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_gp_par_worker_started(void)
 432 {
 433         return !!READ_ONCE(rcu_exp_par_gp_kworker);
 434 }
 435
 436 static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
 437 {
 438         kthread_init_work(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
 439         /*
 440          * Use rcu_exp_par_gp_kworker, because flushing a work item from
 441          * another work item on the same kthread worker can result in
 442          * deadlock.
 443          */
 444         kthread_queue_work(rcu_exp_par_gp_kworker, &rnp->rew.rew_work);
 445 }
 446
 447 static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
 448 {
 449         kthread_flush_work(&rnp->rew.rew_work);
 450 }
 451
 452 /*
 453  * Work-queue handler to drive an expedited grace period forward.
 454  */
 455 static void wait_rcu_exp_gp(struct kthread_work *wp)
 456 {
 457         struct rcu_exp_work *rewp;
 458
 459         rewp = container_of(wp, struct rcu_exp_work, rew_work);
 460         rcu_exp_sel_wait_wake(rewp->rew_s);
 461 }
 462
 463 static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
 464 {
 465         kthread_init_work(&rew->rew_work, wait_rcu_exp_gp);
 466         kthread_queue_work(rcu_exp_gp_kworker, &rew->rew_work);
 467 }
 468
 469 static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
 470 {
 471 }
 472 #else /* !CONFIG_RCU_EXP_KTHREAD */
 473 static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
 474 {
 475         struct rcu_exp_work *rewp =
 476                 container_of(wp, struct rcu_exp_work, rew_work);
 477
 478         __sync_rcu_exp_select_node_cpus(rewp);
 479 }
 480
 481 static inline bool rcu_gp_par_worker_started(void)
 482 {
 483         return !!READ_ONCE(rcu_par_gp_wq);
 484 }
 485
 486 static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
 487 {
 488         int cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
 489
 490         INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
 491         /* If all offline, queue the work on an unbound CPU. */
 492         if (unlikely(cpu > rnp->grphi - rnp->grplo))
 493                 cpu = WORK_CPU_UNBOUND;
 494         else
 495                 cpu += rnp->grplo;
 496         queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
 497 }
 498
 499 static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
 500 {
 501         flush_work(&rnp->rew.rew_work);
 502 }
 503
 504 /*
 505  * Work-queue handler to drive an expedited grace period forward.
 506  */
 507 static void wait_rcu_exp_gp(struct work_struct *wp)
 508 {
 509         struct rcu_exp_work *rewp;
 510
 511         rewp = container_of(wp, struct rcu_exp_work, rew_work);
 512         rcu_exp_sel_wait_wake(rewp->rew_s);
 513 }
 514
 515 static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
 516 {
 517         INIT_WORK_ONSTACK(&rew->rew_work, wait_rcu_exp_gp);
 518         queue_work(rcu_gp_wq, &rew->rew_work);
 519 }
 520
 521 static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
 522 {
 523         destroy_work_on_stack(&rew->rew_work);
 524 }
 525 #endif /* CONFIG_RCU_EXP_KTHREAD */
 526
 527 /*
 528  * Select the nodes that the upcoming expedited grace period needs
 529  * to wait for.
 530  */
 531 static void sync_rcu_exp_select_cpus(void)
 532 {
 533         struct rcu_node *rnp;
 534
 535         trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset"));
 536         sync_exp_reset_tree();
 537         trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select"));
 538
 539         /* Schedule work for each leaf rcu_node structure. */
 540         rcu_for_each_leaf_node(rnp) {
 541                 rnp->exp_need_flush = false;
 542                 if (!READ_ONCE(rnp->expmask))
 543                         continue; /* Avoid early boot non-existent wq. */
 544                 if (!rcu_gp_par_worker_started() ||
 545                     rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
 546                     rcu_is_last_leaf_node(rnp)) {
 547                         /* No worker started yet or last leaf, do direct call. */
 548                         sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
 549                         continue;
 550                 }
 551                 sync_rcu_exp_select_cpus_queue_work(rnp);
 552                 rnp->exp_need_flush = true;
 553         }
 554
 555         /* Wait for jobs (if any) to complete. */
 556         rcu_for_each_leaf_node(rnp)
 557                 if (rnp->exp_need_flush)
 558                         sync_rcu_exp_select_cpus_flush_work(rnp);
 559 }
 560
 561 /*
 562  * Wait for the expedited grace period to elapse, within time limit.
 563  * If the time limit is exceeded without the grace period elapsing,
 564  * return false, otherwise return true.
 565  */
 566 static bool synchronize_rcu_expedited_wait_once(long tlimit)
 567 {
 568         int t;
 569         struct rcu_node *rnp_root = rcu_get_root();
 570
 571         t = swait_event_timeout_exclusive(rcu_state.expedited_wq,
 572                                           sync_rcu_exp_done_unlocked(rnp_root),
 573                                           tlimit);
 574         // Workqueues should not be signaled.
 575         if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root))
 576                 return true;
 577         WARN_ON(t < 0);  /* workqueues should not be signaled. */
 578         return false;
 579 }
 580
 581 /*
 582  * Wait for the expedited grace period to elapse, issuing any needed
 583  * RCU CPU stall warnings along the way.
 584  */
 585 static void synchronize_rcu_expedited_wait(void)
 586 {
 587         int cpu;
 588         unsigned long j;
 589         unsigned long jiffies_stall;
 590         unsigned long jiffies_start;
 591         unsigned long mask;
 592         int ndetected;
 593         struct rcu_data *rdp;
 594         struct rcu_node *rnp;
 595         struct rcu_node *rnp_root = rcu_get_root();
 596         unsigned long flags;
 597
 598         trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
 599         jiffies_stall = rcu_exp_jiffies_till_stall_check();
 600         jiffies_start = jiffies;
 601         if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) {
 602                 if (synchronize_rcu_expedited_wait_once(1))
 603                         return;
 604                 rcu_for_each_leaf_node(rnp) {
 605                         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 606                         mask = READ_ONCE(rnp->expmask);
 607                         for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
 608                                 rdp = per_cpu_ptr(&rcu_data, cpu);
 609                                 if (rdp->rcu_forced_tick_exp)
 610                                         continue;
 611                                 rdp->rcu_forced_tick_exp = true;
 612                                 if (cpu_online(cpu))
 613                                         tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
 614                         }
 615                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 616                 }
 617                 j = READ_ONCE(jiffies_till_first_fqs);
 618                 if (synchronize_rcu_expedited_wait_once(j + HZ))
 619                         return;
 620         }
 621
 622         for (;;) {
 623                 unsigned long j;
 624
 625                 if (synchronize_rcu_expedited_wait_once(jiffies_stall))
 626                         return;
 627                 if (rcu_stall_is_suppressed())
 628                         continue;
 629                 j = jiffies;
 630                 rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_EXP, (void *)(j - jiffies_start));
 631                 trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
 632                 pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
 633                        rcu_state.name);
 634                 ndetected = 0;
 635                 rcu_for_each_leaf_node(rnp) {
 636                         ndetected += rcu_print_task_exp_stall(rnp);
 637                         for_each_leaf_node_possible_cpu(rnp, cpu) {
 638                                 struct rcu_data *rdp;
 639
 640                                 mask = leaf_node_cpu_bit(rnp, cpu);
 641                                 if (!(READ_ONCE(rnp->expmask) & mask))
 642                                         continue;
 643                                 ndetected++;
 644                                 rdp = per_cpu_ptr(&rcu_data, cpu);
 645                                 pr_cont(" %d-%c%c%c%c", cpu,
 646                                         "O."[!!cpu_online(cpu)],
 647                                         "o."[!!(rdp->grpmask & rnp->expmaskinit)],
 648                                         "N."[!!(rdp->grpmask & rnp->expmaskinitnext)],
 649                                         "D."[!!data_race(rdp->cpu_no_qs.b.exp)]);
 650                         }
 651                 }
 652                 pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
 653                         j - jiffies_start, rcu_state.expedited_sequence,
 654                         data_race(rnp_root->expmask),
 655                         ".T"[!!data_race(rnp_root->exp_tasks)]);
 656                 if (ndetected) {
 657                         pr_err("blocking rcu_node structures (internal RCU debug):");
 658                         rcu_for_each_node_breadth_first(rnp) {
 659                                 if (rnp == rnp_root)
 660                                         continue; /* printed unconditionally */
 661                                 if (sync_rcu_exp_done_unlocked(rnp))
 662                                         continue;
 663                                 pr_cont(" l=%u:%d-%d:%#lx/%c",
 664                                         rnp->level, rnp->grplo, rnp->grphi,
 665                                         data_race(rnp->expmask),
 666                                         ".T"[!!data_race(rnp->exp_tasks)]);
 667                         }
 668                         pr_cont("\n");
 669                 }
 670                 rcu_for_each_leaf_node(rnp) {
 671                         for_each_leaf_node_possible_cpu(rnp, cpu) {
 672                                 mask = leaf_node_cpu_bit(rnp, cpu);
 673                                 if (!(READ_ONCE(rnp->expmask) & mask))
 674                                         continue;
 675                                 preempt_disable(); // For smp_processor_id() in dump_cpu_task().
 676                                 dump_cpu_task(cpu);
 677                                 preempt_enable();
 678                         }
 679                         rcu_exp_print_detail_task_stall_rnp(rnp);
 680                 }
 681                 jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
 682                 panic_on_rcu_stall();
 683         }
 684 }
 685
 686 /*
 687  * Wait for the current expedited grace period to complete, and then
 688  * wake up everyone who piggybacked on the just-completed expedited
 689  * grace period.  Also update all the ->exp_seq_rq counters as needed
 690  * in order to avoid counter-wrap problems.
 691  */
 692 static void rcu_exp_wait_wake(unsigned long s)
 693 {
 694         struct rcu_node *rnp;
 695
 696         synchronize_rcu_expedited_wait();
 697
 698         // Switch over to wakeup mode, allowing the next GP to proceed.
 699         // End the previous grace period only after acquiring the mutex
 700         // to ensure that only one GP runs concurrently with wakeups.
 701         mutex_lock(&rcu_state.exp_wake_mutex);
 702         rcu_exp_gp_seq_end();
 703         trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end"));
 704
 705         rcu_for_each_node_breadth_first(rnp) {
 706                 if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
 707                         spin_lock(&rnp->exp_lock);
 708                         /* Recheck, avoid hang in case someone just arrived. */
 709                         if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
 710                                 WRITE_ONCE(rnp->exp_seq_rq, s);
 711                         spin_unlock(&rnp->exp_lock);
 712                 }
 713                 smp_mb(); /* All above changes before wakeup. */
 714                 wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]);
 715         }
 716         trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake"));
 717         mutex_unlock(&rcu_state.exp_wake_mutex);
 718 }
 719
 720 /*
 721  * Common code to drive an expedited grace period forward, used by
 722  * workqueues and mid-boot-time tasks.
 723  */
 724 static void rcu_exp_sel_wait_wake(unsigned long s)
 725 {
 726         /* Initialize the rcu_node tree in preparation for the wait. */
 727         sync_rcu_exp_select_cpus();
 728
 729         /* Wait and clean up, including waking everyone. */
 730         rcu_exp_wait_wake(s);
 731 }
 732
 733 #ifdef CONFIG_PREEMPT_RCU
 734
 735 /*
 736  * Remote handler for smp_call_function_single().  If there is an
 737  * RCU read-side critical section in effect, request that the
 738  * next rcu_read_unlock() record the quiescent state up the
 739  * ->expmask fields in the rcu_node tree.  Otherwise, immediately
 740  * report the quiescent state.
 741  */
 742 static void rcu_exp_handler(void *unused)
 743 {
 744         int depth = rcu_preempt_depth();
 745         unsigned long flags;
 746         struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 747         struct rcu_node *rnp = rdp->mynode;
 748         struct task_struct *t = current;
 749
 750         /*
 751          * First, the common case of not being in an RCU read-side
 752          * critical section.  If also enabled or idle, immediately
 753          * report the quiescent state, otherwise defer.
 754          */
 755         if (!depth) {
 756                 if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
 757                     rcu_is_cpu_rrupt_from_idle()) {
 758                         rcu_report_exp_rdp(rdp);
 759                 } else {
 760                         WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
 761                         set_tsk_need_resched(t);
 762                         set_preempt_need_resched();
 763                 }
 764                 return;
 765         }
 766
 767         /*
 768          * Second, the less-common case of being in an RCU read-side
 769          * critical section.  In this case we can count on a future
 770          * rcu_read_unlock().  However, this rcu_read_unlock() might
 771          * execute on some other CPU, but in that case there will be
 772          * a future context switch.  Either way, if the expedited
 773          * grace period is still waiting on this CPU, set ->deferred_qs
 774          * so that the eventual quiescent state will be reported.
 775          * Note that there is a large group of race conditions that
 776          * can have caused this quiescent state to already have been
 777          * reported, so we really do need to check ->expmask.
 778          */
 779         if (depth > 0) {
 780                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
 781                 if (rnp->expmask & rdp->grpmask) {
 782                         WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
 783                         t->rcu_read_unlock_special.b.exp_hint = true;
 784                 }
 785                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 786                 return;
 787         }
 788
 789         // Finally, negative nesting depth should not happen.
 790         WARN_ON_ONCE(1);
 791 }
 792
 793 /* PREEMPTION=y, so no PREEMPTION=n expedited grace period to clean up after. */
 794 static void sync_sched_exp_online_cleanup(int cpu)
 795 {
 796 }
 797
 798 /*
 799  * Scan the current list of tasks blocked within RCU read-side critical
 800  * sections, printing out the tid of each that is blocking the current
 801  * expedited grace period.
 802  */
 803 static int rcu_print_task_exp_stall(struct rcu_node *rnp)
 804 {
 805         unsigned long flags;
 806         int ndetected = 0;
 807         struct task_struct *t;
 808
 809         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 810         if (!rnp->exp_tasks) {
 811                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 812                 return 0;
 813         }
 814         t = list_entry(rnp->exp_tasks->prev,
 815                        struct task_struct, rcu_node_entry);
 816         list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
 817                 pr_cont(" P%d", t->pid);
 818                 ndetected++;
 819         }
 820         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 821         return ndetected;
 822 }
 823
 824 /*
 825  * Scan the current list of tasks blocked within RCU read-side critical
 826  * sections, dumping the stack of each that is blocking the current
 827  * expedited grace period.
 828  */
 829 static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
 830 {
 831         unsigned long flags;
 832         struct task_struct *t;
 833
 834         if (!rcu_exp_stall_task_details)
 835                 return;
 836         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 837         if (!READ_ONCE(rnp->exp_tasks)) {
 838                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 839                 return;
 840         }
 841         t = list_entry(rnp->exp_tasks->prev,
 842                        struct task_struct, rcu_node_entry);
 843         list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
 844                 /*
 845                  * We could be printing a lot while holding a spinlock.
 846                  * Avoid triggering hard lockup.
 847                  */
 848                 touch_nmi_watchdog();
 849                 sched_show_task(t);
 850         }
 851         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 852 }
 853
 854 #else /* #ifdef CONFIG_PREEMPT_RCU */
 855
 856 /* Request an expedited quiescent state. */
 857 static void rcu_exp_need_qs(void)
 858 {
 859         __this_cpu_write(rcu_data.cpu_no_qs.b.exp, true);
 860         /* Store .exp before .rcu_urgent_qs. */
 861         smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true);
 862         set_tsk_need_resched(current);
 863         set_preempt_need_resched();
 864 }
 865
 866 /* Invoked on each online non-idle CPU for expedited quiescent state. */
 867 static void rcu_exp_handler(void *unused)
 868 {
 869         struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 870         struct rcu_node *rnp = rdp->mynode;
 871         bool preempt_bh_enabled = !(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
 872
 873         if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
 874             __this_cpu_read(rcu_data.cpu_no_qs.b.exp))
 875                 return;
 876         if (rcu_is_cpu_rrupt_from_idle() ||
 877             (IS_ENABLED(CONFIG_PREEMPT_COUNT) && preempt_bh_enabled)) {
 878                 rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
 879                 return;
 880         }
 881         rcu_exp_need_qs();
 882 }
 883
 884 /* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
 885 static void sync_sched_exp_online_cleanup(int cpu)
 886 {
 887         unsigned long flags;
 888         int my_cpu;
 889         struct rcu_data *rdp;
 890         int ret;
 891         struct rcu_node *rnp;
 892
 893         rdp = per_cpu_ptr(&rcu_data, cpu);
 894         rnp = rdp->mynode;
 895         my_cpu = get_cpu();
 896         /* Quiescent state either not needed or already requested, leave. */
 897         if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
 898             READ_ONCE(rdp->cpu_no_qs.b.exp)) {
 899                 put_cpu();
 900                 return;
 901         }
 902         /* Quiescent state needed on current CPU, so set it up locally. */
 903         if (my_cpu == cpu) {
 904                 local_irq_save(flags);
 905                 rcu_exp_need_qs();
 906                 local_irq_restore(flags);
 907                 put_cpu();
 908                 return;
 909         }
 910         /* Quiescent state needed on some other CPU, send IPI. */
 911         ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
 912         put_cpu();
 913         WARN_ON_ONCE(ret);
 914 }
 915
 916 /*
 917  * Because preemptible RCU does not exist, we never have to check for
 918  * tasks blocked within RCU read-side critical sections that are
 919  * blocking the current expedited grace period.
 920  */
 921 static int rcu_print_task_exp_stall(struct rcu_node *rnp)
 922 {
 923         return 0;
 924 }
 925
 926 /*
 927  * Because preemptible RCU does not exist, we never have to print out
 928  * tasks blocked within RCU read-side critical sections that are blocking
 929  * the current expedited grace period.
 930  */
 931 static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
 932 {
 933 }
 934
 935 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 936
 937 /**
 938  * synchronize_rcu_expedited - Brute-force RCU grace period
 939  *
 940  * Wait for an RCU grace period, but expedite it.  The basic idea is to
 941  * IPI all non-idle non-nohz online CPUs.  The IPI handler checks whether
 942  * the CPU is in an RCU critical section, and if so, it sets a flag that
 943  * causes the outermost rcu_read_unlock() to report the quiescent state
 944  * for RCU-preempt or asks the scheduler for help for RCU-sched.  On the
 945  * other hand, if the CPU is not in an RCU read-side critical section,
 946  * the IPI handler reports the quiescent state immediately.
 947  *
 948  * Although this is a great improvement over previous expedited
 949  * implementations, it is still unfriendly to real-time workloads, so is
 950  * thus not recommended for any sort of common-case code.  In fact, if
 951  * you are using synchronize_rcu_expedited() in a loop, please restructure
 952  * your code to batch your updates, and then use a single synchronize_rcu()
 953  * instead.
 954  *
 955  * This has the same semantics as (but is more brutal than) synchronize_rcu().
 956  */
 957 void synchronize_rcu_expedited(void)
 958 {
 959         bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT);
 960         unsigned long flags;
 961         struct rcu_exp_work rew;
 962         struct rcu_node *rnp;
 963         unsigned long s;
 964
 965         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
 966                          lock_is_held(&rcu_lock_map) ||
 967                          lock_is_held(&rcu_sched_lock_map),
 968                          "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
 969
 970         /* Is the state is such that the call is a grace period? */
 971         if (rcu_blocking_is_gp()) {
 972                 // Note well that this code runs with !PREEMPT && !SMP.
 973                 // In addition, all code that advances grace periods runs
 974                 // at process level.  Therefore, this expedited GP overlaps
 975                 // with other expedited GPs only by being fully nested within
 976                 // them, which allows reuse of ->gp_seq_polled_exp_snap.
 977                 rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
 978                 rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
 979
 980                 local_irq_save(flags);
 981                 WARN_ON_ONCE(num_online_cpus() > 1);
 982                 rcu_state.expedited_sequence += (1 << RCU_SEQ_CTR_SHIFT);
 983                 local_irq_restore(flags);
 984                 return;  // Context allows vacuous grace periods.
 985         }
 986
 987         /* If expedited grace periods are prohibited, fall back to normal. */
 988         if (rcu_gp_is_normal()) {
 989                 wait_rcu_gp(call_rcu_hurry);
 990                 return;
 991         }
 992
 993         /* Take a snapshot of the sequence number.  */
 994         s = rcu_exp_gp_seq_snap();
 995         if (exp_funnel_lock(s))
 996                 return;  /* Someone else did our work for us. */
 997
 998         /* Ensure that load happens before action based on it. */
 999         if (unlikely(boottime)) {
1000                 /* Direct call during scheduler init and early_initcalls(). */
1001                 rcu_exp_sel_wait_wake(s);
1002         } else {
1003                 /* Marshall arguments & schedule the expedited grace period. */
1004                 rew.rew_s = s;
1005                 synchronize_rcu_expedited_queue_work(&rew);
1006         }
1007
1008         /* Wait for expedited grace period to complete. */
1009         rnp = rcu_get_root();
1010         wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
1011                    sync_exp_work_done(s));
1012         smp_mb(); /* Work actions happen before return. */
1013
1014         /* Let the next expedited grace period start. */
1015         mutex_unlock(&rcu_state.exp_mutex);
1016
1017         if (likely(!boottime))
1018                 synchronize_rcu_expedited_destroy_work(&rew);
1019 }
1020 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1021
1022 /*
1023  * Ensure that start_poll_synchronize_rcu_expedited() has the expedited
1024  * RCU grace periods that it needs.
1025  */
1026 static void sync_rcu_do_polled_gp(struct work_struct *wp)
1027 {
1028         unsigned long flags;
1029         int i = 0;
1030         struct rcu_node *rnp = container_of(wp, struct rcu_node, exp_poll_wq);
1031         unsigned long s;
1032
1033         raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
1034         s = rnp->exp_seq_poll_rq;
1035         rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
1036         raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
1037         if (s == RCU_GET_STATE_COMPLETED)
1038                 return;
1039         while (!poll_state_synchronize_rcu(s)) {
1040                 synchronize_rcu_expedited();
1041                 if (i == 10 || i == 20)
1042                         pr_info("%s: i = %d s = %lx gp_seq_polled = %lx\n", __func__, i, s, READ_ONCE(rcu_state.gp_seq_polled));
1043                 i++;
1044         }
1045         raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
1046         s = rnp->exp_seq_poll_rq;
1047         if (poll_state_synchronize_rcu(s))
1048                 rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
1049         raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
1050 }
1051
1052 /**
1053  * start_poll_synchronize_rcu_expedited - Snapshot current RCU state and start expedited grace period
1054  *
1055  * Returns a cookie to pass to a call to cond_synchronize_rcu(),
1056  * cond_synchronize_rcu_expedited(), or poll_state_synchronize_rcu(),
1057  * allowing them to determine whether or not any sort of grace period has
1058  * elapsed in the meantime.  If the needed expedited grace period is not
1059  * already slated to start, initiates that grace period.
1060  */
1061 unsigned long start_poll_synchronize_rcu_expedited(void)
1062 {
1063         unsigned long flags;
1064         struct rcu_data *rdp;
1065         struct rcu_node *rnp;
1066         unsigned long s;
1067
1068         s = get_state_synchronize_rcu();
1069         rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
1070         rnp = rdp->mynode;
1071         if (rcu_init_invoked())
1072                 raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
1073         if (!poll_state_synchronize_rcu(s)) {
1074                 if (rcu_init_invoked()) {
1075                         rnp->exp_seq_poll_rq = s;
1076                         queue_work(rcu_gp_wq, &rnp->exp_poll_wq);
1077                 }
1078         }
1079         if (rcu_init_invoked())
1080                 raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
1081
1082         return s;
1083 }
1084 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited);
1085
1086 /**
1087  * start_poll_synchronize_rcu_expedited_full - Take a full snapshot and start expedited grace period
1088  * @rgosp: Place to put snapshot of grace-period state
1089  *
1090  * Places the normal and expedited grace-period states in rgosp.  This
1091  * state value can be passed to a later call to cond_synchronize_rcu_full()
1092  * or poll_state_synchronize_rcu_full() to determine whether or not a
1093  * grace period (whether normal or expedited) has elapsed in the meantime.
1094  * If the needed expedited grace period is not already slated to start,
1095  * initiates that grace period.
1096  */
1097 void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
1098 {
1099         get_state_synchronize_rcu_full(rgosp);
1100         (void)start_poll_synchronize_rcu_expedited();
1101 }
1102 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited_full);
1103
1104 /**
1105  * cond_synchronize_rcu_expedited - Conditionally wait for an expedited RCU grace period
1106  *
1107  * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
1108  *
1109  * If any type of full RCU grace period has elapsed since the earlier
1110  * call to get_state_synchronize_rcu(), start_poll_synchronize_rcu(),
1111  * or start_poll_synchronize_rcu_expedited(), just return.  Otherwise,
1112  * invoke synchronize_rcu_expedited() to wait for a full grace period.
1113  *
1114  * Yes, this function does not take counter wrap into account.
1115  * But counter wrap is harmless.  If the counter wraps, we have waited for
1116  * more than 2 billion grace periods (and way more on a 64-bit system!),
1117  * so waiting for a couple of additional grace periods should be just fine.
1118  *
1119  * This function provides the same memory-ordering guarantees that
1120  * would be provided by a synchronize_rcu() that was invoked at the call
1121  * to the function that provided @oldstate and that returned at the end
1122  * of this function.
1123  */
1124 void cond_synchronize_rcu_expedited(unsigned long oldstate)
1125 {
1126         if (!poll_state_synchronize_rcu(oldstate))
1127                 synchronize_rcu_expedited();
1128 }
1129 EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited);
1130
1131 /**
1132  * cond_synchronize_rcu_expedited_full - Conditionally wait for an expedited RCU grace period
1133  * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
1134  *
1135  * If a full RCU grace period has elapsed since the call to
1136  * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
1137  * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
1138  * obtained, just return.  Otherwise, invoke synchronize_rcu_expedited()
1139  * to wait for a full grace period.
1140  *
1141  * Yes, this function does not take counter wrap into account.
1142  * But counter wrap is harmless.  If the counter wraps, we have waited for
1143  * more than 2 billion grace periods (and way more on a 64-bit system!),
1144  * so waiting for a couple of additional grace periods should be just fine.
1145  *
1146  * This function provides the same memory-ordering guarantees that
1147  * would be provided by a synchronize_rcu() that was invoked at the call
1148  * to the function that provided @rgosp and that returned at the end of
1149  * this function.
1150  */
1151 void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
1152 {
1153         if (!poll_state_synchronize_rcu_full(rgosp))
1154                 synchronize_rcu_expedited();
1155 }
1156 EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited_full);