[net-next-2.6.git] / include / linux / rcupdate.h

/*
 * 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/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);
};

/* Exported common interfaces */
#ifdef CONFIG_TREE_PREEMPT_RCU
extern void synchronize_rcu(void);
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
#define synchronize_rcu synchronize_sched
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
extern void synchronize_rcu_bh(void);
extern void synchronize_sched(void);
extern void rcu_barrier(void);
extern void rcu_barrier_bh(void);
extern void rcu_barrier_sched(void);
extern void synchronize_sched_expedited(void);
extern int sched_expedited_torture_stats(char *page);

/* Internal to kernel */
extern void rcu_init(void);
extern void rcu_scheduler_starting(void);
extern int rcu_needs_cpu(int cpu);
extern int rcu_scheduler_active;

#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
#include <linux/rcutree.h>
#else
#error "Unknown RCU implementation specified to kernel configuration"
#endif

#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)

#ifdef CONFIG_DEBUG_LOCK_ALLOC
extern struct lockdep_map rcu_lock_map;
# define rcu_read_acquire()	\
			lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
# define rcu_read_release()	lock_release(&rcu_lock_map, 1, _THIS_IP_)
#else
# define rcu_read_acquire()	do { } while (0)
# define rcu_read_release()	do { } while (0)
#endif

/**
 * 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.
 */
static inline void rcu_read_lock(void)
{
	__rcu_read_lock();
	__acquire(RCU);
	rcu_read_acquire();
}

/**
 * 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.
 */
static inline void rcu_read_unlock(void)
{
	rcu_read_release();
	__release(RCU);
	__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().
 *
 */
static inline void rcu_read_lock_bh(void)
{
	__rcu_read_lock_bh();
	__acquire(RCU_BH);
	rcu_read_acquire();
}

/*
 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 *
 * See rcu_read_lock_bh() for more information.
 */
static inline void rcu_read_unlock_bh(void)
{
	rcu_read_release();
	__release(RCU_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.
 */
static inline void rcu_read_lock_sched(void)
{
	preempt_disable();
	__acquire(RCU_SCHED);
	rcu_read_acquire();
}
static inline notrace void rcu_read_lock_sched_notrace(void)
{
	preempt_disable_notrace();
	__acquire(RCU_SCHED);
}

/*
 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 *
 * See rcu_read_lock_sched for more information.
 */
static inline void rcu_read_unlock_sched(void)
{
	rcu_read_release();
	__release(RCU_SCHED);
	preempt_enable();
}
static inline notrace void rcu_read_unlock_sched_notrace(void)
{
	__release(RCU_SCHED);
	preempt_enable_notrace();
}


/**
 * 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);

/**
 * 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));

#endif /* __LINUX_RCUPDATE_H */
Commit	Line	Data
1da177e4 LT	1	/*
	2	* Read-Copy Update mechanism for mutual exclusion
	3	*
	4	* This program is free software; you can redistribute it and/or modify
	5	* it under the terms of the GNU General Public License as published by
	6	* the Free Software Foundation; either version 2 of the License, or
	7	* (at your option) any later version.
	8	*
	9	* This program is distributed in the hope that it will be useful,
	10	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	11	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	12	* GNU General Public License for more details.
	13	*
	14	* You should have received a copy of the GNU General Public License
	15	* along with this program; if not, write to the Free Software
	16	* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	17	*
01c1c660	18	* Copyright IBM Corporation, 2001
1da177e4 LT	19	*
	20	* Author: Dipankar Sarma <dipankar@in.ibm.com>
	21	*
595182bc	22	* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
1da177e4 LT	23	* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
	24	* Papers:
	25	* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
	26	* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
	27	*
	28	* For detailed explanation of Read-Copy Update mechanism see -
	29	* http://lse.sourceforge.net/locking/rcupdate.html
	30	*
	31	*/
	32
	33	#ifndef __LINUX_RCUPDATE_H
	34	#define __LINUX_RCUPDATE_H
	35
1da177e4 LT	36	#include <linux/cache.h>
	37	#include <linux/spinlock.h>
	38	#include <linux/threads.h>
1da177e4 LT	39	#include <linux/cpumask.h>
1da177e4 LT	40	#include <linux/seqlock.h>
851a67b8	41	#include <linux/lockdep.h>
4446a36f	42	#include <linux/completion.h>
1da177e4 LT	43
	44	/**
	45	* struct rcu_head - callback structure for use with RCU
	46	* @next: next update requests in a list
	47	* @func: actual update function to call after the grace period.
	48	*/
	49	struct rcu_head {
	50	struct rcu_head *next;
	51	void (func)(struct rcu_head head);
	52	};
	53
03b042bf	54	/* Exported common interfaces */
16e30811	55	#ifdef CONFIG_TREE_PREEMPT_RCU
03b042bf	56	extern void synchronize_rcu(void);
16e30811 PM	57	#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
	58	#define synchronize_rcu synchronize_sched
	59	#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
03b042bf	60	extern void synchronize_rcu_bh(void);
16e30811	61	extern void synchronize_sched(void);
03b042bf PM	62	extern void rcu_barrier(void);
	63	extern void rcu_barrier_bh(void);
	64	extern void rcu_barrier_sched(void);
	65	extern void synchronize_sched_expedited(void);
	66	extern int sched_expedited_torture_stats(char *page);
	67
	68	/* Internal to kernel */
	69	extern void rcu_init(void);
	70	extern void rcu_scheduler_starting(void);
	71	extern int rcu_needs_cpu(int cpu);
a6826048 PM	72	extern int rcu_scheduler_active;
a6826048 PM	73
f41d911f	74	#if defined(CONFIG_TREE_RCU) \|\| defined(CONFIG_TREE_PREEMPT_RCU)
64db4cff	75	#include <linux/rcutree.h>
64db4cff PM	76	#else
64db4cff PM	77	#error "Unknown RCU implementation specified to kernel configuration"
6b3ef48a	78	#endif
01c1c660	79
8b6490e5 DS	80	#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
8b6490e5 DS	81	#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
1da177e4 LT	82	#define INIT_RCU_HEAD(ptr) do { \
	83	(ptr)->next = NULL; (ptr)->func = NULL; \
	84	} while (0)
	85
bc33f24b PM	86	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	87	extern struct lockdep_map rcu_lock_map;
	88	# define rcu_read_acquire() \
	89	lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
	90	# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
	91	#else
	92	# define rcu_read_acquire() do { } while (0)
	93	# define rcu_read_release() do { } while (0)
	94	#endif
	95
1da177e4 LT	96	/**
	97	* rcu_read_lock - mark the beginning of an RCU read-side critical section.
	98	*
9b06e818	99	* When synchronize_rcu() is invoked on one CPU while other CPUs
1da177e4	100	* are within RCU read-side critical sections, then the
9b06e818	101	* synchronize_rcu() is guaranteed to block until after all the other
1da177e4 LT	102	* CPUs exit their critical sections. Similarly, if call_rcu() is invoked
	103	* on one CPU while other CPUs are within RCU read-side critical
	104	* sections, invocation of the corresponding RCU callback is deferred
	105	* until after the all the other CPUs exit their critical sections.
	106	*
	107	* Note, however, that RCU callbacks are permitted to run concurrently
	108	* with RCU read-side critical sections. One way that this can happen
	109	* is via the following sequence of events: (1) CPU 0 enters an RCU
	110	* read-side critical section, (2) CPU 1 invokes call_rcu() to register
	111	* an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
	112	* (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
	113	* callback is invoked. This is legal, because the RCU read-side critical
	114	* section that was running concurrently with the call_rcu() (and which
	115	* therefore might be referencing something that the corresponding RCU
	116	* callback would free up) has completed before the corresponding
	117	* RCU callback is invoked.
	118	*
	119	* RCU read-side critical sections may be nested. Any deferred actions
	120	* will be deferred until the outermost RCU read-side critical section
	121	* completes.
	122	*
	123	* It is illegal to block while in an RCU read-side critical section.
	124	*/
bc33f24b PM	125	static inline void rcu_read_lock(void)
	126	{
	127	__rcu_read_lock();
	128	__acquire(RCU);
	129	rcu_read_acquire();
	130	}
1da177e4 LT	131
	132	/**
	133	* rcu_read_unlock - marks the end of an RCU read-side critical section.
	134	*
	135	* See rcu_read_lock() for more information.
	136	*/
1da177e4 LT	137
	138	/*
	139	* So where is rcu_write_lock()? It does not exist, as there is no
	140	* way for writers to lock out RCU readers. This is a feature, not
	141	* a bug -- this property is what provides RCU's performance benefits.
	142	* Of course, writers must coordinate with each other. The normal
	143	* spinlock primitives work well for this, but any other technique may be
	144	* used as well. RCU does not care how the writers keep out of each
	145	* others' way, as long as they do so.
	146	*/
bc33f24b PM	147	static inline void rcu_read_unlock(void)
	148	{
	149	rcu_read_release();
	150	__release(RCU);
	151	__rcu_read_unlock();
	152	}
1da177e4 LT	153
	154	/**
	155	* rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
	156	*
	157	* This is equivalent of rcu_read_lock(), but to be used when updates
	158	* are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
	159	* consider completion of a softirq handler to be a quiescent state,
	160	* a process in RCU read-side critical section must be protected by
	161	* disabling softirqs. Read-side critical sections in interrupt context
	162	* can use just rcu_read_lock().
	163	*
	164	*/
bc33f24b PM	165	static inline void rcu_read_lock_bh(void)
	166	{
	167	__rcu_read_lock_bh();
	168	__acquire(RCU_BH);
	169	rcu_read_acquire();
	170	}
1da177e4 LT	171
	172	/*
	173	* rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
	174	*
	175	* See rcu_read_lock_bh() for more information.
	176	*/
bc33f24b PM	177	static inline void rcu_read_unlock_bh(void)
	178	{
	179	rcu_read_release();
	180	__release(RCU_BH);
	181	__rcu_read_unlock_bh();
	182	}
1da177e4	183
1c50b728 MD	184	/**
	185	* rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
	186	*
	187	* Should be used with either
	188	* - synchronize_sched()
	189	* or
	190	* - call_rcu_sched() and rcu_barrier_sched()
	191	* on the write-side to insure proper synchronization.
	192	*/
d6714c22 PM	193	static inline void rcu_read_lock_sched(void)
	194	{
	195	preempt_disable();
bc33f24b PM	196	__acquire(RCU_SCHED);
bc33f24b PM	197	rcu_read_acquire();
d6714c22	198	}
7c614d64	199	static inline notrace void rcu_read_lock_sched_notrace(void)
d6714c22 PM	200	{
d6714c22 PM	201	preempt_disable_notrace();
bc33f24b	202	__acquire(RCU_SCHED);
d6714c22	203	}
1c50b728 MD	204
	205	/*
	206	* rcu_read_unlock_sched - marks the end of a RCU-classic critical section
	207	*
	208	* See rcu_read_lock_sched for more information.
	209	*/
d6714c22 PM	210	static inline void rcu_read_unlock_sched(void)
d6714c22 PM	211	{
bc33f24b PM	212	rcu_read_release();
bc33f24b PM	213	__release(RCU_SCHED);
d6714c22 PM	214	preempt_enable();
d6714c22 PM	215	}
7c614d64	216	static inline notrace void rcu_read_unlock_sched_notrace(void)
d6714c22	217	{
bc33f24b	218	__release(RCU_SCHED);
d6714c22 PM	219	preempt_enable_notrace();
d6714c22 PM	220	}
1c50b728 MD	221
1c50b728 MD	222
1da177e4 LT	223	/**
	224	* rcu_dereference - fetch an RCU-protected pointer in an
	225	* RCU read-side critical section. This pointer may later
	226	* be safely dereferenced.
	227	*
	228	* Inserts memory barriers on architectures that require them
	229	* (currently only the Alpha), and, more importantly, documents
	230	* exactly which pointers are protected by RCU.
	231	*/
	232
	233	#define rcu_dereference(p) ({ \
97b43032	234	typeof(p) _________p1 = ACCESS_ONCE(p); \
1da177e4 LT	235	smp_read_barrier_depends(); \
	236	(_________p1); \
	237	})
	238
	239	/**
	240	* rcu_assign_pointer - assign (publicize) a pointer to a newly
	241	* initialized structure that will be dereferenced by RCU read-side
	242	* critical sections. Returns the value assigned.
	243	*
	244	* Inserts memory barriers on architectures that require them
	245	* (pretty much all of them other than x86), and also prevents
	246	* the compiler from reordering the code that initializes the
	247	* structure after the pointer assignment. More importantly, this
	248	* call documents which pointers will be dereferenced by RCU read-side
	249	* code.
	250	*/
	251
d99c4f6b PM	252	#define rcu_assign_pointer(p, v) \
	253	({ \
	254	if (!__builtin_constant_p(v) \|\| \
	255	((v) != NULL)) \
	256	smp_wmb(); \
	257	(p) = (v); \
	258	})
1da177e4	259
4446a36f PM	260	/* Infrastructure to implement the synchronize_() primitives. */
	261
	262	struct rcu_synchronize {
	263	struct rcu_head head;
	264	struct completion completion;
	265	};
	266
	267	extern void wakeme_after_rcu(struct rcu_head *head);
	268
01c1c660 PM	269	/**
	270	* call_rcu - Queue an RCU callback for invocation after a grace period.
	271	* @head: structure to be used for queueing the RCU updates.
	272	* @func: actual update function to be invoked after the grace period
	273	*
	274	* The update function will be invoked some time after a full grace
	275	* period elapses, in other words after all currently executing RCU
	276	* read-side critical sections have completed. RCU read-side critical
	277	* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
	278	* and may be nested.
	279	*/
	280	extern void call_rcu(struct rcu_head *head,
	281	void (func)(struct rcu_head head));
	282
	283	/**
	284	* call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
	285	* @head: structure to be used for queueing the RCU updates.
	286	* @func: actual update function to be invoked after the grace period
	287	*
	288	* The update function will be invoked some time after a full grace
	289	* period elapses, in other words after all currently executing RCU
	290	* read-side critical sections have completed. call_rcu_bh() assumes
	291	* that the read-side critical sections end on completion of a softirq
	292	* handler. This means that read-side critical sections in process
	293	* context must not be interrupted by softirqs. This interface is to be
	294	* used when most of the read-side critical sections are in softirq context.
	295	* RCU read-side critical sections are delimited by :
	296	* - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
	297	* OR
	298	* - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
	299	* These may be nested.
	300	*/
	301	extern void call_rcu_bh(struct rcu_head *head,
	302	void (func)(struct rcu_head head));
	303
1da177e4	304	#endif /* __LINUX_RCUPDATE_H */