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, 2831 insertions, 0 deletions

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
new file mode 100644
index 000000000000..3822ac0c4b27
--- /dev/null
+++ b/kernel/rcu/tree_plugin.h
@@ -0,0 +1,2831 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion (tree-based version)
+ * Internal non-public definitions that provide either classic
+ * or preemptible semantics.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright Red Hat, 2009
+ * Copyright IBM Corporation, 2009
+ *
+ * Author: Ingo Molnar <mingo@elte.hu>
+ *         Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ */
+
+#include <linux/delay.h>
+#include <linux/gfp.h>
+#include <linux/oom.h>
+#include <linux/smpboot.h>
+#include "../time/tick-internal.h"
+
+#define RCU_KTHREAD_PRIO 1
+
+#ifdef CONFIG_RCU_BOOST
+#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
+#else
+#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
+#endif
+
+#ifdef CONFIG_RCU_NOCB_CPU
+static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
+static bool have_rcu_nocb_mask;     /* Was rcu_nocb_mask allocated? */
+static bool __read_mostly rcu_nocb_poll;    /* Offload kthread are to poll. */
+static char __initdata nocb_buf[NR_CPUS * 5];
+#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
+
+/*
+ * Check the RCU kernel configuration parameters and print informative
+ * messages about anything out of the ordinary.  If you like #ifdef, you
+ * will love this function.
+ */
+static void __init rcu_bootup_announce_oddness(void)
+{
+#ifdef CONFIG_RCU_TRACE
+        pr_info("\tRCU debugfs-based tracing is enabled.\n");
+#endif
+#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
+        pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
+               CONFIG_RCU_FANOUT);
+#endif
+#ifdef CONFIG_RCU_FANOUT_EXACT
+        pr_info("\tHierarchical RCU autobalancing is disabled.\n");
+#endif
+#ifdef CONFIG_RCU_FAST_NO_HZ
+        pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
+#endif
+#ifdef CONFIG_PROVE_RCU
+        pr_info("\tRCU lockdep checking is enabled.\n");
+#endif
+#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
+        pr_info("\tRCU torture testing starts during boot.\n");
+#endif
+#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
+        pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
+#endif
+#if defined(CONFIG_RCU_CPU_STALL_INFO)
+        pr_info("\tAdditional per-CPU info printed with stalls.\n");
+#endif
+#if NUM_RCU_LVL_4 != 0
+        pr_info("\tFour-level hierarchy is enabled.\n");
+#endif
+        if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
+                pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
+        if (nr_cpu_ids != NR_CPUS)
+                pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
+#ifdef CONFIG_RCU_NOCB_CPU
+#ifndef CONFIG_RCU_NOCB_CPU_NONE
+        if (!have_rcu_nocb_mask) {
+                zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
+                have_rcu_nocb_mask = true;
+        }
+#ifdef CONFIG_RCU_NOCB_CPU_ZERO
+        pr_info("\tOffload RCU callbacks from CPU 0\n");
+        cpumask_set_cpu(0, rcu_nocb_mask);
+#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
+#ifdef CONFIG_RCU_NOCB_CPU_ALL
+        pr_info("\tOffload RCU callbacks from all CPUs\n");
+        cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
+#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
+        if (have_rcu_nocb_mask) {
+                if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
+                        pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
+                        cpumask_and(rcu_nocb_mask, cpu_possible_mask,
+                                    rcu_nocb_mask);
+                }
+                cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
+                pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
+                if (rcu_nocb_poll)
+                        pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
+        }
+#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
+}
+
+#ifdef CONFIG_TREE_PREEMPT_RCU
+
+RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
+static struct rcu_state *rcu_state = &rcu_preempt_state;
+
+static int rcu_preempted_readers_exp(struct rcu_node *rnp);
+
+/*
+ * Tell them what RCU they are running.
+ */
+static void __init rcu_bootup_announce(void)
+{
+        pr_info("Preemptible hierarchical RCU implementation.\n");
+        rcu_bootup_announce_oddness();
+}
+
+/*
+ * Return the number of RCU-preempt batches processed thus far
+ * for debug and statistics.
+ */
+long rcu_batches_completed_preempt(void)
+{
+        return rcu_preempt_state.completed;
+}
+EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
+
+/*
+ * Return the number of RCU batches processed thus far for debug & stats.
+ */
+long rcu_batches_completed(void)
+{
+        return rcu_batches_completed_preempt();
+}
+EXPORT_SYMBOL_GPL(rcu_batches_completed);
+
+/*
+ * Force a quiescent state for preemptible RCU.
+ */
+void rcu_force_quiescent_state(void)
+{
+        force_quiescent_state(&rcu_preempt_state);
+}
+EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
+
+/*
+ * Record a preemptible-RCU quiescent state for the specified CPU.  Note
+ * that this just means that the task currently running on the CPU is
+ * not in a quiescent state.  There might be any number of tasks blocked
+ * while in an RCU read-side critical section.
+ *
+ * Unlike the other rcu_*_qs() functions, callers to this function
+ * must disable irqs in order to protect the assignment to
+ * ->rcu_read_unlock_special.
+ */
+static void rcu_preempt_qs(int cpu)
+{
+        struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
+
+        if (rdp->passed_quiesce == 0)
+                trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
+        rdp->passed_quiesce = 1;
+        current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
+}
+
+/*
+ * We have entered the scheduler, and the current task might soon be
+ * context-switched away from.  If this task is in an RCU read-side
+ * critical section, we will no longer be able to rely on the CPU to
+ * record that fact, so we enqueue the task on the blkd_tasks list.
+ * The task will dequeue itself when it exits the outermost enclosing
+ * RCU read-side critical section.  Therefore, the current grace period
+ * cannot be permitted to complete until the blkd_tasks list entries
+ * predating the current grace period drain, in other words, until
+ * rnp->gp_tasks becomes NULL.
+ *
+ * Caller must disable preemption.
+ */
+static void rcu_preempt_note_context_switch(int cpu)
+{
+        struct task_struct *t = current;
+        unsigned long flags;
+        struct rcu_data *rdp;
+        struct rcu_node *rnp;
+
+        if (t->rcu_read_lock_nesting > 0 &&
+            (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
+
+                /* Possibly blocking in an RCU read-side critical section. */
+                rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
+                rnp = rdp->mynode;
+                raw_spin_lock_irqsave(&rnp->lock, flags);
+                t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
+                t->rcu_blocked_node = rnp;
+
+                /*
+                 * If this CPU has already checked in, then this task
+                 * will hold up the next grace period rather than the
+                 * current grace period.  Queue the task accordingly.
+                 * If the task is queued for the current grace period
+                 * (i.e., this CPU has not yet passed through a quiescent
+                 * state for the current grace period), then as long
+                 * as that task remains queued, the current grace period
+                 * cannot end.  Note that there is some uncertainty as
+                 * to exactly when the current grace period started.
+                 * We take a conservative approach, which can result
+                 * in unnecessarily waiting on tasks that started very
+                 * slightly after the current grace period began.  C'est
+                 * la vie!!!
+                 *
+                 * But first, note that the current CPU must still be
+                 * on line!
+                 */
+                WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
+                WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
+                if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
+                        list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
+                        rnp->gp_tasks = &t->rcu_node_entry;
+#ifdef CONFIG_RCU_BOOST
+                        if (rnp->boost_tasks != NULL)
+                                rnp->boost_tasks = rnp->gp_tasks;
+#endif /* #ifdef CONFIG_RCU_BOOST */
+                } else {
+                        list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
+                        if (rnp->qsmask & rdp->grpmask)
+                                rnp->gp_tasks = &t->rcu_node_entry;
+                }
+                trace_rcu_preempt_task(rdp->rsp->name,
+                                       t->pid,
+                                       (rnp->qsmask & rdp->grpmask)
+                                       ? rnp->gpnum
+                                       : rnp->gpnum + 1);
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        } else if (t->rcu_read_lock_nesting < 0 &&
+                   t->rcu_read_unlock_special) {
+
+                /*
+                 * Complete exit from RCU read-side critical section on
+                 * behalf of preempted instance of __rcu_read_unlock().
+                 */
+                rcu_read_unlock_special(t);
+        }
+
+        /*
+         * Either we were not in an RCU read-side critical section to
+         * begin with, or we have now recorded that critical section
+         * globally.  Either way, we can now note a quiescent state
+         * for this CPU.  Again, if we were in an RCU read-side critical
+         * section, and if that critical section was blocking the current
+         * grace period, then the fact that the task has been enqueued
+         * means that we continue to block the current grace period.
+         */
+        local_irq_save(flags);
+        rcu_preempt_qs(cpu);
+        local_irq_restore(flags);
+}
+
+/*
+ * Check for preempted RCU readers blocking the current grace period
+ * for the specified rcu_node structure.  If the caller needs a reliable
+ * answer, it must hold the rcu_node's ->lock.
+ */
+static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
+{
+        return rnp->gp_tasks != NULL;
+}
+
+/*
+ * Record a quiescent state for all tasks that were previously queued
+ * on the specified rcu_node structure and that were blocking the current
+ * RCU grace period.  The caller must hold the specified rnp->lock with
+ * irqs disabled, and this lock is released upon return, but irqs remain
+ * disabled.
+ */
+static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
+        __releases(rnp->lock)
+{
+        unsigned long mask;
+        struct rcu_node *rnp_p;
+
+        if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                return;  /* Still need more quiescent states! */
+        }
+
+        rnp_p = rnp->parent;
+        if (rnp_p == NULL) {
+                /*
+                 * Either there is only one rcu_node in the tree,
+                 * or tasks were kicked up to root rcu_node due to
+                 * CPUs going offline.
+                 */
+                rcu_report_qs_rsp(&rcu_preempt_state, flags);
+                return;
+        }
+
+        /* Report up the rest of the hierarchy. */
+        mask = rnp->grpmask;
+        raw_spin_unlock(&rnp->lock);    /* irqs remain disabled. */
+        raw_spin_lock(&rnp_p->lock);    /* irqs already disabled. */
+        rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
+}
+
+/*
+ * Advance a ->blkd_tasks-list pointer to the next entry, instead
+ * returning NULL if at the end of the list.
+ */
+static struct list_head *rcu_next_node_entry(struct task_struct *t,
+                                             struct rcu_node *rnp)
+{
+        struct list_head *np;
+
+        np = t->rcu_node_entry.next;
+        if (np == &rnp->blkd_tasks)
+                np = NULL;
+        return np;
+}
+
+/*
+ * Handle special cases during rcu_read_unlock(), such as needing to
+ * notify RCU core processing or task having blocked during the RCU
+ * read-side critical section.
+ */
+void rcu_read_unlock_special(struct task_struct *t)
+{
+        int empty;
+        int empty_exp;
+        int empty_exp_now;
+        unsigned long flags;
+        struct list_head *np;
+#ifdef CONFIG_RCU_BOOST
+        struct rt_mutex *rbmp = NULL;
+#endif /* #ifdef CONFIG_RCU_BOOST */
+        struct rcu_node *rnp;
+        int special;
+
+        /* NMI handlers cannot block and cannot safely manipulate state. */
+        if (in_nmi())
+                return;
+
+        local_irq_save(flags);
+
+        /*
+         * If RCU core is waiting for this CPU to exit critical section,
+         * let it know that we have done so.
+         */
+        special = t->rcu_read_unlock_special;
+        if (special & RCU_READ_UNLOCK_NEED_QS) {
+                rcu_preempt_qs(smp_processor_id());
+        }
+
+        /* Hardware IRQ handlers cannot block. */
+        if (in_irq() || in_serving_softirq()) {
+                local_irq_restore(flags);
+                return;
+        }
+
+        /* Clean up if blocked during RCU read-side critical section. */
+        if (special & RCU_READ_UNLOCK_BLOCKED) {
+                t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
+
+                /*
+                 * Remove this task from the list it blocked on.  The
+                 * task can migrate while we acquire the lock, but at
+                 * most one time.  So at most two passes through loop.
+                 */
+                for (;;) {
+                        rnp = t->rcu_blocked_node;
+                        raw_spin_lock(&rnp->lock);  /* irqs already disabled. */
+                        if (rnp == t->rcu_blocked_node)
+                                break;
+                        raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+                }
+                empty = !rcu_preempt_blocked_readers_cgp(rnp);
+                empty_exp = !rcu_preempted_readers_exp(rnp);
+                smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
+                np = rcu_next_node_entry(t, rnp);
+                list_del_init(&t->rcu_node_entry);
+                t->rcu_blocked_node = NULL;
+                trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
+                                                rnp->gpnum, t->pid);
+                if (&t->rcu_node_entry == rnp->gp_tasks)
+                        rnp->gp_tasks = np;
+                if (&t->rcu_node_entry == rnp->exp_tasks)
+                        rnp->exp_tasks = np;
+#ifdef CONFIG_RCU_BOOST
+                if (&t->rcu_node_entry == rnp->boost_tasks)
+                        rnp->boost_tasks = np;
+                /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
+                if (t->rcu_boost_mutex) {
+                        rbmp = t->rcu_boost_mutex;
+                        t->rcu_boost_mutex = NULL;
+                }
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+                /*
+                 * If this was the last task on the current list, and if
+                 * we aren't waiting on any CPUs, report the quiescent state.
+                 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
+                 * so we must take a snapshot of the expedited state.
+                 */
+                empty_exp_now = !rcu_preempted_readers_exp(rnp);
+                if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
+                        trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
+                                                         rnp->gpnum,
+                                                         0, rnp->qsmask,
+                                                         rnp->level,
+                                                         rnp->grplo,
+                                                         rnp->grphi,
+                                                         !!rnp->gp_tasks);
+                        rcu_report_unblock_qs_rnp(rnp, flags);
+                } else {
+                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                }
+
+#ifdef CONFIG_RCU_BOOST
+                /* Unboost if we were boosted. */
+                if (rbmp)
+                        rt_mutex_unlock(rbmp);
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+                /*
+                 * If this was the last task on the expedited lists,
+                 * then we need to report up the rcu_node hierarchy.
+                 */
+                if (!empty_exp && empty_exp_now)
+                        rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
+        } else {
+                local_irq_restore(flags);
+        }
+}
+
+#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
+
+/*
+ * Dump detailed information for all tasks blocking the current RCU
+ * grace period on the specified rcu_node structure.
+ */
+static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
+{
+        unsigned long flags;
+        struct task_struct *t;
+
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        if (!rcu_preempt_blocked_readers_cgp(rnp)) {
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                return;
+        }
+        t = list_entry(rnp->gp_tasks,
+                       struct task_struct, rcu_node_entry);
+        list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
+                sched_show_task(t);
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+/*
+ * Dump detailed information for all tasks blocking the current RCU
+ * grace period.
+ */
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+        struct rcu_node *rnp = rcu_get_root(rsp);
+
+        rcu_print_detail_task_stall_rnp(rnp);
+        rcu_for_each_leaf_node(rsp, rnp)
+                rcu_print_detail_task_stall_rnp(rnp);
+}
+
+#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
+
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
+
+#ifdef CONFIG_RCU_CPU_STALL_INFO
+
+static void rcu_print_task_stall_begin(struct rcu_node *rnp)
+{
+        pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
+               rnp->level, rnp->grplo, rnp->grphi);
+}
+
+static void rcu_print_task_stall_end(void)
+{
+        pr_cont("\n");
+}
+
+#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
+
+static void rcu_print_task_stall_begin(struct rcu_node *rnp)
+{
+}
+
+static void rcu_print_task_stall_end(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
+
+/*
+ * Scan the current list of tasks blocked within RCU read-side critical
+ * sections, printing out the tid of each.
+ */
+static int rcu_print_task_stall(struct rcu_node *rnp)
+{
+        struct task_struct *t;
+        int ndetected = 0;
+
+        if (!rcu_preempt_blocked_readers_cgp(rnp))
+                return 0;
+        rcu_print_task_stall_begin(rnp);
+        t = list_entry(rnp->gp_tasks,
+                       struct task_struct, rcu_node_entry);
+        list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+                pr_cont(" P%d", t->pid);
+                ndetected++;
+        }
+        rcu_print_task_stall_end();
+        return ndetected;
+}
+
+/*
+ * Check that the list of blocked tasks for the newly completed grace
+ * period is in fact empty.  It is a serious bug to complete a grace
+ * period that still has RCU readers blocked!  This function must be
+ * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
+ * must be held by the caller.
+ *
+ * Also, if there are blocked tasks on the list, they automatically
+ * block the newly created grace period, so set up ->gp_tasks accordingly.
+ */
+static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
+{
+        WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
+        if (!list_empty(&rnp->blkd_tasks))
+                rnp->gp_tasks = rnp->blkd_tasks.next;
+        WARN_ON_ONCE(rnp->qsmask);
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Handle tasklist migration for case in which all CPUs covered by the
+ * specified rcu_node have gone offline.  Move them up to the root
+ * rcu_node.  The reason for not just moving them to the immediate
+ * parent is to remove the need for rcu_read_unlock_special() to
+ * make more than two attempts to acquire the target rcu_node's lock.
+ * Returns true if there were tasks blocking the current RCU grace
+ * period.
+ *
+ * Returns 1 if there was previously a task blocking the current grace
+ * period on the specified rcu_node structure.
+ *
+ * The caller must hold rnp->lock with irqs disabled.
+ */
+static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
+                                     struct rcu_node *rnp,
+                                     struct rcu_data *rdp)
+{
+        struct list_head *lp;
+        struct list_head *lp_root;
+        int retval = 0;
+        struct rcu_node *rnp_root = rcu_get_root(rsp);
+        struct task_struct *t;
+
+        if (rnp == rnp_root) {
+                WARN_ONCE(1, "Last CPU thought to be offlined?");
+                return 0;  /* Shouldn't happen: at least one CPU online. */
+        }
+
+        /* If we are on an internal node, complain bitterly. */
+        WARN_ON_ONCE(rnp != rdp->mynode);
+
+        /*
+         * Move tasks up to root rcu_node.  Don't try to get fancy for
+         * this corner-case operation -- just put this node's tasks
+         * at the head of the root node's list, and update the root node's
+         * ->gp_tasks and ->exp_tasks pointers to those of this node's,
+         * if non-NULL.  This might result in waiting for more tasks than
+         * absolutely necessary, but this is a good performance/complexity
+         * tradeoff.
+         */
+        if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
+                retval |= RCU_OFL_TASKS_NORM_GP;
+        if (rcu_preempted_readers_exp(rnp))
+                retval |= RCU_OFL_TASKS_EXP_GP;
+        lp = &rnp->blkd_tasks;
+        lp_root = &rnp_root->blkd_tasks;
+        while (!list_empty(lp)) {
+                t = list_entry(lp->next, typeof(*t), rcu_node_entry);
+                raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
+                list_del(&t->rcu_node_entry);
+                t->rcu_blocked_node = rnp_root;
+                list_add(&t->rcu_node_entry, lp_root);
+                if (&t->rcu_node_entry == rnp->gp_tasks)
+                        rnp_root->gp_tasks = rnp->gp_tasks;
+                if (&t->rcu_node_entry == rnp->exp_tasks)
+                        rnp_root->exp_tasks = rnp->exp_tasks;
+#ifdef CONFIG_RCU_BOOST
+                if (&t->rcu_node_entry == rnp->boost_tasks)
+                        rnp_root->boost_tasks = rnp->boost_tasks;
+#endif /* #ifdef CONFIG_RCU_BOOST */
+                raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
+        }
+
+        rnp->gp_tasks = NULL;
+        rnp->exp_tasks = NULL;
+#ifdef CONFIG_RCU_BOOST
+        rnp->boost_tasks = NULL;
+        /*
+         * In case root is being boosted and leaf was not.  Make sure
+         * that we boost the tasks blocking the current grace period
+         * in this case.
+         */
+        raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
+        if (rnp_root->boost_tasks != NULL &&
+            rnp_root->boost_tasks != rnp_root->gp_tasks &&
+            rnp_root->boost_tasks != rnp_root->exp_tasks)
+                rnp_root->boost_tasks = rnp_root->gp_tasks;
+        raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+        return retval;
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
+/*
+ * Check for a quiescent state from the current CPU.  When a task blocks,
+ * the task is recorded in the corresponding CPU's rcu_node structure,
+ * which is checked elsewhere.
+ *
+ * Caller must disable hard irqs.
+ */
+static void rcu_preempt_check_callbacks(int cpu)
+{
+        struct task_struct *t = current;
+
+        if (t->rcu_read_lock_nesting == 0) {
+                rcu_preempt_qs(cpu);
+                return;
+        }
+        if (t->rcu_read_lock_nesting > 0 &&
+            per_cpu(rcu_preempt_data, cpu).qs_pending)
+                t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
+}
+
+#ifdef CONFIG_RCU_BOOST
+
+static void rcu_preempt_do_callbacks(void)
+{
+        rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
+}
+
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+/*
+ * Queue a preemptible-RCU callback for invocation after a grace period.
+ */
+void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
+{
+        __call_rcu(head, func, &rcu_preempt_state, -1, 0);
+}
+EXPORT_SYMBOL_GPL(call_rcu);
+
+/*
+ * Queue an RCU callback for lazy invocation after a grace period.
+ * This will likely be later named something like "call_rcu_lazy()",
+ * but this change will require some way of tagging the lazy RCU
+ * callbacks in the list of pending callbacks.  Until then, this
+ * function may only be called from __kfree_rcu().
+ */
+void kfree_call_rcu(struct rcu_head *head,
+                    void (*func)(struct rcu_head *rcu))
+{
+        __call_rcu(head, func, &rcu_preempt_state, -1, 1);
+}
+EXPORT_SYMBOL_GPL(kfree_call_rcu);
+
+/**
+ * synchronize_rcu - wait until a grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full grace
+ * period has elapsed, in other words after all currently executing RCU
+ * read-side critical sections have completed.  Note, however, that
+ * upon return from synchronize_rcu(), the caller might well be executing
+ * concurrently with new RCU read-side critical sections that began while
+ * synchronize_rcu() was waiting.  RCU read-side critical sections are
+ * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
+ *
+ * See the description of synchronize_sched() for more detailed information
+ * on memory ordering guarantees.
+ */
+void synchronize_rcu(void)
+{
+        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
+                           !lock_is_held(&rcu_lock_map) &&
+                           !lock_is_held(&rcu_sched_lock_map),
+                           "Illegal synchronize_rcu() in RCU read-side critical section");
+        if (!rcu_scheduler_active)
+                return;
+        if (rcu_expedited)
+                synchronize_rcu_expedited();
+        else
+                wait_rcu_gp(call_rcu);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu);
+
+static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
+static unsigned long sync_rcu_preempt_exp_count;
+static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
+
+/*
+ * Return non-zero if there are any tasks in RCU read-side critical
+ * sections blocking the current preemptible-RCU expedited grace period.
+ * If there is no preemptible-RCU expedited grace period currently in
+ * progress, returns zero unconditionally.
+ */
+static int rcu_preempted_readers_exp(struct rcu_node *rnp)
+{
+        return rnp->exp_tasks != NULL;
+}
+
+/*
+ * return non-zero if there is no RCU expedited grace period in progress
+ * for the specified rcu_node structure, in other words, if all CPUs and
+ * tasks covered by the specified rcu_node structure have done their bit
+ * for the current expedited grace period.  Works only for preemptible
+ * RCU -- other RCU implementation use other means.
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex.
+ */
+static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
+{
+        return !rcu_preempted_readers_exp(rnp) &&
+               ACCESS_ONCE(rnp->expmask) == 0;
+}
+
+/*
+ * Report the exit from RCU read-side critical section for the last task
+ * that queued itself during or before the current expedited preemptible-RCU
+ * grace period.  This event is reported either to the rcu_node structure on
+ * which the task was queued or to one of that rcu_node structure's ancestors,
+ * recursively up the tree.  (Calm down, calm down, we do the recursion
+ * iteratively!)
+ *
+ * Most callers will set the "wake" flag, but the task initiating the
+ * expedited grace period need not wake itself.
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex.
+ */
+static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
+                               bool wake)
+{
+        unsigned long flags;
+        unsigned long mask;
+
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        for (;;) {
+                if (!sync_rcu_preempt_exp_done(rnp)) {
+                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                        break;
+                }
+                if (rnp->parent == NULL) {
+                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                        if (wake)
+                                wake_up(&sync_rcu_preempt_exp_wq);
+                        break;
+                }
+                mask = rnp->grpmask;
+                raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
+                rnp = rnp->parent;
+                raw_spin_lock(&rnp->lock); /* irqs already disabled */
+                rnp->expmask &= ~mask;
+        }
+}
+
+/*
+ * Snapshot the tasks blocking the newly started preemptible-RCU expedited
+ * grace period for the specified rcu_node structure.  If there are no such
+ * tasks, report it up the rcu_node hierarchy.
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
+ * CPU hotplug operations.
+ */
+static void
+sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+        unsigned long flags;
+        int must_wait = 0;
+
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        if (list_empty(&rnp->blkd_tasks)) {
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        } else {
+                rnp->exp_tasks = rnp->blkd_tasks.next;
+                rcu_initiate_boost(rnp, flags);  /* releases rnp->lock */
+                must_wait = 1;
+        }
+        if (!must_wait)
+                rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
+}
+
+/**
+ * synchronize_rcu_expedited - Brute-force RCU grace period
+ *
+ * Wait for an RCU-preempt grace period, but expedite it.  The basic
+ * idea is to invoke synchronize_sched_expedited() to push all the tasks to
+ * the ->blkd_tasks lists and wait for this list to drain.  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_rcu_expedited() in a loop,
+ * please restructure your code to batch your updates, and then Use a
+ * single synchronize_rcu() 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.
+ */
+void synchronize_rcu_expedited(void)
+{
+        unsigned long flags;
+        struct rcu_node *rnp;
+        struct rcu_state *rsp = &rcu_preempt_state;
+        unsigned long snap;
+        int trycount = 0;
+
+        smp_mb(); /* Caller's modifications seen first by other CPUs. */
+        snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
+        smp_mb(); /* Above access cannot bleed into critical section. */
+
+        /*
+         * Block CPU-hotplug operations.  This means that any CPU-hotplug
+         * operation that finds an rcu_node structure with tasks in the
+         * process of being boosted will know that all tasks blocking
+         * this expedited grace period will already be in the process of
+         * being boosted.  This simplifies the process of moving tasks
+         * from leaf to root rcu_node structures.
+         */
+        get_online_cpus();
+
+        /*
+         * Acquire lock, falling back to synchronize_rcu() if too many
+         * lock-acquisition failures.  Of course, if someone does the
+         * expedited grace period for us, just leave.
+         */
+        while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
+                if (ULONG_CMP_LT(snap,
+                    ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
+                        put_online_cpus();
+                        goto mb_ret; /* Others did our work for us. */
+                }
+                if (trycount++ < 10) {
+                        udelay(trycount * num_online_cpus());
+                } else {
+                        put_online_cpus();
+                        wait_rcu_gp(call_rcu);
+                        return;
+                }
+        }
+        if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
+                put_online_cpus();
+                goto unlock_mb_ret; /* Others did our work for us. */
+        }
+
+        /* force all RCU readers onto ->blkd_tasks lists. */
+        synchronize_sched_expedited();
+
+        /* Initialize ->expmask for all non-leaf rcu_node structures. */
+        rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
+                raw_spin_lock_irqsave(&rnp->lock, flags);
+                rnp->expmask = rnp->qsmaskinit;
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        }
+
+        /* Snapshot current state of ->blkd_tasks lists. */
+        rcu_for_each_leaf_node(rsp, rnp)
+                sync_rcu_preempt_exp_init(rsp, rnp);
+        if (NUM_RCU_NODES > 1)
+                sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
+
+        put_online_cpus();
+
+        /* Wait for snapshotted ->blkd_tasks lists to drain. */
+        rnp = rcu_get_root(rsp);
+        wait_event(sync_rcu_preempt_exp_wq,
+                   sync_rcu_preempt_exp_done(rnp));
+
+        /* Clean up and exit. */
+        smp_mb(); /* ensure expedited GP seen before counter increment. */
+        ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
+unlock_mb_ret:
+        mutex_unlock(&sync_rcu_preempt_exp_mutex);
+mb_ret:
+        smp_mb(); /* ensure subsequent action seen after grace period. */
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+/**
+ * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
+ *
+ * Note that this primitive does not necessarily wait for an RCU grace period
+ * to complete.  For example, if there are no RCU callbacks queued anywhere
+ * in the system, then rcu_barrier() is within its rights to return
+ * immediately, without waiting for anything, much less an RCU grace period.
+ */
+void rcu_barrier(void)
+{
+        _rcu_barrier(&rcu_preempt_state);
+}
+EXPORT_SYMBOL_GPL(rcu_barrier);
+
+/*
+ * Initialize preemptible RCU's state structures.
+ */
+static void __init __rcu_init_preempt(void)
+{
+        rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
+}
+
+/*
+ * Check for a task exiting while in a preemptible-RCU read-side
+ * critical section, clean up if so.  No need to issue warnings,
+ * as debug_check_no_locks_held() already does this if lockdep
+ * is enabled.
+ */
+void exit_rcu(void)
+{
+        struct task_struct *t = current;
+
+        if (likely(list_empty(&current->rcu_node_entry)))
+                return;
+        t->rcu_read_lock_nesting = 1;
+        barrier();
+        t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
+        __rcu_read_unlock();
+}
+
+#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
+
+static struct rcu_state *rcu_state = &rcu_sched_state;
+
+/*
+ * Tell them what RCU they are running.
+ */
+static void __init rcu_bootup_announce(void)
+{
+        pr_info("Hierarchical RCU implementation.\n");
+        rcu_bootup_announce_oddness();
+}
+
+/*
+ * Return the number of RCU batches processed thus far for debug & stats.
+ */
+long rcu_batches_completed(void)
+{
+        return rcu_batches_completed_sched();
+}
+EXPORT_SYMBOL_GPL(rcu_batches_completed);
+
+/*
+ * Force a quiescent state for RCU, which, because there is no preemptible
+ * RCU, becomes the same as rcu-sched.
+ */
+void rcu_force_quiescent_state(void)
+{
+        rcu_sched_force_quiescent_state();
+}
+EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * CPUs being in quiescent states.
+ */
+static void rcu_preempt_note_context_switch(int cpu)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, there are never any preempted
+ * RCU readers.
+ */
+static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
+{
+        return 0;
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+/* Because preemptible RCU does not exist, no quieting of tasks. */
+static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
+{
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
+static int rcu_print_task_stall(struct rcu_node *rnp)
+{
+        return 0;
+}
+
+/*
+ * Because there is no preemptible RCU, there can be no readers blocked,
+ * so there is no need to check for blocked tasks.  So check only for
+ * bogus qsmask values.
+ */
+static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
+{
+        WARN_ON_ONCE(rnp->qsmask);
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Because preemptible RCU does not exist, it never needs to migrate
+ * tasks that were blocked within RCU read-side critical sections, and
+ * such non-existent tasks cannot possibly have been blocking the current
+ * grace period.
+ */
+static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
+                                     struct rcu_node *rnp,
+                                     struct rcu_data *rdp)
+{
+        return 0;
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
+/*
+ * Because preemptible RCU does not exist, it never has any callbacks
+ * to check.
+ */
+static void rcu_preempt_check_callbacks(int cpu)
+{
+}
+
+/*
+ * Queue an RCU callback for lazy invocation after a grace period.
+ * This will likely be later named something like "call_rcu_lazy()",
+ * but this change will require some way of tagging the lazy RCU
+ * callbacks in the list of pending callbacks.  Until then, this
+ * function may only be called from __kfree_rcu().
+ *
+ * Because there is no preemptible RCU, we use RCU-sched instead.
+ */
+void kfree_call_rcu(struct rcu_head *head,
+                    void (*func)(struct rcu_head *rcu))
+{
+        __call_rcu(head, func, &rcu_sched_state, -1, 1);
+}
+EXPORT_SYMBOL_GPL(kfree_call_rcu);
+
+/*
+ * Wait for an rcu-preempt grace period, but make it happen quickly.
+ * But because preemptible RCU does not exist, map to rcu-sched.
+ */
+void synchronize_rcu_expedited(void)
+{
+        synchronize_sched_expedited();
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Because preemptible RCU does not exist, there is never any need to
+ * report on tasks preempted in RCU read-side critical sections during
+ * expedited RCU grace periods.
+ */
+static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
+                               bool wake)
+{
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
+/*
+ * Because preemptible RCU does not exist, rcu_barrier() is just
+ * another name for rcu_barrier_sched().
+ */
+void rcu_barrier(void)
+{
+        rcu_barrier_sched();
+}
+EXPORT_SYMBOL_GPL(rcu_barrier);
+
+/*
+ * Because preemptible RCU does not exist, it need not be initialized.
+ */
+static void __init __rcu_init_preempt(void)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, tasks cannot possibly exit
+ * while in preemptible RCU read-side critical sections.
+ */
+void exit_rcu(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
+
+#ifdef CONFIG_RCU_BOOST
+
+#include "../rtmutex_common.h"
+
+#ifdef CONFIG_RCU_TRACE
+
+static void rcu_initiate_boost_trace(struct rcu_node *rnp)
+{
+        if (list_empty(&rnp->blkd_tasks))
+                rnp->n_balk_blkd_tasks++;
+        else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
+                rnp->n_balk_exp_gp_tasks++;
+        else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
+                rnp->n_balk_boost_tasks++;
+        else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
+                rnp->n_balk_notblocked++;
+        else if (rnp->gp_tasks != NULL &&
+                 ULONG_CMP_LT(jiffies, rnp->boost_time))
+                rnp->n_balk_notyet++;
+        else
+                rnp->n_balk_nos++;
+}
+
+#else /* #ifdef CONFIG_RCU_TRACE */
+
+static void rcu_initiate_boost_trace(struct rcu_node *rnp)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_TRACE */
+
+static void rcu_wake_cond(struct task_struct *t, int status)
+{
+        /*
+         * If the thread is yielding, only wake it when this
+         * is invoked from idle
+         */
+        if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
+                wake_up_process(t);
+}
+
+/*
+ * Carry out RCU priority boosting on the task indicated by ->exp_tasks
+ * or ->boost_tasks, advancing the pointer to the next task in the
+ * ->blkd_tasks list.
+ *
+ * Note that irqs must be enabled: boosting the task can block.
+ * Returns 1 if there are more tasks needing to be boosted.
+ */
+static int rcu_boost(struct rcu_node *rnp)
+{
+        unsigned long flags;
+        struct rt_mutex mtx;
+        struct task_struct *t;
+        struct list_head *tb;
+
+        if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
+                return 0;  /* Nothing left to boost. */
+
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+
+        /*
+         * Recheck under the lock: all tasks in need of boosting
+         * might exit their RCU read-side critical sections on their own.
+         */
+        if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                return 0;
+        }
+
+        /*
+         * Preferentially boost tasks blocking expedited grace periods.
+         * This cannot starve the normal grace periods because a second
+         * expedited grace period must boost all blocked tasks, including
+         * those blocking the pre-existing normal grace period.
+         */
+        if (rnp->exp_tasks != NULL) {
+                tb = rnp->exp_tasks;
+                rnp->n_exp_boosts++;
+        } else {
+                tb = rnp->boost_tasks;
+                rnp->n_normal_boosts++;
+        }
+        rnp->n_tasks_boosted++;
+
+        /*
+         * We boost task t by manufacturing an rt_mutex that appears to
+         * be held by task t.  We leave a pointer to that rt_mutex where
+         * task t can find it, and task t will release the mutex when it
+         * exits its outermost RCU read-side critical section.  Then
+         * simply acquiring this artificial rt_mutex will boost task
+         * t's priority.  (Thanks to tglx for suggesting this approach!)
+         *
+         * Note that task t must acquire rnp->lock to remove itself from
+         * the ->blkd_tasks list, which it will do from exit() if from
+         * nowhere else.  We therefore are guaranteed that task t will
+         * stay around at least until we drop rnp->lock.  Note that
+         * rnp->lock also resolves races between our priority boosting
+         * and task t's exiting its outermost RCU read-side critical
+         * section.
+         */
+        t = container_of(tb, struct task_struct, rcu_node_entry);
+        rt_mutex_init_proxy_locked(&mtx, t);
+        t->rcu_boost_mutex = &mtx;
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */
+        rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
+
+        return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
+               ACCESS_ONCE(rnp->boost_tasks) != NULL;
+}
+
+/*
+ * Priority-boosting kthread.  One per leaf rcu_node and one for the
+ * root rcu_node.
+ */
+static int rcu_boost_kthread(void *arg)
+{
+        struct rcu_node *rnp = (struct rcu_node *)arg;
+        int spincnt = 0;
+        int more2boost;
+
+        trace_rcu_utilization(TPS("Start boost kthread@init"));
+        for (;;) {
+                rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
+                trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
+                rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
+                trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
+                rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
+                more2boost = rcu_boost(rnp);
+                if (more2boost)
+                        spincnt++;
+                else
+                        spincnt = 0;
+                if (spincnt > 10) {
+                        rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
+                        trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
+                        schedule_timeout_interruptible(2);
+                        trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
+                        spincnt = 0;
+                }
+        }
+        /* NOTREACHED */
+        trace_rcu_utilization(TPS("End boost kthread@notreached"));
+        return 0;
+}
+
+/*
+ * Check to see if it is time to start boosting RCU readers that are
+ * blocking the current grace period, and, if so, tell the per-rcu_node
+ * kthread to start boosting them.  If there is an expedited grace
+ * period in progress, it is always time to boost.
+ *
+ * The caller must hold rnp->lock, which this function releases.
+ * The ->boost_kthread_task is immortal, so we don't need to worry
+ * about it going away.
+ */
+static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
+{
+        struct task_struct *t;
+
+        if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
+                rnp->n_balk_exp_gp_tasks++;
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                return;
+        }
+        if (rnp->exp_tasks != NULL ||
+            (rnp->gp_tasks != NULL &&
+             rnp->boost_tasks == NULL &&
+             rnp->qsmask == 0 &&
+             ULONG_CMP_GE(jiffies, rnp->boost_time))) {
+                if (rnp->exp_tasks == NULL)
+                        rnp->boost_tasks = rnp->gp_tasks;
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                t = rnp->boost_kthread_task;
+                if (t)
+                        rcu_wake_cond(t, rnp->boost_kthread_status);
+        } else {
+                rcu_initiate_boost_trace(rnp);
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        }
+}
+
+/*
+ * Wake up the per-CPU kthread to invoke RCU callbacks.
+ */
+static void invoke_rcu_callbacks_kthread(void)
+{
+        unsigned long flags;
+
+        local_irq_save(flags);
+        __this_cpu_write(rcu_cpu_has_work, 1);
+        if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
+            current != __this_cpu_read(rcu_cpu_kthread_task)) {
+                rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
+                              __this_cpu_read(rcu_cpu_kthread_status));
+        }
+        local_irq_restore(flags);
+}
+
+/*
+ * Is the current CPU running the RCU-callbacks kthread?
+ * Caller must have preemption disabled.
+ */
+static bool rcu_is_callbacks_kthread(void)
+{
+        return __this_cpu_read(rcu_cpu_kthread_task) == current;
+}
+
+#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
+
+/*
+ * Do priority-boost accounting for the start of a new grace period.
+ */
+static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
+{
+        rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
+}
+
+/*
+ * Create an RCU-boost kthread for the specified node if one does not
+ * already exist.  We only create this kthread for preemptible RCU.
+ * Returns zero if all is well, a negated errno otherwise.
+ */
+static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
+                                                 struct rcu_node *rnp)
+{
+        int rnp_index = rnp - &rsp->node[0];
+        unsigned long flags;
+        struct sched_param sp;
+        struct task_struct *t;
+
+        if (&rcu_preempt_state != rsp)
+                return 0;
+
+        if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
+                return 0;
+
+        rsp->boost = 1;
+        if (rnp->boost_kthread_task != NULL)
+                return 0;
+        t = kthread_create(rcu_boost_kthread, (void *)rnp,
+                           "rcub/%d", rnp_index);
+        if (IS_ERR(t))
+                return PTR_ERR(t);
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        rnp->boost_kthread_task = t;
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        sp.sched_priority = RCU_BOOST_PRIO;
+        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+        wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
+        return 0;
+}
+
+static void rcu_kthread_do_work(void)
+{
+        rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
+        rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
+        rcu_preempt_do_callbacks();
+}
+
+static void rcu_cpu_kthread_setup(unsigned int cpu)
+{
+        struct sched_param sp;
+
+        sp.sched_priority = RCU_KTHREAD_PRIO;
+        sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+}
+
+static void rcu_cpu_kthread_park(unsigned int cpu)
+{
+        per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
+}
+
+static int rcu_cpu_kthread_should_run(unsigned int cpu)
+{
+        return __this_cpu_read(rcu_cpu_has_work);
+}
+
+/*
+ * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
+ * RCU softirq used in flavors and configurations of RCU that do not
+ * support RCU priority boosting.
+ */
+static void rcu_cpu_kthread(unsigned int cpu)
+{
+        unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
+        char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
+        int spincnt;
+
+        for (spincnt = 0; spincnt < 10; spincnt++) {
+                trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
+                local_bh_disable();
+                *statusp = RCU_KTHREAD_RUNNING;
+                this_cpu_inc(rcu_cpu_kthread_loops);
+                local_irq_disable();
+                work = *workp;
+                *workp = 0;
+                local_irq_enable();
+                if (work)
+                        rcu_kthread_do_work();
+                local_bh_enable();
+                if (*workp == 0) {
+                        trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
+                        *statusp = RCU_KTHREAD_WAITING;
+                        return;
+                }
+        }
+        *statusp = RCU_KTHREAD_YIELDING;
+        trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
+        schedule_timeout_interruptible(2);
+        trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
+        *statusp = RCU_KTHREAD_WAITING;
+}
+
+/*
+ * Set the per-rcu_node kthread's affinity to cover all CPUs that are
+ * served by the rcu_node in question.  The CPU hotplug lock is still
+ * held, so the value of rnp->qsmaskinit will be stable.
+ *
+ * We don't include outgoingcpu in the affinity set, use -1 if there is
+ * no outgoing CPU.  If there are no CPUs left in the affinity set,
+ * this function allows the kthread to execute on any CPU.
+ */
+static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+        struct task_struct *t = rnp->boost_kthread_task;
+        unsigned long mask = rnp->qsmaskinit;
+        cpumask_var_t cm;
+        int cpu;
+
+        if (!t)
+                return;
+        if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
+                return;
+        for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
+                if ((mask & 0x1) && cpu != outgoingcpu)
+                        cpumask_set_cpu(cpu, cm);
+        if (cpumask_weight(cm) == 0) {
+                cpumask_setall(cm);
+                for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
+                        cpumask_clear_cpu(cpu, cm);
+                WARN_ON_ONCE(cpumask_weight(cm) == 0);
+        }
+        set_cpus_allowed_ptr(t, cm);
+        free_cpumask_var(cm);
+}
+
+static struct smp_hotplug_thread rcu_cpu_thread_spec = {
+        .store                  = &rcu_cpu_kthread_task,
+        .thread_should_run      = rcu_cpu_kthread_should_run,
+        .thread_fn              = rcu_cpu_kthread,
+        .thread_comm            = "rcuc/%u",
+        .setup                  = rcu_cpu_kthread_setup,
+        .park                   = rcu_cpu_kthread_park,
+};
+
+/*
+ * Spawn all kthreads -- called as soon as the scheduler is running.
+ */
+static int __init rcu_spawn_kthreads(void)
+{
+        struct rcu_node *rnp;
+        int cpu;
+
+        rcu_scheduler_fully_active = 1;
+        for_each_possible_cpu(cpu)
+                per_cpu(rcu_cpu_has_work, cpu) = 0;
+        BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
+        rnp = rcu_get_root(rcu_state);
+        (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
+        if (NUM_RCU_NODES > 1) {
+                rcu_for_each_leaf_node(rcu_state, rnp)
+                        (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
+        }
+        return 0;
+}
+early_initcall(rcu_spawn_kthreads);
+
+static void rcu_prepare_kthreads(int cpu)
+{
+        struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
+        struct rcu_node *rnp = rdp->mynode;
+
+        /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
+        if (rcu_scheduler_fully_active)
+                (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
+}
+
+#else /* #ifdef CONFIG_RCU_BOOST */
+
+static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
+{
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+static void invoke_rcu_callbacks_kthread(void)
+{
+        WARN_ON_ONCE(1);
+}
+
+static bool rcu_is_callbacks_kthread(void)
+{
+        return false;
+}
+
+static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
+{
+}
+
+static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+}
+
+static int __init rcu_scheduler_really_started(void)
+{
+        rcu_scheduler_fully_active = 1;
+        return 0;
+}
+early_initcall(rcu_scheduler_really_started);
+
+static void rcu_prepare_kthreads(int cpu)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_BOOST */
+
+#if !defined(CONFIG_RCU_FAST_NO_HZ)
+
+/*
+ * Check to see if any future RCU-related work will need to be done
+ * by the current CPU, even if none need be done immediately, returning
+ * 1 if so.  This function is part of the RCU implementation; it is -not-
+ * an exported member of the RCU API.
+ *
+ * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
+ * any flavor of RCU.
+ */
+int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
+{
+        *delta_jiffies = ULONG_MAX;
+        return rcu_cpu_has_callbacks(cpu, NULL);
+}
+
+/*
+ * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
+ * after it.
+ */
+static void rcu_cleanup_after_idle(int cpu)
+{
+}
+
+/*
+ * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
+ * is nothing.
+ */
+static void rcu_prepare_for_idle(int cpu)
+{
+}
+
+/*
+ * Don't bother keeping a running count of the number of RCU callbacks
+ * posted because CONFIG_RCU_FAST_NO_HZ=n.
+ */
+static void rcu_idle_count_callbacks_posted(void)
+{
+}
+
+#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
+
+/*
+ * This code is invoked when a CPU goes idle, at which point we want
+ * to have the CPU do everything required for RCU so that it can enter
+ * the energy-efficient dyntick-idle mode.  This is handled by a
+ * state machine implemented by rcu_prepare_for_idle() below.
+ *
+ * The following three proprocessor symbols control this state machine:
+ *
+ * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
+ *      to sleep in dyntick-idle mode with RCU callbacks pending.  This
+ *      is sized to be roughly one RCU grace period.  Those energy-efficiency
+ *      benchmarkers who might otherwise be tempted to set this to a large
+ *      number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
+ *      system.  And if you are -that- concerned about energy efficiency,
+ *      just power the system down and be done with it!
+ * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
+ *      permitted to sleep in dyntick-idle mode with only lazy RCU
+ *      callbacks pending.  Setting this too high can OOM your system.
+ *
+ * The values below work well in practice.  If future workloads require
+ * adjustment, they can be converted into kernel config parameters, though
+ * making the state machine smarter might be a better option.
+ */
+#define RCU_IDLE_GP_DELAY 4             /* Roughly one grace period. */
+#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
+
+static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
+module_param(rcu_idle_gp_delay, int, 0644);
+static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
+module_param(rcu_idle_lazy_gp_delay, int, 0644);
+
+extern int tick_nohz_enabled;
+
+/*
+ * Try to advance callbacks for all flavors of RCU on the current CPU, but
+ * only if it has been awhile since the last time we did so.  Afterwards,
+ * if there are any callbacks ready for immediate invocation, return true.
+ */
+static bool rcu_try_advance_all_cbs(void)
+{
+        bool cbs_ready = false;
+        struct rcu_data *rdp;
+        struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+        struct rcu_node *rnp;
+        struct rcu_state *rsp;
+
+        /* Exit early if we advanced recently. */
+        if (jiffies == rdtp->last_advance_all)
+                return 0;
+        rdtp->last_advance_all = jiffies;
+
+        for_each_rcu_flavor(rsp) {
+                rdp = this_cpu_ptr(rsp->rda);
+                rnp = rdp->mynode;
+
+                /*
+                 * Don't bother checking unless a grace period has
+                 * completed since we last checked and there are
+                 * callbacks not yet ready to invoke.
+                 */
+                if (rdp->completed != rnp->completed &&
+                    rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
+                        note_gp_changes(rsp, rdp);
+
+                if (cpu_has_callbacks_ready_to_invoke(rdp))
+                        cbs_ready = true;
+        }
+        return cbs_ready;
+}
+
+/*
+ * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
+ * to invoke.  If the CPU has callbacks, try to advance them.  Tell the
+ * caller to set the timeout based on whether or not there are non-lazy
+ * callbacks.
+ *
+ * The caller must have disabled interrupts.
+ */
+int rcu_needs_cpu(int cpu, unsigned long *dj)
+{
+        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+
+        /* Snapshot to detect later posting of non-lazy callback. */
+        rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
+
+        /* If no callbacks, RCU doesn't need the CPU. */
+        if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
+                *dj = ULONG_MAX;
+                return 0;
+        }
+
+        /* Attempt to advance callbacks. */
+        if (rcu_try_advance_all_cbs()) {
+                /* Some ready to invoke, so initiate later invocation. */
+                invoke_rcu_core();
+                return 1;
+        }
+        rdtp->last_accelerate = jiffies;
+
+        /* Request timer delay depending on laziness, and round. */
+        if (!rdtp->all_lazy) {
+                *dj = round_up(rcu_idle_gp_delay + jiffies,
+                               rcu_idle_gp_delay) - jiffies;
+        } else {
+                *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
+        }
+        return 0;
+}
+
+/*
+ * Prepare a CPU for idle from an RCU perspective.  The first major task
+ * is to sense whether nohz mode has been enabled or disabled via sysfs.
+ * The second major task is to check to see if a non-lazy callback has
+ * arrived at a CPU that previously had only lazy callbacks.  The third
+ * major task is to accelerate (that is, assign grace-period numbers to)
+ * any recently arrived callbacks.
+ *
+ * The caller must have disabled interrupts.
+ */
+static void rcu_prepare_for_idle(int cpu)
+{
+        struct rcu_data *rdp;
+        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+        struct rcu_node *rnp;
+        struct rcu_state *rsp;
+        int tne;
+
+        /* Handle nohz enablement switches conservatively. */
+        tne = ACCESS_ONCE(tick_nohz_enabled);
+        if (tne != rdtp->tick_nohz_enabled_snap) {
+                if (rcu_cpu_has_callbacks(cpu, NULL))
+                        invoke_rcu_core(); /* force nohz to see update. */
+                rdtp->tick_nohz_enabled_snap = tne;
+                return;
+        }
+        if (!tne)
+                return;
+
+        /* If this is a no-CBs CPU, no callbacks, just return. */
+        if (rcu_is_nocb_cpu(cpu))
+                return;
+
+        /*
+         * If a non-lazy callback arrived at a CPU having only lazy
+         * callbacks, invoke RCU core for the side-effect of recalculating
+         * idle duration on re-entry to idle.
+         */
+        if (rdtp->all_lazy &&
+            rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
+                rdtp->all_lazy = false;
+                rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
+                invoke_rcu_core();
+                return;
+        }
+
+        /*
+         * If we have not yet accelerated this jiffy, accelerate all
+         * callbacks on this CPU.
+         */
+        if (rdtp->last_accelerate == jiffies)
+                return;
+        rdtp->last_accelerate = jiffies;
+        for_each_rcu_flavor(rsp) {
+                rdp = per_cpu_ptr(rsp->rda, cpu);
+                if (!*rdp->nxttail[RCU_DONE_TAIL])
+                        continue;
+                rnp = rdp->mynode;
+                raw_spin_lock(&rnp->lock); /* irqs already disabled. */
+                rcu_accelerate_cbs(rsp, rnp, rdp);
+                raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+        }
+}
+
+/*
+ * Clean up for exit from idle.  Attempt to advance callbacks based on
+ * any grace periods that elapsed while the CPU was idle, and if any
+ * callbacks are now ready to invoke, initiate invocation.
+ */
+static void rcu_cleanup_after_idle(int cpu)
+{
+
+        if (rcu_is_nocb_cpu(cpu))
+                return;
+        if (rcu_try_advance_all_cbs())
+                invoke_rcu_core();
+}
+
+/*
+ * Keep a running count of the number of non-lazy callbacks posted
+ * on this CPU.  This running counter (which is never decremented) allows
+ * rcu_prepare_for_idle() to detect when something out of the idle loop
+ * posts a callback, even if an equal number of callbacks are invoked.
+ * Of course, callbacks should only be posted from within a trace event
+ * designed to be called from idle or from within RCU_NONIDLE().
+ */
+static void rcu_idle_count_callbacks_posted(void)
+{
+        __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
+}
+
+/*
+ * Data for flushing lazy RCU callbacks at OOM time.
+ */
+static atomic_t oom_callback_count;
+static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
+
+/*
+ * RCU OOM callback -- decrement the outstanding count and deliver the
+ * wake-up if we are the last one.
+ */
+static void rcu_oom_callback(struct rcu_head *rhp)
+{
+        if (atomic_dec_and_test(&oom_callback_count))
+                wake_up(&oom_callback_wq);
+}
+
+/*
+ * Post an rcu_oom_notify callback on the current CPU if it has at
+ * least one lazy callback.  This will unnecessarily post callbacks
+ * to CPUs that already have a non-lazy callback at the end of their
+ * callback list, but this is an infrequent operation, so accept some
+ * extra overhead to keep things simple.
+ */
+static void rcu_oom_notify_cpu(void *unused)
+{
+        struct rcu_state *rsp;
+        struct rcu_data *rdp;
+
+        for_each_rcu_flavor(rsp) {
+                rdp = __this_cpu_ptr(rsp->rda);
+                if (rdp->qlen_lazy != 0) {
+                        atomic_inc(&oom_callback_count);
+                        rsp->call(&rdp->oom_head, rcu_oom_callback);
+                }
+        }
+}
+
+/*
+ * If low on memory, ensure that each CPU has a non-lazy callback.
+ * This will wake up CPUs that have only lazy callbacks, in turn
+ * ensuring that they free up the corresponding memory in a timely manner.
+ * Because an uncertain amount of memory will be freed in some uncertain
+ * timeframe, we do not claim to have freed anything.
+ */
+static int rcu_oom_notify(struct notifier_block *self,
+                          unsigned long notused, void *nfreed)
+{
+        int cpu;
+
+        /* Wait for callbacks from earlier instance to complete. */
+        wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
+
+        /*
+         * Prevent premature wakeup: ensure that all increments happen
+         * before there is a chance of the counter reaching zero.
+         */
+        atomic_set(&oom_callback_count, 1);
+
+        get_online_cpus();
+        for_each_online_cpu(cpu) {
+                smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
+                cond_resched();
+        }
+        put_online_cpus();
+
+        /* Unconditionally decrement: no need to wake ourselves up. */
+        atomic_dec(&oom_callback_count);
+
+        return NOTIFY_OK;
+}
+
+static struct notifier_block rcu_oom_nb = {
+        .notifier_call = rcu_oom_notify
+};
+
+static int __init rcu_register_oom_notifier(void)
+{
+        register_oom_notifier(&rcu_oom_nb);
+        return 0;
+}
+early_initcall(rcu_register_oom_notifier);
+
+#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
+
+#ifdef CONFIG_RCU_CPU_STALL_INFO
+
+#ifdef CONFIG_RCU_FAST_NO_HZ
+
+static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
+{
+        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+        unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
+
+        sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
+                rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
+                ulong2long(nlpd),
+                rdtp->all_lazy ? 'L' : '.',
+                rdtp->tick_nohz_enabled_snap ? '.' : 'D');
+}
+
+#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
+
+static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
+{
+        *cp = '\0';
+}
+
+#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
+
+/* Initiate the stall-info list. */
+static void print_cpu_stall_info_begin(void)
+{
+        pr_cont("\n");
+}
+
+/*
+ * Print out diagnostic information for the specified stalled CPU.
+ *
+ * If the specified CPU is aware of the current RCU grace period
+ * (flavor specified by rsp), then print the number of scheduling
+ * clock interrupts the CPU has taken during the time that it has
+ * been aware.  Otherwise, print the number of RCU grace periods
+ * that this CPU is ignorant of, for example, "1" if the CPU was
+ * aware of the previous grace period.
+ *
+ * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
+ */
+static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
+{
+        char fast_no_hz[72];
+        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+        struct rcu_dynticks *rdtp = rdp->dynticks;
+        char *ticks_title;
+        unsigned long ticks_value;
+
+        if (rsp->gpnum == rdp->gpnum) {
+                ticks_title = "ticks this GP";
+                ticks_value = rdp->ticks_this_gp;
+        } else {
+                ticks_title = "GPs behind";
+                ticks_value = rsp->gpnum - rdp->gpnum;
+        }
+        print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
+        pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
+               cpu, ticks_value, ticks_title,
+               atomic_read(&rdtp->dynticks) & 0xfff,
+               rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
+               rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
+               fast_no_hz);
+}
+
+/* Terminate the stall-info list. */
+static void print_cpu_stall_info_end(void)
+{
+        pr_err("\t");
+}
+
+/* Zero ->ticks_this_gp for all flavors of RCU. */
+static void zero_cpu_stall_ticks(struct rcu_data *rdp)
+{
+        rdp->ticks_this_gp = 0;
+        rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
+}
+
+/* Increment ->ticks_this_gp for all flavors of RCU. */
+static void increment_cpu_stall_ticks(void)
+{
+        struct rcu_state *rsp;
+
+        for_each_rcu_flavor(rsp)
+                __this_cpu_ptr(rsp->rda)->ticks_this_gp++;
+}
+
+#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
+
+static void print_cpu_stall_info_begin(void)
+{
+        pr_cont(" {");
+}
+
+static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
+{
+        pr_cont(" %d", cpu);
+}
+
+static void print_cpu_stall_info_end(void)
+{
+        pr_cont("} ");
+}
+
+static void zero_cpu_stall_ticks(struct rcu_data *rdp)
+{
+}
+
+static void increment_cpu_stall_ticks(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
+
+#ifdef CONFIG_RCU_NOCB_CPU
+
+/*
+ * Offload callback processing from the boot-time-specified set of CPUs
+ * specified by rcu_nocb_mask.  For each CPU in the set, there is a
+ * kthread created that pulls the callbacks from the corresponding CPU,
+ * waits for a grace period to elapse, and invokes the callbacks.
+ * The no-CBs CPUs do a wake_up() on their kthread when they insert
+ * a callback into any empty list, unless the rcu_nocb_poll boot parameter
+ * has been specified, in which case each kthread actively polls its
+ * CPU.  (Which isn't so great for energy efficiency, but which does
+ * reduce RCU's overhead on that CPU.)
+ *
+ * This is intended to be used in conjunction with Frederic Weisbecker's
+ * adaptive-idle work, which would seriously reduce OS jitter on CPUs
+ * running CPU-bound user-mode computations.
+ *
+ * Offloading of callback processing could also in theory be used as
+ * an energy-efficiency measure because CPUs with no RCU callbacks
+ * queued are more aggressive about entering dyntick-idle mode.
+ */
+
+
+/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
+static int __init rcu_nocb_setup(char *str)
+{
+        alloc_bootmem_cpumask_var(&rcu_nocb_mask);
+        have_rcu_nocb_mask = true;
+        cpulist_parse(str, rcu_nocb_mask);
+        return 1;
+}
+__setup("rcu_nocbs=", rcu_nocb_setup);
+
+static int __init parse_rcu_nocb_poll(char *arg)
+{
+        rcu_nocb_poll = 1;
+        return 0;
+}
+early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
+
+/*
+ * Do any no-CBs CPUs need another grace period?
+ *
+ * Interrupts must be disabled.  If the caller does not hold the root
+ * rnp_node structure's ->lock, the results are advisory only.
+ */
+static int rcu_nocb_needs_gp(struct rcu_state *rsp)
+{
+        struct rcu_node *rnp = rcu_get_root(rsp);
+
+        return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
+}
+
+/*
+ * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
+ * grace period.
+ */
+static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+        wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
+}
+
+/*
+ * Set the root rcu_node structure's ->need_future_gp field
+ * based on the sum of those of all rcu_node structures.  This does
+ * double-count the root rcu_node structure's requests, but this
+ * is necessary to handle the possibility of a rcu_nocb_kthread()
+ * having awakened during the time that the rcu_node structures
+ * were being updated for the end of the previous grace period.
+ */
+static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
+{
+        rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
+}
+
+static void rcu_init_one_nocb(struct rcu_node *rnp)
+{
+        init_waitqueue_head(&rnp->nocb_gp_wq[0]);
+        init_waitqueue_head(&rnp->nocb_gp_wq[1]);
+}
+
+/* Is the specified CPU a no-CPUs CPU? */
+bool rcu_is_nocb_cpu(int cpu)
+{
+        if (have_rcu_nocb_mask)
+                return cpumask_test_cpu(cpu, rcu_nocb_mask);
+        return false;
+}
+
+/*
+ * Enqueue the specified string of rcu_head structures onto the specified
+ * CPU's no-CBs lists.  The CPU is specified by rdp, the head of the
+ * string by rhp, and the tail of the string by rhtp.  The non-lazy/lazy
+ * counts are supplied by rhcount and rhcount_lazy.
+ *
+ * If warranted, also wake up the kthread servicing this CPUs queues.
+ */
+static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
+                                    struct rcu_head *rhp,
+                                    struct rcu_head **rhtp,
+                                    int rhcount, int rhcount_lazy)
+{
+        int len;
+        struct rcu_head **old_rhpp;
+        struct task_struct *t;
+
+        /* Enqueue the callback on the nocb list and update counts. */
+        old_rhpp = xchg(&rdp->nocb_tail, rhtp);
+        ACCESS_ONCE(*old_rhpp) = rhp;
+        atomic_long_add(rhcount, &rdp->nocb_q_count);
+        atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
+
+        /* If we are not being polled and there is a kthread, awaken it ... */
+        t = ACCESS_ONCE(rdp->nocb_kthread);
+        if (rcu_nocb_poll || !t) {
+                trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+                                    TPS("WakeNotPoll"));
+                return;
+        }
+        len = atomic_long_read(&rdp->nocb_q_count);
+        if (old_rhpp == &rdp->nocb_head) {
+                wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */
+                rdp->qlen_last_fqs_check = 0;
+                trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeEmpty"));
+        } else if (len > rdp->qlen_last_fqs_check + qhimark) {
+                wake_up_process(t); /* ... or if many callbacks queued. */
+                rdp->qlen_last_fqs_check = LONG_MAX / 2;
+                trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
+        } else {
+                trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
+        }
+        return;
+}
+
+/*
+ * This is a helper for __call_rcu(), which invokes this when the normal
+ * callback queue is inoperable.  If this is not a no-CBs CPU, this
+ * function returns failure back to __call_rcu(), which can complain
+ * appropriately.
+ *
+ * Otherwise, this function queues the callback where the corresponding
+ * "rcuo" kthread can find it.
+ */
+static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
+                            bool lazy)
+{
+
+        if (!rcu_is_nocb_cpu(rdp->cpu))
+                return 0;
+        __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy);
+        if (__is_kfree_rcu_offset((unsigned long)rhp->func))
+                trace_rcu_kfree_callback(rdp->rsp->name, rhp,
+                                         (unsigned long)rhp->func,
+                                         -atomic_long_read(&rdp->nocb_q_count_lazy),
+                                         -atomic_long_read(&rdp->nocb_q_count));
+        else
+                trace_rcu_callback(rdp->rsp->name, rhp,
+                                   -atomic_long_read(&rdp->nocb_q_count_lazy),
+                                   -atomic_long_read(&rdp->nocb_q_count));
+        return 1;
+}
+
+/*
+ * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
+ * not a no-CBs CPU.
+ */
+static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
+                                                     struct rcu_data *rdp)
+{
+        long ql = rsp->qlen;
+        long qll = rsp->qlen_lazy;
+
+        /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
+        if (!rcu_is_nocb_cpu(smp_processor_id()))
+                return 0;
+        rsp->qlen = 0;
+        rsp->qlen_lazy = 0;
+
+        /* First, enqueue the donelist, if any.  This preserves CB ordering. */
+        if (rsp->orphan_donelist != NULL) {
+                __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
+                                        rsp->orphan_donetail, ql, qll);
+                ql = qll = 0;
+                rsp->orphan_donelist = NULL;
+                rsp->orphan_donetail = &rsp->orphan_donelist;
+        }
+        if (rsp->orphan_nxtlist != NULL) {
+                __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
+                                        rsp->orphan_nxttail, ql, qll);
+                ql = qll = 0;
+                rsp->orphan_nxtlist = NULL;
+                rsp->orphan_nxttail = &rsp->orphan_nxtlist;
+        }
+        return 1;
+}
+
+/*
+ * If necessary, kick off a new grace period, and either way wait
+ * for a subsequent grace period to complete.
+ */
+static void rcu_nocb_wait_gp(struct rcu_data *rdp)
+{
+        unsigned long c;
+        bool d;
+        unsigned long flags;
+        struct rcu_node *rnp = rdp->mynode;
+
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        c = rcu_start_future_gp(rnp, rdp);
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+
+        /*
+         * Wait for the grace period.  Do so interruptibly to avoid messing
+         * up the load average.
+         */
+        trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
+        for (;;) {
+                wait_event_interruptible(
+                        rnp->nocb_gp_wq[c & 0x1],
+                        (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
+                if (likely(d))
+                        break;
+                flush_signals(current);
+                trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
+        }
+        trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
+        smp_mb(); /* Ensure that CB invocation happens after GP end. */
+}
+
+/*
+ * Per-rcu_data kthread, but only for no-CBs CPUs.  Each kthread invokes
+ * callbacks queued by the corresponding no-CBs CPU.
+ */
+static int rcu_nocb_kthread(void *arg)
+{
+        int c, cl;
+        bool firsttime = 1;
+        struct rcu_head *list;
+        struct rcu_head *next;
+        struct rcu_head **tail;
+        struct rcu_data *rdp = arg;
+
+        /* Each pass through this loop invokes one batch of callbacks */
+        for (;;) {
+                /* If not polling, wait for next batch of callbacks. */
+                if (!rcu_nocb_poll) {
+                        trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+                                            TPS("Sleep"));
+                        wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
+                } else if (firsttime) {
+                        firsttime = 0;
+                        trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+                                            TPS("Poll"));
+                }
+                list = ACCESS_ONCE(rdp->nocb_head);
+                if (!list) {
+                        if (!rcu_nocb_poll)
+                                trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+                                                    TPS("WokeEmpty"));
+                        schedule_timeout_interruptible(1);
+                        flush_signals(current);
+                        continue;
+                }
+                firsttime = 1;
+                trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+                                    TPS("WokeNonEmpty"));
+
+                /*
+                 * Extract queued callbacks, update counts, and wait
+                 * for a grace period to elapse.
+                 */
+                ACCESS_ONCE(rdp->nocb_head) = NULL;
+                tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
+                c = atomic_long_xchg(&rdp->nocb_q_count, 0);
+                cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
+                ACCESS_ONCE(rdp->nocb_p_count) += c;
+                ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl;
+                rcu_nocb_wait_gp(rdp);
+
+                /* Each pass through the following loop invokes a callback. */
+                trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
+                c = cl = 0;
+                while (list) {
+                        next = list->next;
+                        /* Wait for enqueuing to complete, if needed. */
+                        while (next == NULL && &list->next != tail) {
+                                trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+                                                    TPS("WaitQueue"));
+                                schedule_timeout_interruptible(1);
+                                trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+                                                    TPS("WokeQueue"));
+                                next = list->next;
+                        }
+                        debug_rcu_head_unqueue(list);
+                        local_bh_disable();
+                        if (__rcu_reclaim(rdp->rsp->name, list))
+                                cl++;
+                        c++;
+                        local_bh_enable();
+                        list = next;
+                }
+                trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
+                ACCESS_ONCE(rdp->nocb_p_count) -= c;
+                ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
+                rdp->n_nocbs_invoked += c;
+        }
+        return 0;
+}
+
+/* Initialize per-rcu_data variables for no-CBs CPUs. */
+static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
+{
+        rdp->nocb_tail = &rdp->nocb_head;
+        init_waitqueue_head(&rdp->nocb_wq);
+}
+
+/* Create a kthread for each RCU flavor for each no-CBs CPU. */
+static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
+{
+        int cpu;
+        struct rcu_data *rdp;
+        struct task_struct *t;
+
+        if (rcu_nocb_mask == NULL)
+                return;
+        for_each_cpu(cpu, rcu_nocb_mask) {
+                rdp = per_cpu_ptr(rsp->rda, cpu);
+                t = kthread_run(rcu_nocb_kthread, rdp,
+                                "rcuo%c/%d", rsp->abbr, cpu);
+                BUG_ON(IS_ERR(t));
+                ACCESS_ONCE(rdp->nocb_kthread) = t;
+        }
+}
+
+/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
+static bool init_nocb_callback_list(struct rcu_data *rdp)
+{
+        if (rcu_nocb_mask == NULL ||
+            !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
+                return false;
+        rdp->nxttail[RCU_NEXT_TAIL] = NULL;
+        return true;
+}
+
+#else /* #ifdef CONFIG_RCU_NOCB_CPU */
+
+static int rcu_nocb_needs_gp(struct rcu_state *rsp)
+{
+        return 0;
+}
+
+static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+}
+
+static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
+{
+}
+
+static void rcu_init_one_nocb(struct rcu_node *rnp)
+{
+}
+
+static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
+                            bool lazy)
+{
+        return 0;
+}
+
+static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
+                                                     struct rcu_data *rdp)
+{
+        return 0;
+}
+
+static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
+{
+}
+
+static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
+{
+}
+
+static bool init_nocb_callback_list(struct rcu_data *rdp)
+{
+        return false;
+}
+
+#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
+
+/*
+ * An adaptive-ticks CPU can potentially execute in kernel mode for an
+ * arbitrarily long period of time with the scheduling-clock tick turned
+ * off.  RCU will be paying attention to this CPU because it is in the
+ * kernel, but the CPU cannot be guaranteed to be executing the RCU state
+ * machine because the scheduling-clock tick has been disabled.  Therefore,
+ * if an adaptive-ticks CPU is failing to respond to the current grace
+ * period and has not be idle from an RCU perspective, kick it.
+ */
+static void rcu_kick_nohz_cpu(int cpu)
+{
+#ifdef CONFIG_NO_HZ_FULL
+        if (tick_nohz_full_cpu(cpu))
+                smp_send_reschedule(cpu);
+#endif /* #ifdef CONFIG_NO_HZ_FULL */
+}
+
+
+#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
+
+/*
+ * Define RCU flavor that holds sysidle state.  This needs to be the
+ * most active flavor of RCU.
+ */
+#ifdef CONFIG_PREEMPT_RCU
+static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
+#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+
+static int full_sysidle_state;          /* Current system-idle state. */
+#define RCU_SYSIDLE_NOT         0       /* Some CPU is not idle. */
+#define RCU_SYSIDLE_SHORT       1       /* All CPUs idle for brief period. */
+#define RCU_SYSIDLE_LONG        2       /* All CPUs idle for long enough. */
+#define RCU_SYSIDLE_FULL        3       /* All CPUs idle, ready for sysidle. */
+#define RCU_SYSIDLE_FULL_NOTED  4       /* Actually entered sysidle state. */
+
+/*
+ * Invoked to note exit from irq or task transition to idle.  Note that
+ * usermode execution does -not- count as idle here!  After all, we want
+ * to detect full-system idle states, not RCU quiescent states and grace
+ * periods.  The caller must have disabled interrupts.
+ */
+static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
+{
+        unsigned long j;
+
+        /* Adjust nesting, check for fully idle. */
+        if (irq) {
+                rdtp->dynticks_idle_nesting--;
+                WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
+                if (rdtp->dynticks_idle_nesting != 0)
+                        return;  /* Still not fully idle. */
+        } else {
+                if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
+                    DYNTICK_TASK_NEST_VALUE) {
+                        rdtp->dynticks_idle_nesting = 0;
+                } else {
+                        rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
+                        WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
+                        return;  /* Still not fully idle. */
+                }
+        }
+
+        /* Record start of fully idle period. */
+        j = jiffies;
+        ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
+        smp_mb__before_atomic_inc();
+        atomic_inc(&rdtp->dynticks_idle);
+        smp_mb__after_atomic_inc();
+        WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
+}
+
+/*
+ * Unconditionally force exit from full system-idle state.  This is
+ * invoked when a normal CPU exits idle, but must be called separately
+ * for the timekeeping CPU (tick_do_timer_cpu).  The reason for this
+ * is that the timekeeping CPU is permitted to take scheduling-clock
+ * interrupts while the system is in system-idle state, and of course
+ * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
+ * interrupt from any other type of interrupt.
+ */
+void rcu_sysidle_force_exit(void)
+{
+        int oldstate = ACCESS_ONCE(full_sysidle_state);
+        int newoldstate;
+
+        /*
+         * Each pass through the following loop attempts to exit full
+         * system-idle state.  If contention proves to be a problem,
+         * a trylock-based contention tree could be used here.
+         */
+        while (oldstate > RCU_SYSIDLE_SHORT) {
+                newoldstate = cmpxchg(&full_sysidle_state,
+                                      oldstate, RCU_SYSIDLE_NOT);
+                if (oldstate == newoldstate &&
+                    oldstate == RCU_SYSIDLE_FULL_NOTED) {
+                        rcu_kick_nohz_cpu(tick_do_timer_cpu);
+                        return; /* We cleared it, done! */
+                }
+                oldstate = newoldstate;
+        }
+        smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
+}
+
+/*
+ * Invoked to note entry to irq or task transition from idle.  Note that
+ * usermode execution does -not- count as idle here!  The caller must
+ * have disabled interrupts.
+ */
+static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
+{
+        /* Adjust nesting, check for already non-idle. */
+        if (irq) {
+                rdtp->dynticks_idle_nesting++;
+                WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
+                if (rdtp->dynticks_idle_nesting != 1)
+                        return; /* Already non-idle. */
+        } else {
+                /*
+                 * Allow for irq misnesting.  Yes, it really is possible
+                 * to enter an irq handler then never leave it, and maybe
+                 * also vice versa.  Handle both possibilities.
+                 */
+                if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
+                        rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
+                        WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
+                        return; /* Already non-idle. */
+                } else {
+                        rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
+                }
+        }
+
+        /* Record end of idle period. */
+        smp_mb__before_atomic_inc();
+        atomic_inc(&rdtp->dynticks_idle);
+        smp_mb__after_atomic_inc();
+        WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
+
+        /*
+         * If we are the timekeeping CPU, we are permitted to be non-idle
+         * during a system-idle state.  This must be the case, because
+         * the timekeeping CPU has to take scheduling-clock interrupts
+         * during the time that the system is transitioning to full
+         * system-idle state.  This means that the timekeeping CPU must
+         * invoke rcu_sysidle_force_exit() directly if it does anything
+         * more than take a scheduling-clock interrupt.
+         */
+        if (smp_processor_id() == tick_do_timer_cpu)
+                return;
+
+        /* Update system-idle state: We are clearly no longer fully idle! */
+        rcu_sysidle_force_exit();
+}
+
+/*
+ * Check to see if the current CPU is idle.  Note that usermode execution
+ * does not count as idle.  The caller must have disabled interrupts.
+ */
+static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
+                                  unsigned long *maxj)
+{
+        int cur;
+        unsigned long j;
+        struct rcu_dynticks *rdtp = rdp->dynticks;
+
+        /*
+         * If some other CPU has already reported non-idle, if this is
+         * not the flavor of RCU that tracks sysidle state, or if this
+         * is an offline or the timekeeping CPU, nothing to do.
+         */
+        if (!*isidle || rdp->rsp != rcu_sysidle_state ||
+            cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
+                return;
+        if (rcu_gp_in_progress(rdp->rsp))
+                WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
+
+        /* Pick up current idle and NMI-nesting counter and check. */
+        cur = atomic_read(&rdtp->dynticks_idle);
+        if (cur & 0x1) {
+                *isidle = false; /* We are not idle! */
+                return;
+        }
+        smp_mb(); /* Read counters before timestamps. */
+
+        /* Pick up timestamps. */
+        j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
+        /* If this CPU entered idle more recently, update maxj timestamp. */
+        if (ULONG_CMP_LT(*maxj, j))
+                *maxj = j;
+}
+
+/*
+ * Is this the flavor of RCU that is handling full-system idle?
+ */
+static bool is_sysidle_rcu_state(struct rcu_state *rsp)
+{
+        return rsp == rcu_sysidle_state;
+}
+
+/*
+ * Bind the grace-period kthread for the sysidle flavor of RCU to the
+ * timekeeping CPU.
+ */
+static void rcu_bind_gp_kthread(void)
+{
+        int cpu = ACCESS_ONCE(tick_do_timer_cpu);
+
+        if (cpu < 0 || cpu >= nr_cpu_ids)
+                return;
+        if (raw_smp_processor_id() != cpu)
+                set_cpus_allowed_ptr(current, cpumask_of(cpu));
+}
+
+/*
+ * Return a delay in jiffies based on the number of CPUs, rcu_node
+ * leaf fanout, and jiffies tick rate.  The idea is to allow larger
+ * systems more time to transition to full-idle state in order to
+ * avoid the cache thrashing that otherwise occur on the state variable.
+ * Really small systems (less than a couple of tens of CPUs) should
+ * instead use a single global atomically incremented counter, and later
+ * versions of this will automatically reconfigure themselves accordingly.
+ */
+static unsigned long rcu_sysidle_delay(void)
+{
+        if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
+                return 0;
+        return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
+}
+
+/*
+ * Advance the full-system-idle state.  This is invoked when all of
+ * the non-timekeeping CPUs are idle.
+ */
+static void rcu_sysidle(unsigned long j)
+{
+        /* Check the current state. */
+        switch (ACCESS_ONCE(full_sysidle_state)) {
+        case RCU_SYSIDLE_NOT:
+
+                /* First time all are idle, so note a short idle period. */
+                ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
+                break;
+
+        case RCU_SYSIDLE_SHORT:
+
+                /*
+                 * Idle for a bit, time to advance to next state?
+                 * cmpxchg failure means race with non-idle, let them win.
+                 */
+                if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
+                        (void)cmpxchg(&full_sysidle_state,
+                                      RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
+                break;
+
+        case RCU_SYSIDLE_LONG:
+
+                /*
+                 * Do an additional check pass before advancing to full.
+                 * cmpxchg failure means race with non-idle, let them win.
+                 */
+                if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
+                        (void)cmpxchg(&full_sysidle_state,
+                                      RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
+                break;
+
+        default:
+                break;
+        }
+}
+
+/*
+ * Found a non-idle non-timekeeping CPU, so kick the system-idle state
+ * back to the beginning.
+ */
+static void rcu_sysidle_cancel(void)
+{
+        smp_mb();
+        ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
+}
+
+/*
+ * Update the sysidle state based on the results of a force-quiescent-state
+ * scan of the CPUs' dyntick-idle state.
+ */
+static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
+                               unsigned long maxj, bool gpkt)
+{
+        if (rsp != rcu_sysidle_state)
+                return;  /* Wrong flavor, ignore. */
+        if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
+                return;  /* Running state machine from timekeeping CPU. */
+        if (isidle)
+                rcu_sysidle(maxj);    /* More idle! */
+        else
+                rcu_sysidle_cancel(); /* Idle is over. */
+}
+
+/*
+ * Wrapper for rcu_sysidle_report() when called from the grace-period
+ * kthread's context.
+ */
+static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
+                                  unsigned long maxj)
+{
+        rcu_sysidle_report(rsp, isidle, maxj, true);
+}
+
+/* Callback and function for forcing an RCU grace period. */
+struct rcu_sysidle_head {
+        struct rcu_head rh;
+        int inuse;
+};
+
+static void rcu_sysidle_cb(struct rcu_head *rhp)
+{
+        struct rcu_sysidle_head *rshp;
+
+        /*
+         * The following memory barrier is needed to replace the
+         * memory barriers that would normally be in the memory
+         * allocator.
+         */
+        smp_mb();  /* grace period precedes setting inuse. */
+
+        rshp = container_of(rhp, struct rcu_sysidle_head, rh);
+        ACCESS_ONCE(rshp->inuse) = 0;
+}
+
+/*
+ * Check to see if the system is fully idle, other than the timekeeping CPU.
+ * The caller must have disabled interrupts.
+ */
+bool rcu_sys_is_idle(void)
+{
+        static struct rcu_sysidle_head rsh;
+        int rss = ACCESS_ONCE(full_sysidle_state);
+
+        if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
+                return false;
+
+        /* Handle small-system case by doing a full scan of CPUs. */
+        if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
+                int oldrss = rss - 1;
+
+                /*
+                 * One pass to advance to each state up to _FULL.
+                 * Give up if any pass fails to advance the state.
+                 */
+                while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
+                        int cpu;
+                        bool isidle = true;
+                        unsigned long maxj = jiffies - ULONG_MAX / 4;
+                        struct rcu_data *rdp;
+
+                        /* Scan all the CPUs looking for nonidle CPUs. */
+                        for_each_possible_cpu(cpu) {
+                                rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
+                                rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
+                                if (!isidle)
+                                        break;
+                        }
+                        rcu_sysidle_report(rcu_sysidle_state,
+                                           isidle, maxj, false);
+                        oldrss = rss;
+                        rss = ACCESS_ONCE(full_sysidle_state);
+                }
+        }
+
+        /* If this is the first observation of an idle period, record it. */
+        if (rss == RCU_SYSIDLE_FULL) {
+                rss = cmpxchg(&full_sysidle_state,
+                              RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
+                return rss == RCU_SYSIDLE_FULL;
+        }
+
+        smp_mb(); /* ensure rss load happens before later caller actions. */
+
+        /* If already fully idle, tell the caller (in case of races). */
+        if (rss == RCU_SYSIDLE_FULL_NOTED)
+                return true;
+
+        /*
+         * If we aren't there yet, and a grace period is not in flight,
+         * initiate a grace period.  Either way, tell the caller that
+         * we are not there yet.  We use an xchg() rather than an assignment
+         * to make up for the memory barriers that would otherwise be
+         * provided by the memory allocator.
+         */
+        if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
+            !rcu_gp_in_progress(rcu_sysidle_state) &&
+            !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
+                call_rcu(&rsh.rh, rcu_sysidle_cb);
+        return false;
+}
+
+/*
+ * Initialize dynticks sysidle state for CPUs coming online.
+ */
+static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
+{
+        rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
+}
+
+#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
+
+static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
+{
+}
+
+static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
+{
+}
+
+static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
+                                  unsigned long *maxj)
+{
+}
+
+static bool is_sysidle_rcu_state(struct rcu_state *rsp)
+{
+        return false;
+}
+
+static void rcu_bind_gp_kthread(void)
+{
+}
+
+static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
+                                  unsigned long maxj)
+{
+}
+
+static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
+{
+}
+
+#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */