src/bin/lttng-sessiond/notification-thread.c

   1 /*
   2  * Copyright (C) 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
   3  *
   4  * This program is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License, version 2 only, as
   6  * published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
  11  * more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along with
  14  * this program; if not, write to the Free Software Foundation, Inc., 51
  15  * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  16  */
  17
  18 #define _LGPL_SOURCE
  19 #include <lttng/trigger/trigger.h>
  20 #include <lttng/notification/channel-internal.h>
  21 #include <lttng/notification/notification-internal.h>
  22 #include <lttng/condition/condition-internal.h>
  23 #include <lttng/condition/buffer-usage-internal.h>
  24 #include <common/error.h>
  25 #include <common/config/session-config.h>
  26 #include <common/defaults.h>
  27 #include <common/utils.h>
  28 #include <common/futex.h>
  29 #include <common/align.h>
  30 #include <common/time.h>
  31 #include <sys/eventfd.h>
  32 #include <sys/stat.h>
  33 #include <time.h>
  34 #include <signal.h>
  35
  36 #include "notification-thread.h"
  37 #include "notification-thread-events.h"
  38 #include "notification-thread-commands.h"
  39 #include "lttng-sessiond.h"
  40 #include "health-sessiond.h"
  41
  42 #include <urcu.h>
  43 #include <urcu/list.h>
  44 #include <urcu/rculfhash.h>
  45
  46 /**
  47  * This thread maintains an internal state associating clients and triggers.
  48  *
  49  * In order to speed-up and simplify queries, hash tables providing the
  50  * following associations are maintained:
  51  *
  52  *   - client_socket_ht: associate a client's socket (fd) to its "struct client"
  53  *             This hash table owns the "struct client" which must thus be
  54  *             disposed-of on removal from the hash table.
  55  *
  56  *   - channel_triggers_ht:
  57  *             associates a channel key to a list of
  58  *             struct lttng_trigger_list_nodes. The triggers in this list are
  59  *             those that have conditions that apply to this channel.
  60  *             This hash table owns the list, but not the triggers themselves.
  61  *
  62  *   - channel_state_ht:
  63  *             associates a pair (channel key, channel domain) to its last
  64  *             sampled state received from the consumer daemon
  65  *             (struct channel_state).
  66  *             This previous sample is kept to implement edge-triggered
  67  *             conditions as we need to detect the state transitions.
  68  *             This hash table owns the channel state.
  69  *
  70  *   - notification_trigger_clients_ht:
  71  *             associates notification-emitting triggers to clients
  72  *             (struct notification_client_ht_node) subscribed to those
  73  *             conditions.
  74  *             The condition's hash and match functions are used directly since
  75  *             all triggers in this hash table have the "notify" action.
  76  *             This hash table holds no ownership.
  77  *
  78  *   - channels_ht:
  79  *             associates a channel_key to a struct channel_info. The hash table
  80  *             holds the ownership of the struct channel_info.
  81  *
  82  *   - triggers_ht:
  83  *             associated a condition to a struct lttng_trigger_ht_element.
  84  *             The hash table holds the ownership of the
  85  *             lttng_trigger_ht_elements along with the triggers themselves.
  86  *
  87  * The thread reacts to the following internal events:
  88  *   1) creation of a tracing channel,
  89  *   2) destruction of a tracing channel,
  90  *   3) registration of a trigger,
  91  *   4) unregistration of a trigger,
  92  *   5) reception of a channel monitor sample from the consumer daemon.
  93  *
  94  * Events specific to notification-emitting triggers:
  95  *   6) connection of a notification client,
  96  *   7) disconnection of a notification client,
  97  *   8) subscription of a client to a conditions' notifications,
  98  *   9) unsubscription of a client from a conditions' notifications,
  99  *
 100  *
 101  * 1) Creation of a tracing channel
 102  *    - notification_trigger_clients_ht is traversed to identify
 103  *      triggers which apply to this new channel,
 104  *    - triggers identified are added to the channel_triggers_ht.
 105  *    - add channel to channels_ht
 106  *
 107  * 2) Destruction of a tracing channel
 108  *    - remove entry from channel_triggers_ht, releasing the list wrapper and
 109  *      elements,
 110  *    - remove entry from the channel_state_ht.
 111  *    - remove channel from channels_ht
 112  *
 113  * 3) Registration of a trigger
 114  *    - if the trigger's action is of type "notify",
 115  *      - traverse the list of conditions of every client to build a list of
 116  *        clients which have to be notified when this trigger's condition is met,
 117  *        - add list of clients (even if it is empty) to the
 118  *          notification_trigger_clients_ht,
 119  *    - add trigger to channel_triggers_ht (if applicable),
 120  *    - add trigger to triggers_ht
 121  *
 122  * 4) Unregistration of a trigger
 123  *    - if the trigger's action is of type "notify",
 124  *      - remove the trigger from the notification_trigger_clients_ht,
 125  *    - remove trigger from channel_triggers_ht (if applicable),
 126  *    - remove trigger from triggers_ht
 127  *
 128  * 5) Reception of a channel monitor sample from the consumer daemon
 129  *    - evaluate the conditions associated with the triggers found in
 130  *      the channel_triggers_ht,
 131  *      - if a condition evaluates to "true" and the condition is of type
 132  *        "notify", query the notification_trigger_clients_ht and send
 133  *        a notification to the clients.
 134  *
 135  * 6) Connection of a client
 136  *    - add client socket to the client_socket_ht.
 137  *
 138  * 7) Disconnection of a client
 139  *    - remove client socket from the client_socket_ht,
 140  *    - traverse all conditions to which the client is subscribed and remove
 141  *      the client from the notification_trigger_clients_ht.
 142  *
 143  * 8) Subscription of a client to a condition's notifications
 144  *    - Add the condition to the client's list of subscribed conditions,
 145  *    - Look-up notification_trigger_clients_ht and add the client to
 146  *      list of clients.
 147  *
 148  * 9) Unsubscription of a client to a condition's notifications
 149  *    - Remove the condition from the client's list of subscribed conditions,
 150  *    - Look-up notification_trigger_clients_ht and remove the client
 151  *      from the list of clients.
 152  */
 153
 154 /*
 155  * Destroy the thread data previously created by the init function.
 156  */
 157 void notification_thread_handle_destroy(
 158                 struct notification_thread_handle *handle)
 159 {
 160         int ret;
 161         struct notification_thread_command *cmd, *tmp;
 162
 163         if (!handle) {
 164                 goto end;
 165         }
 166
 167         if (handle->cmd_queue.event_fd < 0) {
 168                 goto end;
 169         }
 170         ret = close(handle->cmd_queue.event_fd);
 171         if (ret < 0) {
 172                 PERROR("close notification command queue event_fd");
 173         }
 174
 175         pthread_mutex_lock(&handle->cmd_queue.lock);
 176         /* Purge queue of in-flight commands and mark them as cancelled. */
 177         cds_list_for_each_entry_safe(cmd, tmp, &handle->cmd_queue.list,
 178                         cmd_list_node) {
 179                 cds_list_del(&cmd->cmd_list_node);
 180                 cmd->reply_code = LTTNG_ERR_COMMAND_CANCELLED;
 181                 futex_nto1_wake(&cmd->reply_futex);
 182         }
 183         pthread_mutex_unlock(&handle->cmd_queue.lock);
 184         pthread_mutex_destroy(&handle->cmd_queue.lock);
 185
 186         if (handle->channel_monitoring_pipes.ust32_consumer >= 0) {
 187                 ret = close(handle->channel_monitoring_pipes.ust32_consumer);
 188                 if (ret) {
 189                         PERROR("close 32-bit consumer channel monitoring pipe");
 190                 }
 191         }
 192         if (handle->channel_monitoring_pipes.ust64_consumer >= 0) {
 193                 ret = close(handle->channel_monitoring_pipes.ust64_consumer);
 194                 if (ret) {
 195                         PERROR("close 64-bit consumer channel monitoring pipe");
 196                 }
 197         }
 198         if (handle->channel_monitoring_pipes.kernel_consumer >= 0) {
 199                 ret = close(handle->channel_monitoring_pipes.kernel_consumer);
 200                 if (ret) {
 201                         PERROR("close kernel consumer channel monitoring pipe");
 202                 }
 203         }
 204 end:
 205         free(handle);
 206 }
 207
 208 struct notification_thread_handle *notification_thread_handle_create(
 209                 struct lttng_pipe *ust32_channel_monitor_pipe,
 210                 struct lttng_pipe *ust64_channel_monitor_pipe,
 211                 struct lttng_pipe *kernel_channel_monitor_pipe)
 212 {
 213         int ret;
 214         struct notification_thread_handle *handle;
 215
 216         handle = zmalloc(sizeof(*handle));
 217         if (!handle) {
 218                 goto end;
 219         }
 220
 221         /* FIXME Replace eventfd by a pipe to support older kernels. */
 222         handle->cmd_queue.event_fd = eventfd(0, EFD_CLOEXEC);
 223         if (handle->cmd_queue.event_fd < 0) {
 224                 PERROR("eventfd notification command queue");
 225                 goto error;
 226         }
 227         CDS_INIT_LIST_HEAD(&handle->cmd_queue.list);
 228         ret = pthread_mutex_init(&handle->cmd_queue.lock, NULL);
 229         if (ret) {
 230                 goto error;
 231         }
 232
 233         if (ust32_channel_monitor_pipe) {
 234                 handle->channel_monitoring_pipes.ust32_consumer =
 235                                 lttng_pipe_release_readfd(
 236                                         ust32_channel_monitor_pipe);
 237                 if (handle->channel_monitoring_pipes.ust32_consumer < 0) {
 238                         goto error;
 239                 }
 240         } else {
 241                 handle->channel_monitoring_pipes.ust32_consumer = -1;
 242         }
 243         if (ust64_channel_monitor_pipe) {
 244                 handle->channel_monitoring_pipes.ust64_consumer =
 245                                 lttng_pipe_release_readfd(
 246                                         ust64_channel_monitor_pipe);
 247                 if (handle->channel_monitoring_pipes.ust64_consumer < 0) {
 248                         goto error;
 249                 }
 250         } else {
 251                 handle->channel_monitoring_pipes.ust64_consumer = -1;
 252         }
 253         if (kernel_channel_monitor_pipe) {
 254                 handle->channel_monitoring_pipes.kernel_consumer =
 255                                 lttng_pipe_release_readfd(
 256                                         kernel_channel_monitor_pipe);
 257                 if (handle->channel_monitoring_pipes.kernel_consumer < 0) {
 258                         goto error;
 259                 }
 260         } else {
 261                 handle->channel_monitoring_pipes.kernel_consumer = -1;
 262         }
 263 end:
 264         return handle;
 265 error:
 266         notification_thread_handle_destroy(handle);
 267         return NULL;
 268 }
 269
 270 static
 271 char *get_notification_channel_sock_path(void)
 272 {
 273         int ret;
 274         bool is_root = !getuid();
 275         char *sock_path;
 276
 277         sock_path = zmalloc(LTTNG_PATH_MAX);
 278         if (!sock_path) {
 279                 goto error;
 280         }
 281
 282         if (is_root) {
 283                 ret = snprintf(sock_path, LTTNG_PATH_MAX,
 284                                 DEFAULT_GLOBAL_NOTIFICATION_CHANNEL_UNIX_SOCK);
 285                 if (ret < 0) {
 286                         goto error;
 287                 }
 288         } else {
 289                 char *home_path = utils_get_home_dir();
 290
 291                 if (!home_path) {
 292                         ERR("Can't get HOME directory for socket creation");
 293                         goto error;
 294                 }
 295
 296                 ret = snprintf(sock_path, LTTNG_PATH_MAX,
 297                                 DEFAULT_HOME_NOTIFICATION_CHANNEL_UNIX_SOCK,
 298                                 home_path);
 299                 if (ret < 0) {
 300                         goto error;
 301                 }
 302         }
 303
 304         return sock_path;
 305 error:
 306         free(sock_path);
 307         return NULL;
 308 }
 309
 310 static
 311 void notification_channel_socket_destroy(int fd)
 312 {
 313         int ret;
 314         char *sock_path = get_notification_channel_sock_path();
 315
 316         DBG("[notification-thread] Destroying notification channel socket");
 317
 318         if (sock_path) {
 319                 ret = unlink(sock_path);
 320                 free(sock_path);
 321                 if (ret < 0) {
 322                         PERROR("unlink notification channel socket");
 323                 }
 324         }
 325
 326         ret = close(fd);
 327         if (ret) {
 328                 PERROR("close notification channel socket");
 329         }
 330 }
 331
 332 static
 333 int notification_channel_socket_create(void)
 334 {
 335         int fd = -1, ret;
 336         char *sock_path = get_notification_channel_sock_path();
 337
 338         DBG("[notification-thread] Creating notification channel UNIX socket at %s",
 339                         sock_path);
 340
 341         ret = lttcomm_create_unix_sock(sock_path);
 342         if (ret < 0) {
 343                 ERR("[notification-thread] Failed to create notification socket");
 344                 goto error;
 345         }
 346         fd = ret;
 347
 348         ret = chmod(sock_path, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
 349         if (ret < 0) {
 350                 ERR("Set file permissions failed: %s", sock_path);
 351                 PERROR("chmod notification channel socket");
 352                 goto error;
 353         }
 354
 355         DBG("[notification-thread] Notification channel UNIX socket created (fd = %i)",
 356                         fd);
 357         free(sock_path);
 358         return fd;
 359 error:
 360         if (fd >= 0 && close(fd) < 0) {
 361                 PERROR("close notification channel socket");
 362         }
 363         free(sock_path);
 364         return ret;
 365 }
 366
 367 static
 368 int init_poll_set(struct lttng_poll_event *poll_set,
 369                 struct notification_thread_handle *handle,
 370                 int notification_channel_socket)
 371 {
 372         int ret;
 373
 374         /*
 375          * Create pollset with size 6:
 376          *      - quit pipe,
 377          *      - notification channel socket (listen for new connections),
 378          *      - command queue event fd (internal sessiond commands),
 379          *      - consumerd (32-bit user space) channel monitor pipe,
 380          *      - consumerd (64-but user space) channel monitor pipe,
 381          *      - consumerd (kernel) channel monitor pipe.
 382          */
 383         ret = sessiond_set_thread_pollset(poll_set, 6);
 384         if (ret < 0) {
 385                 goto end;
 386         }
 387
 388         ret = lttng_poll_add(poll_set, notification_channel_socket,
 389                         LPOLLIN | LPOLLERR | LPOLLHUP | LPOLLRDHUP);
 390         if (ret < 0) {
 391                 ERR("[notification-thread] Failed to add notification channel socket to pollset");
 392                 goto error;
 393         }
 394         ret = lttng_poll_add(poll_set, handle->cmd_queue.event_fd,
 395                         LPOLLIN | LPOLLERR);
 396         if (ret < 0) {
 397                 ERR("[notification-thread] Failed to add notification command queue event fd to pollset");
 398                 goto error;
 399         }
 400         ret = lttng_poll_add(poll_set,
 401                         handle->channel_monitoring_pipes.ust32_consumer,
 402                         LPOLLIN | LPOLLERR);
 403         if (ret < 0) {
 404                 ERR("[notification-thread] Failed to add ust-32 channel monitoring pipe fd to pollset");
 405                 goto error;
 406         }
 407         ret = lttng_poll_add(poll_set,
 408                         handle->channel_monitoring_pipes.ust64_consumer,
 409                         LPOLLIN | LPOLLERR);
 410         if (ret < 0) {
 411                 ERR("[notification-thread] Failed to add ust-64 channel monitoring pipe fd to pollset");
 412                 goto error;
 413         }
 414         if (handle->channel_monitoring_pipes.kernel_consumer < 0) {
 415                 goto end;
 416         }
 417         ret = lttng_poll_add(poll_set,
 418                         handle->channel_monitoring_pipes.kernel_consumer,
 419                         LPOLLIN | LPOLLERR);
 420         if (ret < 0) {
 421                 ERR("[notification-thread] Failed to add kernel channel monitoring pipe fd to pollset");
 422                 goto error;
 423         }
 424 end:
 425         return ret;
 426 error:
 427         lttng_poll_clean(poll_set);
 428         return ret;
 429 }
 430
 431 static
 432 void fini_thread_state(struct notification_thread_state *state)
 433 {
 434         int ret;
 435
 436         if (state->client_socket_ht) {
 437                 ret = handle_notification_thread_client_disconnect_all(state);
 438                 assert(!ret);
 439                 ret = cds_lfht_destroy(state->client_socket_ht, NULL);
 440                 assert(!ret);
 441         }
 442         if (state->triggers_ht) {
 443                 ret = handle_notification_thread_trigger_unregister_all(state);
 444                 assert(!ret);
 445                 ret = cds_lfht_destroy(state->triggers_ht, NULL);
 446                 assert(!ret);
 447         }
 448         if (state->channel_triggers_ht) {
 449                 ret = cds_lfht_destroy(state->channel_triggers_ht, NULL);
 450                 assert(!ret);
 451         }
 452         if (state->channel_state_ht) {
 453                 ret = cds_lfht_destroy(state->channel_state_ht, NULL);
 454                 assert(!ret);
 455         }
 456         if (state->notification_trigger_clients_ht) {
 457                 ret = cds_lfht_destroy(state->notification_trigger_clients_ht,
 458                                 NULL);
 459                 assert(!ret);
 460         }
 461         if (state->channels_ht) {
 462                 ret = cds_lfht_destroy(state->channels_ht,
 463                                 NULL);
 464                 assert(!ret);
 465         }
 466
 467         if (state->notification_channel_socket >= 0) {
 468                 notification_channel_socket_destroy(
 469                                 state->notification_channel_socket);
 470         }
 471         lttng_poll_clean(&state->events);
 472 }
 473
 474 static
 475 int init_thread_state(struct notification_thread_handle *handle,
 476                 struct notification_thread_state *state)
 477 {
 478         int ret;
 479
 480         memset(state, 0, sizeof(*state));
 481         state->notification_channel_socket = -1;
 482         lttng_poll_init(&state->events);
 483
 484         ret = notification_channel_socket_create();
 485         if (ret < 0) {
 486                 goto end;
 487         }
 488         state->notification_channel_socket = ret;
 489
 490         ret = init_poll_set(&state->events, handle,
 491                         state->notification_channel_socket);
 492         if (ret) {
 493                 goto end;
 494         }
 495
 496         DBG("[notification-thread] Listening on notification channel socket");
 497         ret = lttcomm_listen_unix_sock(state->notification_channel_socket);
 498         if (ret < 0) {
 499                 ERR("[notification-thread] Listen failed on notification channel socket");
 500                 goto error;
 501         }
 502
 503         state->client_socket_ht = cds_lfht_new(DEFAULT_HT_SIZE, 1, 0,
 504                         CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
 505         if (!state->client_socket_ht) {
 506                 goto error;
 507         }
 508
 509         state->channel_triggers_ht = cds_lfht_new(DEFAULT_HT_SIZE, 1, 0,
 510                         CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
 511         if (!state->channel_triggers_ht) {
 512                 goto error;
 513         }
 514
 515         state->channel_state_ht = cds_lfht_new(DEFAULT_HT_SIZE, 1, 0,
 516                         CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
 517         if (!state->channel_state_ht) {
 518                 goto error;
 519         }
 520
 521         state->notification_trigger_clients_ht = cds_lfht_new(DEFAULT_HT_SIZE,
 522                         1, 0, CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
 523         if (!state->notification_trigger_clients_ht) {
 524                 goto error;
 525         }
 526
 527         state->channels_ht = cds_lfht_new(DEFAULT_HT_SIZE,
 528                         1, 0, CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
 529         if (!state->channels_ht) {
 530                 goto error;
 531         }
 532
 533         state->triggers_ht = cds_lfht_new(DEFAULT_HT_SIZE,
 534                         1, 0, CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
 535         if (!state->triggers_ht) {
 536                 goto error;
 537         }
 538 end:
 539         return 0;
 540 error:
 541         fini_thread_state(state);
 542         return -1;
 543 }
 544
 545 /*
 546  * This thread services notification channel clients and received notifications
 547  * from various lttng-sessiond components over a command queue.
 548  */
 549 void *thread_notification(void *data)
 550 {
 551         int ret;
 552         struct notification_thread_handle *handle = data;
 553         struct notification_thread_state state;
 554
 555         DBG("[notification-thread] Started notification thread");
 556
 557         if (!handle) {
 558                 ERR("[notification-thread] Invalid thread context provided");
 559                 goto end;
 560         }
 561
 562         rcu_register_thread();
 563         rcu_thread_online();
 564
 565         health_register(health_sessiond, HEALTH_SESSIOND_TYPE_NOTIFICATION);
 566         health_code_update();
 567
 568         ret = init_thread_state(handle, &state);
 569         if (ret) {
 570                 goto end;
 571         }
 572
 573         /* Ready to handle client connections. */
 574         sessiond_notify_ready();
 575
 576         while (true) {
 577                 int fd_count, i;
 578
 579                 health_poll_entry();
 580                 DBG("[notification-thread] Entering poll wait");
 581                 ret = lttng_poll_wait(&state.events, -1);
 582                 DBG("[notification-thread] Poll wait returned (%i)", ret);
 583                 health_poll_exit();
 584                 if (ret < 0) {
 585                         /*
 586                          * Restart interrupted system call.
 587                          */
 588                         if (errno == EINTR) {
 589                                 continue;
 590                         }
 591                         ERR("[notification-thread] Error encountered during lttng_poll_wait (%i)", ret);
 592                         goto error;
 593                 }
 594
 595                 fd_count = ret;
 596                 for (i = 0; i < fd_count; i++) {
 597                         int fd = LTTNG_POLL_GETFD(&state.events, i);
 598                         uint32_t revents = LTTNG_POLL_GETEV(&state.events, i);
 599
 600                         DBG("[notification-thread] Handling fd (%i) activity (%u)", fd, revents);
 601
 602                         /* Thread quit pipe has been closed. Killing thread. */
 603                         if (sessiond_check_thread_quit_pipe(fd, revents)) {
 604                                 DBG("[notification-thread] Quit pipe signaled, exiting.");
 605                                 goto exit;
 606                         }
 607
 608                         if (fd == state.notification_channel_socket) {
 609                                 if (revents & LPOLLIN) {
 610                                         ret = handle_notification_thread_client_connect(
 611                                                         &state);
 612                                         if (ret < 0) {
 613                                                 goto error;
 614                                         }
 615                                 } else if (revents &
 616                                                 (LPOLLERR | LPOLLHUP | LPOLLRDHUP)) {
 617                                         ERR("[notification-thread] Notification socket poll error");
 618                                         goto error;
 619                                 } else {
 620                                         ERR("[notification-thread] Unexpected poll events %u for notification socket %i", revents, fd);
 621                                         goto error;
 622                                 }
 623                         } else if (fd == handle->cmd_queue.event_fd) {
 624                                 ret = handle_notification_thread_command(handle,
 625                                                 &state);
 626                                 if (ret) {
 627                                         goto error;
 628                                 }
 629                         } else if (fd == handle->channel_monitoring_pipes.ust32_consumer) {
 630                                 ret = handle_notification_thread_channel_sample(
 631                                                 &state, fd, LTTNG_DOMAIN_UST);
 632                                 if (ret) {
 633                                         goto error;
 634                                 }
 635                         } else if (fd == handle->channel_monitoring_pipes.ust64_consumer) {
 636                                 ret = handle_notification_thread_channel_sample(
 637                                                 &state, fd, LTTNG_DOMAIN_UST);
 638                                 if (ret) {
 639                                         goto error;
 640                                 }
 641                         } else if (fd == handle->channel_monitoring_pipes.kernel_consumer) {
 642                                 ret = handle_notification_thread_channel_sample(
 643                                                 &state, fd, LTTNG_DOMAIN_KERNEL);
 644                                 if (ret) {
 645                                         goto error;
 646                                 }
 647                         } else {
 648                                 /* Activity on a client's socket. */
 649                                 if (revents & (LPOLLERR | LPOLLHUP | LPOLLRDHUP)) {
 650                                         /*
 651                                          * It doesn't matter if a command was
 652                                          * pending on the client socket at this
 653                                          * point since it now has now way to
 654                                          * receive the notifications to which
 655                                          * it was subscribing or unsubscribing.
 656                                          */
 657                                         ret = handle_notification_thread_client_disconnect(
 658                                                         fd, &state);
 659                                         if (ret) {
 660                                                 goto error;
 661                                         }
 662                                 } else if (revents & LPOLLIN) {
 663                                         ret = handle_notification_thread_client(
 664                                                         &state, fd);
 665                                         if (ret) {
 666                                                 goto error;
 667                                         }
 668                                 } else {
 669                                         DBG("[notification-thread] Unexpected poll events %u for notification socket %i", revents, fd);
 670                                 }
 671                         }
 672                 }
 673         }
 674 exit:
 675 error:
 676         fini_thread_state(&state);
 677         health_unregister(health_sessiond);
 678         rcu_thread_offline();
 679         rcu_unregister_thread();
 680 end:
 681         return NULL;
 682 }