rcutree.c

Go to the documentation of this file.

/*
 * Read-Copy Update mechanism for mutual exclusion
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright IBM Corporation, 2008
 *
 * Authors: Dipankar Sarma <[email protected]>
 *      Manfred Spraul <[email protected]>
 *      Paul E. McKenney <[email protected]> Hierarchical version
 *
 * Based on the original work by Paul McKenney <[email protected]>
 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 *
 * For detailed explanation of Read-Copy Update mechanism see -
 *  Documentation/RCU
 */
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/rcupdate.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/nmi.h>
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/export.h>
#include <linux/completion.h>
#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/time.h>
#include <linux/kernel_stat.h>
#include <linux/wait.h>
#include <linux/kthread.h>
#include <linux/prefetch.h>
#include <linux/delay.h>
#include <linux/stop_machine.h>
#include <linux/random.h>

#include "rcutree.h"
#include <trace/events/rcu.h>

#include "rcu.h"

/* Data structures. */

static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];

#define RCU_STATE_INITIALIZER(sname, cr) { \
    .level = { &sname##_state.node[0] }, \
    .call = cr, \
    .fqs_state = RCU_GP_IDLE, \
    .gpnum = -300, \
    .completed = -300, \
    .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.onofflock), \
    .orphan_nxttail = &sname##_state.orphan_nxtlist, \
    .orphan_donetail = &sname##_state.orphan_donelist, \
    .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
    .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
    .name = #sname, \
}

struct rcu_state rcu_sched_state =
    RCU_STATE_INITIALIZER(rcu_sched, call_rcu_sched);
DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);

struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh, call_rcu_bh);
DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);

static struct rcu_state *rcu_state;
LIST_HEAD(rcu_struct_flavors);

/* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF;
module_param(rcu_fanout_leaf, int, 0444);
int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
static int num_rcu_lvl[] = {  /* Number of rcu_nodes at specified level. */
    NUM_RCU_LVL_0,
    NUM_RCU_LVL_1,
    NUM_RCU_LVL_2,
    NUM_RCU_LVL_3,
    NUM_RCU_LVL_4,
};
int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */

/*
 * The rcu_scheduler_active variable transitions from zero to one just
 * before the first task is spawned.  So when this variable is zero, RCU
 * can assume that there is but one task, allowing RCU to (for example)
 * optimized synchronize_sched() to a simple barrier().  When this variable
 * is one, RCU must actually do all the hard work required to detect real
 * grace periods.  This variable is also used to suppress boot-time false
 * positives from lockdep-RCU error checking.
 */
int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);

/*
 * The rcu_scheduler_fully_active variable transitions from zero to one
 * during the early_initcall() processing, which is after the scheduler
 * is capable of creating new tasks.  So RCU processing (for example,
 * creating tasks for RCU priority boosting) must be delayed until after
 * rcu_scheduler_fully_active transitions from zero to one.  We also
 * currently delay invocation of any RCU callbacks until after this point.
 *
 * It might later prove better for people registering RCU callbacks during
 * early boot to take responsibility for these callbacks, but one step at
 * a time.
 */
static int rcu_scheduler_fully_active __read_mostly;

#ifdef CONFIG_RCU_BOOST

/*
 * Control variables for per-CPU and per-rcu_node kthreads.  These
 * handle all flavors of RCU.
 */
static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
DEFINE_PER_CPU(char, rcu_cpu_has_work);

#endif /* #ifdef CONFIG_RCU_BOOST */

static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
static void invoke_rcu_core(void);
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);

/*
 * Track the rcutorture test sequence number and the update version
 * number within a given test.  The rcutorture_testseq is incremented
 * on every rcutorture module load and unload, so has an odd value
 * when a test is running.  The rcutorture_vernum is set to zero
 * when rcutorture starts and is incremented on each rcutorture update.
 * These variables enable correlating rcutorture output with the
 * RCU tracing information.
 */
unsigned long rcutorture_testseq;
unsigned long rcutorture_vernum;

/*
 * Return true if an RCU grace period is in progress.  The ACCESS_ONCE()s
 * permit this function to be invoked without holding the root rcu_node
 * structure's ->lock, but of course results can be subject to change.
 */
static int rcu_gp_in_progress(struct rcu_state *rsp)
{
    return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
}

/*
 * Note a quiescent state.  Because we do not need to know
 * how many quiescent states passed, just if there was at least
 * one since the start of the grace period, this just sets a flag.
 * The caller must have disabled preemption.
 */
void rcu_sched_qs(int cpu)
{
    struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);

    if (rdp->passed_quiesce == 0)
        trace_rcu_grace_period("rcu_sched", rdp->gpnum, "cpuqs");
    rdp->passed_quiesce = 1;
}

void rcu_bh_qs(int cpu)
{
    struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);

    if (rdp->passed_quiesce == 0)
        trace_rcu_grace_period("rcu_bh", rdp->gpnum, "cpuqs");
    rdp->passed_quiesce = 1;
}

/*
 * Note a context switch.  This is a quiescent state for RCU-sched,
 * and requires special handling for preemptible RCU.
 * The caller must have disabled preemption.
 */
void rcu_note_context_switch(int cpu)
{
    trace_rcu_utilization("Start context switch");
    rcu_sched_qs(cpu);
    rcu_preempt_note_context_switch(cpu);
    trace_rcu_utilization("End context switch");
}
EXPORT_SYMBOL_GPL(rcu_note_context_switch);

DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
    .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
    .dynticks = ATOMIC_INIT(1),
#if defined(CONFIG_RCU_USER_QS) && !defined(CONFIG_RCU_USER_QS_FORCE)
    .ignore_user_qs = true,
#endif
};

static long blimit = 10;    /* Maximum callbacks per rcu_do_batch. */
static long qhimark = 10000;    /* If this many pending, ignore blimit. */
static long qlowmark = 100; /* Once only this many pending, use blimit. */

module_param(blimit, long, 0444);
module_param(qhimark, long, 0444);
module_param(qlowmark, long, 0444);

int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;

module_param(rcu_cpu_stall_suppress, int, 0644);
module_param(rcu_cpu_stall_timeout, int, 0644);

static ulong jiffies_till_first_fqs = RCU_JIFFIES_TILL_FORCE_QS;
static ulong jiffies_till_next_fqs = RCU_JIFFIES_TILL_FORCE_QS;

module_param(jiffies_till_first_fqs, ulong, 0644);
module_param(jiffies_till_next_fqs, ulong, 0644);

static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *));
static void force_quiescent_state(struct rcu_state *rsp);
static int rcu_pending(int cpu);

/*
 * Return the number of RCU-sched batches processed thus far for debug & stats.
 */
long rcu_batches_completed_sched(void)
{
    return rcu_sched_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);

/*
 * Return the number of RCU BH batches processed thus far for debug & stats.
 */
long rcu_batches_completed_bh(void)
{
    return rcu_bh_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);

/*
 * Force a quiescent state for RCU BH.
 */
void rcu_bh_force_quiescent_state(void)
{
    force_quiescent_state(&rcu_bh_state);
}
EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);

/*
 * Record the number of times rcutorture tests have been initiated and
 * terminated.  This information allows the debugfs tracing stats to be
 * correlated to the rcutorture messages, even when the rcutorture module
 * is being repeatedly loaded and unloaded.  In other words, we cannot
 * store this state in rcutorture itself.
 */
void rcutorture_record_test_transition(void)
{
    rcutorture_testseq++;
    rcutorture_vernum = 0;
}
EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);

/*
 * Record the number of writer passes through the current rcutorture test.
 * This is also used to correlate debugfs tracing stats with the rcutorture
 * messages.
 */
void rcutorture_record_progress(unsigned long vernum)
{
    rcutorture_vernum++;
}
EXPORT_SYMBOL_GPL(rcutorture_record_progress);

/*
 * Force a quiescent state for RCU-sched.
 */
void rcu_sched_force_quiescent_state(void)
{
    force_quiescent_state(&rcu_sched_state);
}
EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);

/*
 * Does the CPU have callbacks ready to be invoked?
 */
static int
cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
{
    return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
}

/*
 * Does the current CPU require a yet-as-unscheduled grace period?
 */
static int
cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
{
    return *rdp->nxttail[RCU_DONE_TAIL +
                 ACCESS_ONCE(rsp->completed) != rdp->completed] &&
           !rcu_gp_in_progress(rsp);
}

/*
 * Return the root node of the specified rcu_state structure.
 */
static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
{
    return &rsp->node[0];
}

/*
 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
 *
 * If the new value of the ->dynticks_nesting counter now is zero,
 * we really have entered idle, and must do the appropriate accounting.
 * The caller must have disabled interrupts.
 */
static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
                bool user)
{
    trace_rcu_dyntick("Start", oldval, 0);
    if (!user && !is_idle_task(current)) {
        struct task_struct *idle = idle_task(smp_processor_id());

        trace_rcu_dyntick("Error on entry: not idle task", oldval, 0);
        ftrace_dump(DUMP_ORIG);
        WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
              current->pid, current->comm,
              idle->pid, idle->comm); /* must be idle task! */
    }
    rcu_prepare_for_idle(smp_processor_id());
    /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
    smp_mb__before_atomic_inc();  /* See above. */
    atomic_inc(&rdtp->dynticks);
    smp_mb__after_atomic_inc();  /* Force ordering with next sojourn. */
    WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);

    /*
     * It is illegal to enter an extended quiescent state while
     * in an RCU read-side critical section.
     */
    rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
               "Illegal idle entry in RCU read-side critical section.");
    rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
               "Illegal idle entry in RCU-bh read-side critical section.");
    rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
               "Illegal idle entry in RCU-sched read-side critical section.");
}

/*
 * Enter an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
 */
static void rcu_eqs_enter(bool user)
{
    long long oldval;
    struct rcu_dynticks *rdtp;

    rdtp = &__get_cpu_var(rcu_dynticks);
    oldval = rdtp->dynticks_nesting;
    WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
    if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE)
        rdtp->dynticks_nesting = 0;
    else
        rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
    rcu_eqs_enter_common(rdtp, oldval, user);
}

void rcu_idle_enter(void)
{
    unsigned long flags;

    local_irq_save(flags);
    rcu_eqs_enter(false);
    local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_enter);

#ifdef CONFIG_RCU_USER_QS

void rcu_user_enter(void)
{
    unsigned long flags;
    struct rcu_dynticks *rdtp;

    /*
     * Some contexts may involve an exception occuring in an irq,
     * leading to that nesting:
     * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
     * This would mess up the dyntick_nesting count though. And rcu_irq_*()
     * helpers are enough to protect RCU uses inside the exception. So
     * just return immediately if we detect we are in an IRQ.
     */
    if (in_interrupt())
        return;

    WARN_ON_ONCE(!current->mm);

    local_irq_save(flags);
    rdtp = &__get_cpu_var(rcu_dynticks);
    if (!rdtp->ignore_user_qs && !rdtp->in_user) {
        rdtp->in_user = true;
        rcu_eqs_enter(true);
    }
    local_irq_restore(flags);
}

void rcu_user_enter_after_irq(void)
{
    unsigned long flags;
    struct rcu_dynticks *rdtp;

    local_irq_save(flags);
    rdtp = &__get_cpu_var(rcu_dynticks);
    /* Ensure this irq is interrupting a non-idle RCU state.  */
    WARN_ON_ONCE(!(rdtp->dynticks_nesting & DYNTICK_TASK_MASK));
    rdtp->dynticks_nesting = 1;
    local_irq_restore(flags);
}
#endif /* CONFIG_RCU_USER_QS */

void rcu_irq_exit(void)
{
    unsigned long flags;
    long long oldval;
    struct rcu_dynticks *rdtp;

    local_irq_save(flags);
    rdtp = &__get_cpu_var(rcu_dynticks);
    oldval = rdtp->dynticks_nesting;
    rdtp->dynticks_nesting--;
    WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
    if (rdtp->dynticks_nesting)
        trace_rcu_dyntick("--=", oldval, rdtp->dynticks_nesting);
    else
        rcu_eqs_enter_common(rdtp, oldval, true);
    local_irq_restore(flags);
}

/*
 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
 *
 * If the new value of the ->dynticks_nesting counter was previously zero,
 * we really have exited idle, and must do the appropriate accounting.
 * The caller must have disabled interrupts.
 */
static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval,
                   int user)
{
    smp_mb__before_atomic_inc();  /* Force ordering w/previous sojourn. */
    atomic_inc(&rdtp->dynticks);
    /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
    smp_mb__after_atomic_inc();  /* See above. */
    WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
    rcu_cleanup_after_idle(smp_processor_id());
    trace_rcu_dyntick("End", oldval, rdtp->dynticks_nesting);
    if (!user && !is_idle_task(current)) {
        struct task_struct *idle = idle_task(smp_processor_id());

        trace_rcu_dyntick("Error on exit: not idle task",
                  oldval, rdtp->dynticks_nesting);
        ftrace_dump(DUMP_ORIG);
        WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
              current->pid, current->comm,
              idle->pid, idle->comm); /* must be idle task! */
    }
}

/*
 * Exit an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
 */
static void rcu_eqs_exit(bool user)
{
    struct rcu_dynticks *rdtp;
    long long oldval;

    rdtp = &__get_cpu_var(rcu_dynticks);
    oldval = rdtp->dynticks_nesting;
    WARN_ON_ONCE(oldval < 0);
    if (oldval & DYNTICK_TASK_NEST_MASK)
        rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
    else
        rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
    rcu_eqs_exit_common(rdtp, oldval, user);
}

void rcu_idle_exit(void)
{
    unsigned long flags;

    local_irq_save(flags);
    rcu_eqs_exit(false);
    local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_exit);

#ifdef CONFIG_RCU_USER_QS

void rcu_user_exit(void)
{
    unsigned long flags;
    struct rcu_dynticks *rdtp;

    /*
     * Some contexts may involve an exception occuring in an irq,
     * leading to that nesting:
     * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
     * This would mess up the dyntick_nesting count though. And rcu_irq_*()
     * helpers are enough to protect RCU uses inside the exception. So
     * just return immediately if we detect we are in an IRQ.
     */
    if (in_interrupt())
        return;

    local_irq_save(flags);
    rdtp = &__get_cpu_var(rcu_dynticks);
    if (rdtp->in_user) {
        rdtp->in_user = false;
        rcu_eqs_exit(true);
    }
    local_irq_restore(flags);
}

void rcu_user_exit_after_irq(void)
{
    unsigned long flags;
    struct rcu_dynticks *rdtp;

    local_irq_save(flags);
    rdtp = &__get_cpu_var(rcu_dynticks);
    /* Ensure we are interrupting an RCU idle mode. */
    WARN_ON_ONCE(rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK);
    rdtp->dynticks_nesting += DYNTICK_TASK_EXIT_IDLE;
    local_irq_restore(flags);
}
#endif /* CONFIG_RCU_USER_QS */

void rcu_irq_enter(void)
{
    unsigned long flags;
    struct rcu_dynticks *rdtp;
    long long oldval;

    local_irq_save(flags);
    rdtp = &__get_cpu_var(rcu_dynticks);
    oldval = rdtp->dynticks_nesting;
    rdtp->dynticks_nesting++;
    WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
    if (oldval)
        trace_rcu_dyntick("++=", oldval, rdtp->dynticks_nesting);
    else
        rcu_eqs_exit_common(rdtp, oldval, true);
    local_irq_restore(flags);
}

void rcu_nmi_enter(void)
{
    struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);

    if (rdtp->dynticks_nmi_nesting == 0 &&
        (atomic_read(&rdtp->dynticks) & 0x1))
        return;
    rdtp->dynticks_nmi_nesting++;
    smp_mb__before_atomic_inc();  /* Force delay from prior write. */
    atomic_inc(&rdtp->dynticks);
    /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
    smp_mb__after_atomic_inc();  /* See above. */
    WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
}

void rcu_nmi_exit(void)
{
    struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);

    if (rdtp->dynticks_nmi_nesting == 0 ||
        --rdtp->dynticks_nmi_nesting != 0)
        return;
    /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
    smp_mb__before_atomic_inc();  /* See above. */
    atomic_inc(&rdtp->dynticks);
    smp_mb__after_atomic_inc();  /* Force delay to next write. */
    WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
}

int rcu_is_cpu_idle(void)
{
    int ret;

    preempt_disable();
    ret = (atomic_read(&__get_cpu_var(rcu_dynticks).dynticks) & 0x1) == 0;
    preempt_enable();
    return ret;
}
EXPORT_SYMBOL(rcu_is_cpu_idle);

#ifdef CONFIG_RCU_USER_QS
void rcu_user_hooks_switch(struct task_struct *prev,
               struct task_struct *next)
{
    struct rcu_dynticks *rdtp;

    /* Interrupts are disabled in context switch */
    rdtp = &__get_cpu_var(rcu_dynticks);
    if (!rdtp->ignore_user_qs) {
        clear_tsk_thread_flag(prev, TIF_NOHZ);
        set_tsk_thread_flag(next, TIF_NOHZ);
    }
}
#endif /* #ifdef CONFIG_RCU_USER_QS */

#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)

/*
 * Is the current CPU online?  Disable preemption to avoid false positives
 * that could otherwise happen due to the current CPU number being sampled,
 * this task being preempted, its old CPU being taken offline, resuming
 * on some other CPU, then determining that its old CPU is now offline.
 * It is OK to use RCU on an offline processor during initial boot, hence
 * the check for rcu_scheduler_fully_active.  Note also that it is OK
 * for a CPU coming online to use RCU for one jiffy prior to marking itself
 * online in the cpu_online_mask.  Similarly, it is OK for a CPU going
 * offline to continue to use RCU for one jiffy after marking itself
 * offline in the cpu_online_mask.  This leniency is necessary given the
 * non-atomic nature of the online and offline processing, for example,
 * the fact that a CPU enters the scheduler after completing the CPU_DYING
 * notifiers.
 *
 * This is also why RCU internally marks CPUs online during the
 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
 *
 * Disable checking if in an NMI handler because we cannot safely report
 * errors from NMI handlers anyway.
 */
bool rcu_lockdep_current_cpu_online(void)
{
    struct rcu_data *rdp;
    struct rcu_node *rnp;
    bool ret;

    if (in_nmi())
        return 1;
    preempt_disable();
    rdp = &__get_cpu_var(rcu_sched_data);
    rnp = rdp->mynode;
    ret = (rdp->grpmask & rnp->qsmaskinit) ||
          !rcu_scheduler_fully_active;
    preempt_enable();
    return ret;
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);

#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */

int rcu_is_cpu_rrupt_from_idle(void)
{
    return __get_cpu_var(rcu_dynticks).dynticks_nesting <= 1;
}

/*
 * Snapshot the specified CPU's dynticks counter so that we can later
 * credit them with an implicit quiescent state.  Return 1 if this CPU
 * is in dynticks idle mode, which is an extended quiescent state.
 */
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
    rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
    return (rdp->dynticks_snap & 0x1) == 0;
}

/*
 * Return true if the specified CPU has passed through a quiescent
 * state by virtue of being in or having passed through an dynticks
 * idle state since the last call to dyntick_save_progress_counter()
 * for this same CPU, or by virtue of having been offline.
 */
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
{
    unsigned int curr;
    unsigned int snap;

    curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
    snap = (unsigned int)rdp->dynticks_snap;

    /*
     * If the CPU passed through or entered a dynticks idle phase with
     * no active irq/NMI handlers, then we can safely pretend that the CPU
     * already acknowledged the request to pass through a quiescent
     * state.  Either way, that CPU cannot possibly be in an RCU
     * read-side critical section that started before the beginning
     * of the current RCU grace period.
     */
    if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
        trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "dti");
        rdp->dynticks_fqs++;
        return 1;
    }

    /*
     * Check for the CPU being offline, but only if the grace period
     * is old enough.  We don't need to worry about the CPU changing
     * state: If we see it offline even once, it has been through a
     * quiescent state.
     *
     * The reason for insisting that the grace period be at least
     * one jiffy old is that CPUs that are not quite online and that
     * have just gone offline can still execute RCU read-side critical
     * sections.
     */
    if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))
        return 0;  /* Grace period is not old enough. */
    barrier();
    if (cpu_is_offline(rdp->cpu)) {
        trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl");
        rdp->offline_fqs++;
        return 1;
    }
    return 0;
}

static int jiffies_till_stall_check(void)
{
    int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);

    /*
     * Limit check must be consistent with the Kconfig limits
     * for CONFIG_RCU_CPU_STALL_TIMEOUT.
     */
    if (till_stall_check < 3) {
        ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
        till_stall_check = 3;
    } else if (till_stall_check > 300) {
        ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
        till_stall_check = 300;
    }
    return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
}

static void record_gp_stall_check_time(struct rcu_state *rsp)
{
    rsp->gp_start = jiffies;
    rsp->jiffies_stall = jiffies + jiffies_till_stall_check();
}

static void print_other_cpu_stall(struct rcu_state *rsp)
{
    int cpu;
    long delta;
    unsigned long flags;
    int ndetected = 0;
    struct rcu_node *rnp = rcu_get_root(rsp);

    /* Only let one CPU complain about others per time interval. */

    raw_spin_lock_irqsave(&rnp->lock, flags);
    delta = jiffies - rsp->jiffies_stall;
    if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
        return;
    }
    rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3;
    raw_spin_unlock_irqrestore(&rnp->lock, flags);

    /*
     * OK, time to rat on our buddy...
     * See Documentation/RCU/stallwarn.txt for info on how to debug
     * RCU CPU stall warnings.
     */
    printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks:",
           rsp->name);
    print_cpu_stall_info_begin();
    rcu_for_each_leaf_node(rsp, rnp) {
        raw_spin_lock_irqsave(&rnp->lock, flags);
        ndetected += rcu_print_task_stall(rnp);
        if (rnp->qsmask != 0) {
            for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
                if (rnp->qsmask & (1UL << cpu)) {
                    print_cpu_stall_info(rsp,
                                 rnp->grplo + cpu);
                    ndetected++;
                }
        }
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
    }

    /*
     * Now rat on any tasks that got kicked up to the root rcu_node
     * due to CPU offlining.
     */
    rnp = rcu_get_root(rsp);
    raw_spin_lock_irqsave(&rnp->lock, flags);
    ndetected += rcu_print_task_stall(rnp);
    raw_spin_unlock_irqrestore(&rnp->lock, flags);

    print_cpu_stall_info_end();
    printk(KERN_CONT "(detected by %d, t=%ld jiffies)\n",
           smp_processor_id(), (long)(jiffies - rsp->gp_start));
    if (ndetected == 0)
        printk(KERN_ERR "INFO: Stall ended before state dump start\n");
    else if (!trigger_all_cpu_backtrace())
        dump_stack();

    /* Complain about tasks blocking the grace period. */

    rcu_print_detail_task_stall(rsp);

    force_quiescent_state(rsp);  /* Kick them all. */
}

static void print_cpu_stall(struct rcu_state *rsp)
{
    unsigned long flags;
    struct rcu_node *rnp = rcu_get_root(rsp);

    /*
     * OK, time to rat on ourselves...
     * See Documentation/RCU/stallwarn.txt for info on how to debug
     * RCU CPU stall warnings.
     */
    printk(KERN_ERR "INFO: %s self-detected stall on CPU", rsp->name);
    print_cpu_stall_info_begin();
    print_cpu_stall_info(rsp, smp_processor_id());
    print_cpu_stall_info_end();
    printk(KERN_CONT " (t=%lu jiffies)\n", jiffies - rsp->gp_start);
    if (!trigger_all_cpu_backtrace())
        dump_stack();

    raw_spin_lock_irqsave(&rnp->lock, flags);
    if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
        rsp->jiffies_stall = jiffies +
                     3 * jiffies_till_stall_check() + 3;
    raw_spin_unlock_irqrestore(&rnp->lock, flags);

    set_need_resched();  /* kick ourselves to get things going. */
}

static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
    unsigned long j;
    unsigned long js;
    struct rcu_node *rnp;

    if (rcu_cpu_stall_suppress)
        return;
    j = ACCESS_ONCE(jiffies);
    js = ACCESS_ONCE(rsp->jiffies_stall);
    rnp = rdp->mynode;
    if (rcu_gp_in_progress(rsp) &&
        (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) {

        /* We haven't checked in, so go dump stack. */
        print_cpu_stall(rsp);

    } else if (rcu_gp_in_progress(rsp) &&
           ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {

        /* They had a few time units to dump stack, so complain. */
        print_other_cpu_stall(rsp);
    }
}

static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
{
    rcu_cpu_stall_suppress = 1;
    return NOTIFY_DONE;
}

void rcu_cpu_stall_reset(void)
{
    struct rcu_state *rsp;

    for_each_rcu_flavor(rsp)
        rsp->jiffies_stall = jiffies + ULONG_MAX / 2;
}

static struct notifier_block rcu_panic_block = {
    .notifier_call = rcu_panic,
};

static void __init check_cpu_stall_init(void)
{
    atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
}

/*
 * Update CPU-local rcu_data state to record the newly noticed grace period.
 * This is used both when we started the grace period and when we notice
 * that someone else started the grace period.  The caller must hold the
 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
 *  and must have irqs disabled.
 */
static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
{
    if (rdp->gpnum != rnp->gpnum) {
        /*
         * If the current grace period is waiting for this CPU,
         * set up to detect a quiescent state, otherwise don't
         * go looking for one.
         */
        rdp->gpnum = rnp->gpnum;
        trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpustart");
        rdp->passed_quiesce = 0;
        rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
        zero_cpu_stall_ticks(rdp);
    }
}

static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
{
    unsigned long flags;
    struct rcu_node *rnp;

    local_irq_save(flags);
    rnp = rdp->mynode;
    if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) || /* outside lock. */
        !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
        local_irq_restore(flags);
        return;
    }
    __note_new_gpnum(rsp, rnp, rdp);
    raw_spin_unlock_irqrestore(&rnp->lock, flags);
}

/*
 * Did someone else start a new RCU grace period start since we last
 * checked?  Update local state appropriately if so.  Must be called
 * on the CPU corresponding to rdp.
 */
static int
check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
{
    unsigned long flags;
    int ret = 0;

    local_irq_save(flags);
    if (rdp->gpnum != rsp->gpnum) {
        note_new_gpnum(rsp, rdp);
        ret = 1;
    }
    local_irq_restore(flags);
    return ret;
}

/*
 * Initialize the specified rcu_data structure's callback list to empty.
 */
static void init_callback_list(struct rcu_data *rdp)
{
    int i;

    rdp->nxtlist = NULL;
    for (i = 0; i < RCU_NEXT_SIZE; i++)
        rdp->nxttail[i] = &rdp->nxtlist;
}

/*
 * Advance this CPU's callbacks, but only if the current grace period
 * has ended.  This may be called only from the CPU to whom the rdp
 * belongs.  In addition, the corresponding leaf rcu_node structure's
 * ->lock must be held by the caller, with irqs disabled.
 */
static void
__rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
{
    /* Did another grace period end? */
    if (rdp->completed != rnp->completed) {

        /* Advance callbacks.  No harm if list empty. */
        rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
        rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
        rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];

        /* Remember that we saw this grace-period completion. */
        rdp->completed = rnp->completed;
        trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuend");

        /*
         * If we were in an extended quiescent state, we may have
         * missed some grace periods that others CPUs handled on
         * our behalf. Catch up with this state to avoid noting
         * spurious new grace periods.  If another grace period
         * has started, then rnp->gpnum will have advanced, so
         * we will detect this later on.  Of course, any quiescent
         * states we found for the old GP are now invalid.
         */
        if (ULONG_CMP_LT(rdp->gpnum, rdp->completed)) {
            rdp->gpnum = rdp->completed;
            rdp->passed_quiesce = 0;
        }

        /*
         * If RCU does not need a quiescent state from this CPU,
         * then make sure that this CPU doesn't go looking for one.
         */
        if ((rnp->qsmask & rdp->grpmask) == 0)
            rdp->qs_pending = 0;
    }
}

/*
 * Advance this CPU's callbacks, but only if the current grace period
 * has ended.  This may be called only from the CPU to whom the rdp
 * belongs.
 */
static void
rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
{
    unsigned long flags;
    struct rcu_node *rnp;

    local_irq_save(flags);
    rnp = rdp->mynode;
    if (rdp->completed == ACCESS_ONCE(rnp->completed) || /* outside lock. */
        !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
        local_irq_restore(flags);
        return;
    }
    __rcu_process_gp_end(rsp, rnp, rdp);
    raw_spin_unlock_irqrestore(&rnp->lock, flags);
}

/*
 * Do per-CPU grace-period initialization for running CPU.  The caller
 * must hold the lock of the leaf rcu_node structure corresponding to
 * this CPU.
 */
static void
rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
{
    /* Prior grace period ended, so advance callbacks for current CPU. */
    __rcu_process_gp_end(rsp, rnp, rdp);

    /* Set state so that this CPU will detect the next quiescent state. */
    __note_new_gpnum(rsp, rnp, rdp);
}

/*
 * Initialize a new grace period.
 */
static int rcu_gp_init(struct rcu_state *rsp)
{
    struct rcu_data *rdp;
    struct rcu_node *rnp = rcu_get_root(rsp);

    raw_spin_lock_irq(&rnp->lock);
    rsp->gp_flags = 0; /* Clear all flags: New grace period. */

    if (rcu_gp_in_progress(rsp)) {
        /* Grace period already in progress, don't start another.  */
        raw_spin_unlock_irq(&rnp->lock);
        return 0;
    }

    /* Advance to a new grace period and initialize state. */
    rsp->gpnum++;
    trace_rcu_grace_period(rsp->name, rsp->gpnum, "start");
    record_gp_stall_check_time(rsp);
    raw_spin_unlock_irq(&rnp->lock);

    /* Exclude any concurrent CPU-hotplug operations. */
    mutex_lock(&rsp->onoff_mutex);

    /*
     * Set the quiescent-state-needed bits in all the rcu_node
     * structures for all currently online CPUs in breadth-first order,
     * starting from the root rcu_node structure, relying on the layout
     * of the tree within the rsp->node[] array.  Note that other CPUs
     * will access only the leaves of the hierarchy, thus seeing that no
     * grace period is in progress, at least until the corresponding
     * leaf node has been initialized.  In addition, we have excluded
     * CPU-hotplug operations.
     *
     * The grace period cannot complete until the initialization
     * process finishes, because this kthread handles both.
     */
    rcu_for_each_node_breadth_first(rsp, rnp) {
        raw_spin_lock_irq(&rnp->lock);
        rdp = this_cpu_ptr(rsp->rda);
        rcu_preempt_check_blocked_tasks(rnp);
        rnp->qsmask = rnp->qsmaskinit;
        rnp->gpnum = rsp->gpnum;
        WARN_ON_ONCE(rnp->completed != rsp->completed);
        rnp->completed = rsp->completed;
        if (rnp == rdp->mynode)
            rcu_start_gp_per_cpu(rsp, rnp, rdp);
        rcu_preempt_boost_start_gp(rnp);
        trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
                        rnp->level, rnp->grplo,
                        rnp->grphi, rnp->qsmask);
        raw_spin_unlock_irq(&rnp->lock);
#ifdef CONFIG_PROVE_RCU_DELAY
        if ((random32() % (rcu_num_nodes * 8)) == 0)
            schedule_timeout_uninterruptible(2);
#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
        cond_resched();
    }

    mutex_unlock(&rsp->onoff_mutex);
    return 1;
}

/*
 * Do one round of quiescent-state forcing.
 */
int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
{
    int fqs_state = fqs_state_in;
    struct rcu_node *rnp = rcu_get_root(rsp);

    rsp->n_force_qs++;
    if (fqs_state == RCU_SAVE_DYNTICK) {
        /* Collect dyntick-idle snapshots. */
        force_qs_rnp(rsp, dyntick_save_progress_counter);
        fqs_state = RCU_FORCE_QS;
    } else {
        /* Handle dyntick-idle and offline CPUs. */
        force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
    }
    /* Clear flag to prevent immediate re-entry. */
    if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
        raw_spin_lock_irq(&rnp->lock);
        rsp->gp_flags &= ~RCU_GP_FLAG_FQS;
        raw_spin_unlock_irq(&rnp->lock);
    }
    return fqs_state;
}

/*
 * Clean up after the old grace period.
 */
static void rcu_gp_cleanup(struct rcu_state *rsp)
{
    unsigned long gp_duration;
    struct rcu_data *rdp;
    struct rcu_node *rnp = rcu_get_root(rsp);

    raw_spin_lock_irq(&rnp->lock);
    gp_duration = jiffies - rsp->gp_start;
    if (gp_duration > rsp->gp_max)
        rsp->gp_max = gp_duration;

    /*
     * We know the grace period is complete, but to everyone else
     * it appears to still be ongoing.  But it is also the case
     * that to everyone else it looks like there is nothing that
     * they can do to advance the grace period.  It is therefore
     * safe for us to drop the lock in order to mark the grace
     * period as completed in all of the rcu_node structures.
     */
    raw_spin_unlock_irq(&rnp->lock);

    /*
     * Propagate new ->completed value to rcu_node structures so
     * that other CPUs don't have to wait until the start of the next
     * grace period to process their callbacks.  This also avoids
     * some nasty RCU grace-period initialization races by forcing
     * the end of the current grace period to be completely recorded in
     * all of the rcu_node structures before the beginning of the next
     * grace period is recorded in any of the rcu_node structures.
     */
    rcu_for_each_node_breadth_first(rsp, rnp) {
        raw_spin_lock_irq(&rnp->lock);
        rnp->completed = rsp->gpnum;
        raw_spin_unlock_irq(&rnp->lock);
        cond_resched();
    }
    rnp = rcu_get_root(rsp);
    raw_spin_lock_irq(&rnp->lock);

    rsp->completed = rsp->gpnum; /* Declare grace period done. */
    trace_rcu_grace_period(rsp->name, rsp->completed, "end");
    rsp->fqs_state = RCU_GP_IDLE;
    rdp = this_cpu_ptr(rsp->rda);
    if (cpu_needs_another_gp(rsp, rdp))
        rsp->gp_flags = 1;
    raw_spin_unlock_irq(&rnp->lock);
}

/*
 * Body of kthread that handles grace periods.
 */
static int __noreturn rcu_gp_kthread(void *arg)
{
    int fqs_state;
    unsigned long j;
    int ret;
    struct rcu_state *rsp = arg;
    struct rcu_node *rnp = rcu_get_root(rsp);

    for (;;) {

        /* Handle grace-period start. */
        for (;;) {
            wait_event_interruptible(rsp->gp_wq,
                         rsp->gp_flags &
                         RCU_GP_FLAG_INIT);
            if ((rsp->gp_flags & RCU_GP_FLAG_INIT) &&
                rcu_gp_init(rsp))
                break;
            cond_resched();
            flush_signals(current);
        }

        /* Handle quiescent-state forcing. */
        fqs_state = RCU_SAVE_DYNTICK;
        j = jiffies_till_first_fqs;
        if (j > HZ) {
            j = HZ;
            jiffies_till_first_fqs = HZ;
        }
        for (;;) {
            rsp->jiffies_force_qs = jiffies + j;
            ret = wait_event_interruptible_timeout(rsp->gp_wq,
                    (rsp->gp_flags & RCU_GP_FLAG_FQS) ||
                    (!ACCESS_ONCE(rnp->qsmask) &&
                     !rcu_preempt_blocked_readers_cgp(rnp)),
                    j);
            /* If grace period done, leave loop. */
            if (!ACCESS_ONCE(rnp->qsmask) &&
                !rcu_preempt_blocked_readers_cgp(rnp))
                break;
            /* If time for quiescent-state forcing, do it. */
            if (ret == 0 || (rsp->gp_flags & RCU_GP_FLAG_FQS)) {
                fqs_state = rcu_gp_fqs(rsp, fqs_state);
                cond_resched();
            } else {
                /* Deal with stray signal. */
                cond_resched();
                flush_signals(current);
            }
            j = jiffies_till_next_fqs;
            if (j > HZ) {
                j = HZ;
                jiffies_till_next_fqs = HZ;
            } else if (j < 1) {
                j = 1;
                jiffies_till_next_fqs = 1;
            }
        }

        /* Handle grace-period end. */
        rcu_gp_cleanup(rsp);
    }
}

/*
 * Start a new RCU grace period if warranted, re-initializing the hierarchy
 * in preparation for detecting the next grace period.  The caller must hold
 * the root node's ->lock, which is released before return.  Hard irqs must
 * be disabled.
 *
 * Note that it is legal for a dying CPU (which is marked as offline) to
 * invoke this function.  This can happen when the dying CPU reports its
 * quiescent state.
 */
static void
rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
    __releases(rcu_get_root(rsp)->lock)
{
    struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
    struct rcu_node *rnp = rcu_get_root(rsp);

    if (!rsp->gp_kthread ||
        !cpu_needs_another_gp(rsp, rdp)) {
        /*
         * Either we have not yet spawned the grace-period
         * task or this CPU does not need another grace period.
         * Either way, don't start a new grace period.
         */
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
        return;
    }

    rsp->gp_flags = RCU_GP_FLAG_INIT;
    raw_spin_unlock_irqrestore(&rnp->lock, flags);
    wake_up(&rsp->gp_wq);
}

/*
 * Report a full set of quiescent states to the specified rcu_state
 * data structure.  This involves cleaning up after the prior grace
 * period and letting rcu_start_gp() start up the next grace period
 * if one is needed.  Note that the caller must hold rnp->lock, as
 * required by rcu_start_gp(), which will release it.
 */
static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
    __releases(rcu_get_root(rsp)->lock)
{
    WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
    raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
    wake_up(&rsp->gp_wq);  /* Memory barrier implied by wake_up() path. */
}

/*
 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
 * Allows quiescent states for a group of CPUs to be reported at one go
 * to the specified rcu_node structure, though all the CPUs in the group
 * must be represented by the same rcu_node structure (which need not be
 * a leaf rcu_node structure, though it often will be).  That structure's
 * lock must be held upon entry, and it is released before return.
 */
static void
rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
          struct rcu_node *rnp, unsigned long flags)
    __releases(rnp->lock)
{
    struct rcu_node *rnp_c;

    /* Walk up the rcu_node hierarchy. */
    for (;;) {
        if (!(rnp->qsmask & mask)) {

            /* Our bit has already been cleared, so done. */
            raw_spin_unlock_irqrestore(&rnp->lock, flags);
            return;
        }
        rnp->qsmask &= ~mask;
        trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
                         mask, rnp->qsmask, rnp->level,
                         rnp->grplo, rnp->grphi,
                         !!rnp->gp_tasks);
        if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {

            /* Other bits still set at this level, so done. */
            raw_spin_unlock_irqrestore(&rnp->lock, flags);
            return;
        }
        mask = rnp->grpmask;
        if (rnp->parent == NULL) {

            /* No more levels.  Exit loop holding root lock. */

            break;
        }
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
        rnp_c = rnp;
        rnp = rnp->parent;
        raw_spin_lock_irqsave(&rnp->lock, flags);
        WARN_ON_ONCE(rnp_c->qsmask);
    }

    /*
     * Get here if we are the last CPU to pass through a quiescent
     * state for this grace period.  Invoke rcu_report_qs_rsp()
     * to clean up and start the next grace period if one is needed.
     */
    rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
}

/*
 * Record a quiescent state for the specified CPU to that CPU's rcu_data
 * structure.  This must be either called from the specified CPU, or
 * called when the specified CPU is known to be offline (and when it is
 * also known that no other CPU is concurrently trying to help the offline
 * CPU).  The lastcomp argument is used to make sure we are still in the
 * grace period of interest.  We don't want to end the current grace period
 * based on quiescent states detected in an earlier grace period!
 */
static void
rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
{
    unsigned long flags;
    unsigned long mask;
    struct rcu_node *rnp;

    rnp = rdp->mynode;
    raw_spin_lock_irqsave(&rnp->lock, flags);
    if (rdp->passed_quiesce == 0 || rdp->gpnum != rnp->gpnum ||
        rnp->completed == rnp->gpnum) {

        /*
         * The grace period in which this quiescent state was
         * recorded has ended, so don't report it upwards.
         * We will instead need a new quiescent state that lies
         * within the current grace period.
         */
        rdp->passed_quiesce = 0;    /* need qs for new gp. */
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
        return;
    }
    mask = rdp->grpmask;
    if ((rnp->qsmask & mask) == 0) {
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
    } else {
        rdp->qs_pending = 0;

        /*
         * This GP can't end until cpu checks in, so all of our
         * callbacks can be processed during the next GP.
         */
        rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];

        rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
    }
}

/*
 * Check to see if there is a new grace period of which this CPU
 * is not yet aware, and if so, set up local rcu_data state for it.
 * Otherwise, see if this CPU has just passed through its first
 * quiescent state for this grace period, and record that fact if so.
 */
static void
rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
{
    /* If there is now a new grace period, record and return. */
    if (check_for_new_grace_period(rsp, rdp))
        return;

    /*
     * Does this CPU still need to do its part for current grace period?
     * If no, return and let the other CPUs do their part as well.
     */
    if (!rdp->qs_pending)
        return;

    /*
     * Was there a quiescent state since the beginning of the grace
     * period? If no, then exit and wait for the next call.
     */
    if (!rdp->passed_quiesce)
        return;

    /*
     * Tell RCU we are done (but rcu_report_qs_rdp() will be the
     * judge of that).
     */
    rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
}

#ifdef CONFIG_HOTPLUG_CPU

/*
 * Send the specified CPU's RCU callbacks to the orphanage.  The
 * specified CPU must be offline, and the caller must hold the
 * ->onofflock.
 */
static void
rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
              struct rcu_node *rnp, struct rcu_data *rdp)
{
    /*
     * Orphan the callbacks.  First adjust the counts.  This is safe
     * because ->onofflock excludes _rcu_barrier()'s adoption of
     * the callbacks, thus no memory barrier is required.
     */
    if (rdp->nxtlist != NULL) {
        rsp->qlen_lazy += rdp->qlen_lazy;
        rsp->qlen += rdp->qlen;
        rdp->n_cbs_orphaned += rdp->qlen;
        rdp->qlen_lazy = 0;
        ACCESS_ONCE(rdp->qlen) = 0;
    }

    /*
     * Next, move those callbacks still needing a grace period to
     * the orphanage, where some other CPU will pick them up.
     * Some of the callbacks might have gone partway through a grace
     * period, but that is too bad.  They get to start over because we
     * cannot assume that grace periods are synchronized across CPUs.
     * We don't bother updating the ->nxttail[] array yet, instead
     * we just reset the whole thing later on.
     */
    if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
        *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
        rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
        *rdp->nxttail[RCU_DONE_TAIL] = NULL;
    }

    /*
     * Then move the ready-to-invoke callbacks to the orphanage,
     * where some other CPU will pick them up.  These will not be
     * required to pass though another grace period: They are done.
     */
    if (rdp->nxtlist != NULL) {
        *rsp->orphan_donetail = rdp->nxtlist;
        rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
    }

    /* Finally, initialize the rcu_data structure's list to empty.  */
    init_callback_list(rdp);
}

/*
 * Adopt the RCU callbacks from the specified rcu_state structure's
 * orphanage.  The caller must hold the ->onofflock.
 */
static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
{
    int i;
    struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);

    /* Do the accounting first. */
    rdp->qlen_lazy += rsp->qlen_lazy;
    rdp->qlen += rsp->qlen;
    rdp->n_cbs_adopted += rsp->qlen;
    if (rsp->qlen_lazy != rsp->qlen)
        rcu_idle_count_callbacks_posted();
    rsp->qlen_lazy = 0;
    rsp->qlen = 0;

    /*
     * We do not need a memory barrier here because the only way we
     * can get here if there is an rcu_barrier() in flight is if
     * we are the task doing the rcu_barrier().
     */

    /* First adopt the ready-to-invoke callbacks. */
    if (rsp->orphan_donelist != NULL) {
        *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
        *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
        for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
            if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
                rdp->nxttail[i] = rsp->orphan_donetail;
        rsp->orphan_donelist = NULL;
        rsp->orphan_donetail = &rsp->orphan_donelist;
    }

    /* And then adopt the callbacks that still need a grace period. */
    if (rsp->orphan_nxtlist != NULL) {
        *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
        rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
        rsp->orphan_nxtlist = NULL;
        rsp->orphan_nxttail = &rsp->orphan_nxtlist;
    }
}

/*
 * Trace the fact that this CPU is going offline.
 */
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
{
    RCU_TRACE(unsigned long mask);
    RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
    RCU_TRACE(struct rcu_node *rnp = rdp->mynode);

    RCU_TRACE(mask = rdp->grpmask);
    trace_rcu_grace_period(rsp->name,
                   rnp->gpnum + 1 - !!(rnp->qsmask & mask),
                   "cpuofl");
}

/*
 * The CPU has been completely removed, and some other CPU is reporting
 * this fact from process context.  Do the remainder of the cleanup,
 * including orphaning the outgoing CPU's RCU callbacks, and also
 * adopting them.  There can only be one CPU hotplug operation at a time,
 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
 */
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
{
    unsigned long flags;
    unsigned long mask;
    int need_report = 0;
    struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
    struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */

    /* Adjust any no-longer-needed kthreads. */
    rcu_boost_kthread_setaffinity(rnp, -1);

    /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */

    /* Exclude any attempts to start a new grace period. */
    mutex_lock(&rsp->onoff_mutex);
    raw_spin_lock_irqsave(&rsp->onofflock, flags);

    /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
    rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
    rcu_adopt_orphan_cbs(rsp);

    /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
    mask = rdp->grpmask;    /* rnp->grplo is constant. */
    do {
        raw_spin_lock(&rnp->lock);  /* irqs already disabled. */
        rnp->qsmaskinit &= ~mask;
        if (rnp->qsmaskinit != 0) {
            if (rnp != rdp->mynode)
                raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
            break;
        }
        if (rnp == rdp->mynode)
            need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
        else
            raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
        mask = rnp->grpmask;
        rnp = rnp->parent;
    } while (rnp != NULL);

    /*
     * We still hold the leaf rcu_node structure lock here, and
     * irqs are still disabled.  The reason for this subterfuge is
     * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
     * held leads to deadlock.
     */
    raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
    rnp = rdp->mynode;
    if (need_report & RCU_OFL_TASKS_NORM_GP)
        rcu_report_unblock_qs_rnp(rnp, flags);
    else
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
    if (need_report & RCU_OFL_TASKS_EXP_GP)
        rcu_report_exp_rnp(rsp, rnp, true);
    WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
          "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
          cpu, rdp->qlen, rdp->nxtlist);
    init_callback_list(rdp);
    /* Disallow further callbacks on this CPU. */
    rdp->nxttail[RCU_NEXT_TAIL] = NULL;
    mutex_unlock(&rsp->onoff_mutex);
}

#else /* #ifdef CONFIG_HOTPLUG_CPU */

static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
{
}

static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
{
}

#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */

/*
 * Invoke any RCU callbacks that have made it to the end of their grace
 * period.  Thottle as specified by rdp->blimit.
 */
static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
{
    unsigned long flags;
    struct rcu_head *next, *list, **tail;
    long bl, count, count_lazy;
    int i;

    /* If no callbacks are ready, just return.*/
    if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
        trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
        trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
                    need_resched(), is_idle_task(current),
                    rcu_is_callbacks_kthread());
        return;
    }

    /*
     * Extract the list of ready callbacks, disabling to prevent
     * races with call_rcu() from interrupt handlers.
     */
    local_irq_save(flags);
    WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
    bl = rdp->blimit;
    trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
    list = rdp->nxtlist;
    rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
    *rdp->nxttail[RCU_DONE_TAIL] = NULL;
    tail = rdp->nxttail[RCU_DONE_TAIL];
    for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
        if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
            rdp->nxttail[i] = &rdp->nxtlist;
    local_irq_restore(flags);

    /* Invoke callbacks. */
    count = count_lazy = 0;
    while (list) {
        next = list->next;
        prefetch(next);
        debug_rcu_head_unqueue(list);
        if (__rcu_reclaim(rsp->name, list))
            count_lazy++;
        list = next;
        /* Stop only if limit reached and CPU has something to do. */
        if (++count >= bl &&
            (need_resched() ||
             (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
            break;
    }

    local_irq_save(flags);
    trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
                is_idle_task(current),
                rcu_is_callbacks_kthread());

    /* Update count, and requeue any remaining callbacks. */
    if (list != NULL) {
        *tail = rdp->nxtlist;
        rdp->nxtlist = list;
        for (i = 0; i < RCU_NEXT_SIZE; i++)
            if (&rdp->nxtlist == rdp->nxttail[i])
                rdp->nxttail[i] = tail;
            else
                break;
    }
    smp_mb(); /* List handling before counting for rcu_barrier(). */
    rdp->qlen_lazy -= count_lazy;
    ACCESS_ONCE(rdp->qlen) -= count;
    rdp->n_cbs_invoked += count;

    /* Reinstate batch limit if we have worked down the excess. */
    if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
        rdp->blimit = blimit;

    /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
    if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
        rdp->qlen_last_fqs_check = 0;
        rdp->n_force_qs_snap = rsp->n_force_qs;
    } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
        rdp->qlen_last_fqs_check = rdp->qlen;
    WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));

    local_irq_restore(flags);

    /* Re-invoke RCU core processing if there are callbacks remaining. */
    if (cpu_has_callbacks_ready_to_invoke(rdp))
        invoke_rcu_core();
}

/*
 * Check to see if this CPU is in a non-context-switch quiescent state
 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
 * Also schedule RCU core processing.
 *
 * This function must be called from hardirq context.  It is normally
 * invoked from the scheduling-clock interrupt.  If rcu_pending returns
 * false, there is no point in invoking rcu_check_callbacks().
 */
void rcu_check_callbacks(int cpu, int user)
{
    trace_rcu_utilization("Start scheduler-tick");
    increment_cpu_stall_ticks();
    if (user || rcu_is_cpu_rrupt_from_idle()) {

        /*
         * Get here if this CPU took its interrupt from user
         * mode or from the idle loop, and if this is not a
         * nested interrupt.  In this case, the CPU is in
         * a quiescent state, so note it.
         *
         * No memory barrier is required here because both
         * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
         * variables that other CPUs neither access nor modify,
         * at least not while the corresponding CPU is online.
         */

        rcu_sched_qs(cpu);
        rcu_bh_qs(cpu);

    } else if (!in_softirq()) {

        /*
         * Get here if this CPU did not take its interrupt from
         * softirq, in other words, if it is not interrupting
         * a rcu_bh read-side critical section.  This is an _bh
         * critical section, so note it.
         */

        rcu_bh_qs(cpu);
    }
    rcu_preempt_check_callbacks(cpu);
    if (rcu_pending(cpu))
        invoke_rcu_core();
    trace_rcu_utilization("End scheduler-tick");
}

/*
 * Scan the leaf rcu_node structures, processing dyntick state for any that
 * have not yet encountered a quiescent state, using the function specified.
 * Also initiate boosting for any threads blocked on the root rcu_node.
 *
 * The caller must have suppressed start of new grace periods.
 */
static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
{
    unsigned long bit;
    int cpu;
    unsigned long flags;
    unsigned long mask;
    struct rcu_node *rnp;

    rcu_for_each_leaf_node(rsp, rnp) {
        cond_resched();
        mask = 0;
        raw_spin_lock_irqsave(&rnp->lock, flags);
        if (!rcu_gp_in_progress(rsp)) {
            raw_spin_unlock_irqrestore(&rnp->lock, flags);
            return;
        }
        if (rnp->qsmask == 0) {
            rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
            continue;
        }
        cpu = rnp->grplo;
        bit = 1;
        for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
            if ((rnp->qsmask & bit) != 0 &&
                f(per_cpu_ptr(rsp->rda, cpu)))
                mask |= bit;
        }
        if (mask != 0) {

            /* rcu_report_qs_rnp() releases rnp->lock. */
            rcu_report_qs_rnp(mask, rsp, rnp, flags);
            continue;
        }
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
    }
    rnp = rcu_get_root(rsp);
    if (rnp->qsmask == 0) {
        raw_spin_lock_irqsave(&rnp->lock, flags);
        rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
    }
}

/*
 * Force quiescent states on reluctant CPUs, and also detect which
 * CPUs are in dyntick-idle mode.
 */
static void force_quiescent_state(struct rcu_state *rsp)
{
    unsigned long flags;
    bool ret;
    struct rcu_node *rnp;
    struct rcu_node *rnp_old = NULL;

    /* Funnel through hierarchy to reduce memory contention. */
    rnp = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
    for (; rnp != NULL; rnp = rnp->parent) {
        ret = (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
              !raw_spin_trylock(&rnp->fqslock);
        if (rnp_old != NULL)
            raw_spin_unlock(&rnp_old->fqslock);
        if (ret) {
            rsp->n_force_qs_lh++;
            return;
        }
        rnp_old = rnp;
    }
    /* rnp_old == rcu_get_root(rsp), rnp == NULL. */

    /* Reached the root of the rcu_node tree, acquire lock. */
    raw_spin_lock_irqsave(&rnp_old->lock, flags);
    raw_spin_unlock(&rnp_old->fqslock);
    if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
        rsp->n_force_qs_lh++;
        raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
        return;  /* Someone beat us to it. */
    }
    rsp->gp_flags |= RCU_GP_FLAG_FQS;
    raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
    wake_up(&rsp->gp_wq);  /* Memory barrier implied by wake_up() path. */
}

/*
 * This does the RCU core processing work for the specified rcu_state
 * and rcu_data structures.  This may be called only from the CPU to
 * whom the rdp belongs.
 */
static void
__rcu_process_callbacks(struct rcu_state *rsp)
{
    unsigned long flags;
    struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);

    WARN_ON_ONCE(rdp->beenonline == 0);

    /*
     * Advance callbacks in response to end of earlier grace
     * period that some other CPU ended.
     */
    rcu_process_gp_end(rsp, rdp);

    /* Update RCU state based on any recent quiescent states. */
    rcu_check_quiescent_state(rsp, rdp);

    /* Does this CPU require a not-yet-started grace period? */
    if (cpu_needs_another_gp(rsp, rdp)) {
        raw_spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
        rcu_start_gp(rsp, flags);  /* releases above lock */
    }

    /* If there are callbacks ready, invoke them. */
    if (cpu_has_callbacks_ready_to_invoke(rdp))
        invoke_rcu_callbacks(rsp, rdp);
}

/*
 * Do RCU core processing for the current CPU.
 */
static void rcu_process_callbacks(struct softirq_action *unused)
{
    struct rcu_state *rsp;

    if (cpu_is_offline(smp_processor_id()))
        return;
    trace_rcu_utilization("Start RCU core");
    for_each_rcu_flavor(rsp)
        __rcu_process_callbacks(rsp);
    trace_rcu_utilization("End RCU core");
}

/*
 * Schedule RCU callback invocation.  If the specified type of RCU
 * does not support RCU priority boosting, just do a direct call,
 * otherwise wake up the per-CPU kernel kthread.  Note that because we
 * are running on the current CPU with interrupts disabled, the
 * rcu_cpu_kthread_task cannot disappear out from under us.
 */
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
{
    if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
        return;
    if (likely(!rsp->boost)) {
        rcu_do_batch(rsp, rdp);
        return;
    }
    invoke_rcu_callbacks_kthread();
}

static void invoke_rcu_core(void)
{
    raise_softirq(RCU_SOFTIRQ);
}

/*
 * Handle any core-RCU processing required by a call_rcu() invocation.
 */
static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
                struct rcu_head *head, unsigned long flags)
{
    /*
     * If called from an extended quiescent state, invoke the RCU
     * core in order to force a re-evaluation of RCU's idleness.
     */
    if (rcu_is_cpu_idle() && cpu_online(smp_processor_id()))
        invoke_rcu_core();

    /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
    if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
        return;

    /*
     * Force the grace period if too many callbacks or too long waiting.
     * Enforce hysteresis, and don't invoke force_quiescent_state()
     * if some other CPU has recently done so.  Also, don't bother
     * invoking force_quiescent_state() if the newly enqueued callback
     * is the only one waiting for a grace period to complete.
     */
    if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {

        /* Are we ignoring a completed grace period? */
        rcu_process_gp_end(rsp, rdp);
        check_for_new_grace_period(rsp, rdp);

        /* Start a new grace period if one not already started. */
        if (!rcu_gp_in_progress(rsp)) {
            unsigned long nestflag;
            struct rcu_node *rnp_root = rcu_get_root(rsp);

            raw_spin_lock_irqsave(&rnp_root->lock, nestflag);
            rcu_start_gp(rsp, nestflag);  /* rlses rnp_root->lock */
        } else {
            /* Give the grace period a kick. */
            rdp->blimit = LONG_MAX;
            if (rsp->n_force_qs == rdp->n_force_qs_snap &&
                *rdp->nxttail[RCU_DONE_TAIL] != head)
                force_quiescent_state(rsp);
            rdp->n_force_qs_snap = rsp->n_force_qs;
            rdp->qlen_last_fqs_check = rdp->qlen;
        }
    }
}

static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
       struct rcu_state *rsp, bool lazy)
{
    unsigned long flags;
    struct rcu_data *rdp;

    WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
    debug_rcu_head_queue(head);
    head->func = func;
    head->next = NULL;

    /*
     * Opportunistically note grace-period endings and beginnings.
     * Note that we might see a beginning right after we see an
     * end, but never vice versa, since this CPU has to pass through
     * a quiescent state betweentimes.
     */
    local_irq_save(flags);
    rdp = this_cpu_ptr(rsp->rda);

    /* Add the callback to our list. */
    if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL)) {
        /* _call_rcu() is illegal on offline CPU; leak the callback. */
        WARN_ON_ONCE(1);
        local_irq_restore(flags);
        return;
    }
    ACCESS_ONCE(rdp->qlen)++;
    if (lazy)
        rdp->qlen_lazy++;
    else
        rcu_idle_count_callbacks_posted();
    smp_mb();  /* Count before adding callback for rcu_barrier(). */
    *rdp->nxttail[RCU_NEXT_TAIL] = head;
    rdp->nxttail[RCU_NEXT_TAIL] = &head->next;

    if (__is_kfree_rcu_offset((unsigned long)func))
        trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
                     rdp->qlen_lazy, rdp->qlen);
    else
        trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);

    /* Go handle any RCU core processing required. */
    __call_rcu_core(rsp, rdp, head, flags);
    local_irq_restore(flags);
}

/*
 * Queue an RCU-sched callback for invocation after a grace period.
 */
void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
    __call_rcu(head, func, &rcu_sched_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_sched);

/*
 * Queue an RCU callback for invocation after a quicker grace period.
 */
void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
    __call_rcu(head, func, &rcu_bh_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);

/*
 * Because a context switch is a grace period for RCU-sched and RCU-bh,
 * any blocking grace-period wait automatically implies a grace period
 * if there is only one CPU online at any point time during execution
 * of either synchronize_sched() or synchronize_rcu_bh().  It is OK to
 * occasionally incorrectly indicate that there are multiple CPUs online
 * when there was in fact only one the whole time, as this just adds
 * some overhead: RCU still operates correctly.
 */
static inline int rcu_blocking_is_gp(void)
{
    int ret;

    might_sleep();  /* Check for RCU read-side critical section. */
    preempt_disable();
    ret = num_online_cpus() <= 1;
    preempt_enable();
    return ret;
}

void synchronize_sched(void)
{
    rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
               !lock_is_held(&rcu_lock_map) &&
               !lock_is_held(&rcu_sched_lock_map),
               "Illegal synchronize_sched() in RCU-sched read-side critical section");
    if (rcu_blocking_is_gp())
        return;
    wait_rcu_gp(call_rcu_sched);
}
EXPORT_SYMBOL_GPL(synchronize_sched);

void synchronize_rcu_bh(void)
{
    rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
               !lock_is_held(&rcu_lock_map) &&
               !lock_is_held(&rcu_sched_lock_map),
               "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
    if (rcu_blocking_is_gp())
        return;
    wait_rcu_gp(call_rcu_bh);
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);

static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);

static int synchronize_sched_expedited_cpu_stop(void *data)
{
    /*
     * There must be a full memory barrier on each affected CPU
     * between the time that try_stop_cpus() is called and the
     * time that it returns.
     *
     * In the current initial implementation of cpu_stop, the
     * above condition is already met when the control reaches
     * this point and the following smp_mb() is not strictly
     * necessary.  Do smp_mb() anyway for documentation and
     * robustness against future implementation changes.
     */
    smp_mb(); /* See above comment block. */
    return 0;
}

void synchronize_sched_expedited(void)
{
    int firstsnap, s, snap, trycount = 0;

    /* Note that atomic_inc_return() implies full memory barrier. */
    firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
    get_online_cpus();
    WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));

    /*
     * Each pass through the following loop attempts to force a
     * context switch on each CPU.
     */
    while (try_stop_cpus(cpu_online_mask,
                 synchronize_sched_expedited_cpu_stop,
                 NULL) == -EAGAIN) {
        put_online_cpus();

        /* No joy, try again later.  Or just synchronize_sched(). */
        if (trycount++ < 10) {
            udelay(trycount * num_online_cpus());
        } else {
            synchronize_sched();
            return;
        }

        /* Check to see if someone else did our work for us. */
        s = atomic_read(&sync_sched_expedited_done);
        if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) {
            smp_mb(); /* ensure test happens before caller kfree */
            return;
        }

        /*
         * Refetching sync_sched_expedited_started allows later
         * callers to piggyback on our grace period.  We subtract
         * 1 to get the same token that the last incrementer got.
         * We retry after they started, so our grace period works
         * for them, and they started after our first try, so their
         * grace period works for us.
         */
        get_online_cpus();
        snap = atomic_read(&sync_sched_expedited_started);
        smp_mb(); /* ensure read is before try_stop_cpus(). */
    }

    /*
     * Everyone up to our most recent fetch is covered by our grace
     * period.  Update the counter, but only if our work is still
     * relevant -- which it won't be if someone who started later
     * than we did beat us to the punch.
     */
    do {
        s = atomic_read(&sync_sched_expedited_done);
        if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
            smp_mb(); /* ensure test happens before caller kfree */
            break;
        }
    } while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);

    put_online_cpus();
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);

/*
 * Check to see if there is any immediate RCU-related work to be done
 * by the current CPU, for the specified type of RCU, returning 1 if so.
 * The checks are in order of increasing expense: checks that can be
 * carried out against CPU-local state are performed first.  However,
 * we must check for CPU stalls first, else we might not get a chance.
 */
static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
{
    struct rcu_node *rnp = rdp->mynode;

    rdp->n_rcu_pending++;

    /* Check for CPU stalls, if enabled. */
    check_cpu_stall(rsp, rdp);

    /* Is the RCU core waiting for a quiescent state from this CPU? */
    if (rcu_scheduler_fully_active &&
        rdp->qs_pending && !rdp->passed_quiesce) {
        rdp->n_rp_qs_pending++;
    } else if (rdp->qs_pending && rdp->passed_quiesce) {
        rdp->n_rp_report_qs++;
        return 1;
    }

    /* Does this CPU have callbacks ready to invoke? */
    if (cpu_has_callbacks_ready_to_invoke(rdp)) {
        rdp->n_rp_cb_ready++;
        return 1;
    }

    /* Has RCU gone idle with this CPU needing another grace period? */
    if (cpu_needs_another_gp(rsp, rdp)) {
        rdp->n_rp_cpu_needs_gp++;
        return 1;
    }

    /* Has another RCU grace period completed?  */
    if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
        rdp->n_rp_gp_completed++;
        return 1;
    }

    /* Has a new RCU grace period started? */
    if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
        rdp->n_rp_gp_started++;
        return 1;
    }

    /* nothing to do */
    rdp->n_rp_need_nothing++;
    return 0;
}

/*
 * Check to see if there is any immediate RCU-related work to be done
 * by the current CPU, returning 1 if so.  This function is part of the
 * RCU implementation; it is -not- an exported member of the RCU API.
 */
static int rcu_pending(int cpu)
{
    struct rcu_state *rsp;

    for_each_rcu_flavor(rsp)
        if (__rcu_pending(rsp, per_cpu_ptr(rsp->rda, cpu)))
            return 1;
    return 0;
}

/*
 * Check to see if any future RCU-related work will need to be done
 * by the current CPU, even if none need be done immediately, returning
 * 1 if so.
 */
static int rcu_cpu_has_callbacks(int cpu)
{
    struct rcu_state *rsp;

    /* RCU callbacks either ready or pending? */
    for_each_rcu_flavor(rsp)
        if (per_cpu_ptr(rsp->rda, cpu)->nxtlist)
            return 1;
    return 0;
}

/*
 * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
 * the compiler is expected to optimize this away.
 */
static void _rcu_barrier_trace(struct rcu_state *rsp, char *s,
                   int cpu, unsigned long done)
{
    trace_rcu_barrier(rsp->name, s, cpu,
              atomic_read(&rsp->barrier_cpu_count), done);
}

/*
 * RCU callback function for _rcu_barrier().  If we are last, wake
 * up the task executing _rcu_barrier().
 */
static void rcu_barrier_callback(struct rcu_head *rhp)
{
    struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
    struct rcu_state *rsp = rdp->rsp;

    if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
        _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
        complete(&rsp->barrier_completion);
    } else {
        _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
    }
}

/*
 * Called with preemption disabled, and from cross-cpu IRQ context.
 */
static void rcu_barrier_func(void *type)
{
    struct rcu_state *rsp = type;
    struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);

    _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
    atomic_inc(&rsp->barrier_cpu_count);
    rsp->call(&rdp->barrier_head, rcu_barrier_callback);
}

/*
 * Orchestrate the specified type of RCU barrier, waiting for all
 * RCU callbacks of the specified type to complete.
 */
static void _rcu_barrier(struct rcu_state *rsp)
{
    int cpu;
    struct rcu_data *rdp;
    unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done);
    unsigned long snap_done;

    _rcu_barrier_trace(rsp, "Begin", -1, snap);

    /* Take mutex to serialize concurrent rcu_barrier() requests. */
    mutex_lock(&rsp->barrier_mutex);

    /*
     * Ensure that all prior references, including to ->n_barrier_done,
     * are ordered before the _rcu_barrier() machinery.
     */
    smp_mb();  /* See above block comment. */

    /*
     * Recheck ->n_barrier_done to see if others did our work for us.
     * This means checking ->n_barrier_done for an even-to-odd-to-even
     * transition.  The "if" expression below therefore rounds the old
     * value up to the next even number and adds two before comparing.
     */
    snap_done = ACCESS_ONCE(rsp->n_barrier_done);
    _rcu_barrier_trace(rsp, "Check", -1, snap_done);
    if (ULONG_CMP_GE(snap_done, ((snap + 1) & ~0x1) + 2)) {
        _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
        smp_mb(); /* caller's subsequent code after above check. */
        mutex_unlock(&rsp->barrier_mutex);
        return;
    }

    /*
     * Increment ->n_barrier_done to avoid duplicate work.  Use
     * ACCESS_ONCE() to prevent the compiler from speculating
     * the increment to precede the early-exit check.
     */
    ACCESS_ONCE(rsp->n_barrier_done)++;
    WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
    _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
    smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */

    /*
     * Initialize the count to one rather than to zero in order to
     * avoid a too-soon return to zero in case of a short grace period
     * (or preemption of this task).  Exclude CPU-hotplug operations
     * to ensure that no offline CPU has callbacks queued.
     */
    init_completion(&rsp->barrier_completion);
    atomic_set(&rsp->barrier_cpu_count, 1);
    get_online_cpus();

    /*
     * Force each CPU with callbacks to register a new callback.
     * When that callback is invoked, we will know that all of the
     * corresponding CPU's preceding callbacks have been invoked.
     */
    for_each_online_cpu(cpu) {
        rdp = per_cpu_ptr(rsp->rda, cpu);
        if (ACCESS_ONCE(rdp->qlen)) {
            _rcu_barrier_trace(rsp, "OnlineQ", cpu,
                       rsp->n_barrier_done);
            smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
        } else {
            _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
                       rsp->n_barrier_done);
        }
    }
    put_online_cpus();

    /*
     * Now that we have an rcu_barrier_callback() callback on each
     * CPU, and thus each counted, remove the initial count.
     */
    if (atomic_dec_and_test(&rsp->barrier_cpu_count))
        complete(&rsp->barrier_completion);

    /* Increment ->n_barrier_done to prevent duplicate work. */
    smp_mb(); /* Keep increment after above mechanism. */
    ACCESS_ONCE(rsp->n_barrier_done)++;
    WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
    _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
    smp_mb(); /* Keep increment before caller's subsequent code. */

    /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
    wait_for_completion(&rsp->barrier_completion);

    /* Other rcu_barrier() invocations can now safely proceed. */
    mutex_unlock(&rsp->barrier_mutex);
}

void rcu_barrier_bh(void)
{
    _rcu_barrier(&rcu_bh_state);
}
EXPORT_SYMBOL_GPL(rcu_barrier_bh);

void rcu_barrier_sched(void)
{
    _rcu_barrier(&rcu_sched_state);
}
EXPORT_SYMBOL_GPL(rcu_barrier_sched);

/*
 * Do boot-time initialization of a CPU's per-CPU RCU data.
 */
static void __init
rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
{
    unsigned long flags;
    struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
    struct rcu_node *rnp = rcu_get_root(rsp);

    /* Set up local state, ensuring consistent view of global state. */
    raw_spin_lock_irqsave(&rnp->lock, flags);
    rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
    init_callback_list(rdp);
    rdp->qlen_lazy = 0;
    ACCESS_ONCE(rdp->qlen) = 0;
    rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
    WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
    WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
#ifdef CONFIG_RCU_USER_QS
    WARN_ON_ONCE(rdp->dynticks->in_user);
#endif
    rdp->cpu = cpu;
    rdp->rsp = rsp;
    raw_spin_unlock_irqrestore(&rnp->lock, flags);
}

/*
 * Initialize a CPU's per-CPU RCU data.  Note that only one online or
 * offline event can be happening at a given time.  Note also that we
 * can accept some slop in the rsp->completed access due to the fact
 * that this CPU cannot possibly have any RCU callbacks in flight yet.
 */
static void __cpuinit
rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
{
    unsigned long flags;
    unsigned long mask;
    struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
    struct rcu_node *rnp = rcu_get_root(rsp);

    /* Exclude new grace periods. */
    mutex_lock(&rsp->onoff_mutex);

    /* Set up local state, ensuring consistent view of global state. */
    raw_spin_lock_irqsave(&rnp->lock, flags);
    rdp->beenonline = 1;     /* We have now been online. */
    rdp->preemptible = preemptible;
    rdp->qlen_last_fqs_check = 0;
    rdp->n_force_qs_snap = rsp->n_force_qs;
    rdp->blimit = blimit;
    init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
    rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
    atomic_set(&rdp->dynticks->dynticks,
           (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
    rcu_prepare_for_idle_init(cpu);
    raw_spin_unlock(&rnp->lock);        /* irqs remain disabled. */

    /* Add CPU to rcu_node bitmasks. */
    rnp = rdp->mynode;
    mask = rdp->grpmask;
    do {
        /* Exclude any attempts to start a new GP on small systems. */
        raw_spin_lock(&rnp->lock);  /* irqs already disabled. */
        rnp->qsmaskinit |= mask;
        mask = rnp->grpmask;
        if (rnp == rdp->mynode) {
            /*
             * If there is a grace period in progress, we will
             * set up to wait for it next time we run the
             * RCU core code.
             */
            rdp->gpnum = rnp->completed;
            rdp->completed = rnp->completed;
            rdp->passed_quiesce = 0;
            rdp->qs_pending = 0;
            trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuonl");
        }
        raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
        rnp = rnp->parent;
    } while (rnp != NULL && !(rnp->qsmaskinit & mask));
    local_irq_restore(flags);

    mutex_unlock(&rsp->onoff_mutex);
}

static void __cpuinit rcu_prepare_cpu(int cpu)
{
    struct rcu_state *rsp;

    for_each_rcu_flavor(rsp)
        rcu_init_percpu_data(cpu, rsp,
                     strcmp(rsp->name, "rcu_preempt") == 0);
}

/*
 * Handle CPU online/offline notification events.
 */
static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
                    unsigned long action, void *hcpu)
{
    long cpu = (long)hcpu;
    struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
    struct rcu_node *rnp = rdp->mynode;
    struct rcu_state *rsp;

    trace_rcu_utilization("Start CPU hotplug");
    switch (action) {
    case CPU_UP_PREPARE:
    case CPU_UP_PREPARE_FROZEN:
        rcu_prepare_cpu(cpu);
        rcu_prepare_kthreads(cpu);
        break;
    case CPU_ONLINE:
    case CPU_DOWN_FAILED:
        rcu_boost_kthread_setaffinity(rnp, -1);
        break;
    case CPU_DOWN_PREPARE:
        rcu_boost_kthread_setaffinity(rnp, cpu);
        break;
    case CPU_DYING:
    case CPU_DYING_FROZEN:
        /*
         * The whole machine is "stopped" except this CPU, so we can
         * touch any data without introducing corruption. We send the
         * dying CPU's callbacks to an arbitrarily chosen online CPU.
         */
        for_each_rcu_flavor(rsp)
            rcu_cleanup_dying_cpu(rsp);
        rcu_cleanup_after_idle(cpu);
        break;
    case CPU_DEAD:
    case CPU_DEAD_FROZEN:
    case CPU_UP_CANCELED:
    case CPU_UP_CANCELED_FROZEN:
        for_each_rcu_flavor(rsp)
            rcu_cleanup_dead_cpu(cpu, rsp);
        break;
    default:
        break;
    }
    trace_rcu_utilization("End CPU hotplug");
    return NOTIFY_OK;
}

/*
 * Spawn the kthread that handles this RCU flavor's grace periods.
 */
static int __init rcu_spawn_gp_kthread(void)
{
    unsigned long flags;
    struct rcu_node *rnp;
    struct rcu_state *rsp;
    struct task_struct *t;

    for_each_rcu_flavor(rsp) {
        t = kthread_run(rcu_gp_kthread, rsp, rsp->name);
        BUG_ON(IS_ERR(t));
        rnp = rcu_get_root(rsp);
        raw_spin_lock_irqsave(&rnp->lock, flags);
        rsp->gp_kthread = t;
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
    }
    return 0;
}
early_initcall(rcu_spawn_gp_kthread);

/*
 * This function is invoked towards the end of the scheduler's initialization
 * process.  Before this is called, the idle task might contain
 * RCU read-side critical sections (during which time, this idle
 * task is booting the system).  After this function is called, the
 * idle tasks are prohibited from containing RCU read-side critical
 * sections.  This function also enables RCU lockdep checking.
 */
void rcu_scheduler_starting(void)
{
    WARN_ON(num_online_cpus() != 1);
    WARN_ON(nr_context_switches() > 0);
    rcu_scheduler_active = 1;
}

/*
 * Compute the per-level fanout, either using the exact fanout specified
 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
 */
#ifdef CONFIG_RCU_FANOUT_EXACT
static void __init rcu_init_levelspread(struct rcu_state *rsp)
{
    int i;

    for (i = rcu_num_lvls - 1; i > 0; i--)
        rsp->levelspread[i] = CONFIG_RCU_FANOUT;
    rsp->levelspread[0] = rcu_fanout_leaf;
}
#else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
static void __init rcu_init_levelspread(struct rcu_state *rsp)
{
    int ccur;
    int cprv;
    int i;

    cprv = nr_cpu_ids;
    for (i = rcu_num_lvls - 1; i >= 0; i--) {
        ccur = rsp->levelcnt[i];
        rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
        cprv = ccur;
    }
}
#endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */

/*
 * Helper function for rcu_init() that initializes one rcu_state structure.
 */
static void __init rcu_init_one(struct rcu_state *rsp,
        struct rcu_data __percpu *rda)
{
    static char *buf[] = { "rcu_node_0",
                   "rcu_node_1",
                   "rcu_node_2",
                   "rcu_node_3" };  /* Match MAX_RCU_LVLS */
    static char *fqs[] = { "rcu_node_fqs_0",
                   "rcu_node_fqs_1",
                   "rcu_node_fqs_2",
                   "rcu_node_fqs_3" };  /* Match MAX_RCU_LVLS */
    int cpustride = 1;
    int i;
    int j;
    struct rcu_node *rnp;

    BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */

    /* Initialize the level-tracking arrays. */

    for (i = 0; i < rcu_num_lvls; i++)
        rsp->levelcnt[i] = num_rcu_lvl[i];
    for (i = 1; i < rcu_num_lvls; i++)
        rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
    rcu_init_levelspread(rsp);

    /* Initialize the elements themselves, starting from the leaves. */

    for (i = rcu_num_lvls - 1; i >= 0; i--) {
        cpustride *= rsp->levelspread[i];
        rnp = rsp->level[i];
        for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
            raw_spin_lock_init(&rnp->lock);
            lockdep_set_class_and_name(&rnp->lock,
                           &rcu_node_class[i], buf[i]);
            raw_spin_lock_init(&rnp->fqslock);
            lockdep_set_class_and_name(&rnp->fqslock,
                           &rcu_fqs_class[i], fqs[i]);
            rnp->gpnum = rsp->gpnum;
            rnp->completed = rsp->completed;
            rnp->qsmask = 0;
            rnp->qsmaskinit = 0;
            rnp->grplo = j * cpustride;
            rnp->grphi = (j + 1) * cpustride - 1;
            if (rnp->grphi >= NR_CPUS)
                rnp->grphi = NR_CPUS - 1;
            if (i == 0) {
                rnp->grpnum = 0;
                rnp->grpmask = 0;
                rnp->parent = NULL;
            } else {
                rnp->grpnum = j % rsp->levelspread[i - 1];
                rnp->grpmask = 1UL << rnp->grpnum;
                rnp->parent = rsp->level[i - 1] +
                          j / rsp->levelspread[i - 1];
            }
            rnp->level = i;
            INIT_LIST_HEAD(&rnp->blkd_tasks);
        }
    }

    rsp->rda = rda;
    init_waitqueue_head(&rsp->gp_wq);
    rnp = rsp->level[rcu_num_lvls - 1];
    for_each_possible_cpu(i) {
        while (i > rnp->grphi)
            rnp++;
        per_cpu_ptr(rsp->rda, i)->mynode = rnp;
        rcu_boot_init_percpu_data(i, rsp);
    }
    list_add(&rsp->flavors, &rcu_struct_flavors);
}

/*
 * Compute the rcu_node tree geometry from kernel parameters.  This cannot
 * replace the definitions in rcutree.h because those are needed to size
 * the ->node array in the rcu_state structure.
 */
static void __init rcu_init_geometry(void)
{
    int i;
    int j;
    int n = nr_cpu_ids;
    int rcu_capacity[MAX_RCU_LVLS + 1];

    /* If the compile-time values are accurate, just leave. */
    if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
        nr_cpu_ids == NR_CPUS)
        return;

    /*
     * Compute number of nodes that can be handled an rcu_node tree
     * with the given number of levels.  Setting rcu_capacity[0] makes
     * some of the arithmetic easier.
     */
    rcu_capacity[0] = 1;
    rcu_capacity[1] = rcu_fanout_leaf;
    for (i = 2; i <= MAX_RCU_LVLS; i++)
        rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT;

    /*
     * The boot-time rcu_fanout_leaf parameter is only permitted
     * to increase the leaf-level fanout, not decrease it.  Of course,
     * the leaf-level fanout cannot exceed the number of bits in
     * the rcu_node masks.  Finally, the tree must be able to accommodate
     * the configured number of CPUs.  Complain and fall back to the
     * compile-time values if these limits are exceeded.
     */
    if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF ||
        rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
        n > rcu_capacity[MAX_RCU_LVLS]) {
        WARN_ON(1);
        return;
    }

    /* Calculate the number of rcu_nodes at each level of the tree. */
    for (i = 1; i <= MAX_RCU_LVLS; i++)
        if (n <= rcu_capacity[i]) {
            for (j = 0; j <= i; j++)
                num_rcu_lvl[j] =
                    DIV_ROUND_UP(n, rcu_capacity[i - j]);
            rcu_num_lvls = i;
            for (j = i + 1; j <= MAX_RCU_LVLS; j++)
                num_rcu_lvl[j] = 0;
            break;
        }

    /* Calculate the total number of rcu_node structures. */
    rcu_num_nodes = 0;
    for (i = 0; i <= MAX_RCU_LVLS; i++)
        rcu_num_nodes += num_rcu_lvl[i];
    rcu_num_nodes -= n;
}

void __init rcu_init(void)
{
    int cpu;

    rcu_bootup_announce();
    rcu_init_geometry();
    rcu_init_one(&rcu_sched_state, &rcu_sched_data);
    rcu_init_one(&rcu_bh_state, &rcu_bh_data);
    __rcu_init_preempt();
     open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);

    /*
     * We don't need protection against CPU-hotplug here because
     * this is called early in boot, before either interrupts
     * or the scheduler are operational.
     */
    cpu_notifier(rcu_cpu_notify, 0);
    for_each_online_cpu(cpu)
        rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
    check_cpu_stall_init();
}

#include "rcutree_plugin.h"