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41 results

topology.c

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  • rcutree.c 79.27 KiB
    /*
     * 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 <dipankar@in.ibm.com>
     *	    Manfred Spraul <manfred@colorfullife.com>
     *	    Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
     *
     * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
     * 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 "rcutree.h"
    #include <trace/events/rcu.h>
    
    #include "rcu.h"
    
    /* Data structures. */
    
    static struct lock_class_key rcu_node_class[NUM_RCU_LVLS];
    
    #define RCU_STATE_INITIALIZER(structname) { \
    	.level = { &structname##_state.node[0] }, \
    	.levelcnt = { \
    		NUM_RCU_LVL_0,  /* root of hierarchy. */ \
    		NUM_RCU_LVL_1, \
    		NUM_RCU_LVL_2, \
    		NUM_RCU_LVL_3, \
    		NUM_RCU_LVL_4, /* == MAX_RCU_LVLS */ \
    	}, \
    	.fqs_state = RCU_GP_IDLE, \
    	.gpnum = -300, \
    	.completed = -300, \
    	.onofflock = __RAW_SPIN_LOCK_UNLOCKED(&structname##_state.onofflock), \
    	.fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname##_state.fqslock), \
    	.n_force_qs = 0, \
    	.n_force_qs_ngp = 0, \
    	.name = #structname, \
    }
    
    struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched);
    DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
    
    struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh);
    DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
    
    static struct rcu_state *rcu_state;
    
    /*
     * 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(int, rcu_cpu_kthread_cpu);
    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_node_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);
    
    	rdp->passed_quiesce_gpnum = rdp->gpnum;
    	barrier();
    	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);
    
    	rdp->passed_quiesce_gpnum = rdp->gpnum;
    	barrier();
    	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),
    };
    
    static int blimit = 10;		/* Maximum callbacks per rcu_do_batch. */
    static int qhimark = 10000;	/* If this many pending, ignore blimit. */
    static int qlowmark = 100;	/* Once only this many pending, use blimit. */
    
    module_param(blimit, int, 0);
    module_param(qhimark, int, 0);
    module_param(qlowmark, int, 0);
    
    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 void force_quiescent_state(struct rcu_state *rsp, int relaxed);
    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, 0);
    }
    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, 0);
    }
    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];
    }
    
    /*
     * If the specified CPU is offline, tell the caller that it is in
     * a quiescent state.  Otherwise, whack it with a reschedule IPI.
     * Grace periods can end up waiting on an offline CPU when that
     * CPU is in the process of coming online -- it will be added to the
     * rcu_node bitmasks before it actually makes it online.  The same thing
     * can happen while a CPU is in the process of coming online.  Because this
     * race is quite rare, we check for it after detecting that the grace
     * period has been delayed rather than checking each and every CPU
     * each and every time we start a new grace period.
     */
    static int rcu_implicit_offline_qs(struct rcu_data *rdp)
    {
    	/*
    	 * If the CPU is offline for more than a jiffy, it is in a quiescent
    	 * state.  We can trust its state not to change because interrupts
    	 * are disabled.  The reason for the jiffy's worth of slack is to
    	 * handle CPUs initializing on the way up and finding their way
    	 * to the idle loop on the way down.
    	 */
    	if (cpu_is_offline(rdp->cpu) &&
    	    ULONG_CMP_LT(rdp->rsp->gp_start + 2, jiffies)) {
    		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl");
    		rdp->offline_fqs++;
    		return 1;
    	}
    	return 0;
    }
    
    /*
     * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle
     *
     * 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_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
    {
    	trace_rcu_dyntick("Start", oldval, 0);
    	if (!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_ALL);
    		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);
    
    	/*
    	 * The idle task is not permitted to enter the idle loop 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.");
    }
    
    /**
     * rcu_idle_enter - inform RCU that current CPU is entering idle
     *
     * Enter idle mode, in other words, -leave- the mode in which RCU
     * read-side critical sections can occur.  (Though RCU read-side
     * critical sections can occur in irq handlers in idle, a possibility
     * handled by irq_enter() and irq_exit().)
     *
     * We crowbar the ->dynticks_nesting field to zero to allow for
     * the possibility of usermode upcalls having messed up our count
     * of interrupt nesting level during the prior busy period.
     */
    void rcu_idle_enter(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;
    	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_idle_enter_common(rdtp, oldval);
    	local_irq_restore(flags);
    }
    EXPORT_SYMBOL_GPL(rcu_idle_enter);
    
    /**
     * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
     *
     * Exit from an interrupt handler, which might possibly result in entering
     * idle mode, in other words, leaving the mode in which read-side critical
     * sections can occur.
     *
     * This code assumes that the idle loop never does anything that might
     * result in unbalanced calls to irq_enter() and irq_exit().  If your
     * architecture violates this assumption, RCU will give you what you
     * deserve, good and hard.  But very infrequently and irreproducibly.
     *
     * Use things like work queues to work around this limitation.
     *
     * You have been warned.
     */
    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_idle_enter_common(rdtp, oldval);
    	local_irq_restore(flags);
    }
    
    /*
     * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle
     *
     * 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_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
    {
    	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 (!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_ALL);
    		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_idle_exit - inform RCU that current CPU is leaving idle
     *
     * Exit idle mode, in other words, -enter- the mode in which RCU
     * read-side critical sections can occur.
     *
     * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
     * allow for the possibility of usermode upcalls messing up our count
     * of interrupt nesting level during the busy period that is just
     * now starting.
     */
    void rcu_idle_exit(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;
    	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_idle_exit_common(rdtp, oldval);
    	local_irq_restore(flags);
    }
    EXPORT_SYMBOL_GPL(rcu_idle_exit);
    
    /**
     * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
     *
     * Enter an interrupt handler, which might possibly result in exiting
     * idle mode, in other words, entering the mode in which read-side critical
     * sections can occur.
     *
     * Note that the Linux kernel is fully capable of entering an interrupt
     * handler that it never exits, for example when doing upcalls to
     * user mode!  This code assumes that the idle loop never does upcalls to
     * user mode.  If your architecture does do upcalls from the idle loop (or
     * does anything else that results in unbalanced calls to the irq_enter()
     * and irq_exit() functions), RCU will give you what you deserve, good
     * and hard.  But very infrequently and irreproducibly.
     *
     * Use things like work queues to work around this limitation.
     *
     * You have been warned.
     */
    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_idle_exit_common(rdtp, oldval);
    	local_irq_restore(flags);
    }
    
    /**
     * rcu_nmi_enter - inform RCU of entry to NMI context
     *
     * If the CPU was idle with dynamic ticks active, and there is no
     * irq handler running, this updates rdtp->dynticks_nmi to let the
     * RCU grace-period handling know that the CPU is active.
     */
    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));
    }
    
    /**
     * rcu_nmi_exit - inform RCU of exit from NMI context
     *
     * If the CPU was idle with dynamic ticks active, and there is no
     * irq handler running, this updates rdtp->dynticks_nmi to let the
     * RCU grace-period handling know that the CPU is no longer active.
     */
    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);
    }
    
    #ifdef CONFIG_PROVE_RCU
    
    /**
     * rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle
     *
     * If the current CPU is in its idle loop and is neither in an interrupt
     * or NMI handler, return true.
     */
    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_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 /* #ifdef CONFIG_HOTPLUG_CPU */
    
    #endif /* #ifdef CONFIG_PROVE_RCU */
    
    /**
     * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
     *
     * If the current CPU is idle or running at a first-level (not nested)
     * interrupt from idle, return true.  The caller must have at least
     * disabled preemption.
     */
    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.
     */
    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;
    	}
    
    	/* Go check for the CPU being offline. */
    	return rcu_implicit_offline_qs(rdp);
    }
    
    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;
    	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);
    		raw_spin_unlock_irqrestore(&rnp->lock, flags);
    		if (rnp->qsmask == 0)
    			continue;
    		for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
    			if (rnp->qsmask & (1UL << cpu)) {
    				print_cpu_stall_info(rsp, rnp->grplo + cpu);
    				ndetected++;
    			}
    	}
    
    	/*
    	 * 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();
    
    	/* If so configured, complain about tasks blocking the grace period. */
    
    	rcu_print_detail_task_stall(rsp);
    
    	force_quiescent_state(rsp, 0);  /* 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 ((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;
    }
    
    /**
     * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
     *
     * Set the stall-warning timeout way off into the future, thus preventing
     * any RCU CPU stall-warning messages from appearing in the current set of
     * RCU grace periods.
     *
     * The caller must disable hard irqs.
     */
    void rcu_cpu_stall_reset(void)
    {
    	rcu_sched_state.jiffies_stall = jiffies + ULONG_MAX / 2;
    	rcu_bh_state.jiffies_stall = jiffies + ULONG_MAX / 2;
    	rcu_preempt_stall_reset();
    }
    
    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");
    		if (rnp->qsmask & rdp->grpmask) {
    			rdp->qs_pending = 1;
    			rdp->passed_quiesce = 0;
    		} else
    			rdp->qs_pending = 0;
    		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;
    }
    
    /*
     * 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.
    		 */
    		if (ULONG_CMP_LT(rdp->gpnum, rdp->completed))
    			rdp->gpnum = rdp->completed;
    
    		/*
    		 * 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);
    
    	/*
    	 * Because this CPU just now started the new grace period, we know
    	 * that all of its callbacks will be covered by this upcoming grace
    	 * period, even the ones that were registered arbitrarily recently.
    	 * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
    	 *
    	 * Other CPUs cannot be sure exactly when the grace period started.
    	 * Therefore, their recently registered callbacks must pass through
    	 * an additional RCU_NEXT_READY stage, so that they will be handled
    	 * by the next RCU grace period.
    	 */
    	rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
    	rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
    
    	/* Set state so that this CPU will detect the next quiescent state. */
    	__note_new_gpnum(rsp, rnp, rdp);
    }
    
    /*
     * 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 (!rcu_scheduler_fully_active ||
    	    !cpu_needs_another_gp(rsp, rdp)) {
    		/*
    		 * Either the scheduler hasn't yet spawned the first
    		 * non-idle 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;
    	}
    
    	if (rsp->fqs_active) {
    		/*
    		 * This CPU needs a grace period, but force_quiescent_state()
    		 * is running.  Tell it to start one on this CPU's behalf.
    		 */
    		rsp->fqs_need_gp = 1;
    		raw_spin_unlock_irqrestore(&rnp->lock, flags);
    		return;
    	}
    
    	/* Advance to a new grace period and initialize state. */
    	rsp->gpnum++;
    	trace_rcu_grace_period(rsp->name, rsp->gpnum, "start");
    	WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT);
    	rsp->fqs_state = RCU_GP_INIT; /* Hold off force_quiescent_state. */
    	rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
    	record_gp_stall_check_time(rsp);
    	raw_spin_unlock(&rnp->lock);  /* leave irqs disabled. */
    
    	/* Exclude any concurrent CPU-hotplug operations. */
    	raw_spin_lock(&rsp->onofflock);  /* irqs already disabled. */
    
    	/*
    	 * 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.  This
    	 * operation relies on the layout of the hierarchy within the
    	 * rsp->node[] array.  Note that other CPUs will access only
    	 * the leaves of the hierarchy, which still indicate 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.
    	 *
    	 * Note that the grace period cannot complete until we finish
    	 * the initialization process, as there will be at least one
    	 * qsmask bit set in the root node until that time, namely the
    	 * one corresponding to this CPU, due to the fact that we have
    	 * irqs disabled.
    	 */
    	rcu_for_each_node_breadth_first(rsp, rnp) {
    		raw_spin_lock(&rnp->lock);	/* irqs already disabled. */
    		rcu_preempt_check_blocked_tasks(rnp);
    		rnp->qsmask = rnp->qsmaskinit;
    		rnp->gpnum = rsp->gpnum;
    		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(&rnp->lock);	/* irqs remain disabled. */
    	}
    
    	rnp = rcu_get_root(rsp);
    	raw_spin_lock(&rnp->lock);		/* irqs already disabled. */
    	rsp->fqs_state = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
    	raw_spin_unlock(&rnp->lock);		/* irqs remain disabled. */
    	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
    }
    
    /*
     * 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)
    {
    	unsigned long gp_duration;
    	struct rcu_node *rnp = rcu_get_root(rsp);
    	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
    
    	WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
    
    	/*
    	 * Ensure that all grace-period and pre-grace-period activity
    	 * is seen before the assignment to rsp->completed.
    	 */
    	smp_mb(); /* See above block comment. */
    	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.
    	 *
    	 * But if this CPU needs another grace period, it will take
    	 * care of this while initializing the next grace period.
    	 * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL
    	 * because the callbacks have not yet been advanced: Those
    	 * callbacks are waiting on the grace period that just now
    	 * completed.
    	 */
    	if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) {
    		raw_spin_unlock(&rnp->lock);	 /* irqs remain disabled. */
    
    		/*
    		 * 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.
    		 */
    		rcu_for_each_node_breadth_first(rsp, rnp) {
    			raw_spin_lock(&rnp->lock); /* irqs already disabled. */
    			rnp->completed = rsp->gpnum;
    			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
    		}
    		rnp = rcu_get_root(rsp);
    		raw_spin_lock(&rnp->lock); /* irqs already disabled. */
    	}
    
    	rsp->completed = rsp->gpnum;  /* Declare the grace period complete. */
    	trace_rcu_grace_period(rsp->name, rsp->completed, "end");
    	rsp->fqs_state = RCU_GP_IDLE;
    	rcu_start_gp(rsp, flags);  /* releases root node's rnp->lock. */
    }
    
    /*
     * 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, long lastgp)
    {
    	unsigned long flags;
    	unsigned long mask;
    	struct rcu_node *rnp;
    
    	rnp = rdp->mynode;
    	raw_spin_lock_irqsave(&rnp->lock, flags);
    	if (lastgp != 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, rdp->passed_quiesce_gpnum);
    }
    
    #ifdef CONFIG_HOTPLUG_CPU
    
    /*
     * Move a dying CPU's RCU callbacks to online CPU's callback list.
     * Also record a quiescent state for this CPU for the current grace period.
     * Synchronization and interrupt disabling are not required because
     * this function executes in stop_machine() context.  Therefore, cleanup
     * operations that might block must be done later from the CPU_DEAD
     * notifier.
     *
     * Note that the outgoing CPU's bit has already been cleared in the
     * cpu_online_mask.  This allows us to randomly pick a callback
     * destination from the bits set in that mask.
     */
    static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
    {
    	int i;
    	unsigned long mask;
    	int receive_cpu = cpumask_any(cpu_online_mask);
    	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
    	struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu);
    	RCU_TRACE(struct rcu_node *rnp = rdp->mynode); /* For dying CPU. */
    
    	/* First, adjust the counts. */
    	if (rdp->nxtlist != NULL) {
    		receive_rdp->qlen_lazy += rdp->qlen_lazy;
    		receive_rdp->qlen += rdp->qlen;
    		rdp->qlen_lazy = 0;
    		rdp->qlen = 0;
    	}
    
    	/*
    	 * Next, move ready-to-invoke callbacks to be invoked on some
    	 * other CPU.  These will not be required to pass through another
    	 * grace period:  They are done, regardless of CPU.
    	 */
    	if (rdp->nxtlist != NULL &&
    	    rdp->nxttail[RCU_DONE_TAIL] != &rdp->nxtlist) {
    		struct rcu_head *oldhead;
    		struct rcu_head **oldtail;
    		struct rcu_head **newtail;
    
    		oldhead = rdp->nxtlist;
    		oldtail = receive_rdp->nxttail[RCU_DONE_TAIL];
    		rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
    		*rdp->nxttail[RCU_DONE_TAIL] = *oldtail;
    		*receive_rdp->nxttail[RCU_DONE_TAIL] = oldhead;
    		newtail = rdp->nxttail[RCU_DONE_TAIL];
    		for (i = RCU_DONE_TAIL; i < RCU_NEXT_SIZE; i++) {
    			if (receive_rdp->nxttail[i] == oldtail)
    				receive_rdp->nxttail[i] = newtail;
    			if (rdp->nxttail[i] == newtail)
    				rdp->nxttail[i] = &rdp->nxtlist;
    		}
    	}
    
    	/*
    	 * Finally, put the rest of the callbacks at the end of the list.
    	 * The ones that made it partway through get to start over:  We
    	 * cannot assume that grace periods are synchronized across CPUs.
    	 * (We could splice RCU_WAIT_TAIL into RCU_NEXT_READY_TAIL, but
    	 * this does not seem compelling.  Not yet, anyway.)
    	 */
    	if (rdp->nxtlist != NULL) {
    		*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
    		receive_rdp->nxttail[RCU_NEXT_TAIL] =
    				rdp->nxttail[RCU_NEXT_TAIL];
    		receive_rdp->n_cbs_adopted += rdp->qlen;
    		rdp->n_cbs_orphaned += rdp->qlen;
    
    		rdp->nxtlist = NULL;
    		for (i = 0; i < RCU_NEXT_SIZE; i++)
    			rdp->nxttail[i] = &rdp->nxtlist;
    	}
    
    	/*
    	 * Record a quiescent state for the dying CPU.  This is safe
    	 * only because we have already cleared out the callbacks.
    	 * (Otherwise, the RCU core might try to schedule the invocation
    	 * of callbacks on this now-offline CPU, which would be bad.)
    	 */
    	mask = rdp->grpmask;	/* rnp->grplo is constant. */
    	trace_rcu_grace_period(rsp->name,
    			       rnp->gpnum + 1 - !!(rnp->qsmask & mask),
    			       "cpuofl");
    	rcu_report_qs_rdp(smp_processor_id(), rsp, rdp, rsp->gpnum);
    	/* Note that rcu_report_qs_rdp() might call trace_rcu_grace_period(). */
    }
    
    /*
     * The CPU has been completely removed, and some other CPU is reporting
     * this fact from process context.  Do the remainder of the cleanup.
     * 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 rnp. */
    
    	/* Adjust any no-longer-needed kthreads. */
    	rcu_stop_cpu_kthread(cpu);
    	rcu_node_kthread_setaffinity(rnp, -1);
    
    	/* Remove the dying CPU from the bitmasks in the rcu_node hierarchy. */
    
    	/* Exclude any attempts to start a new grace period. */
    	raw_spin_lock_irqsave(&rsp->onofflock, flags);
    
    	/* 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);
    }
    
    #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;
    	int bl, count, count_lazy;
    
    	/* 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 (count = RCU_NEXT_SIZE - 1; count >= 0; count--)
    		if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL])
    			rdp->nxttail[count] = &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. */
    	rdp->qlen_lazy -= count_lazy;
    	rdp->qlen -= count;
    	rdp->n_cbs_invoked += count;
    	if (list != NULL) {
    		*tail = rdp->nxtlist;
    		rdp->nxtlist = list;
    		for (count = 0; count < RCU_NEXT_SIZE; count++)
    			if (&rdp->nxtlist == rdp->nxttail[count])
    				rdp->nxttail[count] = tail;
    			else
    				break;
    	}
    
    	/* 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;
    
    	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) {
    		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, int relaxed)
    {
    	unsigned long flags;
    	struct rcu_node *rnp = rcu_get_root(rsp);
    
    	trace_rcu_utilization("Start fqs");
    	if (!rcu_gp_in_progress(rsp)) {
    		trace_rcu_utilization("End fqs");
    		return;  /* No grace period in progress, nothing to force. */
    	}
    	if (!raw_spin_trylock_irqsave(&rsp->fqslock, flags)) {
    		rsp->n_force_qs_lh++; /* Inexact, can lose counts.  Tough! */
    		trace_rcu_utilization("End fqs");
    		return;	/* Someone else is already on the job. */
    	}
    	if (relaxed && ULONG_CMP_GE(rsp->jiffies_force_qs, jiffies))
    		goto unlock_fqs_ret; /* no emergency and done recently. */
    	rsp->n_force_qs++;
    	raw_spin_lock(&rnp->lock);  /* irqs already disabled */
    	rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
    	if(!rcu_gp_in_progress(rsp)) {
    		rsp->n_force_qs_ngp++;
    		raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
    		goto unlock_fqs_ret;  /* no GP in progress, time updated. */
    	}
    	rsp->fqs_active = 1;
    	switch (rsp->fqs_state) {
    	case RCU_GP_IDLE:
    	case RCU_GP_INIT:
    
    		break; /* grace period idle or initializing, ignore. */
    
    	case RCU_SAVE_DYNTICK:
    		if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
    			break; /* So gcc recognizes the dead code. */
    
    		raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
    
    		/* Record dyntick-idle state. */
    		force_qs_rnp(rsp, dyntick_save_progress_counter);
    		raw_spin_lock(&rnp->lock);  /* irqs already disabled */
    		if (rcu_gp_in_progress(rsp))
    			rsp->fqs_state = RCU_FORCE_QS;
    		break;
    
    	case RCU_FORCE_QS:
    
    		/* Check dyntick-idle state, send IPI to laggarts. */
    		raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
    		force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
    
    		/* Leave state in case more forcing is required. */
    
    		raw_spin_lock(&rnp->lock);  /* irqs already disabled */
    		break;
    	}
    	rsp->fqs_active = 0;
    	if (rsp->fqs_need_gp) {
    		raw_spin_unlock(&rsp->fqslock); /* irqs remain disabled */
    		rsp->fqs_need_gp = 0;
    		rcu_start_gp(rsp, flags); /* releases rnp->lock */
    		trace_rcu_utilization("End fqs");
    		return;
    	}
    	raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
    unlock_fqs_ret:
    	raw_spin_unlock_irqrestore(&rsp->fqslock, flags);
    	trace_rcu_utilization("End fqs");
    }
    
    /*
     * 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, struct rcu_data *rdp)
    {
    	unsigned long flags;
    
    	WARN_ON_ONCE(rdp->beenonline == 0);
    
    	/*
    	 * If an RCU GP has gone long enough, go check for dyntick
    	 * idle CPUs and, if needed, send resched IPIs.
    	 */
    	if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
    		force_quiescent_state(rsp, 1);
    
    	/*
    	 * 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)
    {
    	trace_rcu_utilization("Start RCU core");
    	__rcu_process_callbacks(&rcu_sched_state,
    				&__get_cpu_var(rcu_sched_data));
    	__rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
    	rcu_preempt_process_callbacks();
    	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);
    }
    
    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;
    
    	smp_mb(); /* Ensure RCU update seen before callback registry. */
    
    	/*
    	 * 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. */
    	*rdp->nxttail[RCU_NEXT_TAIL] = head;
    	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
    	rdp->qlen++;
    	if (lazy)
    		rdp->qlen_lazy++;
    
    	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);
    
    	/* If interrupts were disabled, don't dive into RCU core. */
    	if (irqs_disabled_flags(flags)) {
    		local_irq_restore(flags);
    		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, 0);
    			rdp->n_force_qs_snap = rsp->n_force_qs;
    			rdp->qlen_last_fqs_check = rdp->qlen;
    		}
    	} else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
    		force_quiescent_state(rsp, 1);
    	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);
    
    /**
     * synchronize_sched - wait until an rcu-sched grace period has elapsed.
     *
     * Control will return to the caller some time after a full rcu-sched
     * grace period has elapsed, in other words after all currently executing
     * rcu-sched read-side critical sections have completed.   These read-side
     * critical sections are delimited by rcu_read_lock_sched() and
     * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
     * local_irq_disable(), and so on may be used in place of
     * rcu_read_lock_sched().
     *
     * This means that all preempt_disable code sequences, including NMI and
     * hardware-interrupt handlers, in progress on entry will have completed
     * before this primitive returns.  However, this does not guarantee that
     * softirq handlers will have completed, since in some kernels, these
     * handlers can run in process context, and can block.
     *
     * This primitive provides the guarantees made by the (now removed)
     * synchronize_kernel() API.  In contrast, synchronize_rcu() only
     * guarantees that rcu_read_lock() sections will have completed.
     * In "classic RCU", these two guarantees happen to be one and
     * the same, but can differ in realtime RCU implementations.
     */
    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);
    
    /**
     * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
     *
     * Control will return to the caller some time after a full rcu_bh grace
     * period has elapsed, in other words after all currently executing rcu_bh
     * read-side critical sections have completed.  RCU read-side critical
     * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
     * and may be nested.
     */
    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;
    }
    
    /**
     * synchronize_sched_expedited - Brute-force RCU-sched grace period
     *
     * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
     * approach to force the grace period to end quickly.  This consumes
     * significant time on all CPUs and is unfriendly to real-time workloads,
     * so is thus not recommended for any sort of common-case code.  In fact,
     * if you are using synchronize_sched_expedited() in a loop, please
     * restructure your code to batch your updates, and then use a single
     * synchronize_sched() instead.
     *
     * Note that it is illegal to call this function while holding any lock
     * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
     * to call this function from a CPU-hotplug notifier.  Failing to observe
     * these restriction will result in deadlock.
     *
     * This implementation can be thought of as an application of ticket
     * locking to RCU, with sync_sched_expedited_started and
     * sync_sched_expedited_done taking on the roles of the halves
     * of the ticket-lock word.  Each task atomically increments
     * sync_sched_expedited_started upon entry, snapshotting the old value,
     * then attempts to stop all the CPUs.  If this succeeds, then each
     * CPU will have executed a context switch, resulting in an RCU-sched
     * grace period.  We are then done, so we use atomic_cmpxchg() to
     * update sync_sched_expedited_done to match our snapshot -- but
     * only if someone else has not already advanced past our snapshot.
     *
     * On the other hand, if try_stop_cpus() fails, we check the value
     * of sync_sched_expedited_done.  If it has advanced past our
     * initial snapshot, then someone else must have forced a grace period
     * some time after we took our snapshot.  In this case, our work is
     * done for us, and we can simply return.  Otherwise, we try again,
     * but keep our initial snapshot for purposes of checking for someone
     * doing our work for us.
     *
     * If we fail too many times in a row, we fall back to synchronize_sched().
     */
    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) {
    
    		/*
    		 * If force_quiescent_state() coming soon and this CPU
    		 * needs a quiescent state, and this is either RCU-sched
    		 * or RCU-bh, force a local reschedule.
    		 */
    		rdp->n_rp_qs_pending++;
    		if (!rdp->preemptible &&
    		    ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1,
    				 jiffies))
    			set_need_resched();
    	} 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;
    	}
    
    	/* Has an RCU GP gone long enough to send resched IPIs &c? */
    	if (rcu_gp_in_progress(rsp) &&
    	    ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) {
    		rdp->n_rp_need_fqs++;
    		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)
    {
    	return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
    	       __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) ||
    	       rcu_preempt_pending(cpu);
    }
    
    /*
     * 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)
    {
    	/* RCU callbacks either ready or pending? */
    	return per_cpu(rcu_sched_data, cpu).nxtlist ||
    	       per_cpu(rcu_bh_data, cpu).nxtlist ||
    	       rcu_preempt_cpu_has_callbacks(cpu);
    }
    
    static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
    static atomic_t rcu_barrier_cpu_count;
    static DEFINE_MUTEX(rcu_barrier_mutex);
    static struct completion rcu_barrier_completion;
    
    static void rcu_barrier_callback(struct rcu_head *notused)
    {
    	if (atomic_dec_and_test(&rcu_barrier_cpu_count))
    		complete(&rcu_barrier_completion);
    }
    
    /*
     * Called with preemption disabled, and from cross-cpu IRQ context.
     */
    static void rcu_barrier_func(void *type)
    {
    	int cpu = smp_processor_id();
    	struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
    	void (*call_rcu_func)(struct rcu_head *head,
    			      void (*func)(struct rcu_head *head));
    
    	atomic_inc(&rcu_barrier_cpu_count);
    	call_rcu_func = type;
    	call_rcu_func(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,
    			 void (*call_rcu_func)(struct rcu_head *head,
    					       void (*func)(struct rcu_head *head)))
    {
    	BUG_ON(in_interrupt());
    	/* Take mutex to serialize concurrent rcu_barrier() requests. */
    	mutex_lock(&rcu_barrier_mutex);
    	init_completion(&rcu_barrier_completion);
    	/*
    	 * Initialize rcu_barrier_cpu_count to 1, then invoke
    	 * rcu_barrier_func() on each CPU, so that each CPU also has
    	 * incremented rcu_barrier_cpu_count.  Only then is it safe to
    	 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
    	 * might complete its grace period before all of the other CPUs
    	 * did their increment, causing this function to return too
    	 * early.  Note that on_each_cpu() disables irqs, which prevents
    	 * any CPUs from coming online or going offline until each online
    	 * CPU has queued its RCU-barrier callback.
    	 */
    	atomic_set(&rcu_barrier_cpu_count, 1);
    	on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
    	if (atomic_dec_and_test(&rcu_barrier_cpu_count))
    		complete(&rcu_barrier_completion);
    	wait_for_completion(&rcu_barrier_completion);
    	mutex_unlock(&rcu_barrier_mutex);
    }
    
    /**
     * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
     */
    void rcu_barrier_bh(void)
    {
    	_rcu_barrier(&rcu_bh_state, call_rcu_bh);
    }
    EXPORT_SYMBOL_GPL(rcu_barrier_bh);
    
    /**
     * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
     */
    void rcu_barrier_sched(void)
    {
    	_rcu_barrier(&rcu_sched_state, call_rcu_sched);
    }
    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;
    	int i;
    	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);
    	rdp->nxtlist = NULL;
    	for (i = 0; i < RCU_NEXT_SIZE; i++)
    		rdp->nxttail[i] = &rdp->nxtlist;
    	rdp->qlen_lazy = 0;
    	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);
    	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);
    
    	/* 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;
    	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. */
    
    	/*
    	 * A new grace period might start here.  If so, we won't be part
    	 * of it, but that is OK, as we are currently in a quiescent state.
    	 */
    
    	/* Exclude any attempts to start a new GP on large systems. */
    	raw_spin_lock(&rsp->onofflock);		/* irqs already 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;
    			rdp->passed_quiesce_gpnum = rnp->gpnum - 1;
    			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));
    
    	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
    }
    
    static void __cpuinit rcu_prepare_cpu(int cpu)
    {
    	rcu_init_percpu_data(cpu, &rcu_sched_state, 0);
    	rcu_init_percpu_data(cpu, &rcu_bh_state, 0);
    	rcu_preempt_init_percpu_data(cpu);
    }
    
    /*
     * 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;
    
    	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_node_kthread_setaffinity(rnp, -1);
    		rcu_cpu_kthread_setrt(cpu, 1);
    		break;
    	case CPU_DOWN_PREPARE:
    		rcu_node_kthread_setaffinity(rnp, cpu);
    		rcu_cpu_kthread_setrt(cpu, 0);
    		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.
    		 */
    		rcu_cleanup_dying_cpu(&rcu_bh_state);
    		rcu_cleanup_dying_cpu(&rcu_sched_state);
    		rcu_preempt_cleanup_dying_cpu();
    		rcu_cleanup_after_idle(cpu);
    		break;
    	case CPU_DEAD:
    	case CPU_DEAD_FROZEN:
    	case CPU_UP_CANCELED:
    	case CPU_UP_CANCELED_FROZEN:
    		rcu_cleanup_dead_cpu(cpu, &rcu_bh_state);
    		rcu_cleanup_dead_cpu(cpu, &rcu_sched_state);
    		rcu_preempt_cleanup_dead_cpu(cpu);
    		break;
    	default:
    		break;
    	}
    	trace_rcu_utilization("End CPU hotplug");
    	return NOTIFY_OK;
    }
    
    /*
     * 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 = NUM_RCU_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_CPUS;
    	for (i = NUM_RCU_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_level_0",
    			       "rcu_node_level_1",
    			       "rcu_node_level_2",
    			       "rcu_node_level_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 = 1; i < NUM_RCU_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 = NUM_RCU_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]);
    			rnp->gpnum = 0;
    			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;
    	rnp = rsp->level[NUM_RCU_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);
    	}
    }
    
    void __init rcu_init(void)
    {
    	int cpu;
    
    	rcu_bootup_announce();
    	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"