/*
 * Sleepable 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 (C) IBM Corporation, 2006
 *
 * Author: Paul McKenney <paulmck@us.ibm.com>
 *
 * For detailed explanation of Read-Copy Update mechanism see -
 * 		Documentation/RCU/ *.txt
 *
 */

#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/percpu.h>
#include <linux/preempt.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/delay.h>
#include <linux/srcu.h>

static int init_srcu_struct_fields(struct srcu_struct *sp)
{
	sp->completed = 0;
	mutex_init(&sp->mutex);
	sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
	return sp->per_cpu_ref ? 0 : -ENOMEM;
}

#ifdef CONFIG_DEBUG_LOCK_ALLOC

int __init_srcu_struct(struct srcu_struct *sp, const char *name,
		       struct lock_class_key *key)
{
	
	debug_check_no_locks_freed((void *)sp, sizeof(*sp));
	lockdep_init_map(&sp->dep_map, name, key, 0);
	return init_srcu_struct_fields(sp);
}
EXPORT_SYMBOL_GPL(__init_srcu_struct);

#else 

int init_srcu_struct(struct srcu_struct *sp)
{
	return init_srcu_struct_fields(sp);
}
EXPORT_SYMBOL_GPL(init_srcu_struct);

#endif 


static int srcu_readers_active_idx(struct srcu_struct *sp, int idx)
{
	int cpu;
	int sum;

	sum = 0;
	for_each_possible_cpu(cpu)
		sum += per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx];
	return sum;
}

static int srcu_readers_active(struct srcu_struct *sp)
{
	return srcu_readers_active_idx(sp, 0) + srcu_readers_active_idx(sp, 1);
}

void cleanup_srcu_struct(struct srcu_struct *sp)
{
	int sum;

	sum = srcu_readers_active(sp);
	WARN_ON(sum);  
	if (sum != 0)
		return;
	free_percpu(sp->per_cpu_ref);
	sp->per_cpu_ref = NULL;
}
EXPORT_SYMBOL_GPL(cleanup_srcu_struct);

int __srcu_read_lock(struct srcu_struct *sp)
{
	int idx;

	preempt_disable();
	idx = sp->completed & 0x1;
	barrier();  
	per_cpu_ptr(sp->per_cpu_ref, smp_processor_id())->c[idx]++;
	srcu_barrier();  
	preempt_enable();
	return idx;
}
EXPORT_SYMBOL_GPL(__srcu_read_lock);

void __srcu_read_unlock(struct srcu_struct *sp, int idx)
{
	preempt_disable();
	srcu_barrier();  
	per_cpu_ptr(sp->per_cpu_ref, smp_processor_id())->c[idx]--;
	preempt_enable();
}
EXPORT_SYMBOL_GPL(__srcu_read_unlock);

#define SYNCHRONIZE_SRCU_READER_DELAY 10

static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
{
	int idx;

	rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
			   !lock_is_held(&rcu_bh_lock_map) &&
			   !lock_is_held(&rcu_lock_map) &&
			   !lock_is_held(&rcu_sched_lock_map),
			   "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");

	idx = sp->completed;
	mutex_lock(&sp->mutex);


	if ((sp->completed - idx) >= 2) {
		mutex_unlock(&sp->mutex);
		return;
	}

	sync_func();  


	idx = sp->completed & 0x1;
	sp->completed++;

	sync_func();  


	if (srcu_readers_active_idx(sp, idx))
		udelay(SYNCHRONIZE_SRCU_READER_DELAY);
	while (srcu_readers_active_idx(sp, idx))
		schedule_timeout_interruptible(1);

	sync_func();  


	mutex_unlock(&sp->mutex);
}

void synchronize_srcu(struct srcu_struct *sp)
{
	__synchronize_srcu(sp, synchronize_sched);
}
EXPORT_SYMBOL_GPL(synchronize_srcu);

void synchronize_srcu_expedited(struct srcu_struct *sp)
{
	__synchronize_srcu(sp, synchronize_sched_expedited);
}
EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);


long srcu_batches_completed(struct srcu_struct *sp)
{
	return sp->completed;
}
EXPORT_SYMBOL_GPL(srcu_batches_completed);