rcutree_plugin.h

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/*
 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
 * Internal non-public definitions that provide either classic
 * or preemptible semantics.
 *
 * 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 Red Hat, 2009
 * Copyright IBM Corporation, 2009
 *
 * Author: Ingo Molnar <[email protected]>
 *     Paul E. McKenney <[email protected]>
 */

#include <linux/delay.h>
#include <linux/oom.h>
#include <linux/smpboot.h>

#define RCU_KTHREAD_PRIO 1

#ifdef CONFIG_RCU_BOOST
#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
#else
#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
#endif

/*
 * Check the RCU kernel configuration parameters and print informative
 * messages about anything out of the ordinary.  If you like #ifdef, you
 * will love this function.
 */
static void __init rcu_bootup_announce_oddness(void)
{
#ifdef CONFIG_RCU_TRACE
    printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
#endif
#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
    printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
           CONFIG_RCU_FANOUT);
#endif
#ifdef CONFIG_RCU_FANOUT_EXACT
    printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
#endif
#ifdef CONFIG_RCU_FAST_NO_HZ
    printk(KERN_INFO
           "\tRCU dyntick-idle grace-period acceleration is enabled.\n");
#endif
#ifdef CONFIG_PROVE_RCU
    printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
#endif
#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
    printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
#endif
#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
    printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
#endif
#if defined(CONFIG_RCU_CPU_STALL_INFO)
    printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
#endif
#if NUM_RCU_LVL_4 != 0
    printk(KERN_INFO "\tFour-level hierarchy is enabled.\n");
#endif
    if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
        printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
    if (nr_cpu_ids != NR_CPUS)
        printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
}

#ifdef CONFIG_TREE_PREEMPT_RCU

struct rcu_state rcu_preempt_state =
    RCU_STATE_INITIALIZER(rcu_preempt, call_rcu);
DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
static struct rcu_state *rcu_state = &rcu_preempt_state;

static int rcu_preempted_readers_exp(struct rcu_node *rnp);

/*
 * Tell them what RCU they are running.
 */
static void __init rcu_bootup_announce(void)
{
    printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
    rcu_bootup_announce_oddness();
}

/*
 * Return the number of RCU-preempt batches processed thus far
 * for debug and statistics.
 */
long rcu_batches_completed_preempt(void)
{
    return rcu_preempt_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);

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

/*
 * Force a quiescent state for preemptible RCU.
 */
void rcu_force_quiescent_state(void)
{
    force_quiescent_state(&rcu_preempt_state);
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);

/*
 * Record a preemptible-RCU quiescent state for the specified CPU.  Note
 * that this just means that the task currently running on the CPU is
 * not in a quiescent state.  There might be any number of tasks blocked
 * while in an RCU read-side critical section.
 *
 * Unlike the other rcu_*_qs() functions, callers to this function
 * must disable irqs in order to protect the assignment to
 * ->rcu_read_unlock_special.
 */
static void rcu_preempt_qs(int cpu)
{
    struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);

    if (rdp->passed_quiesce == 0)
        trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs");
    rdp->passed_quiesce = 1;
    current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
}

/*
 * We have entered the scheduler, and the current task might soon be
 * context-switched away from.  If this task is in an RCU read-side
 * critical section, we will no longer be able to rely on the CPU to
 * record that fact, so we enqueue the task on the blkd_tasks list.
 * The task will dequeue itself when it exits the outermost enclosing
 * RCU read-side critical section.  Therefore, the current grace period
 * cannot be permitted to complete until the blkd_tasks list entries
 * predating the current grace period drain, in other words, until
 * rnp->gp_tasks becomes NULL.
 *
 * Caller must disable preemption.
 */
static void rcu_preempt_note_context_switch(int cpu)
{
    struct task_struct *t = current;
    unsigned long flags;
    struct rcu_data *rdp;
    struct rcu_node *rnp;

    if (t->rcu_read_lock_nesting > 0 &&
        (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {

        /* Possibly blocking in an RCU read-side critical section. */
        rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
        rnp = rdp->mynode;
        raw_spin_lock_irqsave(&rnp->lock, flags);
        t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
        t->rcu_blocked_node = rnp;

        /*
         * If this CPU has already checked in, then this task
         * will hold up the next grace period rather than the
         * current grace period.  Queue the task accordingly.
         * If the task is queued for the current grace period
         * (i.e., this CPU has not yet passed through a quiescent
         * state for the current grace period), then as long
         * as that task remains queued, the current grace period
         * cannot end.  Note that there is some uncertainty as
         * to exactly when the current grace period started.
         * We take a conservative approach, which can result
         * in unnecessarily waiting on tasks that started very
         * slightly after the current grace period began.  C'est
         * la vie!!!
         *
         * But first, note that the current CPU must still be
         * on line!
         */
        WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
        WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
        if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
            list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
            rnp->gp_tasks = &t->rcu_node_entry;
#ifdef CONFIG_RCU_BOOST
            if (rnp->boost_tasks != NULL)
                rnp->boost_tasks = rnp->gp_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
        } else {
            list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
            if (rnp->qsmask & rdp->grpmask)
                rnp->gp_tasks = &t->rcu_node_entry;
        }
        trace_rcu_preempt_task(rdp->rsp->name,
                       t->pid,
                       (rnp->qsmask & rdp->grpmask)
                       ? rnp->gpnum
                       : rnp->gpnum + 1);
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
    } else if (t->rcu_read_lock_nesting < 0 &&
           t->rcu_read_unlock_special) {

        /*
         * Complete exit from RCU read-side critical section on
         * behalf of preempted instance of __rcu_read_unlock().
         */
        rcu_read_unlock_special(t);
    }

    /*
     * Either we were not in an RCU read-side critical section to
     * begin with, or we have now recorded that critical section
     * globally.  Either way, we can now note a quiescent state
     * for this CPU.  Again, if we were in an RCU read-side critical
     * section, and if that critical section was blocking the current
     * grace period, then the fact that the task has been enqueued
     * means that we continue to block the current grace period.
     */
    local_irq_save(flags);
    rcu_preempt_qs(cpu);
    local_irq_restore(flags);
}

/*
 * Check for preempted RCU readers blocking the current grace period
 * for the specified rcu_node structure.  If the caller needs a reliable
 * answer, it must hold the rcu_node's ->lock.
 */
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
{
    return rnp->gp_tasks != NULL;
}

/*
 * Record a quiescent state for all tasks that were previously queued
 * on the specified rcu_node structure and that were blocking the current
 * RCU grace period.  The caller must hold the specified rnp->lock with
 * irqs disabled, and this lock is released upon return, but irqs remain
 * disabled.
 */
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
    __releases(rnp->lock)
{
    unsigned long mask;
    struct rcu_node *rnp_p;

    if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
        return;  /* Still need more quiescent states! */
    }

    rnp_p = rnp->parent;
    if (rnp_p == NULL) {
        /*
         * Either there is only one rcu_node in the tree,
         * or tasks were kicked up to root rcu_node due to
         * CPUs going offline.
         */
        rcu_report_qs_rsp(&rcu_preempt_state, flags);
        return;
    }

    /* Report up the rest of the hierarchy. */
    mask = rnp->grpmask;
    raw_spin_unlock(&rnp->lock);    /* irqs remain disabled. */
    raw_spin_lock(&rnp_p->lock);    /* irqs already disabled. */
    rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
}

/*
 * Advance a ->blkd_tasks-list pointer to the next entry, instead
 * returning NULL if at the end of the list.
 */
static struct list_head *rcu_next_node_entry(struct task_struct *t,
                         struct rcu_node *rnp)
{
    struct list_head *np;

    np = t->rcu_node_entry.next;
    if (np == &rnp->blkd_tasks)
        np = NULL;
    return np;
}

/*
 * Handle special cases during rcu_read_unlock(), such as needing to
 * notify RCU core processing or task having blocked during the RCU
 * read-side critical section.
 */
void rcu_read_unlock_special(struct task_struct *t)
{
    int empty;
    int empty_exp;
    int empty_exp_now;
    unsigned long flags;
    struct list_head *np;
#ifdef CONFIG_RCU_BOOST
    struct rt_mutex *rbmp = NULL;
#endif /* #ifdef CONFIG_RCU_BOOST */
    struct rcu_node *rnp;
    int special;

    /* NMI handlers cannot block and cannot safely manipulate state. */
    if (in_nmi())
        return;

    local_irq_save(flags);

    /*
     * If RCU core is waiting for this CPU to exit critical section,
     * let it know that we have done so.
     */
    special = t->rcu_read_unlock_special;
    if (special & RCU_READ_UNLOCK_NEED_QS) {
        rcu_preempt_qs(smp_processor_id());
    }

    /* Hardware IRQ handlers cannot block. */
    if (in_irq() || in_serving_softirq()) {
        local_irq_restore(flags);
        return;
    }

    /* Clean up if blocked during RCU read-side critical section. */
    if (special & RCU_READ_UNLOCK_BLOCKED) {
        t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;

        /*
         * Remove this task from the list it blocked on.  The
         * task can migrate while we acquire the lock, but at
         * most one time.  So at most two passes through loop.
         */
        for (;;) {
            rnp = t->rcu_blocked_node;
            raw_spin_lock(&rnp->lock);  /* irqs already disabled. */
            if (rnp == t->rcu_blocked_node)
                break;
            raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
        }
        empty = !rcu_preempt_blocked_readers_cgp(rnp);
        empty_exp = !rcu_preempted_readers_exp(rnp);
        smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
        np = rcu_next_node_entry(t, rnp);
        list_del_init(&t->rcu_node_entry);
        t->rcu_blocked_node = NULL;
        trace_rcu_unlock_preempted_task("rcu_preempt",
                        rnp->gpnum, t->pid);
        if (&t->rcu_node_entry == rnp->gp_tasks)
            rnp->gp_tasks = np;
        if (&t->rcu_node_entry == rnp->exp_tasks)
            rnp->exp_tasks = np;
#ifdef CONFIG_RCU_BOOST
        if (&t->rcu_node_entry == rnp->boost_tasks)
            rnp->boost_tasks = np;
        /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
        if (t->rcu_boost_mutex) {
            rbmp = t->rcu_boost_mutex;
            t->rcu_boost_mutex = NULL;
        }
#endif /* #ifdef CONFIG_RCU_BOOST */

        /*
         * If this was the last task on the current list, and if
         * we aren't waiting on any CPUs, report the quiescent state.
         * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
         * so we must take a snapshot of the expedited state.
         */
        empty_exp_now = !rcu_preempted_readers_exp(rnp);
        if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
            trace_rcu_quiescent_state_report("preempt_rcu",
                             rnp->gpnum,
                             0, rnp->qsmask,
                             rnp->level,
                             rnp->grplo,
                             rnp->grphi,
                             !!rnp->gp_tasks);
            rcu_report_unblock_qs_rnp(rnp, flags);
        } else {
            raw_spin_unlock_irqrestore(&rnp->lock, flags);
        }

#ifdef CONFIG_RCU_BOOST
        /* Unboost if we were boosted. */
        if (rbmp)
            rt_mutex_unlock(rbmp);
#endif /* #ifdef CONFIG_RCU_BOOST */

        /*
         * If this was the last task on the expedited lists,
         * then we need to report up the rcu_node hierarchy.
         */
        if (!empty_exp && empty_exp_now)
            rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
    } else {
        local_irq_restore(flags);
    }
}

#ifdef CONFIG_RCU_CPU_STALL_VERBOSE

/*
 * Dump detailed information for all tasks blocking the current RCU
 * grace period on the specified rcu_node structure.
 */
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
    unsigned long flags;
    struct task_struct *t;

    raw_spin_lock_irqsave(&rnp->lock, flags);
    if (!rcu_preempt_blocked_readers_cgp(rnp)) {
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
        return;
    }
    t = list_entry(rnp->gp_tasks,
               struct task_struct, rcu_node_entry);
    list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
        sched_show_task(t);
    raw_spin_unlock_irqrestore(&rnp->lock, flags);
}

/*
 * Dump detailed information for all tasks blocking the current RCU
 * grace period.
 */
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
    struct rcu_node *rnp = rcu_get_root(rsp);

    rcu_print_detail_task_stall_rnp(rnp);
    rcu_for_each_leaf_node(rsp, rnp)
        rcu_print_detail_task_stall_rnp(rnp);
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */

static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */

#ifdef CONFIG_RCU_CPU_STALL_INFO

static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
    printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
           rnp->level, rnp->grplo, rnp->grphi);
}

static void rcu_print_task_stall_end(void)
{
    printk(KERN_CONT "\n");
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
}

static void rcu_print_task_stall_end(void)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */

/*
 * Scan the current list of tasks blocked within RCU read-side critical
 * sections, printing out the tid of each.
 */
static int rcu_print_task_stall(struct rcu_node *rnp)
{
    struct task_struct *t;
    int ndetected = 0;

    if (!rcu_preempt_blocked_readers_cgp(rnp))
        return 0;
    rcu_print_task_stall_begin(rnp);
    t = list_entry(rnp->gp_tasks,
               struct task_struct, rcu_node_entry);
    list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
        printk(KERN_CONT " P%d", t->pid);
        ndetected++;
    }
    rcu_print_task_stall_end();
    return ndetected;
}

/*
 * Check that the list of blocked tasks for the newly completed grace
 * period is in fact empty.  It is a serious bug to complete a grace
 * period that still has RCU readers blocked!  This function must be
 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
 * must be held by the caller.
 *
 * Also, if there are blocked tasks on the list, they automatically
 * block the newly created grace period, so set up ->gp_tasks accordingly.
 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
    WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
    if (!list_empty(&rnp->blkd_tasks))
        rnp->gp_tasks = rnp->blkd_tasks.next;
    WARN_ON_ONCE(rnp->qsmask);
}

#ifdef CONFIG_HOTPLUG_CPU

/*
 * Handle tasklist migration for case in which all CPUs covered by the
 * specified rcu_node have gone offline.  Move them up to the root
 * rcu_node.  The reason for not just moving them to the immediate
 * parent is to remove the need for rcu_read_unlock_special() to
 * make more than two attempts to acquire the target rcu_node's lock.
 * Returns true if there were tasks blocking the current RCU grace
 * period.
 *
 * Returns 1 if there was previously a task blocking the current grace
 * period on the specified rcu_node structure.
 *
 * The caller must hold rnp->lock with irqs disabled.
 */
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
                     struct rcu_node *rnp,
                     struct rcu_data *rdp)
{
    struct list_head *lp;
    struct list_head *lp_root;
    int retval = 0;
    struct rcu_node *rnp_root = rcu_get_root(rsp);
    struct task_struct *t;

    if (rnp == rnp_root) {
        WARN_ONCE(1, "Last CPU thought to be offlined?");
        return 0;  /* Shouldn't happen: at least one CPU online. */
    }

    /* If we are on an internal node, complain bitterly. */
    WARN_ON_ONCE(rnp != rdp->mynode);

    /*
     * Move tasks up to root rcu_node.  Don't try to get fancy for
     * this corner-case operation -- just put this node's tasks
     * at the head of the root node's list, and update the root node's
     * ->gp_tasks and ->exp_tasks pointers to those of this node's,
     * if non-NULL.  This might result in waiting for more tasks than
     * absolutely necessary, but this is a good performance/complexity
     * tradeoff.
     */
    if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
        retval |= RCU_OFL_TASKS_NORM_GP;
    if (rcu_preempted_readers_exp(rnp))
        retval |= RCU_OFL_TASKS_EXP_GP;
    lp = &rnp->blkd_tasks;
    lp_root = &rnp_root->blkd_tasks;
    while (!list_empty(lp)) {
        t = list_entry(lp->next, typeof(*t), rcu_node_entry);
        raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
        list_del(&t->rcu_node_entry);
        t->rcu_blocked_node = rnp_root;
        list_add(&t->rcu_node_entry, lp_root);
        if (&t->rcu_node_entry == rnp->gp_tasks)
            rnp_root->gp_tasks = rnp->gp_tasks;
        if (&t->rcu_node_entry == rnp->exp_tasks)
            rnp_root->exp_tasks = rnp->exp_tasks;
#ifdef CONFIG_RCU_BOOST
        if (&t->rcu_node_entry == rnp->boost_tasks)
            rnp_root->boost_tasks = rnp->boost_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
        raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
    }

    rnp->gp_tasks = NULL;
    rnp->exp_tasks = NULL;
#ifdef CONFIG_RCU_BOOST
    rnp->boost_tasks = NULL;
    /*
     * In case root is being boosted and leaf was not.  Make sure
     * that we boost the tasks blocking the current grace period
     * in this case.
     */
    raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
    if (rnp_root->boost_tasks != NULL &&
        rnp_root->boost_tasks != rnp_root->gp_tasks &&
        rnp_root->boost_tasks != rnp_root->exp_tasks)
        rnp_root->boost_tasks = rnp_root->gp_tasks;
    raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
#endif /* #ifdef CONFIG_RCU_BOOST */

    return retval;
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

/*
 * Check for a quiescent state from the current CPU.  When a task blocks,
 * the task is recorded in the corresponding CPU's rcu_node structure,
 * which is checked elsewhere.
 *
 * Caller must disable hard irqs.
 */
static void rcu_preempt_check_callbacks(int cpu)
{
    struct task_struct *t = current;

    if (t->rcu_read_lock_nesting == 0) {
        rcu_preempt_qs(cpu);
        return;
    }
    if (t->rcu_read_lock_nesting > 0 &&
        per_cpu(rcu_preempt_data, cpu).qs_pending)
        t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
}

#ifdef CONFIG_RCU_BOOST

static void rcu_preempt_do_callbacks(void)
{
    rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
}

#endif /* #ifdef CONFIG_RCU_BOOST */

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

/*
 * Queue an RCU callback for lazy invocation after a grace period.
 * This will likely be later named something like "call_rcu_lazy()",
 * but this change will require some way of tagging the lazy RCU
 * callbacks in the list of pending callbacks.  Until then, this
 * function may only be called from __kfree_rcu().
 */
void kfree_call_rcu(struct rcu_head *head,
            void (*func)(struct rcu_head *rcu))
{
    __call_rcu(head, func, &rcu_preempt_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);

void synchronize_rcu(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() in RCU read-side critical section");
    if (!rcu_scheduler_active)
        return;
    wait_rcu_gp(call_rcu);
}
EXPORT_SYMBOL_GPL(synchronize_rcu);

static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
static unsigned long sync_rcu_preempt_exp_count;
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);

/*
 * Return non-zero if there are any tasks in RCU read-side critical
 * sections blocking the current preemptible-RCU expedited grace period.
 * If there is no preemptible-RCU expedited grace period currently in
 * progress, returns zero unconditionally.
 */
static int rcu_preempted_readers_exp(struct rcu_node *rnp)
{
    return rnp->exp_tasks != NULL;
}

/*
 * return non-zero if there is no RCU expedited grace period in progress
 * for the specified rcu_node structure, in other words, if all CPUs and
 * tasks covered by the specified rcu_node structure have done their bit
 * for the current expedited grace period.  Works only for preemptible
 * RCU -- other RCU implementation use other means.
 *
 * Caller must hold sync_rcu_preempt_exp_mutex.
 */
static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
{
    return !rcu_preempted_readers_exp(rnp) &&
           ACCESS_ONCE(rnp->expmask) == 0;
}

/*
 * Report the exit from RCU read-side critical section for the last task
 * that queued itself during or before the current expedited preemptible-RCU
 * grace period.  This event is reported either to the rcu_node structure on
 * which the task was queued or to one of that rcu_node structure's ancestors,
 * recursively up the tree.  (Calm down, calm down, we do the recursion
 * iteratively!)
 *
 * Most callers will set the "wake" flag, but the task initiating the
 * expedited grace period need not wake itself.
 *
 * Caller must hold sync_rcu_preempt_exp_mutex.
 */
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
                   bool wake)
{
    unsigned long flags;
    unsigned long mask;

    raw_spin_lock_irqsave(&rnp->lock, flags);
    for (;;) {
        if (!sync_rcu_preempt_exp_done(rnp)) {
            raw_spin_unlock_irqrestore(&rnp->lock, flags);
            break;
        }
        if (rnp->parent == NULL) {
            raw_spin_unlock_irqrestore(&rnp->lock, flags);
            if (wake)
                wake_up(&sync_rcu_preempt_exp_wq);
            break;
        }
        mask = rnp->grpmask;
        raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
        rnp = rnp->parent;
        raw_spin_lock(&rnp->lock); /* irqs already disabled */
        rnp->expmask &= ~mask;
    }
}

/*
 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
 * grace period for the specified rcu_node structure.  If there are no such
 * tasks, report it up the rcu_node hierarchy.
 *
 * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
 */
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
    unsigned long flags;
    int must_wait = 0;

    raw_spin_lock_irqsave(&rnp->lock, flags);
    if (list_empty(&rnp->blkd_tasks)) {
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
    } else {
        rnp->exp_tasks = rnp->blkd_tasks.next;
        rcu_initiate_boost(rnp, flags);  /* releases rnp->lock */
        must_wait = 1;
    }
    if (!must_wait)
        rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
}

void synchronize_rcu_expedited(void)
{
    unsigned long flags;
    struct rcu_node *rnp;
    struct rcu_state *rsp = &rcu_preempt_state;
    unsigned long snap;
    int trycount = 0;

    smp_mb(); /* Caller's modifications seen first by other CPUs. */
    snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
    smp_mb(); /* Above access cannot bleed into critical section. */

    /*
     * Block CPU-hotplug operations.  This means that any CPU-hotplug
     * operation that finds an rcu_node structure with tasks in the
     * process of being boosted will know that all tasks blocking
     * this expedited grace period will already be in the process of
     * being boosted.  This simplifies the process of moving tasks
     * from leaf to root rcu_node structures.
     */
    get_online_cpus();

    /*
     * Acquire lock, falling back to synchronize_rcu() if too many
     * lock-acquisition failures.  Of course, if someone does the
     * expedited grace period for us, just leave.
     */
    while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
        if (ULONG_CMP_LT(snap,
            ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
            put_online_cpus();
            goto mb_ret; /* Others did our work for us. */
        }
        if (trycount++ < 10) {
            udelay(trycount * num_online_cpus());
        } else {
            put_online_cpus();
            synchronize_rcu();
            return;
        }
    }
    if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
        put_online_cpus();
        goto unlock_mb_ret; /* Others did our work for us. */
    }

    /* force all RCU readers onto ->blkd_tasks lists. */
    synchronize_sched_expedited();

    /* Initialize ->expmask for all non-leaf rcu_node structures. */
    rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
        raw_spin_lock_irqsave(&rnp->lock, flags);
        rnp->expmask = rnp->qsmaskinit;
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
    }

    /* Snapshot current state of ->blkd_tasks lists. */
    rcu_for_each_leaf_node(rsp, rnp)
        sync_rcu_preempt_exp_init(rsp, rnp);
    if (NUM_RCU_NODES > 1)
        sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));

    put_online_cpus();

    /* Wait for snapshotted ->blkd_tasks lists to drain. */
    rnp = rcu_get_root(rsp);
    wait_event(sync_rcu_preempt_exp_wq,
           sync_rcu_preempt_exp_done(rnp));

    /* Clean up and exit. */
    smp_mb(); /* ensure expedited GP seen before counter increment. */
    ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
unlock_mb_ret:
    mutex_unlock(&sync_rcu_preempt_exp_mutex);
mb_ret:
    smp_mb(); /* ensure subsequent action seen after grace period. */
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

void rcu_barrier(void)
{
    _rcu_barrier(&rcu_preempt_state);
}
EXPORT_SYMBOL_GPL(rcu_barrier);

/*
 * Initialize preemptible RCU's state structures.
 */
static void __init __rcu_init_preempt(void)
{
    rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
}

#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */

static struct rcu_state *rcu_state = &rcu_sched_state;

/*
 * Tell them what RCU they are running.
 */
static void __init rcu_bootup_announce(void)
{
    printk(KERN_INFO "Hierarchical RCU implementation.\n");
    rcu_bootup_announce_oddness();
}

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

/*
 * Force a quiescent state for RCU, which, because there is no preemptible
 * RCU, becomes the same as rcu-sched.
 */
void rcu_force_quiescent_state(void)
{
    rcu_sched_force_quiescent_state();
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);

/*
 * Because preemptible RCU does not exist, we never have to check for
 * CPUs being in quiescent states.
 */
static void rcu_preempt_note_context_switch(int cpu)
{
}

/*
 * Because preemptible RCU does not exist, there are never any preempted
 * RCU readers.
 */
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
{
    return 0;
}

#ifdef CONFIG_HOTPLUG_CPU

/* Because preemptible RCU does not exist, no quieting of tasks. */
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
{
    raw_spin_unlock_irqrestore(&rnp->lock, flags);
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

/*
 * Because preemptible RCU does not exist, we never have to check for
 * tasks blocked within RCU read-side critical sections.
 */
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}

/*
 * Because preemptible RCU does not exist, we never have to check for
 * tasks blocked within RCU read-side critical sections.
 */
static int rcu_print_task_stall(struct rcu_node *rnp)
{
    return 0;
}

/*
 * Because there is no preemptible RCU, there can be no readers blocked,
 * so there is no need to check for blocked tasks.  So check only for
 * bogus qsmask values.
 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
    WARN_ON_ONCE(rnp->qsmask);
}

#ifdef CONFIG_HOTPLUG_CPU

/*
 * Because preemptible RCU does not exist, it never needs to migrate
 * tasks that were blocked within RCU read-side critical sections, and
 * such non-existent tasks cannot possibly have been blocking the current
 * grace period.
 */
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
                     struct rcu_node *rnp,
                     struct rcu_data *rdp)
{
    return 0;
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

/*
 * Because preemptible RCU does not exist, it never has any callbacks
 * to check.
 */
static void rcu_preempt_check_callbacks(int cpu)
{
}

/*
 * Queue an RCU callback for lazy invocation after a grace period.
 * This will likely be later named something like "call_rcu_lazy()",
 * but this change will require some way of tagging the lazy RCU
 * callbacks in the list of pending callbacks.  Until then, this
 * function may only be called from __kfree_rcu().
 *
 * Because there is no preemptible RCU, we use RCU-sched instead.
 */
void kfree_call_rcu(struct rcu_head *head,
            void (*func)(struct rcu_head *rcu))
{
    __call_rcu(head, func, &rcu_sched_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);

/*
 * Wait for an rcu-preempt grace period, but make it happen quickly.
 * But because preemptible RCU does not exist, map to rcu-sched.
 */
void synchronize_rcu_expedited(void)
{
    synchronize_sched_expedited();
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

#ifdef CONFIG_HOTPLUG_CPU

/*
 * Because preemptible RCU does not exist, there is never any need to
 * report on tasks preempted in RCU read-side critical sections during
 * expedited RCU grace periods.
 */
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
                   bool wake)
{
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

/*
 * Because preemptible RCU does not exist, rcu_barrier() is just
 * another name for rcu_barrier_sched().
 */
void rcu_barrier(void)
{
    rcu_barrier_sched();
}
EXPORT_SYMBOL_GPL(rcu_barrier);

/*
 * Because preemptible RCU does not exist, it need not be initialized.
 */
static void __init __rcu_init_preempt(void)
{
}

#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */

#ifdef CONFIG_RCU_BOOST

#include "rtmutex_common.h"

#ifdef CONFIG_RCU_TRACE

static void rcu_initiate_boost_trace(struct rcu_node *rnp)
{
    if (list_empty(&rnp->blkd_tasks))
        rnp->n_balk_blkd_tasks++;
    else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
        rnp->n_balk_exp_gp_tasks++;
    else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
        rnp->n_balk_boost_tasks++;
    else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
        rnp->n_balk_notblocked++;
    else if (rnp->gp_tasks != NULL &&
         ULONG_CMP_LT(jiffies, rnp->boost_time))
        rnp->n_balk_notyet++;
    else
        rnp->n_balk_nos++;
}

#else /* #ifdef CONFIG_RCU_TRACE */

static void rcu_initiate_boost_trace(struct rcu_node *rnp)
{
}

#endif /* #else #ifdef CONFIG_RCU_TRACE */

static void rcu_wake_cond(struct task_struct *t, int status)
{
    /*
     * If the thread is yielding, only wake it when this
     * is invoked from idle
     */
    if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
        wake_up_process(t);
}

/*
 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
 * or ->boost_tasks, advancing the pointer to the next task in the
 * ->blkd_tasks list.
 *
 * Note that irqs must be enabled: boosting the task can block.
 * Returns 1 if there are more tasks needing to be boosted.
 */
static int rcu_boost(struct rcu_node *rnp)
{
    unsigned long flags;
    struct rt_mutex mtx;
    struct task_struct *t;
    struct list_head *tb;

    if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
        return 0;  /* Nothing left to boost. */

    raw_spin_lock_irqsave(&rnp->lock, flags);

    /*
     * Recheck under the lock: all tasks in need of boosting
     * might exit their RCU read-side critical sections on their own.
     */
    if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
        return 0;
    }

    /*
     * Preferentially boost tasks blocking expedited grace periods.
     * This cannot starve the normal grace periods because a second
     * expedited grace period must boost all blocked tasks, including
     * those blocking the pre-existing normal grace period.
     */
    if (rnp->exp_tasks != NULL) {
        tb = rnp->exp_tasks;
        rnp->n_exp_boosts++;
    } else {
        tb = rnp->boost_tasks;
        rnp->n_normal_boosts++;
    }
    rnp->n_tasks_boosted++;

    /*
     * We boost task t by manufacturing an rt_mutex that appears to
     * be held by task t.  We leave a pointer to that rt_mutex where
     * task t can find it, and task t will release the mutex when it
     * exits its outermost RCU read-side critical section.  Then
     * simply acquiring this artificial rt_mutex will boost task
     * t's priority.  (Thanks to tglx for suggesting this approach!)
     *
     * Note that task t must acquire rnp->lock to remove itself from
     * the ->blkd_tasks list, which it will do from exit() if from
     * nowhere else.  We therefore are guaranteed that task t will
     * stay around at least until we drop rnp->lock.  Note that
     * rnp->lock also resolves races between our priority boosting
     * and task t's exiting its outermost RCU read-side critical
     * section.
     */
    t = container_of(tb, struct task_struct, rcu_node_entry);
    rt_mutex_init_proxy_locked(&mtx, t);
    t->rcu_boost_mutex = &mtx;
    raw_spin_unlock_irqrestore(&rnp->lock, flags);
    rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */
    rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */

    return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
           ACCESS_ONCE(rnp->boost_tasks) != NULL;
}

/*
 * Priority-boosting kthread.  One per leaf rcu_node and one for the
 * root rcu_node.
 */
static int rcu_boost_kthread(void *arg)
{
    struct rcu_node *rnp = (struct rcu_node *)arg;
    int spincnt = 0;
    int more2boost;

    trace_rcu_utilization("Start boost kthread@init");
    for (;;) {
        rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
        trace_rcu_utilization("End boost kthread@rcu_wait");
        rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
        trace_rcu_utilization("Start boost kthread@rcu_wait");
        rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
        more2boost = rcu_boost(rnp);
        if (more2boost)
            spincnt++;
        else
            spincnt = 0;
        if (spincnt > 10) {
            rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
            trace_rcu_utilization("End boost kthread@rcu_yield");
            schedule_timeout_interruptible(2);
            trace_rcu_utilization("Start boost kthread@rcu_yield");
            spincnt = 0;
        }
    }
    /* NOTREACHED */
    trace_rcu_utilization("End boost kthread@notreached");
    return 0;
}

/*
 * Check to see if it is time to start boosting RCU readers that are
 * blocking the current grace period, and, if so, tell the per-rcu_node
 * kthread to start boosting them.  If there is an expedited grace
 * period in progress, it is always time to boost.
 *
 * The caller must hold rnp->lock, which this function releases.
 * The ->boost_kthread_task is immortal, so we don't need to worry
 * about it going away.
 */
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
{
    struct task_struct *t;

    if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
        rnp->n_balk_exp_gp_tasks++;
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
        return;
    }
    if (rnp->exp_tasks != NULL ||
        (rnp->gp_tasks != NULL &&
         rnp->boost_tasks == NULL &&
         rnp->qsmask == 0 &&
         ULONG_CMP_GE(jiffies, rnp->boost_time))) {
        if (rnp->exp_tasks == NULL)
            rnp->boost_tasks = rnp->gp_tasks;
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
        t = rnp->boost_kthread_task;
        if (t)
            rcu_wake_cond(t, rnp->boost_kthread_status);
    } else {
        rcu_initiate_boost_trace(rnp);
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
    }
}

/*
 * Wake up the per-CPU kthread to invoke RCU callbacks.
 */
static void invoke_rcu_callbacks_kthread(void)
{
    unsigned long flags;

    local_irq_save(flags);
    __this_cpu_write(rcu_cpu_has_work, 1);
    if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
        current != __this_cpu_read(rcu_cpu_kthread_task)) {
        rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
                  __this_cpu_read(rcu_cpu_kthread_status));
    }
    local_irq_restore(flags);
}

/*
 * Is the current CPU running the RCU-callbacks kthread?
 * Caller must have preemption disabled.
 */
static bool rcu_is_callbacks_kthread(void)
{
    return __get_cpu_var(rcu_cpu_kthread_task) == current;
}

#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)

/*
 * Do priority-boost accounting for the start of a new grace period.
 */
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
    rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
}

/*
 * Create an RCU-boost kthread for the specified node if one does not
 * already exist.  We only create this kthread for preemptible RCU.
 * Returns zero if all is well, a negated errno otherwise.
 */
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
                         struct rcu_node *rnp)
{
    int rnp_index = rnp - &rsp->node[0];
    unsigned long flags;
    struct sched_param sp;
    struct task_struct *t;

    if (&rcu_preempt_state != rsp)
        return 0;

    if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
        return 0;

    rsp->boost = 1;
    if (rnp->boost_kthread_task != NULL)
        return 0;
    t = kthread_create(rcu_boost_kthread, (void *)rnp,
               "rcub/%d", rnp_index);
    if (IS_ERR(t))
        return PTR_ERR(t);
    raw_spin_lock_irqsave(&rnp->lock, flags);
    rnp->boost_kthread_task = t;
    raw_spin_unlock_irqrestore(&rnp->lock, flags);
    sp.sched_priority = RCU_BOOST_PRIO;
    sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
    wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
    return 0;
}

static void rcu_kthread_do_work(void)
{
    rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
    rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
    rcu_preempt_do_callbacks();
}

static void rcu_cpu_kthread_setup(unsigned int cpu)
{
    struct sched_param sp;

    sp.sched_priority = RCU_KTHREAD_PRIO;
    sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
}

static void rcu_cpu_kthread_park(unsigned int cpu)
{
    per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
}

static int rcu_cpu_kthread_should_run(unsigned int cpu)
{
    return __get_cpu_var(rcu_cpu_has_work);
}

/*
 * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
 * RCU softirq used in flavors and configurations of RCU that do not
 * support RCU priority boosting.
 */
static void rcu_cpu_kthread(unsigned int cpu)
{
    unsigned int *statusp = &__get_cpu_var(rcu_cpu_kthread_status);
    char work, *workp = &__get_cpu_var(rcu_cpu_has_work);
    int spincnt;

    for (spincnt = 0; spincnt < 10; spincnt++) {
        trace_rcu_utilization("Start CPU kthread@rcu_wait");
        local_bh_disable();
        *statusp = RCU_KTHREAD_RUNNING;
        this_cpu_inc(rcu_cpu_kthread_loops);
        local_irq_disable();
        work = *workp;
        *workp = 0;
        local_irq_enable();
        if (work)
            rcu_kthread_do_work();
        local_bh_enable();
        if (*workp == 0) {
            trace_rcu_utilization("End CPU kthread@rcu_wait");
            *statusp = RCU_KTHREAD_WAITING;
            return;
        }
    }
    *statusp = RCU_KTHREAD_YIELDING;
    trace_rcu_utilization("Start CPU kthread@rcu_yield");
    schedule_timeout_interruptible(2);
    trace_rcu_utilization("End CPU kthread@rcu_yield");
    *statusp = RCU_KTHREAD_WAITING;
}

/*
 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
 * served by the rcu_node in question.  The CPU hotplug lock is still
 * held, so the value of rnp->qsmaskinit will be stable.
 *
 * We don't include outgoingcpu in the affinity set, use -1 if there is
 * no outgoing CPU.  If there are no CPUs left in the affinity set,
 * this function allows the kthread to execute on any CPU.
 */
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
    struct task_struct *t = rnp->boost_kthread_task;
    unsigned long mask = rnp->qsmaskinit;
    cpumask_var_t cm;
    int cpu;

    if (!t)
        return;
    if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
        return;
    for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
        if ((mask & 0x1) && cpu != outgoingcpu)
            cpumask_set_cpu(cpu, cm);
    if (cpumask_weight(cm) == 0) {
        cpumask_setall(cm);
        for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
            cpumask_clear_cpu(cpu, cm);
        WARN_ON_ONCE(cpumask_weight(cm) == 0);
    }
    set_cpus_allowed_ptr(t, cm);
    free_cpumask_var(cm);
}

static struct smp_hotplug_thread rcu_cpu_thread_spec = {
    .store          = &rcu_cpu_kthread_task,
    .thread_should_run  = rcu_cpu_kthread_should_run,
    .thread_fn      = rcu_cpu_kthread,
    .thread_comm        = "rcuc/%u",
    .setup          = rcu_cpu_kthread_setup,
    .park           = rcu_cpu_kthread_park,
};

/*
 * Spawn all kthreads -- called as soon as the scheduler is running.
 */
static int __init rcu_spawn_kthreads(void)
{
    struct rcu_node *rnp;
    int cpu;

    rcu_scheduler_fully_active = 1;
    for_each_possible_cpu(cpu)
        per_cpu(rcu_cpu_has_work, cpu) = 0;
    BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
    rnp = rcu_get_root(rcu_state);
    (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
    if (NUM_RCU_NODES > 1) {
        rcu_for_each_leaf_node(rcu_state, rnp)
            (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
    }
    return 0;
}
early_initcall(rcu_spawn_kthreads);

static void __cpuinit rcu_prepare_kthreads(int cpu)
{
    struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
    struct rcu_node *rnp = rdp->mynode;

    /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
    if (rcu_scheduler_fully_active)
        (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
}

#else /* #ifdef CONFIG_RCU_BOOST */

static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
{
    raw_spin_unlock_irqrestore(&rnp->lock, flags);
}

static void invoke_rcu_callbacks_kthread(void)
{
    WARN_ON_ONCE(1);
}

static bool rcu_is_callbacks_kthread(void)
{
    return false;
}

static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}

static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
}

static int __init rcu_scheduler_really_started(void)
{
    rcu_scheduler_fully_active = 1;
    return 0;
}
early_initcall(rcu_scheduler_really_started);

static void __cpuinit rcu_prepare_kthreads(int cpu)
{
}

#endif /* #else #ifdef CONFIG_RCU_BOOST */

#if !defined(CONFIG_RCU_FAST_NO_HZ)

/*
 * 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.  This function is part of the RCU implementation; it is -not-
 * an exported member of the RCU API.
 *
 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
 * any flavor of RCU.
 */
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
{
    *delta_jiffies = ULONG_MAX;
    return rcu_cpu_has_callbacks(cpu);
}

/*
 * Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it.
 */
static void rcu_prepare_for_idle_init(int cpu)
{
}

/*
 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
 * after it.
 */
static void rcu_cleanup_after_idle(int cpu)
{
}

/*
 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
 * is nothing.
 */
static void rcu_prepare_for_idle(int cpu)
{
}

/*
 * Don't bother keeping a running count of the number of RCU callbacks
 * posted because CONFIG_RCU_FAST_NO_HZ=n.
 */
static void rcu_idle_count_callbacks_posted(void)
{
}

#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */

/*
 * This code is invoked when a CPU goes idle, at which point we want
 * to have the CPU do everything required for RCU so that it can enter
 * the energy-efficient dyntick-idle mode.  This is handled by a
 * state machine implemented by rcu_prepare_for_idle() below.
 *
 * The following three proprocessor symbols control this state machine:
 *
 * RCU_IDLE_FLUSHES gives the maximum number of times that we will attempt
 *  to satisfy RCU.  Beyond this point, it is better to incur a periodic
 *  scheduling-clock interrupt than to loop through the state machine
 *  at full power.
 * RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are
 *  optional if RCU does not need anything immediately from this
 *  CPU, even if this CPU still has RCU callbacks queued.  The first
 *  times through the state machine are mandatory: we need to give
 *  the state machine a chance to communicate a quiescent state
 *  to the RCU core.
 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
 *  to sleep in dyntick-idle mode with RCU callbacks pending.  This
 *  is sized to be roughly one RCU grace period.  Those energy-efficiency
 *  benchmarkers who might otherwise be tempted to set this to a large
 *  number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
 *  system.  And if you are -that- concerned about energy efficiency,
 *  just power the system down and be done with it!
 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
 *  permitted to sleep in dyntick-idle mode with only lazy RCU
 *  callbacks pending.  Setting this too high can OOM your system.
 *
 * The values below work well in practice.  If future workloads require
 * adjustment, they can be converted into kernel config parameters, though
 * making the state machine smarter might be a better option.
 */
#define RCU_IDLE_FLUSHES 5      /* Number of dyntick-idle tries. */
#define RCU_IDLE_OPT_FLUSHES 3      /* Optional dyntick-idle tries. */
#define RCU_IDLE_GP_DELAY 4     /* Roughly one grace period. */
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */

extern int tick_nohz_enabled;

/*
 * Does the specified flavor of RCU have non-lazy callbacks pending on
 * the specified CPU?  Both RCU flavor and CPU are specified by the
 * rcu_data structure.
 */
static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
{
    return rdp->qlen != rdp->qlen_lazy;
}

#ifdef CONFIG_TREE_PREEMPT_RCU

/*
 * Are there non-lazy RCU-preempt callbacks?  (There cannot be if there
 * is no RCU-preempt in the kernel.)
 */
static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
    struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);

    return __rcu_cpu_has_nonlazy_callbacks(rdp);
}

#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */

static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
    return 0;
}

#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */

/*
 * Does any flavor of RCU have non-lazy callbacks on the specified CPU?
 */
static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
{
    return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
           __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
           rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
}

/*
 * Allow the CPU to enter dyntick-idle mode if either: (1) There are no
 * callbacks on this CPU, (2) this CPU has not yet attempted to enter
 * dyntick-idle mode, or (3) this CPU is in the process of attempting to
 * enter dyntick-idle mode.  Otherwise, if we have recently tried and failed
 * to enter dyntick-idle mode, we refuse to try to enter it.  After all,
 * it is better to incur scheduling-clock interrupts than to spin
 * continuously for the same time duration!
 *
 * The delta_jiffies argument is used to store the time when RCU is
 * going to need the CPU again if it still has callbacks.  The reason
 * for this is that rcu_prepare_for_idle() might need to post a timer,
 * but if so, it will do so after tick_nohz_stop_sched_tick() has set
 * the wakeup time for this CPU.  This means that RCU's timer can be
 * delayed until the wakeup time, which defeats the purpose of posting
 * a timer.
 */
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
{
    struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

    /* Flag a new idle sojourn to the idle-entry state machine. */
    rdtp->idle_first_pass = 1;
    /* If no callbacks, RCU doesn't need the CPU. */
    if (!rcu_cpu_has_callbacks(cpu)) {
        *delta_jiffies = ULONG_MAX;
        return 0;
    }
    if (rdtp->dyntick_holdoff == jiffies) {
        /* RCU recently tried and failed, so don't try again. */
        *delta_jiffies = 1;
        return 1;
    }
    /* Set up for the possibility that RCU will post a timer. */
    if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
        *delta_jiffies = round_up(RCU_IDLE_GP_DELAY + jiffies,
                      RCU_IDLE_GP_DELAY) - jiffies;
    } else {
        *delta_jiffies = jiffies + RCU_IDLE_LAZY_GP_DELAY;
        *delta_jiffies = round_jiffies(*delta_jiffies) - jiffies;
    }
    return 0;
}

/*
 * Handler for smp_call_function_single().  The only point of this
 * handler is to wake the CPU up, so the handler does only tracing.
 */
void rcu_idle_demigrate(void *unused)
{
    trace_rcu_prep_idle("Demigrate");
}

/*
 * Timer handler used to force CPU to start pushing its remaining RCU
 * callbacks in the case where it entered dyntick-idle mode with callbacks
 * pending.  The hander doesn't really need to do anything because the
 * real work is done upon re-entry to idle, or by the next scheduling-clock
 * interrupt should idle not be re-entered.
 *
 * One special case: the timer gets migrated without awakening the CPU
 * on which the timer was scheduled on.  In this case, we must wake up
 * that CPU.  We do so with smp_call_function_single().
 */
static void rcu_idle_gp_timer_func(unsigned long cpu_in)
{
    int cpu = (int)cpu_in;

    trace_rcu_prep_idle("Timer");
    if (cpu != smp_processor_id())
        smp_call_function_single(cpu, rcu_idle_demigrate, NULL, 0);
    else
        WARN_ON_ONCE(1); /* Getting here can hang the system... */
}

/*
 * Initialize the timer used to pull CPUs out of dyntick-idle mode.
 */
static void rcu_prepare_for_idle_init(int cpu)
{
    struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

    rdtp->dyntick_holdoff = jiffies - 1;
    setup_timer(&rdtp->idle_gp_timer, rcu_idle_gp_timer_func, cpu);
    rdtp->idle_gp_timer_expires = jiffies - 1;
    rdtp->idle_first_pass = 1;
}

/*
 * Clean up for exit from idle.  Because we are exiting from idle, there
 * is no longer any point to ->idle_gp_timer, so cancel it.  This will
 * do nothing if this timer is not active, so just cancel it unconditionally.
 */
static void rcu_cleanup_after_idle(int cpu)
{
    struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

    del_timer(&rdtp->idle_gp_timer);
    trace_rcu_prep_idle("Cleanup after idle");
    rdtp->tick_nohz_enabled_snap = ACCESS_ONCE(tick_nohz_enabled);
}

/*
 * Check to see if any RCU-related work can be done by the current CPU,
 * and if so, schedule a softirq to get it done.  This function is part
 * of the RCU implementation; it is -not- an exported member of the RCU API.
 *
 * The idea is for the current CPU to clear out all work required by the
 * RCU core for the current grace period, so that this CPU can be permitted
 * to enter dyntick-idle mode.  In some cases, it will need to be awakened
 * at the end of the grace period by whatever CPU ends the grace period.
 * This allows CPUs to go dyntick-idle more quickly, and to reduce the
 * number of wakeups by a modest integer factor.
 *
 * Because it is not legal to invoke rcu_process_callbacks() with irqs
 * disabled, we do one pass of force_quiescent_state(), then do a
 * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
 * later.  The ->dyntick_drain field controls the sequencing.
 *
 * The caller must have disabled interrupts.
 */
static void rcu_prepare_for_idle(int cpu)
{
    struct timer_list *tp;
    struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
    int tne;

    /* Handle nohz enablement switches conservatively. */
    tne = ACCESS_ONCE(tick_nohz_enabled);
    if (tne != rdtp->tick_nohz_enabled_snap) {
        if (rcu_cpu_has_callbacks(cpu))
            invoke_rcu_core(); /* force nohz to see update. */
        rdtp->tick_nohz_enabled_snap = tne;
        return;
    }
    if (!tne)
        return;

    /* Adaptive-tick mode, where usermode execution is idle to RCU. */
    if (!is_idle_task(current)) {
        rdtp->dyntick_holdoff = jiffies - 1;
        if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
            trace_rcu_prep_idle("User dyntick with callbacks");
            rdtp->idle_gp_timer_expires =
                round_up(jiffies + RCU_IDLE_GP_DELAY,
                     RCU_IDLE_GP_DELAY);
        } else if (rcu_cpu_has_callbacks(cpu)) {
            rdtp->idle_gp_timer_expires =
                round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
            trace_rcu_prep_idle("User dyntick with lazy callbacks");
        } else {
            return;
        }
        tp = &rdtp->idle_gp_timer;
        mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
        return;
    }

    /*
     * If this is an idle re-entry, for example, due to use of
     * RCU_NONIDLE() or the new idle-loop tracing API within the idle
     * loop, then don't take any state-machine actions, unless the
     * momentary exit from idle queued additional non-lazy callbacks.
     * Instead, repost the ->idle_gp_timer if this CPU has callbacks
     * pending.
     */
    if (!rdtp->idle_first_pass &&
        (rdtp->nonlazy_posted == rdtp->nonlazy_posted_snap)) {
        if (rcu_cpu_has_callbacks(cpu)) {
            tp = &rdtp->idle_gp_timer;
            mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
        }
        return;
    }
    rdtp->idle_first_pass = 0;
    rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted - 1;

    /*
     * If there are no callbacks on this CPU, enter dyntick-idle mode.
     * Also reset state to avoid prejudicing later attempts.
     */
    if (!rcu_cpu_has_callbacks(cpu)) {
        rdtp->dyntick_holdoff = jiffies - 1;
        rdtp->dyntick_drain = 0;
        trace_rcu_prep_idle("No callbacks");
        return;
    }

    /*
     * If in holdoff mode, just return.  We will presumably have
     * refrained from disabling the scheduling-clock tick.
     */
    if (rdtp->dyntick_holdoff == jiffies) {
        trace_rcu_prep_idle("In holdoff");
        return;
    }

    /* Check and update the ->dyntick_drain sequencing. */
    if (rdtp->dyntick_drain <= 0) {
        /* First time through, initialize the counter. */
        rdtp->dyntick_drain = RCU_IDLE_FLUSHES;
    } else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES &&
           !rcu_pending(cpu) &&
           !local_softirq_pending()) {
        /* Can we go dyntick-idle despite still having callbacks? */
        rdtp->dyntick_drain = 0;
        rdtp->dyntick_holdoff = jiffies;
        if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
            trace_rcu_prep_idle("Dyntick with callbacks");
            rdtp->idle_gp_timer_expires =
                round_up(jiffies + RCU_IDLE_GP_DELAY,
                     RCU_IDLE_GP_DELAY);
        } else {
            rdtp->idle_gp_timer_expires =
                round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
            trace_rcu_prep_idle("Dyntick with lazy callbacks");
        }
        tp = &rdtp->idle_gp_timer;
        mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
        rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
        return; /* Nothing more to do immediately. */
    } else if (--(rdtp->dyntick_drain) <= 0) {
        /* We have hit the limit, so time to give up. */
        rdtp->dyntick_holdoff = jiffies;
        trace_rcu_prep_idle("Begin holdoff");
        invoke_rcu_core();  /* Force the CPU out of dyntick-idle. */
        return;
    }

    /*
     * Do one step of pushing the remaining RCU callbacks through
     * the RCU core state machine.
     */
#ifdef CONFIG_TREE_PREEMPT_RCU
    if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
        rcu_preempt_qs(cpu);
        force_quiescent_state(&rcu_preempt_state);
    }
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
    if (per_cpu(rcu_sched_data, cpu).nxtlist) {
        rcu_sched_qs(cpu);
        force_quiescent_state(&rcu_sched_state);
    }
    if (per_cpu(rcu_bh_data, cpu).nxtlist) {
        rcu_bh_qs(cpu);
        force_quiescent_state(&rcu_bh_state);
    }

    /*
     * If RCU callbacks are still pending, RCU still needs this CPU.
     * So try forcing the callbacks through the grace period.
     */
    if (rcu_cpu_has_callbacks(cpu)) {
        trace_rcu_prep_idle("More callbacks");
        invoke_rcu_core();
    } else {
        trace_rcu_prep_idle("Callbacks drained");
    }
}

/*
 * Keep a running count of the number of non-lazy callbacks posted
 * on this CPU.  This running counter (which is never decremented) allows
 * rcu_prepare_for_idle() to detect when something out of the idle loop
 * posts a callback, even if an equal number of callbacks are invoked.
 * Of course, callbacks should only be posted from within a trace event
 * designed to be called from idle or from within RCU_NONIDLE().
 */
static void rcu_idle_count_callbacks_posted(void)
{
    __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
}

/*
 * Data for flushing lazy RCU callbacks at OOM time.
 */
static atomic_t oom_callback_count;
static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);

/*
 * RCU OOM callback -- decrement the outstanding count and deliver the
 * wake-up if we are the last one.
 */
static void rcu_oom_callback(struct rcu_head *rhp)
{
    if (atomic_dec_and_test(&oom_callback_count))
        wake_up(&oom_callback_wq);
}

/*
 * Post an rcu_oom_notify callback on the current CPU if it has at
 * least one lazy callback.  This will unnecessarily post callbacks
 * to CPUs that already have a non-lazy callback at the end of their
 * callback list, but this is an infrequent operation, so accept some
 * extra overhead to keep things simple.
 */
static void rcu_oom_notify_cpu(void *unused)
{
    struct rcu_state *rsp;
    struct rcu_data *rdp;

    for_each_rcu_flavor(rsp) {
        rdp = __this_cpu_ptr(rsp->rda);
        if (rdp->qlen_lazy != 0) {
            atomic_inc(&oom_callback_count);
            rsp->call(&rdp->oom_head, rcu_oom_callback);
        }
    }
}

/*
 * If low on memory, ensure that each CPU has a non-lazy callback.
 * This will wake up CPUs that have only lazy callbacks, in turn
 * ensuring that they free up the corresponding memory in a timely manner.
 * Because an uncertain amount of memory will be freed in some uncertain
 * timeframe, we do not claim to have freed anything.
 */
static int rcu_oom_notify(struct notifier_block *self,
              unsigned long notused, void *nfreed)
{
    int cpu;

    /* Wait for callbacks from earlier instance to complete. */
    wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);

    /*
     * Prevent premature wakeup: ensure that all increments happen
     * before there is a chance of the counter reaching zero.
     */
    atomic_set(&oom_callback_count, 1);

    get_online_cpus();
    for_each_online_cpu(cpu) {
        smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
        cond_resched();
    }
    put_online_cpus();

    /* Unconditionally decrement: no need to wake ourselves up. */
    atomic_dec(&oom_callback_count);

    return NOTIFY_OK;
}

static struct notifier_block rcu_oom_nb = {
    .notifier_call = rcu_oom_notify
};

static int __init rcu_register_oom_notifier(void)
{
    register_oom_notifier(&rcu_oom_nb);
    return 0;
}
early_initcall(rcu_register_oom_notifier);

#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */

#ifdef CONFIG_RCU_CPU_STALL_INFO

#ifdef CONFIG_RCU_FAST_NO_HZ

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
    struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
    struct timer_list *tltp = &rdtp->idle_gp_timer;
    char c;

    c = rdtp->dyntick_holdoff == jiffies ? 'H' : '.';
    if (timer_pending(tltp))
        sprintf(cp, "drain=%d %c timer=%lu",
            rdtp->dyntick_drain, c, tltp->expires - jiffies);
    else
        sprintf(cp, "drain=%d %c timer not pending",
            rdtp->dyntick_drain, c);
}

#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
    *cp = '\0';
}

#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */

/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
    printk(KERN_CONT "\n");
}

/*
 * Print out diagnostic information for the specified stalled CPU.
 *
 * If the specified CPU is aware of the current RCU grace period
 * (flavor specified by rsp), then print the number of scheduling
 * clock interrupts the CPU has taken during the time that it has
 * been aware.  Otherwise, print the number of RCU grace periods
 * that this CPU is ignorant of, for example, "1" if the CPU was
 * aware of the previous grace period.
 *
 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
 */
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
    char fast_no_hz[72];
    struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
    struct rcu_dynticks *rdtp = rdp->dynticks;
    char *ticks_title;
    unsigned long ticks_value;

    if (rsp->gpnum == rdp->gpnum) {
        ticks_title = "ticks this GP";
        ticks_value = rdp->ticks_this_gp;
    } else {
        ticks_title = "GPs behind";
        ticks_value = rsp->gpnum - rdp->gpnum;
    }
    print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
    printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n",
           cpu, ticks_value, ticks_title,
           atomic_read(&rdtp->dynticks) & 0xfff,
           rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
           fast_no_hz);
}

/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
    printk(KERN_ERR "\t");
}

/* Zero ->ticks_this_gp for all flavors of RCU. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
    rdp->ticks_this_gp = 0;
}

/* Increment ->ticks_this_gp for all flavors of RCU. */
static void increment_cpu_stall_ticks(void)
{
    struct rcu_state *rsp;

    for_each_rcu_flavor(rsp)
        __this_cpu_ptr(rsp->rda)->ticks_this_gp++;
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void print_cpu_stall_info_begin(void)
{
    printk(KERN_CONT " {");
}

static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
    printk(KERN_CONT " %d", cpu);
}

static void print_cpu_stall_info_end(void)
{
    printk(KERN_CONT "} ");
}

static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
}

static void increment_cpu_stall_ticks(void)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */