/*
   * Read-Copy Update mechanism for mutual exclusion
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
   *

   * Copyright IBM Corporation, 2001

   *
   * Authors: Dipankar Sarma <dipankar@in.ibm.com>
   *	    Manfred Spraul <manfred@colorfullife.com>

   *

   * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
   * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
   * Papers:
   * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
   * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
   *
   * For detailed explanation of Read-Copy Update mechanism see -

   *		http://lse.sourceforge.net/locking/rcupdate.html

   *
   */
  #include <linux/types.h>
  #include <linux/kernel.h>
  #include <linux/init.h>
  #include <linux/spinlock.h>
  #include <linux/smp.h>
  #include <linux/interrupt.h>
  #include <linux/sched.h>
  #include <asm/atomic.h>
  #include <linux/bitops.h>

  #include <linux/percpu.h>
  #include <linux/notifier.h>

  #include <linux/cpu.h>

  #include <linux/mutex.h>

  #include <linux/module.h>

  #include <linux/kernel_stat.h>

  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  static struct lock_class_key rcu_lock_key;
  struct lockdep_map rcu_lock_map =
  	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
  EXPORT_SYMBOL_GPL(rcu_lock_map);
  #endif

  int rcu_scheduler_active __read_mostly;

  /*
   * Awaken the corresponding synchronize_rcu() instance now that a
   * grace period has elapsed.
   */

  void wakeme_after_rcu(struct rcu_head  *head)

  {

  	struct rcu_synchronize *rcu;
  
  	rcu = container_of(head, struct rcu_synchronize, head);
  	complete(&rcu->completion);

  }

  #ifdef CONFIG_TREE_PREEMPT_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);

  #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
  
  /**
   * synchronize_sched - wait until an rcu-sched grace period has elapsed.
   *
   * Control will return to the caller some time after a full rcu-sched
   * grace period has elapsed, in other words after all currently executing
   * rcu-sched read-side critical sections have completed.   These read-side
   * critical sections are delimited by rcu_read_lock_sched() and
   * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
   * local_irq_disable(), and so on may be used in place of
   * rcu_read_lock_sched().
   *
   * This means that all preempt_disable code sequences, including NMI and
   * hardware-interrupt handlers, in progress on entry will have completed
   * before this primitive returns.  However, this does not guarantee that
   * softirq handlers will have completed, since in some kernels, these
   * handlers can run in process context, and can block.
   *
   * This primitive provides the guarantees made by the (now removed)
   * synchronize_kernel() API.  In contrast, synchronize_rcu() only
   * guarantees that rcu_read_lock() sections will have completed.
   * In "classic RCU", these two guarantees happen to be one and
   * the same, but can differ in realtime RCU implementations.
   */
  void synchronize_sched(void)
  {
  	struct rcu_synchronize rcu;
  
  	if (rcu_blocking_is_gp())
  		return;
  
  	init_completion(&rcu.completion);
  	/* Will wake me after RCU finished. */
  	call_rcu_sched(&rcu.head, wakeme_after_rcu);
  	/* Wait for it. */
  	wait_for_completion(&rcu.completion);
  }
  EXPORT_SYMBOL_GPL(synchronize_sched);

  /**
   * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
   *
   * Control will return to the caller some time after a full rcu_bh grace
   * period has elapsed, in other words after all currently executing rcu_bh
   * read-side critical sections have completed.  RCU read-side critical
   * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
   * and may be nested.
   */
  void synchronize_rcu_bh(void)
  {
  	struct rcu_synchronize rcu;
  
  	if (rcu_blocking_is_gp())
  		return;
  
  	init_completion(&rcu.completion);
  	/* Will wake me after RCU finished. */
  	call_rcu_bh(&rcu.head, wakeme_after_rcu);
  	/* Wait for it. */
  	wait_for_completion(&rcu.completion);
  }
  EXPORT_SYMBOL_GPL(synchronize_rcu_bh);

  static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
  		unsigned long action, void *hcpu)
  {

  	return rcu_cpu_notify(self, action, hcpu);

  }

  void __init rcu_init(void)
  {

  	int i;

  	__rcu_init();

  	cpu_notifier(rcu_barrier_cpu_hotplug, 0);
  
  	/*
  	 * We don't need protection against CPU-hotplug here because
  	 * this is called early in boot, before either interrupts
  	 * or the scheduler are operational.
  	 */
  	for_each_online_cpu(i)
  		rcu_barrier_cpu_hotplug(NULL, CPU_UP_PREPARE, (void *)(long)i);

  }

  void rcu_scheduler_starting(void)
  {
  	WARN_ON(num_online_cpus() != 1);
  	WARN_ON(nr_context_switches() > 0);
  	rcu_scheduler_active = 1;
  }