kernel/rcu/tree_exp.h

   1 /* SPDX-License-Identifier: GPL-2.0+ */
   2 /*
   3  * RCU expedited grace periods
   4  *
   5  * Copyright IBM Corporation, 2016
   6  *
   7  * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
   8  */
   9
  10 #include <linux/lockdep.h>
  11
  12 static void rcu_exp_handler(void *unused);
  13 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
  14 static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp);
  15
  16 /*
  17  * Record the start of an expedited grace period.
  18  */
  19 static void rcu_exp_gp_seq_start(void)
  20 {
  21         rcu_seq_start(&rcu_state.expedited_sequence);
  22         rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
  23 }
  24
  25 /*
  26  * Return the value that the expedited-grace-period counter will have
  27  * at the end of the current grace period.
  28  */
  29 static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void)
  30 {
  31         return rcu_seq_endval(&rcu_state.expedited_sequence);
  32 }
  33
  34 /*
  35  * Record the end of an expedited grace period.
  36  */
  37 static void rcu_exp_gp_seq_end(void)
  38 {
  39         rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
  40         rcu_seq_end(&rcu_state.expedited_sequence);
  41         smp_mb(); /* Ensure that consecutive grace periods serialize. */
  42 }
  43
  44 /*
  45  * Take a snapshot of the expedited-grace-period counter, which is the
  46  * earliest value that will indicate that a full grace period has
  47  * elapsed since the current time.
  48  */
  49 static unsigned long rcu_exp_gp_seq_snap(void)
  50 {
  51         unsigned long s;
  52
  53         smp_mb(); /* Caller's modifications seen first by other CPUs. */
  54         s = rcu_seq_snap(&rcu_state.expedited_sequence);
  55         trace_rcu_exp_grace_period(rcu_state.name, s, TPS("snap"));
  56         return s;
  57 }
  58
  59 /*
  60  * Given a counter snapshot from rcu_exp_gp_seq_snap(), return true
  61  * if a full expedited grace period has elapsed since that snapshot
  62  * was taken.
  63  */
  64 static bool rcu_exp_gp_seq_done(unsigned long s)
  65 {
  66         return rcu_seq_done(&rcu_state.expedited_sequence, s);
  67 }
  68
  69 /*
  70  * Reset the ->expmaskinit values in the rcu_node tree to reflect any
  71  * recent CPU-online activity.  Note that these masks are not cleared
  72  * when CPUs go offline, so they reflect the union of all CPUs that have
  73  * ever been online.  This means that this function normally takes its
  74  * no-work-to-do fastpath.
  75  */
  76 static void sync_exp_reset_tree_hotplug(void)
  77 {
  78         bool done;
  79         unsigned long flags;
  80         unsigned long mask;
  81         unsigned long oldmask;
  82         int ncpus = smp_load_acquire(&rcu_state.ncpus); /* Order vs. locking. */
  83         struct rcu_node *rnp;
  84         struct rcu_node *rnp_up;
  85
  86         /* If no new CPUs onlined since last time, nothing to do. */
  87         if (likely(ncpus == rcu_state.ncpus_snap))
  88                 return;
  89         rcu_state.ncpus_snap = ncpus;
  90
  91         /*
  92          * Each pass through the following loop propagates newly onlined
  93          * CPUs for the current rcu_node structure up the rcu_node tree.
  94          */
  95         rcu_for_each_leaf_node(rnp) {
  96                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
  97                 if (rnp->expmaskinit == rnp->expmaskinitnext) {
  98                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
  99                         continue;  /* No new CPUs, nothing to do. */
 100                 }
 101
 102                 /* Update this node's mask, track old value for propagation. */
 103                 oldmask = rnp->expmaskinit;
 104                 rnp->expmaskinit = rnp->expmaskinitnext;
 105                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 106
 107                 /* If was already nonzero, nothing to propagate. */
 108                 if (oldmask)
 109                         continue;
 110
 111                 /* Propagate the new CPU up the tree. */
 112                 mask = rnp->grpmask;
 113                 rnp_up = rnp->parent;
 114                 done = false;
 115                 while (rnp_up) {
 116                         raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
 117                         if (rnp_up->expmaskinit)
 118                                 done = true;
 119                         rnp_up->expmaskinit |= mask;
 120                         raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
 121                         if (done)
 122                                 break;
 123                         mask = rnp_up->grpmask;
 124                         rnp_up = rnp_up->parent;
 125                 }
 126         }
 127 }
 128
 129 /*
 130  * Reset the ->expmask values in the rcu_node tree in preparation for
 131  * a new expedited grace period.
 132  */
 133 static void __maybe_unused sync_exp_reset_tree(void)
 134 {
 135         unsigned long flags;
 136         struct rcu_node *rnp;
 137
 138         sync_exp_reset_tree_hotplug();
 139         rcu_for_each_node_breadth_first(rnp) {
 140                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
 141                 WARN_ON_ONCE(rnp->expmask);
 142                 WRITE_ONCE(rnp->expmask, rnp->expmaskinit);
 143                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 144         }
 145 }
 146
 147 /*
 148  * Return non-zero if there is no RCU expedited grace period in progress
 149  * for the specified rcu_node structure, in other words, if all CPUs and
 150  * tasks covered by the specified rcu_node structure have done their bit
 151  * for the current expedited grace period.
 152  */
 153 static bool sync_rcu_exp_done(struct rcu_node *rnp)
 154 {
 155         raw_lockdep_assert_held_rcu_node(rnp);
 156         return READ_ONCE(rnp->exp_tasks) == NULL &&
 157                READ_ONCE(rnp->expmask) == 0;
 158 }
 159
 160 /*
 161  * Like sync_rcu_exp_done(), but where the caller does not hold the
 162  * rcu_node's ->lock.
 163  */
 164 static bool sync_rcu_exp_done_unlocked(struct rcu_node *rnp)
 165 {
 166         unsigned long flags;
 167         bool ret;
 168
 169         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 170         ret = sync_rcu_exp_done(rnp);
 171         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 172
 173         return ret;
 174 }
 175
 176 /*
 177  * Report the exit from RCU read-side critical section for the last task
 178  * that queued itself during or before the current expedited preemptible-RCU
 179  * grace period.  This event is reported either to the rcu_node structure on
 180  * which the task was queued or to one of that rcu_node structure's ancestors,
 181  * recursively up the tree.  (Calm down, calm down, we do the recursion
 182  * iteratively!)
 183  */
 184 static void __rcu_report_exp_rnp(struct rcu_node *rnp,
 185                                  bool wake, unsigned long flags)
 186         __releases(rnp->lock)
 187 {
 188         unsigned long mask;
 189
 190         raw_lockdep_assert_held_rcu_node(rnp);
 191         for (;;) {
 192                 if (!sync_rcu_exp_done(rnp)) {
 193                         if (!rnp->expmask)
 194                                 rcu_initiate_boost(rnp, flags);
 195                         else
 196                                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 197                         break;
 198                 }
 199                 if (rnp->parent == NULL) {
 200                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 201                         if (wake) {
 202                                 smp_mb(); /* EGP done before wake_up(). */
 203                                 swake_up_one_online(&rcu_state.expedited_wq);
 204                         }
 205                         break;
 206                 }
 207                 mask = rnp->grpmask;
 208                 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
 209                 rnp = rnp->parent;
 210                 raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
 211                 WARN_ON_ONCE(!(rnp->expmask & mask));
 212                 WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
 213         }
 214 }
 215
 216 /*
 217  * Report expedited quiescent state for specified node.  This is a
 218  * lock-acquisition wrapper function for __rcu_report_exp_rnp().
 219  */
 220 static void __maybe_unused rcu_report_exp_rnp(struct rcu_node *rnp, bool wake)
 221 {
 222         unsigned long flags;
 223
 224         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 225         __rcu_report_exp_rnp(rnp, wake, flags);
 226 }
 227
 228 /*
 229  * Report expedited quiescent state for multiple CPUs, all covered by the
 230  * specified leaf rcu_node structure.
 231  */
 232 static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
 233                                     unsigned long mask, bool wake)
 234 {
 235         int cpu;
 236         unsigned long flags;
 237         struct rcu_data *rdp;
 238
 239         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 240         if (!(rnp->expmask & mask)) {
 241                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 242                 return;
 243         }
 244         WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
 245         for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
 246                 rdp = per_cpu_ptr(&rcu_data, cpu);
 247                 if (!IS_ENABLED(CONFIG_NO_HZ_FULL) || !rdp->rcu_forced_tick_exp)
 248                         continue;
 249                 rdp->rcu_forced_tick_exp = false;
 250                 tick_dep_clear_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
 251         }
 252         __rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */
 253 }
 254
 255 /*
 256  * Report expedited quiescent state for specified rcu_data (CPU).
 257  */
 258 static void rcu_report_exp_rdp(struct rcu_data *rdp)
 259 {
 260         WRITE_ONCE(rdp->cpu_no_qs.b.exp, false);
 261         rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true);
 262 }
 263
 264 /* Common code for work-done checking. */
 265 static bool sync_exp_work_done(unsigned long s)
 266 {
 267         if (rcu_exp_gp_seq_done(s)) {
 268                 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done"));
 269                 smp_mb(); /* Ensure test happens before caller kfree(). */
 270                 return true;
 271         }
 272         return false;
 273 }
 274
 275 /*
 276  * Funnel-lock acquisition for expedited grace periods.  Returns true
 277  * if some other task completed an expedited grace period that this task
 278  * can piggy-back on, and with no mutex held.  Otherwise, returns false
 279  * with the mutex held, indicating that the caller must actually do the
 280  * expedited grace period.
 281  */
 282 static bool exp_funnel_lock(unsigned long s)
 283 {
 284         struct rcu_data *rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
 285         struct rcu_node *rnp = rdp->mynode;
 286         struct rcu_node *rnp_root = rcu_get_root();
 287
 288         /* Low-contention fastpath. */
 289         if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
 290             (rnp == rnp_root ||
 291              ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
 292             mutex_trylock(&rcu_state.exp_mutex))
 293                 goto fastpath;
 294
 295         /*
 296          * Each pass through the following loop works its way up
 297          * the rcu_node tree, returning if others have done the work or
 298          * otherwise falls through to acquire ->exp_mutex.  The mapping
 299          * from CPU to rcu_node structure can be inexact, as it is just
 300          * promoting locality and is not strictly needed for correctness.
 301          */
 302         for (; rnp != NULL; rnp = rnp->parent) {
 303                 if (sync_exp_work_done(s))
 304                         return true;
 305
 306                 /* Work not done, either wait here or go up. */
 307                 spin_lock(&rnp->exp_lock);
 308                 if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
 309
 310                         /* Someone else doing GP, so wait for them. */
 311                         spin_unlock(&rnp->exp_lock);
 312                         trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
 313                                                   rnp->grplo, rnp->grphi,
 314                                                   TPS("wait"));
 315                         wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
 316                                    sync_exp_work_done(s));
 317                         return true;
 318                 }
 319                 WRITE_ONCE(rnp->exp_seq_rq, s); /* Followers can wait on us. */
 320                 spin_unlock(&rnp->exp_lock);
 321                 trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
 322                                           rnp->grplo, rnp->grphi, TPS("nxtlvl"));
 323         }
 324         mutex_lock(&rcu_state.exp_mutex);
 325 fastpath:
 326         if (sync_exp_work_done(s)) {
 327                 mutex_unlock(&rcu_state.exp_mutex);
 328                 return true;
 329         }
 330         rcu_exp_gp_seq_start();
 331         trace_rcu_exp_grace_period(rcu_state.name, s, TPS("start"));
 332         return false;
 333 }
 334
 335 /*
 336  * Select the CPUs within the specified rcu_node that the upcoming
 337  * expedited grace period needs to wait for.
 338  */
 339 static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp)
 340 {
 341         int cpu;
 342         unsigned long flags;
 343         unsigned long mask_ofl_test;
 344         unsigned long mask_ofl_ipi;
 345         int ret;
 346         struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew);
 347
 348         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 349
 350         /* Each pass checks a CPU for identity, offline, and idle. */
 351         mask_ofl_test = 0;
 352         for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
 353                 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 354                 unsigned long mask = rdp->grpmask;
 355                 int snap;
 356
 357                 if (raw_smp_processor_id() == cpu ||
 358                     !(rnp->qsmaskinitnext & mask)) {
 359                         mask_ofl_test |= mask;
 360                 } else {
 361                         snap = rcu_dynticks_snap(cpu);
 362                         if (rcu_dynticks_in_eqs(snap))
 363                                 mask_ofl_test |= mask;
 364                         else
 365                                 rdp->exp_dynticks_snap = snap;
 366                 }
 367         }
 368         mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
 369
 370         /*
 371          * Need to wait for any blocked tasks as well.  Note that
 372          * additional blocking tasks will also block the expedited GP
 373          * until such time as the ->expmask bits are cleared.
 374          */
 375         if (rcu_preempt_has_tasks(rnp))
 376                 WRITE_ONCE(rnp->exp_tasks, rnp->blkd_tasks.next);
 377         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 378
 379         /* IPI the remaining CPUs for expedited quiescent state. */
 380         for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) {
 381                 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 382                 unsigned long mask = rdp->grpmask;
 383
 384 retry_ipi:
 385                 if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) {
 386                         mask_ofl_test |= mask;
 387                         continue;
 388                 }
 389                 if (get_cpu() == cpu) {
 390                         mask_ofl_test |= mask;
 391                         put_cpu();
 392                         continue;
 393                 }
 394                 ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
 395                 put_cpu();
 396                 /* The CPU will report the QS in response to the IPI. */
 397                 if (!ret)
 398                         continue;
 399
 400                 /* Failed, raced with CPU hotplug operation. */
 401                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
 402                 if ((rnp->qsmaskinitnext & mask) &&
 403                     (rnp->expmask & mask)) {
 404                         /* Online, so delay for a bit and try again. */
 405                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 406                         trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("selectofl"));
 407                         schedule_timeout_idle(1);
 408                         goto retry_ipi;
 409                 }
 410                 /* CPU really is offline, so we must report its QS. */
 411                 if (rnp->expmask & mask)
 412                         mask_ofl_test |= mask;
 413                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 414         }
 415         /* Report quiescent states for those that went offline. */
 416         if (mask_ofl_test)
 417                 rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
 418 }
 419
 420 static void rcu_exp_sel_wait_wake(unsigned long s);
 421
 422 #ifdef CONFIG_RCU_EXP_KTHREAD
 423 static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp)
 424 {
 425         struct rcu_exp_work *rewp =
 426                 container_of(wp, struct rcu_exp_work, rew_work);
 427
 428         __sync_rcu_exp_select_node_cpus(rewp);
 429 }
 430
 431 static inline bool rcu_exp_worker_started(void)
 432 {
 433         return !!READ_ONCE(rcu_exp_gp_kworker);
 434 }
 435
 436 static inline bool rcu_exp_par_worker_started(void)
 437 {
 438         return !!READ_ONCE(rcu_exp_par_gp_kworker);
 439 }
 440
 441 static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
 442 {
 443         kthread_init_work(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
 444         /*
 445          * Use rcu_exp_par_gp_kworker, because flushing a work item from
 446          * another work item on the same kthread worker can result in
 447          * deadlock.
 448          */
 449         kthread_queue_work(rcu_exp_par_gp_kworker, &rnp->rew.rew_work);
 450 }
 451
 452 static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
 453 {
 454         kthread_flush_work(&rnp->rew.rew_work);
 455 }
 456
 457 /*
 458  * Work-queue handler to drive an expedited grace period forward.
 459  */
 460 static void wait_rcu_exp_gp(struct kthread_work *wp)
 461 {
 462         struct rcu_exp_work *rewp;
 463
 464         rewp = container_of(wp, struct rcu_exp_work, rew_work);
 465         rcu_exp_sel_wait_wake(rewp->rew_s);
 466 }
 467
 468 static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
 469 {
 470         kthread_init_work(&rew->rew_work, wait_rcu_exp_gp);
 471         kthread_queue_work(rcu_exp_gp_kworker, &rew->rew_work);
 472 }
 473
 474 static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
 475 {
 476 }
 477 #else /* !CONFIG_RCU_EXP_KTHREAD */
 478 static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
 479 {
 480         struct rcu_exp_work *rewp =
 481                 container_of(wp, struct rcu_exp_work, rew_work);
 482
 483         __sync_rcu_exp_select_node_cpus(rewp);
 484 }
 485
 486 static inline bool rcu_exp_worker_started(void)
 487 {
 488         return !!READ_ONCE(rcu_gp_wq);
 489 }
 490
 491 static inline bool rcu_exp_par_worker_started(void)
 492 {
 493         return !!READ_ONCE(rcu_par_gp_wq);
 494 }
 495
 496 static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
 497 {
 498         int cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
 499
 500         INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
 501         /* If all offline, queue the work on an unbound CPU. */
 502         if (unlikely(cpu > rnp->grphi - rnp->grplo))
 503                 cpu = WORK_CPU_UNBOUND;
 504         else
 505                 cpu += rnp->grplo;
 506         queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
 507 }
 508
 509 static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
 510 {
 511         flush_work(&rnp->rew.rew_work);
 512 }
 513
 514 /*
 515  * Work-queue handler to drive an expedited grace period forward.
 516  */
 517 static void wait_rcu_exp_gp(struct work_struct *wp)
 518 {
 519         struct rcu_exp_work *rewp;
 520
 521         rewp = container_of(wp, struct rcu_exp_work, rew_work);
 522         rcu_exp_sel_wait_wake(rewp->rew_s);
 523 }
 524
 525 static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
 526 {
 527         INIT_WORK_ONSTACK(&rew->rew_work, wait_rcu_exp_gp);
 528         queue_work(rcu_gp_wq, &rew->rew_work);
 529 }
 530
 531 static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
 532 {
 533         destroy_work_on_stack(&rew->rew_work);
 534 }
 535 #endif /* CONFIG_RCU_EXP_KTHREAD */
 536
 537 /*
 538  * Select the nodes that the upcoming expedited grace period needs
 539  * to wait for.
 540  */
 541 static void sync_rcu_exp_select_cpus(void)
 542 {
 543         struct rcu_node *rnp;
 544
 545         trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset"));
 546         sync_exp_reset_tree();
 547         trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select"));
 548
 549         /* Schedule work for each leaf rcu_node structure. */
 550         rcu_for_each_leaf_node(rnp) {
 551                 rnp->exp_need_flush = false;
 552                 if (!READ_ONCE(rnp->expmask))
 553                         continue; /* Avoid early boot non-existent wq. */
 554                 if (!rcu_exp_par_worker_started() ||
 555                     rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
 556                     rcu_is_last_leaf_node(rnp)) {
 557                         /* No worker started yet or last leaf, do direct call. */
 558                         sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
 559                         continue;
 560                 }
 561                 sync_rcu_exp_select_cpus_queue_work(rnp);
 562                 rnp->exp_need_flush = true;
 563         }
 564
 565         /* Wait for jobs (if any) to complete. */
 566         rcu_for_each_leaf_node(rnp)
 567                 if (rnp->exp_need_flush)
 568                         sync_rcu_exp_select_cpus_flush_work(rnp);
 569 }
 570
 571 /*
 572  * Wait for the expedited grace period to elapse, within time limit.
 573  * If the time limit is exceeded without the grace period elapsing,
 574  * return false, otherwise return true.
 575  */
 576 static bool synchronize_rcu_expedited_wait_once(long tlimit)
 577 {
 578         int t;
 579         struct rcu_node *rnp_root = rcu_get_root();
 580
 581         t = swait_event_timeout_exclusive(rcu_state.expedited_wq,
 582                                           sync_rcu_exp_done_unlocked(rnp_root),
 583                                           tlimit);
 584         // Workqueues should not be signaled.
 585         if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root))
 586                 return true;
 587         WARN_ON(t < 0);  /* workqueues should not be signaled. */
 588         return false;
 589 }
 590
 591 /*
 592  * Wait for the expedited grace period to elapse, issuing any needed
 593  * RCU CPU stall warnings along the way.
 594  */
 595 static void synchronize_rcu_expedited_wait(void)
 596 {
 597         int cpu;
 598         unsigned long j;
 599         unsigned long jiffies_stall;
 600         unsigned long jiffies_start;
 601         unsigned long mask;
 602         int ndetected;
 603         struct rcu_data *rdp;
 604         struct rcu_node *rnp;
 605         struct rcu_node *rnp_root = rcu_get_root();
 606         unsigned long flags;
 607
 608         trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
 609         jiffies_stall = rcu_exp_jiffies_till_stall_check();
 610         jiffies_start = jiffies;
 611         if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) {
 612                 if (synchronize_rcu_expedited_wait_once(1))
 613                         return;
 614                 rcu_for_each_leaf_node(rnp) {
 615                         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 616                         mask = READ_ONCE(rnp->expmask);
 617                         for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
 618                                 rdp = per_cpu_ptr(&rcu_data, cpu);
 619                                 if (rdp->rcu_forced_tick_exp)
 620                                         continue;
 621                                 rdp->rcu_forced_tick_exp = true;
 622                                 if (cpu_online(cpu))
 623                                         tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
 624                         }
 625                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 626                 }
 627                 j = READ_ONCE(jiffies_till_first_fqs);
 628                 if (synchronize_rcu_expedited_wait_once(j + HZ))
 629                         return;
 630         }
 631
 632         for (;;) {
 633                 if (synchronize_rcu_expedited_wait_once(jiffies_stall))
 634                         return;
 635                 if (rcu_stall_is_suppressed())
 636                         continue;
 637                 trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
 638                 pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
 639                        rcu_state.name);
 640                 ndetected = 0;
 641                 rcu_for_each_leaf_node(rnp) {
 642                         ndetected += rcu_print_task_exp_stall(rnp);
 643                         for_each_leaf_node_possible_cpu(rnp, cpu) {
 644                                 struct rcu_data *rdp;
 645
 646                                 mask = leaf_node_cpu_bit(rnp, cpu);
 647                                 if (!(READ_ONCE(rnp->expmask) & mask))
 648                                         continue;
 649                                 ndetected++;
 650                                 rdp = per_cpu_ptr(&rcu_data, cpu);
 651                                 pr_cont(" %d-%c%c%c%c", cpu,
 652                                         "O."[!!cpu_online(cpu)],
 653                                         "o."[!!(rdp->grpmask & rnp->expmaskinit)],
 654                                         "N."[!!(rdp->grpmask & rnp->expmaskinitnext)],
 655                                         "D."[!!data_race(rdp->cpu_no_qs.b.exp)]);
 656                         }
 657                 }
 658                 pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
 659                         jiffies - jiffies_start, rcu_state.expedited_sequence,
 660                         data_race(rnp_root->expmask),
 661                         ".T"[!!data_race(rnp_root->exp_tasks)]);
 662                 if (ndetected) {
 663                         pr_err("blocking rcu_node structures (internal RCU debug):");
 664                         rcu_for_each_node_breadth_first(rnp) {
 665                                 if (rnp == rnp_root)
 666                                         continue; /* printed unconditionally */
 667                                 if (sync_rcu_exp_done_unlocked(rnp))
 668                                         continue;
 669                                 pr_cont(" l=%u:%d-%d:%#lx/%c",
 670                                         rnp->level, rnp->grplo, rnp->grphi,
 671                                         data_race(rnp->expmask),
 672                                         ".T"[!!data_race(rnp->exp_tasks)]);
 673                         }
 674                         pr_cont("\n");
 675                 }
 676                 rcu_for_each_leaf_node(rnp) {
 677                         for_each_leaf_node_possible_cpu(rnp, cpu) {
 678                                 mask = leaf_node_cpu_bit(rnp, cpu);
 679                                 if (!(READ_ONCE(rnp->expmask) & mask))
 680                                         continue;
 681                                 preempt_disable(); // For smp_processor_id() in dump_cpu_task().
 682                                 dump_cpu_task(cpu);
 683                                 preempt_enable();
 684                         }
 685                         rcu_exp_print_detail_task_stall_rnp(rnp);
 686                 }
 687                 jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
 688                 panic_on_rcu_stall();
 689         }
 690 }
 691
 692 /*
 693  * Wait for the current expedited grace period to complete, and then
 694  * wake up everyone who piggybacked on the just-completed expedited
 695  * grace period.  Also update all the ->exp_seq_rq counters as needed
 696  * in order to avoid counter-wrap problems.
 697  */
 698 static void rcu_exp_wait_wake(unsigned long s)
 699 {
 700         struct rcu_node *rnp;
 701
 702         synchronize_rcu_expedited_wait();
 703
 704         // Switch over to wakeup mode, allowing the next GP to proceed.
 705         // End the previous grace period only after acquiring the mutex
 706         // to ensure that only one GP runs concurrently with wakeups.
 707         mutex_lock(&rcu_state.exp_wake_mutex);
 708         rcu_exp_gp_seq_end();
 709         trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end"));
 710
 711         rcu_for_each_node_breadth_first(rnp) {
 712                 if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
 713                         spin_lock(&rnp->exp_lock);
 714                         /* Recheck, avoid hang in case someone just arrived. */
 715                         if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
 716                                 WRITE_ONCE(rnp->exp_seq_rq, s);
 717                         spin_unlock(&rnp->exp_lock);
 718                 }
 719                 smp_mb(); /* All above changes before wakeup. */
 720                 wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]);
 721         }
 722         trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake"));
 723         mutex_unlock(&rcu_state.exp_wake_mutex);
 724 }
 725
 726 /*
 727  * Common code to drive an expedited grace period forward, used by
 728  * workqueues and mid-boot-time tasks.
 729  */
 730 static void rcu_exp_sel_wait_wake(unsigned long s)
 731 {
 732         /* Initialize the rcu_node tree in preparation for the wait. */
 733         sync_rcu_exp_select_cpus();
 734
 735         /* Wait and clean up, including waking everyone. */
 736         rcu_exp_wait_wake(s);
 737 }
 738
 739 #ifdef CONFIG_PREEMPT_RCU
 740
 741 /*
 742  * Remote handler for smp_call_function_single().  If there is an
 743  * RCU read-side critical section in effect, request that the
 744  * next rcu_read_unlock() record the quiescent state up the
 745  * ->expmask fields in the rcu_node tree.  Otherwise, immediately
 746  * report the quiescent state.
 747  */
 748 static void rcu_exp_handler(void *unused)
 749 {
 750         int depth = rcu_preempt_depth();
 751         unsigned long flags;
 752         struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 753         struct rcu_node *rnp = rdp->mynode;
 754         struct task_struct *t = current;
 755
 756         /*
 757          * First, the common case of not being in an RCU read-side
 758          * critical section.  If also enabled or idle, immediately
 759          * report the quiescent state, otherwise defer.
 760          */
 761         if (!depth) {
 762                 if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
 763                     rcu_is_cpu_rrupt_from_idle()) {
 764                         rcu_report_exp_rdp(rdp);
 765                 } else {
 766                         WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
 767                         set_tsk_need_resched(t);
 768                         set_preempt_need_resched();
 769                 }
 770                 return;
 771         }
 772
 773         /*
 774          * Second, the less-common case of being in an RCU read-side
 775          * critical section.  In this case we can count on a future
 776          * rcu_read_unlock().  However, this rcu_read_unlock() might
 777          * execute on some other CPU, but in that case there will be
 778          * a future context switch.  Either way, if the expedited
 779          * grace period is still waiting on this CPU, set ->deferred_qs
 780          * so that the eventual quiescent state will be reported.
 781          * Note that there is a large group of race conditions that
 782          * can have caused this quiescent state to already have been
 783          * reported, so we really do need to check ->expmask.
 784          */
 785         if (depth > 0) {
 786                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
 787                 if (rnp->expmask & rdp->grpmask) {
 788                         WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
 789                         t->rcu_read_unlock_special.b.exp_hint = true;
 790                 }
 791                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 792                 return;
 793         }
 794
 795         // Finally, negative nesting depth should not happen.
 796         WARN_ON_ONCE(1);
 797 }
 798
 799 /* PREEMPTION=y, so no PREEMPTION=n expedited grace period to clean up after. */
 800 static void sync_sched_exp_online_cleanup(int cpu)
 801 {
 802 }
 803
 804 /*
 805  * Scan the current list of tasks blocked within RCU read-side critical
 806  * sections, printing out the tid of each that is blocking the current
 807  * expedited grace period.
 808  */
 809 static int rcu_print_task_exp_stall(struct rcu_node *rnp)
 810 {
 811         unsigned long flags;
 812         int ndetected = 0;
 813         struct task_struct *t;
 814
 815         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 816         if (!rnp->exp_tasks) {
 817                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 818                 return 0;
 819         }
 820         t = list_entry(rnp->exp_tasks->prev,
 821                        struct task_struct, rcu_node_entry);
 822         list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
 823                 pr_cont(" P%d", t->pid);
 824                 ndetected++;
 825         }
 826         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 827         return ndetected;
 828 }
 829
 830 /*
 831  * Scan the current list of tasks blocked within RCU read-side critical
 832  * sections, dumping the stack of each that is blocking the current
 833  * expedited grace period.
 834  */
 835 static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
 836 {
 837         unsigned long flags;
 838         struct task_struct *t;
 839
 840         if (!rcu_exp_stall_task_details)
 841                 return;
 842         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 843         if (!READ_ONCE(rnp->exp_tasks)) {
 844                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 845                 return;
 846         }
 847         t = list_entry(rnp->exp_tasks->prev,
 848                        struct task_struct, rcu_node_entry);
 849         list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
 850                 /*
 851                  * We could be printing a lot while holding a spinlock.
 852                  * Avoid triggering hard lockup.
 853                  */
 854                 touch_nmi_watchdog();
 855                 sched_show_task(t);
 856         }
 857         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 858 }
 859
 860 #else /* #ifdef CONFIG_PREEMPT_RCU */
 861
 862 /* Request an expedited quiescent state. */
 863 static void rcu_exp_need_qs(void)
 864 {
 865         __this_cpu_write(rcu_data.cpu_no_qs.b.exp, true);
 866         /* Store .exp before .rcu_urgent_qs. */
 867         smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true);
 868         set_tsk_need_resched(current);
 869         set_preempt_need_resched();
 870 }
 871
 872 /* Invoked on each online non-idle CPU for expedited quiescent state. */
 873 static void rcu_exp_handler(void *unused)
 874 {
 875         struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 876         struct rcu_node *rnp = rdp->mynode;
 877         bool preempt_bh_enabled = !(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
 878
 879         if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
 880             __this_cpu_read(rcu_data.cpu_no_qs.b.exp))
 881                 return;
 882         if (rcu_is_cpu_rrupt_from_idle() ||
 883             (IS_ENABLED(CONFIG_PREEMPT_COUNT) && preempt_bh_enabled)) {
 884                 rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
 885                 return;
 886         }
 887         rcu_exp_need_qs();
 888 }
 889
 890 /* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
 891 static void sync_sched_exp_online_cleanup(int cpu)
 892 {
 893         unsigned long flags;
 894         int my_cpu;
 895         struct rcu_data *rdp;
 896         int ret;
 897         struct rcu_node *rnp;
 898
 899         rdp = per_cpu_ptr(&rcu_data, cpu);
 900         rnp = rdp->mynode;
 901         my_cpu = get_cpu();
 902         /* Quiescent state either not needed or already requested, leave. */
 903         if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
 904             READ_ONCE(rdp->cpu_no_qs.b.exp)) {
 905                 put_cpu();
 906                 return;
 907         }
 908         /* Quiescent state needed on current CPU, so set it up locally. */
 909         if (my_cpu == cpu) {
 910                 local_irq_save(flags);
 911                 rcu_exp_need_qs();
 912                 local_irq_restore(flags);
 913                 put_cpu();
 914                 return;
 915         }
 916         /* Quiescent state needed on some other CPU, send IPI. */
 917         ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
 918         put_cpu();
 919         WARN_ON_ONCE(ret);
 920 }
 921
 922 /*
 923  * Because preemptible RCU does not exist, we never have to check for
 924  * tasks blocked within RCU read-side critical sections that are
 925  * blocking the current expedited grace period.
 926  */
 927 static int rcu_print_task_exp_stall(struct rcu_node *rnp)
 928 {
 929         return 0;
 930 }
 931
 932 /*
 933  * Because preemptible RCU does not exist, we never have to print out
 934  * tasks blocked within RCU read-side critical sections that are blocking
 935  * the current expedited grace period.
 936  */
 937 static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
 938 {
 939 }
 940
 941 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 942
 943 /**
 944  * synchronize_rcu_expedited - Brute-force RCU grace period
 945  *
 946  * Wait for an RCU grace period, but expedite it.  The basic idea is to
 947  * IPI all non-idle non-nohz online CPUs.  The IPI handler checks whether
 948  * the CPU is in an RCU critical section, and if so, it sets a flag that
 949  * causes the outermost rcu_read_unlock() to report the quiescent state
 950  * for RCU-preempt or asks the scheduler for help for RCU-sched.  On the
 951  * other hand, if the CPU is not in an RCU read-side critical section,
 952  * the IPI handler reports the quiescent state immediately.
 953  *
 954  * Although this is a great improvement over previous expedited
 955  * implementations, it is still unfriendly to real-time workloads, so is
 956  * thus not recommended for any sort of common-case code.  In fact, if
 957  * you are using synchronize_rcu_expedited() in a loop, please restructure
 958  * your code to batch your updates, and then use a single synchronize_rcu()
 959  * instead.
 960  *
 961  * This has the same semantics as (but is more brutal than) synchronize_rcu().
 962  */
 963 void synchronize_rcu_expedited(void)
 964 {
 965         bool use_worker;
 966         unsigned long flags;
 967         struct rcu_exp_work rew;
 968         struct rcu_node *rnp;
 969         unsigned long s;
 970
 971         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
 972                          lock_is_held(&rcu_lock_map) ||
 973                          lock_is_held(&rcu_sched_lock_map),
 974                          "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
 975
 976         use_worker = (rcu_scheduler_active != RCU_SCHEDULER_INIT) &&
 977                       rcu_exp_worker_started();
 978
 979         /* Is the state is such that the call is a grace period? */
 980         if (rcu_blocking_is_gp()) {
 981                 // Note well that this code runs with !PREEMPT && !SMP.
 982                 // In addition, all code that advances grace periods runs
 983                 // at process level.  Therefore, this expedited GP overlaps
 984                 // with other expedited GPs only by being fully nested within
 985                 // them, which allows reuse of ->gp_seq_polled_exp_snap.
 986                 rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
 987                 rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
 988
 989                 local_irq_save(flags);
 990                 WARN_ON_ONCE(num_online_cpus() > 1);
 991                 rcu_state.expedited_sequence += (1 << RCU_SEQ_CTR_SHIFT);
 992                 local_irq_restore(flags);
 993                 return;  // Context allows vacuous grace periods.
 994         }
 995
 996         /* If expedited grace periods are prohibited, fall back to normal. */
 997         if (rcu_gp_is_normal()) {
 998                 wait_rcu_gp(call_rcu_hurry);
 999                 return;
1000         }
1001
1002         /* Take a snapshot of the sequence number.  */
1003         s = rcu_exp_gp_seq_snap();
1004         if (exp_funnel_lock(s))
1005                 return;  /* Someone else did our work for us. */
1006
1007         /* Ensure that load happens before action based on it. */
1008         if (unlikely(!use_worker)) {
1009                 /* Direct call during scheduler init and early_initcalls(). */
1010                 rcu_exp_sel_wait_wake(s);
1011         } else {
1012                 /* Marshall arguments & schedule the expedited grace period. */
1013                 rew.rew_s = s;
1014                 synchronize_rcu_expedited_queue_work(&rew);
1015         }
1016
1017         /* Wait for expedited grace period to complete. */
1018         rnp = rcu_get_root();
1019         wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
1020                    sync_exp_work_done(s));
1021         smp_mb(); /* Work actions happen before return. */
1022
1023         /* Let the next expedited grace period start. */
1024         mutex_unlock(&rcu_state.exp_mutex);
1025
1026         if (likely(use_worker))
1027                 synchronize_rcu_expedited_destroy_work(&rew);
1028 }
1029 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1030
1031 /*
1032  * Ensure that start_poll_synchronize_rcu_expedited() has the expedited
1033  * RCU grace periods that it needs.
1034  */
1035 static void sync_rcu_do_polled_gp(struct work_struct *wp)
1036 {
1037         unsigned long flags;
1038         int i = 0;
1039         struct rcu_node *rnp = container_of(wp, struct rcu_node, exp_poll_wq);
1040         unsigned long s;
1041
1042         raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
1043         s = rnp->exp_seq_poll_rq;
1044         rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
1045         raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
1046         if (s == RCU_GET_STATE_COMPLETED)
1047                 return;
1048         while (!poll_state_synchronize_rcu(s)) {
1049                 synchronize_rcu_expedited();
1050                 if (i == 10 || i == 20)
1051                         pr_info("%s: i = %d s = %lx gp_seq_polled = %lx\n", __func__, i, s, READ_ONCE(rcu_state.gp_seq_polled));
1052                 i++;
1053         }
1054         raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
1055         s = rnp->exp_seq_poll_rq;
1056         if (poll_state_synchronize_rcu(s))
1057                 rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
1058         raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
1059 }
1060
1061 /**
1062  * start_poll_synchronize_rcu_expedited - Snapshot current RCU state and start expedited grace period
1063  *
1064  * Returns a cookie to pass to a call to cond_synchronize_rcu(),
1065  * cond_synchronize_rcu_expedited(), or poll_state_synchronize_rcu(),
1066  * allowing them to determine whether or not any sort of grace period has
1067  * elapsed in the meantime.  If the needed expedited grace period is not
1068  * already slated to start, initiates that grace period.
1069  */
1070 unsigned long start_poll_synchronize_rcu_expedited(void)
1071 {
1072         unsigned long flags;
1073         struct rcu_data *rdp;
1074         struct rcu_node *rnp;
1075         unsigned long s;
1076
1077         s = get_state_synchronize_rcu();
1078         rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
1079         rnp = rdp->mynode;
1080         if (rcu_init_invoked())
1081                 raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
1082         if (!poll_state_synchronize_rcu(s)) {
1083                 if (rcu_init_invoked()) {
1084                         rnp->exp_seq_poll_rq = s;
1085                         queue_work(rcu_gp_wq, &rnp->exp_poll_wq);
1086                 }
1087         }
1088         if (rcu_init_invoked())
1089                 raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
1090
1091         return s;
1092 }
1093 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited);
1094
1095 /**
1096  * start_poll_synchronize_rcu_expedited_full - Take a full snapshot and start expedited grace period
1097  * @rgosp: Place to put snapshot of grace-period state
1098  *
1099  * Places the normal and expedited grace-period states in rgosp.  This
1100  * state value can be passed to a later call to cond_synchronize_rcu_full()
1101  * or poll_state_synchronize_rcu_full() to determine whether or not a
1102  * grace period (whether normal or expedited) has elapsed in the meantime.
1103  * If the needed expedited grace period is not already slated to start,
1104  * initiates that grace period.
1105  */
1106 void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
1107 {
1108         get_state_synchronize_rcu_full(rgosp);
1109         (void)start_poll_synchronize_rcu_expedited();
1110 }
1111 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited_full);
1112
1113 /**
1114  * cond_synchronize_rcu_expedited - Conditionally wait for an expedited RCU grace period
1115  *
1116  * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
1117  *
1118  * If any type of full RCU grace period has elapsed since the earlier
1119  * call to get_state_synchronize_rcu(), start_poll_synchronize_rcu(),
1120  * or start_poll_synchronize_rcu_expedited(), just return.  Otherwise,
1121  * invoke synchronize_rcu_expedited() to wait for a full grace period.
1122  *
1123  * Yes, this function does not take counter wrap into account.
1124  * But counter wrap is harmless.  If the counter wraps, we have waited for
1125  * more than 2 billion grace periods (and way more on a 64-bit system!),
1126  * so waiting for a couple of additional grace periods should be just fine.
1127  *
1128  * This function provides the same memory-ordering guarantees that
1129  * would be provided by a synchronize_rcu() that was invoked at the call
1130  * to the function that provided @oldstate and that returned at the end
1131  * of this function.
1132  */
1133 void cond_synchronize_rcu_expedited(unsigned long oldstate)
1134 {
1135         if (!poll_state_synchronize_rcu(oldstate))
1136                 synchronize_rcu_expedited();
1137 }
1138 EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited);
1139
1140 /**
1141  * cond_synchronize_rcu_expedited_full - Conditionally wait for an expedited RCU grace period
1142  * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
1143  *
1144  * If a full RCU grace period has elapsed since the call to
1145  * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
1146  * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
1147  * obtained, just return.  Otherwise, invoke synchronize_rcu_expedited()
1148  * to wait for a full grace period.
1149  *
1150  * Yes, this function does not take counter wrap into account.
1151  * But counter wrap is harmless.  If the counter wraps, we have waited for
1152  * more than 2 billion grace periods (and way more on a 64-bit system!),
1153  * so waiting for a couple of additional grace periods should be just fine.
1154  *
1155  * This function provides the same memory-ordering guarantees that
1156  * would be provided by a synchronize_rcu() that was invoked at the call
1157  * to the function that provided @rgosp and that returned at the end of
1158  * this function.
1159  */
1160 void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
1161 {
1162         if (!poll_state_synchronize_rcu_full(rgosp))
1163                 synchronize_rcu_expedited();
1164 }
1165 EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited_full);