", name);
 134                         return ERR_PTR(-EEXIST);        /* Already there */
 135                 }
 136         }
 137         /*
 138          * Using kmalloc here to allocate a variable length element. Could
 139          * cause some memory fragmentation if overused.
 140          */
 141         e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
 142         if (!e)
 143                 return ERR_PTR(-ENOMEM);
 144         memcpy(&e->name[0], name, name_len);
 145         e->tp = NULL;
 146         e->refcount = 0;
 147         INIT_LIST_HEAD(&e->probes);
 148         hlist_add_head(&e->hlist, head);
 149         return e;
 150 }
 151
 152 /*
 153  * Remove the tracepoint from the tracepoint hash table. Must be called
 154  * with lttng_tracepoint_mutex held.
 155  */
 156 static
 157 void remove_tracepoint(struct tracepoint_entry *e)
 158 {
 159         hlist_del(&e->hlist);
 160         kfree(e);
 161 }
 162
 163 int lttng_tracepoint_probe_register(const char *name, void *probe, void *data)
 164 {
 165         struct tracepoint_entry *e;
 166         int ret = 0;
 167
 168         mutex_lock(&lttng_tracepoint_mutex);
 169         e = get_tracepoint(name);
 170         if (!e) {
 171                 e = add_tracepoint(name);
 172                 if (IS_ERR(e)) {
 173                         ret = PTR_ERR(e);
 174                         goto end;
 175                 }
 176         }
 177         /* add (probe, data) to entry */
 178         ret = add_probe(e, probe, data);
 179         if (ret)
 180                 goto end;
 181         e->refcount++;
 182         if (e->tp) {
 183                 ret = tracepoint_probe_register(e->tp, probe, data);
 184                 WARN_ON_ONCE(ret);
 185                 ret = 0;
 186         }
 187 end:
 188         mutex_unlock(&lttng_tracepoint_mutex);
 189         return ret;
 190 }
 191
 192 int lttng_tracepoint_probe_unregister(const char *name, void *probe, void *data)
 193 {
 194         struct tracepoint_entry *e;
 195         int ret = 0;
 196
 197         mutex_lock(&lttng_tracepoint_mutex);
 198         e = get_tracepoint(name);
 199         if (!e) {
 200                 ret = -ENOENT;
 201                 goto end;
 202         }
 203         /* remove (probe, data) from entry */
 204         ret = remove_probe(e, probe, data);
 205         if (ret)
 206                 goto end;
 207         if (e->tp) {
 208                 ret = tracepoint_probe_unregister(e->tp, probe, data);
 209                 WARN_ON_ONCE(ret);
 210                 ret = 0;
 211         }
 212         if (!--e->refcount)
 213                 remove_tracepoint(e);
 214 end:
 215         mutex_unlock(&lttng_tracepoint_mutex);
 216         return ret;
 217 }
 218
 219 #ifdef CONFIG_MODULES
 220
 221 static
 222 int lttng_tracepoint_coming(struct tp_module *tp_mod)
 223 {
 224         int i;
 225
 226         mutex_lock(&lttng_tracepoint_mutex);
 227         for (i = 0; i < tp_mod->mod->num_tracepoints; i++) {
 228                 struct tracepoint *tp;
 229                 struct tracepoint_entry *e;
 230                 struct lttng_tp_probe *p;
 231
 232                 tp = lttng_tracepoint_ptr_deref(&tp_mod->mod->tracepoints_ptrs[i]);
 233                 e = get_tracepoint(tp->name);
 234                 if (!e) {
 235                         e = add_tracepoint(tp->name);
 236                         if (IS_ERR(e)) {
 237                                 pr_warn("LTTng: error (%ld) adding tracepoint\n",
 238                                         PTR_ERR(e));
 239                                 continue;
 240                         }
 241                 }
 242                 /* If already enabled, just check consistency */
 243                 if (e->tp) {
 244                         WARN_ON(e->tp != tp);
 245                         continue;
 246                 }
 247                 e->tp = tp;
 248                 e->refcount++;
 249                 /* register each (probe, data) */
 250                 list_for_each_entry(p, &e->probes, list) {
 251                         int ret;
 252
 253                         ret = tracepoint_probe_register(e->tp,
 254                                         p->tp_func.func, p->tp_func.data);
 255                         WARN_ON_ONCE(ret);
 256                 }
 257         }
 258         mutex_unlock(&lttng_tracepoint_mutex);
 259         return NOTIFY_OK;
 260 }
 261
 262 static
 263 int lttng_tracepoint_going(struct tp_module *tp_mod)
 264 {
 265         int i;
 266
 267         mutex_lock(&lttng_tracepoint_mutex);
 268         for (i = 0; i < tp_mod->mod->num_tracepoints; i++) {
 269                 struct tracepoint *tp;
 270                 struct tracepoint_entry *e;
 271                 struct lttng_tp_probe *p;
 272
 273                 tp = lttng_tracepoint_ptr_deref(&tp_mod->mod->tracepoints_ptrs[i]);
 274                 e = get_tracepoint(tp->name);
 275                 if (!e || !e->tp)
 276                         continue;
 277                 /* unregister each (probe, data) */
 278                 list_for_each_entry(p, &e->probes, list) {
 279                         int ret;
 280
 281                         ret = tracepoint_probe_unregister(e->tp,
 282                                         p->tp_func.func, p->tp_func.data);
 283                         WARN_ON_ONCE(ret);
 284                 }
 285                 e->tp = NULL;
 286                 if (!--e->refcount)
 287                         remove_tracepoint(e);
 288         }
 289         mutex_unlock(&lttng_tracepoint_mutex);
 290         return 0;
 291 }
 292
 293 static
 294 int lttng_tracepoint_notify(struct notifier_block *self,
 295                 unsigned long val, void *data)
 296 {
 297         struct tp_module *tp_mod = data;
 298         int ret = 0;
 299
 300         switch (val) {
 301         case MODULE_STATE_COMING:
 302                 ret = lttng_tracepoint_coming(tp_mod);
 303                 break;
 304         case MODULE_STATE_GOING:
 305                 ret = lttng_tracepoint_going(tp_mod);
 306                 break;
 307         default:
 308                 break;
 309         }
 310         return ret;
 311 }
 312
 313 static
 314 struct notifier_block lttng_tracepoint_notifier = {
 315         .notifier_call = lttng_tracepoint_notify,
 316         .priority = 0,
 317 };
 318
 319 static
 320 int lttng_tracepoint_module_init(void)
 321 {
 322         return register_tracepoint_module_notifier(&lttng_tracepoint_notifier);
 323 }
 324
 325 static
 326 void lttng_tracepoint_module_exit(void)
 327 {
 328         WARN_ON(unregister_tracepoint_module_notifier(&lttng_tracepoint_notifier));
 329 }
 330
 331 #else /* #ifdef CONFIG_MODULES */
 332
 333 static
 334 int lttng_tracepoint_module_init(void)
 335 {
 336         return 0;
 337 }
 338
 339 static
 340 void lttng_tracepoint_module_exit(void)
 341 {
 342 }
 343
 344 #endif /* #else #ifdef CONFIG_MODULES */
 345
 346 static
 347 void lttng_kernel_tracepoint_add(struct tracepoint *tp, void *priv)
 348 {
 349         struct tracepoint_entry *e;
 350         struct lttng_tp_probe *p;
 351         int *ret = priv;
 352
 353         mutex_lock(&lttng_tracepoint_mutex);
 354         e = get_tracepoint(tp->name);
 355         if (!e) {
 356                 e = add_tracepoint(tp->name);
 357                 if (IS_ERR(e)) {
 358                         pr_warn("LTTng: error (%ld) adding tracepoint\n",
 359                                 PTR_ERR(e));
 360                         *ret = (int) PTR_ERR(e);
 361                         goto end;
 362                 }
 363         }
 364         /* If already enabled, just check consistency */
 365         if (e->tp) {
 366                 WARN_ON(e->tp != tp);
 367                 goto end;
 368         }
 369         e->tp = tp;
 370         e->refcount++;
 371         /* register each (probe, data) */
 372         list_for_each_entry(p, &e->probes, list) {
 373                 int ret;
 374
 375                 ret = tracepoint_probe_register(e->tp,
 376                                 p->tp_func.func, p->tp_func.data);
 377                 WARN_ON_ONCE(ret);
 378         }
 379 end:
 380         mutex_unlock(&lttng_tracepoint_mutex);
 381 }
 382
 383 static
 384 void lttng_kernel_tracepoint_remove(struct tracepoint *tp, void *priv)
 385 {
 386         struct tracepoint_entry *e;
 387         int *ret = priv;
 388
 389         mutex_lock(&lttng_tracepoint_mutex);
 390         e = get_tracepoint(tp->name);
 391         if (!e || e->refcount != 1 || !list_empty(&e->probes)) {
 392                 *ret = -EINVAL;
 393                 goto end;
 394         }
 395         remove_tracepoint(e);
 396 end:
 397         mutex_unlock(&lttng_tracepoint_mutex);
 398 }
 399
 400 int __init lttng_tracepoint_init(void)
 401 {
 402         int ret = 0;
 403
 404         for_each_kernel_tracepoint(lttng_kernel_tracepoint_add, &ret);
 405         if (ret)
 406                 goto error;
 407         ret = lttng_tracepoint_module_init();
 408         if (ret)
 409                 goto error_module;
 410         return 0;
 411
 412 error_module:
 413         {
 414                 int error_ret = 0;
 415
 416                 for_each_kernel_tracepoint(lttng_kernel_tracepoint_remove,
 417                                 &error_ret);
 418                 WARN_ON(error_ret);
 419         }
 420 error:
 421         return ret;
 422 }
 423
 424 void lttng_tracepoint_exit(void)
 425 {
 426         int i, ret = 0;
 427
 428         lttng_tracepoint_module_exit();
 429         for_each_kernel_tracepoint(lttng_kernel_tracepoint_remove, &ret);
 430         WARN_ON(ret);
 431         mutex_lock(&lttng_tracepoint_mutex);
 432         for (i = 0; i < TRACEPOINT_TABLE_SIZE; i++) {
 433                 struct hlist_head *head = &tracepoint_table[i];
 434
 435                 /* All tracepoints should be removed */
 436                 WARN_ON(!hlist_empty(head));
 437         }
 438         mutex_unlock(&lttng_tracepoint_mutex);
 439 }