rcutree.c 44.3 KB
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/*
 * 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 <asm/atomic.h>
#include <linux/bitops.h>
#include <linux/module.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>

#ifdef CONFIG_DEBUG_LOCK_ALLOC
static struct lock_class_key rcu_lock_key;
struct lockdep_map rcu_lock_map =
	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
EXPORT_SYMBOL_GPL(rcu_lock_map);
#endif

/* Data structures. */

#define RCU_STATE_INITIALIZER(name) { \
	.level = { &name.node[0] }, \
	.levelcnt = { \
		NUM_RCU_LVL_0,  /* root of hierarchy. */ \
		NUM_RCU_LVL_1, \
		NUM_RCU_LVL_2, \
		NUM_RCU_LVL_3, /* == MAX_RCU_LVLS */ \
	}, \
	.signaled = RCU_SIGNAL_INIT, \
	.gpnum = -300, \
	.completed = -300, \
	.onofflock = __SPIN_LOCK_UNLOCKED(&name.onofflock), \
	.fqslock = __SPIN_LOCK_UNLOCKED(&name.fqslock), \
	.n_force_qs = 0, \
	.n_force_qs_ngp = 0, \
}

struct rcu_state rcu_state = RCU_STATE_INITIALIZER(rcu_state);
DEFINE_PER_CPU(struct rcu_data, rcu_data);

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

#ifdef CONFIG_NO_HZ
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DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
	.dynticks_nesting = 1,
	.dynticks = 1,
};
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#endif /* #ifdef CONFIG_NO_HZ */

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

static void force_quiescent_state(struct rcu_state *rsp, int relaxed);

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

/*
 * 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);

/*
 * 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)
{
	/* ACCESS_ONCE() because we are accessing outside of lock. */
	return *rdp->nxttail[RCU_DONE_TAIL] &&
	       ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum);
}

/*
 * 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];
}

#ifdef CONFIG_SMP

/*
 * 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, it is in a quiescent state.  We can
	 * trust its state not to change because interrupts are disabled.
	 */
	if (cpu_is_offline(rdp->cpu)) {
		rdp->offline_fqs++;
		return 1;
	}

	/* The CPU is online, so send it a reschedule IPI. */
	if (rdp->cpu != smp_processor_id())
		smp_send_reschedule(rdp->cpu);
	else
		set_need_resched();
	rdp->resched_ipi++;
	return 0;
}

#endif /* #ifdef CONFIG_SMP */

#ifdef CONFIG_NO_HZ
static DEFINE_RATELIMIT_STATE(rcu_rs, 10 * HZ, 5);

/**
 * rcu_enter_nohz - inform RCU that current CPU is entering nohz
 *
 * Enter nohz 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 nohz mode, a possibility
 * handled by rcu_irq_enter() and rcu_irq_exit()).
 */
void rcu_enter_nohz(void)
{
	unsigned long flags;
	struct rcu_dynticks *rdtp;

	smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
	local_irq_save(flags);
	rdtp = &__get_cpu_var(rcu_dynticks);
	rdtp->dynticks++;
	rdtp->dynticks_nesting--;
	WARN_ON_RATELIMIT(rdtp->dynticks & 0x1, &rcu_rs);
	local_irq_restore(flags);
}

/*
 * rcu_exit_nohz - inform RCU that current CPU is leaving nohz
 *
 * Exit nohz mode, in other words, -enter- the mode in which RCU
 * read-side critical sections normally occur.
 */
void rcu_exit_nohz(void)
{
	unsigned long flags;
	struct rcu_dynticks *rdtp;

	local_irq_save(flags);
	rdtp = &__get_cpu_var(rcu_dynticks);
	rdtp->dynticks++;
	rdtp->dynticks_nesting++;
	WARN_ON_RATELIMIT(!(rdtp->dynticks & 0x1), &rcu_rs);
	local_irq_restore(flags);
	smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
}

/**
 * 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 & 0x1)
		return;
	rdtp->dynticks_nmi++;
	WARN_ON_RATELIMIT(!(rdtp->dynticks_nmi & 0x1), &rcu_rs);
	smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
}

/**
 * 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 & 0x1)
		return;
	smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
	rdtp->dynticks_nmi++;
	WARN_ON_RATELIMIT(rdtp->dynticks_nmi & 0x1, &rcu_rs);
}

/**
 * rcu_irq_enter - inform RCU of entry to hard irq context
 *
 * If the CPU was idle with dynamic ticks active, this updates the
 * rdtp->dynticks to let the RCU handling know that the CPU is active.
 */
void rcu_irq_enter(void)
{
	struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);

	if (rdtp->dynticks_nesting++)
		return;
	rdtp->dynticks++;
	WARN_ON_RATELIMIT(!(rdtp->dynticks & 0x1), &rcu_rs);
	smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
}

/**
 * rcu_irq_exit - inform RCU of exit from hard irq context
 *
 * If the CPU was idle with dynamic ticks active, update the rdp->dynticks
 * to put let the RCU handling be aware that the CPU is going back to idle
 * with no ticks.
 */
void rcu_irq_exit(void)
{
	struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);

	if (--rdtp->dynticks_nesting)
		return;
	smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
	rdtp->dynticks++;
	WARN_ON_RATELIMIT(rdtp->dynticks & 0x1, &rcu_rs);

	/* If the interrupt queued a callback, get out of dyntick mode. */
	if (__get_cpu_var(rcu_data).nxtlist ||
	    __get_cpu_var(rcu_bh_data).nxtlist)
		set_need_resched();
}

/*
 * Record the specified "completed" value, which is later used to validate
 * dynticks counter manipulations.  Specify "rsp->completed - 1" to
 * unconditionally invalidate any future dynticks manipulations (which is
 * useful at the beginning of a grace period).
 */
static void dyntick_record_completed(struct rcu_state *rsp, long comp)
{
	rsp->dynticks_completed = comp;
}

#ifdef CONFIG_SMP

/*
 * Recall the previously recorded value of the completion for dynticks.
 */
static long dyntick_recall_completed(struct rcu_state *rsp)
{
	return rsp->dynticks_completed;
}

/*
 * 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 already in a quiescent state courtesy of dynticks idle mode.
 */
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
	int ret;
	int snap;
	int snap_nmi;

	snap = rdp->dynticks->dynticks;
	snap_nmi = rdp->dynticks->dynticks_nmi;
	smp_mb();	/* Order sampling of snap with end of grace period. */
	rdp->dynticks_snap = snap;
	rdp->dynticks_nmi_snap = snap_nmi;
	ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0);
	if (ret)
		rdp->dynticks_fqs++;
	return ret;
}

/*
 * 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)
{
	long curr;
	long curr_nmi;
	long snap;
	long snap_nmi;

	curr = rdp->dynticks->dynticks;
	snap = rdp->dynticks_snap;
	curr_nmi = rdp->dynticks->dynticks_nmi;
	snap_nmi = rdp->dynticks_nmi_snap;
	smp_mb(); /* force ordering with cpu entering/leaving dynticks. */

	/*
	 * 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 != snap || (curr & 0x1) == 0) &&
	    (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) {
		rdp->dynticks_fqs++;
		return 1;
	}

	/* Go check for the CPU being offline. */
	return rcu_implicit_offline_qs(rdp);
}

#endif /* #ifdef CONFIG_SMP */

#else /* #ifdef CONFIG_NO_HZ */

static void dyntick_record_completed(struct rcu_state *rsp, long comp)
{
}

#ifdef CONFIG_SMP

/*
 * If there are no dynticks, then the only way that a CPU can passively
 * be in a quiescent state is to be offline.  Unlike dynticks idle, which
 * is a point in time during the prior (already finished) grace period,
 * an offline CPU is always in a quiescent state, and thus can be
 * unconditionally applied.  So just return the current value of completed.
 */
static long dyntick_recall_completed(struct rcu_state *rsp)
{
	return rsp->completed;
}

static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
	return 0;
}

static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
{
	return rcu_implicit_offline_qs(rdp);
}

#endif /* #ifdef CONFIG_SMP */

#endif /* #else #ifdef CONFIG_NO_HZ */

#ifdef CONFIG_RCU_CPU_STALL_DETECTOR

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

static void print_other_cpu_stall(struct rcu_state *rsp)
{
	int cpu;
	long delta;
	unsigned long flags;
	struct rcu_node *rnp = rcu_get_root(rsp);
	struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
	struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];

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

	spin_lock_irqsave(&rnp->lock, flags);
	delta = jiffies - rsp->jiffies_stall;
	if (delta < RCU_STALL_RAT_DELAY || rsp->gpnum == rsp->completed) {
		spin_unlock_irqrestore(&rnp->lock, flags);
		return;
	}
	rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
	spin_unlock_irqrestore(&rnp->lock, flags);

	/* OK, time to rat on our buddy... */

	printk(KERN_ERR "INFO: RCU detected CPU stalls:");
	for (; rnp_cur < rnp_end; rnp_cur++) {
		if (rnp_cur->qsmask == 0)
			continue;
		for (cpu = 0; cpu <= rnp_cur->grphi - rnp_cur->grplo; cpu++)
			if (rnp_cur->qsmask & (1UL << cpu))
				printk(" %d", rnp_cur->grplo + cpu);
	}
	printk(" (detected by %d, t=%ld jiffies)\n",
	       smp_processor_id(), (long)(jiffies - rsp->gp_start));
	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);

	printk(KERN_ERR "INFO: RCU detected CPU %d stall (t=%lu jiffies)\n",
			smp_processor_id(), jiffies - rsp->gp_start);
	dump_stack();
	spin_lock_irqsave(&rnp->lock, flags);
	if ((long)(jiffies - rsp->jiffies_stall) >= 0)
		rsp->jiffies_stall =
			jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
	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)
{
	long delta;
	struct rcu_node *rnp;

	delta = jiffies - rsp->jiffies_stall;
	rnp = rdp->mynode;
	if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {

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

	} else if (rsp->gpnum != rsp->completed &&
		   delta >= RCU_STALL_RAT_DELAY) {

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

#else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */

static void record_gp_stall_check_time(struct rcu_state *rsp)
{
}

static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */

/*
 * 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.
 */
static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
{
	rdp->qs_pending = 1;
	rdp->passed_quiesc = 0;
	rdp->gpnum = rsp->gpnum;
	rdp->n_rcu_pending_force_qs = rdp->n_rcu_pending +
				      RCU_JIFFIES_TILL_FORCE_QS;
}

/*
 * 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;
}

/*
 * 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.
 */
static void
rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
	__releases(rcu_get_root(rsp)->lock)
{
	struct rcu_data *rdp = rsp->rda[smp_processor_id()];
	struct rcu_node *rnp = rcu_get_root(rsp);
	struct rcu_node *rnp_cur;
	struct rcu_node *rnp_end;

	if (!cpu_needs_another_gp(rsp, rdp)) {
		spin_unlock_irqrestore(&rnp->lock, flags);
		return;
	}

	/* Advance to a new grace period and initialize state. */
	rsp->gpnum++;
	rsp->signaled = RCU_GP_INIT; /* Hold off force_quiescent_state. */
	rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
	rdp->n_rcu_pending_force_qs = rdp->n_rcu_pending +
				      RCU_JIFFIES_TILL_FORCE_QS;
	record_gp_stall_check_time(rsp);
	dyntick_record_completed(rsp, rsp->completed - 1);
	note_new_gpnum(rsp, rdp);

	/*
	 * Because we are first, we know that all our callbacks will
	 * be covered by this upcoming grace period, even the ones
	 * that were registered arbitrarily recently.
	 */
	rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
	rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];

	/* Special-case the common single-level case. */
	if (NUM_RCU_NODES == 1) {
		rnp->qsmask = rnp->qsmaskinit;
578
		rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
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		spin_unlock_irqrestore(&rnp->lock, flags);
		return;
	}

	spin_unlock(&rnp->lock);  /* leave irqs disabled. */


	/* Exclude any concurrent CPU-hotplug operations. */
	spin_lock(&rsp->onofflock);  /* irqs already disabled. */

	/*
	 * Set the quiescent-state-needed bits in all the non-leaf RCU
	 * nodes for all currently online CPUs.  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.  In addition, we have excluded CPU-hotplug operations.
	 *
	 * We therefore do not need to hold any locks.  Any required
	 * memory barriers will be supplied by the locks guarding the
	 * leaf rcu_nodes in the hierarchy.
	 */

	rnp_end = rsp->level[NUM_RCU_LVLS - 1];
	for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++)
		rnp_cur->qsmask = rnp_cur->qsmaskinit;

	/*
	 * Now set up the leaf nodes.  Here we must be careful.  First,
	 * we need to hold the lock in order to exclude other CPUs, which
	 * might be contending for the leaf nodes' locks.  Second, as
	 * soon as we initialize a given leaf node, its CPUs might run
	 * up the rest of the hierarchy.  We must therefore acquire locks
	 * for each node that we touch during this stage.  (But we still
	 * are excluding 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.
	 */
	rnp_end = &rsp->node[NUM_RCU_NODES];
	rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
	for (; rnp_cur < rnp_end; rnp_cur++) {
		spin_lock(&rnp_cur->lock);	/* irqs already disabled. */
		rnp_cur->qsmask = rnp_cur->qsmaskinit;
		spin_unlock(&rnp_cur->lock);	/* irqs already disabled. */
	}

	rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
	spin_unlock_irqrestore(&rsp->onofflock, flags);
}

/*
 * 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)
{
	long completed_snap;
	unsigned long flags;

	local_irq_save(flags);
	completed_snap = ACCESS_ONCE(rsp->completed);  /* outside of lock. */

	/* Did another grace period end? */
	if (rdp->completed != completed_snap) {

		/* 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 = completed_snap;
	}
	local_irq_restore(flags);
}

/*
 * Similar to cpu_quiet(), for which it is a helper function.  Allows
 * a group of CPUs to be quieted at one go, though all the CPUs in the
 * group must be represented by the same leaf rcu_node structure.
 * That structure's lock must be held upon entry, and it is released
 * before return.
 */
static void
cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp, struct rcu_node *rnp,
	      unsigned long flags)
	__releases(rnp->lock)
{
	/* Walk up the rcu_node hierarchy. */
	for (;;) {
		if (!(rnp->qsmask & mask)) {

			/* Our bit has already been cleared, so done. */
			spin_unlock_irqrestore(&rnp->lock, flags);
			return;
		}
		rnp->qsmask &= ~mask;
		if (rnp->qsmask != 0) {

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

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

			break;
		}
		spin_unlock_irqrestore(&rnp->lock, flags);
		rnp = rnp->parent;
		spin_lock_irqsave(&rnp->lock, flags);
	}

	/*
	 * Get here if we are the last CPU to pass through a quiescent
	 * state for this grace period.  Clean up and let rcu_start_gp()
	 * start up the next grace period if one is needed.  Note that
	 * we still hold rnp->lock, as required by rcu_start_gp(), which
	 * will release it.
	 */
	rsp->completed = rsp->gpnum;
	rcu_process_gp_end(rsp, rsp->rda[smp_processor_id()]);
	rcu_start_gp(rsp, flags);  /* releases rnp->lock. */
}

/*
 * Record a quiescent state for the specified CPU, which must either be
 * the current CPU or an 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
cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
{
	unsigned long flags;
	unsigned long mask;
	struct rcu_node *rnp;

	rnp = rdp->mynode;
	spin_lock_irqsave(&rnp->lock, flags);
	if (lastcomp != ACCESS_ONCE(rsp->completed)) {

		/*
		 * Someone beat us to it for this grace period, so leave.
		 * The race with GP start is resolved by the fact that we
		 * hold the leaf rcu_node lock, so that the per-CPU bits
		 * cannot yet be initialized -- so we would simply find our
		 * CPU's bit already cleared in cpu_quiet_msk() if this race
		 * occurred.
		 */
		rdp->passed_quiesc = 0;	/* try again later! */
		spin_unlock_irqrestore(&rnp->lock, flags);
		return;
	}
	mask = rdp->grpmask;
	if ((rnp->qsmask & mask) == 0) {
		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 = rsp->rda[smp_processor_id()];
		rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];

		cpu_quiet_msk(mask, rsp, rnp, flags); /* releases 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_quiesc)
		return;

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

#ifdef CONFIG_HOTPLUG_CPU

/*
 * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
 * and move all callbacks from the outgoing CPU to the current one.
 */
static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
{
	int i;
	unsigned long flags;
	long lastcomp;
	unsigned long mask;
	struct rcu_data *rdp = rsp->rda[cpu];
	struct rcu_data *rdp_me;
	struct rcu_node *rnp;

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

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

	spin_unlock(&rsp->onofflock);		/* irqs remain disabled. */

	/* Being offline is a quiescent state, so go record it. */
	cpu_quiet(cpu, rsp, rdp, lastcomp);

	/*
	 * Move callbacks from the outgoing CPU to the running CPU.
	 * Note that the outgoing CPU is now quiscent, so it is now
	 * (uncharacteristically) safe to access it rcu_data structure.
	 * Note also that we must carefully retain the order of the
	 * outgoing CPU's callbacks in order for rcu_barrier() to work
	 * correctly.  Finally, note that we start all the callbacks
	 * afresh, even those that have passed through a grace period
	 * and are therefore ready to invoke.  The theory is that hotplug
	 * events are rare, and that if they are frequent enough to
	 * indefinitely delay callbacks, you have far worse things to
	 * be worrying about.
	 */
	rdp_me = rsp->rda[smp_processor_id()];
	if (rdp->nxtlist != NULL) {
		*rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
		rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
		rdp->nxtlist = NULL;
		for (i = 0; i < RCU_NEXT_SIZE; i++)
			rdp->nxttail[i] = &rdp->nxtlist;
		rdp_me->qlen += rdp->qlen;
		rdp->qlen = 0;
	}
	local_irq_restore(flags);
}

/*
 * Remove the specified CPU from the RCU hierarchy and move any pending
 * callbacks that it might have to the current CPU.  This code assumes
 * that at least one CPU in the system will remain running at all times.
 * Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
 */
static void rcu_offline_cpu(int cpu)
{
	__rcu_offline_cpu(cpu, &rcu_state);
	__rcu_offline_cpu(cpu, &rcu_bh_state);
}

#else /* #ifdef CONFIG_HOTPLUG_CPU */

static void rcu_offline_cpu(int cpu)
{
}

#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_data *rdp)
{
	unsigned long flags;
	struct rcu_head *next, *list, **tail;
	int count;

	/* If no callbacks are ready, just return.*/
	if (!cpu_has_callbacks_ready_to_invoke(rdp))
		return;

	/*
	 * Extract the list of ready callbacks, disabling to prevent
	 * races with call_rcu() from interrupt handlers.
	 */
	local_irq_save(flags);
	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 = 0;
	while (list) {
		next = list->next;
		prefetch(next);
		list->func(list);
		list = next;
		if (++count >= rdp->blimit)
			break;
	}

	local_irq_save(flags);

	/* Update count, and requeue any remaining callbacks. */
	rdp->qlen -= 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;

	local_irq_restore(flags);

	/* Re-raise the RCU softirq if there are callbacks remaining. */
	if (cpu_has_callbacks_ready_to_invoke(rdp))
		raise_softirq(RCU_SOFTIRQ);
}

/*
 * 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 the RCU softirq handler.
 *
 * This function must be called with hardirqs disabled.  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)
{
	if (user ||
951 952
	    (idle_cpu(cpu) && rcu_scheduler_active &&
	     !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316

		/*
		 * 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 count it.
		 *
		 * No memory barrier is required here because both
		 * rcu_qsctr_inc() and rcu_bh_qsctr_inc() reference
		 * only CPU-local variables that other CPUs neither
		 * access nor modify, at least not while the corresponding
		 * CPU is online.
		 */

		rcu_qsctr_inc(cpu);
		rcu_bh_qsctr_inc(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 count it.
		 */

		rcu_bh_qsctr_inc(cpu);
	}
	raise_softirq(RCU_SOFTIRQ);
}

#ifdef CONFIG_SMP

/*
 * Scan the leaf rcu_node structures, processing dyntick state for any that
 * have not yet encountered a quiescent state, using the function specified.
 * Returns 1 if the current grace period ends while scanning (possibly
 * because we made it end).
 */
static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
			       int (*f)(struct rcu_data *))
{
	unsigned long bit;
	int cpu;
	unsigned long flags;
	unsigned long mask;
	struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
	struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];

	for (; rnp_cur < rnp_end; rnp_cur++) {
		mask = 0;
		spin_lock_irqsave(&rnp_cur->lock, flags);
		if (rsp->completed != lastcomp) {
			spin_unlock_irqrestore(&rnp_cur->lock, flags);
			return 1;
		}
		if (rnp_cur->qsmask == 0) {
			spin_unlock_irqrestore(&rnp_cur->lock, flags);
			continue;
		}
		cpu = rnp_cur->grplo;
		bit = 1;
		for (; cpu <= rnp_cur->grphi; cpu++, bit <<= 1) {
			if ((rnp_cur->qsmask & bit) != 0 && f(rsp->rda[cpu]))
				mask |= bit;
		}
		if (mask != 0 && rsp->completed == lastcomp) {

			/* cpu_quiet_msk() releases rnp_cur->lock. */
			cpu_quiet_msk(mask, rsp, rnp_cur, flags);
			continue;
		}
		spin_unlock_irqrestore(&rnp_cur->lock, flags);
	}
	return 0;
}

/*
 * 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;
	long lastcomp;
	struct rcu_data *rdp = rsp->rda[smp_processor_id()];
	struct rcu_node *rnp = rcu_get_root(rsp);
	u8 signaled;

	if (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum))
		return;  /* No grace period in progress, nothing to force. */
	if (!spin_trylock_irqsave(&rsp->fqslock, flags)) {
		rsp->n_force_qs_lh++; /* Inexact, can lose counts.  Tough! */
		return;	/* Someone else is already on the job. */
	}
	if (relaxed &&
	    (long)(rsp->jiffies_force_qs - jiffies) >= 0 &&
	    (rdp->n_rcu_pending_force_qs - rdp->n_rcu_pending) >= 0)
		goto unlock_ret; /* no emergency and done recently. */
	rsp->n_force_qs++;
	spin_lock(&rnp->lock);
	lastcomp = rsp->completed;
	signaled = rsp->signaled;
	rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
	rdp->n_rcu_pending_force_qs = rdp->n_rcu_pending +
				      RCU_JIFFIES_TILL_FORCE_QS;
	if (lastcomp == rsp->gpnum) {
		rsp->n_force_qs_ngp++;
		spin_unlock(&rnp->lock);
		goto unlock_ret;  /* no GP in progress, time updated. */
	}
	spin_unlock(&rnp->lock);
	switch (signaled) {
	case RCU_GP_INIT:

		break; /* grace period still initializing, ignore. */

	case RCU_SAVE_DYNTICK:

		if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
			break; /* So gcc recognizes the dead code. */

		/* Record dyntick-idle state. */
		if (rcu_process_dyntick(rsp, lastcomp,
					dyntick_save_progress_counter))
			goto unlock_ret;

		/* Update state, record completion counter. */
		spin_lock(&rnp->lock);
		if (lastcomp == rsp->completed) {
			rsp->signaled = RCU_FORCE_QS;
			dyntick_record_completed(rsp, lastcomp);
		}
		spin_unlock(&rnp->lock);
		break;

	case RCU_FORCE_QS:

		/* Check dyntick-idle state, send IPI to laggarts. */
		if (rcu_process_dyntick(rsp, dyntick_recall_completed(rsp),
					rcu_implicit_dynticks_qs))
			goto unlock_ret;

		/* Leave state in case more forcing is required. */

		break;
	}
unlock_ret:
	spin_unlock_irqrestore(&rsp->fqslock, flags);
}

#else /* #ifdef CONFIG_SMP */

static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
{
	set_need_resched();
}

#endif /* #else #ifdef CONFIG_SMP */

/*
 * This does the RCU processing work from softirq context 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;

	/*
	 * If an RCU GP has gone long enough, go check for dyntick
	 * idle CPUs and, if needed, send resched IPIs.
	 */
	if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0 ||
	    (rdp->n_rcu_pending_force_qs - rdp->n_rcu_pending) < 0)
		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)) {
		spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
		rcu_start_gp(rsp, flags);  /* releases above lock */
	}

	/* If there are callbacks ready, invoke them. */
	rcu_do_batch(rdp);
}

/*
 * Do softirq processing for the current CPU.
 */
static void rcu_process_callbacks(struct softirq_action *unused)
{
	/*
	 * Memory references from any prior RCU read-side critical sections
	 * executed by the interrupted code must be seen before any RCU
	 * grace-period manipulations below.
	 */
	smp_mb(); /* See above block comment. */

	__rcu_process_callbacks(&rcu_state, &__get_cpu_var(rcu_data));
	__rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));

	/*
	 * Memory references from any later RCU read-side critical sections
	 * executed by the interrupted code must be seen after any RCU
	 * grace-period manipulations above.
	 */
	smp_mb(); /* See above block comment. */
}

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

	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 = rsp->rda[smp_processor_id()];
	rcu_process_gp_end(rsp, rdp);
	check_for_new_grace_period(rsp, rdp);

	/* Add the callback to our list. */
	*rdp->nxttail[RCU_NEXT_TAIL] = head;
	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;

	/* Start a new grace period if one not already started. */
	if (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum)) {
		unsigned long nestflag;
		struct rcu_node *rnp_root = rcu_get_root(rsp);

		spin_lock_irqsave(&rnp_root->lock, nestflag);
		rcu_start_gp(rsp, nestflag);  /* releases rnp_root->lock. */
	}

	/* Force the grace period if too many callbacks or too long waiting. */
	if (unlikely(++rdp->qlen > qhimark)) {
		rdp->blimit = LONG_MAX;
		force_quiescent_state(rsp, 0);
	} else if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0 ||
		   (rdp->n_rcu_pending_force_qs - rdp->n_rcu_pending) < 0)
		force_quiescent_state(rsp, 1);
	local_irq_restore(flags);
}

/*
 * Queue an 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_state);
}
EXPORT_SYMBOL_GPL(call_rcu);

/*
 * Queue an RCU 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);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);

/*
 * 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)
{
	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 (rdp->qs_pending)
		return 1;

	/* Does this CPU have callbacks ready to invoke? */
	if (cpu_has_callbacks_ready_to_invoke(rdp))
		return 1;

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

	/* Has another RCU grace period completed?  */
	if (ACCESS_ONCE(rsp->completed) != rdp->completed) /* outside of lock */
		return 1;

	/* Has a new RCU grace period started? */
	if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) /* outside of lock */
		return 1;

	/* Has an RCU GP gone long enough to send resched IPIs &c? */
	if (ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum) &&
	    ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0 ||
	     (rdp->n_rcu_pending_force_qs - rdp->n_rcu_pending) < 0))
		return 1;

	/* nothing to do */
	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.
 */
int rcu_pending(int cpu)
{
	return __rcu_pending(&rcu_state, &per_cpu(rcu_data, cpu)) ||
	       __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, 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.  This function is part of the RCU implementation; it is -not-
 * an exported member of the RCU API.
 */
int rcu_needs_cpu(int cpu)
{
	/* RCU callbacks either ready or pending? */
	return per_cpu(rcu_data, cpu).nxtlist ||
	       per_cpu(rcu_bh_data, cpu).nxtlist;
}

/*
 * Initialize a CPU's per-CPU RCU data.  We take this "scorched earth"
 * approach so that we don't have to worry about how long the CPU has
 * been gone, or whether it ever was online previously.  We do trust the
 * ->mynode field, as it is constant for a given struct rcu_data and
 * initialized during early boot.
 *
 * 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.
 */
1317
static void __cpuinit
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rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
{
	unsigned long flags;
	int i;
	long lastcomp;
	unsigned long mask;
	struct rcu_data *rdp = rsp->rda[cpu];
	struct rcu_node *rnp = rcu_get_root(rsp);

	/* Set up local state, ensuring consistent view of global state. */
	spin_lock_irqsave(&rnp->lock, flags);
	lastcomp = rsp->completed;
	rdp->completed = lastcomp;
	rdp->gpnum = lastcomp;
	rdp->passed_quiesc = 0;  /* We could be racing with new GP, */
	rdp->qs_pending = 1;	 /*  so set up to respond to current GP. */
	rdp->beenonline = 1;	 /* We have now been online. */
	rdp->passed_quiesc_completed = lastcomp - 1;
	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 = 0;
	rdp->blimit = blimit;
#ifdef CONFIG_NO_HZ
	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
#endif /* #ifdef CONFIG_NO_HZ */
	rdp->cpu = cpu;
	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. */
	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. */
		spin_lock(&rnp->lock);	/* irqs already disabled. */
		rnp->qsmaskinit |= mask;
		mask = rnp->grpmask;
		spin_unlock(&rnp->lock); /* irqs already disabled. */
		rnp = rnp->parent;
	} while (rnp != NULL && !(rnp->qsmaskinit & mask));

	spin_unlock(&rsp->onofflock);		/* irqs remain disabled. */

	/*
	 * A new grace period might start here.  If so, we will be part of
	 * it, and its gpnum will be greater than ours, so we will
	 * participate.  It is also possible for the gpnum to have been
	 * incremented before this function was called, and the bitmasks
	 * to not be filled out until now, in which case we will also
	 * participate due to our gpnum being behind.
	 */

	/* Since it is coming online, the CPU is in a quiescent state. */
	cpu_quiet(cpu, rsp, rdp, lastcomp);
	local_irq_restore(flags);
}

static void __cpuinit rcu_online_cpu(int cpu)
{
	rcu_init_percpu_data(cpu, &rcu_state);
	rcu_init_percpu_data(cpu, &rcu_bh_state);
	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
}

/*
 * Handle CPU online/offline notifcation events.
 */
static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
				unsigned long action, void *hcpu)
{
	long cpu = (long)hcpu;

	switch (action) {
	case CPU_UP_PREPARE:
	case CPU_UP_PREPARE_FROZEN:
		rcu_online_cpu(cpu);
		break;
	case CPU_DEAD:
	case CPU_DEAD_FROZEN:
	case CPU_UP_CANCELED:
	case CPU_UP_CANCELED_FROZEN:
		rcu_offline_cpu(cpu);
		break;
	default:
		break;
	}
	return NOTIFY_OK;
}

/*
 * 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;
}
#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)
{
	int cpustride = 1;
	int i;
	int j;
	struct rcu_node *rnp;

	/* 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++) {
			spin_lock_init(&rnp->lock);
			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;
		}
	}
}

/*
 * Helper macro for __rcu_init().  To be used nowhere else!
 * Assigns leaf node pointers into each CPU's rcu_data structure.
 */
#define RCU_DATA_PTR_INIT(rsp, rcu_data) \
do { \
	rnp = (rsp)->level[NUM_RCU_LVLS - 1]; \
	j = 0; \
	for_each_possible_cpu(i) { \
		if (i > rnp[j].grphi) \
			j++; \
		per_cpu(rcu_data, i).mynode = &rnp[j]; \
		(rsp)->rda[i] = &per_cpu(rcu_data, i); \
	} \
} while (0)

static struct notifier_block __cpuinitdata rcu_nb = {
	.notifier_call	= rcu_cpu_notify,
};

void __init __rcu_init(void)
{
	int i;			/* All used by RCU_DATA_PTR_INIT(). */
	int j;
	struct rcu_node *rnp;

	printk(KERN_WARNING "Experimental hierarchical RCU implementation.\n");
#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
	printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n");
#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
	rcu_init_one(&rcu_state);
	RCU_DATA_PTR_INIT(&rcu_state, rcu_data);
	rcu_init_one(&rcu_bh_state);
	RCU_DATA_PTR_INIT(&rcu_bh_state, rcu_bh_data);

	for_each_online_cpu(i)
		rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long)i);
	/* Register notifier for non-boot CPUs */
	register_cpu_notifier(&rcu_nb);
	printk(KERN_WARNING "Experimental hierarchical RCU init done.\n");
}

module_param(blimit, int, 0);
module_param(qhimark, int, 0);
module_param(qlowmark, int, 0);