linux/kernel/rcutree.c
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   1/*
   2 * Read-Copy Update mechanism for mutual exclusion
   3 *
   4 * This program is free software; you can redistribute it and/or modify
   5 * it under the terms of the GNU General Public License as published by
   6 * the Free Software Foundation; either version 2 of the License, or
   7 * (at your option) any later version.
   8 *
   9 * This program is distributed in the hope that it will be useful,
  10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 * GNU General Public License for more details.
  13 *
  14 * You should have received a copy of the GNU General Public License
  15 * along with this program; if not, write to the Free Software
  16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17 *
  18 * Copyright IBM Corporation, 2008
  19 *
  20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
  21 *          Manfred Spraul <manfred@colorfullife.com>
  22 *          Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
  23 *
  24 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
  25 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
  26 *
  27 * For detailed explanation of Read-Copy Update mechanism see -
  28 *      Documentation/RCU
  29 */
  30#include <linux/types.h>
  31#include <linux/kernel.h>
  32#include <linux/init.h>
  33#include <linux/spinlock.h>
  34#include <linux/smp.h>
  35#include <linux/rcupdate.h>
  36#include <linux/interrupt.h>
  37#include <linux/sched.h>
  38#include <linux/nmi.h>
  39#include <linux/atomic.h>
  40#include <linux/bitops.h>
  41#include <linux/module.h>
  42#include <linux/completion.h>
  43#include <linux/moduleparam.h>
  44#include <linux/percpu.h>
  45#include <linux/notifier.h>
  46#include <linux/cpu.h>
  47#include <linux/mutex.h>
  48#include <linux/time.h>
  49#include <linux/kernel_stat.h>
  50#include <linux/wait.h>
  51#include <linux/kthread.h>
  52#include <linux/prefetch.h>
  53
  54#include "rcutree.h"
  55
  56/* Data structures. */
  57
  58static struct lock_class_key rcu_node_class[NUM_RCU_LVLS];
  59
  60#define RCU_STATE_INITIALIZER(structname) { \
  61        .level = { &structname.node[0] }, \
  62        .levelcnt = { \
  63                NUM_RCU_LVL_0,  /* root of hierarchy. */ \
  64                NUM_RCU_LVL_1, \
  65                NUM_RCU_LVL_2, \
  66                NUM_RCU_LVL_3, \
  67                NUM_RCU_LVL_4, /* == MAX_RCU_LVLS */ \
  68        }, \
  69        .signaled = RCU_GP_IDLE, \
  70        .gpnum = -300, \
  71        .completed = -300, \
  72        .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&structname.onofflock), \
  73        .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname.fqslock), \
  74        .n_force_qs = 0, \
  75        .n_force_qs_ngp = 0, \
  76        .name = #structname, \
  77}
  78
  79struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched_state);
  80DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
  81
  82struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
  83DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
  84
  85static struct rcu_state *rcu_state;
  86
  87/*
  88 * The rcu_scheduler_active variable transitions from zero to one just
  89 * before the first task is spawned.  So when this variable is zero, RCU
  90 * can assume that there is but one task, allowing RCU to (for example)
  91 * optimized synchronize_sched() to a simple barrier().  When this variable
  92 * is one, RCU must actually do all the hard work required to detect real
  93 * grace periods.  This variable is also used to suppress boot-time false
  94 * positives from lockdep-RCU error checking.
  95 */
  96int rcu_scheduler_active __read_mostly;
  97EXPORT_SYMBOL_GPL(rcu_scheduler_active);
  98
  99/*
 100 * The rcu_scheduler_fully_active variable transitions from zero to one
 101 * during the early_initcall() processing, which is after the scheduler
 102 * is capable of creating new tasks.  So RCU processing (for example,
 103 * creating tasks for RCU priority boosting) must be delayed until after
 104 * rcu_scheduler_fully_active transitions from zero to one.  We also
 105 * currently delay invocation of any RCU callbacks until after this point.
 106 *
 107 * It might later prove better for people registering RCU callbacks during
 108 * early boot to take responsibility for these callbacks, but one step at
 109 * a time.
 110 */
 111static int rcu_scheduler_fully_active __read_mostly;
 112
 113#ifdef CONFIG_RCU_BOOST
 114
 115/*
 116 * Control variables for per-CPU and per-rcu_node kthreads.  These
 117 * handle all flavors of RCU.
 118 */
 119static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
 120DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
 121DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu);
 122DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
 123DEFINE_PER_CPU(char, rcu_cpu_has_work);
 124
 125#endif /* #ifdef CONFIG_RCU_BOOST */
 126
 127static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
 128static void invoke_rcu_core(void);
 129static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
 130
 131#define RCU_KTHREAD_PRIO 1      /* RT priority for per-CPU kthreads. */
 132
 133/*
 134 * Track the rcutorture test sequence number and the update version
 135 * number within a given test.  The rcutorture_testseq is incremented
 136 * on every rcutorture module load and unload, so has an odd value
 137 * when a test is running.  The rcutorture_vernum is set to zero
 138 * when rcutorture starts and is incremented on each rcutorture update.
 139 * These variables enable correlating rcutorture output with the
 140 * RCU tracing information.
 141 */
 142unsigned long rcutorture_testseq;
 143unsigned long rcutorture_vernum;
 144
 145/*
 146 * Return true if an RCU grace period is in progress.  The ACCESS_ONCE()s
 147 * permit this function to be invoked without holding the root rcu_node
 148 * structure's ->lock, but of course results can be subject to change.
 149 */
 150static int rcu_gp_in_progress(struct rcu_state *rsp)
 151{
 152        return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
 153}
 154
 155/*
 156 * Note a quiescent state.  Because we do not need to know
 157 * how many quiescent states passed, just if there was at least
 158 * one since the start of the grace period, this just sets a flag.
 159 */
 160void rcu_sched_qs(int cpu)
 161{
 162        struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
 163
 164        rdp->passed_quiesc_completed = rdp->gpnum - 1;
 165        barrier();
 166        rdp->passed_quiesc = 1;
 167}
 168
 169void rcu_bh_qs(int cpu)
 170{
 171        struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
 172
 173        rdp->passed_quiesc_completed = rdp->gpnum - 1;
 174        barrier();
 175        rdp->passed_quiesc = 1;
 176}
 177
 178/*
 179 * Note a context switch.  This is a quiescent state for RCU-sched,
 180 * and requires special handling for preemptible RCU.
 181 */
 182void rcu_note_context_switch(int cpu)
 183{
 184        rcu_sched_qs(cpu);
 185        rcu_preempt_note_context_switch(cpu);
 186}
 187EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 188
 189#ifdef CONFIG_NO_HZ
 190DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
 191        .dynticks_nesting = 1,
 192        .dynticks = ATOMIC_INIT(1),
 193};
 194#endif /* #ifdef CONFIG_NO_HZ */
 195
 196static int blimit = 10;         /* Maximum callbacks per softirq. */
 197static int qhimark = 10000;     /* If this many pending, ignore blimit. */
 198static int qlowmark = 100;      /* Once only this many pending, use blimit. */
 199
 200module_param(blimit, int, 0);
 201module_param(qhimark, int, 0);
 202module_param(qlowmark, int, 0);
 203
 204int rcu_cpu_stall_suppress __read_mostly;
 205module_param(rcu_cpu_stall_suppress, int, 0644);
 206
 207static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
 208static int rcu_pending(int cpu);
 209
 210/*
 211 * Return the number of RCU-sched batches processed thus far for debug & stats.
 212 */
 213long rcu_batches_completed_sched(void)
 214{
 215        return rcu_sched_state.completed;
 216}
 217EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
 218
 219/*
 220 * Return the number of RCU BH batches processed thus far for debug & stats.
 221 */
 222long rcu_batches_completed_bh(void)
 223{
 224        return rcu_bh_state.completed;
 225}
 226EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
 227
 228/*
 229 * Force a quiescent state for RCU BH.
 230 */
 231void rcu_bh_force_quiescent_state(void)
 232{
 233        force_quiescent_state(&rcu_bh_state, 0);
 234}
 235EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
 236
 237/*
 238 * Record the number of times rcutorture tests have been initiated and
 239 * terminated.  This information allows the debugfs tracing stats to be
 240 * correlated to the rcutorture messages, even when the rcutorture module
 241 * is being repeatedly loaded and unloaded.  In other words, we cannot
 242 * store this state in rcutorture itself.
 243 */
 244void rcutorture_record_test_transition(void)
 245{
 246        rcutorture_testseq++;
 247        rcutorture_vernum = 0;
 248}
 249EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
 250
 251/*
 252 * Record the number of writer passes through the current rcutorture test.
 253 * This is also used to correlate debugfs tracing stats with the rcutorture
 254 * messages.
 255 */
 256void rcutorture_record_progress(unsigned long vernum)
 257{
 258        rcutorture_vernum++;
 259}
 260EXPORT_SYMBOL_GPL(rcutorture_record_progress);
 261
 262/*
 263 * Force a quiescent state for RCU-sched.
 264 */
 265void rcu_sched_force_quiescent_state(void)
 266{
 267        force_quiescent_state(&rcu_sched_state, 0);
 268}
 269EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
 270
 271/*
 272 * Does the CPU have callbacks ready to be invoked?
 273 */
 274static int
 275cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
 276{
 277        return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
 278}
 279
 280/*
 281 * Does the current CPU require a yet-as-unscheduled grace period?
 282 */
 283static int
 284cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
 285{
 286        return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp);
 287}
 288
 289/*
 290 * Return the root node of the specified rcu_state structure.
 291 */
 292static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
 293{
 294        return &rsp->node[0];
 295}
 296
 297#ifdef CONFIG_SMP
 298
 299/*
 300 * If the specified CPU is offline, tell the caller that it is in
 301 * a quiescent state.  Otherwise, whack it with a reschedule IPI.
 302 * Grace periods can end up waiting on an offline CPU when that
 303 * CPU is in the process of coming online -- it will be added to the
 304 * rcu_node bitmasks before it actually makes it online.  The same thing
 305 * can happen while a CPU is in the process of coming online.  Because this
 306 * race is quite rare, we check for it after detecting that the grace
 307 * period has been delayed rather than checking each and every CPU
 308 * each and every time we start a new grace period.
 309 */
 310static int rcu_implicit_offline_qs(struct rcu_data *rdp)
 311{
 312        /*
 313         * If the CPU is offline, it is in a quiescent state.  We can
 314         * trust its state not to change because interrupts are disabled.
 315         */
 316        if (cpu_is_offline(rdp->cpu)) {
 317                rdp->offline_fqs++;
 318                return 1;
 319        }
 320
 321        /* If preemptible RCU, no point in sending reschedule IPI. */
 322        if (rdp->preemptible)
 323                return 0;
 324
 325        /* The CPU is online, so send it a reschedule IPI. */
 326        if (rdp->cpu != smp_processor_id())
 327                smp_send_reschedule(rdp->cpu);
 328        else
 329                set_need_resched();
 330        rdp->resched_ipi++;
 331        return 0;
 332}
 333
 334#endif /* #ifdef CONFIG_SMP */
 335
 336#ifdef CONFIG_NO_HZ
 337
 338/**
 339 * rcu_enter_nohz - inform RCU that current CPU is entering nohz
 340 *
 341 * Enter nohz mode, in other words, -leave- the mode in which RCU
 342 * read-side critical sections can occur.  (Though RCU read-side
 343 * critical sections can occur in irq handlers in nohz mode, a possibility
 344 * handled by rcu_irq_enter() and rcu_irq_exit()).
 345 */
 346void rcu_enter_nohz(void)
 347{
 348        unsigned long flags;
 349        struct rcu_dynticks *rdtp;
 350
 351        local_irq_save(flags);
 352        rdtp = &__get_cpu_var(rcu_dynticks);
 353        if (--rdtp->dynticks_nesting) {
 354                local_irq_restore(flags);
 355                return;
 356        }
 357        /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
 358        smp_mb__before_atomic_inc();  /* See above. */
 359        atomic_inc(&rdtp->dynticks);
 360        smp_mb__after_atomic_inc();  /* Force ordering with next sojourn. */
 361        WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
 362        local_irq_restore(flags);
 363
 364        /* If the interrupt queued a callback, get out of dyntick mode. */
 365        if (in_irq() &&
 366            (__get_cpu_var(rcu_sched_data).nxtlist ||
 367             __get_cpu_var(rcu_bh_data).nxtlist ||
 368             rcu_preempt_needs_cpu(smp_processor_id())))
 369                set_need_resched();
 370}
 371
 372/*
 373 * rcu_exit_nohz - inform RCU that current CPU is leaving nohz
 374 *
 375 * Exit nohz mode, in other words, -enter- the mode in which RCU
 376 * read-side critical sections normally occur.
 377 */
 378void rcu_exit_nohz(void)
 379{
 380        unsigned long flags;
 381        struct rcu_dynticks *rdtp;
 382
 383        local_irq_save(flags);
 384        rdtp = &__get_cpu_var(rcu_dynticks);
 385        if (rdtp->dynticks_nesting++) {
 386                local_irq_restore(flags);
 387                return;
 388        }
 389        smp_mb__before_atomic_inc();  /* Force ordering w/previous sojourn. */
 390        atomic_inc(&rdtp->dynticks);
 391        /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
 392        smp_mb__after_atomic_inc();  /* See above. */
 393        WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
 394        local_irq_restore(flags);
 395}
 396
 397/**
 398 * rcu_nmi_enter - inform RCU of entry to NMI context
 399 *
 400 * If the CPU was idle with dynamic ticks active, and there is no
 401 * irq handler running, this updates rdtp->dynticks_nmi to let the
 402 * RCU grace-period handling know that the CPU is active.
 403 */
 404void rcu_nmi_enter(void)
 405{
 406        struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
 407
 408        if (rdtp->dynticks_nmi_nesting == 0 &&
 409            (atomic_read(&rdtp->dynticks) & 0x1))
 410                return;
 411        rdtp->dynticks_nmi_nesting++;
 412        smp_mb__before_atomic_inc();  /* Force delay from prior write. */
 413        atomic_inc(&rdtp->dynticks);
 414        /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
 415        smp_mb__after_atomic_inc();  /* See above. */
 416        WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
 417}
 418
 419/**
 420 * rcu_nmi_exit - inform RCU of exit from NMI context
 421 *
 422 * If the CPU was idle with dynamic ticks active, and there is no
 423 * irq handler running, this updates rdtp->dynticks_nmi to let the
 424 * RCU grace-period handling know that the CPU is no longer active.
 425 */
 426void rcu_nmi_exit(void)
 427{
 428        struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
 429
 430        if (rdtp->dynticks_nmi_nesting == 0 ||
 431            --rdtp->dynticks_nmi_nesting != 0)
 432                return;
 433        /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
 434        smp_mb__before_atomic_inc();  /* See above. */
 435        atomic_inc(&rdtp->dynticks);
 436        smp_mb__after_atomic_inc();  /* Force delay to next write. */
 437        WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
 438}
 439
 440/**
 441 * rcu_irq_enter - inform RCU of entry to hard irq context
 442 *
 443 * If the CPU was idle with dynamic ticks active, this updates the
 444 * rdtp->dynticks to let the RCU handling know that the CPU is active.
 445 */
 446void rcu_irq_enter(void)
 447{
 448        rcu_exit_nohz();
 449}
 450
 451/**
 452 * rcu_irq_exit - inform RCU of exit from hard irq context
 453 *
 454 * If the CPU was idle with dynamic ticks active, update the rdp->dynticks
 455 * to put let the RCU handling be aware that the CPU is going back to idle
 456 * with no ticks.
 457 */
 458void rcu_irq_exit(void)
 459{
 460        rcu_enter_nohz();
 461}
 462
 463#ifdef CONFIG_SMP
 464
 465/*
 466 * Snapshot the specified CPU's dynticks counter so that we can later
 467 * credit them with an implicit quiescent state.  Return 1 if this CPU
 468 * is in dynticks idle mode, which is an extended quiescent state.
 469 */
 470static int dyntick_save_progress_counter(struct rcu_data *rdp)
 471{
 472        rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
 473        return 0;
 474}
 475
 476/*
 477 * Return true if the specified CPU has passed through a quiescent
 478 * state by virtue of being in or having passed through an dynticks
 479 * idle state since the last call to dyntick_save_progress_counter()
 480 * for this same CPU.
 481 */
 482static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 483{
 484        unsigned long curr;
 485        unsigned long snap;
 486
 487        curr = (unsigned long)atomic_add_return(0, &rdp->dynticks->dynticks);
 488        snap = (unsigned long)rdp->dynticks_snap;
 489
 490        /*
 491         * If the CPU passed through or entered a dynticks idle phase with
 492         * no active irq/NMI handlers, then we can safely pretend that the CPU
 493         * already acknowledged the request to pass through a quiescent
 494         * state.  Either way, that CPU cannot possibly be in an RCU
 495         * read-side critical section that started before the beginning
 496         * of the current RCU grace period.
 497         */
 498        if ((curr & 0x1) == 0 || ULONG_CMP_GE(curr, snap + 2)) {
 499                rdp->dynticks_fqs++;
 500                return 1;
 501        }
 502
 503        /* Go check for the CPU being offline. */
 504        return rcu_implicit_offline_qs(rdp);
 505}
 506
 507#endif /* #ifdef CONFIG_SMP */
 508
 509#else /* #ifdef CONFIG_NO_HZ */
 510
 511#ifdef CONFIG_SMP
 512
 513static int dyntick_save_progress_counter(struct rcu_data *rdp)
 514{
 515        return 0;
 516}
 517
 518static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 519{
 520        return rcu_implicit_offline_qs(rdp);
 521}
 522
 523#endif /* #ifdef CONFIG_SMP */
 524
 525#endif /* #else #ifdef CONFIG_NO_HZ */
 526
 527int rcu_cpu_stall_suppress __read_mostly;
 528
 529static void record_gp_stall_check_time(struct rcu_state *rsp)
 530{
 531        rsp->gp_start = jiffies;
 532        rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
 533}
 534
 535static void print_other_cpu_stall(struct rcu_state *rsp)
 536{
 537        int cpu;
 538        long delta;
 539        unsigned long flags;
 540        struct rcu_node *rnp = rcu_get_root(rsp);
 541
 542        /* Only let one CPU complain about others per time interval. */
 543
 544        raw_spin_lock_irqsave(&rnp->lock, flags);
 545        delta = jiffies - rsp->jiffies_stall;
 546        if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
 547                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 548                return;
 549        }
 550        rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
 551
 552        /*
 553         * Now rat on any tasks that got kicked up to the root rcu_node
 554         * due to CPU offlining.
 555         */
 556        rcu_print_task_stall(rnp);
 557        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 558
 559        /*
 560         * OK, time to rat on our buddy...
 561         * See Documentation/RCU/stallwarn.txt for info on how to debug
 562         * RCU CPU stall warnings.
 563         */
 564        printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks: {",
 565               rsp->name);
 566        rcu_for_each_leaf_node(rsp, rnp) {
 567                raw_spin_lock_irqsave(&rnp->lock, flags);
 568                rcu_print_task_stall(rnp);
 569                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 570                if (rnp->qsmask == 0)
 571                        continue;
 572                for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
 573                        if (rnp->qsmask & (1UL << cpu))
 574                                printk(" %d", rnp->grplo + cpu);
 575        }
 576        printk("} (detected by %d, t=%ld jiffies)\n",
 577               smp_processor_id(), (long)(jiffies - rsp->gp_start));
 578        trigger_all_cpu_backtrace();
 579
 580        /* If so configured, complain about tasks blocking the grace period. */
 581
 582        rcu_print_detail_task_stall(rsp);
 583
 584        force_quiescent_state(rsp, 0);  /* Kick them all. */
 585}
 586
 587static void print_cpu_stall(struct rcu_state *rsp)
 588{
 589        unsigned long flags;
 590        struct rcu_node *rnp = rcu_get_root(rsp);
 591
 592        /*
 593         * OK, time to rat on ourselves...
 594         * See Documentation/RCU/stallwarn.txt for info on how to debug
 595         * RCU CPU stall warnings.
 596         */
 597        printk(KERN_ERR "INFO: %s detected stall on CPU %d (t=%lu jiffies)\n",
 598               rsp->name, smp_processor_id(), jiffies - rsp->gp_start);
 599        trigger_all_cpu_backtrace();
 600
 601        raw_spin_lock_irqsave(&rnp->lock, flags);
 602        if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
 603                rsp->jiffies_stall =
 604                        jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
 605        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 606
 607        set_need_resched();  /* kick ourselves to get things going. */
 608}
 609
 610static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
 611{
 612        unsigned long j;
 613        unsigned long js;
 614        struct rcu_node *rnp;
 615
 616        if (rcu_cpu_stall_suppress)
 617                return;
 618        j = ACCESS_ONCE(jiffies);
 619        js = ACCESS_ONCE(rsp->jiffies_stall);
 620        rnp = rdp->mynode;
 621        if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) {
 622
 623                /* We haven't checked in, so go dump stack. */
 624                print_cpu_stall(rsp);
 625
 626        } else if (rcu_gp_in_progress(rsp) &&
 627                   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
 628
 629                /* They had a few time units to dump stack, so complain. */
 630                print_other_cpu_stall(rsp);
 631        }
 632}
 633
 634static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
 635{
 636        rcu_cpu_stall_suppress = 1;
 637        return NOTIFY_DONE;
 638}
 639
 640/**
 641 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
 642 *
 643 * Set the stall-warning timeout way off into the future, thus preventing
 644 * any RCU CPU stall-warning messages from appearing in the current set of
 645 * RCU grace periods.
 646 *
 647 * The caller must disable hard irqs.
 648 */
 649void rcu_cpu_stall_reset(void)
 650{
 651        rcu_sched_state.jiffies_stall = jiffies + ULONG_MAX / 2;
 652        rcu_bh_state.jiffies_stall = jiffies + ULONG_MAX / 2;
 653        rcu_preempt_stall_reset();
 654}
 655
 656static struct notifier_block rcu_panic_block = {
 657        .notifier_call = rcu_panic,
 658};
 659
 660static void __init check_cpu_stall_init(void)
 661{
 662        atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
 663}
 664
 665/*
 666 * Update CPU-local rcu_data state to record the newly noticed grace period.
 667 * This is used both when we started the grace period and when we notice
 668 * that someone else started the grace period.  The caller must hold the
 669 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
 670 *  and must have irqs disabled.
 671 */
 672static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
 673{
 674        if (rdp->gpnum != rnp->gpnum) {
 675                /*
 676                 * If the current grace period is waiting for this CPU,
 677                 * set up to detect a quiescent state, otherwise don't
 678                 * go looking for one.
 679                 */
 680                rdp->gpnum = rnp->gpnum;
 681                if (rnp->qsmask & rdp->grpmask) {
 682                        rdp->qs_pending = 1;
 683                        rdp->passed_quiesc = 0;
 684                } else
 685                        rdp->qs_pending = 0;
 686        }
 687}
 688
 689static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
 690{
 691        unsigned long flags;
 692        struct rcu_node *rnp;
 693
 694        local_irq_save(flags);
 695        rnp = rdp->mynode;
 696        if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) || /* outside lock. */
 697            !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
 698                local_irq_restore(flags);
 699                return;
 700        }
 701        __note_new_gpnum(rsp, rnp, rdp);
 702        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 703}
 704
 705/*
 706 * Did someone else start a new RCU grace period start since we last
 707 * checked?  Update local state appropriately if so.  Must be called
 708 * on the CPU corresponding to rdp.
 709 */
 710static int
 711check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
 712{
 713        unsigned long flags;
 714        int ret = 0;
 715
 716        local_irq_save(flags);
 717        if (rdp->gpnum != rsp->gpnum) {
 718                note_new_gpnum(rsp, rdp);
 719                ret = 1;
 720        }
 721        local_irq_restore(flags);
 722        return ret;
 723}
 724
 725/*
 726 * Advance this CPU's callbacks, but only if the current grace period
 727 * has ended.  This may be called only from the CPU to whom the rdp
 728 * belongs.  In addition, the corresponding leaf rcu_node structure's
 729 * ->lock must be held by the caller, with irqs disabled.
 730 */
 731static void
 732__rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
 733{
 734        /* Did another grace period end? */
 735        if (rdp->completed != rnp->completed) {
 736
 737                /* Advance callbacks.  No harm if list empty. */
 738                rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
 739                rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
 740                rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
 741
 742                /* Remember that we saw this grace-period completion. */
 743                rdp->completed = rnp->completed;
 744
 745                /*
 746                 * If we were in an extended quiescent state, we may have
 747                 * missed some grace periods that others CPUs handled on
 748                 * our behalf. Catch up with this state to avoid noting
 749                 * spurious new grace periods.  If another grace period
 750                 * has started, then rnp->gpnum will have advanced, so
 751                 * we will detect this later on.
 752                 */
 753                if (ULONG_CMP_LT(rdp->gpnum, rdp->completed))
 754                        rdp->gpnum = rdp->completed;
 755
 756                /*
 757                 * If RCU does not need a quiescent state from this CPU,
 758                 * then make sure that this CPU doesn't go looking for one.
 759                 */
 760                if ((rnp->qsmask & rdp->grpmask) == 0)
 761                        rdp->qs_pending = 0;
 762        }
 763}
 764
 765/*
 766 * Advance this CPU's callbacks, but only if the current grace period
 767 * has ended.  This may be called only from the CPU to whom the rdp
 768 * belongs.
 769 */
 770static void
 771rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
 772{
 773        unsigned long flags;
 774        struct rcu_node *rnp;
 775
 776        local_irq_save(flags);
 777        rnp = rdp->mynode;
 778        if (rdp->completed == ACCESS_ONCE(rnp->completed) || /* outside lock. */
 779            !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
 780                local_irq_restore(flags);
 781                return;
 782        }
 783        __rcu_process_gp_end(rsp, rnp, rdp);
 784        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 785}
 786
 787/*
 788 * Do per-CPU grace-period initialization for running CPU.  The caller
 789 * must hold the lock of the leaf rcu_node structure corresponding to
 790 * this CPU.
 791 */
 792static void
 793rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
 794{
 795        /* Prior grace period ended, so advance callbacks for current CPU. */
 796        __rcu_process_gp_end(rsp, rnp, rdp);
 797
 798        /*
 799         * Because this CPU just now started the new grace period, we know
 800         * that all of its callbacks will be covered by this upcoming grace
 801         * period, even the ones that were registered arbitrarily recently.
 802         * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
 803         *
 804         * Other CPUs cannot be sure exactly when the grace period started.
 805         * Therefore, their recently registered callbacks must pass through
 806         * an additional RCU_NEXT_READY stage, so that they will be handled
 807         * by the next RCU grace period.
 808         */
 809        rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
 810        rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
 811
 812        /* Set state so that this CPU will detect the next quiescent state. */
 813        __note_new_gpnum(rsp, rnp, rdp);
 814}
 815
 816/*
 817 * Start a new RCU grace period if warranted, re-initializing the hierarchy
 818 * in preparation for detecting the next grace period.  The caller must hold
 819 * the root node's ->lock, which is released before return.  Hard irqs must
 820 * be disabled.
 821 */
 822static void
 823rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
 824        __releases(rcu_get_root(rsp)->lock)
 825{
 826        struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
 827        struct rcu_node *rnp = rcu_get_root(rsp);
 828
 829        if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) {
 830                if (cpu_needs_another_gp(rsp, rdp))
 831                        rsp->fqs_need_gp = 1;
 832                if (rnp->completed == rsp->completed) {
 833                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 834                        return;
 835                }
 836                raw_spin_unlock(&rnp->lock);     /* irqs remain disabled. */
 837
 838                /*
 839                 * Propagate new ->completed value to rcu_node structures
 840                 * so that other CPUs don't have to wait until the start
 841                 * of the next grace period to process their callbacks.
 842                 */
 843                rcu_for_each_node_breadth_first(rsp, rnp) {
 844                        raw_spin_lock(&rnp->lock); /* irqs already disabled. */
 845                        rnp->completed = rsp->completed;
 846                        raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
 847                }
 848                local_irq_restore(flags);
 849                return;
 850        }
 851
 852        /* Advance to a new grace period and initialize state. */
 853        rsp->gpnum++;
 854        WARN_ON_ONCE(rsp->signaled == RCU_GP_INIT);
 855        rsp->signaled = RCU_GP_INIT; /* Hold off force_quiescent_state. */
 856        rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
 857        record_gp_stall_check_time(rsp);
 858
 859        /* Special-case the common single-level case. */
 860        if (NUM_RCU_NODES == 1) {
 861                rcu_preempt_check_blocked_tasks(rnp);
 862                rnp->qsmask = rnp->qsmaskinit;
 863                rnp->gpnum = rsp->gpnum;
 864                rnp->completed = rsp->completed;
 865                rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
 866                rcu_start_gp_per_cpu(rsp, rnp, rdp);
 867                rcu_preempt_boost_start_gp(rnp);
 868                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 869                return;
 870        }
 871
 872        raw_spin_unlock(&rnp->lock);  /* leave irqs disabled. */
 873
 874
 875        /* Exclude any concurrent CPU-hotplug operations. */
 876        raw_spin_lock(&rsp->onofflock);  /* irqs already disabled. */
 877
 878        /*
 879         * Set the quiescent-state-needed bits in all the rcu_node
 880         * structures for all currently online CPUs in breadth-first
 881         * order, starting from the root rcu_node structure.  This
 882         * operation relies on the layout of the hierarchy within the
 883         * rsp->node[] array.  Note that other CPUs will access only
 884         * the leaves of the hierarchy, which still indicate that no
 885         * grace period is in progress, at least until the corresponding
 886         * leaf node has been initialized.  In addition, we have excluded
 887         * CPU-hotplug operations.
 888         *
 889         * Note that the grace period cannot complete until we finish
 890         * the initialization process, as there will be at least one
 891         * qsmask bit set in the root node until that time, namely the
 892         * one corresponding to this CPU, due to the fact that we have
 893         * irqs disabled.
 894         */
 895        rcu_for_each_node_breadth_first(rsp, rnp) {
 896                raw_spin_lock(&rnp->lock);      /* irqs already disabled. */
 897                rcu_preempt_check_blocked_tasks(rnp);
 898                rnp->qsmask = rnp->qsmaskinit;
 899                rnp->gpnum = rsp->gpnum;
 900                rnp->completed = rsp->completed;
 901                if (rnp == rdp->mynode)
 902                        rcu_start_gp_per_cpu(rsp, rnp, rdp);
 903                rcu_preempt_boost_start_gp(rnp);
 904                raw_spin_unlock(&rnp->lock);    /* irqs remain disabled. */
 905        }
 906
 907        rnp = rcu_get_root(rsp);
 908        raw_spin_lock(&rnp->lock);              /* irqs already disabled. */
 909        rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
 910        raw_spin_unlock(&rnp->lock);            /* irqs remain disabled. */
 911        raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
 912}
 913
 914/*
 915 * Report a full set of quiescent states to the specified rcu_state
 916 * data structure.  This involves cleaning up after the prior grace
 917 * period and letting rcu_start_gp() start up the next grace period
 918 * if one is needed.  Note that the caller must hold rnp->lock, as
 919 * required by rcu_start_gp(), which will release it.
 920 */
 921static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
 922        __releases(rcu_get_root(rsp)->lock)
 923{
 924        unsigned long gp_duration;
 925
 926        WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
 927
 928        /*
 929         * Ensure that all grace-period and pre-grace-period activity
 930         * is seen before the assignment to rsp->completed.
 931         */
 932        smp_mb(); /* See above block comment. */
 933        gp_duration = jiffies - rsp->gp_start;
 934        if (gp_duration > rsp->gp_max)
 935                rsp->gp_max = gp_duration;
 936        rsp->completed = rsp->gpnum;
 937        rsp->signaled = RCU_GP_IDLE;
 938        rcu_start_gp(rsp, flags);  /* releases root node's rnp->lock. */
 939}
 940
 941/*
 942 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
 943 * Allows quiescent states for a group of CPUs to be reported at one go
 944 * to the specified rcu_node structure, though all the CPUs in the group
 945 * must be represented by the same rcu_node structure (which need not be
 946 * a leaf rcu_node structure, though it often will be).  That structure's
 947 * lock must be held upon entry, and it is released before return.
 948 */
 949static void
 950rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
 951                  struct rcu_node *rnp, unsigned long flags)
 952        __releases(rnp->lock)
 953{
 954        struct rcu_node *rnp_c;
 955
 956        /* Walk up the rcu_node hierarchy. */
 957        for (;;) {
 958                if (!(rnp->qsmask & mask)) {
 959
 960                        /* Our bit has already been cleared, so done. */
 961                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 962                        return;
 963                }
 964                rnp->qsmask &= ~mask;
 965                if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
 966
 967                        /* Other bits still set at this level, so done. */
 968                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 969                        return;
 970                }
 971                mask = rnp->grpmask;
 972                if (rnp->parent == NULL) {
 973
 974                        /* No more levels.  Exit loop holding root lock. */
 975
 976                        break;
 977                }
 978                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 979                rnp_c = rnp;
 980                rnp = rnp->parent;
 981                raw_spin_lock_irqsave(&rnp->lock, flags);
 982                WARN_ON_ONCE(rnp_c->qsmask);
 983        }
 984
 985        /*
 986         * Get here if we are the last CPU to pass through a quiescent
 987         * state for this grace period.  Invoke rcu_report_qs_rsp()
 988         * to clean up and start the next grace period if one is needed.
 989         */
 990        rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
 991}
 992
 993/*
 994 * Record a quiescent state for the specified CPU to that CPU's rcu_data
 995 * structure.  This must be either called from the specified CPU, or
 996 * called when the specified CPU is known to be offline (and when it is
 997 * also known that no other CPU is concurrently trying to help the offline
 998 * CPU).  The lastcomp argument is used to make sure we are still in the
 999 * grace period of interest.  We don't want to end the current grace period
1000 * based on quiescent states detected in an earlier grace period!
1001 */
1002static void
1003rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
1004{
1005        unsigned long flags;
1006        unsigned long mask;
1007        struct rcu_node *rnp;
1008
1009        rnp = rdp->mynode;
1010        raw_spin_lock_irqsave(&rnp->lock, flags);
1011        if (lastcomp != rnp->completed) {
1012
1013                /*
1014                 * Someone beat us to it for this grace period, so leave.
1015                 * The race with GP start is resolved by the fact that we
1016                 * hold the leaf rcu_node lock, so that the per-CPU bits
1017                 * cannot yet be initialized -- so we would simply find our
1018                 * CPU's bit already cleared in rcu_report_qs_rnp() if this
1019                 * race occurred.
1020                 */
1021                rdp->passed_quiesc = 0; /* try again later! */
1022                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1023                return;
1024        }
1025        mask = rdp->grpmask;
1026        if ((rnp->qsmask & mask) == 0) {
1027                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1028        } else {
1029                rdp->qs_pending = 0;
1030
1031                /*
1032                 * This GP can't end until cpu checks in, so all of our
1033                 * callbacks can be processed during the next GP.
1034                 */
1035                rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
1036
1037                rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
1038        }
1039}
1040
1041/*
1042 * Check to see if there is a new grace period of which this CPU
1043 * is not yet aware, and if so, set up local rcu_data state for it.
1044 * Otherwise, see if this CPU has just passed through its first
1045 * quiescent state for this grace period, and record that fact if so.
1046 */
1047static void
1048rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
1049{
1050        /* If there is now a new grace period, record and return. */
1051        if (check_for_new_grace_period(rsp, rdp))
1052                return;
1053
1054        /*
1055         * Does this CPU still need to do its part for current grace period?
1056         * If no, return and let the other CPUs do their part as well.
1057         */
1058        if (!rdp->qs_pending)
1059                return;
1060
1061        /*
1062         * Was there a quiescent state since the beginning of the grace
1063         * period? If no, then exit and wait for the next call.
1064         */
1065        if (!rdp->passed_quiesc)
1066                return;
1067
1068        /*
1069         * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1070         * judge of that).
1071         */
1072        rcu_report_qs_rdp(rdp->cpu, rsp, rdp, rdp->passed_quiesc_completed);
1073}
1074
1075#ifdef CONFIG_HOTPLUG_CPU
1076
1077/*
1078 * Move a dying CPU's RCU callbacks to online CPU's callback list.
1079 * Synchronization is not required because this function executes
1080 * in stop_machine() context.
1081 */
1082static void rcu_send_cbs_to_online(struct rcu_state *rsp)
1083{
1084        int i;
1085        /* current DYING CPU is cleared in the cpu_online_mask */
1086        int receive_cpu = cpumask_any(cpu_online_mask);
1087        struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1088        struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu);
1089
1090        if (rdp->nxtlist == NULL)
1091                return;  /* irqs disabled, so comparison is stable. */
1092
1093        *receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
1094        receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
1095        receive_rdp->qlen += rdp->qlen;
1096        receive_rdp->n_cbs_adopted += rdp->qlen;
1097        rdp->n_cbs_orphaned += rdp->qlen;
1098
1099        rdp->nxtlist = NULL;
1100        for (i = 0; i < RCU_NEXT_SIZE; i++)
1101                rdp->nxttail[i] = &rdp->nxtlist;
1102        rdp->qlen = 0;
1103}
1104
1105/*
1106 * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
1107 * and move all callbacks from the outgoing CPU to the current one.
1108 * There can only be one CPU hotplug operation at a time, so no other
1109 * CPU can be attempting to update rcu_cpu_kthread_task.
1110 */
1111static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
1112{
1113        unsigned long flags;
1114        unsigned long mask;
1115        int need_report = 0;
1116        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1117        struct rcu_node *rnp;
1118
1119        rcu_stop_cpu_kthread(cpu);
1120
1121        /* Exclude any attempts to start a new grace period. */
1122        raw_spin_lock_irqsave(&rsp->onofflock, flags);
1123
1124        /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
1125        rnp = rdp->mynode;      /* this is the outgoing CPU's rnp. */
1126        mask = rdp->grpmask;    /* rnp->grplo is constant. */
1127        do {
1128                raw_spin_lock(&rnp->lock);      /* irqs already disabled. */
1129                rnp->qsmaskinit &= ~mask;
1130                if (rnp->qsmaskinit != 0) {
1131                        if (rnp != rdp->mynode)
1132                                raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1133                        break;
1134                }
1135                if (rnp == rdp->mynode)
1136                        need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
1137                else
1138                        raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1139                mask = rnp->grpmask;
1140                rnp = rnp->parent;
1141        } while (rnp != NULL);
1142
1143        /*
1144         * We still hold the leaf rcu_node structure lock here, and
1145         * irqs are still disabled.  The reason for this subterfuge is
1146         * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
1147         * held leads to deadlock.
1148         */
1149        raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
1150        rnp = rdp->mynode;
1151        if (need_report & RCU_OFL_TASKS_NORM_GP)
1152                rcu_report_unblock_qs_rnp(rnp, flags);
1153        else
1154                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1155        if (need_report & RCU_OFL_TASKS_EXP_GP)
1156                rcu_report_exp_rnp(rsp, rnp);
1157        rcu_node_kthread_setaffinity(rnp, -1);
1158}
1159
1160/*
1161 * Remove the specified CPU from the RCU hierarchy and move any pending
1162 * callbacks that it might have to the current CPU.  This code assumes
1163 * that at least one CPU in the system will remain running at all times.
1164 * Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
1165 */
1166static void rcu_offline_cpu(int cpu)
1167{
1168        __rcu_offline_cpu(cpu, &rcu_sched_state);
1169        __rcu_offline_cpu(cpu, &rcu_bh_state);
1170        rcu_preempt_offline_cpu(cpu);
1171}
1172
1173#else /* #ifdef CONFIG_HOTPLUG_CPU */
1174
1175static void rcu_send_cbs_to_online(struct rcu_state *rsp)
1176{
1177}
1178
1179static void rcu_offline_cpu(int cpu)
1180{
1181}
1182
1183#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1184
1185/*
1186 * Invoke any RCU callbacks that have made it to the end of their grace
1187 * period.  Thottle as specified by rdp->blimit.
1188 */
1189static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
1190{
1191        unsigned long flags;
1192        struct rcu_head *next, *list, **tail;
1193        int count;
1194
1195        /* If no callbacks are ready, just return.*/
1196        if (!cpu_has_callbacks_ready_to_invoke(rdp))
1197                return;
1198
1199        /*
1200         * Extract the list of ready callbacks, disabling to prevent
1201         * races with call_rcu() from interrupt handlers.
1202         */
1203        local_irq_save(flags);
1204        list = rdp->nxtlist;
1205        rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
1206        *rdp->nxttail[RCU_DONE_TAIL] = NULL;
1207        tail = rdp->nxttail[RCU_DONE_TAIL];
1208        for (count = RCU_NEXT_SIZE - 1; count >= 0; count--)
1209                if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL])
1210                        rdp->nxttail[count] = &rdp->nxtlist;
1211        local_irq_restore(flags);
1212
1213        /* Invoke callbacks. */
1214        count = 0;
1215        while (list) {
1216                next = list->next;
1217                prefetch(next);
1218                debug_rcu_head_unqueue(list);
1219                __rcu_reclaim(list);
1220                list = next;
1221                if (++count >= rdp->blimit)
1222                        break;
1223        }
1224
1225        local_irq_save(flags);
1226
1227        /* Update count, and requeue any remaining callbacks. */
1228        rdp->qlen -= count;
1229        rdp->n_cbs_invoked += count;
1230        if (list != NULL) {
1231                *tail = rdp->nxtlist;
1232                rdp->nxtlist = list;
1233                for (count = 0; count < RCU_NEXT_SIZE; count++)
1234                        if (&rdp->nxtlist == rdp->nxttail[count])
1235                                rdp->nxttail[count] = tail;
1236                        else
1237                                break;
1238        }
1239
1240        /* Reinstate batch limit if we have worked down the excess. */
1241        if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
1242                rdp->blimit = blimit;
1243
1244        /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1245        if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
1246                rdp->qlen_last_fqs_check = 0;
1247                rdp->n_force_qs_snap = rsp->n_force_qs;
1248        } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
1249                rdp->qlen_last_fqs_check = rdp->qlen;
1250
1251        local_irq_restore(flags);
1252
1253        /* Re-raise the RCU softirq if there are callbacks remaining. */
1254        if (cpu_has_callbacks_ready_to_invoke(rdp))
1255                invoke_rcu_core();
1256}
1257
1258/*
1259 * Check to see if this CPU is in a non-context-switch quiescent state
1260 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1261 * Also schedule the RCU softirq handler.
1262 *
1263 * This function must be called with hardirqs disabled.  It is normally
1264 * invoked from the scheduling-clock interrupt.  If rcu_pending returns
1265 * false, there is no point in invoking rcu_check_callbacks().
1266 */
1267void rcu_check_callbacks(int cpu, int user)
1268{
1269        if (user ||
1270            (idle_cpu(cpu) && rcu_scheduler_active &&
1271             !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
1272
1273                /*
1274                 * Get here if this CPU took its interrupt from user
1275                 * mode or from the idle loop, and if this is not a
1276                 * nested interrupt.  In this case, the CPU is in
1277                 * a quiescent state, so note it.
1278                 *
1279                 * No memory barrier is required here because both
1280                 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1281                 * variables that other CPUs neither access nor modify,
1282                 * at least not while the corresponding CPU is online.
1283                 */
1284
1285                rcu_sched_qs(cpu);
1286                rcu_bh_qs(cpu);
1287
1288        } else if (!in_softirq()) {
1289
1290                /*
1291                 * Get here if this CPU did not take its interrupt from
1292                 * softirq, in other words, if it is not interrupting
1293                 * a rcu_bh read-side critical section.  This is an _bh
1294                 * critical section, so note it.
1295                 */
1296
1297                rcu_bh_qs(cpu);
1298        }
1299        rcu_preempt_check_callbacks(cpu);
1300        if (rcu_pending(cpu))
1301                invoke_rcu_core();
1302}
1303
1304#ifdef CONFIG_SMP
1305
1306/*
1307 * Scan the leaf rcu_node structures, processing dyntick state for any that
1308 * have not yet encountered a quiescent state, using the function specified.
1309 * Also initiate boosting for any threads blocked on the root rcu_node.
1310 *
1311 * The caller must have suppressed start of new grace periods.
1312 */
1313static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
1314{
1315        unsigned long bit;
1316        int cpu;
1317        unsigned long flags;
1318        unsigned long mask;
1319        struct rcu_node *rnp;
1320
1321        rcu_for_each_leaf_node(rsp, rnp) {
1322                mask = 0;
1323                raw_spin_lock_irqsave(&rnp->lock, flags);
1324                if (!rcu_gp_in_progress(rsp)) {
1325                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
1326                        return;
1327                }
1328                if (rnp->qsmask == 0) {
1329                        rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
1330                        continue;
1331                }
1332                cpu = rnp->grplo;
1333                bit = 1;
1334                for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
1335                        if ((rnp->qsmask & bit) != 0 &&
1336                            f(per_cpu_ptr(rsp->rda, cpu)))
1337                                mask |= bit;
1338                }
1339                if (mask != 0) {
1340
1341                        /* rcu_report_qs_rnp() releases rnp->lock. */
1342                        rcu_report_qs_rnp(mask, rsp, rnp, flags);
1343                        continue;
1344                }
1345                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1346        }
1347        rnp = rcu_get_root(rsp);
1348        if (rnp->qsmask == 0) {
1349                raw_spin_lock_irqsave(&rnp->lock, flags);
1350                rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
1351        }
1352}
1353
1354/*
1355 * Force quiescent states on reluctant CPUs, and also detect which
1356 * CPUs are in dyntick-idle mode.
1357 */
1358static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1359{
1360        unsigned long flags;
1361        struct rcu_node *rnp = rcu_get_root(rsp);
1362
1363        if (!rcu_gp_in_progress(rsp))
1364                return;  /* No grace period in progress, nothing to force. */
1365        if (!raw_spin_trylock_irqsave(&rsp->fqslock, flags)) {
1366                rsp->n_force_qs_lh++; /* Inexact, can lose counts.  Tough! */
1367                return; /* Someone else is already on the job. */
1368        }
1369        if (relaxed && ULONG_CMP_GE(rsp->jiffies_force_qs, jiffies))
1370                goto unlock_fqs_ret; /* no emergency and done recently. */
1371        rsp->n_force_qs++;
1372        raw_spin_lock(&rnp->lock);  /* irqs already disabled */
1373        rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
1374        if(!rcu_gp_in_progress(rsp)) {
1375                rsp->n_force_qs_ngp++;
1376                raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
1377                goto unlock_fqs_ret;  /* no GP in progress, time updated. */
1378        }
1379        rsp->fqs_active = 1;
1380        switch (rsp->signaled) {
1381        case RCU_GP_IDLE:
1382        case RCU_GP_INIT:
1383
1384                break; /* grace period idle or initializing, ignore. */
1385
1386        case RCU_SAVE_DYNTICK:
1387                if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
1388                        break; /* So gcc recognizes the dead code. */
1389
1390                raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
1391
1392                /* Record dyntick-idle state. */
1393                force_qs_rnp(rsp, dyntick_save_progress_counter);
1394                raw_spin_lock(&rnp->lock);  /* irqs already disabled */
1395                if (rcu_gp_in_progress(rsp))
1396                        rsp->signaled = RCU_FORCE_QS;
1397                break;
1398
1399        case RCU_FORCE_QS:
1400
1401                /* Check dyntick-idle state, send IPI to laggarts. */
1402                raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
1403                force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
1404
1405                /* Leave state in case more forcing is required. */
1406
1407                raw_spin_lock(&rnp->lock);  /* irqs already disabled */
1408                break;
1409        }
1410        rsp->fqs_active = 0;
1411        if (rsp->fqs_need_gp) {
1412                raw_spin_unlock(&rsp->fqslock); /* irqs remain disabled */
1413                rsp->fqs_need_gp = 0;
1414                rcu_start_gp(rsp, flags); /* releases rnp->lock */
1415                return;
1416        }
1417        raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
1418unlock_fqs_ret:
1419        raw_spin_unlock_irqrestore(&rsp->fqslock, flags);
1420}
1421
1422#else /* #ifdef CONFIG_SMP */
1423
1424static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1425{
1426        set_need_resched();
1427}
1428
1429#endif /* #else #ifdef CONFIG_SMP */
1430
1431/*
1432 * This does the RCU processing work from softirq context for the
1433 * specified rcu_state and rcu_data structures.  This may be called
1434 * only from the CPU to whom the rdp belongs.
1435 */
1436static void
1437__rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
1438{
1439        unsigned long flags;
1440
1441        WARN_ON_ONCE(rdp->beenonline == 0);
1442
1443        /*
1444         * If an RCU GP has gone long enough, go check for dyntick
1445         * idle CPUs and, if needed, send resched IPIs.
1446         */
1447        if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
1448                force_quiescent_state(rsp, 1);
1449
1450        /*
1451         * Advance callbacks in response to end of earlier grace
1452         * period that some other CPU ended.
1453         */
1454        rcu_process_gp_end(rsp, rdp);
1455
1456        /* Update RCU state based on any recent quiescent states. */
1457        rcu_check_quiescent_state(rsp, rdp);
1458
1459        /* Does this CPU require a not-yet-started grace period? */
1460        if (cpu_needs_another_gp(rsp, rdp)) {
1461                raw_spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
1462                rcu_start_gp(rsp, flags);  /* releases above lock */
1463        }
1464
1465        /* If there are callbacks ready, invoke them. */
1466        if (cpu_has_callbacks_ready_to_invoke(rdp))
1467                invoke_rcu_callbacks(rsp, rdp);
1468}
1469
1470/*
1471 * Do softirq processing for the current CPU.
1472 */
1473static void rcu_process_callbacks(struct softirq_action *unused)
1474{
1475        __rcu_process_callbacks(&rcu_sched_state,
1476                                &__get_cpu_var(rcu_sched_data));
1477        __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1478        rcu_preempt_process_callbacks();
1479
1480        /* If we are last CPU on way to dyntick-idle mode, accelerate it. */
1481        rcu_needs_cpu_flush();
1482}
1483
1484/*
1485 * Wake up the current CPU's kthread.  This replaces raise_softirq()
1486 * in earlier versions of RCU.  Note that because we are running on
1487 * the current CPU with interrupts disabled, the rcu_cpu_kthread_task
1488 * cannot disappear out from under us.
1489 */
1490static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
1491{
1492        if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
1493                return;
1494        if (likely(!rsp->boost)) {
1495                rcu_do_batch(rsp, rdp);
1496                return;
1497        }
1498        invoke_rcu_callbacks_kthread();
1499}
1500
1501static void invoke_rcu_core(void)
1502{
1503        raise_softirq(RCU_SOFTIRQ);
1504}
1505
1506static void
1507__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
1508           struct rcu_state *rsp)
1509{
1510        unsigned long flags;
1511        struct rcu_data *rdp;
1512
1513        debug_rcu_head_queue(head);
1514        head->func = func;
1515        head->next = NULL;
1516
1517        smp_mb(); /* Ensure RCU update seen before callback registry. */
1518
1519        /*
1520         * Opportunistically note grace-period endings and beginnings.
1521         * Note that we might see a beginning right after we see an
1522         * end, but never vice versa, since this CPU has to pass through
1523         * a quiescent state betweentimes.
1524         */
1525        local_irq_save(flags);
1526        rdp = this_cpu_ptr(rsp->rda);
1527
1528        /* Add the callback to our list. */
1529        *rdp->nxttail[RCU_NEXT_TAIL] = head;
1530        rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
1531        rdp->qlen++;
1532
1533        /* If interrupts were disabled, don't dive into RCU core. */
1534        if (irqs_disabled_flags(flags)) {
1535                local_irq_restore(flags);
1536                return;
1537        }
1538
1539        /*
1540         * Force the grace period if too many callbacks or too long waiting.
1541         * Enforce hysteresis, and don't invoke force_quiescent_state()
1542         * if some other CPU has recently done so.  Also, don't bother
1543         * invoking force_quiescent_state() if the newly enqueued callback
1544         * is the only one waiting for a grace period to complete.
1545         */
1546        if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
1547
1548                /* Are we ignoring a completed grace period? */
1549                rcu_process_gp_end(rsp, rdp);
1550                check_for_new_grace_period(rsp, rdp);
1551
1552                /* Start a new grace period if one not already started. */
1553                if (!rcu_gp_in_progress(rsp)) {
1554                        unsigned long nestflag;
1555                        struct rcu_node *rnp_root = rcu_get_root(rsp);
1556
1557                        raw_spin_lock_irqsave(&rnp_root->lock, nestflag);
1558                        rcu_start_gp(rsp, nestflag);  /* rlses rnp_root->lock */
1559                } else {
1560                        /* Give the grace period a kick. */
1561                        rdp->blimit = LONG_MAX;
1562                        if (rsp->n_force_qs == rdp->n_force_qs_snap &&
1563                            *rdp->nxttail[RCU_DONE_TAIL] != head)
1564                                force_quiescent_state(rsp, 0);
1565                        rdp->n_force_qs_snap = rsp->n_force_qs;
1566                        rdp->qlen_last_fqs_check = rdp->qlen;
1567                }
1568        } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
1569                force_quiescent_state(rsp, 1);
1570        local_irq_restore(flags);
1571}
1572
1573/*
1574 * Queue an RCU-sched callback for invocation after a grace period.
1575 */
1576void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1577{
1578        __call_rcu(head, func, &rcu_sched_state);
1579}
1580EXPORT_SYMBOL_GPL(call_rcu_sched);
1581
1582/*
1583 * Queue an RCU for invocation after a quicker grace period.
1584 */
1585void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1586{
1587        __call_rcu(head, func, &rcu_bh_state);
1588}
1589EXPORT_SYMBOL_GPL(call_rcu_bh);
1590
1591/**
1592 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
1593 *
1594 * Control will return to the caller some time after a full rcu-sched
1595 * grace period has elapsed, in other words after all currently executing
1596 * rcu-sched read-side critical sections have completed.   These read-side
1597 * critical sections are delimited by rcu_read_lock_sched() and
1598 * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
1599 * local_irq_disable(), and so on may be used in place of
1600 * rcu_read_lock_sched().
1601 *
1602 * This means that all preempt_disable code sequences, including NMI and
1603 * hardware-interrupt handlers, in progress on entry will have completed
1604 * before this primitive returns.  However, this does not guarantee that
1605 * softirq handlers will have completed, since in some kernels, these
1606 * handlers can run in process context, and can block.
1607 *
1608 * This primitive provides the guarantees made by the (now removed)
1609 * synchronize_kernel() API.  In contrast, synchronize_rcu() only
1610 * guarantees that rcu_read_lock() sections will have completed.
1611 * In "classic RCU", these two guarantees happen to be one and
1612 * the same, but can differ in realtime RCU implementations.
1613 */
1614void synchronize_sched(void)
1615{
1616        struct rcu_synchronize rcu;
1617
1618        if (rcu_blocking_is_gp())
1619                return;
1620
1621        init_rcu_head_on_stack(&rcu.head);
1622        init_completion(&rcu.completion);
1623        /* Will wake me after RCU finished. */
1624        call_rcu_sched(&rcu.head, wakeme_after_rcu);
1625        /* Wait for it. */
1626        wait_for_completion(&rcu.completion);
1627        destroy_rcu_head_on_stack(&rcu.head);
1628}
1629EXPORT_SYMBOL_GPL(synchronize_sched);
1630
1631/**
1632 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
1633 *
1634 * Control will return to the caller some time after a full rcu_bh grace
1635 * period has elapsed, in other words after all currently executing rcu_bh
1636 * read-side critical sections have completed.  RCU read-side critical
1637 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
1638 * and may be nested.
1639 */
1640void synchronize_rcu_bh(void)
1641{
1642        struct rcu_synchronize rcu;
1643
1644        if (rcu_blocking_is_gp())
1645                return;
1646
1647        init_rcu_head_on_stack(&rcu.head);
1648        init_completion(&rcu.completion);
1649        /* Will wake me after RCU finished. */
1650        call_rcu_bh(&rcu.head, wakeme_after_rcu);
1651        /* Wait for it. */
1652        wait_for_completion(&rcu.completion);
1653        destroy_rcu_head_on_stack(&rcu.head);
1654}
1655EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
1656
1657/*
1658 * Check to see if there is any immediate RCU-related work to be done
1659 * by the current CPU, for the specified type of RCU, returning 1 if so.
1660 * The checks are in order of increasing expense: checks that can be
1661 * carried out against CPU-local state are performed first.  However,
1662 * we must check for CPU stalls first, else we might not get a chance.
1663 */
1664static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
1665{
1666        struct rcu_node *rnp = rdp->mynode;
1667
1668        rdp->n_rcu_pending++;
1669
1670        /* Check for CPU stalls, if enabled. */
1671        check_cpu_stall(rsp, rdp);
1672
1673        /* Is the RCU core waiting for a quiescent state from this CPU? */
1674        if (rdp->qs_pending && !rdp->passed_quiesc) {
1675
1676                /*
1677                 * If force_quiescent_state() coming soon and this CPU
1678                 * needs a quiescent state, and this is either RCU-sched
1679                 * or RCU-bh, force a local reschedule.
1680                 */
1681                rdp->n_rp_qs_pending++;
1682                if (!rdp->preemptible &&
1683                    ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1,
1684                                 jiffies))
1685                        set_need_resched();
1686        } else if (rdp->qs_pending && rdp->passed_quiesc) {
1687                rdp->n_rp_report_qs++;
1688                return 1;
1689        }
1690
1691        /* Does this CPU have callbacks ready to invoke? */
1692        if (cpu_has_callbacks_ready_to_invoke(rdp)) {
1693                rdp->n_rp_cb_ready++;
1694                return 1;
1695        }
1696
1697        /* Has RCU gone idle with this CPU needing another grace period? */
1698        if (cpu_needs_another_gp(rsp, rdp)) {
1699                rdp->n_rp_cpu_needs_gp++;
1700                return 1;
1701        }
1702
1703        /* Has another RCU grace period completed?  */
1704        if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
1705                rdp->n_rp_gp_completed++;
1706                return 1;
1707        }
1708
1709        /* Has a new RCU grace period started? */
1710        if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
1711                rdp->n_rp_gp_started++;
1712                return 1;
1713        }
1714
1715        /* Has an RCU GP gone long enough to send resched IPIs &c? */
1716        if (rcu_gp_in_progress(rsp) &&
1717            ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) {
1718                rdp->n_rp_need_fqs++;
1719                return 1;
1720        }
1721
1722        /* nothing to do */
1723        rdp->n_rp_need_nothing++;
1724        return 0;
1725}
1726
1727/*
1728 * Check to see if there is any immediate RCU-related work to be done
1729 * by the current CPU, returning 1 if so.  This function is part of the
1730 * RCU implementation; it is -not- an exported member of the RCU API.
1731 */
1732static int rcu_pending(int cpu)
1733{
1734        return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
1735               __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) ||
1736               rcu_preempt_pending(cpu);
1737}
1738
1739/*
1740 * Check to see if any future RCU-related work will need to be done
1741 * by the current CPU, even if none need be done immediately, returning
1742 * 1 if so.
1743 */
1744static int rcu_needs_cpu_quick_check(int cpu)
1745{
1746        /* RCU callbacks either ready or pending? */
1747        return per_cpu(rcu_sched_data, cpu).nxtlist ||
1748               per_cpu(rcu_bh_data, cpu).nxtlist ||
1749               rcu_preempt_needs_cpu(cpu);
1750}
1751
1752static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
1753static atomic_t rcu_barrier_cpu_count;
1754static DEFINE_MUTEX(rcu_barrier_mutex);
1755static struct completion rcu_barrier_completion;
1756
1757static void rcu_barrier_callback(struct rcu_head *notused)
1758{
1759        if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1760                complete(&rcu_barrier_completion);
1761}
1762
1763/*
1764 * Called with preemption disabled, and from cross-cpu IRQ context.
1765 */
1766static void rcu_barrier_func(void *type)
1767{
1768        int cpu = smp_processor_id();
1769        struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
1770        void (*call_rcu_func)(struct rcu_head *head,
1771                              void (*func)(struct rcu_head *head));
1772
1773        atomic_inc(&rcu_barrier_cpu_count);
1774        call_rcu_func = type;
1775        call_rcu_func(head, rcu_barrier_callback);
1776}
1777
1778/*
1779 * Orchestrate the specified type of RCU barrier, waiting for all
1780 * RCU callbacks of the specified type to complete.
1781 */
1782static void _rcu_barrier(struct rcu_state *rsp,
1783                         void (*call_rcu_func)(struct rcu_head *head,
1784                                               void (*func)(struct rcu_head *head)))
1785{
1786        BUG_ON(in_interrupt());
1787        /* Take mutex to serialize concurrent rcu_barrier() requests. */
1788        mutex_lock(&rcu_barrier_mutex);
1789        init_completion(&rcu_barrier_completion);
1790        /*
1791         * Initialize rcu_barrier_cpu_count to 1, then invoke
1792         * rcu_barrier_func() on each CPU, so that each CPU also has
1793         * incremented rcu_barrier_cpu_count.  Only then is it safe to
1794         * decrement rcu_barrier_cpu_count -- otherwise the first CPU
1795         * might complete its grace period before all of the other CPUs
1796         * did their increment, causing this function to return too
1797         * early.  Note that on_each_cpu() disables irqs, which prevents
1798         * any CPUs from coming online or going offline until each online
1799         * CPU has queued its RCU-barrier callback.
1800         */
1801        atomic_set(&rcu_barrier_cpu_count, 1);
1802        on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
1803        if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1804                complete(&rcu_barrier_completion);
1805        wait_for_completion(&rcu_barrier_completion);
1806        mutex_unlock(&rcu_barrier_mutex);
1807}
1808
1809/**
1810 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
1811 */
1812void rcu_barrier_bh(void)
1813{
1814        _rcu_barrier(&rcu_bh_state, call_rcu_bh);
1815}
1816EXPORT_SYMBOL_GPL(rcu_barrier_bh);
1817
1818/**
1819 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
1820 */
1821void rcu_barrier_sched(void)
1822{
1823        _rcu_barrier(&rcu_sched_state, call_rcu_sched);
1824}
1825EXPORT_SYMBOL_GPL(rcu_barrier_sched);
1826
1827/*
1828 * Do boot-time initialization of a CPU's per-CPU RCU data.
1829 */
1830static void __init
1831rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
1832{
1833        unsigned long flags;
1834        int i;
1835        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1836        struct rcu_node *rnp = rcu_get_root(rsp);
1837
1838        /* Set up local state, ensuring consistent view of global state. */
1839        raw_spin_lock_irqsave(&rnp->lock, flags);
1840        rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
1841        rdp->nxtlist = NULL;
1842        for (i = 0; i < RCU_NEXT_SIZE; i++)
1843                rdp->nxttail[i] = &rdp->nxtlist;
1844        rdp->qlen = 0;
1845#ifdef CONFIG_NO_HZ
1846        rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
1847#endif /* #ifdef CONFIG_NO_HZ */
1848        rdp->cpu = cpu;
1849        raw_spin_unlock_irqrestore(&rnp->lock, flags);
1850}
1851
1852/*
1853 * Initialize a CPU's per-CPU RCU data.  Note that only one online or
1854 * offline event can be happening at a given time.  Note also that we
1855 * can accept some slop in the rsp->completed access due to the fact
1856 * that this CPU cannot possibly have any RCU callbacks in flight yet.
1857 */
1858static void __cpuinit
1859rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
1860{
1861        unsigned long flags;
1862        unsigned long mask;
1863        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1864        struct rcu_node *rnp = rcu_get_root(rsp);
1865
1866        /* Set up local state, ensuring consistent view of global state. */
1867        raw_spin_lock_irqsave(&rnp->lock, flags);
1868        rdp->passed_quiesc = 0;  /* We could be racing with new GP, */
1869        rdp->qs_pending = 1;     /*  so set up to respond to current GP. */
1870        rdp->beenonline = 1;     /* We have now been online. */
1871        rdp->preemptible = preemptible;
1872        rdp->qlen_last_fqs_check = 0;
1873        rdp->n_force_qs_snap = rsp->n_force_qs;
1874        rdp->blimit = blimit;
1875        raw_spin_unlock(&rnp->lock);            /* irqs remain disabled. */
1876
1877        /*
1878         * A new grace period might start here.  If so, we won't be part
1879         * of it, but that is OK, as we are currently in a quiescent state.
1880         */
1881
1882        /* Exclude any attempts to start a new GP on large systems. */
1883        raw_spin_lock(&rsp->onofflock);         /* irqs already disabled. */
1884
1885        /* Add CPU to rcu_node bitmasks. */
1886        rnp = rdp->mynode;
1887        mask = rdp->grpmask;
1888        do {
1889                /* Exclude any attempts to start a new GP on small systems. */
1890                raw_spin_lock(&rnp->lock);      /* irqs already disabled. */
1891                rnp->qsmaskinit |= mask;
1892                mask = rnp->grpmask;
1893                if (rnp == rdp->mynode) {
1894                        rdp->gpnum = rnp->completed; /* if GP in progress... */
1895                        rdp->completed = rnp->completed;
1896                        rdp->passed_quiesc_completed = rnp->completed - 1;
1897                }
1898                raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
1899                rnp = rnp->parent;
1900        } while (rnp != NULL && !(rnp->qsmaskinit & mask));
1901
1902        raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
1903}
1904
1905static void __cpuinit rcu_prepare_cpu(int cpu)
1906{
1907        rcu_init_percpu_data(cpu, &rcu_sched_state, 0);
1908        rcu_init_percpu_data(cpu, &rcu_bh_state, 0);
1909        rcu_preempt_init_percpu_data(cpu);
1910}
1911
1912/*
1913 * Handle CPU online/offline notification events.
1914 */
1915static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
1916                                    unsigned long action, void *hcpu)
1917{
1918        long cpu = (long)hcpu;
1919        struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
1920        struct rcu_node *rnp = rdp->mynode;
1921
1922        switch (action) {
1923        case CPU_UP_PREPARE:
1924        case CPU_UP_PREPARE_FROZEN:
1925                rcu_prepare_cpu(cpu);
1926                rcu_prepare_kthreads(cpu);
1927                break;
1928        case CPU_ONLINE:
1929        case CPU_DOWN_FAILED:
1930                rcu_node_kthread_setaffinity(rnp, -1);
1931                rcu_cpu_kthread_setrt(cpu, 1);
1932                break;
1933        case CPU_DOWN_PREPARE:
1934                rcu_node_kthread_setaffinity(rnp, cpu);
1935                rcu_cpu_kthread_setrt(cpu, 0);
1936                break;
1937        case CPU_DYING:
1938        case CPU_DYING_FROZEN:
1939                /*
1940                 * The whole machine is "stopped" except this CPU, so we can
1941                 * touch any data without introducing corruption. We send the
1942                 * dying CPU's callbacks to an arbitrarily chosen online CPU.
1943                 */
1944                rcu_send_cbs_to_online(&rcu_bh_state);
1945                rcu_send_cbs_to_online(&rcu_sched_state);
1946                rcu_preempt_send_cbs_to_online();
1947                break;
1948        case CPU_DEAD:
1949        case CPU_DEAD_FROZEN:
1950        case CPU_UP_CANCELED:
1951        case CPU_UP_CANCELED_FROZEN:
1952                rcu_offline_cpu(cpu);
1953                break;
1954        default:
1955                break;
1956        }
1957        return NOTIFY_OK;
1958}
1959
1960/*
1961 * This function is invoked towards the end of the scheduler's initialization
1962 * process.  Before this is called, the idle task might contain
1963 * RCU read-side critical sections (during which time, this idle
1964 * task is booting the system).  After this function is called, the
1965 * idle tasks are prohibited from containing RCU read-side critical
1966 * sections.  This function also enables RCU lockdep checking.
1967 */
1968void rcu_scheduler_starting(void)
1969{
1970        WARN_ON(num_online_cpus() != 1);
1971        WARN_ON(nr_context_switches() > 0);
1972        rcu_scheduler_active = 1;
1973}
1974
1975/*
1976 * Compute the per-level fanout, either using the exact fanout specified
1977 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
1978 */
1979#ifdef CONFIG_RCU_FANOUT_EXACT
1980static void __init rcu_init_levelspread(struct rcu_state *rsp)
1981{
1982        int i;
1983
1984        for (i = NUM_RCU_LVLS - 1; i > 0; i--)
1985                rsp->levelspread[i] = CONFIG_RCU_FANOUT;
1986        rsp->levelspread[0] = RCU_FANOUT_LEAF;
1987}
1988#else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
1989static void __init rcu_init_levelspread(struct rcu_state *rsp)
1990{
1991        int ccur;
1992        int cprv;
1993        int i;
1994
1995        cprv = NR_CPUS;
1996        for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1997                ccur = rsp->levelcnt[i];
1998                rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
1999                cprv = ccur;
2000        }
2001}
2002#endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
2003
2004/*
2005 * Helper function for rcu_init() that initializes one rcu_state structure.
2006 */
2007static void __init rcu_init_one(struct rcu_state *rsp,
2008                struct rcu_data __percpu *rda)
2009{
2010        static char *buf[] = { "rcu_node_level_0",
2011                               "rcu_node_level_1",
2012                               "rcu_node_level_2",
2013                               "rcu_node_level_3" };  /* Match MAX_RCU_LVLS */
2014        int cpustride = 1;
2015        int i;
2016        int j;
2017        struct rcu_node *rnp;
2018
2019        BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
2020
2021        /* Initialize the level-tracking arrays. */
2022
2023        for (i = 1; i < NUM_RCU_LVLS; i++)
2024                rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
2025        rcu_init_levelspread(rsp);
2026
2027        /* Initialize the elements themselves, starting from the leaves. */
2028
2029        for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
2030                cpustride *= rsp->levelspread[i];
2031                rnp = rsp->level[i];
2032                for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
2033                        raw_spin_lock_init(&rnp->lock);
2034                        lockdep_set_class_and_name(&rnp->lock,
2035                                                   &rcu_node_class[i], buf[i]);
2036                        rnp->gpnum = 0;
2037                        rnp->qsmask = 0;
2038                        rnp->qsmaskinit = 0;
2039                        rnp->grplo = j * cpustride;
2040                        rnp->grphi = (j + 1) * cpustride - 1;
2041                        if (rnp->grphi >= NR_CPUS)
2042                                rnp->grphi = NR_CPUS - 1;
2043                        if (i == 0) {
2044                                rnp->grpnum = 0;
2045                                rnp->grpmask = 0;
2046                                rnp->parent = NULL;
2047                        } else {
2048                                rnp->grpnum = j % rsp->levelspread[i - 1];
2049                                rnp->grpmask = 1UL << rnp->grpnum;
2050                                rnp->parent = rsp->level[i - 1] +
2051                                              j / rsp->levelspread[i - 1];
2052                        }
2053                        rnp->level = i;
2054                        INIT_LIST_HEAD(&rnp->blkd_tasks);
2055                }
2056        }
2057
2058        rsp->rda = rda;
2059        rnp = rsp->level[NUM_RCU_LVLS - 1];
2060        for_each_possible_cpu(i) {
2061                while (i > rnp->grphi)
2062                        rnp++;
2063                per_cpu_ptr(rsp->rda, i)->mynode = rnp;
2064                rcu_boot_init_percpu_data(i, rsp);
2065        }
2066}
2067
2068void __init rcu_init(void)
2069{
2070        int cpu;
2071
2072        rcu_bootup_announce();
2073        rcu_init_one(&rcu_sched_state, &rcu_sched_data);
2074        rcu_init_one(&rcu_bh_state, &rcu_bh_data);
2075        __rcu_init_preempt();
2076         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
2077
2078        /*
2079         * We don't need protection against CPU-hotplug here because
2080         * this is called early in boot, before either interrupts
2081         * or the scheduler are operational.
2082         */
2083        cpu_notifier(rcu_cpu_notify, 0);
2084        for_each_online_cpu(cpu)
2085                rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
2086        check_cpu_stall_init();
2087}
2088
2089#include "rcutree_plugin.h"
2090
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