Merge commit 'v2.6.29-rc1' into timers/hrtimers

Conflicts:
	kernel/time/tick-common.c

1 files changed, 1532 insertions, 0 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
new file mode 100644
index 000000000000..f2d8638e6c60
--- /dev/null
+++ b/kernel/rcutree.c
@@ -0,0 +1,1532 @@
+/*
+ * 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
+DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
+        .dynticks_nesting = 1,
+        .dynticks = 1,
+};
+#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;
+                rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
+                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 ||
+            (idle_cpu(cpu) && !in_softirq() &&
+                                hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
+
+                /*
+                 * 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.
+ */
+static void
+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);