[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 */
extern void synchronize_rcu(void);
extern void synchronize_rcu_bh(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)
#include <linux/rcutree.h>
#elif defined(CONFIG_PREEMPT_RCU)
#include <linux/rcupreempt.h>
#else
#error "Unknown RCU implementation specified to kernel configuration"
#endif /* #else #if defined(CONFIG_CLASSIC_RCU) */

#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()
#define rcu_read_lock_sched_notrace() preempt_disable_notrace()

/*
 * 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()
#define rcu_read_unlock_sched_notrace() 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);

/**
 * 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));

#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 PM	54	/* Exported common interfaces */
	55	extern void synchronize_rcu(void);
	56	extern void synchronize_rcu_bh(void);
	57	extern void rcu_barrier(void);
	58	extern void rcu_barrier_bh(void);
	59	extern void rcu_barrier_sched(void);
	60	extern void synchronize_sched_expedited(void);
	61	extern int sched_expedited_torture_stats(char *page);
	62
	63	/* Internal to kernel */
	64	extern void rcu_init(void);
	65	extern void rcu_scheduler_starting(void);
	66	extern int rcu_needs_cpu(int cpu);
a6826048 PM	67	extern int rcu_scheduler_active;
a6826048 PM	68
c17ef453	69	#if defined(CONFIG_TREE_RCU)
64db4cff PM	70	#include <linux/rcutree.h>
64db4cff PM	71	#elif defined(CONFIG_PREEMPT_RCU)
e260be67	72	#include <linux/rcupreempt.h>
64db4cff PM	73	#else
	74	#error "Unknown RCU implementation specified to kernel configuration"
	75	#endif /* #else #if defined(CONFIG_CLASSIC_RCU) */
01c1c660	76
8b6490e5 DS	77	#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
8b6490e5 DS	78	#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
1da177e4 LT	79	#define INIT_RCU_HEAD(ptr) do { \
	80	(ptr)->next = NULL; (ptr)->func = NULL; \
	81	} while (0)
	82
1da177e4 LT	83	/**
	84	* rcu_read_lock - mark the beginning of an RCU read-side critical section.
	85	*
9b06e818	86	* When synchronize_rcu() is invoked on one CPU while other CPUs
1da177e4	87	* are within RCU read-side critical sections, then the
9b06e818	88	* synchronize_rcu() is guaranteed to block until after all the other
1da177e4 LT	89	* CPUs exit their critical sections. Similarly, if call_rcu() is invoked
	90	* on one CPU while other CPUs are within RCU read-side critical
	91	* sections, invocation of the corresponding RCU callback is deferred
	92	* until after the all the other CPUs exit their critical sections.
	93	*
	94	* Note, however, that RCU callbacks are permitted to run concurrently
	95	* with RCU read-side critical sections. One way that this can happen
	96	* is via the following sequence of events: (1) CPU 0 enters an RCU
	97	* read-side critical section, (2) CPU 1 invokes call_rcu() to register
	98	* an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
	99	* (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
	100	* callback is invoked. This is legal, because the RCU read-side critical
	101	* section that was running concurrently with the call_rcu() (and which
	102	* therefore might be referencing something that the corresponding RCU
	103	* callback would free up) has completed before the corresponding
	104	* RCU callback is invoked.
	105	*
	106	* RCU read-side critical sections may be nested. Any deferred actions
	107	* will be deferred until the outermost RCU read-side critical section
	108	* completes.
	109	*
	110	* It is illegal to block while in an RCU read-side critical section.
	111	*/
01c1c660	112	#define rcu_read_lock() __rcu_read_lock()
1da177e4 LT	113
	114	/**
	115	* rcu_read_unlock - marks the end of an RCU read-side critical section.
	116	*
	117	* See rcu_read_lock() for more information.
	118	*/
1da177e4 LT	119
	120	/*
	121	* So where is rcu_write_lock()? It does not exist, as there is no
	122	* way for writers to lock out RCU readers. This is a feature, not
	123	* a bug -- this property is what provides RCU's performance benefits.
	124	* Of course, writers must coordinate with each other. The normal
	125	* spinlock primitives work well for this, but any other technique may be
	126	* used as well. RCU does not care how the writers keep out of each
	127	* others' way, as long as they do so.
	128	*/
01c1c660	129	#define rcu_read_unlock() __rcu_read_unlock()
1da177e4 LT	130
	131	/**
	132	* rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
	133	*
	134	* This is equivalent of rcu_read_lock(), but to be used when updates
	135	* are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
	136	* consider completion of a softirq handler to be a quiescent state,
	137	* a process in RCU read-side critical section must be protected by
	138	* disabling softirqs. Read-side critical sections in interrupt context
	139	* can use just rcu_read_lock().
	140	*
	141	*/
01c1c660	142	#define rcu_read_lock_bh() __rcu_read_lock_bh()
1da177e4 LT	143
	144	/*
	145	* rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
	146	*
	147	* See rcu_read_lock_bh() for more information.
	148	*/
01c1c660	149	#define rcu_read_unlock_bh() __rcu_read_unlock_bh()
1da177e4	150
1c50b728 MD	151	/**
	152	* rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
	153	*
	154	* Should be used with either
	155	* - synchronize_sched()
	156	* or
	157	* - call_rcu_sched() and rcu_barrier_sched()
	158	* on the write-side to insure proper synchronization.
	159	*/
	160	#define rcu_read_lock_sched() preempt_disable()
954e100d	161	#define rcu_read_lock_sched_notrace() preempt_disable_notrace()
1c50b728 MD	162
	163	/*
	164	* rcu_read_unlock_sched - marks the end of a RCU-classic critical section
	165	*
	166	* See rcu_read_lock_sched for more information.
	167	*/
	168	#define rcu_read_unlock_sched() preempt_enable()
954e100d	169	#define rcu_read_unlock_sched_notrace() preempt_enable_notrace()
1c50b728 MD	170
	171
	172
1da177e4 LT	173	/**
	174	* rcu_dereference - fetch an RCU-protected pointer in an
	175	* RCU read-side critical section. This pointer may later
	176	* be safely dereferenced.
	177	*
	178	* Inserts memory barriers on architectures that require them
	179	* (currently only the Alpha), and, more importantly, documents
	180	* exactly which pointers are protected by RCU.
	181	*/
	182
	183	#define rcu_dereference(p) ({ \
97b43032	184	typeof(p) _________p1 = ACCESS_ONCE(p); \
1da177e4 LT	185	smp_read_barrier_depends(); \
	186	(_________p1); \
	187	})
	188
	189	/**
	190	* rcu_assign_pointer - assign (publicize) a pointer to a newly
	191	* initialized structure that will be dereferenced by RCU read-side
	192	* critical sections. Returns the value assigned.
	193	*
	194	* Inserts memory barriers on architectures that require them
	195	* (pretty much all of them other than x86), and also prevents
	196	* the compiler from reordering the code that initializes the
	197	* structure after the pointer assignment. More importantly, this
	198	* call documents which pointers will be dereferenced by RCU read-side
	199	* code.
	200	*/
	201
d99c4f6b PM	202	#define rcu_assign_pointer(p, v) \
	203	({ \
	204	if (!__builtin_constant_p(v) \|\| \
	205	((v) != NULL)) \
	206	smp_wmb(); \
	207	(p) = (v); \
	208	})
1da177e4	209
4446a36f PM	210	/* Infrastructure to implement the synchronize_() primitives. */
	211
	212	struct rcu_synchronize {
	213	struct rcu_head head;
	214	struct completion completion;
	215	};
	216
	217	extern void wakeme_after_rcu(struct rcu_head *head);
	218
9b06e818 PM	219	/**
	220	* synchronize_sched - block until all CPUs have exited any non-preemptive
	221	* kernel code sequences.
	222	*
	223	* This means that all preempt_disable code sequences, including NMI and
	224	* hardware-interrupt handlers, in progress on entry will have completed
	225	* before this primitive returns. However, this does not guarantee that
bb3b9cf1 PM	226	* softirq handlers will have completed, since in some kernels, these
bb3b9cf1 PM	227	* handlers can run in process context, and can block.
9b06e818	228	*
d83015b8	229	* This primitive provides the guarantees made by the (now removed)
9b06e818 PM	230	* synchronize_kernel() API. In contrast, synchronize_rcu() only
9b06e818 PM	231	* guarantees that rcu_read_lock() sections will have completed.
bb3b9cf1 PM	232	* In "classic RCU", these two guarantees happen to be one and
bb3b9cf1 PM	233	* the same, but can differ in realtime RCU implementations.
9b06e818	234	*/
01c1c660 PM	235	#define synchronize_sched() __synchronize_sched()
	236
	237	/**
	238	* call_rcu - Queue an RCU callback for invocation after a grace period.
	239	* @head: structure to be used for queueing the RCU updates.
	240	* @func: actual update function to be invoked after the grace period
	241	*
	242	* The update function will be invoked some time after a full grace
	243	* period elapses, in other words after all currently executing RCU
	244	* read-side critical sections have completed. RCU read-side critical
	245	* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
	246	* and may be nested.
	247	*/
	248	extern void call_rcu(struct rcu_head *head,
	249	void (func)(struct rcu_head head));
	250
	251	/**
	252	* call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
	253	* @head: structure to be used for queueing the RCU updates.
	254	* @func: actual update function to be invoked after the grace period
	255	*
	256	* The update function will be invoked some time after a full grace
	257	* period elapses, in other words after all currently executing RCU
	258	* read-side critical sections have completed. call_rcu_bh() assumes
	259	* that the read-side critical sections end on completion of a softirq
	260	* handler. This means that read-side critical sections in process
	261	* context must not be interrupted by softirqs. This interface is to be
	262	* used when most of the read-side critical sections are in softirq context.
	263	* RCU read-side critical sections are delimited by :
	264	* - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
	265	* OR
	266	* - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
	267	* These may be nested.
	268	*/
	269	extern void call_rcu_bh(struct rcu_head *head,
	270	void (func)(struct rcu_head head));
	271
1da177e4	272	#endif /* __LINUX_RCUPDATE_H */