libust/lttng-ust-comm.c

   1 /*
   2  * lttng-ust-comm.c
   3  *
   4  * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
   5  * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   6  *
   7  * This library is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; only
  10  * version 2.1 of the License.
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with this library; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 #include <sys/types.h>
  23 #include <sys/socket.h>
  24 #include <sys/prctl.h>
  25 #include <sys/mman.h>
  26 #include <sys/stat.h>
  27 #include <fcntl.h>
  28 #include <unistd.h>
  29 #include <errno.h>
  30 #include <pthread.h>
  31 #include <semaphore.h>
  32 #include <time.h>
  33 #include <assert.h>
  34 #include <signal.h>
  35 #include <urcu/uatomic.h>
  36
  37 #include <lttng-ust-comm.h>
  38 #include <ust/usterr-signal-safe.h>
  39 #include <ust/lttng-ust-abi.h>
  40 #include <ust/tracepoint.h>
  41 #include <ust/tracepoint-internal.h>
  42 #include <ust/ust.h>
  43 #include "ltt-tracer-core.h"
  44
  45 /*
  46  * Has lttng ust comm constructor been called ?
  47  */
  48 static int initialized;
  49
  50 /*
  51  * The ust_lock/ust_unlock lock is used as a communication thread mutex.
  52  * Held when handling a command, also held by fork() to deal with
  53  * removal of threads, and by exit path.
  54  */
  55
  56 /* Should the ust comm thread quit ? */
  57 static int lttng_ust_comm_should_quit;
  58
  59 /*
  60  * Wait for either of these before continuing to the main
  61  * program:
  62  * - the register_done message from sessiond daemon
  63  *   (will let the sessiond daemon enable sessions before main
  64  *   starts.)
  65  * - sessiond daemon is not reachable.
  66  * - timeout (ensuring applications are resilient to session
  67  *   daemon problems).
  68  */
  69 static sem_t constructor_wait;
  70 /*
  71  * Doing this for both the global and local sessiond.
  72  */
  73 static int sem_count = { 2 };
  74
  75 /*
  76  * Info about socket and associated listener thread.
  77  */
  78 struct sock_info {
  79         const char *name;
  80         pthread_t ust_listener; /* listener thread */
  81         int root_handle;
  82         int constructor_sem_posted;
  83         int allowed;
  84
  85         char sock_path[PATH_MAX];
  86         int socket;
  87
  88         char wait_shm_path[PATH_MAX];
  89         char *wait_shm_mmap;
  90 };
  91
  92 /* Socket from app (connect) to session daemon (listen) for communication */
  93 struct sock_info global_apps = {
  94         .name = "global",
  95
  96         .root_handle = -1,
  97         .allowed = 1,
  98
  99         .sock_path = DEFAULT_GLOBAL_APPS_UNIX_SOCK,
 100         .socket = -1,
 101
 102         .wait_shm_path = DEFAULT_GLOBAL_APPS_WAIT_SHM_PATH,
 103 };
 104
 105 /* TODO: allow global_apps_sock_path override */
 106
 107 struct sock_info local_apps = {
 108         .name = "local",
 109         .root_handle = -1,
 110         .allowed = 0,   /* Check setuid bit first */
 111
 112         .socket = -1,
 113 };
 114
 115 extern void ltt_ring_buffer_client_overwrite_init(void);
 116 extern void ltt_ring_buffer_client_discard_init(void);
 117 extern void ltt_ring_buffer_metadata_client_init(void);
 118 extern void ltt_ring_buffer_client_overwrite_exit(void);
 119 extern void ltt_ring_buffer_client_discard_exit(void);
 120 extern void ltt_ring_buffer_metadata_client_exit(void);
 121
 122 static
 123 int setup_local_apps(void)
 124 {
 125         const char *home_dir;
 126         uid_t uid;
 127
 128         uid = getuid();
 129         /*
 130          * Disallow per-user tracing for setuid binaries.
 131          */
 132         if (uid != geteuid()) {
 133                 local_apps.allowed = 0;
 134                 return 0;
 135         } else {
 136                 local_apps.allowed = 1;
 137         }
 138         home_dir = (const char *) getenv("HOME");
 139         if (!home_dir)
 140                 return -ENOENT;
 141         snprintf(local_apps.sock_path, PATH_MAX,
 142                  DEFAULT_HOME_APPS_UNIX_SOCK, home_dir);
 143         snprintf(local_apps.wait_shm_path, PATH_MAX,
 144                  DEFAULT_HOME_APPS_WAIT_SHM_PATH, uid);
 145         return 0;
 146 }
 147
 148 static
 149 int register_app_to_sessiond(int socket)
 150 {
 151         ssize_t ret;
 152         int prctl_ret;
 153         struct {
 154                 uint32_t major;
 155                 uint32_t minor;
 156                 pid_t pid;
 157                 pid_t ppid;
 158                 uid_t uid;
 159                 gid_t gid;
 160                 char name[16];  /* process name */
 161         } reg_msg;
 162
 163         reg_msg.major = LTTNG_UST_COMM_VERSION_MAJOR;
 164         reg_msg.minor = LTTNG_UST_COMM_VERSION_MINOR;
 165         reg_msg.pid = getpid();
 166         reg_msg.ppid = getppid();
 167         reg_msg.uid = getuid();
 168         reg_msg.gid = getgid();
 169         prctl_ret = prctl(PR_GET_NAME, (unsigned long) reg_msg.name, 0, 0, 0);
 170         if (prctl_ret) {
 171                 ERR("Error executing prctl");
 172                 return -errno;
 173         }
 174
 175         ret = lttcomm_send_unix_sock(socket, &reg_msg, sizeof(reg_msg));
 176         if (ret >= 0 && ret != sizeof(reg_msg))
 177                 return -EIO;
 178         return ret;
 179 }
 180
 181 static
 182 int send_reply(int sock, struct lttcomm_ust_reply *lur)
 183 {
 184         ssize_t len;
 185
 186         len = lttcomm_send_unix_sock(sock, lur, sizeof(*lur));
 187         switch (len) {
 188         case sizeof(*lur):
 189                 DBG("message successfully sent");
 190                 return 0;
 191         case -1:
 192                 if (errno == ECONNRESET) {
 193                         printf("remote end closed connection\n");
 194                         return 0;
 195                 }
 196                 return -1;
 197         default:
 198                 printf("incorrect message size: %zd\n", len);
 199                 return -1;
 200         }
 201 }
 202
 203 static
 204 int handle_register_done(struct sock_info *sock_info)
 205 {
 206         int ret;
 207
 208         if (sock_info->constructor_sem_posted)
 209                 return 0;
 210         sock_info->constructor_sem_posted = 1;
 211         ret = uatomic_add_return(&sem_count, -1);
 212         if (ret == 0) {
 213                 ret = sem_post(&constructor_wait);
 214                 assert(!ret);
 215         }
 216         return 0;
 217 }
 218
 219 static
 220 int handle_message(struct sock_info *sock_info,
 221                 int sock, struct lttcomm_ust_msg *lum)
 222 {
 223         int ret = 0;
 224         const struct objd_ops *ops;
 225         struct lttcomm_ust_reply lur;
 226
 227         ust_lock();
 228
 229         memset(&lur, 0, sizeof(lur));
 230
 231         if (lttng_ust_comm_should_quit) {
 232                 ret = -EPERM;
 233                 goto end;
 234         }
 235
 236         ops = objd_ops(lum->handle);
 237         if (!ops) {
 238                 ret = -ENOENT;
 239                 goto end;
 240         }
 241
 242         switch (lum->cmd) {
 243         case LTTNG_UST_REGISTER_DONE:
 244                 if (lum->handle == LTTNG_UST_ROOT_HANDLE)
 245                         ret = handle_register_done(sock_info);
 246                 else
 247                         ret = -EINVAL;
 248                 break;
 249         case LTTNG_UST_RELEASE:
 250                 if (lum->handle == LTTNG_UST_ROOT_HANDLE)
 251                         ret = -EPERM;
 252                 else
 253                         ret = objd_unref(lum->handle);
 254                 break;
 255         default:
 256                 if (ops->cmd)
 257                         ret = ops->cmd(lum->handle, lum->cmd,
 258                                         (unsigned long) &lum->u);
 259                 else
 260                         ret = -ENOSYS;
 261                 break;
 262         }
 263
 264 end:
 265         lur.handle = lum->handle;
 266         lur.cmd = lum->cmd;
 267         lur.ret_val = ret;
 268         if (ret >= 0) {
 269                 lur.ret_code = LTTCOMM_OK;
 270         } else {
 271                 lur.ret_code = LTTCOMM_SESSION_FAIL;
 272         }
 273         ret = send_reply(sock, &lur);
 274
 275         ust_unlock();
 276         return ret;
 277 }
 278
 279 static
 280 void cleanup_sock_info(struct sock_info *sock_info)
 281 {
 282         int ret;
 283
 284         if (sock_info->socket != -1) {
 285                 ret = close(sock_info->socket);
 286                 if (ret) {
 287                         ERR("Error closing apps socket");
 288                 }
 289                 sock_info->socket = -1;
 290         }
 291         if (sock_info->root_handle != -1) {
 292                 ret = objd_unref(sock_info->root_handle);
 293                 if (ret) {
 294                         ERR("Error unref root handle");
 295                 }
 296                 sock_info->root_handle = -1;
 297         }
 298         sock_info->constructor_sem_posted = 0;
 299         if (sock_info->wait_shm_mmap) {
 300                 ret = munmap(sock_info->wait_shm_mmap, sysconf(_SC_PAGE_SIZE));
 301                 if (ret) {
 302                         ERR("Error unmapping wait shm");
 303                 }
 304                 sock_info->wait_shm_mmap = NULL;
 305         }
 306 }
 307
 308 static
 309 char *get_map_shm(struct sock_info *sock_info)
 310 {
 311         size_t mmap_size = sysconf(_SC_PAGE_SIZE);
 312         int wait_shm_fd, ret;
 313         char *wait_shm_mmap;
 314
 315         /*
 316          * Get existing (read-only) shm, or open new shm.
 317          * First try to open read-only.
 318          */
 319         wait_shm_fd = shm_open(sock_info->wait_shm_path,
 320                         O_RDONLY, 0700);
 321         if (wait_shm_fd >= 0)
 322                 goto got_shm;
 323         /*
 324          * Real-only open did not work. If it is because it did
 325          * not exist, try creating it. Else it's a failure that
 326          * prohibits using shm.
 327          */
 328         if (errno != ENOENT) {
 329                 ERR("Error opening shm %s", sock_info->wait_shm_path);
 330                 goto error;
 331         }
 332         wait_shm_fd = shm_open(sock_info->wait_shm_path,
 333                         O_RDWR | O_CREAT | O_EXCL, 0700);
 334         if (wait_shm_fd >= 0)
 335                 goto created_shm;
 336         if (errno != EEXIST) {
 337                 ERR("Error opening shm %s", sock_info->wait_shm_path);
 338                 goto error;
 339         }
 340         /*
 341          * If another process beat us to create the shm, we are
 342          * pretty certain the shm is available for us in
 343          * read-only mode.
 344          */
 345         wait_shm_fd = shm_open(sock_info->wait_shm_path,
 346                         O_RDWR | O_CREAT | O_EXCL, 0700);
 347         if (wait_shm_fd >= 0)
 348                 goto got_shm;
 349         else
 350                 goto error;
 351
 352 created_shm:
 353         ret = ftruncate(wait_shm_fd, mmap_size);
 354         if (ret) {
 355                 PERROR("ftruncate");
 356                 ret = close(wait_shm_fd);
 357                 if (ret) {
 358                         ERR("Error closing fd");
 359                 }
 360                 wait_shm_fd = -1;
 361                 goto error;
 362         }
 363 got_shm:
 364         wait_shm_mmap = mmap(NULL, mmap_size, PROT_READ,
 365                   MAP_SHARED, wait_shm_fd, 0);
 366         if (wait_shm_mmap == MAP_FAILED) {
 367                 PERROR("mmap");
 368                 goto error;
 369         }
 370         /* close shm fd immediately after taking the mmap reference */
 371         ret = close(wait_shm_fd);
 372         if (ret) {
 373                 ERR("Error closing fd");
 374         }
 375         return wait_shm_mmap;
 376
 377 error:
 378         return NULL;
 379 }
 380
 381 static
 382 void wait_for_sessiond(struct sock_info *sock_info)
 383 {
 384         ust_lock();
 385         if (lttng_ust_comm_should_quit) {
 386                 goto quit;
 387         }
 388         if (!sock_info->wait_shm_mmap) {
 389                 sock_info->wait_shm_mmap = get_map_shm(sock_info);
 390                 if (!sock_info->wait_shm_mmap)
 391                         goto error;
 392         }
 393         ust_unlock();
 394
 395         DBG("Waiting for %s apps sessiond", sock_info->name);
 396         /* Wait for futex wakeup TODO */
 397         sleep(5);
 398
 399         return;
 400
 401 quit:
 402         ust_unlock();
 403         return;
 404
 405 error:
 406         ust_unlock();
 407         /* Error handling: fallback on a 5 seconds sleep. */
 408         sleep(5);
 409         return;
 410 }
 411
 412 /*
 413  * This thread does not allocate any resource, except within
 414  * handle_message, within mutex protection. This mutex protects against
 415  * fork and exit.
 416  * The other moment it allocates resources is at socket connexion, which
 417  * is also protected by the mutex.
 418  */
 419 static
 420 void *ust_listener_thread(void *arg)
 421 {
 422         struct sock_info *sock_info = arg;
 423         int sock, ret;
 424
 425         /* Restart trying to connect to the session daemon */
 426 restart:
 427         ust_lock();
 428
 429         if (lttng_ust_comm_should_quit) {
 430                 ust_unlock();
 431                 goto quit;
 432         }
 433
 434         if (sock_info->socket != -1) {
 435                 ret = close(sock_info->socket);
 436                 if (ret) {
 437                         ERR("Error closing %s apps socket", sock_info->name);
 438                 }
 439                 sock_info->socket = -1;
 440         }
 441
 442         /* Register */
 443         ret = lttcomm_connect_unix_sock(sock_info->sock_path);
 444         if (ret < 0) {
 445                 ERR("Error connecting to %s apps socket", sock_info->name);
 446                 /*
 447                  * If we cannot find the sessiond daemon, don't delay
 448                  * constructor execution.
 449                  */
 450                 ret = handle_register_done(sock_info);
 451                 assert(!ret);
 452                 ust_unlock();
 453
 454                 /* Wait for sessiond availability with pipe */
 455                 wait_for_sessiond(sock_info);
 456                 goto restart;
 457         }
 458
 459         sock_info->socket = sock = ret;
 460
 461         /*
 462          * Create only one root handle per listener thread for the whole
 463          * process lifetime.
 464          */
 465         if (sock_info->root_handle == -1) {
 466                 ret = lttng_abi_create_root_handle();
 467                 if (ret) {
 468                         ERR("Error creating root handle");
 469                         ust_unlock();
 470                         goto quit;
 471                 }
 472                 sock_info->root_handle = ret;
 473         }
 474
 475         ret = register_app_to_sessiond(sock);
 476         if (ret < 0) {
 477                 ERR("Error registering to %s apps socket", sock_info->name);
 478                 /*
 479                  * If we cannot register to the sessiond daemon, don't
 480                  * delay constructor execution.
 481                  */
 482                 ret = handle_register_done(sock_info);
 483                 assert(!ret);
 484                 ust_unlock();
 485                 wait_for_sessiond(sock_info);
 486                 goto restart;
 487         }
 488         ust_unlock();
 489
 490         for (;;) {
 491                 ssize_t len;
 492                 struct lttcomm_ust_msg lum;
 493
 494                 len = lttcomm_recv_unix_sock(sock, &lum, sizeof(lum));
 495                 switch (len) {
 496                 case 0: /* orderly shutdown */
 497                         DBG("%s ltt-sessiond has performed an orderly shutdown\n", sock_info->name);
 498                         goto end;
 499                 case sizeof(lum):
 500                         DBG("message received\n");
 501                         ret = handle_message(sock_info, sock, &lum);
 502                         if (ret < 0) {
 503                                 ERR("Error handling message for %s socket", sock_info->name);
 504                         }
 505                         continue;
 506                 case -1:
 507                         if (errno == ECONNRESET) {
 508                                 ERR("%s remote end closed connection\n", sock_info->name);
 509                                 goto end;
 510                         }
 511                         goto end;
 512                 default:
 513                         ERR("incorrect message size (%s socket): %zd\n", sock_info->name, len);
 514                         continue;
 515                 }
 516
 517         }
 518 end:
 519         goto restart;   /* try to reconnect */
 520 quit:
 521         return NULL;
 522 }
 523
 524 /*
 525  * Return values: -1: don't wait. 0: wait forever. 1: timeout wait.
 526  */
 527 static
 528 int get_timeout(struct timespec *constructor_timeout)
 529 {
 530         long constructor_delay_ms = LTTNG_UST_DEFAULT_CONSTRUCTOR_TIMEOUT_MS;
 531         char *str_delay;
 532         int ret;
 533
 534         str_delay = getenv("UST_REGISTER_TIMEOUT");
 535         if (str_delay) {
 536                 constructor_delay_ms = strtol(str_delay, NULL, 10);
 537         }
 538
 539         switch (constructor_delay_ms) {
 540         case -1:/* fall-through */
 541         case 0:
 542                 return constructor_delay_ms;
 543         default:
 544                 break;
 545         }
 546
 547         /*
 548          * If we are unable to find the current time, don't wait.
 549          */
 550         ret = clock_gettime(CLOCK_REALTIME, constructor_timeout);
 551         if (ret) {
 552                 return -1;
 553         }
 554         constructor_timeout->tv_sec += constructor_delay_ms / 1000UL;
 555         constructor_timeout->tv_nsec +=
 556                 (constructor_delay_ms % 1000UL) * 1000000UL;
 557         if (constructor_timeout->tv_nsec >= 1000000000UL) {
 558                 constructor_timeout->tv_sec++;
 559                 constructor_timeout->tv_nsec -= 1000000000UL;
 560         }
 561         return 1;
 562 }
 563
 564 /*
 565  * sessiond monitoring thread: monitor presence of global and per-user
 566  * sessiond by polling the application common named pipe.
 567  */
 568 /* TODO */
 569
 570 void __attribute__((constructor)) lttng_ust_init(void)
 571 {
 572         struct timespec constructor_timeout;
 573         int timeout_mode;
 574         int ret;
 575
 576         if (uatomic_xchg(&initialized, 1) == 1)
 577                 return;
 578
 579         /*
 580          * We want precise control over the order in which we construct
 581          * our sub-libraries vs starting to receive commands from
 582          * sessiond (otherwise leading to errors when trying to create
 583          * sessiond before the init functions are completed).
 584          */
 585         init_usterr();
 586         init_tracepoint();
 587         ltt_ring_buffer_metadata_client_init();
 588         ltt_ring_buffer_client_overwrite_init();
 589         ltt_ring_buffer_client_discard_init();
 590
 591         timeout_mode = get_timeout(&constructor_timeout);
 592
 593         ret = sem_init(&constructor_wait, 0, 0);
 594         assert(!ret);
 595
 596         ret = setup_local_apps();
 597         if (ret) {
 598                 ERR("Error setting up to local apps");
 599         }
 600         ret = pthread_create(&local_apps.ust_listener, NULL,
 601                         ust_listener_thread, &local_apps);
 602
 603         if (local_apps.allowed) {
 604                 ret = pthread_create(&global_apps.ust_listener, NULL,
 605                                 ust_listener_thread, &global_apps);
 606         } else {
 607                 handle_register_done(&local_apps);
 608         }
 609
 610         switch (timeout_mode) {
 611         case 1: /* timeout wait */
 612                 do {
 613                         ret = sem_timedwait(&constructor_wait,
 614                                         &constructor_timeout);
 615                 } while (ret < 0 && errno == EINTR);
 616                 if (ret < 0 && errno == ETIMEDOUT) {
 617                         ERR("Timed out waiting for ltt-sessiond");
 618                 } else {
 619                         assert(!ret);
 620                 }
 621                 break;
 622         case -1:/* wait forever */
 623                 do {
 624                         ret = sem_wait(&constructor_wait);
 625                 } while (ret < 0 && errno == EINTR);
 626                 assert(!ret);
 627                 break;
 628         case 0: /* no timeout */
 629                 break;
 630         }
 631 }
 632
 633 static
 634 void lttng_ust_cleanup(int exiting)
 635 {
 636         cleanup_sock_info(&global_apps);
 637         if (local_apps.allowed) {
 638                 cleanup_sock_info(&local_apps);
 639         }
 640         lttng_ust_abi_exit();
 641         ltt_events_exit();
 642         ltt_ring_buffer_client_discard_exit();
 643         ltt_ring_buffer_client_overwrite_exit();
 644         ltt_ring_buffer_metadata_client_exit();
 645         exit_tracepoint();
 646         if (!exiting) {
 647                 /* Reinitialize values for fork */
 648                 sem_count = 2;
 649                 lttng_ust_comm_should_quit = 0;
 650                 initialized = 0;
 651         }
 652 }
 653
 654 void __attribute__((destructor)) lttng_ust_exit(void)
 655 {
 656         int ret;
 657
 658         /*
 659          * Using pthread_cancel here because:
 660          * A) we don't want to hang application teardown.
 661          * B) the thread is not allocating any resource.
 662          */
 663
 664         /*
 665          * Require the communication thread to quit. Synchronize with
 666          * mutexes to ensure it is not in a mutex critical section when
 667          * pthread_cancel is later called.
 668          */
 669         ust_lock();
 670         lttng_ust_comm_should_quit = 1;
 671         ust_unlock();
 672
 673         ret = pthread_cancel(global_apps.ust_listener);
 674         if (ret) {
 675                 ERR("Error cancelling global ust listener thread");
 676         }
 677         if (local_apps.allowed) {
 678                 ret = pthread_cancel(local_apps.ust_listener);
 679                 if (ret) {
 680                         ERR("Error cancelling local ust listener thread");
 681                 }
 682         }
 683         lttng_ust_cleanup(1);
 684 }
 685
 686 /*
 687  * We exclude the worker threads across fork and clone (except
 688  * CLONE_VM), because these system calls only keep the forking thread
 689  * running in the child.  Therefore, we don't want to call fork or clone
 690  * in the middle of an tracepoint or ust tracing state modification.
 691  * Holding this mutex protects these structures across fork and clone.
 692  */
 693 void ust_before_fork(ust_fork_info_t *fork_info)
 694 {
 695         /*
 696          * Disable signals. This is to avoid that the child intervenes
 697          * before it is properly setup for tracing. It is safer to
 698          * disable all signals, because then we know we are not breaking
 699          * anything by restoring the original mask.
 700          */
 701         sigset_t all_sigs;
 702         int ret;
 703
 704         /* Disable signals */
 705         sigfillset(&all_sigs);
 706         ret = sigprocmask(SIG_BLOCK, &all_sigs, &fork_info->orig_sigs);
 707         if (ret == -1) {
 708                 PERROR("sigprocmask");
 709         }
 710         ust_lock();
 711         rcu_bp_before_fork();
 712 }
 713
 714 static void ust_after_fork_common(ust_fork_info_t *fork_info)
 715 {
 716         int ret;
 717
 718         DBG("process %d", getpid());
 719         ust_unlock();
 720         /* Restore signals */
 721         ret = sigprocmask(SIG_SETMASK, &fork_info->orig_sigs, NULL);
 722         if (ret == -1) {
 723                 PERROR("sigprocmask");
 724         }
 725 }
 726
 727 void ust_after_fork_parent(ust_fork_info_t *fork_info)
 728 {
 729         DBG("process %d", getpid());
 730         rcu_bp_after_fork_parent();
 731         /* Release mutexes and reenable signals */
 732         ust_after_fork_common(fork_info);
 733 }
 734
 735 /*
 736  * After fork, in the child, we need to cleanup all the leftover state,
 737  * except the worker thread which already magically disappeared thanks
 738  * to the weird Linux fork semantics. After tyding up, we call
 739  * lttng_ust_init() again to start over as a new PID.
 740  *
 741  * This is meant for forks() that have tracing in the child between the
 742  * fork and following exec call (if there is any).
 743  */
 744 void ust_after_fork_child(ust_fork_info_t *fork_info)
 745 {
 746         DBG("process %d", getpid());
 747         /* Release urcu mutexes */
 748         rcu_bp_after_fork_child();
 749         lttng_ust_cleanup(0);
 750         /* Release mutexes and reenable signals */
 751         ust_after_fork_common(fork_info);
 752         lttng_ust_init();
 753 }