/*
   * Read-Copy Update mechanism for mutual exclusion (tree-based version)
   * Internal non-public definitions that provide either classic
   * or preemptable 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>

  
  #ifdef CONFIG_TREE_PREEMPT_RCU
  
  struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
  DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);

  static int rcu_preempted_readers_exp(struct rcu_node *rnp);

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

  static void __init rcu_bootup_announce(void)

  {
  	printk(KERN_INFO
  	       "Experimental preemptable hierarchical RCU implementation.
  ");
  }
  
  /*
   * 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, 0);
  }
  EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
  
  /*

   * Record a preemptable-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.
   */

  static void rcu_preempt_qs(int cpu)

  {
  	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);

  	rdp->passed_quiesc_completed = rdp->gpnum - 1;

  	barrier();
  	rdp->passed_quiesc = 1;

  }
  
  /*

   * 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 appropriate entry
   * of the blocked_tasks[] array.  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 blocked_tasks[] entry indexed by the low-order bit of
   * rnp->gpnum empties.
   *
   * Caller must disable preemption.

   */

  static void rcu_preempt_note_context_switch(int cpu)

  {
  	struct task_struct *t = current;

  	unsigned long flags;

  	int phase;
  	struct rcu_data *rdp;
  	struct rcu_node *rnp;
  
  	if (t->rcu_read_lock_nesting &&
  	    (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
  
  		/* Possibly blocking in an RCU read-side critical section. */
  		rdp = 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.

  		 *
  		 * 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));
  		phase = (rnp->gpnum + !(rnp->qsmask & rdp->grpmask)) & 0x1;

  		list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);

  		raw_spin_unlock_irqrestore(&rnp->lock, flags);

  	}
  
  	/*
  	 * 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(cpu);

  	local_irq_save(flags);

  	t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;

  	local_irq_restore(flags);

  }
  
  /*
   * Tree-preemptable RCU implementation for rcu_read_lock().
   * Just increment ->rcu_read_lock_nesting, shared state will be updated
   * if we block.
   */
  void __rcu_read_lock(void)
  {
  	ACCESS_ONCE(current->rcu_read_lock_nesting)++;
  	barrier();  /* needed if we ever invoke rcu_read_lock in rcutree.c */
  }
  EXPORT_SYMBOL_GPL(__rcu_read_lock);

  /*
   * 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_preempted_readers(struct rcu_node *rnp)
  {

  	int phase = rnp->gpnum & 0x1;
  
  	return !list_empty(&rnp->blocked_tasks[phase]) ||
  	       !list_empty(&rnp->blocked_tasks[phase + 2]);

  }

  /*
   * 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_preempted_readers(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);

  }
  
  /*
   * 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.
   */

  static void rcu_read_unlock_special(struct task_struct *t)
  {
  	int empty;

  	int empty_exp;

  	unsigned long flags;

  	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) {
  		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;

  		rcu_preempt_qs(smp_processor_id());

  	}
  
  	/* Hardware IRQ handlers cannot block. */
  	if (in_irq()) {
  		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_preempted_readers(rnp);

  		empty_exp = !rcu_preempted_readers_exp(rnp);
  		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */

  		list_del_init(&t->rcu_node_entry);

  		t->rcu_blocked_node = NULL;

  
  		/*
  		 * 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.

  		 */

  		if (empty)

  			raw_spin_unlock_irqrestore(&rnp->lock, flags);

  		else

  			rcu_report_unblock_qs_rnp(rnp, flags);

  
  		/*
  		 * If this was the last task on the expedited lists,
  		 * then we need to report up the rcu_node hierarchy.
  		 */
  		if (!empty_exp && !rcu_preempted_readers_exp(rnp))
  			rcu_report_exp_rnp(&rcu_preempt_state, rnp);

  	} else {
  		local_irq_restore(flags);

  	}

  }
  
  /*
   * Tree-preemptable RCU implementation for rcu_read_unlock().
   * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
   * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
   * invoke rcu_read_unlock_special() to clean up after a context switch
   * in an RCU read-side critical section and other special cases.
   */
  void __rcu_read_unlock(void)
  {
  	struct task_struct *t = current;
  
  	barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */
  	if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
  	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
  		rcu_read_unlock_special(t);

  #ifdef CONFIG_PROVE_LOCKING
  	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
  #endif /* #ifdef CONFIG_PROVE_LOCKING */

  }
  EXPORT_SYMBOL_GPL(__rcu_read_unlock);
  
  #ifdef CONFIG_RCU_CPU_STALL_DETECTOR

  #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 list_head *lp;
  	int phase;
  	struct task_struct *t;
  
  	if (rcu_preempted_readers(rnp)) {
  		raw_spin_lock_irqsave(&rnp->lock, flags);
  		phase = rnp->gpnum & 0x1;
  		lp = &rnp->blocked_tasks[phase];
  		list_for_each_entry(t, lp, 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 */

  /*
   * Scan the current list of tasks blocked within RCU read-side critical
   * sections, printing out the tid of each.
   */
  static void rcu_print_task_stall(struct rcu_node *rnp)
  {

  	struct list_head *lp;

  	int phase;

  	struct task_struct *t;

  	if (rcu_preempted_readers(rnp)) {

  		phase = rnp->gpnum & 0x1;

  		lp = &rnp->blocked_tasks[phase];
  		list_for_each_entry(t, lp, rcu_node_entry)
  			printk(" P%d", t->pid);

  	}
  }
  
  #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
  
  /*

   * 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.
   */
  static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
  {

  	WARN_ON_ONCE(rcu_preempted_readers(rnp));

  	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)

  {
  	int i;
  	struct list_head *lp;
  	struct list_head *lp_root;

  	int retval = 0;

  	struct rcu_node *rnp_root = rcu_get_root(rsp);
  	struct task_struct *tp;

  	if (rnp == rnp_root) {
  		WARN_ONCE(1, "Last CPU thought to be offlined?");

  		return 0;  /* Shouldn't happen: at least one CPU online. */

  	}

  	WARN_ON_ONCE(rnp != rdp->mynode &&
  		     (!list_empty(&rnp->blocked_tasks[0]) ||

  		      !list_empty(&rnp->blocked_tasks[1]) ||
  		      !list_empty(&rnp->blocked_tasks[2]) ||
  		      !list_empty(&rnp->blocked_tasks[3])));

  
  	/*
  	 * Move tasks up to root rcu_node.  Rely on the fact that the
  	 * root rcu_node can be at most one ahead of the rest of the
  	 * rcu_nodes in terms of gp_num value.  This fact allows us to
  	 * move the blocked_tasks[] array directly, element by element.
  	 */

  	if (rcu_preempted_readers(rnp))
  		retval |= RCU_OFL_TASKS_NORM_GP;
  	if (rcu_preempted_readers_exp(rnp))
  		retval |= RCU_OFL_TASKS_EXP_GP;
  	for (i = 0; i < 4; i++) {

  		lp = &rnp->blocked_tasks[i];
  		lp_root = &rnp_root->blocked_tasks[i];
  		while (!list_empty(lp)) {
  			tp = list_entry(lp->next, typeof(*tp), rcu_node_entry);

  			raw_spin_lock(&rnp_root->lock); /* irqs already disabled */

  			list_del(&tp->rcu_node_entry);
  			tp->rcu_blocked_node = rnp_root;
  			list_add(&tp->rcu_node_entry, lp_root);

  			raw_spin_unlock(&rnp_root->lock); /* irqs remain disabled */

  		}
  	}

  	return retval;

  }
  
  /*

   * Do CPU-offline processing for preemptable RCU.
   */
  static void rcu_preempt_offline_cpu(int cpu)
  {
  	__rcu_offline_cpu(cpu, &rcu_preempt_state);
  }
  
  #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) {

  		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
  		rcu_preempt_qs(cpu);

  		return;
  	}

  	if (per_cpu(rcu_preempt_data, cpu).qs_pending)

  		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;

  }
  
  /*
   * Process callbacks for preemptable RCU.
   */
  static void rcu_preempt_process_callbacks(void)
  {
  	__rcu_process_callbacks(&rcu_preempt_state,
  				&__get_cpu_var(rcu_preempt_data));
  }
  
  /*
   * Queue a preemptable-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);
  }
  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.  RCU read-side critical
   * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
   * and may be nested.
   */
  void synchronize_rcu(void)
  {
  	struct rcu_synchronize rcu;
  
  	if (!rcu_scheduler_active)
  		return;
  
  	init_completion(&rcu.completion);
  	/* Will wake me after RCU finished. */
  	call_rcu(&rcu.head, wakeme_after_rcu);
  	/* Wait for it. */
  	wait_for_completion(&rcu.completion);
  }
  EXPORT_SYMBOL_GPL(synchronize_rcu);

  static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
  static 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 !list_empty(&rnp->blocked_tasks[2]) ||
  	       !list_empty(&rnp->blocked_tasks[3]);
  }
  
  /*
   * 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!)
   *
   * Caller must hold sync_rcu_preempt_exp_mutex.
   */
  static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
  {
  	unsigned long flags;
  	unsigned long mask;

  	raw_spin_lock_irqsave(&rnp->lock, flags);

  	for (;;) {
  		if (!sync_rcu_preempt_exp_done(rnp))
  			break;
  		if (rnp->parent == NULL) {
  			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;
  	}

  	raw_spin_unlock_irqrestore(&rnp->lock, flags);

  }
  
  /*
   * 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 rsp->onofflock.
   */
  static void
  sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
  {
  	int must_wait;

  	raw_spin_lock(&rnp->lock); /* irqs already disabled */

  	list_splice_init(&rnp->blocked_tasks[0], &rnp->blocked_tasks[2]);
  	list_splice_init(&rnp->blocked_tasks[1], &rnp->blocked_tasks[3]);
  	must_wait = rcu_preempted_readers_exp(rnp);

  	raw_spin_unlock(&rnp->lock); /* irqs remain disabled */

  	if (!must_wait)
  		rcu_report_exp_rnp(rsp, rnp);
  }

  /*

   * 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 ->blocked_tasks[] lists, move all entries from the first set of
   * ->blocked_tasks[] lists to the second set, and finally wait for this
   * second set to drain.

   */
  void synchronize_rcu_expedited(void)
  {

  	unsigned long flags;
  	struct rcu_node *rnp;
  	struct rcu_state *rsp = &rcu_preempt_state;
  	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. */
  
  	/*
  	 * 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 (trycount++ < 10)
  			udelay(trycount * num_online_cpus());
  		else {
  			synchronize_rcu();
  			return;
  		}
  		if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
  			goto mb_ret; /* Others did our work for us. */
  	}
  	if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
  		goto unlock_mb_ret; /* Others did our work for us. */
  
  	/* force all RCU readers onto blocked_tasks[]. */
  	synchronize_sched_expedited();

  	raw_spin_lock_irqsave(&rsp->onofflock, flags);

  
  	/* Initialize ->expmask for all non-leaf rcu_node structures. */
  	rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {

  		raw_spin_lock(&rnp->lock); /* irqs already disabled. */

  		rnp->expmask = rnp->qsmaskinit;

  		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */

  	}
  
  	/* Snapshot current state of ->blocked_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));

  	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);

  
  	/* Wait for snapshotted ->blocked_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);
  
  /*

   * Check to see if there is any immediate preemptable-RCU-related work
   * to be done.
   */
  static int rcu_preempt_pending(int cpu)
  {
  	return __rcu_pending(&rcu_preempt_state,
  			     &per_cpu(rcu_preempt_data, cpu));
  }
  
  /*
   * Does preemptable RCU need the CPU to stay out of dynticks mode?
   */
  static int rcu_preempt_needs_cpu(int cpu)
  {
  	return !!per_cpu(rcu_preempt_data, cpu).nxtlist;
  }

  /**
   * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
   */
  void rcu_barrier(void)
  {
  	_rcu_barrier(&rcu_preempt_state, call_rcu);
  }
  EXPORT_SYMBOL_GPL(rcu_barrier);

  /*
   * Initialize preemptable RCU's per-CPU data.
   */
  static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
  {
  	rcu_init_percpu_data(cpu, &rcu_preempt_state, 1);
  }
  
  /*

   * Move preemptable RCU's callbacks to ->orphan_cbs_list.
   */
  static void rcu_preempt_send_cbs_to_orphanage(void)
  {
  	rcu_send_cbs_to_orphanage(&rcu_preempt_state);
  }
  
  /*

   * Initialize preemptable RCU's state structures.
   */
  static void __init __rcu_init_preempt(void)
  {

  	RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data);
  }
  
  /*

   * Check for a task exiting while in a preemptable-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 (t->rcu_read_lock_nesting == 0)
  		return;
  	t->rcu_read_lock_nesting = 1;
  	rcu_read_unlock();
  }
  
  #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
  
  /*
   * Tell them what RCU they are running.
   */

  static void __init rcu_bootup_announce(void)

  {
  	printk(KERN_INFO "Hierarchical RCU implementation.
  ");
  }
  
  /*
   * 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 preemptable 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 preemptable RCU does not exist, there are never any preempted
   * RCU readers.
   */
  static int rcu_preempted_readers(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 */

  #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
  
  /*
   * Because preemptable 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 preemptable RCU does not exist, we never have to check for
   * tasks blocked within RCU read-side critical sections.
   */

  static void rcu_print_task_stall(struct rcu_node *rnp)
  {
  }
  
  #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
  
  /*

   * Because there is no preemptable 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 preemptable 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;

  }
  
  /*

   * Because preemptable RCU does not exist, it never needs CPU-offline
   * processing.
   */
  static void rcu_preempt_offline_cpu(int cpu)
  {
  }
  
  #endif /* #ifdef CONFIG_HOTPLUG_CPU */

  /*
   * Because preemptable RCU does not exist, it never has any callbacks
   * to check.
   */

  static void rcu_preempt_check_callbacks(int cpu)

  {
  }
  
  /*
   * Because preemptable RCU does not exist, it never has any callbacks
   * to process.
   */

  static void rcu_preempt_process_callbacks(void)

  {
  }
  
  /*
   * In classic RCU, call_rcu() is just call_rcu_sched().
   */
  void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
  {
  	call_rcu_sched(head, func);
  }
  EXPORT_SYMBOL_GPL(call_rcu);
  
  /*

   * Wait for an rcu-preempt grace period, but make it happen quickly.
   * But because preemptable 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 preemptable 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)
  {
  	return;
  }
  
  #endif /* #ifdef CONFIG_HOTPLUG_CPU */

  /*

   * Because preemptable RCU does not exist, it never has any work to do.
   */
  static int rcu_preempt_pending(int cpu)
  {
  	return 0;
  }
  
  /*
   * Because preemptable RCU does not exist, it never needs any CPU.
   */
  static int rcu_preempt_needs_cpu(int cpu)
  {
  	return 0;
  }
  
  /*

   * Because preemptable 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 preemptable RCU does not exist, there is no per-CPU
   * data to initialize.
   */
  static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
  {
  }

  /*

   * Because there is no preemptable RCU, there are no callbacks to move.
   */
  static void rcu_preempt_send_cbs_to_orphanage(void)
  {
  }
  
  /*

   * Because preemptable RCU does not exist, it need not be initialized.
   */
  static void __init __rcu_init_preempt(void)
  {
  }

  #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */

  
  #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 have preemptible RCU, just check whether this CPU needs
   * any flavor of RCU.  Do not chew up lots of CPU cycles with preemption
   * disabled in a most-likely vain attempt to cause RCU not to need this CPU.
   */
  int rcu_needs_cpu(int cpu)
  {
  	return rcu_needs_cpu_quick_check(cpu);
  }

  /*
   * Check to see if we need to continue a callback-flush operations to
   * allow the last CPU to enter dyntick-idle mode.  But fast dyntick-idle
   * entry is not configured, so we never do need to.
   */
  static void rcu_needs_cpu_flush(void)
  {
  }

  #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
  
  #define RCU_NEEDS_CPU_FLUSHES 5

  static DEFINE_PER_CPU(int, rcu_dyntick_drain);

  static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);

  
  /*
   * 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 are not supporting preemptible RCU, attempt to accelerate
   * any current grace periods so that RCU no longer needs this CPU, but
   * only if all other CPUs are already in dynticks-idle mode.  This will
   * allow the CPU cores to be powered down immediately, as opposed to after
   * waiting many milliseconds for grace periods to elapse.

   *
   * Because it is not legal to invoke rcu_process_callbacks() with irqs
   * disabled, we do one pass of force_quiescent_state(), then do a
   * raise_softirq() to cause rcu_process_callbacks() to be invoked later.
   * The per-cpu rcu_dyntick_drain variable controls the sequencing.

   */
  int rcu_needs_cpu(int cpu)
  {

  	int c = 0;

  	int thatcpu;

  	/* Check for being in the holdoff period. */
  	if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies)
  		return rcu_needs_cpu_quick_check(cpu);

  	/* Don't bother unless we are the last non-dyntick-idle CPU. */
  	for_each_cpu_not(thatcpu, nohz_cpu_mask)

  		if (thatcpu != cpu) {
  			per_cpu(rcu_dyntick_drain, cpu) = 0;

  			per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;

  			return rcu_needs_cpu_quick_check(cpu);

  		}

  
  	/* Check and update the rcu_dyntick_drain sequencing. */
  	if (per_cpu(rcu_dyntick_drain, cpu) <= 0) {
  		/* First time through, initialize the counter. */
  		per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES;
  	} else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) {
  		/* We have hit the limit, so time to give up. */

  		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;

  		return rcu_needs_cpu_quick_check(cpu);
  	}
  
  	/* Do one step pushing remaining RCU callbacks through. */
  	if (per_cpu(rcu_sched_data, cpu).nxtlist) {
  		rcu_sched_qs(cpu);
  		force_quiescent_state(&rcu_sched_state, 0);
  		c = c || per_cpu(rcu_sched_data, cpu).nxtlist;
  	}
  	if (per_cpu(rcu_bh_data, cpu).nxtlist) {
  		rcu_bh_qs(cpu);
  		force_quiescent_state(&rcu_bh_state, 0);
  		c = c || per_cpu(rcu_bh_data, cpu).nxtlist;

  	}
  
  	/* If RCU callbacks are still pending, RCU still needs this CPU. */

  	if (c)

  		raise_softirq(RCU_SOFTIRQ);

  	return c;
  }

  /*
   * Check to see if we need to continue a callback-flush operations to
   * allow the last CPU to enter dyntick-idle mode.
   */
  static void rcu_needs_cpu_flush(void)
  {
  	int cpu = smp_processor_id();

  	unsigned long flags;

  
  	if (per_cpu(rcu_dyntick_drain, cpu) <= 0)
  		return;

  	local_irq_save(flags);

  	(void)rcu_needs_cpu(cpu);

  	local_irq_restore(flags);

  }

  #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */