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