lib/ovs-rcu.c

   1 /*
   2  * Copyright (c) 2014, 2017 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18 #include <errno.h>
  19 #include "ovs-rcu.h"
  20 #include "fatal-signal.h"
  21 #include "guarded-list.h"
  22 #include "openvswitch/list.h"
  23 #include "ovs-thread.h"
  24 #include "poll-loop.h"
  25 #include "seq.h"
  26 #include "timeval.h"
  27 #include "util.h"
  28 #include "openvswitch/vlog.h"
  29
  30 VLOG_DEFINE_THIS_MODULE(ovs_rcu);
  31
  32 struct ovsrcu_cb {
  33     void (*function)(void *aux);
  34     void *aux;
  35 };
  36
  37 struct ovsrcu_cbset {
  38     struct ovs_list list_node;
  39     struct ovsrcu_cb cbs[16];
  40     int n_cbs;
  41 };
  42
  43 struct ovsrcu_perthread {
  44     struct ovs_list list_node;  /* In global list. */
  45
  46     struct ovs_mutex mutex;
  47     uint64_t seqno;
  48     struct ovsrcu_cbset *cbset;
  49     char name[16];              /* This thread's name. */
  50 };
  51
  52 static struct seq *global_seqno;
  53
  54 static pthread_key_t perthread_key;
  55 static struct ovs_list ovsrcu_threads;
  56 static struct ovs_mutex ovsrcu_threads_mutex;
  57
  58 static struct guarded_list flushed_cbsets;
  59 static struct seq *flushed_cbsets_seq;
  60
  61 static void ovsrcu_init_module(void);
  62 static void ovsrcu_flush_cbset__(struct ovsrcu_perthread *, bool);
  63 static void ovsrcu_flush_cbset(struct ovsrcu_perthread *);
  64 static void ovsrcu_unregister__(struct ovsrcu_perthread *);
  65 static bool ovsrcu_call_postponed(void);
  66 static void *ovsrcu_postpone_thread(void *arg OVS_UNUSED);
  67
  68 static struct ovsrcu_perthread *
  69 ovsrcu_perthread_get(void)
  70 {
  71     struct ovsrcu_perthread *perthread;
  72
  73     ovsrcu_init_module();
  74
  75     perthread = pthread_getspecific(perthread_key);
  76     if (!perthread) {
  77         const char *name = get_subprogram_name();
  78
  79         perthread = xmalloc(sizeof *perthread);
  80         ovs_mutex_init(&perthread->mutex);
  81         perthread->seqno = seq_read(global_seqno);
  82         perthread->cbset = NULL;
  83         ovs_strlcpy(perthread->name, name[0] ? name : "main",
  84                     sizeof perthread->name);
  85
  86         ovs_mutex_lock(&ovsrcu_threads_mutex);
  87         ovs_list_push_back(&ovsrcu_threads, &perthread->list_node);
  88         ovs_mutex_unlock(&ovsrcu_threads_mutex);
  89
  90         pthread_setspecific(perthread_key, perthread);
  91     }
  92     return perthread;
  93 }
  94
  95 /* Indicates the end of a quiescent state.  See "Details" near the top of
  96  * ovs-rcu.h.
  97  *
  98  * Quiescent states don't stack or nest, so this always ends a quiescent state
  99  * even if ovsrcu_quiesce_start() was called multiple times in a row. */
 100 void
 101 ovsrcu_quiesce_end(void)
 102 {
 103     ovsrcu_perthread_get();
 104 }
 105
 106 static void
 107 ovsrcu_quiesced(void)
 108 {
 109     if (single_threaded()) {
 110         ovsrcu_call_postponed();
 111     } else {
 112         static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
 113         if (ovsthread_once_start(&once)) {
 114             ovs_thread_create("urcu", ovsrcu_postpone_thread, NULL);
 115             ovsthread_once_done(&once);
 116         }
 117     }
 118 }
 119
 120 /* Indicates the beginning of a quiescent state.  See "Details" near the top of
 121  * ovs-rcu.h. */
 122 void
 123 ovsrcu_quiesce_start(void)
 124 {
 125     struct ovsrcu_perthread *perthread;
 126
 127     ovsrcu_init_module();
 128     perthread = pthread_getspecific(perthread_key);
 129     if (perthread) {
 130         pthread_setspecific(perthread_key, NULL);
 131         ovsrcu_unregister__(perthread);
 132     }
 133
 134     ovsrcu_quiesced();
 135 }
 136
 137 /* Indicates a momentary quiescent state.  See "Details" near the top of
 138  * ovs-rcu.h.
 139  *
 140  * Provides a full memory barrier via seq_change().
 141  */
 142 void
 143 ovsrcu_quiesce(void)
 144 {
 145     struct ovsrcu_perthread *perthread;
 146
 147     perthread = ovsrcu_perthread_get();
 148     perthread->seqno = seq_read(global_seqno);
 149     if (perthread->cbset) {
 150         ovsrcu_flush_cbset(perthread);
 151     }
 152     seq_change(global_seqno);
 153
 154     ovsrcu_quiesced();
 155 }
 156
 157 int
 158 ovsrcu_try_quiesce(void)
 159 {
 160     struct ovsrcu_perthread *perthread;
 161     int ret = EBUSY;
 162
 163     ovs_assert(!single_threaded());
 164     perthread = ovsrcu_perthread_get();
 165     if (!seq_try_lock()) {
 166         perthread->seqno = seq_read_protected(global_seqno);
 167         if (perthread->cbset) {
 168             ovsrcu_flush_cbset__(perthread, true);
 169         }
 170         seq_change_protected(global_seqno);
 171         seq_unlock();
 172         ovsrcu_quiesced();
 173         ret = 0;
 174     }
 175     return ret;
 176 }
 177
 178 bool
 179 ovsrcu_is_quiescent(void)
 180 {
 181     ovsrcu_init_module();
 182     return pthread_getspecific(perthread_key) == NULL;
 183 }
 184
 185 void
 186 ovsrcu_synchronize(void)
 187 {
 188     unsigned int warning_threshold = 1000;
 189     uint64_t target_seqno;
 190     long long int start;
 191
 192     if (single_threaded()) {
 193         return;
 194     }
 195
 196     target_seqno = seq_read(global_seqno);
 197     ovsrcu_quiesce_start();
 198     start = time_msec();
 199
 200     for (;;) {
 201         uint64_t cur_seqno = seq_read(global_seqno);
 202         struct ovsrcu_perthread *perthread;
 203         char stalled_thread[16];
 204         unsigned int elapsed;
 205         bool done = true;
 206
 207         ovs_mutex_lock(&ovsrcu_threads_mutex);
 208         LIST_FOR_EACH (perthread, list_node, &ovsrcu_threads) {
 209             if (perthread->seqno <= target_seqno) {
 210                 ovs_strlcpy_arrays(stalled_thread, perthread->name);
 211                 done = false;
 212                 break;
 213             }
 214         }
 215         ovs_mutex_unlock(&ovsrcu_threads_mutex);
 216
 217         if (done) {
 218             break;
 219         }
 220
 221         elapsed = time_msec() - start;
 222         if (elapsed >= warning_threshold) {
 223             VLOG_WARN("blocked %u ms waiting for %s to quiesce",
 224                       elapsed, stalled_thread);
 225             warning_threshold *= 2;
 226         }
 227         poll_timer_wait_until(start + warning_threshold);
 228
 229         seq_wait(global_seqno, cur_seqno);
 230         poll_block();
 231     }
 232     ovsrcu_quiesce_end();
 233 }
 234
 235 /* Registers 'function' to be called, passing 'aux' as argument, after the
 236  * next grace period.
 237  *
 238  * The call is guaranteed to happen after the next time all participating
 239  * threads have quiesced at least once, but there is no quarantee that all
 240  * registered functions are called as early as possible, or that the functions
 241  * registered by different threads would be called in the order the
 242  * registrations took place.  In particular, even if two threads provably
 243  * register a function each in a specific order, the functions may still be
 244  * called in the opposite order, depending on the timing of when the threads
 245  * call ovsrcu_quiesce(), how many functions they postpone, and when the
 246  * ovs-rcu thread happens to grab the functions to be called.
 247  *
 248  * All functions registered by a single thread are guaranteed to execute in the
 249  * registering order, however.
 250  *
 251  * This function is more conveniently called through the ovsrcu_postpone()
 252  * macro, which provides a type-safe way to allow 'function''s parameter to be
 253  * any pointer type. */
 254 void
 255 ovsrcu_postpone__(void (*function)(void *aux), void *aux)
 256 {
 257     struct ovsrcu_perthread *perthread = ovsrcu_perthread_get();
 258     struct ovsrcu_cbset *cbset;
 259     struct ovsrcu_cb *cb;
 260
 261     cbset = perthread->cbset;
 262     if (!cbset) {
 263         cbset = perthread->cbset = xmalloc(sizeof *perthread->cbset);
 264         cbset->n_cbs = 0;
 265     }
 266
 267     cb = &cbset->cbs[cbset->n_cbs++];
 268     cb->function = function;
 269     cb->aux = aux;
 270
 271     if (cbset->n_cbs >= ARRAY_SIZE(cbset->cbs)) {
 272         ovsrcu_flush_cbset(perthread);
 273     }
 274 }
 275
 276 static bool
 277 ovsrcu_call_postponed(void)
 278 {
 279     struct ovsrcu_cbset *cbset;
 280     struct ovs_list cbsets;
 281
 282     guarded_list_pop_all(&flushed_cbsets, &cbsets);
 283     if (ovs_list_is_empty(&cbsets)) {
 284         return false;
 285     }
 286
 287     ovsrcu_synchronize();
 288
 289     LIST_FOR_EACH_POP (cbset, list_node, &cbsets) {
 290         struct ovsrcu_cb *cb;
 291
 292         for (cb = cbset->cbs; cb < &cbset->cbs[cbset->n_cbs]; cb++) {
 293             cb->function(cb->aux);
 294         }
 295         free(cbset);
 296     }
 297
 298     return true;
 299 }
 300
 301 static void *
 302 ovsrcu_postpone_thread(void *arg OVS_UNUSED)
 303 {
 304     pthread_detach(pthread_self());
 305
 306     for (;;) {
 307         uint64_t seqno = seq_read(flushed_cbsets_seq);
 308         if (!ovsrcu_call_postponed()) {
 309             seq_wait(flushed_cbsets_seq, seqno);
 310             poll_block();
 311         }
 312     }
 313
 314     OVS_NOT_REACHED();
 315 }
 316
 317 static void
 318 ovsrcu_flush_cbset__(struct ovsrcu_perthread *perthread, bool protected)
 319 {
 320     struct ovsrcu_cbset *cbset = perthread->cbset;
 321
 322     if (cbset) {
 323         guarded_list_push_back(&flushed_cbsets, &cbset->list_node, SIZE_MAX);
 324         perthread->cbset = NULL;
 325
 326         if (protected) {
 327             seq_change_protected(flushed_cbsets_seq);
 328         } else {
 329             seq_change(flushed_cbsets_seq);
 330         }
 331     }
 332 }
 333
 334 static void
 335 ovsrcu_flush_cbset(struct ovsrcu_perthread *perthread)
 336 {
 337     ovsrcu_flush_cbset__(perthread, false);
 338 }
 339
 340 static void
 341 ovsrcu_unregister__(struct ovsrcu_perthread *perthread)
 342 {
 343     if (perthread->cbset) {
 344         ovsrcu_flush_cbset(perthread);
 345     }
 346
 347     ovs_mutex_lock(&ovsrcu_threads_mutex);
 348     ovs_list_remove(&perthread->list_node);
 349     ovs_mutex_unlock(&ovsrcu_threads_mutex);
 350
 351     ovs_mutex_destroy(&perthread->mutex);
 352     free(perthread);
 353
 354     seq_change(global_seqno);
 355 }
 356
 357 static void
 358 ovsrcu_thread_exit_cb(void *perthread)
 359 {
 360     ovsrcu_unregister__(perthread);
 361 }
 362
 363 /* Cancels the callback to ovsrcu_thread_exit_cb().
 364  *
 365  * Cancelling the call to the destructor during the main thread exit
 366  * is needed while using pthreads-win32 library in Windows. It has been
 367  * observed that in pthreads-win32, a call to the destructor during
 368  * main thread exit causes undefined behavior. */
 369 static void
 370 ovsrcu_cancel_thread_exit_cb(void *aux OVS_UNUSED)
 371 {
 372     pthread_setspecific(perthread_key, NULL);
 373 }
 374
 375 static void
 376 ovsrcu_init_module(void)
 377 {
 378     static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
 379     if (ovsthread_once_start(&once)) {
 380         global_seqno = seq_create();
 381         xpthread_key_create(&perthread_key, ovsrcu_thread_exit_cb);
 382         fatal_signal_add_hook(ovsrcu_cancel_thread_exit_cb, NULL, NULL, true);
 383         ovs_list_init(&ovsrcu_threads);
 384         ovs_mutex_init(&ovsrcu_threads_mutex);
 385
 386         guarded_list_init(&flushed_cbsets);
 387         flushed_cbsets_seq = seq_create();
 388
 389         ovsthread_once_done(&once);
 390     }
 391 }