/*
   * 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, you can access it online at
   * http://www.gnu.org/licenses/gpl-2.0.html.

   *
   * 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"

  #ifdef CONFIG_RCU_BOOST

  #include "../locking/rtmutex_common.h"

  /*
   * Control variables for per-CPU and per-rcu_node kthreads.  These
   * handle all flavors of RCU.
   */
  static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
  DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
  DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
  DEFINE_PER_CPU(char, rcu_cpu_has_work);

  #else /* #ifdef CONFIG_RCU_BOOST */
  
  /*
   * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST,
   * all uses are in dead code.  Provide a definition to keep the compiler
   * happy, but add WARN_ON_ONCE() to complain if used in the wrong place.
   * This probably needs to be excluded from -rt builds.
   */
  #define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
  
  #endif /* #else #ifdef CONFIG_RCU_BOOST */

  #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. */

  #endif /* #ifdef CONFIG_RCU_NOCB_CPU */

  /*
   * Check the RCU kernel configuration parameters and print informative

   * messages about anything out of the ordinary.

   */
  static void __init rcu_bootup_announce_oddness(void)
  {

  	if (IS_ENABLED(CONFIG_RCU_TRACE))
  		pr_info("\tRCU debugfs-based tracing is enabled.
  ");

  	if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
  	    (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))

  		pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d
  ",

  		       RCU_FANOUT);

  	if (rcu_fanout_exact)

  		pr_info("\tHierarchical RCU autobalancing is disabled.
  ");
  	if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
  		pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.
  ");
  	if (IS_ENABLED(CONFIG_PROVE_RCU))
  		pr_info("\tRCU lockdep checking is enabled.
  ");

  	if (RCU_NUM_LVLS >= 4)
  		pr_info("\tFour(or more)-level hierarchy is enabled.
  ");

  	if (RCU_FANOUT_LEAF != 16)

  		pr_info("\tBuild-time adjustment of leaf fanout to %d.
  ",

  			RCU_FANOUT_LEAF);
  	if (rcu_fanout_leaf != RCU_FANOUT_LEAF)

  		pr_info("\tBoot-time adjustment of leaf fanout to %d.
  ", rcu_fanout_leaf);

  	if (nr_cpu_ids != NR_CPUS)

  		pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.
  ", NR_CPUS, nr_cpu_ids);

  	if (IS_ENABLED(CONFIG_RCU_BOOST))
  		pr_info("\tRCU kthread priority: %d.
  ", kthread_prio);

  }

  #ifdef CONFIG_PREEMPT_RCU

  RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);

  static struct rcu_state *const rcu_state_p = &rcu_preempt_state;

  static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data;

  static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
  			       bool wake);

  /*
   * Tell them what RCU they are running.
   */

  static void __init rcu_bootup_announce(void)

  {

  	pr_info("Preemptible hierarchical RCU implementation.
  ");

  	rcu_bootup_announce_oddness();

  }

  /* Flags for rcu_preempt_ctxt_queue() decision table. */
  #define RCU_GP_TASKS	0x8
  #define RCU_EXP_TASKS	0x4
  #define RCU_GP_BLKD	0x2
  #define RCU_EXP_BLKD	0x1
  
  /*
   * Queues a task preempted within an RCU-preempt read-side critical
   * section into the appropriate location within the ->blkd_tasks list,
   * depending on the states of any ongoing normal and expedited grace
   * periods.  The ->gp_tasks pointer indicates which element the normal
   * grace period is waiting on (NULL if none), and the ->exp_tasks pointer
   * indicates which element the expedited grace period is waiting on (again,
   * NULL if none).  If a grace period is waiting on a given element in the
   * ->blkd_tasks list, it also waits on all subsequent elements.  Thus,
   * adding a task to the tail of the list blocks any grace period that is
   * already waiting on one of the elements.  In contrast, adding a task
   * to the head of the list won't block any grace period that is already
   * waiting on one of the elements.
   *
   * This queuing is imprecise, and can sometimes make an ongoing grace
   * period wait for a task that is not strictly speaking blocking it.
   * Given the choice, we needlessly block a normal grace period rather than
   * blocking an expedited grace period.
   *
   * Note that an endless sequence of expedited grace periods still cannot
   * indefinitely postpone a normal grace period.  Eventually, all of the
   * fixed number of preempted tasks blocking the normal grace period that are
   * not also blocking the expedited grace period will resume and complete
   * their RCU read-side critical sections.  At that point, the ->gp_tasks
   * pointer will equal the ->exp_tasks pointer, at which point the end of
   * the corresponding expedited grace period will also be the end of the
   * normal grace period.
   */

  static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
  	__releases(rnp->lock) /* But leaves rrupts disabled. */

  {
  	int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
  			 (rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
  			 (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
  			 (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
  	struct task_struct *t = current;
  
  	/*
  	 * Decide where to queue the newly blocked task.  In theory,
  	 * this could be an if-statement.  In practice, when I tried
  	 * that, it was quite messy.
  	 */
  	switch (blkd_state) {
  	case 0:
  	case                RCU_EXP_TASKS:
  	case                RCU_EXP_TASKS + RCU_GP_BLKD:
  	case RCU_GP_TASKS:
  	case RCU_GP_TASKS + RCU_EXP_TASKS:
  
  		/*
  		 * Blocking neither GP, or first task blocking the normal
  		 * GP but not blocking the already-waiting expedited GP.
  		 * Queue at the head of the list to avoid unnecessarily
  		 * blocking the already-waiting GPs.
  		 */
  		list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
  		break;
  
  	case                                              RCU_EXP_BLKD:
  	case                                RCU_GP_BLKD:
  	case                                RCU_GP_BLKD + RCU_EXP_BLKD:
  	case RCU_GP_TASKS +                               RCU_EXP_BLKD:
  	case RCU_GP_TASKS +                 RCU_GP_BLKD + RCU_EXP_BLKD:
  	case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
  
  		/*
  		 * First task arriving that blocks either GP, or first task
  		 * arriving that blocks the expedited GP (with the normal
  		 * GP already waiting), or a task arriving that blocks
  		 * both GPs with both GPs already waiting.  Queue at the
  		 * tail of the list to avoid any GP waiting on any of the
  		 * already queued tasks that are not blocking it.
  		 */
  		list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
  		break;
  
  	case                RCU_EXP_TASKS +               RCU_EXP_BLKD:
  	case                RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
  	case RCU_GP_TASKS + RCU_EXP_TASKS +               RCU_EXP_BLKD:
  
  		/*
  		 * Second or subsequent task blocking the expedited GP.
  		 * The task either does not block the normal GP, or is the
  		 * first task blocking the normal GP.  Queue just after
  		 * the first task blocking the expedited GP.
  		 */
  		list_add(&t->rcu_node_entry, rnp->exp_tasks);
  		break;
  
  	case RCU_GP_TASKS +                 RCU_GP_BLKD:
  	case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
  
  		/*
  		 * Second or subsequent task blocking the normal GP.
  		 * The task does not block the expedited GP. Queue just
  		 * after the first task blocking the normal GP.
  		 */
  		list_add(&t->rcu_node_entry, rnp->gp_tasks);
  		break;
  
  	default:
  
  		/* Yet another exercise in excessive paranoia. */
  		WARN_ON_ONCE(1);
  		break;
  	}
  
  	/*
  	 * We have now queued the task.  If it was the first one to
  	 * block either grace period, update the ->gp_tasks and/or
  	 * ->exp_tasks pointers, respectively, to reference the newly
  	 * blocked tasks.
  	 */
  	if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD))
  		rnp->gp_tasks = &t->rcu_node_entry;
  	if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
  		rnp->exp_tasks = &t->rcu_node_entry;

  	raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */

  
  	/*
  	 * Report the quiescent state for the expedited GP.  This expedited
  	 * GP should not be able to end until we report, so there should be
  	 * no need to check for a subsequent expedited GP.  (Though we are
  	 * still in a quiescent state in any case.)
  	 */
  	if (blkd_state & RCU_EXP_BLKD &&
  	    t->rcu_read_unlock_special.b.exp_need_qs) {
  		t->rcu_read_unlock_special.b.exp_need_qs = false;
  		rcu_report_exp_rdp(rdp->rsp, rdp, true);
  	} else {
  		WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs);
  	}

  }

  /*

   * 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.

   *

   * As with the other rcu_*_qs() functions, callers to this function
   * must disable preemption.

   */

  static void rcu_preempt_qs(void)

  {

  	if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) {

  		trace_rcu_grace_period(TPS("rcu_preempt"),

  				       __this_cpu_read(rcu_data_p->gpnum),

  				       TPS("cpuqs"));

  		__this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false);

  		barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
  		current->rcu_read_unlock_special.b.need_qs = false;
  	}

  }
  
  /*

   * 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 interrupts.

   */

  static void rcu_preempt_note_context_switch(void)

  {
  	struct task_struct *t = current;

  	struct rcu_data *rdp;
  	struct rcu_node *rnp;

  	if (t->rcu_read_lock_nesting > 0 &&

  	    !t->rcu_read_unlock_special.b.blocked) {

  
  		/* Possibly blocking in an RCU read-side critical section. */

  		rdp = this_cpu_ptr(rcu_state_p->rda);

  		rnp = rdp->mynode;

  		raw_spin_lock_rcu_node(rnp);

  		t->rcu_read_unlock_special.b.blocked = true;

  		t->rcu_blocked_node = rnp;

  
  		/*

  		 * Verify the CPU's sanity, trace the preemption, and
  		 * then queue the task as required based on the states
  		 * of any ongoing and expedited grace periods.

  		 */

  		WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);

  		WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));

  		trace_rcu_preempt_task(rdp->rsp->name,
  				       t->pid,
  				       (rnp->qsmask & rdp->grpmask)
  				       ? rnp->gpnum
  				       : rnp->gpnum + 1);

  		rcu_preempt_ctxt_queue(rnp, rdp);

  	} else if (t->rcu_read_lock_nesting < 0 &&

  		   t->rcu_read_unlock_special.s) {

  
  		/*
  		 * 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.
  	 */

  	rcu_preempt_qs();

  }
  
  /*

   * 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;

  }

  /*

   * 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;
  }
  
  /*

   * Return true if the specified rcu_node structure has tasks that were
   * preempted within an RCU read-side critical section.
   */
  static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
  {
  	return !list_empty(&rnp->blkd_tasks);
  }
  
  /*

   * 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)

  {

  	bool empty_exp;
  	bool empty_norm;
  	bool empty_exp_now;

  	unsigned long flags;

  	struct list_head *np;

  	bool drop_boost_mutex = false;

  	struct rcu_data *rdp;

  	struct rcu_node *rnp;

  	union rcu_special 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 its critical section,
  	 * report the fact that it has exited.  Because irqs are disabled,

  	 * t->rcu_read_unlock_special cannot change.

  	 */
  	special = t->rcu_read_unlock_special;

  	if (special.b.need_qs) {

  		rcu_preempt_qs();

  		t->rcu_read_unlock_special.b.need_qs = false;

  		if (!t->rcu_read_unlock_special.s) {

  			local_irq_restore(flags);
  			return;
  		}

  	}

  	/*
  	 * Respond to a request for an expedited grace period, but only if
  	 * we were not preempted, meaning that we were running on the same
  	 * CPU throughout.  If we were preempted, the exp_need_qs flag
  	 * would have been cleared at the time of the first preemption,
  	 * and the quiescent state would be reported when we were dequeued.
  	 */
  	if (special.b.exp_need_qs) {
  		WARN_ON_ONCE(special.b.blocked);
  		t->rcu_read_unlock_special.b.exp_need_qs = false;
  		rdp = this_cpu_ptr(rcu_state_p->rda);
  		rcu_report_exp_rdp(rcu_state_p, rdp, true);
  		if (!t->rcu_read_unlock_special.s) {
  			local_irq_restore(flags);
  			return;
  		}
  	}

  	/* Hardware IRQ handlers cannot block, complain if they get here. */

  	if (in_irq() || in_serving_softirq()) {
  		lockdep_rcu_suspicious(__FILE__, __LINE__,
  				       "rcu_read_unlock() from irq or softirq with blocking in critical section!!!
  ");

  		pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)
  ",

  			 t->rcu_read_unlock_special.s,
  			 t->rcu_read_unlock_special.b.blocked,

  			 t->rcu_read_unlock_special.b.exp_need_qs,

  			 t->rcu_read_unlock_special.b.need_qs);

  		local_irq_restore(flags);
  		return;
  	}
  
  	/* Clean up if blocked during RCU read-side critical section. */

  	if (special.b.blocked) {
  		t->rcu_read_unlock_special.b.blocked = false;

  		/*

  		 * Remove this task from the list it blocked on.  The task

  		 * now remains queued on the rcu_node corresponding to the
  		 * CPU it first blocked on, so there is no longer any need
  		 * to loop.  Retain a WARN_ON_ONCE() out of sheer paranoia.

  		 */

  		rnp = t->rcu_blocked_node;
  		raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
  		WARN_ON_ONCE(rnp != t->rcu_blocked_node);

  		empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);

  		empty_exp = sync_rcu_preempt_exp_done(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;

  		if (IS_ENABLED(CONFIG_RCU_BOOST)) {
  			if (&t->rcu_node_entry == rnp->boost_tasks)
  				rnp->boost_tasks = np;
  			/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
  			drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
  		}

  
  		/*
  		 * 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 = sync_rcu_preempt_exp_done(rnp);

  		if (!empty_norm && !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(rcu_state_p, rnp, flags);

  		} else {

  			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

  		}

  		/* Unboost if we were boosted. */

  		if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)

  			rt_mutex_unlock(&rnp->boost_mtx);

  		/*
  		 * 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_state_p, rnp, true);

  	} else {
  		local_irq_restore(flags);

  	}

  }

  /*
   * 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_rcu_node(rnp, flags);

  	if (!rcu_preempt_blocked_readers_cgp(rnp)) {

  		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

  		return;
  	}

  	t = list_entry(rnp->gp_tasks->prev,

  		       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_rcu_node(rnp, 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);
  }

  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("
  ");

  }

  /*
   * 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->prev,

  		       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;

  }

  /*

   * Scan the current list of tasks blocked within RCU read-side critical
   * sections, printing out the tid of each that is blocking the current
   * expedited grace period.
   */
  static int rcu_print_task_exp_stall(struct rcu_node *rnp)
  {
  	struct task_struct *t;
  	int ndetected = 0;
  
  	if (!rnp->exp_tasks)
  		return 0;
  	t = list_entry(rnp->exp_tasks->prev,
  		       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++;
  	}
  	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 (rcu_preempt_has_tasks(rnp))

  		rnp->gp_tasks = rnp->blkd_tasks.next;

  	WARN_ON_ONCE(rnp->qsmask);

  }

  /*

   * 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(void)

  {
  	struct task_struct *t = current;
  
  	if (t->rcu_read_lock_nesting == 0) {

  		rcu_preempt_qs();

  		return;
  	}

  	if (t->rcu_read_lock_nesting > 0 &&

  	    __this_cpu_read(rcu_data_p->core_needs_qs) &&

  	    __this_cpu_read(rcu_data_p->cpu_no_qs.b.norm))

  		t->rcu_read_unlock_special.b.need_qs = true;

  }

  #ifdef CONFIG_RCU_BOOST

  static void rcu_preempt_do_callbacks(void)
  {

  	rcu_do_batch(rcu_state_p, this_cpu_ptr(rcu_data_p));

  }

  #endif /* #ifdef CONFIG_RCU_BOOST */

  /*

   * Queue a preemptible-RCU callback for invocation after a grace period.

   */

  void call_rcu(struct rcu_head *head, rcu_callback_t func)

  {

  	__call_rcu(head, func, rcu_state_p, -1, 0);

  }
  EXPORT_SYMBOL_GPL(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_WARN(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 == RCU_SCHEDULER_INACTIVE)

  		return;

  	if (rcu_gp_is_expedited())

  		synchronize_rcu_expedited();
  	else
  		wait_rcu_gp(call_rcu);

  }
  EXPORT_SYMBOL_GPL(synchronize_rcu);

  /**
   * 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_state_p);

  }
  EXPORT_SYMBOL_GPL(rcu_barrier);

  /*

   * Initialize preemptible RCU's state structures.

   */
  static void __init __rcu_init_preempt(void)
  {

  	rcu_init_one(rcu_state_p);

  }

  /*
   * 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.b.blocked = true;

  	__rcu_read_unlock();
  }

  #else /* #ifdef CONFIG_PREEMPT_RCU */

  static struct rcu_state *const rcu_state_p = &rcu_sched_state;

  /*
   * Tell them what RCU they are running.
   */

  static void __init rcu_bootup_announce(void)

  {

  	pr_info("Hierarchical RCU implementation.
  ");

  	rcu_bootup_announce_oddness();

  }
  
  /*

   * Because preemptible RCU does not exist, we never have to check for
   * CPUs being in quiescent states.
   */

  static void rcu_preempt_note_context_switch(void)

  {
  }
  
  /*

   * 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;
  }

  /*
   * Because there is no preemptible RCU, there can be no readers blocked.
   */
  static bool rcu_preempt_has_tasks(struct rcu_node *rnp)

  {

  	return false;

  }

  /*

   * 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 preemptible RCU does not exist, we never have to check for
   * tasks blocked within RCU read-side critical sections that are
   * blocking the current expedited grace period.
   */
  static int rcu_print_task_exp_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);

  }

  /*

   * Because preemptible RCU does not exist, it never has any callbacks

   * to check.
   */

  static void rcu_preempt_check_callbacks(void)

  {
  }
  
  /*

   * 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_PREEMPT_RCU */

  #ifdef CONFIG_RCU_BOOST

  #include "../locking/rtmutex_common.h"

  #ifdef CONFIG_RCU_TRACE
  
  static void rcu_initiate_boost_trace(struct rcu_node *rnp)
  {

  	if (!rcu_preempt_has_tasks(rnp))

  		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 task_struct *t;
  	struct list_head *tb;

  	if (READ_ONCE(rnp->exp_tasks) == NULL &&
  	    READ_ONCE(rnp->boost_tasks) == NULL)

  		return 0;  /* Nothing left to boost. */

  	raw_spin_lock_irqsave_rcu_node(rnp, 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_rcu_node(rnp, 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(&rnp->boost_mtx, t);

  	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

  	/* Lock only for side effect: boosts task t's priority. */
  	rt_mutex_lock(&rnp->boost_mtx);
  	rt_mutex_unlock(&rnp->boost_mtx);  /* Then keep lockdep happy. */

  	return READ_ONCE(rnp->exp_tasks) != NULL ||
  	       READ_ONCE(rnp->boost_tasks) != NULL;

  }
  
  /*

   * Priority-boosting kthread, one per leaf 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)

  	__releases(rnp->lock)

  {
  	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_rcu_node(rnp, 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_rcu_node(rnp, 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_rcu_node(rnp, 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_state_p != rsp)

  		return 0;

  	if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 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_rcu_node(rnp, flags);

  	rnp->boost_kthread_task = t;

  	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

  	sp.sched_priority = kthread_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 = 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 = rcu_rnp_online_cpus(rnp);

  	cpumask_var_t cm;
  	int cpu;

  	if (!t)

  		return;

  	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))

  		return;

  	for_each_leaf_node_possible_cpu(rnp, cpu)
  		if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
  		    cpu != outgoingcpu)

  			cpumask_set_cpu(cpu, cm);

  	if (cpumask_weight(cm) == 0)

  		cpumask_setall(cm);

  	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 boost kthreads -- called as soon as the scheduler is running.

   */

  static void __init rcu_spawn_boost_kthreads(void)

  {

  	struct rcu_node *rnp;

  	int cpu;

  	for_each_possible_cpu(cpu)

  		per_cpu(rcu_cpu_has_work, cpu) = 0;

  	BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));

  	rcu_for_each_leaf_node(rcu_state_p, rnp)
  		(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);

  }

  static void rcu_prepare_kthreads(int cpu)

  {

  	struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->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_p, rnp);

  }

  #else /* #ifdef CONFIG_RCU_BOOST */

  static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)

  	__releases(rnp->lock)

  {

  	raw_spin_unlock_irqrestore_rcu_node(rnp, 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 void __init rcu_spawn_boost_kthreads(void)

  {

  }

  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(u64 basemono, u64 *nextevt)

  {

  	*nextevt = KTIME_MAX;

  	return IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL)
  	       ? 0 : rcu_cpu_has_callbacks(NULL);

  }
  
  /*
   * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
   * after it.
   */

  static void rcu_cleanup_after_idle(void)

  {
  }
  
  /*

   * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,

   * is nothing.
   */

  static void rcu_prepare_for_idle(void)

  {
  }

  /*
   * 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);

  /*

   * 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 __maybe_unused 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 false;

  	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 ||

  		     unlikely(READ_ONCE(rdp->gpwrap))) &&

  		    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(u64 basemono, u64 *nextevt)

  {

  	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

  	unsigned long dj;

  	if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL)) {

  		*nextevt = KTIME_MAX;

  		return 0;
  	}

  	/* 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(&rdtp->all_lazy)) {

  		*nextevt = KTIME_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;

  	}

  	*nextevt = basemono + dj * TICK_NSEC;

  	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(void)

  {

  	bool needwake;

  	struct rcu_data *rdp;

  	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

  	struct rcu_node *rnp;
  	struct rcu_state *rsp;

  	int tne;

  	if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) ||
  	    rcu_is_nocb_cpu(smp_processor_id()))

  		return;

  	/* Handle nohz enablement switches conservatively. */

  	tne = READ_ONCE(tick_nohz_active);

  	if (tne != rdtp->tick_nohz_enabled_snap) {

  		if (rcu_cpu_has_callbacks(NULL))

  			invoke_rcu_core(); /* force nohz to see update. */
  		rdtp->tick_nohz_enabled_snap = tne;
  		return;
  	}
  	if (!tne)
  		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 = this_cpu_ptr(rsp->rda);

  		if (!*rdp->nxttail[RCU_DONE_TAIL])
  			continue;
  		rnp = rdp->mynode;

  		raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */

  		needwake = rcu_accelerate_cbs(rsp, rnp, rdp);

  		raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */

  		if (needwake)
  			rcu_gp_kthread_wake(rsp);

  	}

  }

  /*
   * 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(void)

  {

  	if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) ||
  	    rcu_is_nocb_cpu(smp_processor_id()))

  		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 = raw_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);

  	smp_mb(); /* Ensure callback reuse happens after callback invocation. */

  
  	/*
  	 * Prevent premature wakeup: ensure that all increments happen
  	 * before there is a chance of the counter reaching zero.
  	 */
  	atomic_set(&oom_callback_count, 1);

  	for_each_online_cpu(cpu) {
  		smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);

  		cond_resched_rcu_qs();

  	}

  
  	/* 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_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("
  ");

  }
  
  /*
   * 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-%c%c%c: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s
  ",
  	       cpu,
  	       "O."[!!cpu_online(cpu)],
  	       "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
  	       "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
  	       ticks_value, ticks_title,