src/side.c

   1 // SPDX-License-Identifier: MIT
   2 /*
   3  * Copyright 2022 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   4  */
   5
   6 #include <side/trace.h>
   7 #include <string.h>
   8 #include <assert.h>
   9 #include <pthread.h>
  10 #include <unistd.h>
  11 #include <poll.h>
  12
  13 #include "compiler.h"
  14 #include "rcu.h"
  15 #include "list.h"
  16 #include "rculist.h"
  17
  18 /* Top 8 bits reserved for shared tracer use. */
  19 #if SIDE_BITS_PER_LONG == 64
  20 # define SIDE_EVENT_ENABLED_SHARED_MASK                 0xFF00000000000000ULL
  21 # define SIDE_EVENT_ENABLED_SHARED_USER_EVENT_MASK      0x8000000000000000ULL
  22 # define SIDE_EVENT_ENABLED_SHARED_PTRACE_MASK          0x4000000000000000ULL
  23
  24 /* Allow 2^56 private tracer references on an event. */
  25 # define SIDE_EVENT_ENABLED_PRIVATE_MASK                0x00FFFFFFFFFFFFFFULL
  26 #else
  27 # define SIDE_EVENT_ENABLED_SHARED_MASK                 0xFF000000UL
  28 # define SIDE_EVENT_ENABLED_SHARED_USER_EVENT_MASK      0x80000000UL
  29 # define SIDE_EVENT_ENABLED_SHARED_PTRACE_MASK          0x40000000UL
  30
  31 /* Allow 2^24 private tracer references on an event. */
  32 # define SIDE_EVENT_ENABLED_PRIVATE_MASK                0x00FFFFFFUL
  33 #endif
  34
  35 #define SIDE_KEY_RESERVED_RANGE_END                     0x8
  36
  37 /* Key 0x0 is reserved to match all. */
  38 #define SIDE_KEY_MATCH_ALL                              0x0
  39 /* Key 0x1 is reserved for user event. */
  40 #define SIDE_KEY_USER_EVENT                             0x1
  41 /* Key 0x2 is reserved for ptrace. */
  42 #define SIDE_KEY_PTRACE                                 0x2
  43
  44 #define SIDE_RETRY_BUSY_LOOP_ATTEMPTS                   100
  45 #define SIDE_RETRY_DELAY_MS                             1
  46
  47 struct side_events_register_handle {
  48         struct side_list_node node;
  49         struct side_event_description **events;
  50         uint32_t nr_events;
  51 };
  52
  53 struct side_tracer_handle {
  54         struct side_list_node node;
  55         void (*cb)(enum side_tracer_notification notif,
  56                 struct side_event_description **events, uint32_t nr_events, void *priv);
  57         void *priv;
  58 };
  59
  60 struct side_statedump_notification {
  61         struct side_list_node node;
  62         uint64_t key;
  63 };
  64
  65 struct side_statedump_request_handle {
  66         struct side_list_node node;                     /* Statedump request RCU list node. */
  67         struct side_list_head notification_queue;       /* Queue of struct side_statedump_notification */
  68         void (*cb)(void *statedump_request_key);
  69         char *name;
  70         enum side_statedump_mode mode;
  71 };
  72
  73 struct side_callback {
  74         union {
  75                 void (*call)(const struct side_event_description *desc,
  76                         const struct side_arg_vec *side_arg_vec,
  77                         void *priv, void *caller_addr);
  78                 void (*call_variadic)(const struct side_event_description *desc,
  79                         const struct side_arg_vec *side_arg_vec,
  80                         const struct side_arg_dynamic_struct *var_struct,
  81                         void *priv, void *caller_addr);
  82         } u;
  83         void *priv;
  84         uint64_t key;
  85 };
  86
  87 enum agent_thread_state {
  88         AGENT_THREAD_STATE_BLOCKED = 0,
  89         AGENT_THREAD_STATE_HANDLE_REQUEST = (1 << 0),
  90         AGENT_THREAD_STATE_EXIT = (1 << 1),
  91         AGENT_THREAD_STATE_PAUSE = (1 << 2),
  92         AGENT_THREAD_STATE_PAUSE_ACK = (1 << 3),
  93 };
  94
  95 struct statedump_agent_thread {
  96         long ref;
  97         pthread_t id;
  98         enum agent_thread_state state;
  99         pthread_cond_t worker_cond;
 100         pthread_cond_t waiter_cond;
 101 };
 102
 103 static struct side_rcu_gp_state event_rcu_gp, statedump_rcu_gp;
 104
 105 /*
 106  * Lazy initialization for early use within library constructors.
 107  */
 108 static bool initialized;
 109 /*
 110  * Do not register/unregister any more events after destructor.
 111  */
 112 static bool finalized;
 113
 114 /*
 115  * Recursive mutex to allow tracer callbacks to use the side API.
 116  */
 117 static pthread_mutex_t side_event_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
 118 static pthread_mutex_t side_statedump_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
 119 static pthread_mutex_t side_key_lock = PTHREAD_MUTEX_INITIALIZER;
 120 /*
 121  * The side_agent_thread_lock protects the life-time of the agent
 122  * thread: reference counting, creation, join. It is not taken by
 123  * the agent thread per se so it does not have a circular dependency
 124  * with pthread join.
 125  * The side_statedump_lock nests inside the side_agent_thread_lock.
 126  */
 127 static pthread_mutex_t side_agent_thread_lock = PTHREAD_MUTEX_INITIALIZER;
 128
 129 /* Dynamic tracer key allocation. */
 130 static uint64_t side_key_next = SIDE_KEY_RESERVED_RANGE_END;
 131
 132 static struct statedump_agent_thread statedump_agent_thread;
 133
 134 static DEFINE_SIDE_LIST_HEAD(side_events_list);
 135 static DEFINE_SIDE_LIST_HEAD(side_tracer_list);
 136
 137 /*
 138  * The statedump request list is a RCU list to allow the agent thread to
 139  * iterate over this list with a RCU read-side lock.
 140  */
 141 static DEFINE_SIDE_LIST_HEAD(side_statedump_list);
 142
 143 /*
 144  * The empty callback has a NULL function callback pointer, which stops
 145  * iteration on the array of callbacks immediately.
 146  */
 147 const char side_empty_callback[sizeof(struct side_callback)];
 148
 149 side_static_event(side_statedump_begin, "side", "statedump_begin",
 150         SIDE_LOGLEVEL_INFO, side_field_list(side_field_string("name")));
 151 side_static_event(side_statedump_end, "side", "statedump_end",
 152         SIDE_LOGLEVEL_INFO, side_field_list(side_field_string("name")));
 153
 154 /*
 155  * side_ptrace_hook is a place holder for a debugger breakpoint.
 156  * var_struct is NULL if not variadic.
 157  */
 158 void side_ptrace_hook(const struct side_event_state *event_state __attribute__((unused)),
 159                 const struct side_arg_vec *side_arg_vec __attribute__((unused)),
 160                 const struct side_arg_dynamic_struct *var_struct __attribute__((unused)),
 161                 void *caller_addr __attribute__((unused)))
 162                 __attribute__((noinline));
 163 void side_ptrace_hook(const struct side_event_state *event_state __attribute__((unused)),
 164                 const struct side_arg_vec *side_arg_vec __attribute__((unused)),
 165                 const struct side_arg_dynamic_struct *var_struct __attribute__((unused)),
 166                 void *caller_addr __attribute__((unused)))
 167 {
 168 }
 169
 170 static inline __attribute__((always_inline))
 171 void _side_call(const struct side_event_state *event_state, const struct side_arg_vec *side_arg_vec, uint64_t key)
 172 {
 173         void *caller_addr = __builtin_return_address(0);
 174         struct side_rcu_read_state rcu_read_state;
 175         const struct side_event_state_0 *es0;
 176         const struct side_callback *side_cb;
 177         uintptr_t enabled;
 178
 179         if (side_unlikely(finalized))
 180                 return;
 181         if (side_unlikely(!initialized))
 182                 side_init();
 183         if (side_unlikely(event_state->version != 0))
 184                 abort();
 185         es0 = side_container_of(event_state, const struct side_event_state_0, parent);
 186         assert(!(es0->desc->flags & SIDE_EVENT_FLAG_VARIADIC));
 187         enabled = __atomic_load_n(&es0->enabled, __ATOMIC_RELAXED);
 188         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_SHARED_MASK)) {
 189                 if ((enabled & SIDE_EVENT_ENABLED_SHARED_USER_EVENT_MASK) &&
 190                     (key == SIDE_KEY_MATCH_ALL || key == SIDE_KEY_USER_EVENT)) {
 191                         // TODO: call kernel write.
 192                 }
 193                 if ((enabled & SIDE_EVENT_ENABLED_SHARED_PTRACE_MASK) &&
 194                     (key == SIDE_KEY_MATCH_ALL || key == SIDE_KEY_PTRACE))
 195                         side_ptrace_hook(event_state, side_arg_vec, NULL, caller_addr);
 196         }
 197         side_rcu_read_begin(&event_rcu_gp, &rcu_read_state);
 198         for (side_cb = side_rcu_dereference(es0->callbacks); side_cb->u.call != NULL; side_cb++) {
 199                 if (key != SIDE_KEY_MATCH_ALL && side_cb->key != SIDE_KEY_MATCH_ALL && side_cb->key != key)
 200                         continue;
 201                 side_cb->u.call(es0->desc, side_arg_vec, side_cb->priv, caller_addr);
 202         }
 203         side_rcu_read_end(&event_rcu_gp, &rcu_read_state);
 204 }
 205
 206 void side_call(const struct side_event_state *event_state, const struct side_arg_vec *side_arg_vec)
 207 {
 208         _side_call(event_state, side_arg_vec, SIDE_KEY_MATCH_ALL);
 209 }
 210
 211 void side_statedump_call(const struct side_event_state *event_state,
 212                 const struct side_arg_vec *side_arg_vec,
 213                 void *statedump_request_key)
 214 {
 215         _side_call(event_state, side_arg_vec, *(const uint64_t *) statedump_request_key);
 216 }
 217
 218 static inline __attribute__((always_inline))
 219 void _side_call_variadic(const struct side_event_state *event_state,
 220                 const struct side_arg_vec *side_arg_vec,
 221                 const struct side_arg_dynamic_struct *var_struct,
 222                 uint64_t key)
 223 {
 224         void *caller_addr = __builtin_return_address(0);
 225         struct side_rcu_read_state rcu_read_state;
 226         const struct side_event_state_0 *es0;
 227         const struct side_callback *side_cb;
 228         uintptr_t enabled;
 229
 230         if (side_unlikely(finalized))
 231                 return;
 232         if (side_unlikely(!initialized))
 233                 side_init();
 234         if (side_unlikely(event_state->version != 0))
 235                 abort();
 236         es0 = side_container_of(event_state, const struct side_event_state_0, parent);
 237         assert(es0->desc->flags & SIDE_EVENT_FLAG_VARIADIC);
 238         enabled = __atomic_load_n(&es0->enabled, __ATOMIC_RELAXED);
 239         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_SHARED_MASK)) {
 240                 if ((enabled & SIDE_EVENT_ENABLED_SHARED_USER_EVENT_MASK) &&
 241                     (key == SIDE_KEY_MATCH_ALL || key == SIDE_KEY_USER_EVENT)) {
 242                         // TODO: call kernel write.
 243                 }
 244                 if ((enabled & SIDE_EVENT_ENABLED_SHARED_PTRACE_MASK) &&
 245                     (key == SIDE_KEY_MATCH_ALL || key == SIDE_KEY_PTRACE))
 246                         side_ptrace_hook(event_state, side_arg_vec, var_struct, caller_addr);
 247         }
 248         side_rcu_read_begin(&event_rcu_gp, &rcu_read_state);
 249         for (side_cb = side_rcu_dereference(es0->callbacks); side_cb->u.call_variadic != NULL; side_cb++) {
 250                 if (key != SIDE_KEY_MATCH_ALL && side_cb->key != SIDE_KEY_MATCH_ALL && side_cb->key != key)
 251                         continue;
 252                 side_cb->u.call_variadic(es0->desc, side_arg_vec, var_struct, side_cb->priv, caller_addr);
 253         }
 254         side_rcu_read_end(&event_rcu_gp, &rcu_read_state);
 255 }
 256
 257 void side_call_variadic(const struct side_event_state *event_state,
 258                 const struct side_arg_vec *side_arg_vec,
 259                 const struct side_arg_dynamic_struct *var_struct)
 260 {
 261         _side_call_variadic(event_state, side_arg_vec, var_struct, SIDE_KEY_MATCH_ALL);
 262 }
 263
 264 void side_statedump_call_variadic(const struct side_event_state *event_state,
 265                 const struct side_arg_vec *side_arg_vec,
 266                 const struct side_arg_dynamic_struct *var_struct,
 267                 void *statedump_request_key)
 268 {
 269         _side_call_variadic(event_state, side_arg_vec, var_struct, *(const uint64_t *) statedump_request_key);
 270 }
 271
 272 static
 273 const struct side_callback *side_tracer_callback_lookup(
 274                 const struct side_event_description *desc,
 275                 void *call, void *priv, uint64_t key)
 276 {
 277         struct side_event_state *event_state = side_ptr_get(desc->state);
 278         const struct side_event_state_0 *es0;
 279         const struct side_callback *cb;
 280
 281         if (side_unlikely(event_state->version != 0))
 282                 abort();
 283         es0 = side_container_of(event_state, const struct side_event_state_0, parent);
 284         for (cb = es0->callbacks; cb->u.call != NULL; cb++) {
 285                 if ((void *) cb->u.call == call && cb->priv == priv && cb->key == key)
 286                         return cb;
 287         }
 288         return NULL;
 289 }
 290
 291 static
 292 int _side_tracer_callback_register(struct side_event_description *desc,
 293                 void *call, void *priv, uint64_t key)
 294 {
 295         struct side_event_state *event_state;
 296         struct side_callback *old_cb, *new_cb;
 297         struct side_event_state_0 *es0;
 298         int ret = SIDE_ERROR_OK;
 299         uint32_t old_nr_cb;
 300
 301         if (!call)
 302                 return SIDE_ERROR_INVAL;
 303         if (finalized)
 304                 return SIDE_ERROR_EXITING;
 305         if (!initialized)
 306                 side_init();
 307         pthread_mutex_lock(&side_event_lock);
 308         event_state = side_ptr_get(desc->state);
 309         if (side_unlikely(event_state->version != 0))
 310                 abort();
 311         es0 = side_container_of(event_state, struct side_event_state_0, parent);
 312         old_nr_cb = es0->nr_callbacks;
 313         if (old_nr_cb == UINT32_MAX) {
 314                 ret = SIDE_ERROR_INVAL;
 315                 goto unlock;
 316         }
 317         /* Reject duplicate (call, priv) tuples. */
 318         if (side_tracer_callback_lookup(desc, call, priv, key)) {
 319                 ret = SIDE_ERROR_EXIST;
 320                 goto unlock;
 321         }
 322         old_cb = (struct side_callback *) es0->callbacks;
 323         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 324         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 325         if (!new_cb) {
 326                 ret = SIDE_ERROR_NOMEM;
 327                 goto unlock;
 328         }
 329         memcpy(new_cb, old_cb, old_nr_cb);
 330         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 331                 new_cb[old_nr_cb].u.call_variadic =
 332                         (side_tracer_callback_variadic_func) call;
 333         else
 334                 new_cb[old_nr_cb].u.call =
 335                         (side_tracer_callback_func) call;
 336         new_cb[old_nr_cb].priv = priv;
 337         new_cb[old_nr_cb].key = key;
 338         /* High order bits are already zeroed. */
 339         side_rcu_assign_pointer(es0->callbacks, new_cb);
 340         side_rcu_wait_grace_period(&event_rcu_gp);
 341         if (old_nr_cb)
 342                 free(old_cb);
 343         es0->nr_callbacks++;
 344         /* Increment concurrently with kernel setting the top bits. */
 345         if (!old_nr_cb)
 346                 (void) __atomic_add_fetch(&es0->enabled, 1, __ATOMIC_RELAXED);
 347 unlock:
 348         pthread_mutex_unlock(&side_event_lock);
 349         return ret;
 350 }
 351
 352 int side_tracer_callback_register(struct side_event_description *desc,
 353                 side_tracer_callback_func call,
 354                 void *priv, uint64_t key)
 355 {
 356         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 357                 return SIDE_ERROR_INVAL;
 358         return _side_tracer_callback_register(desc, (void *) call, priv, key);
 359 }
 360
 361 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 362                 side_tracer_callback_variadic_func call_variadic,
 363                 void *priv, uint64_t key)
 364 {
 365         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 366                 return SIDE_ERROR_INVAL;
 367         return _side_tracer_callback_register(desc, (void *) call_variadic, priv, key);
 368 }
 369
 370 static int _side_tracer_callback_unregister(struct side_event_description *desc,
 371                 void *call, void *priv, uint64_t key)
 372 {
 373         struct side_event_state *event_state;
 374         struct side_callback *old_cb, *new_cb;
 375         const struct side_callback *cb_pos;
 376         struct side_event_state_0 *es0;
 377         uint32_t pos_idx;
 378         int ret = SIDE_ERROR_OK;
 379         uint32_t old_nr_cb;
 380
 381         if (!call)
 382                 return SIDE_ERROR_INVAL;
 383         if (finalized)
 384                 return SIDE_ERROR_EXITING;
 385         if (!initialized)
 386                 side_init();
 387         pthread_mutex_lock(&side_event_lock);
 388         event_state = side_ptr_get(desc->state);
 389         if (side_unlikely(event_state->version != 0))
 390                 abort();
 391         es0 = side_container_of(event_state, struct side_event_state_0, parent);
 392         cb_pos = side_tracer_callback_lookup(desc, call, priv, key);
 393         if (!cb_pos) {
 394                 ret = SIDE_ERROR_NOENT;
 395                 goto unlock;
 396         }
 397         old_nr_cb = es0->nr_callbacks;
 398         old_cb = (struct side_callback *) es0->callbacks;
 399         if (old_nr_cb == 1) {
 400                 new_cb = (struct side_callback *) &side_empty_callback;
 401         } else {
 402                 pos_idx = cb_pos - es0->callbacks;
 403                 /* Remove entry at pos_idx. */
 404                 /* old_nr_cb - 1 (removed cb) + 1 (NULL) */
 405                 new_cb = (struct side_callback *) calloc(old_nr_cb, sizeof(struct side_callback));
 406                 if (!new_cb) {
 407                         ret = SIDE_ERROR_NOMEM;
 408                         goto unlock;
 409                 }
 410                 memcpy(new_cb, old_cb, pos_idx);
 411                 memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
 412         }
 413         /* High order bits are already zeroed. */
 414         side_rcu_assign_pointer(es0->callbacks, new_cb);
 415         side_rcu_wait_grace_period(&event_rcu_gp);
 416         free(old_cb);
 417         es0->nr_callbacks--;
 418         /* Decrement concurrently with kernel setting the top bits. */
 419         if (old_nr_cb == 1)
 420                 (void) __atomic_add_fetch(&es0->enabled, -1, __ATOMIC_RELAXED);
 421 unlock:
 422         pthread_mutex_unlock(&side_event_lock);
 423         return ret;
 424 }
 425
 426 int side_tracer_callback_unregister(struct side_event_description *desc,
 427                 side_tracer_callback_func call,
 428                 void *priv, uint64_t key)
 429 {
 430         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 431                 return SIDE_ERROR_INVAL;
 432         return _side_tracer_callback_unregister(desc, (void *) call, priv, key);
 433 }
 434
 435 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 436                 side_tracer_callback_variadic_func call_variadic,
 437                 void *priv, uint64_t key)
 438 {
 439         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 440                 return SIDE_ERROR_INVAL;
 441         return _side_tracer_callback_unregister(desc, (void *) call_variadic, priv, key);
 442 }
 443
 444 struct side_events_register_handle *side_events_register(struct side_event_description **events, uint32_t nr_events)
 445 {
 446         struct side_events_register_handle *events_handle = NULL;
 447         struct side_tracer_handle *tracer_handle;
 448
 449         if (finalized)
 450                 return NULL;
 451         if (!initialized)
 452                 side_init();
 453         events_handle = (struct side_events_register_handle *)
 454                         calloc(1, sizeof(struct side_events_register_handle));
 455         if (!events_handle)
 456                 return NULL;
 457         events_handle->events = events;
 458         events_handle->nr_events = nr_events;
 459
 460         pthread_mutex_lock(&side_event_lock);
 461         side_list_insert_node_tail(&side_events_list, &events_handle->node);
 462         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 463                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 464                         events, nr_events, tracer_handle->priv);
 465         }
 466         pthread_mutex_unlock(&side_event_lock);
 467         //TODO: call event batch register ioctl
 468         return events_handle;
 469 }
 470
 471 static
 472 void side_event_remove_callbacks(struct side_event_description *desc)
 473 {
 474         struct side_event_state *event_state = side_ptr_get(desc->state);
 475         struct side_event_state_0 *es0;
 476         struct side_callback *old_cb;
 477         uint32_t nr_cb;
 478
 479         if (side_unlikely(event_state->version != 0))
 480                 abort();
 481         es0 = side_container_of(event_state, struct side_event_state_0, parent);
 482         nr_cb = es0->nr_callbacks;
 483         if (!nr_cb)
 484                 return;
 485         old_cb = (struct side_callback *) es0->callbacks;
 486         (void) __atomic_add_fetch(&es0->enabled, -1, __ATOMIC_RELAXED);
 487         /*
 488          * Setting the state back to 0 cb and empty callbacks out of
 489          * caution. This should not matter because instrumentation is
 490          * unreachable.
 491          */
 492         es0->nr_callbacks = 0;
 493         side_rcu_assign_pointer(es0->callbacks, &side_empty_callback);
 494         /*
 495          * No need to wait for grace period because instrumentation is
 496          * unreachable.
 497          */
 498         free(old_cb);
 499 }
 500
 501 /*
 502  * Unregister event handle. At this point, all side events in that
 503  * handle should be unreachable.
 504  */
 505 void side_events_unregister(struct side_events_register_handle *events_handle)
 506 {
 507         struct side_tracer_handle *tracer_handle;
 508         uint32_t i;
 509
 510         if (!events_handle)
 511                 return;
 512         if (finalized)
 513                 return;
 514         if (!initialized)
 515                 side_init();
 516         pthread_mutex_lock(&side_event_lock);
 517         side_list_remove_node(&events_handle->node);
 518         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 519                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 520                         events_handle->events, events_handle->nr_events,
 521                         tracer_handle->priv);
 522         }
 523         for (i = 0; i < events_handle->nr_events; i++) {
 524                 struct side_event_description *event = events_handle->events[i];
 525
 526                 /* Skip NULL pointers */
 527                 if (!event)
 528                         continue;
 529                 side_event_remove_callbacks(event);
 530         }
 531         pthread_mutex_unlock(&side_event_lock);
 532         //TODO: call event batch unregister ioctl
 533         free(events_handle);
 534 }
 535
 536 struct side_tracer_handle *side_tracer_event_notification_register(
 537                 void (*cb)(enum side_tracer_notification notif,
 538                         struct side_event_description **events, uint32_t nr_events, void *priv),
 539                 void *priv)
 540 {
 541         struct side_tracer_handle *tracer_handle;
 542         struct side_events_register_handle *events_handle;
 543
 544         if (finalized)
 545                 return NULL;
 546         if (!initialized)
 547                 side_init();
 548         tracer_handle = (struct side_tracer_handle *)
 549                                 calloc(1, sizeof(struct side_tracer_handle));
 550         if (!tracer_handle)
 551                 return NULL;
 552         pthread_mutex_lock(&side_event_lock);
 553         tracer_handle->cb = cb;
 554         tracer_handle->priv = priv;
 555         side_list_insert_node_tail(&side_tracer_list, &tracer_handle->node);
 556         side_list_for_each_entry(events_handle, &side_events_list, node) {
 557                 cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 558                         events_handle->events, events_handle->nr_events, priv);
 559         }
 560         pthread_mutex_unlock(&side_event_lock);
 561         return tracer_handle;
 562 }
 563
 564 void side_tracer_event_notification_unregister(struct side_tracer_handle *tracer_handle)
 565 {
 566         struct side_events_register_handle *events_handle;
 567
 568         if (finalized)
 569                 return;
 570         if (!initialized)
 571                 side_init();
 572         pthread_mutex_lock(&side_event_lock);
 573         side_list_for_each_entry(events_handle, &side_events_list, node) {
 574                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 575                         events_handle->events, events_handle->nr_events,
 576                         tracer_handle->priv);
 577         }
 578         side_list_remove_node(&tracer_handle->node);
 579         pthread_mutex_unlock(&side_event_lock);
 580         free(tracer_handle);
 581 }
 582
 583 /* Called with side_statedump_lock held. */
 584 static
 585 void queue_statedump_pending(struct side_statedump_request_handle *handle, uint64_t key)
 586 {
 587         struct side_statedump_notification *notif;
 588
 589         notif = (struct side_statedump_notification *) calloc(1, sizeof(struct side_statedump_notification));
 590         if (!notif)
 591                 abort();
 592         notif->key = key;
 593         side_list_insert_node_tail(&handle->notification_queue, &notif->node);
 594         if (handle->mode == SIDE_STATEDUMP_MODE_AGENT_THREAD) {
 595                 (void)__atomic_or_fetch(&statedump_agent_thread.state, AGENT_THREAD_STATE_HANDLE_REQUEST, __ATOMIC_SEQ_CST);
 596                 pthread_cond_broadcast(&statedump_agent_thread.worker_cond);
 597         }
 598 }
 599
 600 /* Called with side_statedump_lock held. */
 601 static
 602 void unqueue_statedump_pending(struct side_statedump_request_handle *handle, uint64_t key)
 603 {
 604         struct side_statedump_notification *notif, *tmp;
 605
 606         side_list_for_each_entry_safe(notif, tmp, &handle->notification_queue, node) {
 607                 if (key == SIDE_KEY_MATCH_ALL || key == notif->key) {
 608                         side_list_remove_node(&notif->node);
 609                         free(notif);
 610                 }
 611         }
 612 }
 613
 614 static
 615 void side_statedump_run(struct side_statedump_request_handle *handle,
 616                 struct side_statedump_notification *notif)
 617 {
 618         side_statedump_event_call(side_statedump_begin, &notif->key,
 619                 side_arg_list(side_arg_string(handle->name)));
 620         /* Invoke the state dump callback specifically for the tracer key. */
 621         handle->cb(&notif->key);
 622         side_statedump_event_call(side_statedump_end, &notif->key,
 623                 side_arg_list(side_arg_string(handle->name)));
 624 }
 625
 626 static
 627 void _side_statedump_run_pending_requests(struct side_statedump_request_handle *handle)
 628 {
 629         struct side_statedump_notification *notif, *tmp;
 630         DEFINE_SIDE_LIST_HEAD(tmp_head);
 631
 632         pthread_mutex_lock(&side_statedump_lock);
 633         side_list_splice(&handle->notification_queue, &tmp_head);
 634         side_list_head_init(&handle->notification_queue);
 635         pthread_mutex_unlock(&side_statedump_lock);
 636
 637         /* We are now sole owner of the tmp_head list. */
 638         side_list_for_each_entry(notif, &tmp_head, node)
 639                 side_statedump_run(handle, notif);
 640         side_list_for_each_entry_safe(notif, tmp, &tmp_head, node)
 641                 free(notif);
 642
 643         if (handle->mode == SIDE_STATEDUMP_MODE_AGENT_THREAD) {
 644                 pthread_mutex_lock(&side_statedump_lock);
 645                 pthread_cond_broadcast(&statedump_agent_thread.waiter_cond);
 646                 pthread_mutex_unlock(&side_statedump_lock);
 647         }
 648 }
 649
 650 static
 651 void *statedump_agent_func(void *arg __attribute__((unused)))
 652 {
 653         for (;;) {
 654                 struct side_statedump_request_handle *handle;
 655                 struct side_rcu_read_state rcu_read_state;
 656                 enum agent_thread_state state;
 657
 658                 pthread_mutex_lock(&side_statedump_lock);
 659                 for (;;) {
 660                         state = __atomic_load_n(&statedump_agent_thread.state, __ATOMIC_SEQ_CST);
 661                         if (state == AGENT_THREAD_STATE_BLOCKED)
 662                                 pthread_cond_wait(&statedump_agent_thread.worker_cond, &side_statedump_lock);
 663                         else
 664                                 break;
 665                 }
 666                 pthread_mutex_unlock(&side_statedump_lock);
 667                 if (state & AGENT_THREAD_STATE_EXIT)
 668                         break;
 669                 if (state & AGENT_THREAD_STATE_PAUSE) {
 670                         int attempt = 0;
 671
 672                         (void)__atomic_or_fetch(&statedump_agent_thread.state, AGENT_THREAD_STATE_PAUSE_ACK, __ATOMIC_SEQ_CST);
 673                         for (;;) {
 674                                 state = __atomic_load_n(&statedump_agent_thread.state, __ATOMIC_SEQ_CST);
 675                                 if (!(state & AGENT_THREAD_STATE_PAUSE))
 676                                         break;
 677                                 if (attempt > SIDE_RETRY_BUSY_LOOP_ATTEMPTS) {
 678                                         (void)poll(NULL, 0, SIDE_RETRY_DELAY_MS);
 679                                         continue;
 680                                 }
 681                                 attempt++;
 682                                 side_cpu_relax();
 683                         }
 684                         continue;
 685                 }
 686                 (void)__atomic_and_fetch(&statedump_agent_thread.state, ~AGENT_THREAD_STATE_HANDLE_REQUEST, __ATOMIC_SEQ_CST);
 687                 side_rcu_read_begin(&statedump_rcu_gp, &rcu_read_state);
 688                 side_list_for_each_entry_rcu(handle, &side_statedump_list, node)
 689                         _side_statedump_run_pending_requests(handle);
 690                 side_rcu_read_end(&statedump_rcu_gp, &rcu_read_state);
 691         }
 692         return NULL;
 693 }
 694
 695 static
 696 void statedump_agent_thread_init(void)
 697 {
 698         pthread_cond_init(&statedump_agent_thread.worker_cond, NULL);
 699         pthread_cond_init(&statedump_agent_thread.waiter_cond, NULL);
 700         statedump_agent_thread.state = AGENT_THREAD_STATE_BLOCKED;
 701 }
 702
 703 /* Called with side_agent_thread_lock and side_statedump_lock held. */
 704 static
 705 void statedump_agent_thread_get(void)
 706 {
 707         int ret;
 708
 709         if (statedump_agent_thread.ref++)
 710                 return;
 711         statedump_agent_thread_init();
 712         ret = pthread_create(&statedump_agent_thread.id, NULL,
 713                         statedump_agent_func, NULL);
 714         if (ret) {
 715                 abort();
 716         }
 717 }
 718
 719 /*
 720  * Called with side_agent_thread_lock and side_statedump_lock held.
 721  * Returns true if join for agent thread is needed.
 722  */
 723 static
 724 bool statedump_agent_thread_put(void)
 725 {
 726         if (--statedump_agent_thread.ref)
 727                 return false;
 728         (void)__atomic_or_fetch(&statedump_agent_thread.state, AGENT_THREAD_STATE_EXIT, __ATOMIC_SEQ_CST);
 729         pthread_cond_broadcast(&statedump_agent_thread.worker_cond);
 730         return true;
 731 }
 732
 733 static
 734 void statedump_agent_thread_fini(void)
 735 {
 736         statedump_agent_thread.state = AGENT_THREAD_STATE_BLOCKED;
 737         if (pthread_cond_destroy(&statedump_agent_thread.worker_cond))
 738                 abort();
 739         if (pthread_cond_destroy(&statedump_agent_thread.waiter_cond))
 740                 abort();
 741 }
 742
 743 /* Called with side_agent_thread_lock held. */
 744 static
 745 void statedump_agent_thread_join(void)
 746 {
 747         int ret;
 748         void *retval;
 749
 750         ret = pthread_join(statedump_agent_thread.id, &retval);
 751         if (ret) {
 752                 abort();
 753         }
 754         statedump_agent_thread_fini();
 755 }
 756
 757 struct side_statedump_request_handle *
 758         side_statedump_request_notification_register(const char *state_name,
 759                 void (*statedump_cb)(void *statedump_request_key),
 760                 enum side_statedump_mode mode)
 761 {
 762         struct side_statedump_request_handle *handle;
 763         char *name;
 764
 765         if (finalized)
 766                 return NULL;
 767         if (!initialized)
 768                 side_init();
 769         handle = (struct side_statedump_request_handle *)
 770                                 calloc(1, sizeof(struct side_statedump_request_handle));
 771         if (!handle)
 772                 return NULL;
 773         name = strdup(state_name);
 774         if (!name)
 775                 goto name_nomem;
 776         handle->cb = statedump_cb;
 777         handle->name = name;
 778         handle->mode = mode;
 779         side_list_head_init(&handle->notification_queue);
 780
 781         if (mode == SIDE_STATEDUMP_MODE_AGENT_THREAD)
 782                 pthread_mutex_lock(&side_agent_thread_lock);
 783         pthread_mutex_lock(&side_statedump_lock);
 784         if (mode == SIDE_STATEDUMP_MODE_AGENT_THREAD)
 785                 statedump_agent_thread_get();
 786         side_list_insert_node_tail_rcu(&side_statedump_list, &handle->node);
 787         /* Queue statedump pending for all tracers. */
 788         queue_statedump_pending(handle, SIDE_KEY_MATCH_ALL);
 789         pthread_mutex_unlock(&side_statedump_lock);
 790
 791         if (mode == SIDE_STATEDUMP_MODE_AGENT_THREAD) {
 792                 pthread_mutex_unlock(&side_agent_thread_lock);
 793
 794                 pthread_mutex_lock(&side_statedump_lock);
 795                 while (!side_list_empty(&handle->notification_queue))
 796                         pthread_cond_wait(&statedump_agent_thread.waiter_cond, &side_statedump_lock);
 797                 pthread_mutex_unlock(&side_statedump_lock);
 798         }
 799
 800         return handle;
 801
 802 name_nomem:
 803         free(handle);
 804         return NULL;
 805 }
 806
 807 void side_statedump_request_notification_unregister(struct side_statedump_request_handle *handle)
 808 {
 809         bool join = false;
 810
 811         if (finalized)
 812                 return;
 813         if (!initialized)
 814                 side_init();
 815
 816         if (handle->mode == SIDE_STATEDUMP_MODE_AGENT_THREAD)
 817                 pthread_mutex_lock(&side_agent_thread_lock);
 818         pthread_mutex_lock(&side_statedump_lock);
 819         unqueue_statedump_pending(handle, SIDE_KEY_MATCH_ALL);
 820         side_list_remove_node_rcu(&handle->node);
 821         if (handle->mode == SIDE_STATEDUMP_MODE_AGENT_THREAD)
 822                 join = statedump_agent_thread_put();
 823         pthread_mutex_unlock(&side_statedump_lock);
 824         if (join)
 825                 statedump_agent_thread_join();
 826         if (handle->mode == SIDE_STATEDUMP_MODE_AGENT_THREAD)
 827                 pthread_mutex_unlock(&side_agent_thread_lock);
 828
 829         side_rcu_wait_grace_period(&statedump_rcu_gp);
 830         free(handle->name);
 831         free(handle);
 832 }
 833
 834 /* Returns true if the handle has pending statedump requests. */
 835 bool side_statedump_poll_pending_requests(struct side_statedump_request_handle *handle)
 836 {
 837         bool ret;
 838
 839         if (handle->mode != SIDE_STATEDUMP_MODE_POLLING)
 840                 return false;
 841         pthread_mutex_lock(&side_statedump_lock);
 842         ret = !side_list_empty(&handle->notification_queue);
 843         pthread_mutex_unlock(&side_statedump_lock);
 844         return ret;
 845 }
 846
 847 /*
 848  * Only polling mode state dump handles allow application to explicitly handle the
 849  * pending requests.
 850  */
 851 int side_statedump_run_pending_requests(struct side_statedump_request_handle *handle)
 852 {
 853         if (handle->mode != SIDE_STATEDUMP_MODE_POLLING)
 854                 return SIDE_ERROR_INVAL;
 855         _side_statedump_run_pending_requests(handle);
 856         return SIDE_ERROR_OK;
 857 }
 858
 859 /*
 860  * Request a state dump for tracer callbacks identified with "key".
 861  */
 862 int side_tracer_statedump_request(uint64_t key)
 863 {
 864         struct side_statedump_request_handle *handle;
 865
 866         if (key == SIDE_KEY_MATCH_ALL)
 867                 return SIDE_ERROR_INVAL;
 868         pthread_mutex_lock(&side_statedump_lock);
 869         side_list_for_each_entry(handle, &side_statedump_list, node)
 870                 queue_statedump_pending(handle, key);
 871         pthread_mutex_lock(&side_statedump_lock);
 872         return SIDE_ERROR_OK;
 873 }
 874
 875 /*
 876  * Cancel a statedump request.
 877  */
 878 int side_tracer_statedump_request_cancel(uint64_t key)
 879 {
 880         struct side_statedump_request_handle *handle;
 881
 882         if (key == SIDE_KEY_MATCH_ALL)
 883                 return SIDE_ERROR_INVAL;
 884         pthread_mutex_lock(&side_statedump_lock);
 885         side_list_for_each_entry(handle, &side_statedump_list, node)
 886                 unqueue_statedump_pending(handle, key);
 887         pthread_mutex_lock(&side_statedump_lock);
 888         return SIDE_ERROR_OK;
 889 }
 890
 891 /*
 892  * Tracer keys are represented on 64-bit. Return SIDE_ERROR_NOMEM on
 893  * overflow (which should never happen in practice).
 894  */
 895 int side_tracer_request_key(uint64_t *key)
 896 {
 897         int ret = SIDE_ERROR_OK;
 898
 899         pthread_mutex_lock(&side_key_lock);
 900         if (side_key_next == 0) {
 901                 ret = SIDE_ERROR_NOMEM;
 902                 goto end;
 903         }
 904         *key = side_key_next++;
 905 end:
 906         pthread_mutex_unlock(&side_key_lock);
 907         return ret;
 908 }
 909
 910 /*
 911  * Use of pthread_atfork depends on glibc 2.24 to eliminate hangs when
 912  * waiting for the agent thread if the agent thread calls malloc. This
 913  * is corrected by GNU libc
 914  * commit 8a727af925be63aa6ea0f5f90e16751fd541626b.
 915  * Ref. https://bugzilla.redhat.com/show_bug.cgi?id=906468
 916  */
 917 static
 918 void side_before_fork(void)
 919 {
 920         int attempt = 0;
 921
 922         pthread_mutex_lock(&side_agent_thread_lock);
 923         if (!statedump_agent_thread.ref)
 924                 return;
 925         /* Pause agent thread. */
 926         pthread_mutex_lock(&side_statedump_lock);
 927         (void)__atomic_or_fetch(&statedump_agent_thread.state, AGENT_THREAD_STATE_PAUSE, __ATOMIC_SEQ_CST);
 928         pthread_cond_broadcast(&statedump_agent_thread.worker_cond);
 929         pthread_mutex_unlock(&side_statedump_lock);
 930         /* Wait for agent thread acknowledge. */
 931         while (!(__atomic_load_n(&statedump_agent_thread.state, __ATOMIC_SEQ_CST) & AGENT_THREAD_STATE_PAUSE_ACK)) {
 932                 if (attempt > SIDE_RETRY_BUSY_LOOP_ATTEMPTS) {
 933                         (void)poll(NULL, 0, SIDE_RETRY_DELAY_MS);
 934                         continue;
 935                 }
 936                 attempt++;
 937                 side_cpu_relax();
 938         }
 939 }
 940
 941 static
 942 void side_after_fork_parent(void)
 943 {
 944         if (statedump_agent_thread.ref)
 945                 (void)__atomic_and_fetch(&statedump_agent_thread.state,
 946                         ~(AGENT_THREAD_STATE_PAUSE | AGENT_THREAD_STATE_PAUSE_ACK),
 947                         __ATOMIC_SEQ_CST);
 948         pthread_mutex_unlock(&side_agent_thread_lock);
 949 }
 950
 951 /*
 952  * The agent thread does not exist in the child process after a fork.
 953  * Re-initialize its data structures and create a new agent thread.
 954  */
 955 static
 956 void side_after_fork_child(void)
 957 {
 958         if (statedump_agent_thread.ref) {
 959                 int ret;
 960
 961                 statedump_agent_thread_fini();
 962                 statedump_agent_thread_init();
 963                 ret = pthread_create(&statedump_agent_thread.id, NULL,
 964                                 statedump_agent_func, NULL);
 965                 if (ret) {
 966                         abort();
 967                 }
 968         }
 969         pthread_mutex_unlock(&side_agent_thread_lock);
 970 }
 971
 972 void side_init(void)
 973 {
 974         if (initialized)
 975                 return;
 976         side_rcu_gp_init(&event_rcu_gp);
 977         side_rcu_gp_init(&statedump_rcu_gp);
 978         if (pthread_atfork(side_before_fork, side_after_fork_parent, side_after_fork_child))
 979                 abort();
 980         initialized = true;
 981 }
 982
 983 /*
 984  * side_exit() is executed from a library destructor. It can be called
 985  * explicitly at application exit as well. Concurrent side API use is
 986  * not expected at that point.
 987  */
 988 void side_exit(void)
 989 {
 990         struct side_events_register_handle *handle, *tmp;
 991
 992         if (finalized)
 993                 return;
 994         side_list_for_each_entry_safe(handle, tmp, &side_events_list, node)
 995                 side_events_unregister(handle);
 996         side_rcu_gp_exit(&event_rcu_gp);
 997         side_rcu_gp_exit(&statedump_rcu_gp);
 998         finalized = true;
 999 }