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 <sys/types.h>
  28 #include <sys/wait.h>
  29 #include <fcntl.h>
  30 #include <unistd.h>
  31 #include <errno.h>
  32 #include <pthread.h>
  33 #include <semaphore.h>
  34 #include <time.h>
  35 #include <assert.h>
  36 #include <signal.h>
  37 #include <urcu/uatomic.h>
  38
  39 #include <lttng-ust-comm.h>
  40 #include <ust/usterr-signal-safe.h>
  41 #include <ust/lttng-ust-abi.h>
  42 #include <ust/tracepoint.h>
  43 #include <ust/tracepoint-internal.h>
  44 #include <ust/ust.h>
  45 #include "ltt-tracer-core.h"
  46
  47 /*
  48  * Has lttng ust comm constructor been called ?
  49  */
  50 static int initialized;
  51
  52 /*
  53  * The ust_lock/ust_unlock lock is used as a communication thread mutex.
  54  * Held when handling a command, also held by fork() to deal with
  55  * removal of threads, and by exit path.
  56  */
  57
  58 /* Should the ust comm thread quit ? */
  59 static int lttng_ust_comm_should_quit;
  60
  61 /*
  62  * Wait for either of these before continuing to the main
  63  * program:
  64  * - the register_done message from sessiond daemon
  65  *   (will let the sessiond daemon enable sessions before main
  66  *   starts.)
  67  * - sessiond daemon is not reachable.
  68  * - timeout (ensuring applications are resilient to session
  69  *   daemon problems).
  70  */
  71 static sem_t constructor_wait;
  72 /*
  73  * Doing this for both the global and local sessiond.
  74  */
  75 static int sem_count = { 2 };
  76
  77 /*
  78  * Info about socket and associated listener thread.
  79  */
  80 struct sock_info {
  81         const char *name;
  82         pthread_t ust_listener; /* listener thread */
  83         int root_handle;
  84         int constructor_sem_posted;
  85         int allowed;
  86         int global;
  87
  88         char sock_path[PATH_MAX];
  89         int socket;
  90
  91         char wait_shm_path[PATH_MAX];
  92         char *wait_shm_mmap;
  93 };
  94
  95 /* Socket from app (connect) to session daemon (listen) for communication */
  96 struct sock_info global_apps = {
  97         .name = "global",
  98         .global = 1,
  99
 100         .root_handle = -1,
 101         .allowed = 1,
 102
 103         .sock_path = DEFAULT_GLOBAL_APPS_UNIX_SOCK,
 104         .socket = -1,
 105
 106         .wait_shm_path = DEFAULT_GLOBAL_APPS_WAIT_SHM_PATH,
 107 };
 108
 109 /* TODO: allow global_apps_sock_path override */
 110
 111 struct sock_info local_apps = {
 112         .name = "local",
 113         .global = 0,
 114         .root_handle = -1,
 115         .allowed = 0,   /* Check setuid bit first */
 116
 117         .socket = -1,
 118 };
 119
 120 extern void ltt_ring_buffer_client_overwrite_init(void);
 121 extern void ltt_ring_buffer_client_discard_init(void);
 122 extern void ltt_ring_buffer_metadata_client_init(void);
 123 extern void ltt_ring_buffer_client_overwrite_exit(void);
 124 extern void ltt_ring_buffer_client_discard_exit(void);
 125 extern void ltt_ring_buffer_metadata_client_exit(void);
 126
 127 static
 128 int setup_local_apps(void)
 129 {
 130         const char *home_dir;
 131         uid_t uid;
 132
 133         uid = getuid();
 134         /*
 135          * Disallow per-user tracing for setuid binaries.
 136          */
 137         if (uid != geteuid()) {
 138                 local_apps.allowed = 0;
 139                 return 0;
 140         } else {
 141                 local_apps.allowed = 1;
 142         }
 143         home_dir = (const char *) getenv("HOME");
 144         if (!home_dir)
 145                 return -ENOENT;
 146         snprintf(local_apps.sock_path, PATH_MAX,
 147                  DEFAULT_HOME_APPS_UNIX_SOCK, home_dir);
 148         snprintf(local_apps.wait_shm_path, PATH_MAX,
 149                  DEFAULT_HOME_APPS_WAIT_SHM_PATH, uid);
 150         return 0;
 151 }
 152
 153 static
 154 int register_app_to_sessiond(int socket)
 155 {
 156         ssize_t ret;
 157         int prctl_ret;
 158         struct {
 159                 uint32_t major;
 160                 uint32_t minor;
 161                 pid_t pid;
 162                 pid_t ppid;
 163                 uid_t uid;
 164                 gid_t gid;
 165                 char name[16];  /* process name */
 166         } reg_msg;
 167
 168         reg_msg.major = LTTNG_UST_COMM_VERSION_MAJOR;
 169         reg_msg.minor = LTTNG_UST_COMM_VERSION_MINOR;
 170         reg_msg.pid = getpid();
 171         reg_msg.ppid = getppid();
 172         reg_msg.uid = getuid();
 173         reg_msg.gid = getgid();
 174         prctl_ret = prctl(PR_GET_NAME, (unsigned long) reg_msg.name, 0, 0, 0);
 175         if (prctl_ret) {
 176                 ERR("Error executing prctl");
 177                 return -errno;
 178         }
 179
 180         ret = lttcomm_send_unix_sock(socket, &reg_msg, sizeof(reg_msg));
 181         if (ret >= 0 && ret != sizeof(reg_msg))
 182                 return -EIO;
 183         return ret;
 184 }
 185
 186 static
 187 int send_reply(int sock, struct lttcomm_ust_reply *lur)
 188 {
 189         ssize_t len;
 190
 191         len = lttcomm_send_unix_sock(sock, lur, sizeof(*lur));
 192         switch (len) {
 193         case sizeof(*lur):
 194                 DBG("message successfully sent");
 195                 return 0;
 196         case -1:
 197                 if (errno == ECONNRESET) {
 198                         printf("remote end closed connection\n");
 199                         return 0;
 200                 }
 201                 return -1;
 202         default:
 203                 printf("incorrect message size: %zd\n", len);
 204                 return -1;
 205         }
 206 }
 207
 208 static
 209 int handle_register_done(struct sock_info *sock_info)
 210 {
 211         int ret;
 212
 213         if (sock_info->constructor_sem_posted)
 214                 return 0;
 215         sock_info->constructor_sem_posted = 1;
 216         ret = uatomic_add_return(&sem_count, -1);
 217         if (ret == 0) {
 218                 ret = sem_post(&constructor_wait);
 219                 assert(!ret);
 220         }
 221         return 0;
 222 }
 223
 224 static
 225 int handle_message(struct sock_info *sock_info,
 226                 int sock, struct lttcomm_ust_msg *lum)
 227 {
 228         int ret = 0;
 229         const struct objd_ops *ops;
 230         struct lttcomm_ust_reply lur;
 231
 232         ust_lock();
 233
 234         memset(&lur, 0, sizeof(lur));
 235
 236         if (lttng_ust_comm_should_quit) {
 237                 ret = -EPERM;
 238                 goto end;
 239         }
 240
 241         ops = objd_ops(lum->handle);
 242         if (!ops) {
 243                 ret = -ENOENT;
 244                 goto end;
 245         }
 246
 247         switch (lum->cmd) {
 248         case LTTNG_UST_REGISTER_DONE:
 249                 if (lum->handle == LTTNG_UST_ROOT_HANDLE)
 250                         ret = handle_register_done(sock_info);
 251                 else
 252                         ret = -EINVAL;
 253                 break;
 254         case LTTNG_UST_RELEASE:
 255                 if (lum->handle == LTTNG_UST_ROOT_HANDLE)
 256                         ret = -EPERM;
 257                 else
 258                         ret = objd_unref(lum->handle);
 259                 break;
 260         default:
 261                 if (ops->cmd)
 262                         ret = ops->cmd(lum->handle, lum->cmd,
 263                                         (unsigned long) &lum->u);
 264                 else
 265                         ret = -ENOSYS;
 266                 break;
 267         }
 268
 269 end:
 270         lur.handle = lum->handle;
 271         lur.cmd = lum->cmd;
 272         lur.ret_val = ret;
 273         if (ret >= 0) {
 274                 lur.ret_code = LTTCOMM_OK;
 275         } else {
 276                 lur.ret_code = LTTCOMM_SESSION_FAIL;
 277         }
 278         ret = send_reply(sock, &lur);
 279
 280         ust_unlock();
 281         return ret;
 282 }
 283
 284 static
 285 void cleanup_sock_info(struct sock_info *sock_info)
 286 {
 287         int ret;
 288
 289         if (sock_info->socket != -1) {
 290                 ret = close(sock_info->socket);
 291                 if (ret) {
 292                         ERR("Error closing apps socket");
 293                 }
 294                 sock_info->socket = -1;
 295         }
 296         if (sock_info->root_handle != -1) {
 297                 ret = objd_unref(sock_info->root_handle);
 298                 if (ret) {
 299                         ERR("Error unref root handle");
 300                 }
 301                 sock_info->root_handle = -1;
 302         }
 303         sock_info->constructor_sem_posted = 0;
 304         if (sock_info->wait_shm_mmap) {
 305                 ret = munmap(sock_info->wait_shm_mmap, sysconf(_SC_PAGE_SIZE));
 306                 if (ret) {
 307                         ERR("Error unmapping wait shm");
 308                 }
 309                 sock_info->wait_shm_mmap = NULL;
 310         }
 311 }
 312
 313 /*
 314  * Using fork to set umask in the child process (not multi-thread safe).
 315  * We deal with the shm_open vs ftruncate race (happening when the
 316  * sessiond owns the shm and does not let everybody modify it, to ensure
 317  * safety against shm_unlink) by simply letting the mmap fail and
 318  * retrying after a few seconds.
 319  * For global shm, everybody has rw access to it until the sessiond
 320  * starts.
 321  */
 322 static
 323 int get_wait_shm(struct sock_info *sock_info, size_t mmap_size)
 324 {
 325         int wait_shm_fd, ret;
 326         pid_t pid;
 327
 328         /*
 329          * Try to open read-only.
 330          */
 331         wait_shm_fd = shm_open(sock_info->wait_shm_path, O_RDONLY, 0);
 332         if (wait_shm_fd >= 0) {
 333                 goto end;
 334         } else if (wait_shm_fd < 0 && errno != ENOENT) {
 335                 /*
 336                  * Real-only open did not work, and it's not because the
 337                  * entry was not present. It's a failure that prohibits
 338                  * using shm.
 339                  */
 340                 ERR("Error opening shm %s", sock_info->wait_shm_path);
 341                 goto end;
 342         }
 343         /*
 344          * If the open failed because the file did not exist, try
 345          * creating it ourself.
 346          */
 347         pid = fork();
 348         if (pid > 0) {
 349                 int status;
 350
 351                 /*
 352                  * Parent: wait for child to return, in which case the
 353                  * shared memory map will have been created.
 354                  */
 355                 pid = wait(&status);
 356                 if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 357                         wait_shm_fd = -1;
 358                         goto end;
 359                 }
 360                 /*
 361                  * Try to open read-only again after creation.
 362                  */
 363                 wait_shm_fd = shm_open(sock_info->wait_shm_path, O_RDONLY, 0);
 364                 if (wait_shm_fd < 0) {
 365                         /*
 366                          * Real-only open did not work. It's a failure
 367                          * that prohibits using shm.
 368                          */
 369                         ERR("Error opening shm %s", sock_info->wait_shm_path);
 370                         goto end;
 371                 }
 372                 goto end;
 373         } else if (pid == 0) {
 374                 int create_mode;
 375
 376                 /* Child */
 377                 create_mode = S_IRUSR | S_IWUSR | S_IRGRP;
 378                 if (sock_info->global)
 379                         create_mode |= S_IROTH | S_IWGRP | S_IWOTH;
 380                 /*
 381                  * We're alone in a child process, so we can modify the
 382                  * process-wide umask.
 383                  */
 384                 umask(~create_mode);
 385                 /*
 386                  * Try creating shm (or get rw access).
 387                  * We don't do an exclusive open, because we allow other
 388                  * processes to create+ftruncate it concurrently.
 389                  */
 390                 wait_shm_fd = shm_open(sock_info->wait_shm_path,
 391                                 O_RDWR | O_CREAT, create_mode);
 392                 if (wait_shm_fd >= 0) {
 393                         ret = ftruncate(wait_shm_fd, mmap_size);
 394                         if (ret) {
 395                                 PERROR("ftruncate");
 396                                 exit(EXIT_FAILURE);
 397                         }
 398                         exit(EXIT_SUCCESS);
 399                 }
 400                 /*
 401                  * For local shm, we need to have rw access to accept
 402                  * opening it: this means the local sessiond will be
 403                  * able to wake us up. For global shm, we open it even
 404                  * if rw access is not granted, because the root.root
 405                  * sessiond will be able to override all rights and wake
 406                  * us up.
 407                  */
 408                 if (!sock_info->global && errno != EACCES) {
 409                         ERR("Error opening shm %s", sock_info->wait_shm_path);
 410                         exit(EXIT_FAILURE);
 411                 }
 412                 /*
 413                  * The shm exists, but we cannot open it RW. Report
 414                  * success.
 415                  */
 416                 exit(EXIT_SUCCESS);
 417         } else {
 418                 return -1;
 419         }
 420 end:
 421         if (wait_shm_fd >= 0 && !sock_info->global) {
 422                 struct stat statbuf;
 423
 424                 /*
 425                  * Ensure that our user is the owner of the shm file for
 426                  * local shm. If we do not own the file, it means our
 427                  * sessiond will not have access to wake us up (there is
 428                  * probably a rogue process trying to fake our
 429                  * sessiond). Fallback to polling method in this case.
 430                  */
 431                 ret = fstat(wait_shm_fd, &statbuf);
 432                 if (ret) {
 433                         PERROR("fstat");
 434                         goto error_close;
 435                 }
 436                 if (statbuf.st_uid != getuid())
 437                         goto error_close;
 438         }
 439         return wait_shm_fd;
 440
 441 error_close:
 442         ret = close(wait_shm_fd);
 443         if (ret) {
 444                 PERROR("Error closing fd");
 445         }
 446         return -1;
 447 }
 448
 449 static
 450 char *get_map_shm(struct sock_info *sock_info)
 451 {
 452         size_t mmap_size = sysconf(_SC_PAGE_SIZE);
 453         int wait_shm_fd, ret;
 454         char *wait_shm_mmap;
 455
 456         wait_shm_fd = get_wait_shm(sock_info, mmap_size);
 457         if (wait_shm_fd < 0) {
 458                 goto error;
 459         }
 460         wait_shm_mmap = mmap(NULL, mmap_size, PROT_READ,
 461                   MAP_SHARED, wait_shm_fd, 0);
 462         /* close shm fd immediately after taking the mmap reference */
 463         ret = close(wait_shm_fd);
 464         if (ret) {
 465                 PERROR("Error closing fd");
 466         }
 467         if (wait_shm_mmap == MAP_FAILED) {
 468                 DBG("mmap error (can be caused by race with sessiond). Fallback to poll mode.");
 469                 goto error;
 470         }
 471         return wait_shm_mmap;
 472
 473 error:
 474         return NULL;
 475 }
 476
 477 static
 478 void wait_for_sessiond(struct sock_info *sock_info)
 479 {
 480         ust_lock();
 481         if (lttng_ust_comm_should_quit) {
 482                 goto quit;
 483         }
 484         if (!sock_info->wait_shm_mmap) {
 485                 sock_info->wait_shm_mmap = get_map_shm(sock_info);
 486                 if (!sock_info->wait_shm_mmap)
 487                         goto error;
 488         }
 489         ust_unlock();
 490
 491         DBG("Waiting for %s apps sessiond", sock_info->name);
 492         /* Wait for futex wakeup TODO */
 493         sleep(5);
 494
 495         return;
 496
 497 quit:
 498         ust_unlock();
 499         return;
 500
 501 error:
 502         ust_unlock();
 503         /* Error handling: fallback on a 5 seconds sleep. */
 504         sleep(5);
 505         return;
 506 }
 507
 508 /*
 509  * This thread does not allocate any resource, except within
 510  * handle_message, within mutex protection. This mutex protects against
 511  * fork and exit.
 512  * The other moment it allocates resources is at socket connexion, which
 513  * is also protected by the mutex.
 514  */
 515 static
 516 void *ust_listener_thread(void *arg)
 517 {
 518         struct sock_info *sock_info = arg;
 519         int sock, ret;
 520
 521         /* Restart trying to connect to the session daemon */
 522 restart:
 523         ust_lock();
 524
 525         if (lttng_ust_comm_should_quit) {
 526                 ust_unlock();
 527                 goto quit;
 528         }
 529
 530         if (sock_info->socket != -1) {
 531                 ret = close(sock_info->socket);
 532                 if (ret) {
 533                         ERR("Error closing %s apps socket", sock_info->name);
 534                 }
 535                 sock_info->socket = -1;
 536         }
 537
 538         /* Register */
 539         ret = lttcomm_connect_unix_sock(sock_info->sock_path);
 540         if (ret < 0) {
 541                 ERR("Error connecting to %s apps socket", sock_info->name);
 542                 /*
 543                  * If we cannot find the sessiond daemon, don't delay
 544                  * constructor execution.
 545                  */
 546                 ret = handle_register_done(sock_info);
 547                 assert(!ret);
 548                 ust_unlock();
 549
 550                 /* Wait for sessiond availability with pipe */
 551                 wait_for_sessiond(sock_info);
 552                 goto restart;
 553         }
 554
 555         sock_info->socket = sock = ret;
 556
 557         /*
 558          * Create only one root handle per listener thread for the whole
 559          * process lifetime.
 560          */
 561         if (sock_info->root_handle == -1) {
 562                 ret = lttng_abi_create_root_handle();
 563                 if (ret) {
 564                         ERR("Error creating root handle");
 565                         ust_unlock();
 566                         goto quit;
 567                 }
 568                 sock_info->root_handle = ret;
 569         }
 570
 571         ret = register_app_to_sessiond(sock);
 572         if (ret < 0) {
 573                 ERR("Error registering to %s apps socket", sock_info->name);
 574                 /*
 575                  * If we cannot register to the sessiond daemon, don't
 576                  * delay constructor execution.
 577                  */
 578                 ret = handle_register_done(sock_info);
 579                 assert(!ret);
 580                 ust_unlock();
 581                 wait_for_sessiond(sock_info);
 582                 goto restart;
 583         }
 584         ust_unlock();
 585
 586         for (;;) {
 587                 ssize_t len;
 588                 struct lttcomm_ust_msg lum;
 589
 590                 len = lttcomm_recv_unix_sock(sock, &lum, sizeof(lum));
 591                 switch (len) {
 592                 case 0: /* orderly shutdown */
 593                         DBG("%s ltt-sessiond has performed an orderly shutdown\n", sock_info->name);
 594                         goto end;
 595                 case sizeof(lum):
 596                         DBG("message received\n");
 597                         ret = handle_message(sock_info, sock, &lum);
 598                         if (ret < 0) {
 599                                 ERR("Error handling message for %s socket", sock_info->name);
 600                         }
 601                         continue;
 602                 case -1:
 603                         if (errno == ECONNRESET) {
 604                                 ERR("%s remote end closed connection\n", sock_info->name);
 605                                 goto end;
 606                         }
 607                         goto end;
 608                 default:
 609                         ERR("incorrect message size (%s socket): %zd\n", sock_info->name, len);
 610                         continue;
 611                 }
 612
 613         }
 614 end:
 615         goto restart;   /* try to reconnect */
 616 quit:
 617         return NULL;
 618 }
 619
 620 /*
 621  * Return values: -1: don't wait. 0: wait forever. 1: timeout wait.
 622  */
 623 static
 624 int get_timeout(struct timespec *constructor_timeout)
 625 {
 626         long constructor_delay_ms = LTTNG_UST_DEFAULT_CONSTRUCTOR_TIMEOUT_MS;
 627         char *str_delay;
 628         int ret;
 629
 630         str_delay = getenv("UST_REGISTER_TIMEOUT");
 631         if (str_delay) {
 632                 constructor_delay_ms = strtol(str_delay, NULL, 10);
 633         }
 634
 635         switch (constructor_delay_ms) {
 636         case -1:/* fall-through */
 637         case 0:
 638                 return constructor_delay_ms;
 639         default:
 640                 break;
 641         }
 642
 643         /*
 644          * If we are unable to find the current time, don't wait.
 645          */
 646         ret = clock_gettime(CLOCK_REALTIME, constructor_timeout);
 647         if (ret) {
 648                 return -1;
 649         }
 650         constructor_timeout->tv_sec += constructor_delay_ms / 1000UL;
 651         constructor_timeout->tv_nsec +=
 652                 (constructor_delay_ms % 1000UL) * 1000000UL;
 653         if (constructor_timeout->tv_nsec >= 1000000000UL) {
 654                 constructor_timeout->tv_sec++;
 655                 constructor_timeout->tv_nsec -= 1000000000UL;
 656         }
 657         return 1;
 658 }
 659
 660 /*
 661  * sessiond monitoring thread: monitor presence of global and per-user
 662  * sessiond by polling the application common named pipe.
 663  */
 664 /* TODO */
 665
 666 void __attribute__((constructor)) lttng_ust_init(void)
 667 {
 668         struct timespec constructor_timeout;
 669         int timeout_mode;
 670         int ret;
 671
 672         if (uatomic_xchg(&initialized, 1) == 1)
 673                 return;
 674
 675         /*
 676          * We want precise control over the order in which we construct
 677          * our sub-libraries vs starting to receive commands from
 678          * sessiond (otherwise leading to errors when trying to create
 679          * sessiond before the init functions are completed).
 680          */
 681         init_usterr();
 682         init_tracepoint();
 683         ltt_ring_buffer_metadata_client_init();
 684         ltt_ring_buffer_client_overwrite_init();
 685         ltt_ring_buffer_client_discard_init();
 686
 687         timeout_mode = get_timeout(&constructor_timeout);
 688
 689         ret = sem_init(&constructor_wait, 0, 0);
 690         assert(!ret);
 691
 692         ret = setup_local_apps();
 693         if (ret) {
 694                 ERR("Error setting up to local apps");
 695         }
 696         ret = pthread_create(&local_apps.ust_listener, NULL,
 697                         ust_listener_thread, &local_apps);
 698
 699         if (local_apps.allowed) {
 700                 ret = pthread_create(&global_apps.ust_listener, NULL,
 701                                 ust_listener_thread, &global_apps);
 702         } else {
 703                 handle_register_done(&local_apps);
 704         }
 705
 706         switch (timeout_mode) {
 707         case 1: /* timeout wait */
 708                 do {
 709                         ret = sem_timedwait(&constructor_wait,
 710                                         &constructor_timeout);
 711                 } while (ret < 0 && errno == EINTR);
 712                 if (ret < 0 && errno == ETIMEDOUT) {
 713                         ERR("Timed out waiting for ltt-sessiond");
 714                 } else {
 715                         assert(!ret);
 716                 }
 717                 break;
 718         case -1:/* wait forever */
 719                 do {
 720                         ret = sem_wait(&constructor_wait);
 721                 } while (ret < 0 && errno == EINTR);
 722                 assert(!ret);
 723                 break;
 724         case 0: /* no timeout */
 725                 break;
 726         }
 727 }
 728
 729 static
 730 void lttng_ust_cleanup(int exiting)
 731 {
 732         cleanup_sock_info(&global_apps);
 733         if (local_apps.allowed) {
 734                 cleanup_sock_info(&local_apps);
 735         }
 736         lttng_ust_abi_exit();
 737         ltt_events_exit();
 738         ltt_ring_buffer_client_discard_exit();
 739         ltt_ring_buffer_client_overwrite_exit();
 740         ltt_ring_buffer_metadata_client_exit();
 741         exit_tracepoint();
 742         if (!exiting) {
 743                 /* Reinitialize values for fork */
 744                 sem_count = 2;
 745                 lttng_ust_comm_should_quit = 0;
 746                 initialized = 0;
 747         }
 748 }
 749
 750 void __attribute__((destructor)) lttng_ust_exit(void)
 751 {
 752         int ret;
 753
 754         /*
 755          * Using pthread_cancel here because:
 756          * A) we don't want to hang application teardown.
 757          * B) the thread is not allocating any resource.
 758          */
 759
 760         /*
 761          * Require the communication thread to quit. Synchronize with
 762          * mutexes to ensure it is not in a mutex critical section when
 763          * pthread_cancel is later called.
 764          */
 765         ust_lock();
 766         lttng_ust_comm_should_quit = 1;
 767         ust_unlock();
 768
 769         ret = pthread_cancel(global_apps.ust_listener);
 770         if (ret) {
 771                 ERR("Error cancelling global ust listener thread");
 772         }
 773         if (local_apps.allowed) {
 774                 ret = pthread_cancel(local_apps.ust_listener);
 775                 if (ret) {
 776                         ERR("Error cancelling local ust listener thread");
 777                 }
 778         }
 779         lttng_ust_cleanup(1);
 780 }
 781
 782 /*
 783  * We exclude the worker threads across fork and clone (except
 784  * CLONE_VM), because these system calls only keep the forking thread
 785  * running in the child.  Therefore, we don't want to call fork or clone
 786  * in the middle of an tracepoint or ust tracing state modification.
 787  * Holding this mutex protects these structures across fork and clone.
 788  */
 789 void ust_before_fork(ust_fork_info_t *fork_info)
 790 {
 791         /*
 792          * Disable signals. This is to avoid that the child intervenes
 793          * before it is properly setup for tracing. It is safer to
 794          * disable all signals, because then we know we are not breaking
 795          * anything by restoring the original mask.
 796          */
 797         sigset_t all_sigs;
 798         int ret;
 799
 800         /* Disable signals */
 801         sigfillset(&all_sigs);
 802         ret = sigprocmask(SIG_BLOCK, &all_sigs, &fork_info->orig_sigs);
 803         if (ret == -1) {
 804                 PERROR("sigprocmask");
 805         }
 806         ust_lock();
 807         rcu_bp_before_fork();
 808 }
 809
 810 static void ust_after_fork_common(ust_fork_info_t *fork_info)
 811 {
 812         int ret;
 813
 814         DBG("process %d", getpid());
 815         ust_unlock();
 816         /* Restore signals */
 817         ret = sigprocmask(SIG_SETMASK, &fork_info->orig_sigs, NULL);
 818         if (ret == -1) {
 819                 PERROR("sigprocmask");
 820         }
 821 }
 822
 823 void ust_after_fork_parent(ust_fork_info_t *fork_info)
 824 {
 825         DBG("process %d", getpid());
 826         rcu_bp_after_fork_parent();
 827         /* Release mutexes and reenable signals */
 828         ust_after_fork_common(fork_info);
 829 }
 830
 831 /*
 832  * After fork, in the child, we need to cleanup all the leftover state,
 833  * except the worker thread which already magically disappeared thanks
 834  * to the weird Linux fork semantics. After tyding up, we call
 835  * lttng_ust_init() again to start over as a new PID.
 836  *
 837  * This is meant for forks() that have tracing in the child between the
 838  * fork and following exec call (if there is any).
 839  */
 840 void ust_after_fork_child(ust_fork_info_t *fork_info)
 841 {
 842         DBG("process %d", getpid());
 843         /* Release urcu mutexes */
 844         rcu_bp_after_fork_child();
 845         lttng_ust_cleanup(0);
 846         /* Release mutexes and reenable signals */
 847         ust_after_fork_common(fork_info);
 848         lttng_ust_init();
 849 }