/*

 * 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

 *

 * Author: Dipankar Sarma <dipankar@in.ibm.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

 *

 */

#ifndef __LINUX_RCUPDATE_H

#define __LINUX_RCUPDATE_H

#include <linux/cache.h>

#include <linux/spinlock.h>

#include <linux/threads.h>

#include <linux/percpu.h>

#include <linux/cpumask.h>

#include <linux/seqlock.h>

#include <linux/lockdep.h>

#include <linux/completion.h>

/**

 * struct rcu_head - callback structure for use with RCU

 * @next: next update requests in a list

 * @func: actual update function to call after the grace period.

 */

struct rcu_head {

	struct rcu_head *next;

	void (*func)(struct rcu_head *head);

};

#include <linux/rcuclassic.h>

#include <linux/rcupreempt.h>

#define RCU_HEAD_INIT 	{ .next = NULL, .func = NULL }

#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT

#define INIT_RCU_HEAD(ptr) do { \

       (ptr)->next = NULL; (ptr)->func = NULL; \

} while (0)

/**

 * rcu_read_lock - mark the beginning of an RCU read-side critical section.

 *

 * When synchronize_rcu() is invoked on one CPU while other CPUs

 * are within RCU read-side critical sections, then the

 * synchronize_rcu() is guaranteed to block until after all the other

 * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked

 * on one CPU while other CPUs are within RCU read-side critical

 * sections, invocation of the corresponding RCU callback is deferred

 * until after the all the other CPUs exit their critical sections.

 *

 * Note, however, that RCU callbacks are permitted to run concurrently

 * with RCU read-side critical sections.  One way that this can happen

 * is via the following sequence of events: (1) CPU 0 enters an RCU

 * read-side critical section, (2) CPU 1 invokes call_rcu() to register

 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,

 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU

 * callback is invoked.  This is legal, because the RCU read-side critical

 * section that was running concurrently with the call_rcu() (and which

 * therefore might be referencing something that the corresponding RCU

 * callback would free up) has completed before the corresponding

 * RCU callback is invoked.

 *

 * RCU read-side critical sections may be nested.  Any deferred actions

 * will be deferred until the outermost RCU read-side critical section

 * completes.

 *

 * It is illegal to block while in an RCU read-side critical section.

 */

#define rcu_read_lock() __rcu_read_lock()

/**

 * rcu_read_unlock - marks the end of an RCU read-side critical section.

 *

 * See rcu_read_lock() for more information.

 */

/*

 * So where is rcu_write_lock()?  It does not exist, as there is no

 * way for writers to lock out RCU readers.  This is a feature, not

 * a bug -- this property is what provides RCU's performance benefits.

 * Of course, writers must coordinate with each other.  The normal

 * spinlock primitives work well for this, but any other technique may be

 * used as well.  RCU does not care how the writers keep out of each

 * others' way, as long as they do so.

 */

#define rcu_read_unlock() __rcu_read_unlock()

/**

 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section

 *

 * This is equivalent of rcu_read_lock(), but to be used when updates

 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks

 * consider completion of a softirq handler to be a quiescent state,

 * a process in RCU read-side critical section must be protected by

 * disabling softirqs. Read-side critical sections in interrupt context

 * can use just rcu_read_lock().

 *

 */

#define rcu_read_lock_bh() __rcu_read_lock_bh()

/*

 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section

 *

 * See rcu_read_lock_bh() for more information.

 */

#define rcu_read_unlock_bh() __rcu_read_unlock_bh()

/**

 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section

 *

 * Should be used with either

 * - synchronize_sched()

 * or

 * - call_rcu_sched() and rcu_barrier_sched()

 * on the write-side to insure proper synchronization.

 */

#define rcu_read_lock_sched() preempt_disable()

/*

 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section

 *

 * See rcu_read_lock_sched for more information.

 */

#define rcu_read_unlock_sched() preempt_enable()

/**

 * rcu_dereference - fetch an RCU-protected pointer in an

 * RCU read-side critical section.  This pointer may later

 * be safely dereferenced.

 *

 * Inserts memory barriers on architectures that require them

 * (currently only the Alpha), and, more importantly, documents

 * exactly which pointers are protected by RCU.

 */

#define rcu_dereference(p)     ({ \

				typeof(p) _________p1 = ACCESS_ONCE(p); \

				smp_read_barrier_depends(); \

				(_________p1); \

				})

/**

 * rcu_assign_pointer - assign (publicize) a pointer to a newly

 * initialized structure that will be dereferenced by RCU read-side

 * critical sections.  Returns the value assigned.

 *

 * Inserts memory barriers on architectures that require them

 * (pretty much all of them other than x86), and also prevents

 * the compiler from reordering the code that initializes the

 * structure after the pointer assignment.  More importantly, this

 * call documents which pointers will be dereferenced by RCU read-side

 * code.

 */

#define rcu_assign_pointer(p, v) \

	({ \

		if (!__builtin_constant_p(v) || \

		    ((v) != NULL)) \

			smp_wmb(); \

		(p) = (v); \

	})

/* Infrastructure to implement the synchronize_() primitives. */

struct rcu_synchronize {

	struct rcu_head head;

	struct completion completion;

};

extern void wakeme_after_rcu(struct rcu_head  *head);

/**

 * synchronize_sched - block until all CPUs have exited any non-preemptive

 * kernel code sequences.

 *

 * 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.

 */

#define synchronize_sched() __synchronize_sched()

/**

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

 * @head: structure to be used for queueing the RCU updates.

 * @func: actual update function to be invoked after the grace period

 *

 * The update function will be invoked some time after a full grace

 * period elapses, 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.

 */

extern void call_rcu(struct rcu_head *head,

			      void (*func)(struct rcu_head *head));

/**

 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.

 * @head: structure to be used for queueing the RCU updates.

 * @func: actual update function to be invoked after the grace period

 *

 * The update function will be invoked some time after a full grace

 * period elapses, in other words after all currently executing RCU

 * read-side critical sections have completed. call_rcu_bh() assumes

 * that the read-side critical sections end on completion of a softirq

 * handler. This means that read-side critical sections in process

 * context must not be interrupted by softirqs. This interface is to be

 * used when most of the read-side critical sections are in softirq context.

 * RCU read-side critical sections are delimited by :

 *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.

 *  OR

 *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.

 *  These may be nested.

 */

extern void call_rcu_bh(struct rcu_head *head,

			void (*func)(struct rcu_head *head));

/* Exported common interfaces */

extern void synchronize_rcu(void);

extern void rcu_barrier(void);

extern void rcu_barrier_bh(void);

extern void rcu_barrier_sched(void);

/* Internal to kernel */

extern void rcu_init(void);

extern int rcu_needs_cpu(int cpu);

#endif /* __LINUX_RCUPDATE_H */