rcu: Move RCU-related source code to kernel/rcu directory

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 3403 insertions, 0 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
new file mode 100644
index 000000000000..8a2c81e86dda
--- /dev/null
+++ b/kernel/rcu/tree.c
@@ -0,0 +1,3403 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright IBM Corporation, 2008
+ *
+ * Authors: Dipankar Sarma <dipankar@in.ibm.com>
+ *          Manfred Spraul <manfred@colorfullife.com>
+ *          Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
+ *
+ * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
+ * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ *      Documentation/RCU
+ */
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/smp.h>
+#include <linux/rcupdate.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <linux/nmi.h>
+#include <linux/atomic.h>
+#include <linux/bitops.h>
+#include <linux/export.h>
+#include <linux/completion.h>
+#include <linux/moduleparam.h>
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/notifier.h>
+#include <linux/cpu.h>
+#include <linux/mutex.h>
+#include <linux/time.h>
+#include <linux/kernel_stat.h>
+#include <linux/wait.h>
+#include <linux/kthread.h>
+#include <linux/prefetch.h>
+#include <linux/delay.h>
+#include <linux/stop_machine.h>
+#include <linux/random.h>
+#include <linux/ftrace_event.h>
+#include <linux/suspend.h>
+
+#include "tree.h"
+#include <trace/events/rcu.h>
+
+#include "rcu.h"
+
+MODULE_ALIAS("rcutree");
+#ifdef MODULE_PARAM_PREFIX
+#undef MODULE_PARAM_PREFIX
+#endif
+#define MODULE_PARAM_PREFIX "rcutree."
+
+/* Data structures. */
+
+static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
+static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
+
+/*
+ * In order to export the rcu_state name to the tracing tools, it
+ * needs to be added in the __tracepoint_string section.
+ * This requires defining a separate variable tp_<sname>_varname
+ * that points to the string being used, and this will allow
+ * the tracing userspace tools to be able to decipher the string
+ * address to the matching string.
+ */
+#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
+static char sname##_varname[] = #sname; \
+static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
+struct rcu_state sname##_state = { \
+        .level = { &sname##_state.node[0] }, \
+        .call = cr, \
+        .fqs_state = RCU_GP_IDLE, \
+        .gpnum = 0UL - 300UL, \
+        .completed = 0UL - 300UL, \
+        .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
+        .orphan_nxttail = &sname##_state.orphan_nxtlist, \
+        .orphan_donetail = &sname##_state.orphan_donelist, \
+        .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
+        .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
+        .name = sname##_varname, \
+        .abbr = sabbr, \
+}; \
+DEFINE_PER_CPU(struct rcu_data, sname##_data)
+
+RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
+RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
+
+static struct rcu_state *rcu_state;
+LIST_HEAD(rcu_struct_flavors);
+
+/* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
+static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF;
+module_param(rcu_fanout_leaf, int, 0444);
+int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
+static int num_rcu_lvl[] = {  /* Number of rcu_nodes at specified level. */
+        NUM_RCU_LVL_0,
+        NUM_RCU_LVL_1,
+        NUM_RCU_LVL_2,
+        NUM_RCU_LVL_3,
+        NUM_RCU_LVL_4,
+};
+int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
+
+/*
+ * The rcu_scheduler_active variable transitions from zero to one just
+ * before the first task is spawned.  So when this variable is zero, RCU
+ * can assume that there is but one task, allowing RCU to (for example)
+ * optimize synchronize_sched() to a simple barrier().  When this variable
+ * is one, RCU must actually do all the hard work required to detect real
+ * grace periods.  This variable is also used to suppress boot-time false
+ * positives from lockdep-RCU error checking.
+ */
+int rcu_scheduler_active __read_mostly;
+EXPORT_SYMBOL_GPL(rcu_scheduler_active);
+
+/*
+ * The rcu_scheduler_fully_active variable transitions from zero to one
+ * during the early_initcall() processing, which is after the scheduler
+ * is capable of creating new tasks.  So RCU processing (for example,
+ * creating tasks for RCU priority boosting) must be delayed until after
+ * rcu_scheduler_fully_active transitions from zero to one.  We also
+ * currently delay invocation of any RCU callbacks until after this point.
+ *
+ * It might later prove better for people registering RCU callbacks during
+ * early boot to take responsibility for these callbacks, but one step at
+ * a time.
+ */
+static int rcu_scheduler_fully_active __read_mostly;
+
+#ifdef CONFIG_RCU_BOOST
+
+/*
+ * Control variables for per-CPU and per-rcu_node kthreads.  These
+ * handle all flavors of RCU.
+ */
+static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
+DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
+DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
+DEFINE_PER_CPU(char, rcu_cpu_has_work);
+
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
+static void invoke_rcu_core(void);
+static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
+
+/*
+ * Track the rcutorture test sequence number and the update version
+ * number within a given test.  The rcutorture_testseq is incremented
+ * on every rcutorture module load and unload, so has an odd value
+ * when a test is running.  The rcutorture_vernum is set to zero
+ * when rcutorture starts and is incremented on each rcutorture update.
+ * These variables enable correlating rcutorture output with the
+ * RCU tracing information.
+ */
+unsigned long rcutorture_testseq;
+unsigned long rcutorture_vernum;
+
+/*
+ * Return true if an RCU grace period is in progress.  The ACCESS_ONCE()s
+ * permit this function to be invoked without holding the root rcu_node
+ * structure's ->lock, but of course results can be subject to change.
+ */
+static int rcu_gp_in_progress(struct rcu_state *rsp)
+{
+        return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
+}
+
+/*
+ * Note a quiescent state.  Because we do not need to know
+ * how many quiescent states passed, just if there was at least
+ * one since the start of the grace period, this just sets a flag.
+ * The caller must have disabled preemption.
+ */
+void rcu_sched_qs(int cpu)
+{
+        struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
+
+        if (rdp->passed_quiesce == 0)
+                trace_rcu_grace_period(TPS("rcu_sched"), rdp->gpnum, TPS("cpuqs"));
+        rdp->passed_quiesce = 1;
+}
+
+void rcu_bh_qs(int cpu)
+{
+        struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
+
+        if (rdp->passed_quiesce == 0)
+                trace_rcu_grace_period(TPS("rcu_bh"), rdp->gpnum, TPS("cpuqs"));
+        rdp->passed_quiesce = 1;
+}
+
+/*
+ * Note a context switch.  This is a quiescent state for RCU-sched,
+ * and requires special handling for preemptible RCU.
+ * The caller must have disabled preemption.
+ */
+void rcu_note_context_switch(int cpu)
+{
+        trace_rcu_utilization(TPS("Start context switch"));
+        rcu_sched_qs(cpu);
+        rcu_preempt_note_context_switch(cpu);
+        trace_rcu_utilization(TPS("End context switch"));
+}
+EXPORT_SYMBOL_GPL(rcu_note_context_switch);
+
+static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
+        .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
+        .dynticks = ATOMIC_INIT(1),
+#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
+        .dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
+        .dynticks_idle = ATOMIC_INIT(1),
+#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
+};
+
+static long blimit = 10;        /* Maximum callbacks per rcu_do_batch. */
+static long qhimark = 10000;    /* If this many pending, ignore blimit. */
+static long qlowmark = 100;     /* Once only this many pending, use blimit. */
+
+module_param(blimit, long, 0444);
+module_param(qhimark, long, 0444);
+module_param(qlowmark, long, 0444);
+
+static ulong jiffies_till_first_fqs = ULONG_MAX;
+static ulong jiffies_till_next_fqs = ULONG_MAX;
+
+module_param(jiffies_till_first_fqs, ulong, 0644);
+module_param(jiffies_till_next_fqs, ulong, 0644);
+
+static void rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
+                                  struct rcu_data *rdp);
+static void force_qs_rnp(struct rcu_state *rsp,
+                         int (*f)(struct rcu_data *rsp, bool *isidle,
+                                  unsigned long *maxj),
+                         bool *isidle, unsigned long *maxj);
+static void force_quiescent_state(struct rcu_state *rsp);
+static int rcu_pending(int cpu);
+
+/*
+ * Return the number of RCU-sched batches processed thus far for debug & stats.
+ */
+long rcu_batches_completed_sched(void)
+{
+        return rcu_sched_state.completed;
+}
+EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
+
+/*
+ * Return the number of RCU BH batches processed thus far for debug & stats.
+ */
+long rcu_batches_completed_bh(void)
+{
+        return rcu_bh_state.completed;
+}
+EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
+
+/*
+ * Force a quiescent state for RCU BH.
+ */
+void rcu_bh_force_quiescent_state(void)
+{
+        force_quiescent_state(&rcu_bh_state);
+}
+EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
+
+/*
+ * Record the number of times rcutorture tests have been initiated and
+ * terminated.  This information allows the debugfs tracing stats to be
+ * correlated to the rcutorture messages, even when the rcutorture module
+ * is being repeatedly loaded and unloaded.  In other words, we cannot
+ * store this state in rcutorture itself.
+ */
+void rcutorture_record_test_transition(void)
+{
+        rcutorture_testseq++;
+        rcutorture_vernum = 0;
+}
+EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
+
+/*
+ * Record the number of writer passes through the current rcutorture test.
+ * This is also used to correlate debugfs tracing stats with the rcutorture
+ * messages.
+ */
+void rcutorture_record_progress(unsigned long vernum)
+{
+        rcutorture_vernum++;
+}
+EXPORT_SYMBOL_GPL(rcutorture_record_progress);
+
+/*
+ * Force a quiescent state for RCU-sched.
+ */
+void rcu_sched_force_quiescent_state(void)
+{
+        force_quiescent_state(&rcu_sched_state);
+}
+EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
+
+/*
+ * Does the CPU have callbacks ready to be invoked?
+ */
+static int
+cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
+{
+        return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
+               rdp->nxttail[RCU_DONE_TAIL] != NULL;
+}
+
+/*
+ * Does the current CPU require a not-yet-started grace period?
+ * The caller must have disabled interrupts to prevent races with
+ * normal callback registry.
+ */
+static int
+cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
+{
+        int i;
+
+        if (rcu_gp_in_progress(rsp))
+                return 0;  /* No, a grace period is already in progress. */
+        if (rcu_nocb_needs_gp(rsp))
+                return 1;  /* Yes, a no-CBs CPU needs one. */
+        if (!rdp->nxttail[RCU_NEXT_TAIL])
+                return 0;  /* No, this is a no-CBs (or offline) CPU. */
+        if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
+                return 1;  /* Yes, this CPU has newly registered callbacks. */
+        for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
+                if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
+                    ULONG_CMP_LT(ACCESS_ONCE(rsp->completed),
+                                 rdp->nxtcompleted[i]))
+                        return 1;  /* Yes, CBs for future grace period. */
+        return 0; /* No grace period needed. */
+}
+
+/*
+ * Return the root node of the specified rcu_state structure.
+ */
+static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
+{
+        return &rsp->node[0];
+}
+
+/*
+ * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
+ *
+ * If the new value of the ->dynticks_nesting counter now is zero,
+ * we really have entered idle, and must do the appropriate accounting.
+ * The caller must have disabled interrupts.
+ */
+static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
+                                bool user)
+{
+        trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
+        if (!user && !is_idle_task(current)) {
+                struct task_struct *idle __maybe_unused =
+                        idle_task(smp_processor_id());
+
+                trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
+                ftrace_dump(DUMP_ORIG);
+                WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
+                          current->pid, current->comm,
+                          idle->pid, idle->comm); /* must be idle task! */
+        }
+        rcu_prepare_for_idle(smp_processor_id());
+        /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
+        smp_mb__before_atomic_inc();  /* See above. */
+        atomic_inc(&rdtp->dynticks);
+        smp_mb__after_atomic_inc();  /* Force ordering with next sojourn. */
+        WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
+
+        /*
+         * It is illegal to enter an extended quiescent state while
+         * in an RCU read-side critical section.
+         */
+        rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
+                           "Illegal idle entry in RCU read-side critical section.");
+        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
+                           "Illegal idle entry in RCU-bh read-side critical section.");
+        rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
+                           "Illegal idle entry in RCU-sched read-side critical section.");
+}
+
+/*
+ * Enter an RCU extended quiescent state, which can be either the
+ * idle loop or adaptive-tickless usermode execution.
+ */
+static void rcu_eqs_enter(bool user)
+{
+        long long oldval;
+        struct rcu_dynticks *rdtp;
+
+        rdtp = this_cpu_ptr(&rcu_dynticks);
+        oldval = rdtp->dynticks_nesting;
+        WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
+        if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE)
+                rdtp->dynticks_nesting = 0;
+        else
+                rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
+        rcu_eqs_enter_common(rdtp, oldval, user);
+}
+
+/**
+ * rcu_idle_enter - inform RCU that current CPU is entering idle
+ *
+ * Enter idle mode, in other words, -leave- the mode in which RCU
+ * read-side critical sections can occur.  (Though RCU read-side
+ * critical sections can occur in irq handlers in idle, a possibility
+ * handled by irq_enter() and irq_exit().)
+ *
+ * We crowbar the ->dynticks_nesting field to zero to allow for
+ * the possibility of usermode upcalls having messed up our count
+ * of interrupt nesting level during the prior busy period.
+ */
+void rcu_idle_enter(void)
+{
+        unsigned long flags;
+
+        local_irq_save(flags);
+        rcu_eqs_enter(false);
+        rcu_sysidle_enter(this_cpu_ptr(&rcu_dynticks), 0);
+        local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(rcu_idle_enter);
+
+#ifdef CONFIG_RCU_USER_QS
+/**
+ * rcu_user_enter - inform RCU that we are resuming userspace.
+ *
+ * Enter RCU idle mode right before resuming userspace.  No use of RCU
+ * is permitted between this call and rcu_user_exit(). This way the
+ * CPU doesn't need to maintain the tick for RCU maintenance purposes
+ * when the CPU runs in userspace.
+ */
+void rcu_user_enter(void)
+{
+        rcu_eqs_enter(1);
+}
+#endif /* CONFIG_RCU_USER_QS */
+
+/**
+ * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
+ *
+ * Exit from an interrupt handler, which might possibly result in entering
+ * idle mode, in other words, leaving the mode in which read-side critical
+ * sections can occur.
+ *
+ * This code assumes that the idle loop never does anything that might
+ * result in unbalanced calls to irq_enter() and irq_exit().  If your
+ * architecture violates this assumption, RCU will give you what you
+ * deserve, good and hard.  But very infrequently and irreproducibly.
+ *
+ * Use things like work queues to work around this limitation.
+ *
+ * You have been warned.
+ */
+void rcu_irq_exit(void)
+{
+        unsigned long flags;
+        long long oldval;
+        struct rcu_dynticks *rdtp;
+
+        local_irq_save(flags);
+        rdtp = this_cpu_ptr(&rcu_dynticks);
+        oldval = rdtp->dynticks_nesting;
+        rdtp->dynticks_nesting--;
+        WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
+        if (rdtp->dynticks_nesting)
+                trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
+        else
+                rcu_eqs_enter_common(rdtp, oldval, true);
+        rcu_sysidle_enter(rdtp, 1);
+        local_irq_restore(flags);
+}
+
+/*
+ * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
+ *
+ * If the new value of the ->dynticks_nesting counter was previously zero,
+ * we really have exited idle, and must do the appropriate accounting.
+ * The caller must have disabled interrupts.
+ */
+static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval,
+                               int user)
+{
+        smp_mb__before_atomic_inc();  /* Force ordering w/previous sojourn. */
+        atomic_inc(&rdtp->dynticks);
+        /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
+        smp_mb__after_atomic_inc();  /* See above. */
+        WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+        rcu_cleanup_after_idle(smp_processor_id());
+        trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
+        if (!user && !is_idle_task(current)) {
+                struct task_struct *idle __maybe_unused =
+                        idle_task(smp_processor_id());
+
+                trace_rcu_dyntick(TPS("Error on exit: not idle task"),
+                                  oldval, rdtp->dynticks_nesting);
+                ftrace_dump(DUMP_ORIG);
+                WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
+                          current->pid, current->comm,
+                          idle->pid, idle->comm); /* must be idle task! */
+        }
+}
+
+/*
+ * Exit an RCU extended quiescent state, which can be either the
+ * idle loop or adaptive-tickless usermode execution.
+ */
+static void rcu_eqs_exit(bool user)
+{
+        struct rcu_dynticks *rdtp;
+        long long oldval;
+
+        rdtp = this_cpu_ptr(&rcu_dynticks);
+        oldval = rdtp->dynticks_nesting;
+        WARN_ON_ONCE(oldval < 0);
+        if (oldval & DYNTICK_TASK_NEST_MASK)
+                rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
+        else
+                rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
+        rcu_eqs_exit_common(rdtp, oldval, user);
+}
+
+/**
+ * rcu_idle_exit - inform RCU that current CPU is leaving idle
+ *
+ * Exit idle mode, in other words, -enter- the mode in which RCU
+ * read-side critical sections can occur.
+ *
+ * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
+ * allow for the possibility of usermode upcalls messing up our count
+ * of interrupt nesting level during the busy period that is just
+ * now starting.
+ */
+void rcu_idle_exit(void)
+{
+        unsigned long flags;
+
+        local_irq_save(flags);
+        rcu_eqs_exit(false);
+        rcu_sysidle_exit(this_cpu_ptr(&rcu_dynticks), 0);
+        local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(rcu_idle_exit);
+
+#ifdef CONFIG_RCU_USER_QS
+/**
+ * rcu_user_exit - inform RCU that we are exiting userspace.
+ *
+ * Exit RCU idle mode while entering the kernel because it can
+ * run a RCU read side critical section anytime.
+ */
+void rcu_user_exit(void)
+{
+        rcu_eqs_exit(1);
+}
+#endif /* CONFIG_RCU_USER_QS */
+
+/**
+ * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
+ *
+ * Enter an interrupt handler, which might possibly result in exiting
+ * idle mode, in other words, entering the mode in which read-side critical
+ * sections can occur.
+ *
+ * Note that the Linux kernel is fully capable of entering an interrupt
+ * handler that it never exits, for example when doing upcalls to
+ * user mode!  This code assumes that the idle loop never does upcalls to
+ * user mode.  If your architecture does do upcalls from the idle loop (or
+ * does anything else that results in unbalanced calls to the irq_enter()
+ * and irq_exit() functions), RCU will give you what you deserve, good
+ * and hard.  But very infrequently and irreproducibly.
+ *
+ * Use things like work queues to work around this limitation.
+ *
+ * You have been warned.
+ */
+void rcu_irq_enter(void)
+{
+        unsigned long flags;
+        struct rcu_dynticks *rdtp;
+        long long oldval;
+
+        local_irq_save(flags);
+        rdtp = this_cpu_ptr(&rcu_dynticks);
+        oldval = rdtp->dynticks_nesting;
+        rdtp->dynticks_nesting++;
+        WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
+        if (oldval)
+                trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
+        else
+                rcu_eqs_exit_common(rdtp, oldval, true);
+        rcu_sysidle_exit(rdtp, 1);
+        local_irq_restore(flags);
+}
+
+/**
+ * rcu_nmi_enter - inform RCU of entry to NMI context
+ *
+ * If the CPU was idle with dynamic ticks active, and there is no
+ * irq handler running, this updates rdtp->dynticks_nmi to let the
+ * RCU grace-period handling know that the CPU is active.
+ */
+void rcu_nmi_enter(void)
+{
+        struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+
+        if (rdtp->dynticks_nmi_nesting == 0 &&
+            (atomic_read(&rdtp->dynticks) & 0x1))
+                return;
+        rdtp->dynticks_nmi_nesting++;
+        smp_mb__before_atomic_inc();  /* Force delay from prior write. */
+        atomic_inc(&rdtp->dynticks);
+        /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
+        smp_mb__after_atomic_inc();  /* See above. */
+        WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+}
+
+/**
+ * rcu_nmi_exit - inform RCU of exit from NMI context
+ *
+ * If the CPU was idle with dynamic ticks active, and there is no
+ * irq handler running, this updates rdtp->dynticks_nmi to let the
+ * RCU grace-period handling know that the CPU is no longer active.
+ */
+void rcu_nmi_exit(void)
+{
+        struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+
+        if (rdtp->dynticks_nmi_nesting == 0 ||
+            --rdtp->dynticks_nmi_nesting != 0)
+                return;
+        /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
+        smp_mb__before_atomic_inc();  /* See above. */
+        atomic_inc(&rdtp->dynticks);
+        smp_mb__after_atomic_inc();  /* Force delay to next write. */
+        WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
+}
+
+/**
+ * __rcu_is_watching - are RCU read-side critical sections safe?
+ *
+ * Return true if RCU is watching the running CPU, which means that
+ * this CPU can safely enter RCU read-side critical sections.  Unlike
+ * rcu_is_watching(), the caller of __rcu_is_watching() must have at
+ * least disabled preemption.
+ */
+bool __rcu_is_watching(void)
+{
+        return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
+}
+
+/**
+ * rcu_is_watching - see if RCU thinks that the current CPU is idle
+ *
+ * If the current CPU is in its idle loop and is neither in an interrupt
+ * or NMI handler, return true.
+ */
+bool rcu_is_watching(void)
+{
+        int ret;
+
+        preempt_disable();
+        ret = __rcu_is_watching();
+        preempt_enable();
+        return ret;
+}
+EXPORT_SYMBOL_GPL(rcu_is_watching);
+
+#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
+
+/*
+ * Is the current CPU online?  Disable preemption to avoid false positives
+ * that could otherwise happen due to the current CPU number being sampled,
+ * this task being preempted, its old CPU being taken offline, resuming
+ * on some other CPU, then determining that its old CPU is now offline.
+ * It is OK to use RCU on an offline processor during initial boot, hence
+ * the check for rcu_scheduler_fully_active.  Note also that it is OK
+ * for a CPU coming online to use RCU for one jiffy prior to marking itself
+ * online in the cpu_online_mask.  Similarly, it is OK for a CPU going
+ * offline to continue to use RCU for one jiffy after marking itself
+ * offline in the cpu_online_mask.  This leniency is necessary given the
+ * non-atomic nature of the online and offline processing, for example,
+ * the fact that a CPU enters the scheduler after completing the CPU_DYING
+ * notifiers.
+ *
+ * This is also why RCU internally marks CPUs online during the
+ * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
+ *
+ * Disable checking if in an NMI handler because we cannot safely report
+ * errors from NMI handlers anyway.
+ */
+bool rcu_lockdep_current_cpu_online(void)
+{
+        struct rcu_data *rdp;
+        struct rcu_node *rnp;
+        bool ret;
+
+        if (in_nmi())
+                return 1;
+        preempt_disable();
+        rdp = this_cpu_ptr(&rcu_sched_data);
+        rnp = rdp->mynode;
+        ret = (rdp->grpmask & rnp->qsmaskinit) ||
+              !rcu_scheduler_fully_active;
+        preempt_enable();
+        return ret;
+}
+EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
+
+#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
+
+/**
+ * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
+ *
+ * If the current CPU is idle or running at a first-level (not nested)
+ * interrupt from idle, return true.  The caller must have at least
+ * disabled preemption.
+ */
+static int rcu_is_cpu_rrupt_from_idle(void)
+{
+        return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
+}
+
+/*
+ * Snapshot the specified CPU's dynticks counter so that we can later
+ * credit them with an implicit quiescent state.  Return 1 if this CPU
+ * is in dynticks idle mode, which is an extended quiescent state.
+ */
+static int dyntick_save_progress_counter(struct rcu_data *rdp,
+                                         bool *isidle, unsigned long *maxj)
+{
+        rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
+        rcu_sysidle_check_cpu(rdp, isidle, maxj);
+        return (rdp->dynticks_snap & 0x1) == 0;
+}
+
+/*
+ * Return true if the specified CPU has passed through a quiescent
+ * state by virtue of being in or having passed through an dynticks
+ * idle state since the last call to dyntick_save_progress_counter()
+ * for this same CPU, or by virtue of having been offline.
+ */
+static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
+                                    bool *isidle, unsigned long *maxj)
+{
+        unsigned int curr;
+        unsigned int snap;
+
+        curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
+        snap = (unsigned int)rdp->dynticks_snap;
+
+        /*
+         * If the CPU passed through or entered a dynticks idle phase with
+         * no active irq/NMI handlers, then we can safely pretend that the CPU
+         * already acknowledged the request to pass through a quiescent
+         * state.  Either way, that CPU cannot possibly be in an RCU
+         * read-side critical section that started before the beginning
+         * of the current RCU grace period.
+         */
+        if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
+                trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
+                rdp->dynticks_fqs++;
+                return 1;
+        }
+
+        /*
+         * Check for the CPU being offline, but only if the grace period
+         * is old enough.  We don't need to worry about the CPU changing
+         * state: If we see it offline even once, it has been through a
+         * quiescent state.
+         *
+         * The reason for insisting that the grace period be at least
+         * one jiffy old is that CPUs that are not quite online and that
+         * have just gone offline can still execute RCU read-side critical
+         * sections.
+         */
+        if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))
+                return 0;  /* Grace period is not old enough. */
+        barrier();
+        if (cpu_is_offline(rdp->cpu)) {
+                trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
+                rdp->offline_fqs++;
+                return 1;
+        }
+
+        /*
+         * There is a possibility that a CPU in adaptive-ticks state
+         * might run in the kernel with the scheduling-clock tick disabled
+         * for an extended time period.  Invoke rcu_kick_nohz_cpu() to
+         * force the CPU to restart the scheduling-clock tick in this
+         * CPU is in this state.
+         */
+        rcu_kick_nohz_cpu(rdp->cpu);
+
+        return 0;
+}
+
+static void record_gp_stall_check_time(struct rcu_state *rsp)
+{
+        unsigned long j = ACCESS_ONCE(jiffies);
+
+        rsp->gp_start = j;
+        smp_wmb(); /* Record start time before stall time. */
+        rsp->jiffies_stall = j + rcu_jiffies_till_stall_check();
+}
+
+/*
+ * Dump stacks of all tasks running on stalled CPUs.  This is a fallback
+ * for architectures that do not implement trigger_all_cpu_backtrace().
+ * The NMI-triggered stack traces are more accurate because they are
+ * printed by the target CPU.
+ */
+static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
+{
+        int cpu;
+        unsigned long flags;
+        struct rcu_node *rnp;
+
+        rcu_for_each_leaf_node(rsp, rnp) {
+                raw_spin_lock_irqsave(&rnp->lock, flags);
+                if (rnp->qsmask != 0) {
+                        for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
+                                if (rnp->qsmask & (1UL << cpu))
+                                        dump_cpu_task(rnp->grplo + cpu);
+                }
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        }
+}
+
+static void print_other_cpu_stall(struct rcu_state *rsp)
+{
+        int cpu;
+        long delta;
+        unsigned long flags;
+        int ndetected = 0;
+        struct rcu_node *rnp = rcu_get_root(rsp);
+        long totqlen = 0;
+
+        /* Only let one CPU complain about others per time interval. */
+
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        delta = jiffies - rsp->jiffies_stall;
+        if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                return;
+        }
+        rsp->jiffies_stall = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+
+        /*
+         * OK, time to rat on our buddy...
+         * See Documentation/RCU/stallwarn.txt for info on how to debug
+         * RCU CPU stall warnings.
+         */
+        pr_err("INFO: %s detected stalls on CPUs/tasks:",
+               rsp->name);
+        print_cpu_stall_info_begin();
+        rcu_for_each_leaf_node(rsp, rnp) {
+                raw_spin_lock_irqsave(&rnp->lock, flags);
+                ndetected += rcu_print_task_stall(rnp);
+                if (rnp->qsmask != 0) {
+                        for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
+                                if (rnp->qsmask & (1UL << cpu)) {
+                                        print_cpu_stall_info(rsp,
+                                                             rnp->grplo + cpu);
+                                        ndetected++;
+                                }
+                }
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        }
+
+        /*
+         * Now rat on any tasks that got kicked up to the root rcu_node
+         * due to CPU offlining.
+         */
+        rnp = rcu_get_root(rsp);
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        ndetected += rcu_print_task_stall(rnp);
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+
+        print_cpu_stall_info_end();
+        for_each_possible_cpu(cpu)
+                totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
+        pr_cont("(detected by %d, t=%ld jiffies, g=%lu, c=%lu, q=%lu)\n",
+               smp_processor_id(), (long)(jiffies - rsp->gp_start),
+               rsp->gpnum, rsp->completed, totqlen);
+        if (ndetected == 0)
+                pr_err("INFO: Stall ended before state dump start\n");
+        else if (!trigger_all_cpu_backtrace())
+                rcu_dump_cpu_stacks(rsp);
+
+        /* Complain about tasks blocking the grace period. */
+
+        rcu_print_detail_task_stall(rsp);
+
+        force_quiescent_state(rsp);  /* Kick them all. */
+}
+
+static void print_cpu_stall(struct rcu_state *rsp)
+{
+        int cpu;
+        unsigned long flags;
+        struct rcu_node *rnp = rcu_get_root(rsp);
+        long totqlen = 0;
+
+        /*
+         * OK, time to rat on ourselves...
+         * See Documentation/RCU/stallwarn.txt for info on how to debug
+         * RCU CPU stall warnings.
+         */
+        pr_err("INFO: %s self-detected stall on CPU", rsp->name);
+        print_cpu_stall_info_begin();
+        print_cpu_stall_info(rsp, smp_processor_id());
+        print_cpu_stall_info_end();
+        for_each_possible_cpu(cpu)
+                totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
+        pr_cont(" (t=%lu jiffies g=%lu c=%lu q=%lu)\n",
+                jiffies - rsp->gp_start, rsp->gpnum, rsp->completed, totqlen);
+        if (!trigger_all_cpu_backtrace())
+                dump_stack();
+
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
+                rsp->jiffies_stall = jiffies +
+                                     3 * rcu_jiffies_till_stall_check() + 3;
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+
+        set_need_resched();  /* kick ourselves to get things going. */
+}
+
+static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
+{
+        unsigned long completed;
+        unsigned long gpnum;
+        unsigned long gps;
+        unsigned long j;
+        unsigned long js;
+        struct rcu_node *rnp;
+
+        if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
+                return;
+        j = ACCESS_ONCE(jiffies);
+
+        /*
+         * Lots of memory barriers to reject false positives.
+         *
+         * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
+         * then rsp->gp_start, and finally rsp->completed.  These values
+         * are updated in the opposite order with memory barriers (or
+         * equivalent) during grace-period initialization and cleanup.
+         * Now, a false positive can occur if we get an new value of
+         * rsp->gp_start and a old value of rsp->jiffies_stall.  But given
+         * the memory barriers, the only way that this can happen is if one
+         * grace period ends and another starts between these two fetches.
+         * Detect this by comparing rsp->completed with the previous fetch
+         * from rsp->gpnum.
+         *
+         * Given this check, comparisons of jiffies, rsp->jiffies_stall,
+         * and rsp->gp_start suffice to forestall false positives.
+         */
+        gpnum = ACCESS_ONCE(rsp->gpnum);
+        smp_rmb(); /* Pick up ->gpnum first... */
+        js = ACCESS_ONCE(rsp->jiffies_stall);
+        smp_rmb(); /* ...then ->jiffies_stall before the rest... */
+        gps = ACCESS_ONCE(rsp->gp_start);
+        smp_rmb(); /* ...and finally ->gp_start before ->completed. */
+        completed = ACCESS_ONCE(rsp->completed);
+        if (ULONG_CMP_GE(completed, gpnum) ||
+            ULONG_CMP_LT(j, js) ||
+            ULONG_CMP_GE(gps, js))
+                return; /* No stall or GP completed since entering function. */
+        rnp = rdp->mynode;
+        if (rcu_gp_in_progress(rsp) &&
+            (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask)) {
+
+                /* We haven't checked in, so go dump stack. */
+                print_cpu_stall(rsp);
+
+        } else if (rcu_gp_in_progress(rsp) &&
+                   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
+
+                /* They had a few time units to dump stack, so complain. */
+                print_other_cpu_stall(rsp);
+        }
+}
+
+/**
+ * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
+ *
+ * Set the stall-warning timeout way off into the future, thus preventing
+ * any RCU CPU stall-warning messages from appearing in the current set of
+ * RCU grace periods.
+ *
+ * The caller must disable hard irqs.
+ */
+void rcu_cpu_stall_reset(void)
+{
+        struct rcu_state *rsp;
+
+        for_each_rcu_flavor(rsp)
+                rsp->jiffies_stall = jiffies + ULONG_MAX / 2;
+}
+
+/*
+ * Initialize the specified rcu_data structure's callback list to empty.
+ */
+static void init_callback_list(struct rcu_data *rdp)
+{
+        int i;
+
+        if (init_nocb_callback_list(rdp))
+                return;
+        rdp->nxtlist = NULL;
+        for (i = 0; i < RCU_NEXT_SIZE; i++)
+                rdp->nxttail[i] = &rdp->nxtlist;
+}
+
+/*
+ * Determine the value that ->completed will have at the end of the
+ * next subsequent grace period.  This is used to tag callbacks so that
+ * a CPU can invoke callbacks in a timely fashion even if that CPU has
+ * been dyntick-idle for an extended period with callbacks under the
+ * influence of RCU_FAST_NO_HZ.
+ *
+ * The caller must hold rnp->lock with interrupts disabled.
+ */
+static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
+                                       struct rcu_node *rnp)
+{
+        /*
+         * If RCU is idle, we just wait for the next grace period.
+         * But we can only be sure that RCU is idle if we are looking
+         * at the root rcu_node structure -- otherwise, a new grace
+         * period might have started, but just not yet gotten around
+         * to initializing the current non-root rcu_node structure.
+         */
+        if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
+                return rnp->completed + 1;
+
+        /*
+         * Otherwise, wait for a possible partial grace period and
+         * then the subsequent full grace period.
+         */
+        return rnp->completed + 2;
+}
+
+/*
+ * Trace-event helper function for rcu_start_future_gp() and
+ * rcu_nocb_wait_gp().
+ */
+static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
+                                unsigned long c, const char *s)
+{
+        trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
+                                      rnp->completed, c, rnp->level,
+                                      rnp->grplo, rnp->grphi, s);
+}
+
+/*
+ * Start some future grace period, as needed to handle newly arrived
+ * callbacks.  The required future grace periods are recorded in each
+ * rcu_node structure's ->need_future_gp field.
+ *
+ * The caller must hold the specified rcu_node structure's ->lock.
+ */
+static unsigned long __maybe_unused
+rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp)
+{
+        unsigned long c;
+        int i;
+        struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
+
+        /*
+         * Pick up grace-period number for new callbacks.  If this
+         * grace period is already marked as needed, return to the caller.
+         */
+        c = rcu_cbs_completed(rdp->rsp, rnp);
+        trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
+        if (rnp->need_future_gp[c & 0x1]) {
+                trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
+                return c;
+        }
+
+        /*
+         * If either this rcu_node structure or the root rcu_node structure
+         * believe that a grace period is in progress, then we must wait
+         * for the one following, which is in "c".  Because our request
+         * will be noticed at the end of the current grace period, we don't
+         * need to explicitly start one.
+         */
+        if (rnp->gpnum != rnp->completed ||
+            ACCESS_ONCE(rnp->gpnum) != ACCESS_ONCE(rnp->completed)) {
+                rnp->need_future_gp[c & 0x1]++;
+                trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
+                return c;
+        }
+
+        /*
+         * There might be no grace period in progress.  If we don't already
+         * hold it, acquire the root rcu_node structure's lock in order to
+         * start one (if needed).
+         */
+        if (rnp != rnp_root)
+                raw_spin_lock(&rnp_root->lock);
+
+        /*
+         * Get a new grace-period number.  If there really is no grace
+         * period in progress, it will be smaller than the one we obtained
+         * earlier.  Adjust callbacks as needed.  Note that even no-CBs
+         * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
+         */
+        c = rcu_cbs_completed(rdp->rsp, rnp_root);
+        for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
+                if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
+                        rdp->nxtcompleted[i] = c;
+
+        /*
+         * If the needed for the required grace period is already
+         * recorded, trace and leave.
+         */
+        if (rnp_root->need_future_gp[c & 0x1]) {
+                trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
+                goto unlock_out;
+        }
+
+        /* Record the need for the future grace period. */
+        rnp_root->need_future_gp[c & 0x1]++;
+
+        /* If a grace period is not already in progress, start one. */
+        if (rnp_root->gpnum != rnp_root->completed) {
+                trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
+        } else {
+                trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
+                rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
+        }
+unlock_out:
+        if (rnp != rnp_root)
+                raw_spin_unlock(&rnp_root->lock);
+        return c;
+}
+
+/*
+ * Clean up any old requests for the just-ended grace period.  Also return
+ * whether any additional grace periods have been requested.  Also invoke
+ * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
+ * waiting for this grace period to complete.
+ */
+static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+        int c = rnp->completed;
+        int needmore;
+        struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
+
+        rcu_nocb_gp_cleanup(rsp, rnp);
+        rnp->need_future_gp[c & 0x1] = 0;
+        needmore = rnp->need_future_gp[(c + 1) & 0x1];
+        trace_rcu_future_gp(rnp, rdp, c,
+                            needmore ? TPS("CleanupMore") : TPS("Cleanup"));
+        return needmore;
+}
+
+/*
+ * If there is room, assign a ->completed number to any callbacks on
+ * this CPU that have not already been assigned.  Also accelerate any
+ * callbacks that were previously assigned a ->completed number that has
+ * since proven to be too conservative, which can happen if callbacks get
+ * assigned a ->completed number while RCU is idle, but with reference to
+ * a non-root rcu_node structure.  This function is idempotent, so it does
+ * not hurt to call it repeatedly.
+ *
+ * The caller must hold rnp->lock with interrupts disabled.
+ */
+static void rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
+                               struct rcu_data *rdp)
+{
+        unsigned long c;
+        int i;
+
+        /* If the CPU has no callbacks, nothing to do. */
+        if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
+                return;
+
+        /*
+         * Starting from the sublist containing the callbacks most
+         * recently assigned a ->completed number and working down, find the
+         * first sublist that is not assignable to an upcoming grace period.
+         * Such a sublist has something in it (first two tests) and has
+         * a ->completed number assigned that will complete sooner than
+         * the ->completed number for newly arrived callbacks (last test).
+         *
+         * The key point is that any later sublist can be assigned the
+         * same ->completed number as the newly arrived callbacks, which
+         * means that the callbacks in any of these later sublist can be
+         * grouped into a single sublist, whether or not they have already
+         * been assigned a ->completed number.
+         */
+        c = rcu_cbs_completed(rsp, rnp);
+        for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
+                if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
+                    !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
+                        break;
+
+        /*
+         * If there are no sublist for unassigned callbacks, leave.
+         * At the same time, advance "i" one sublist, so that "i" will
+         * index into the sublist where all the remaining callbacks should
+         * be grouped into.
+         */
+        if (++i >= RCU_NEXT_TAIL)
+                return;
+
+        /*
+         * Assign all subsequent callbacks' ->completed number to the next
+         * full grace period and group them all in the sublist initially
+         * indexed by "i".
+         */
+        for (; i <= RCU_NEXT_TAIL; i++) {
+                rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
+                rdp->nxtcompleted[i] = c;
+        }
+        /* Record any needed additional grace periods. */
+        rcu_start_future_gp(rnp, rdp);
+
+        /* Trace depending on how much we were able to accelerate. */
+        if (!*rdp->nxttail[RCU_WAIT_TAIL])
+                trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
+        else
+                trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
+}
+
+/*
+ * Move any callbacks whose grace period has completed to the
+ * RCU_DONE_TAIL sublist, then compact the remaining sublists and
+ * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
+ * sublist.  This function is idempotent, so it does not hurt to
+ * invoke it repeatedly.  As long as it is not invoked -too- often...
+ *
+ * The caller must hold rnp->lock with interrupts disabled.
+ */
+static void rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
+                            struct rcu_data *rdp)
+{
+        int i, j;
+
+        /* If the CPU has no callbacks, nothing to do. */
+        if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
+                return;
+
+        /*
+         * Find all callbacks whose ->completed numbers indicate that they
+         * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
+         */
+        for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
+                if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
+                        break;
+                rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
+        }
+        /* Clean up any sublist tail pointers that were misordered above. */
+        for (j = RCU_WAIT_TAIL; j < i; j++)
+                rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];
+
+        /* Copy down callbacks to fill in empty sublists. */
+        for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
+                if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
+                        break;
+                rdp->nxttail[j] = rdp->nxttail[i];
+                rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
+        }
+
+        /* Classify any remaining callbacks. */
+        rcu_accelerate_cbs(rsp, rnp, rdp);
+}
+
+/*
+ * Update CPU-local rcu_data state to record the beginnings and ends of
+ * grace periods.  The caller must hold the ->lock of the leaf rcu_node
+ * structure corresponding to the current CPU, and must have irqs disabled.
+ */
+static void __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
+{
+        /* Handle the ends of any preceding grace periods first. */
+        if (rdp->completed == rnp->completed) {
+
+                /* No grace period end, so just accelerate recent callbacks. */
+                rcu_accelerate_cbs(rsp, rnp, rdp);
+
+        } else {
+
+                /* Advance callbacks. */
+                rcu_advance_cbs(rsp, rnp, rdp);
+
+                /* Remember that we saw this grace-period completion. */
+                rdp->completed = rnp->completed;
+                trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
+        }
+
+        if (rdp->gpnum != rnp->gpnum) {
+                /*
+                 * If the current grace period is waiting for this CPU,
+                 * set up to detect a quiescent state, otherwise don't
+                 * go looking for one.
+                 */
+                rdp->gpnum = rnp->gpnum;
+                trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
+                rdp->passed_quiesce = 0;
+                rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
+                zero_cpu_stall_ticks(rdp);
+        }
+}
+
+static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
+{
+        unsigned long flags;
+        struct rcu_node *rnp;
+
+        local_irq_save(flags);
+        rnp = rdp->mynode;
+        if ((rdp->gpnum == ACCESS_ONCE(rnp->gpnum) &&
+             rdp->completed == ACCESS_ONCE(rnp->completed)) || /* w/out lock. */
+            !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
+                local_irq_restore(flags);
+                return;
+        }
+        __note_gp_changes(rsp, rnp, rdp);
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+/*
+ * Initialize a new grace period.  Return 0 if no grace period required.
+ */
+static int rcu_gp_init(struct rcu_state *rsp)
+{
+        struct rcu_data *rdp;
+        struct rcu_node *rnp = rcu_get_root(rsp);
+
+        rcu_bind_gp_kthread();
+        raw_spin_lock_irq(&rnp->lock);
+        if (rsp->gp_flags == 0) {
+                /* Spurious wakeup, tell caller to go back to sleep.  */
+                raw_spin_unlock_irq(&rnp->lock);
+                return 0;
+        }
+        rsp->gp_flags = 0; /* Clear all flags: New grace period. */
+
+        if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
+                /*
+                 * Grace period already in progress, don't start another.
+                 * Not supposed to be able to happen.
+                 */
+                raw_spin_unlock_irq(&rnp->lock);
+                return 0;
+        }
+
+        /* Advance to a new grace period and initialize state. */
+        record_gp_stall_check_time(rsp);
+        smp_wmb(); /* Record GP times before starting GP. */
+        rsp->gpnum++;
+        trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
+        raw_spin_unlock_irq(&rnp->lock);
+
+        /* Exclude any concurrent CPU-hotplug operations. */
+        mutex_lock(&rsp->onoff_mutex);
+
+        /*
+         * Set the quiescent-state-needed bits in all the rcu_node
+         * structures for all currently online CPUs in breadth-first order,
+         * starting from the root rcu_node structure, relying on the layout
+         * of the tree within the rsp->node[] array.  Note that other CPUs
+         * will access only the leaves of the hierarchy, thus seeing that no
+         * grace period is in progress, at least until the corresponding
+         * leaf node has been initialized.  In addition, we have excluded
+         * CPU-hotplug operations.
+         *
+         * The grace period cannot complete until the initialization
+         * process finishes, because this kthread handles both.
+         */
+        rcu_for_each_node_breadth_first(rsp, rnp) {
+                raw_spin_lock_irq(&rnp->lock);
+                rdp = this_cpu_ptr(rsp->rda);
+                rcu_preempt_check_blocked_tasks(rnp);
+                rnp->qsmask = rnp->qsmaskinit;
+                ACCESS_ONCE(rnp->gpnum) = rsp->gpnum;
+                WARN_ON_ONCE(rnp->completed != rsp->completed);
+                ACCESS_ONCE(rnp->completed) = rsp->completed;
+                if (rnp == rdp->mynode)
+                        __note_gp_changes(rsp, rnp, rdp);
+                rcu_preempt_boost_start_gp(rnp);
+                trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
+                                            rnp->level, rnp->grplo,
+                                            rnp->grphi, rnp->qsmask);
+                raw_spin_unlock_irq(&rnp->lock);
+#ifdef CONFIG_PROVE_RCU_DELAY
+                if ((prandom_u32() % (rcu_num_nodes + 1)) == 0 &&
+                    system_state == SYSTEM_RUNNING)
+                        udelay(200);
+#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
+                cond_resched();
+        }
+
+        mutex_unlock(&rsp->onoff_mutex);
+        return 1;
+}
+
+/*
+ * Do one round of quiescent-state forcing.
+ */
+static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
+{
+        int fqs_state = fqs_state_in;
+        bool isidle = false;
+        unsigned long maxj;
+        struct rcu_node *rnp = rcu_get_root(rsp);
+
+        rsp->n_force_qs++;
+        if (fqs_state == RCU_SAVE_DYNTICK) {
+                /* Collect dyntick-idle snapshots. */
+                if (is_sysidle_rcu_state(rsp)) {
+                        isidle = 1;
+                        maxj = jiffies - ULONG_MAX / 4;
+                }
+                force_qs_rnp(rsp, dyntick_save_progress_counter,
+                             &isidle, &maxj);
+                rcu_sysidle_report_gp(rsp, isidle, maxj);
+                fqs_state = RCU_FORCE_QS;
+        } else {
+                /* Handle dyntick-idle and offline CPUs. */
+                isidle = 0;
+                force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
+        }
+        /* Clear flag to prevent immediate re-entry. */
+        if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
+                raw_spin_lock_irq(&rnp->lock);
+                rsp->gp_flags &= ~RCU_GP_FLAG_FQS;
+                raw_spin_unlock_irq(&rnp->lock);
+        }
+        return fqs_state;
+}
+
+/*
+ * Clean up after the old grace period.
+ */
+static void rcu_gp_cleanup(struct rcu_state *rsp)
+{
+        unsigned long gp_duration;
+        int nocb = 0;
+        struct rcu_data *rdp;
+        struct rcu_node *rnp = rcu_get_root(rsp);
+
+        raw_spin_lock_irq(&rnp->lock);
+        gp_duration = jiffies - rsp->gp_start;
+        if (gp_duration > rsp->gp_max)
+                rsp->gp_max = gp_duration;
+
+        /*
+         * We know the grace period is complete, but to everyone else
+         * it appears to still be ongoing.  But it is also the case
+         * that to everyone else it looks like there is nothing that
+         * they can do to advance the grace period.  It is therefore
+         * safe for us to drop the lock in order to mark the grace
+         * period as completed in all of the rcu_node structures.
+         */
+        raw_spin_unlock_irq(&rnp->lock);
+
+        /*
+         * Propagate new ->completed value to rcu_node structures so
+         * that other CPUs don't have to wait until the start of the next
+         * grace period to process their callbacks.  This also avoids
+         * some nasty RCU grace-period initialization races by forcing
+         * the end of the current grace period to be completely recorded in
+         * all of the rcu_node structures before the beginning of the next
+         * grace period is recorded in any of the rcu_node structures.
+         */
+        rcu_for_each_node_breadth_first(rsp, rnp) {
+                raw_spin_lock_irq(&rnp->lock);
+                ACCESS_ONCE(rnp->completed) = rsp->gpnum;
+                rdp = this_cpu_ptr(rsp->rda);
+                if (rnp == rdp->mynode)
+                        __note_gp_changes(rsp, rnp, rdp);
+                nocb += rcu_future_gp_cleanup(rsp, rnp);
+                raw_spin_unlock_irq(&rnp->lock);
+                cond_resched();
+        }
+        rnp = rcu_get_root(rsp);
+        raw_spin_lock_irq(&rnp->lock);
+        rcu_nocb_gp_set(rnp, nocb);
+
+        rsp->completed = rsp->gpnum; /* Declare grace period done. */
+        trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
+        rsp->fqs_state = RCU_GP_IDLE;
+        rdp = this_cpu_ptr(rsp->rda);
+        rcu_advance_cbs(rsp, rnp, rdp);  /* Reduce false positives below. */
+        if (cpu_needs_another_gp(rsp, rdp)) {
+                rsp->gp_flags = RCU_GP_FLAG_INIT;
+                trace_rcu_grace_period(rsp->name,
+                                       ACCESS_ONCE(rsp->gpnum),
+                                       TPS("newreq"));
+        }
+        raw_spin_unlock_irq(&rnp->lock);
+}
+
+/*
+ * Body of kthread that handles grace periods.
+ */
+static int __noreturn rcu_gp_kthread(void *arg)
+{
+        int fqs_state;
+        int gf;
+        unsigned long j;
+        int ret;
+        struct rcu_state *rsp = arg;
+        struct rcu_node *rnp = rcu_get_root(rsp);
+
+        for (;;) {
+
+                /* Handle grace-period start. */
+                for (;;) {
+                        trace_rcu_grace_period(rsp->name,
+                                               ACCESS_ONCE(rsp->gpnum),
+                                               TPS("reqwait"));
+                        wait_event_interruptible(rsp->gp_wq,
+                                                 ACCESS_ONCE(rsp->gp_flags) &
+                                                 RCU_GP_FLAG_INIT);
+                        if (rcu_gp_init(rsp))
+                                break;
+                        cond_resched();
+                        flush_signals(current);
+                        trace_rcu_grace_period(rsp->name,
+                                               ACCESS_ONCE(rsp->gpnum),
+                                               TPS("reqwaitsig"));
+                }
+
+                /* Handle quiescent-state forcing. */
+                fqs_state = RCU_SAVE_DYNTICK;
+                j = jiffies_till_first_fqs;
+                if (j > HZ) {
+                        j = HZ;
+                        jiffies_till_first_fqs = HZ;
+                }
+                ret = 0;
+                for (;;) {
+                        if (!ret)
+                                rsp->jiffies_force_qs = jiffies + j;
+                        trace_rcu_grace_period(rsp->name,
+                                               ACCESS_ONCE(rsp->gpnum),
+                                               TPS("fqswait"));
+                        ret = wait_event_interruptible_timeout(rsp->gp_wq,
+                                        ((gf = ACCESS_ONCE(rsp->gp_flags)) &
+                                         RCU_GP_FLAG_FQS) ||
+                                        (!ACCESS_ONCE(rnp->qsmask) &&
+                                         !rcu_preempt_blocked_readers_cgp(rnp)),
+                                        j);
+                        /* If grace period done, leave loop. */
+                        if (!ACCESS_ONCE(rnp->qsmask) &&
+                            !rcu_preempt_blocked_readers_cgp(rnp))
+                                break;
+                        /* If time for quiescent-state forcing, do it. */
+                        if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
+                            (gf & RCU_GP_FLAG_FQS)) {
+                                trace_rcu_grace_period(rsp->name,
+                                                       ACCESS_ONCE(rsp->gpnum),
+                                                       TPS("fqsstart"));
+                                fqs_state = rcu_gp_fqs(rsp, fqs_state);
+                                trace_rcu_grace_period(rsp->name,
+                                                       ACCESS_ONCE(rsp->gpnum),
+                                                       TPS("fqsend"));
+                                cond_resched();
+                        } else {
+                                /* Deal with stray signal. */
+                                cond_resched();
+                                flush_signals(current);
+                                trace_rcu_grace_period(rsp->name,
+                                                       ACCESS_ONCE(rsp->gpnum),
+                                                       TPS("fqswaitsig"));
+                        }
+                        j = jiffies_till_next_fqs;
+                        if (j > HZ) {
+                                j = HZ;
+                                jiffies_till_next_fqs = HZ;
+                        } else if (j < 1) {
+                                j = 1;
+                                jiffies_till_next_fqs = 1;
+                        }
+                }
+
+                /* Handle grace-period end. */
+                rcu_gp_cleanup(rsp);
+        }
+}
+
+static void rsp_wakeup(struct irq_work *work)
+{
+        struct rcu_state *rsp = container_of(work, struct rcu_state, wakeup_work);
+
+        /* Wake up rcu_gp_kthread() to start the grace period. */
+        wake_up(&rsp->gp_wq);
+}
+
+/*
+ * 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 and hard irqs must be disabled.
+ *
+ * Note that it is legal for a dying CPU (which is marked as offline) to
+ * invoke this function.  This can happen when the dying CPU reports its
+ * quiescent state.
+ */
+static void
+rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
+                      struct rcu_data *rdp)
+{
+        if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
+                /*
+                 * Either we have not yet spawned the grace-period
+                 * task, this CPU does not need another grace period,
+                 * or a grace period is already in progress.
+                 * Either way, don't start a new grace period.
+                 */
+                return;
+        }
+        rsp->gp_flags = RCU_GP_FLAG_INIT;
+        trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
+                               TPS("newreq"));
+
+        /*
+         * We can't do wakeups while holding the rnp->lock, as that
+         * could cause possible deadlocks with the rq->lock. Defer
+         * the wakeup to interrupt context.  And don't bother waking
+         * up the running kthread.
+         */
+        if (current != rsp->gp_kthread)
+                irq_work_queue(&rsp->wakeup_work);
+}
+
+/*
+ * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
+ * callbacks.  Note that rcu_start_gp_advanced() cannot do this because it
+ * is invoked indirectly from rcu_advance_cbs(), which would result in
+ * endless recursion -- or would do so if it wasn't for the self-deadlock
+ * that is encountered beforehand.
+ */
+static void
+rcu_start_gp(struct rcu_state *rsp)
+{
+        struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
+        struct rcu_node *rnp = rcu_get_root(rsp);
+
+        /*
+         * If there is no grace period in progress right now, any
+         * callbacks we have up to this point will be satisfied by the
+         * next grace period.  Also, advancing the callbacks reduces the
+         * probability of false positives from cpu_needs_another_gp()
+         * resulting in pointless grace periods.  So, advance callbacks
+         * then start the grace period!
+         */
+        rcu_advance_cbs(rsp, rnp, rdp);
+        rcu_start_gp_advanced(rsp, rnp, rdp);
+}
+
+/*
+ * Report a full set of quiescent states to the specified rcu_state
+ * data structure.  This involves cleaning up after the prior grace
+ * period and letting rcu_start_gp() start up the next grace period
+ * if one is needed.  Note that the caller must hold rnp->lock, which
+ * is released before return.
+ */
+static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
+        __releases(rcu_get_root(rsp)->lock)
+{
+        WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
+        raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
+        wake_up(&rsp->gp_wq);  /* Memory barrier implied by wake_up() path. */
+}
+
+/*
+ * Similar to rcu_report_qs_rdp(), for which it is a helper function.
+ * Allows quiescent states for a group of CPUs to be reported at one go
+ * to the specified rcu_node structure, though all the CPUs in the group
+ * must be represented by the same rcu_node structure (which need not be
+ * a leaf rcu_node structure, though it often will be).  That structure's
+ * lock must be held upon entry, and it is released before return.
+ */
+static void
+rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
+                  struct rcu_node *rnp, unsigned long flags)
+        __releases(rnp->lock)
+{
+        struct rcu_node *rnp_c;
+
+        /* Walk up the rcu_node hierarchy. */
+        for (;;) {
+                if (!(rnp->qsmask & mask)) {
+
+                        /* Our bit has already been cleared, so done. */
+                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                        return;
+                }
+                rnp->qsmask &= ~mask;
+                trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
+                                                 mask, rnp->qsmask, rnp->level,
+                                                 rnp->grplo, rnp->grphi,
+                                                 !!rnp->gp_tasks);
+                if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
+
+                        /* Other bits still set at this level, so done. */
+                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                        return;
+                }
+                mask = rnp->grpmask;
+                if (rnp->parent == NULL) {
+
+                        /* No more levels.  Exit loop holding root lock. */
+
+                        break;
+                }
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                rnp_c = rnp;
+                rnp = rnp->parent;
+                raw_spin_lock_irqsave(&rnp->lock, flags);
+                WARN_ON_ONCE(rnp_c->qsmask);
+        }
+
+        /*
+         * Get here if we are the last CPU to pass through a quiescent
+         * state for this grace period.  Invoke rcu_report_qs_rsp()
+         * to clean up and start the next grace period if one is needed.
+         */
+        rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
+}
+
+/*
+ * Record a quiescent state for the specified CPU to that CPU's rcu_data
+ * structure.  This must be either called from the specified CPU, or
+ * called when the specified CPU is known to be offline (and when it is
+ * also known that no other CPU is concurrently trying to help the offline
+ * CPU).  The lastcomp argument is used to make sure we are still in the
+ * grace period of interest.  We don't want to end the current grace period
+ * based on quiescent states detected in an earlier grace period!
+ */
+static void
+rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
+{
+        unsigned long flags;
+        unsigned long mask;
+        struct rcu_node *rnp;
+
+        rnp = rdp->mynode;
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        if (rdp->passed_quiesce == 0 || rdp->gpnum != rnp->gpnum ||
+            rnp->completed == rnp->gpnum) {
+
+                /*
+                 * The grace period in which this quiescent state was
+                 * recorded has ended, so don't report it upwards.
+                 * We will instead need a new quiescent state that lies
+                 * within the current grace period.
+                 */
+                rdp->passed_quiesce = 0;        /* need qs for new gp. */
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                return;
+        }
+        mask = rdp->grpmask;
+        if ((rnp->qsmask & mask) == 0) {
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        } else {
+                rdp->qs_pending = 0;
+
+                /*
+                 * This GP can't end until cpu checks in, so all of our
+                 * callbacks can be processed during the next GP.
+                 */
+                rcu_accelerate_cbs(rsp, rnp, rdp);
+
+                rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
+        }
+}
+
+/*
+ * Check to see if there is a new grace period of which this CPU
+ * is not yet aware, and if so, set up local rcu_data state for it.
+ * Otherwise, see if this CPU has just passed through its first
+ * quiescent state for this grace period, and record that fact if so.
+ */
+static void
+rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
+{
+        /* Check for grace-period ends and beginnings. */
+        note_gp_changes(rsp, rdp);
+
+        /*
+         * Does this CPU still need to do its part for current grace period?
+         * If no, return and let the other CPUs do their part as well.
+         */
+        if (!rdp->qs_pending)
+                return;
+
+        /*
+         * Was there a quiescent state since the beginning of the grace
+         * period? If no, then exit and wait for the next call.
+         */
+        if (!rdp->passed_quiesce)
+                return;
+
+        /*
+         * Tell RCU we are done (but rcu_report_qs_rdp() will be the
+         * judge of that).
+         */
+        rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Send the specified CPU's RCU callbacks to the orphanage.  The
+ * specified CPU must be offline, and the caller must hold the
+ * ->orphan_lock.
+ */
+static void
+rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
+                          struct rcu_node *rnp, struct rcu_data *rdp)
+{
+        /* No-CBs CPUs do not have orphanable callbacks. */
+        if (rcu_is_nocb_cpu(rdp->cpu))
+                return;
+
+        /*
+         * Orphan the callbacks.  First adjust the counts.  This is safe
+         * because _rcu_barrier() excludes CPU-hotplug operations, so it
+         * cannot be running now.  Thus no memory barrier is required.
+         */
+        if (rdp->nxtlist != NULL) {
+                rsp->qlen_lazy += rdp->qlen_lazy;
+                rsp->qlen += rdp->qlen;
+                rdp->n_cbs_orphaned += rdp->qlen;
+                rdp->qlen_lazy = 0;
+                ACCESS_ONCE(rdp->qlen) = 0;
+        }
+
+        /*
+         * Next, move those callbacks still needing a grace period to
+         * the orphanage, where some other CPU will pick them up.
+         * Some of the callbacks might have gone partway through a grace
+         * period, but that is too bad.  They get to start over because we
+         * cannot assume that grace periods are synchronized across CPUs.
+         * We don't bother updating the ->nxttail[] array yet, instead
+         * we just reset the whole thing later on.
+         */
+        if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
+                *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
+                rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
+                *rdp->nxttail[RCU_DONE_TAIL] = NULL;
+        }
+
+        /*
+         * Then move the ready-to-invoke callbacks to the orphanage,
+         * where some other CPU will pick them up.  These will not be
+         * required to pass though another grace period: They are done.
+         */
+        if (rdp->nxtlist != NULL) {
+                *rsp->orphan_donetail = rdp->nxtlist;
+                rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
+        }
+
+        /* Finally, initialize the rcu_data structure's list to empty.  */
+        init_callback_list(rdp);
+}
+
+/*
+ * Adopt the RCU callbacks from the specified rcu_state structure's
+ * orphanage.  The caller must hold the ->orphan_lock.
+ */
+static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
+{
+        int i;
+        struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
+
+        /* No-CBs CPUs are handled specially. */
+        if (rcu_nocb_adopt_orphan_cbs(rsp, rdp))
+                return;
+
+        /* Do the accounting first. */
+        rdp->qlen_lazy += rsp->qlen_lazy;
+        rdp->qlen += rsp->qlen;
+        rdp->n_cbs_adopted += rsp->qlen;
+        if (rsp->qlen_lazy != rsp->qlen)
+                rcu_idle_count_callbacks_posted();
+        rsp->qlen_lazy = 0;
+        rsp->qlen = 0;
+
+        /*
+         * We do not need a memory barrier here because the only way we
+         * can get here if there is an rcu_barrier() in flight is if
+         * we are the task doing the rcu_barrier().
+         */
+
+        /* First adopt the ready-to-invoke callbacks. */
+        if (rsp->orphan_donelist != NULL) {
+                *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
+                *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
+                for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
+                        if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
+                                rdp->nxttail[i] = rsp->orphan_donetail;
+                rsp->orphan_donelist = NULL;
+                rsp->orphan_donetail = &rsp->orphan_donelist;
+        }
+
+        /* And then adopt the callbacks that still need a grace period. */
+        if (rsp->orphan_nxtlist != NULL) {
+                *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
+                rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
+                rsp->orphan_nxtlist = NULL;
+                rsp->orphan_nxttail = &rsp->orphan_nxtlist;
+        }
+}
+
+/*
+ * Trace the fact that this CPU is going offline.
+ */
+static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
+{
+        RCU_TRACE(unsigned long mask);
+        RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
+        RCU_TRACE(struct rcu_node *rnp = rdp->mynode);
+
+        RCU_TRACE(mask = rdp->grpmask);
+        trace_rcu_grace_period(rsp->name,
+                               rnp->gpnum + 1 - !!(rnp->qsmask & mask),
+                               TPS("cpuofl"));
+}
+
+/*
+ * The CPU has been completely removed, and some other CPU is reporting
+ * this fact from process context.  Do the remainder of the cleanup,
+ * including orphaning the outgoing CPU's RCU callbacks, and also
+ * adopting them.  There can only be one CPU hotplug operation at a time,
+ * so no other CPU can be attempting to update rcu_cpu_kthread_task.
+ */
+static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
+{
+        unsigned long flags;
+        unsigned long mask;
+        int need_report = 0;
+        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+        struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
+
+        /* Adjust any no-longer-needed kthreads. */
+        rcu_boost_kthread_setaffinity(rnp, -1);
+
+        /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
+
+        /* Exclude any attempts to start a new grace period. */
+        mutex_lock(&rsp->onoff_mutex);
+        raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
+
+        /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
+        rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
+        rcu_adopt_orphan_cbs(rsp);
+
+        /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
+        mask = rdp->grpmask;    /* rnp->grplo is constant. */
+        do {
+                raw_spin_lock(&rnp->lock);      /* irqs already disabled. */
+                rnp->qsmaskinit &= ~mask;
+                if (rnp->qsmaskinit != 0) {
+                        if (rnp != rdp->mynode)
+                                raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+                        break;
+                }
+                if (rnp == rdp->mynode)
+                        need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
+                else
+                        raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+                mask = rnp->grpmask;
+                rnp = rnp->parent;
+        } while (rnp != NULL);
+
+        /*
+         * We still hold the leaf rcu_node structure lock here, and
+         * irqs are still disabled.  The reason for this subterfuge is
+         * because invoking rcu_report_unblock_qs_rnp() with ->orphan_lock
+         * held leads to deadlock.
+         */
+        raw_spin_unlock(&rsp->orphan_lock); /* irqs remain disabled. */
+        rnp = rdp->mynode;
+        if (need_report & RCU_OFL_TASKS_NORM_GP)
+                rcu_report_unblock_qs_rnp(rnp, flags);
+        else
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        if (need_report & RCU_OFL_TASKS_EXP_GP)
+                rcu_report_exp_rnp(rsp, rnp, true);
+        WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
+                  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
+                  cpu, rdp->qlen, rdp->nxtlist);
+        init_callback_list(rdp);
+        /* Disallow further callbacks on this CPU. */
+        rdp->nxttail[RCU_NEXT_TAIL] = NULL;
+        mutex_unlock(&rsp->onoff_mutex);
+}
+
+#else /* #ifdef CONFIG_HOTPLUG_CPU */
+
+static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
+{
+}
+
+static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
+{
+}
+
+#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
+
+/*
+ * Invoke any RCU callbacks that have made it to the end of their grace
+ * period.  Thottle as specified by rdp->blimit.
+ */
+static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
+{
+        unsigned long flags;
+        struct rcu_head *next, *list, **tail;
+        long bl, count, count_lazy;
+        int i;
+
+        /* If no callbacks are ready, just return. */
+        if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
+                trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
+                trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
+                                    need_resched(), is_idle_task(current),
+                                    rcu_is_callbacks_kthread());
+                return;
+        }
+
+        /*
+         * Extract the list of ready callbacks, disabling to prevent
+         * races with call_rcu() from interrupt handlers.
+         */
+        local_irq_save(flags);
+        WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
+        bl = rdp->blimit;
+        trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
+        list = rdp->nxtlist;
+        rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
+        *rdp->nxttail[RCU_DONE_TAIL] = NULL;
+        tail = rdp->nxttail[RCU_DONE_TAIL];
+        for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
+                if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
+                        rdp->nxttail[i] = &rdp->nxtlist;
+        local_irq_restore(flags);
+
+        /* Invoke callbacks. */
+        count = count_lazy = 0;
+        while (list) {
+                next = list->next;
+                prefetch(next);
+                debug_rcu_head_unqueue(list);
+                if (__rcu_reclaim(rsp->name, list))
+                        count_lazy++;
+                list = next;
+                /* Stop only if limit reached and CPU has something to do. */
+                if (++count >= bl &&
+                    (need_resched() ||
+                     (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
+                        break;
+        }
+
+        local_irq_save(flags);
+        trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
+                            is_idle_task(current),
+                            rcu_is_callbacks_kthread());
+
+        /* Update count, and requeue any remaining callbacks. */
+        if (list != NULL) {
+                *tail = rdp->nxtlist;
+                rdp->nxtlist = list;
+                for (i = 0; i < RCU_NEXT_SIZE; i++)
+                        if (&rdp->nxtlist == rdp->nxttail[i])
+                                rdp->nxttail[i] = tail;
+                        else
+                                break;
+        }
+        smp_mb(); /* List handling before counting for rcu_barrier(). */
+        rdp->qlen_lazy -= count_lazy;
+        ACCESS_ONCE(rdp->qlen) -= count;
+        rdp->n_cbs_invoked += count;
+
+        /* Reinstate batch limit if we have worked down the excess. */
+        if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
+                rdp->blimit = blimit;
+
+        /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
+        if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
+                rdp->qlen_last_fqs_check = 0;
+                rdp->n_force_qs_snap = rsp->n_force_qs;
+        } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
+                rdp->qlen_last_fqs_check = rdp->qlen;
+        WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
+
+        local_irq_restore(flags);
+
+        /* Re-invoke RCU core processing if there are callbacks remaining. */
+        if (cpu_has_callbacks_ready_to_invoke(rdp))
+                invoke_rcu_core();
+}
+
+/*
+ * Check to see if this CPU is in a non-context-switch quiescent state
+ * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
+ * Also schedule RCU core processing.
+ *
+ * This function must be called from hardirq context.  It is normally
+ * invoked from the scheduling-clock interrupt.  If rcu_pending returns
+ * false, there is no point in invoking rcu_check_callbacks().
+ */
+void rcu_check_callbacks(int cpu, int user)
+{
+        trace_rcu_utilization(TPS("Start scheduler-tick"));
+        increment_cpu_stall_ticks();
+        if (user || rcu_is_cpu_rrupt_from_idle()) {
+
+                /*
+                 * Get here if this CPU took its interrupt from user
+                 * mode or from the idle loop, and if this is not a
+                 * nested interrupt.  In this case, the CPU is in
+                 * a quiescent state, so note it.
+                 *
+                 * No memory barrier is required here because both
+                 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
+                 * variables that other CPUs neither access nor modify,
+                 * at least not while the corresponding CPU is online.
+                 */
+
+                rcu_sched_qs(cpu);
+                rcu_bh_qs(cpu);
+
+        } else if (!in_softirq()) {
+
+                /*
+                 * Get here if this CPU did not take its interrupt from
+                 * softirq, in other words, if it is not interrupting
+                 * a rcu_bh read-side critical section.  This is an _bh
+                 * critical section, so note it.
+                 */
+
+                rcu_bh_qs(cpu);
+        }
+        rcu_preempt_check_callbacks(cpu);
+        if (rcu_pending(cpu))
+                invoke_rcu_core();
+        trace_rcu_utilization(TPS("End scheduler-tick"));
+}
+
+/*
+ * Scan the leaf rcu_node structures, processing dyntick state for any that
+ * have not yet encountered a quiescent state, using the function specified.
+ * Also initiate boosting for any threads blocked on the root rcu_node.
+ *
+ * The caller must have suppressed start of new grace periods.
+ */
+static void force_qs_rnp(struct rcu_state *rsp,
+                         int (*f)(struct rcu_data *rsp, bool *isidle,
+                                  unsigned long *maxj),
+                         bool *isidle, unsigned long *maxj)
+{
+        unsigned long bit;
+        int cpu;
+        unsigned long flags;
+        unsigned long mask;
+        struct rcu_node *rnp;
+
+        rcu_for_each_leaf_node(rsp, rnp) {
+                cond_resched();
+                mask = 0;
+                raw_spin_lock_irqsave(&rnp->lock, flags);
+                if (!rcu_gp_in_progress(rsp)) {
+                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                        return;
+                }
+                if (rnp->qsmask == 0) {
+                        rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
+                        continue;
+                }
+                cpu = rnp->grplo;
+                bit = 1;
+                for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
+                        if ((rnp->qsmask & bit) != 0) {
+                                if ((rnp->qsmaskinit & bit) != 0)
+                                        *isidle = 0;
+                                if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
+                                        mask |= bit;
+                        }
+                }
+                if (mask != 0) {
+
+                        /* rcu_report_qs_rnp() releases rnp->lock. */
+                        rcu_report_qs_rnp(mask, rsp, rnp, flags);
+                        continue;
+                }
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        }
+        rnp = rcu_get_root(rsp);
+        if (rnp->qsmask == 0) {
+                raw_spin_lock_irqsave(&rnp->lock, flags);
+                rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
+        }
+}
+
+/*
+ * Force quiescent states on reluctant CPUs, and also detect which
+ * CPUs are in dyntick-idle mode.
+ */
+static void force_quiescent_state(struct rcu_state *rsp)
+{
+        unsigned long flags;
+        bool ret;
+        struct rcu_node *rnp;
+        struct rcu_node *rnp_old = NULL;
+
+        /* Funnel through hierarchy to reduce memory contention. */
+        rnp = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
+        for (; rnp != NULL; rnp = rnp->parent) {
+                ret = (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
+                      !raw_spin_trylock(&rnp->fqslock);
+                if (rnp_old != NULL)
+                        raw_spin_unlock(&rnp_old->fqslock);
+                if (ret) {
+                        rsp->n_force_qs_lh++;
+                        return;
+                }
+                rnp_old = rnp;
+        }
+        /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
+
+        /* Reached the root of the rcu_node tree, acquire lock. */
+        raw_spin_lock_irqsave(&rnp_old->lock, flags);
+        raw_spin_unlock(&rnp_old->fqslock);
+        if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
+                rsp->n_force_qs_lh++;
+                raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
+                return;  /* Someone beat us to it. */
+        }
+        rsp->gp_flags |= RCU_GP_FLAG_FQS;
+        raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
+        wake_up(&rsp->gp_wq);  /* Memory barrier implied by wake_up() path. */
+}
+
+/*
+ * This does the RCU core processing work for the specified rcu_state
+ * and rcu_data structures.  This may be called only from the CPU to
+ * whom the rdp belongs.
+ */
+static void
+__rcu_process_callbacks(struct rcu_state *rsp)
+{
+        unsigned long flags;
+        struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
+
+        WARN_ON_ONCE(rdp->beenonline == 0);
+
+        /* 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? */
+        local_irq_save(flags);
+        if (cpu_needs_another_gp(rsp, rdp)) {
+                raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
+                rcu_start_gp(rsp);
+                raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
+        } else {
+                local_irq_restore(flags);
+        }
+
+        /* If there are callbacks ready, invoke them. */
+        if (cpu_has_callbacks_ready_to_invoke(rdp))
+                invoke_rcu_callbacks(rsp, rdp);
+}
+
+/*
+ * Do RCU core processing for the current CPU.
+ */
+static void rcu_process_callbacks(struct softirq_action *unused)
+{
+        struct rcu_state *rsp;
+
+        if (cpu_is_offline(smp_processor_id()))
+                return;
+        trace_rcu_utilization(TPS("Start RCU core"));
+        for_each_rcu_flavor(rsp)
+                __rcu_process_callbacks(rsp);
+        trace_rcu_utilization(TPS("End RCU core"));
+}
+
+/*
+ * Schedule RCU callback invocation.  If the specified type of RCU
+ * does not support RCU priority boosting, just do a direct call,
+ * otherwise wake up the per-CPU kernel kthread.  Note that because we
+ * are running on the current CPU with interrupts disabled, the
+ * rcu_cpu_kthread_task cannot disappear out from under us.
+ */
+static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
+{
+        if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
+                return;
+        if (likely(!rsp->boost)) {
+                rcu_do_batch(rsp, rdp);
+                return;
+        }
+        invoke_rcu_callbacks_kthread();
+}
+
+static void invoke_rcu_core(void)
+{
+        if (cpu_online(smp_processor_id()))
+                raise_softirq(RCU_SOFTIRQ);
+}
+
+/*
+ * Handle any core-RCU processing required by a call_rcu() invocation.
+ */
+static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
+                            struct rcu_head *head, unsigned long flags)
+{
+        /*
+         * If called from an extended quiescent state, invoke the RCU
+         * core in order to force a re-evaluation of RCU's idleness.
+         */
+        if (!rcu_is_watching() && cpu_online(smp_processor_id()))
+                invoke_rcu_core();
+
+        /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
+        if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
+                return;
+
+        /*
+         * Force the grace period if too many callbacks or too long waiting.
+         * Enforce hysteresis, and don't invoke force_quiescent_state()
+         * if some other CPU has recently done so.  Also, don't bother
+         * invoking force_quiescent_state() if the newly enqueued callback
+         * is the only one waiting for a grace period to complete.
+         */
+        if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
+
+                /* Are we ignoring a completed grace period? */
+                note_gp_changes(rsp, rdp);
+
+                /* Start a new grace period if one not already started. */
+                if (!rcu_gp_in_progress(rsp)) {
+                        struct rcu_node *rnp_root = rcu_get_root(rsp);
+
+                        raw_spin_lock(&rnp_root->lock);
+                        rcu_start_gp(rsp);
+                        raw_spin_unlock(&rnp_root->lock);
+                } else {
+                        /* Give the grace period a kick. */
+                        rdp->blimit = LONG_MAX;
+                        if (rsp->n_force_qs == rdp->n_force_qs_snap &&
+                            *rdp->nxttail[RCU_DONE_TAIL] != head)
+                                force_quiescent_state(rsp);
+                        rdp->n_force_qs_snap = rsp->n_force_qs;
+                        rdp->qlen_last_fqs_check = rdp->qlen;
+                }
+        }
+}
+
+/*
+ * RCU callback function to leak a callback.
+ */
+static void rcu_leak_callback(struct rcu_head *rhp)
+{
+}
+
+/*
+ * Helper function for call_rcu() and friends.  The cpu argument will
+ * normally be -1, indicating "currently running CPU".  It may specify
+ * a CPU only if that CPU is a no-CBs CPU.  Currently, only _rcu_barrier()
+ * is expected to specify a CPU.
+ */
+static void
+__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
+           struct rcu_state *rsp, int cpu, bool lazy)
+{
+        unsigned long flags;
+        struct rcu_data *rdp;
+
+        WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
+        if (debug_rcu_head_queue(head)) {
+                /* Probable double call_rcu(), so leak the callback. */
+                ACCESS_ONCE(head->func) = rcu_leak_callback;
+                WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
+                return;
+        }
+        head->func = func;
+        head->next = NULL;
+
+        /*
+         * Opportunistically note grace-period endings and beginnings.
+         * Note that we might see a beginning right after we see an
+         * end, but never vice versa, since this CPU has to pass through
+         * a quiescent state betweentimes.
+         */
+        local_irq_save(flags);
+        rdp = this_cpu_ptr(rsp->rda);
+
+        /* Add the callback to our list. */
+        if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
+                int offline;
+
+                if (cpu != -1)
+                        rdp = per_cpu_ptr(rsp->rda, cpu);
+                offline = !__call_rcu_nocb(rdp, head, lazy);
+                WARN_ON_ONCE(offline);
+                /* _call_rcu() is illegal on offline CPU; leak the callback. */
+                local_irq_restore(flags);
+                return;
+        }
+        ACCESS_ONCE(rdp->qlen)++;
+        if (lazy)
+                rdp->qlen_lazy++;
+        else
+                rcu_idle_count_callbacks_posted();
+        smp_mb();  /* Count before adding callback for rcu_barrier(). */
+        *rdp->nxttail[RCU_NEXT_TAIL] = head;
+        rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
+
+        if (__is_kfree_rcu_offset((unsigned long)func))
+                trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
+                                         rdp->qlen_lazy, rdp->qlen);
+        else
+                trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
+
+        /* Go handle any RCU core processing required. */
+        __call_rcu_core(rsp, rdp, head, flags);
+        local_irq_restore(flags);
+}
+
+/*
+ * Queue an RCU-sched callback for invocation after a grace period.
+ */
+void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
+{
+        __call_rcu(head, func, &rcu_sched_state, -1, 0);
+}
+EXPORT_SYMBOL_GPL(call_rcu_sched);
+
+/*
+ * Queue an RCU callback for invocation after a quicker grace period.
+ */
+void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
+{
+        __call_rcu(head, func, &rcu_bh_state, -1, 0);
+}
+EXPORT_SYMBOL_GPL(call_rcu_bh);
+
+/*
+ * Because a context switch is a grace period for RCU-sched and RCU-bh,
+ * any blocking grace-period wait automatically implies a grace period
+ * if there is only one CPU online at any point time during execution
+ * of either synchronize_sched() or synchronize_rcu_bh().  It is OK to
+ * occasionally incorrectly indicate that there are multiple CPUs online
+ * when there was in fact only one the whole time, as this just adds
+ * some overhead: RCU still operates correctly.
+ */
+static inline int rcu_blocking_is_gp(void)
+{
+        int ret;
+
+        might_sleep();  /* Check for RCU read-side critical section. */
+        preempt_disable();
+        ret = num_online_cpus() <= 1;
+        preempt_enable();
+        return ret;
+}
+
+/**
+ * synchronize_sched - wait until an rcu-sched grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full rcu-sched
+ * grace period has elapsed, in other words after all currently executing
+ * rcu-sched read-side critical sections have completed.   These read-side
+ * critical sections are delimited by rcu_read_lock_sched() and
+ * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
+ * local_irq_disable(), and so on may be used in place of
+ * rcu_read_lock_sched().
+ *
+ * This means that all preempt_disable code sequences, including NMI and
+ * non-threaded hardware-interrupt handlers, in progress on entry will
+ * have completed before this primitive returns.  However, this does not
+ * guarantee that softirq handlers will have completed, since in some
+ * kernels, these handlers can run in process context, and can block.
+ *
+ * Note that this guarantee implies further memory-ordering guarantees.
+ * On systems with more than one CPU, when synchronize_sched() returns,
+ * each CPU is guaranteed to have executed a full memory barrier since the
+ * end of its last RCU-sched read-side critical section whose beginning
+ * preceded the call to synchronize_sched().  In addition, each CPU having
+ * an RCU read-side critical section that extends beyond the return from
+ * synchronize_sched() is guaranteed to have executed a full memory barrier
+ * after the beginning of synchronize_sched() and before the beginning of
+ * that RCU read-side critical section.  Note that these guarantees include
+ * CPUs that are offline, idle, or executing in user mode, as well as CPUs
+ * that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked synchronize_sched(), which returned
+ * to its caller on CPU B, then both CPU A and CPU B are guaranteed
+ * to have executed a full memory barrier during the execution of
+ * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
+ * again only if the system has more than one CPU).
+ *
+ * This primitive provides the guarantees made by the (now removed)
+ * synchronize_kernel() API.  In contrast, synchronize_rcu() only
+ * guarantees that rcu_read_lock() sections will have completed.
+ * In "classic RCU", these two guarantees happen to be one and
+ * the same, but can differ in realtime RCU implementations.
+ */
+void synchronize_sched(void)
+{
+        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
+                           !lock_is_held(&rcu_lock_map) &&
+                           !lock_is_held(&rcu_sched_lock_map),
+                           "Illegal synchronize_sched() in RCU-sched read-side critical section");
+        if (rcu_blocking_is_gp())
+                return;
+        if (rcu_expedited)
+                synchronize_sched_expedited();
+        else
+                wait_rcu_gp(call_rcu_sched);
+}
+EXPORT_SYMBOL_GPL(synchronize_sched);
+
+/**
+ * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full rcu_bh grace
+ * period has elapsed, in other words after all currently executing rcu_bh
+ * read-side critical sections have completed.  RCU read-side critical
+ * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
+ * and may be nested.
+ *
+ * See the description of synchronize_sched() for more detailed information
+ * on memory ordering guarantees.
+ */
+void synchronize_rcu_bh(void)
+{
+        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
+                           !lock_is_held(&rcu_lock_map) &&
+                           !lock_is_held(&rcu_sched_lock_map),
+                           "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
+        if (rcu_blocking_is_gp())
+                return;
+        if (rcu_expedited)
+                synchronize_rcu_bh_expedited();
+        else
+                wait_rcu_gp(call_rcu_bh);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
+
+static int synchronize_sched_expedited_cpu_stop(void *data)
+{
+        /*
+         * There must be a full memory barrier on each affected CPU
+         * between the time that try_stop_cpus() is called and the
+         * time that it returns.
+         *
+         * In the current initial implementation of cpu_stop, the
+         * above condition is already met when the control reaches
+         * this point and the following smp_mb() is not strictly
+         * necessary.  Do smp_mb() anyway for documentation and
+         * robustness against future implementation changes.
+         */
+        smp_mb(); /* See above comment block. */
+        return 0;
+}
+
+/**
+ * synchronize_sched_expedited - Brute-force RCU-sched grace period
+ *
+ * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
+ * approach to force the grace period to end quickly.  This consumes
+ * significant time on all CPUs and is unfriendly to real-time workloads,
+ * so is thus not recommended for any sort of common-case code.  In fact,
+ * if you are using synchronize_sched_expedited() in a loop, please
+ * restructure your code to batch your updates, and then use a single
+ * synchronize_sched() instead.
+ *
+ * Note that it is illegal to call this function while holding any lock
+ * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
+ * to call this function from a CPU-hotplug notifier.  Failing to observe
+ * these restriction will result in deadlock.
+ *
+ * This implementation can be thought of as an application of ticket
+ * locking to RCU, with sync_sched_expedited_started and
+ * sync_sched_expedited_done taking on the roles of the halves
+ * of the ticket-lock word.  Each task atomically increments
+ * sync_sched_expedited_started upon entry, snapshotting the old value,
+ * then attempts to stop all the CPUs.  If this succeeds, then each
+ * CPU will have executed a context switch, resulting in an RCU-sched
+ * grace period.  We are then done, so we use atomic_cmpxchg() to
+ * update sync_sched_expedited_done to match our snapshot -- but
+ * only if someone else has not already advanced past our snapshot.
+ *
+ * On the other hand, if try_stop_cpus() fails, we check the value
+ * of sync_sched_expedited_done.  If it has advanced past our
+ * initial snapshot, then someone else must have forced a grace period
+ * some time after we took our snapshot.  In this case, our work is
+ * done for us, and we can simply return.  Otherwise, we try again,
+ * but keep our initial snapshot for purposes of checking for someone
+ * doing our work for us.
+ *
+ * If we fail too many times in a row, we fall back to synchronize_sched().
+ */
+void synchronize_sched_expedited(void)
+{
+        long firstsnap, s, snap;
+        int trycount = 0;
+        struct rcu_state *rsp = &rcu_sched_state;
+
+        /*
+         * If we are in danger of counter wrap, just do synchronize_sched().
+         * By allowing sync_sched_expedited_started to advance no more than
+         * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring
+         * that more than 3.5 billion CPUs would be required to force a
+         * counter wrap on a 32-bit system.  Quite a few more CPUs would of
+         * course be required on a 64-bit system.
+         */
+        if (ULONG_CMP_GE((ulong)atomic_long_read(&rsp->expedited_start),
+                         (ulong)atomic_long_read(&rsp->expedited_done) +
+                         ULONG_MAX / 8)) {
+                synchronize_sched();
+                atomic_long_inc(&rsp->expedited_wrap);
+                return;
+        }
+
+        /*
+         * Take a ticket.  Note that atomic_inc_return() implies a
+         * full memory barrier.
+         */
+        snap = atomic_long_inc_return(&rsp->expedited_start);
+        firstsnap = snap;
+        get_online_cpus();
+        WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
+
+        /*
+         * Each pass through the following loop attempts to force a
+         * context switch on each CPU.
+         */
+        while (try_stop_cpus(cpu_online_mask,
+                             synchronize_sched_expedited_cpu_stop,
+                             NULL) == -EAGAIN) {
+                put_online_cpus();
+                atomic_long_inc(&rsp->expedited_tryfail);
+
+                /* Check to see if someone else did our work for us. */
+                s = atomic_long_read(&rsp->expedited_done);
+                if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
+                        /* ensure test happens before caller kfree */
+                        smp_mb__before_atomic_inc(); /* ^^^ */
+                        atomic_long_inc(&rsp->expedited_workdone1);
+                        return;
+                }
+
+                /* No joy, try again later.  Or just synchronize_sched(). */
+                if (trycount++ < 10) {
+                        udelay(trycount * num_online_cpus());
+                } else {
+                        wait_rcu_gp(call_rcu_sched);
+                        atomic_long_inc(&rsp->expedited_normal);
+                        return;
+                }
+
+                /* Recheck to see if someone else did our work for us. */
+                s = atomic_long_read(&rsp->expedited_done);
+                if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
+                        /* ensure test happens before caller kfree */
+                        smp_mb__before_atomic_inc(); /* ^^^ */
+                        atomic_long_inc(&rsp->expedited_workdone2);
+                        return;
+                }
+
+                /*
+                 * Refetching sync_sched_expedited_started allows later
+                 * callers to piggyback on our grace period.  We retry
+                 * after they started, so our grace period works for them,
+                 * and they started after our first try, so their grace
+                 * period works for us.
+                 */
+                get_online_cpus();
+                snap = atomic_long_read(&rsp->expedited_start);
+                smp_mb(); /* ensure read is before try_stop_cpus(). */
+        }
+        atomic_long_inc(&rsp->expedited_stoppedcpus);
+
+        /*
+         * Everyone up to our most recent fetch is covered by our grace
+         * period.  Update the counter, but only if our work is still
+         * relevant -- which it won't be if someone who started later
+         * than we did already did their update.
+         */
+        do {
+                atomic_long_inc(&rsp->expedited_done_tries);
+                s = atomic_long_read(&rsp->expedited_done);
+                if (ULONG_CMP_GE((ulong)s, (ulong)snap)) {
+                        /* ensure test happens before caller kfree */
+                        smp_mb__before_atomic_inc(); /* ^^^ */
+                        atomic_long_inc(&rsp->expedited_done_lost);
+                        break;
+                }
+        } while (atomic_long_cmpxchg(&rsp->expedited_done, s, snap) != s);
+        atomic_long_inc(&rsp->expedited_done_exit);
+
+        put_online_cpus();
+}
+EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
+
+/*
+ * Check to see if there is any immediate RCU-related work to be done
+ * by the current CPU, for the specified type of RCU, returning 1 if so.
+ * The checks are in order of increasing expense: checks that can be
+ * carried out against CPU-local state are performed first.  However,
+ * we must check for CPU stalls first, else we might not get a chance.
+ */
+static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
+{
+        struct rcu_node *rnp = rdp->mynode;
+
+        rdp->n_rcu_pending++;
+
+        /* Check for CPU stalls, if enabled. */
+        check_cpu_stall(rsp, rdp);
+
+        /* Is the RCU core waiting for a quiescent state from this CPU? */
+        if (rcu_scheduler_fully_active &&
+            rdp->qs_pending && !rdp->passed_quiesce) {
+                rdp->n_rp_qs_pending++;
+        } else if (rdp->qs_pending && rdp->passed_quiesce) {
+                rdp->n_rp_report_qs++;
+                return 1;
+        }
+
+        /* Does this CPU have callbacks ready to invoke? */
+        if (cpu_has_callbacks_ready_to_invoke(rdp)) {
+                rdp->n_rp_cb_ready++;
+                return 1;
+        }
+
+        /* Has RCU gone idle with this CPU needing another grace period? */
+        if (cpu_needs_another_gp(rsp, rdp)) {
+                rdp->n_rp_cpu_needs_gp++;
+                return 1;
+        }
+
+        /* Has another RCU grace period completed?  */
+        if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
+                rdp->n_rp_gp_completed++;
+                return 1;
+        }
+
+        /* Has a new RCU grace period started? */
+        if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
+                rdp->n_rp_gp_started++;
+                return 1;
+        }
+
+        /* nothing to do */
+        rdp->n_rp_need_nothing++;
+        return 0;
+}
+
+/*
+ * Check to see if there is any immediate RCU-related work to be done
+ * by the current CPU, returning 1 if so.  This function is part of the
+ * RCU implementation; it is -not- an exported member of the RCU API.
+ */
+static int rcu_pending(int cpu)
+{
+        struct rcu_state *rsp;
+
+        for_each_rcu_flavor(rsp)
+                if (__rcu_pending(rsp, per_cpu_ptr(rsp->rda, cpu)))
+                        return 1;
+        return 0;
+}
+
+/*
+ * Return true if the specified CPU has any callback.  If all_lazy is
+ * non-NULL, store an indication of whether all callbacks are lazy.
+ * (If there are no callbacks, all of them are deemed to be lazy.)
+ */
+static int rcu_cpu_has_callbacks(int cpu, bool *all_lazy)
+{
+        bool al = true;
+        bool hc = false;
+        struct rcu_data *rdp;
+        struct rcu_state *rsp;
+
+        for_each_rcu_flavor(rsp) {
+                rdp = per_cpu_ptr(rsp->rda, cpu);
+                if (!rdp->nxtlist)
+                        continue;
+                hc = true;
+                if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
+                        al = false;
+                        break;
+                }
+        }
+        if (all_lazy)
+                *all_lazy = al;
+        return hc;
+}
+
+/*
+ * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
+ * the compiler is expected to optimize this away.
+ */
+static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
+                               int cpu, unsigned long done)
+{
+        trace_rcu_barrier(rsp->name, s, cpu,
+                          atomic_read(&rsp->barrier_cpu_count), done);
+}
+
+/*
+ * RCU callback function for _rcu_barrier().  If we are last, wake
+ * up the task executing _rcu_barrier().
+ */
+static void rcu_barrier_callback(struct rcu_head *rhp)
+{
+        struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
+        struct rcu_state *rsp = rdp->rsp;
+
+        if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
+                _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
+                complete(&rsp->barrier_completion);
+        } else {
+                _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
+        }
+}
+
+/*
+ * Called with preemption disabled, and from cross-cpu IRQ context.
+ */
+static void rcu_barrier_func(void *type)
+{
+        struct rcu_state *rsp = type;
+        struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
+
+        _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
+        atomic_inc(&rsp->barrier_cpu_count);
+        rsp->call(&rdp->barrier_head, rcu_barrier_callback);
+}
+
+/*
+ * Orchestrate the specified type of RCU barrier, waiting for all
+ * RCU callbacks of the specified type to complete.
+ */
+static void _rcu_barrier(struct rcu_state *rsp)
+{
+        int cpu;
+        struct rcu_data *rdp;
+        unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done);
+        unsigned long snap_done;
+
+        _rcu_barrier_trace(rsp, "Begin", -1, snap);
+
+        /* Take mutex to serialize concurrent rcu_barrier() requests. */
+        mutex_lock(&rsp->barrier_mutex);
+
+        /*
+         * Ensure that all prior references, including to ->n_barrier_done,
+         * are ordered before the _rcu_barrier() machinery.
+         */
+        smp_mb();  /* See above block comment. */
+
+        /*
+         * Recheck ->n_barrier_done to see if others did our work for us.
+         * This means checking ->n_barrier_done for an even-to-odd-to-even
+         * transition.  The "if" expression below therefore rounds the old
+         * value up to the next even number and adds two before comparing.
+         */
+        snap_done = rsp->n_barrier_done;
+        _rcu_barrier_trace(rsp, "Check", -1, snap_done);
+
+        /*
+         * If the value in snap is odd, we needed to wait for the current
+         * rcu_barrier() to complete, then wait for the next one, in other
+         * words, we need the value of snap_done to be three larger than
+         * the value of snap.  On the other hand, if the value in snap is
+         * even, we only had to wait for the next rcu_barrier() to complete,
+         * in other words, we need the value of snap_done to be only two
+         * greater than the value of snap.  The "(snap + 3) & ~0x1" computes
+         * this for us (thank you, Linus!).
+         */
+        if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) {
+                _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
+                smp_mb(); /* caller's subsequent code after above check. */
+                mutex_unlock(&rsp->barrier_mutex);
+                return;
+        }
+
+        /*
+         * Increment ->n_barrier_done to avoid duplicate work.  Use
+         * ACCESS_ONCE() to prevent the compiler from speculating
+         * the increment to precede the early-exit check.
+         */
+        ACCESS_ONCE(rsp->n_barrier_done)++;
+        WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
+        _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
+        smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
+
+        /*
+         * Initialize the count to one rather than to zero in order to
+         * avoid a too-soon return to zero in case of a short grace period
+         * (or preemption of this task).  Exclude CPU-hotplug operations
+         * to ensure that no offline CPU has callbacks queued.
+         */
+        init_completion(&rsp->barrier_completion);
+        atomic_set(&rsp->barrier_cpu_count, 1);
+        get_online_cpus();
+
+        /*
+         * Force each CPU with callbacks to register a new callback.
+         * When that callback is invoked, we will know that all of the
+         * corresponding CPU's preceding callbacks have been invoked.
+         */
+        for_each_possible_cpu(cpu) {
+                if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
+                        continue;
+                rdp = per_cpu_ptr(rsp->rda, cpu);
+                if (rcu_is_nocb_cpu(cpu)) {
+                        _rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
+                                           rsp->n_barrier_done);
+                        atomic_inc(&rsp->barrier_cpu_count);
+                        __call_rcu(&rdp->barrier_head, rcu_barrier_callback,
+                                   rsp, cpu, 0);
+                } else if (ACCESS_ONCE(rdp->qlen)) {
+                        _rcu_barrier_trace(rsp, "OnlineQ", cpu,
+                                           rsp->n_barrier_done);
+                        smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
+                } else {
+                        _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
+                                           rsp->n_barrier_done);
+                }
+        }
+        put_online_cpus();
+
+        /*
+         * Now that we have an rcu_barrier_callback() callback on each
+         * CPU, and thus each counted, remove the initial count.
+         */
+        if (atomic_dec_and_test(&rsp->barrier_cpu_count))
+                complete(&rsp->barrier_completion);
+
+        /* Increment ->n_barrier_done to prevent duplicate work. */
+        smp_mb(); /* Keep increment after above mechanism. */
+        ACCESS_ONCE(rsp->n_barrier_done)++;
+        WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
+        _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
+        smp_mb(); /* Keep increment before caller's subsequent code. */
+
+        /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
+        wait_for_completion(&rsp->barrier_completion);
+
+        /* Other rcu_barrier() invocations can now safely proceed. */
+        mutex_unlock(&rsp->barrier_mutex);
+}
+
+/**
+ * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
+ */
+void rcu_barrier_bh(void)
+{
+        _rcu_barrier(&rcu_bh_state);
+}
+EXPORT_SYMBOL_GPL(rcu_barrier_bh);
+
+/**
+ * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
+ */
+void rcu_barrier_sched(void)
+{
+        _rcu_barrier(&rcu_sched_state);
+}
+EXPORT_SYMBOL_GPL(rcu_barrier_sched);
+
+/*
+ * Do boot-time initialization of a CPU's per-CPU RCU data.
+ */
+static void __init
+rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
+{
+        unsigned long flags;
+        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+        struct rcu_node *rnp = rcu_get_root(rsp);
+
+        /* Set up local state, ensuring consistent view of global state. */
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
+        init_callback_list(rdp);
+        rdp->qlen_lazy = 0;
+        ACCESS_ONCE(rdp->qlen) = 0;
+        rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
+        WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
+        WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
+        rdp->cpu = cpu;
+        rdp->rsp = rsp;
+        rcu_boot_init_nocb_percpu_data(rdp);
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+/*
+ * Initialize a CPU's per-CPU RCU data.  Note that only one online or
+ * offline event can be happening at a given time.  Note also that we
+ * can accept some slop in the rsp->completed access due to the fact
+ * that this CPU cannot possibly have any RCU callbacks in flight yet.
+ */
+static void
+rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
+{
+        unsigned long flags;
+        unsigned long mask;
+        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+        struct rcu_node *rnp = rcu_get_root(rsp);
+
+        /* Exclude new grace periods. */
+        mutex_lock(&rsp->onoff_mutex);
+
+        /* Set up local state, ensuring consistent view of global state. */
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        rdp->beenonline = 1;     /* We have now been online. */
+        rdp->preemptible = preemptible;
+        rdp->qlen_last_fqs_check = 0;
+        rdp->n_force_qs_snap = rsp->n_force_qs;
+        rdp->blimit = blimit;
+        init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
+        rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
+        rcu_sysidle_init_percpu_data(rdp->dynticks);
+        atomic_set(&rdp->dynticks->dynticks,
+                   (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
+        raw_spin_unlock(&rnp->lock);            /* irqs remain disabled. */
+
+        /* Add CPU to rcu_node bitmasks. */
+        rnp = rdp->mynode;
+        mask = rdp->grpmask;
+        do {
+                /* Exclude any attempts to start a new GP on small systems. */
+                raw_spin_lock(&rnp->lock);      /* irqs already disabled. */
+                rnp->qsmaskinit |= mask;
+                mask = rnp->grpmask;
+                if (rnp == rdp->mynode) {
+                        /*
+                         * If there is a grace period in progress, we will
+                         * set up to wait for it next time we run the
+                         * RCU core code.
+                         */
+                        rdp->gpnum = rnp->completed;
+                        rdp->completed = rnp->completed;
+                        rdp->passed_quiesce = 0;
+                        rdp->qs_pending = 0;
+                        trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
+                }
+                raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
+                rnp = rnp->parent;
+        } while (rnp != NULL && !(rnp->qsmaskinit & mask));
+        local_irq_restore(flags);
+
+        mutex_unlock(&rsp->onoff_mutex);
+}
+
+static void rcu_prepare_cpu(int cpu)
+{
+        struct rcu_state *rsp;
+
+        for_each_rcu_flavor(rsp)
+                rcu_init_percpu_data(cpu, rsp,
+                                     strcmp(rsp->name, "rcu_preempt") == 0);
+}
+
+/*
+ * Handle CPU online/offline notification events.
+ */
+static int rcu_cpu_notify(struct notifier_block *self,
+                                    unsigned long action, void *hcpu)
+{
+        long cpu = (long)hcpu;
+        struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
+        struct rcu_node *rnp = rdp->mynode;
+        struct rcu_state *rsp;
+
+        trace_rcu_utilization(TPS("Start CPU hotplug"));
+        switch (action) {
+        case CPU_UP_PREPARE:
+        case CPU_UP_PREPARE_FROZEN:
+                rcu_prepare_cpu(cpu);
+                rcu_prepare_kthreads(cpu);
+                break;
+        case CPU_ONLINE:
+        case CPU_DOWN_FAILED:
+                rcu_boost_kthread_setaffinity(rnp, -1);
+                break;
+        case CPU_DOWN_PREPARE:
+                rcu_boost_kthread_setaffinity(rnp, cpu);
+                break;
+        case CPU_DYING:
+        case CPU_DYING_FROZEN:
+                for_each_rcu_flavor(rsp)
+                        rcu_cleanup_dying_cpu(rsp);
+                break;
+        case CPU_DEAD:
+        case CPU_DEAD_FROZEN:
+        case CPU_UP_CANCELED:
+        case CPU_UP_CANCELED_FROZEN:
+                for_each_rcu_flavor(rsp)
+                        rcu_cleanup_dead_cpu(cpu, rsp);
+                break;
+        default:
+                break;
+        }
+        trace_rcu_utilization(TPS("End CPU hotplug"));
+        return NOTIFY_OK;
+}
+
+static int rcu_pm_notify(struct notifier_block *self,
+                         unsigned long action, void *hcpu)
+{
+        switch (action) {
+        case PM_HIBERNATION_PREPARE:
+        case PM_SUSPEND_PREPARE:
+                if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
+                        rcu_expedited = 1;
+                break;
+        case PM_POST_HIBERNATION:
+        case PM_POST_SUSPEND:
+                rcu_expedited = 0;
+                break;
+        default:
+                break;
+        }
+        return NOTIFY_OK;
+}
+
+/*
+ * Spawn the kthread that handles this RCU flavor's grace periods.
+ */
+static int __init rcu_spawn_gp_kthread(void)
+{
+        unsigned long flags;
+        struct rcu_node *rnp;
+        struct rcu_state *rsp;
+        struct task_struct *t;
+
+        for_each_rcu_flavor(rsp) {
+                t = kthread_run(rcu_gp_kthread, rsp, "%s", rsp->name);
+                BUG_ON(IS_ERR(t));
+                rnp = rcu_get_root(rsp);
+                raw_spin_lock_irqsave(&rnp->lock, flags);
+                rsp->gp_kthread = t;
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                rcu_spawn_nocb_kthreads(rsp);
+        }
+        return 0;
+}
+early_initcall(rcu_spawn_gp_kthread);
+
+/*
+ * This function is invoked towards the end of the scheduler's initialization
+ * process.  Before this is called, the idle task might contain
+ * RCU read-side critical sections (during which time, this idle
+ * task is booting the system).  After this function is called, the
+ * idle tasks are prohibited from containing RCU read-side critical
+ * sections.  This function also enables RCU lockdep checking.
+ */
+void rcu_scheduler_starting(void)
+{
+        WARN_ON(num_online_cpus() != 1);
+        WARN_ON(nr_context_switches() > 0);
+        rcu_scheduler_active = 1;
+}
+
+/*
+ * Compute the per-level fanout, either using the exact fanout specified
+ * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
+ */
+#ifdef CONFIG_RCU_FANOUT_EXACT
+static void __init rcu_init_levelspread(struct rcu_state *rsp)
+{
+        int i;
+
+        for (i = rcu_num_lvls - 1; i > 0; i--)
+                rsp->levelspread[i] = CONFIG_RCU_FANOUT;
+        rsp->levelspread[0] = rcu_fanout_leaf;
+}
+#else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
+static void __init rcu_init_levelspread(struct rcu_state *rsp)
+{
+        int ccur;
+        int cprv;
+        int i;
+
+        cprv = nr_cpu_ids;
+        for (i = rcu_num_lvls - 1; i >= 0; i--) {
+                ccur = rsp->levelcnt[i];
+                rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
+                cprv = ccur;
+        }
+}
+#endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
+
+/*
+ * Helper function for rcu_init() that initializes one rcu_state structure.
+ */
+static void __init rcu_init_one(struct rcu_state *rsp,
+                struct rcu_data __percpu *rda)
+{
+        static char *buf[] = { "rcu_node_0",
+                               "rcu_node_1",
+                               "rcu_node_2",
+                               "rcu_node_3" };  /* Match MAX_RCU_LVLS */
+        static char *fqs[] = { "rcu_node_fqs_0",
+                               "rcu_node_fqs_1",
+                               "rcu_node_fqs_2",
+                               "rcu_node_fqs_3" };  /* Match MAX_RCU_LVLS */
+        int cpustride = 1;
+        int i;
+        int j;
+        struct rcu_node *rnp;
+
+        BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
+
+        /* Silence gcc 4.8 warning about array index out of range. */
+        if (rcu_num_lvls > RCU_NUM_LVLS)
+                panic("rcu_init_one: rcu_num_lvls overflow");
+
+        /* Initialize the level-tracking arrays. */
+
+        for (i = 0; i < rcu_num_lvls; i++)
+                rsp->levelcnt[i] = num_rcu_lvl[i];
+        for (i = 1; i < rcu_num_lvls; i++)
+                rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
+        rcu_init_levelspread(rsp);
+
+        /* Initialize the elements themselves, starting from the leaves. */
+
+        for (i = rcu_num_lvls - 1; i >= 0; i--) {
+                cpustride *= rsp->levelspread[i];
+                rnp = rsp->level[i];
+                for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
+                        raw_spin_lock_init(&rnp->lock);
+                        lockdep_set_class_and_name(&rnp->lock,
+                                                   &rcu_node_class[i], buf[i]);
+                        raw_spin_lock_init(&rnp->fqslock);
+                        lockdep_set_class_and_name(&rnp->fqslock,
+                                                   &rcu_fqs_class[i], fqs[i]);
+                        rnp->gpnum = rsp->gpnum;
+                        rnp->completed = rsp->completed;
+                        rnp->qsmask = 0;
+                        rnp->qsmaskinit = 0;
+                        rnp->grplo = j * cpustride;
+                        rnp->grphi = (j + 1) * cpustride - 1;
+                        if (rnp->grphi >= NR_CPUS)
+                                rnp->grphi = NR_CPUS - 1;
+                        if (i == 0) {
+                                rnp->grpnum = 0;
+                                rnp->grpmask = 0;
+                                rnp->parent = NULL;
+                        } else {
+                                rnp->grpnum = j % rsp->levelspread[i - 1];
+                                rnp->grpmask = 1UL << rnp->grpnum;
+                                rnp->parent = rsp->level[i - 1] +
+                                              j / rsp->levelspread[i - 1];
+                        }
+                        rnp->level = i;
+                        INIT_LIST_HEAD(&rnp->blkd_tasks);
+                        rcu_init_one_nocb(rnp);
+                }
+        }
+
+        rsp->rda = rda;
+        init_waitqueue_head(&rsp->gp_wq);
+        init_irq_work(&rsp->wakeup_work, rsp_wakeup);
+        rnp = rsp->level[rcu_num_lvls - 1];
+        for_each_possible_cpu(i) {
+                while (i > rnp->grphi)
+                        rnp++;
+                per_cpu_ptr(rsp->rda, i)->mynode = rnp;
+                rcu_boot_init_percpu_data(i, rsp);
+        }
+        list_add(&rsp->flavors, &rcu_struct_flavors);
+}
+
+/*
+ * Compute the rcu_node tree geometry from kernel parameters.  This cannot
+ * replace the definitions in tree.h because those are needed to size
+ * the ->node array in the rcu_state structure.
+ */
+static void __init rcu_init_geometry(void)
+{
+        ulong d;
+        int i;
+        int j;
+        int n = nr_cpu_ids;
+        int rcu_capacity[MAX_RCU_LVLS + 1];
+
+        /*
+         * Initialize any unspecified boot parameters.
+         * The default values of jiffies_till_first_fqs and
+         * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
+         * value, which is a function of HZ, then adding one for each
+         * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
+         */
+        d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
+        if (jiffies_till_first_fqs == ULONG_MAX)
+                jiffies_till_first_fqs = d;
+        if (jiffies_till_next_fqs == ULONG_MAX)
+                jiffies_till_next_fqs = d;
+
+        /* If the compile-time values are accurate, just leave. */
+        if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
+            nr_cpu_ids == NR_CPUS)
+                return;
+
+        /*
+         * Compute number of nodes that can be handled an rcu_node tree
+         * with the given number of levels.  Setting rcu_capacity[0] makes
+         * some of the arithmetic easier.
+         */
+        rcu_capacity[0] = 1;
+        rcu_capacity[1] = rcu_fanout_leaf;
+        for (i = 2; i <= MAX_RCU_LVLS; i++)
+                rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT;
+
+        /*
+         * The boot-time rcu_fanout_leaf parameter is only permitted
+         * to increase the leaf-level fanout, not decrease it.  Of course,
+         * the leaf-level fanout cannot exceed the number of bits in
+         * the rcu_node masks.  Finally, the tree must be able to accommodate
+         * the configured number of CPUs.  Complain and fall back to the
+         * compile-time values if these limits are exceeded.
+         */
+        if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF ||
+            rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
+            n > rcu_capacity[MAX_RCU_LVLS]) {
+                WARN_ON(1);
+                return;
+        }
+
+        /* Calculate the number of rcu_nodes at each level of the tree. */
+        for (i = 1; i <= MAX_RCU_LVLS; i++)
+                if (n <= rcu_capacity[i]) {
+                        for (j = 0; j <= i; j++)
+                                num_rcu_lvl[j] =
+                                        DIV_ROUND_UP(n, rcu_capacity[i - j]);
+                        rcu_num_lvls = i;
+                        for (j = i + 1; j <= MAX_RCU_LVLS; j++)
+                                num_rcu_lvl[j] = 0;
+                        break;
+                }
+
+        /* Calculate the total number of rcu_node structures. */
+        rcu_num_nodes = 0;
+        for (i = 0; i <= MAX_RCU_LVLS; i++)
+                rcu_num_nodes += num_rcu_lvl[i];
+        rcu_num_nodes -= n;
+}
+
+void __init rcu_init(void)
+{
+        int cpu;
+
+        rcu_bootup_announce();
+        rcu_init_geometry();
+        rcu_init_one(&rcu_bh_state, &rcu_bh_data);
+        rcu_init_one(&rcu_sched_state, &rcu_sched_data);
+        __rcu_init_preempt();
+        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+
+        /*
+         * We don't need protection against CPU-hotplug here because
+         * this is called early in boot, before either interrupts
+         * or the scheduler are operational.
+         */
+        cpu_notifier(rcu_cpu_notify, 0);
+        pm_notifier(rcu_pm_notify, 0);
+        for_each_online_cpu(cpu)
+                rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
+}
+
+#include "tree_plugin.h"