src/bin/lttng-sessiond/timer.c

   1 /*
   2  * Copyright (C) 2017 Julien Desfossez <jdesfossez@efficios.com>
   3  * Copyright (C) 2018 Jérémie Galarneau <jeremie.galarneau@efficios.com>
   4  *
   5  * SPDX-License-Identifier: GPL-2.0-only
   6  *
   7  */
   8
   9 #define _LGPL_SOURCE
  10 #include <assert.h>
  11 #include <inttypes.h>
  12 #include <signal.h>
  13
  14 #include "timer.h"
  15 #include "health-sessiond.h"
  16 #include "rotation-thread.h"
  17 #include "thread.h"
  18
  19 #define LTTNG_SESSIOND_SIG_QS                           SIGRTMIN + 10
  20 #define LTTNG_SESSIOND_SIG_EXIT                         SIGRTMIN + 11
  21 #define LTTNG_SESSIOND_SIG_PENDING_ROTATION_CHECK       SIGRTMIN + 12
  22 #define LTTNG_SESSIOND_SIG_SCHEDULED_ROTATION           SIGRTMIN + 13
  23
  24 #define UINT_TO_PTR(value)                              \
  25         ({                                              \
  26                 assert(value <= UINTPTR_MAX);           \
  27                 (void *) (uintptr_t) value;             \
  28         })
  29 #define PTR_TO_UINT(ptr) ((uintptr_t) ptr)
  30
  31 /*
  32  * Handle timer teardown race wrt memory free of private data by sessiond
  33  * signals are handled by a single thread, which permits a synchronization
  34  * point between handling of each signal. Internal lock ensures mutual
  35  * exclusion.
  36  */
  37 static
  38 struct timer_signal_data {
  39         /* Thread managing signals. */
  40         pthread_t tid;
  41         int qs_done;
  42         pthread_mutex_t lock;
  43 } timer_signal = {
  44         .tid = 0,
  45         .qs_done = 0,
  46         .lock = PTHREAD_MUTEX_INITIALIZER,
  47 };
  48
  49 /*
  50  * Set custom signal mask to current thread.
  51  */
  52 static
  53 void setmask(sigset_t *mask)
  54 {
  55         int ret;
  56
  57         ret = sigemptyset(mask);
  58         if (ret) {
  59                 PERROR("sigemptyset");
  60         }
  61         ret = sigaddset(mask, LTTNG_SESSIOND_SIG_QS);
  62         if (ret) {
  63                 PERROR("sigaddset teardown");
  64         }
  65         ret = sigaddset(mask, LTTNG_SESSIOND_SIG_EXIT);
  66         if (ret) {
  67                 PERROR("sigaddset exit");
  68         }
  69         ret = sigaddset(mask, LTTNG_SESSIOND_SIG_PENDING_ROTATION_CHECK);
  70         if (ret) {
  71                 PERROR("sigaddset pending rotation check");
  72         }
  73         ret = sigaddset(mask, LTTNG_SESSIOND_SIG_SCHEDULED_ROTATION);
  74         if (ret) {
  75                 PERROR("sigaddset scheduled rotation");
  76         }
  77 }
  78
  79 /*
  80  * This is the same function as timer_signal_thread_qs, when it
  81  * returns, it means that no timer signr is currently pending or being handled
  82  * by the timer thread. This cannot be called from the timer thread.
  83  */
  84 static
  85 void timer_signal_thread_qs(unsigned int signr)
  86 {
  87         sigset_t pending_set;
  88         int ret;
  89
  90         /*
  91          * We need to be the only thread interacting with the thread
  92          * that manages signals for teardown synchronization.
  93          */
  94         pthread_mutex_lock(&timer_signal.lock);
  95
  96         /* Ensure we don't have any signal queued for this session. */
  97         for (;;) {
  98                 ret = sigemptyset(&pending_set);
  99                 if (ret == -1) {
 100                         PERROR("sigemptyset");
 101                 }
 102                 ret = sigpending(&pending_set);
 103                 if (ret == -1) {
 104                         PERROR("sigpending");
 105                 }
 106                 if (!sigismember(&pending_set, signr)) {
 107                         break;
 108                 }
 109                 caa_cpu_relax();
 110         }
 111
 112         /*
 113          * From this point, no new signal handler will be fired that would try to
 114          * access "session". However, we still need to wait for any currently
 115          * executing handler to complete.
 116          */
 117         cmm_smp_mb();
 118         CMM_STORE_SHARED(timer_signal.qs_done, 0);
 119         cmm_smp_mb();
 120
 121         /*
 122          * Kill with LTTNG_SESSIOND_SIG_QS, so signal management thread
 123          * wakes up.
 124          */
 125         kill(getpid(), LTTNG_SESSIOND_SIG_QS);
 126
 127         while (!CMM_LOAD_SHARED(timer_signal.qs_done)) {
 128                 caa_cpu_relax();
 129         }
 130         cmm_smp_mb();
 131
 132         pthread_mutex_unlock(&timer_signal.lock);
 133 }
 134
 135 /*
 136  * Start a timer on a session that will fire at a given interval
 137  * (timer_interval_us) and fire a given signal (signal).
 138  *
 139  * Returns a negative value on error, 0 if a timer was created, and
 140  * a positive value if no timer was created (not an error).
 141  */
 142 static
 143 int timer_start(timer_t *timer_id, struct ltt_session *session,
 144                 unsigned int timer_interval_us, int signal, bool one_shot)
 145 {
 146         int ret = 0, delete_ret;
 147         struct sigevent sev = {};
 148         struct itimerspec its;
 149
 150         sev.sigev_notify = SIGEV_SIGNAL;
 151         sev.sigev_signo = signal;
 152         sev.sigev_value.sival_ptr = session;
 153         ret = timer_create(CLOCK_MONOTONIC, &sev, timer_id);
 154         if (ret == -1) {
 155                 PERROR("timer_create");
 156                 goto end;
 157         }
 158
 159         its.it_value.tv_sec = timer_interval_us / 1000000;
 160         its.it_value.tv_nsec = (timer_interval_us % 1000000) * 1000;
 161         if (one_shot) {
 162                 its.it_interval.tv_sec = 0;
 163                 its.it_interval.tv_nsec = 0;
 164         } else {
 165                 its.it_interval.tv_sec = its.it_value.tv_sec;
 166                 its.it_interval.tv_nsec = its.it_value.tv_nsec;
 167         }
 168
 169         ret = timer_settime(*timer_id, 0, &its, NULL);
 170         if (ret == -1) {
 171                 PERROR("timer_settime");
 172                 goto error_destroy_timer;
 173         }
 174         goto end;
 175
 176 error_destroy_timer:
 177         delete_ret = timer_delete(*timer_id);
 178         if (delete_ret == -1) {
 179                 PERROR("timer_delete");
 180         }
 181
 182 end:
 183         return ret;
 184 }
 185
 186 static
 187 int timer_stop(timer_t *timer_id, int signal)
 188 {
 189         int ret = 0;
 190
 191         ret = timer_delete(*timer_id);
 192         if (ret == -1) {
 193                 PERROR("timer_delete");
 194                 goto end;
 195         }
 196
 197         timer_signal_thread_qs(signal);
 198         *timer_id = 0;
 199 end:
 200         return ret;
 201 }
 202
 203 int timer_session_rotation_pending_check_start(struct ltt_session *session,
 204                 unsigned int interval_us)
 205 {
 206         int ret;
 207
 208         if (!session_get(session)) {
 209                 ret = -1;
 210                 goto end;
 211         }
 212         DBG("Enabling session rotation pending check timer on session %" PRIu64,
 213                         session->id);
 214         /*
 215          * We arm this timer in a one-shot mode so we don't have to disable it
 216          * explicitly (which could deadlock if the timer thread is blocked
 217          * writing in the rotation_timer_pipe).
 218          *
 219          * Instead, we re-arm it if needed after the rotation_pending check as
 220          * returned. Also, this timer is usually only needed once, so there is
 221          * no need to go through the whole signal teardown scheme everytime.
 222          */
 223         ret = timer_start(&session->rotation_pending_check_timer,
 224                         session, interval_us,
 225                         LTTNG_SESSIOND_SIG_PENDING_ROTATION_CHECK,
 226                         /* one-shot */ true);
 227         if (ret == 0) {
 228                 session->rotation_pending_check_timer_enabled = true;
 229         }
 230 end:
 231         return ret;
 232 }
 233
 234 /*
 235  * Call with session and session_list locks held.
 236  */
 237 int timer_session_rotation_pending_check_stop(struct ltt_session *session)
 238 {
 239         int ret;
 240
 241         assert(session);
 242         assert(session->rotation_pending_check_timer_enabled);
 243
 244         DBG("Disabling session rotation pending check timer on session %" PRIu64,
 245                         session->id);
 246         ret = timer_stop(&session->rotation_pending_check_timer,
 247                         LTTNG_SESSIOND_SIG_PENDING_ROTATION_CHECK);
 248         if (ret == -1) {
 249                 ERR("Failed to stop rotate_pending_check timer");
 250         } else {
 251                 session->rotation_pending_check_timer_enabled = false;
 252                 /*
 253                  * The timer's reference to the session can be released safely.
 254                  */
 255                 session_put(session);
 256         }
 257         return ret;
 258 }
 259
 260 /*
 261  * Call with session and session_list locks held.
 262  */
 263 int timer_session_rotation_schedule_timer_start(struct ltt_session *session,
 264                 unsigned int interval_us)
 265 {
 266         int ret;
 267
 268         if (!session_get(session)) {
 269                 ret = -1;
 270                 goto end;
 271         }
 272         DBG("Enabling scheduled rotation timer on session \"%s\" (%ui %s)", session->name,
 273                         interval_us, USEC_UNIT);
 274         ret = timer_start(&session->rotation_schedule_timer, session,
 275                         interval_us, LTTNG_SESSIOND_SIG_SCHEDULED_ROTATION,
 276                         /* one-shot */ false);
 277         if (ret < 0) {
 278                 goto end;
 279         }
 280         session->rotation_schedule_timer_enabled = true;
 281 end:
 282         return ret;
 283 }
 284
 285 /*
 286  * Call with session and session_list locks held.
 287  */
 288 int timer_session_rotation_schedule_timer_stop(struct ltt_session *session)
 289 {
 290         int ret = 0;
 291
 292         assert(session);
 293
 294         if (!session->rotation_schedule_timer_enabled) {
 295                 goto end;
 296         }
 297
 298         DBG("Disabling scheduled rotation timer on session %s", session->name);
 299         ret = timer_stop(&session->rotation_schedule_timer,
 300                         LTTNG_SESSIOND_SIG_SCHEDULED_ROTATION);
 301         if (ret < 0) {
 302                 ERR("Failed to stop scheduled rotation timer of session \"%s\"",
 303                                 session->name);
 304                 goto end;
 305         }
 306
 307         session->rotation_schedule_timer_enabled = false;
 308         /* The timer's reference to the session can be released safely. */
 309         session_put(session);
 310         ret = 0;
 311 end:
 312         return ret;
 313 }
 314
 315 /*
 316  * Block the RT signals for the entire process. It must be called from the
 317  * sessiond main before creating the threads
 318  */
 319 int timer_signal_init(void)
 320 {
 321         int ret;
 322         sigset_t mask;
 323
 324         /* Block signal for entire process, so only our thread processes it. */
 325         setmask(&mask);
 326         ret = pthread_sigmask(SIG_BLOCK, &mask, NULL);
 327         if (ret) {
 328                 errno = ret;
 329                 PERROR("pthread_sigmask");
 330                 return -1;
 331         }
 332         return 0;
 333 }
 334
 335 /*
 336  * This thread is the sighandler for the timer signals.
 337  */
 338 static
 339 void *thread_timer(void *data)
 340 {
 341         int signr;
 342         sigset_t mask;
 343         siginfo_t info;
 344         struct timer_thread_parameters *ctx = data;
 345
 346         rcu_register_thread();
 347         rcu_thread_online();
 348
 349         health_register(the_health_sessiond, HEALTH_SESSIOND_TYPE_TIMER);
 350         health_code_update();
 351
 352         /* Only self thread will receive signal mask. */
 353         setmask(&mask);
 354         CMM_STORE_SHARED(timer_signal.tid, pthread_self());
 355
 356         while (1) {
 357                 health_code_update();
 358
 359                 health_poll_entry();
 360                 signr = sigwaitinfo(&mask, &info);
 361                 health_poll_exit();
 362
 363                 /*
 364                  * NOTE: cascading conditions are used instead of a switch case
 365                  * since the use of SIGRTMIN in the definition of the signals'
 366                  * values prevents the reduction to an integer constant.
 367                  */
 368                 if (signr == -1) {
 369                         if (errno != EINTR) {
 370                                 PERROR("sigwaitinfo");
 371                         }
 372                         continue;
 373                 } else if (signr == LTTNG_SESSIOND_SIG_QS) {
 374                         cmm_smp_mb();
 375                         CMM_STORE_SHARED(timer_signal.qs_done, 1);
 376                         cmm_smp_mb();
 377                 } else if (signr == LTTNG_SESSIOND_SIG_EXIT) {
 378                         goto end;
 379                 } else if (signr == LTTNG_SESSIOND_SIG_PENDING_ROTATION_CHECK) {
 380                         struct ltt_session *session =
 381                                         (struct ltt_session *) info.si_value.sival_ptr;
 382
 383                         rotation_thread_enqueue_job(ctx->rotation_thread_job_queue,
 384                                         ROTATION_THREAD_JOB_TYPE_CHECK_PENDING_ROTATION,
 385                                         session);
 386                 } else if (signr == LTTNG_SESSIOND_SIG_SCHEDULED_ROTATION) {
 387                         rotation_thread_enqueue_job(ctx->rotation_thread_job_queue,
 388                                         ROTATION_THREAD_JOB_TYPE_SCHEDULED_ROTATION,
 389                                         (struct ltt_session *) info.si_value.sival_ptr);
 390                         /*
 391                          * The scheduled periodic rotation timer is not in
 392                          * "one-shot" mode. The reference to the session is not
 393                          * released since the timer is still enabled and can
 394                          * still fire.
 395                          */
 396                 } else {
 397                         ERR("Unexpected signal %d\n", info.si_signo);
 398                 }
 399         }
 400
 401 end:
 402         DBG("[timer-thread] Exit");
 403         health_unregister(the_health_sessiond);
 404         rcu_thread_offline();
 405         rcu_unregister_thread();
 406         return NULL;
 407 }
 408
 409 static
 410 bool shutdown_timer_thread(void *data)
 411 {
 412         return kill(getpid(), LTTNG_SESSIOND_SIG_EXIT) == 0;
 413 }
 414
 415 bool launch_timer_thread(
 416                 struct timer_thread_parameters *timer_thread_parameters)
 417 {
 418         struct lttng_thread *thread;
 419
 420         thread = lttng_thread_create("Timer",
 421                         thread_timer,
 422                         shutdown_timer_thread,
 423                         NULL,
 424                         timer_thread_parameters);
 425         if (!thread) {
 426                 goto error;
 427         }
 428         lttng_thread_put(thread);
 429         return true;
 430 error:
 431         return false;
 432 }