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  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License, version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
  12  * more details.
  13  *
  14  * You should have received a copy of the GNU General Public License along with
  15  * this program; if not, write to the Free Software Foundation, Inc., 51
  16  * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  17  */
  18
  19 #define _LGPL_SOURCE
  20 #include <assert.h>
  21 #include <inttypes.h>
  22 #include <signal.h>
  23
  24 #include "timer.h"
  25 #include "health-sessiond.h"
  26 #include "rotation-thread.h"
  27 #include "thread.h"
  28
  29 #define LTTNG_SESSIOND_SIG_QS                           SIGRTMIN + 10
  30 #define LTTNG_SESSIOND_SIG_EXIT                         SIGRTMIN + 11
  31 #define LTTNG_SESSIOND_SIG_PENDING_ROTATION_CHECK       SIGRTMIN + 12
  32 #define LTTNG_SESSIOND_SIG_SCHEDULED_ROTATION           SIGRTMIN + 13
  33
  34 #define UINT_TO_PTR(value)                              \
  35         ({                                              \
  36                 assert(value <= UINTPTR_MAX);           \
  37                 (void *) (uintptr_t) value;             \
  38         })
  39 #define PTR_TO_UINT(ptr) ((uintptr_t) ptr)
  40
  41 /*
  42  * Handle timer teardown race wrt memory free of private data by sessiond
  43  * signals are handled by a single thread, which permits a synchronization
  44  * point between handling of each signal. Internal lock ensures mutual
  45  * exclusion.
  46  */
  47 static
  48 struct timer_signal_data {
  49         /* Thread managing signals. */
  50         pthread_t tid;
  51         int qs_done;
  52         pthread_mutex_t lock;
  53 } timer_signal = {
  54         .tid = 0,
  55         .qs_done = 0,
  56         .lock = PTHREAD_MUTEX_INITIALIZER,
  57 };
  58
  59 /*
  60  * Set custom signal mask to current thread.
  61  */
  62 static
  63 void setmask(sigset_t *mask)
  64 {
  65         int ret;
  66
  67         ret = sigemptyset(mask);
  68         if (ret) {
  69                 PERROR("sigemptyset");
  70         }
  71         ret = sigaddset(mask, LTTNG_SESSIOND_SIG_QS);
  72         if (ret) {
  73                 PERROR("sigaddset teardown");
  74         }
  75         ret = sigaddset(mask, LTTNG_SESSIOND_SIG_EXIT);
  76         if (ret) {
  77                 PERROR("sigaddset exit");
  78         }
  79         ret = sigaddset(mask, LTTNG_SESSIOND_SIG_PENDING_ROTATION_CHECK);
  80         if (ret) {
  81                 PERROR("sigaddset pending rotation check");
  82         }
  83         ret = sigaddset(mask, LTTNG_SESSIOND_SIG_SCHEDULED_ROTATION);
  84         if (ret) {
  85                 PERROR("sigaddset scheduled rotation");
  86         }
  87 }
  88
  89 /*
  90  * This is the same function as timer_signal_thread_qs, when it
  91  * returns, it means that no timer signr is currently pending or being handled
  92  * by the timer thread. This cannot be called from the timer thread.
  93  */
  94 static
  95 void timer_signal_thread_qs(unsigned int signr)
  96 {
  97         sigset_t pending_set;
  98         int ret;
  99
 100         /*
 101          * We need to be the only thread interacting with the thread
 102          * that manages signals for teardown synchronization.
 103          */
 104         pthread_mutex_lock(&timer_signal.lock);
 105
 106         /* Ensure we don't have any signal queued for this session. */
 107         for (;;) {
 108                 ret = sigemptyset(&pending_set);
 109                 if (ret == -1) {
 110                         PERROR("sigemptyset");
 111                 }
 112                 ret = sigpending(&pending_set);
 113                 if (ret == -1) {
 114                         PERROR("sigpending");
 115                 }
 116                 if (!sigismember(&pending_set, signr)) {
 117                         break;
 118                 }
 119                 caa_cpu_relax();
 120         }
 121
 122         /*
 123          * From this point, no new signal handler will be fired that would try to
 124          * access "session". However, we still need to wait for any currently
 125          * executing handler to complete.
 126          */
 127         cmm_smp_mb();
 128         CMM_STORE_SHARED(timer_signal.qs_done, 0);
 129         cmm_smp_mb();
 130
 131         /*
 132          * Kill with LTTNG_SESSIOND_SIG_QS, so signal management thread
 133          * wakes up.
 134          */
 135         kill(getpid(), LTTNG_SESSIOND_SIG_QS);
 136
 137         while (!CMM_LOAD_SHARED(timer_signal.qs_done)) {
 138                 caa_cpu_relax();
 139         }
 140         cmm_smp_mb();
 141
 142         pthread_mutex_unlock(&timer_signal.lock);
 143 }
 144
 145 /*
 146  * Start a timer on a session that will fire at a given interval
 147  * (timer_interval_us) and fire a given signal (signal).
 148  *
 149  * Returns a negative value on error, 0 if a timer was created, and
 150  * a positive value if no timer was created (not an error).
 151  */
 152 static
 153 int timer_start(timer_t *timer_id, struct ltt_session *session,
 154                 unsigned int timer_interval_us, int signal, bool one_shot)
 155 {
 156         int ret = 0, delete_ret;
 157         struct sigevent sev;
 158         struct itimerspec its;
 159
 160         sev.sigev_notify = SIGEV_SIGNAL;
 161         sev.sigev_signo = signal;
 162         sev.sigev_value.sival_ptr = session;
 163         ret = timer_create(CLOCK_MONOTONIC, &sev, timer_id);
 164         if (ret == -1) {
 165                 PERROR("timer_create");
 166                 goto end;
 167         }
 168
 169         its.it_value.tv_sec = timer_interval_us / 1000000;
 170         its.it_value.tv_nsec = (timer_interval_us % 1000000) * 1000;
 171         if (one_shot) {
 172                 its.it_interval.tv_sec = 0;
 173                 its.it_interval.tv_nsec = 0;
 174         } else {
 175                 its.it_interval.tv_sec = its.it_value.tv_sec;
 176                 its.it_interval.tv_nsec = its.it_value.tv_nsec;
 177         }
 178
 179         ret = timer_settime(*timer_id, 0, &its, NULL);
 180         if (ret == -1) {
 181                 PERROR("timer_settime");
 182                 goto error_destroy_timer;
 183         }
 184         goto end;
 185
 186 error_destroy_timer:
 187         delete_ret = timer_delete(*timer_id);
 188         if (delete_ret == -1) {
 189                 PERROR("timer_delete");
 190         }
 191
 192 end:
 193         return ret;
 194 }
 195
 196 static
 197 int timer_stop(timer_t *timer_id, int signal)
 198 {
 199         int ret = 0;
 200
 201         ret = timer_delete(*timer_id);
 202         if (ret == -1) {
 203                 PERROR("timer_delete");
 204                 goto end;
 205         }
 206
 207         timer_signal_thread_qs(signal);
 208         *timer_id = 0;
 209 end:
 210         return ret;
 211 }
 212
 213 int timer_session_rotation_pending_check_start(struct ltt_session *session,
 214                 unsigned int interval_us)
 215 {
 216         int ret;
 217
 218         if (!session_get(session)) {
 219                 ret = -1;
 220                 goto end;
 221         }
 222         DBG("Enabling session rotation pending check timer on session %" PRIu64,
 223                         session->id);
 224         /*
 225          * We arm this timer in a one-shot mode so we don't have to disable it
 226          * explicitly (which could deadlock if the timer thread is blocked
 227          * writing in the rotation_timer_pipe).
 228          *
 229          * Instead, we re-arm it if needed after the rotation_pending check as
 230          * returned. Also, this timer is usually only needed once, so there is
 231          * no need to go through the whole signal teardown scheme everytime.
 232          */
 233         ret = timer_start(&session->rotation_pending_check_timer,
 234                         session, interval_us,
 235                         LTTNG_SESSIOND_SIG_PENDING_ROTATION_CHECK,
 236                         /* one-shot */ true);
 237         if (ret == 0) {
 238                 session->rotation_pending_check_timer_enabled = true;
 239         }
 240 end:
 241         return ret;
 242 }
 243
 244 /*
 245  * Call with session and session_list locks held.
 246  */
 247 int timer_session_rotation_pending_check_stop(struct ltt_session *session)
 248 {
 249         int ret;
 250
 251         assert(session);
 252         assert(session->rotation_pending_check_timer_enabled);
 253
 254         DBG("Disabling session rotation pending check timer on session %" PRIu64,
 255                         session->id);
 256         ret = timer_stop(&session->rotation_pending_check_timer,
 257                         LTTNG_SESSIOND_SIG_PENDING_ROTATION_CHECK);
 258         if (ret == -1) {
 259                 ERR("Failed to stop rotate_pending_check timer");
 260         } else {
 261                 session->rotation_pending_check_timer_enabled = false;
 262                 /*
 263                  * The timer's reference to the session can be released safely.
 264                  */
 265                 session_put(session);
 266         }
 267         return ret;
 268 }
 269
 270 /*
 271  * Call with session and session_list locks held.
 272  */
 273 int timer_session_rotation_schedule_timer_start(struct ltt_session *session,
 274                 unsigned int interval_us)
 275 {
 276         int ret;
 277
 278         if (!session_get(session)) {
 279                 ret = -1;
 280                 goto end;
 281         }
 282         DBG("Enabling scheduled rotation timer on session \"%s\" (%ui µs)", session->name,
 283                         interval_us);
 284         ret = timer_start(&session->rotation_schedule_timer, session,
 285                         interval_us, LTTNG_SESSIOND_SIG_SCHEDULED_ROTATION,
 286                         /* one-shot */ false);
 287         if (ret < 0) {
 288                 goto end;
 289         }
 290         session->rotation_schedule_timer_enabled = true;
 291 end:
 292         return ret;
 293 }
 294
 295 /*
 296  * Call with session and session_list locks held.
 297  */
 298 int timer_session_rotation_schedule_timer_stop(struct ltt_session *session)
 299 {
 300         int ret = 0;
 301
 302         assert(session);
 303
 304         if (!session->rotation_schedule_timer_enabled) {
 305                 goto end;
 306         }
 307
 308         DBG("Disabling scheduled rotation timer on session %s", session->name);
 309         ret = timer_stop(&session->rotation_schedule_timer,
 310                         LTTNG_SESSIOND_SIG_SCHEDULED_ROTATION);
 311         if (ret < 0) {
 312                 ERR("Failed to stop scheduled rotation timer of session \"%s\"",
 313                                 session->name);
 314                 goto end;
 315         }
 316
 317         session->rotation_schedule_timer_enabled = false;
 318         /* The timer's reference to the session can be released safely. */
 319         session_put(session);
 320         ret = 0;
 321 end:
 322         return ret;
 323 }
 324
 325 /*
 326  * Block the RT signals for the entire process. It must be called from the
 327  * sessiond main before creating the threads
 328  */
 329 int timer_signal_init(void)
 330 {
 331         int ret;
 332         sigset_t mask;
 333
 334         /* Block signal for entire process, so only our thread processes it. */
 335         setmask(&mask);
 336         ret = pthread_sigmask(SIG_BLOCK, &mask, NULL);
 337         if (ret) {
 338                 errno = ret;
 339                 PERROR("pthread_sigmask");
 340                 return -1;
 341         }
 342         return 0;
 343 }
 344
 345 /*
 346  * This thread is the sighandler for the timer signals.
 347  */
 348 static
 349 void *thread_timer(void *data)
 350 {
 351         int signr;
 352         sigset_t mask;
 353         siginfo_t info;
 354         struct timer_thread_parameters *ctx = data;
 355
 356         rcu_register_thread();
 357         rcu_thread_online();
 358
 359         health_register(health_sessiond, HEALTH_SESSIOND_TYPE_TIMER);
 360         health_code_update();
 361
 362         /* Only self thread will receive signal mask. */
 363         setmask(&mask);
 364         CMM_STORE_SHARED(timer_signal.tid, pthread_self());
 365
 366         while (1) {
 367                 health_code_update();
 368
 369                 health_poll_entry();
 370                 signr = sigwaitinfo(&mask, &info);
 371                 health_poll_exit();
 372
 373                 /*
 374                  * NOTE: cascading conditions are used instead of a switch case
 375                  * since the use of SIGRTMIN in the definition of the signals'
 376                  * values prevents the reduction to an integer constant.
 377                  */
 378                 if (signr == -1) {
 379                         if (errno != EINTR) {
 380                                 PERROR("sigwaitinfo");
 381                         }
 382                         continue;
 383                 } else if (signr == LTTNG_SESSIOND_SIG_QS) {
 384                         cmm_smp_mb();
 385                         CMM_STORE_SHARED(timer_signal.qs_done, 1);
 386                         cmm_smp_mb();
 387                 } else if (signr == LTTNG_SESSIOND_SIG_EXIT) {
 388                         goto end;
 389                 } else if (signr == LTTNG_SESSIOND_SIG_PENDING_ROTATION_CHECK) {
 390                         struct ltt_session *session =
 391                                         (struct ltt_session *) info.si_value.sival_ptr;
 392
 393                         rotation_thread_enqueue_job(ctx->rotation_thread_job_queue,
 394                                         ROTATION_THREAD_JOB_TYPE_CHECK_PENDING_ROTATION,
 395                                         session);
 396                 } else if (signr == LTTNG_SESSIOND_SIG_SCHEDULED_ROTATION) {
 397                         rotation_thread_enqueue_job(ctx->rotation_thread_job_queue,
 398                                         ROTATION_THREAD_JOB_TYPE_SCHEDULED_ROTATION,
 399                                         (struct ltt_session *) info.si_value.sival_ptr);
 400                         /*
 401                          * The scheduled periodic rotation timer is not in
 402                          * "one-shot" mode. The reference to the session is not
 403                          * released since the timer is still enabled and can
 404                          * still fire.
 405                          */
 406                 } else {
 407                         ERR("Unexpected signal %d\n", info.si_signo);
 408                 }
 409         }
 410
 411 end:
 412         DBG("[timer-thread] Exit");
 413         health_unregister(health_sessiond);
 414         rcu_thread_offline();
 415         rcu_unregister_thread();
 416         return NULL;
 417 }
 418
 419 static
 420 bool shutdown_timer_thread(void *data)
 421 {
 422         return kill(getpid(), LTTNG_SESSIOND_SIG_EXIT) == 0;
 423 }
 424
 425 bool launch_timer_thread(
 426                 struct timer_thread_parameters *timer_thread_parameters)
 427 {
 428         struct lttng_thread *thread;
 429
 430         thread = lttng_thread_create("Timer",
 431                         thread_timer,
 432                         shutdown_timer_thread,
 433                         NULL,
 434                         timer_thread_parameters);
 435         if (!thread) {
 436                 goto error;
 437         }
 438         lttng_thread_put(thread);
 439         return true;
 440 error:
 441         return false;
 442 }