[mirror_ubuntu-artful-kernel.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 (C) 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

#ifdef __KERNEL__

#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>

/**
 * 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);
};

#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)


/* Global control variables for rcupdate callback mechanism. */
struct rcu_ctrlblk {
	long	cur;		/* Current batch number.                      */
	long	completed;	/* Number of the last completed batch         */
	int	next_pending;	/* Is the next batch already waiting?         */

	int	signaled;

	spinlock_t	lock	____cacheline_internodealigned_in_smp;
	cpumask_t	cpumask; /* CPUs that need to switch in order    */
	                         /* for current batch to proceed.        */
} ____cacheline_internodealigned_in_smp;

/* Is batch a before batch b ? */
static inline int rcu_batch_before(long a, long b)
{
        return (a - b) < 0;
}

/* Is batch a after batch b ? */
static inline int rcu_batch_after(long a, long b)
{
        return (a - b) > 0;
}

/*
 * Per-CPU data for Read-Copy UPdate.
 * nxtlist - new callbacks are added here
 * curlist - current batch for which quiescent cycle started if any
 */
struct rcu_data {
	/* 1) quiescent state handling : */
	long		quiescbatch;     /* Batch # for grace period */
	int		passed_quiesc;	 /* User-mode/idle loop etc. */
	int		qs_pending;	 /* core waits for quiesc state */

	/* 2) batch handling */
	long  	       	batch;           /* Batch # for current RCU batch */
	struct rcu_head *nxtlist;
	struct rcu_head **nxttail;
	long            qlen; 	 	 /* # of queued callbacks */
	struct rcu_head *curlist;
	struct rcu_head **curtail;
	struct rcu_head *donelist;
	struct rcu_head **donetail;
	long		blimit;		 /* Upper limit on a processed batch */
	int cpu;
	struct rcu_head barrier;
};

DECLARE_PER_CPU(struct rcu_data, rcu_data);
DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);

/*
 * Increment the quiescent state counter.
 * The counter is a bit degenerated: We do not need to know
 * how many quiescent states passed, just if there was at least
 * one since the start of the grace period. Thus just a flag.
 */
static inline void rcu_qsctr_inc(int cpu)
{
	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
	rdp->passed_quiesc = 1;
}
static inline void rcu_bh_qsctr_inc(int cpu)
{
	struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
	rdp->passed_quiesc = 1;
}

extern int rcu_pending(int cpu);
extern int rcu_needs_cpu(int cpu);

#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, _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.
 */
#define rcu_read_lock() \
	do { \
		preempt_disable(); \
		__acquire(RCU); \
		rcu_read_acquire(); \
	} while(0)

/**
 * rcu_read_unlock - marks the end of an RCU read-side critical section.
 *
 * See rcu_read_lock() for more information.
 */
#define rcu_read_unlock() \
	do { \
		rcu_read_release(); \
		__release(RCU); \
		preempt_enable(); \
	} while(0)

/*
 * 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.
 */

/**
 * 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() \
	do { \
		local_bh_disable(); \
		__acquire(RCU_BH); \
		rcu_read_acquire(); \
	} while(0)

/*
 * 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() \
	do { \
		rcu_read_release(); \
		__release(RCU_BH); \
		local_bh_enable(); \
	} while(0)

/**
 * 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 = 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)	({ \
						smp_wmb(); \
						(p) = (v); \
					})

/**
 * 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_rcu()

extern void rcu_init(void);
extern void rcu_check_callbacks(int cpu, int user);
extern void rcu_restart_cpu(int cpu);
extern long rcu_batches_completed(void);
extern long rcu_batches_completed_bh(void);

/* Exported interfaces */
extern void FASTCALL(call_rcu(struct rcu_head *head, 
				void (*func)(struct rcu_head *head)));
extern void FASTCALL(call_rcu_bh(struct rcu_head *head,
				void (*func)(struct rcu_head *head)));
extern void synchronize_rcu(void);
extern void rcu_barrier(void);

#endif /* __KERNEL__ */
#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	*
	18	* Copyright (C) IBM Corporation, 2001
	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
	36	#ifdef __KERNEL__
	37
	38	#include <linux/cache.h>
	39	#include <linux/spinlock.h>
	40	#include <linux/threads.h>
	41	#include <linux/percpu.h>
	42	#include <linux/cpumask.h>
	43	#include <linux/seqlock.h>
851a67b8	44	#include <linux/lockdep.h>
1da177e4 LT	45
	46	/**
	47	* struct rcu_head - callback structure for use with RCU
	48	* @next: next update requests in a list
	49	* @func: actual update function to call after the grace period.
	50	*/
	51	struct rcu_head {
	52	struct rcu_head *next;
	53	void (func)(struct rcu_head head);
	54	};
	55
8b6490e5 DS	56	#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
8b6490e5 DS	57	#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
1da177e4 LT	58	#define INIT_RCU_HEAD(ptr) do { \
	59	(ptr)->next = NULL; (ptr)->func = NULL; \
	60	} while (0)
	61
	62
	63
	64	/* Global control variables for rcupdate callback mechanism. */
	65	struct rcu_ctrlblk {
	66	long cur; /* Current batch number. */
	67	long completed; /* Number of the last completed batch */
	68	int next_pending; /* Is the next batch already waiting? */
69a0b315	69
20e9751b ON	70	int signaled;
20e9751b ON	71
69a0b315 ON	72	spinlock_t lock ____cacheline_internodealigned_in_smp;
	73	cpumask_t cpumask; /* CPUs that need to switch in order */
	74	/* for current batch to proceed. */
22fc6ecc	75	} ____cacheline_internodealigned_in_smp;
1da177e4 LT	76
	77	/* Is batch a before batch b ? */
	78	static inline int rcu_batch_before(long a, long b)
	79	{
	80	return (a - b) < 0;
	81	}
	82
	83	/* Is batch a after batch b ? */
	84	static inline int rcu_batch_after(long a, long b)
	85	{
	86	return (a - b) > 0;
	87	}
	88
	89	/*
	90	* Per-CPU data for Read-Copy UPdate.
	91	* nxtlist - new callbacks are added here
	92	* curlist - current batch for which quiescent cycle started if any
	93	*/
	94	struct rcu_data {
	95	/* 1) quiescent state handling : */
	96	long quiescbatch; /* Batch # for grace period */
	97	int passed_quiesc; /* User-mode/idle loop etc. */
	98	int qs_pending; /* core waits for quiesc state */
	99
	100	/* 2) batch handling */
	101	long batch; /* Batch # for current RCU batch */
	102	struct rcu_head *nxtlist;
	103	struct rcu_head **nxttail;
21a1ea9e	104	long qlen; /* # of queued callbacks */
1da177e4 LT	105	struct rcu_head *curlist;
	106	struct rcu_head **curtail;
	107	struct rcu_head *donelist;
	108	struct rcu_head **donetail;
21a1ea9e	109	long blimit; /* Upper limit on a processed batch */
1da177e4	110	int cpu;
ab4720ec	111	struct rcu_head barrier;
1da177e4 LT	112	};
	113
	114	DECLARE_PER_CPU(struct rcu_data, rcu_data);
	115	DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
1da177e4 LT	116
	117	/*
	118	* Increment the quiescent state counter.
	119	* The counter is a bit degenerated: We do not need to know
	120	* how many quiescent states passed, just if there was at least
	121	* one since the start of the grace period. Thus just a flag.
	122	*/
	123	static inline void rcu_qsctr_inc(int cpu)
	124	{
	125	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
	126	rdp->passed_quiesc = 1;
	127	}
	128	static inline void rcu_bh_qsctr_inc(int cpu)
	129	{
	130	struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
	131	rdp->passed_quiesc = 1;
	132	}
	133
67751777	134	extern int rcu_pending(int cpu);
986733e0	135	extern int rcu_needs_cpu(int cpu);
1da177e4	136
851a67b8 PZ	137	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	138	extern struct lockdep_map rcu_lock_map;
	139	# define rcu_read_acquire() lock_acquire(&rcu_lock_map, 0, 0, 2, 1, _THIS_IP_)
	140	# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
	141	#else
	142	# define rcu_read_acquire() do { } while (0)
	143	# define rcu_read_release() do { } while (0)
	144	#endif
	145
1da177e4 LT	146	/**
	147	* rcu_read_lock - mark the beginning of an RCU read-side critical section.
	148	*
9b06e818	149	* When synchronize_rcu() is invoked on one CPU while other CPUs
1da177e4	150	* are within RCU read-side critical sections, then the
9b06e818	151	* synchronize_rcu() is guaranteed to block until after all the other
1da177e4 LT	152	* CPUs exit their critical sections. Similarly, if call_rcu() is invoked
	153	* on one CPU while other CPUs are within RCU read-side critical
	154	* sections, invocation of the corresponding RCU callback is deferred
	155	* until after the all the other CPUs exit their critical sections.
	156	*
	157	* Note, however, that RCU callbacks are permitted to run concurrently
	158	* with RCU read-side critical sections. One way that this can happen
	159	* is via the following sequence of events: (1) CPU 0 enters an RCU
	160	* read-side critical section, (2) CPU 1 invokes call_rcu() to register
	161	* an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
	162	* (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
	163	* callback is invoked. This is legal, because the RCU read-side critical
	164	* section that was running concurrently with the call_rcu() (and which
	165	* therefore might be referencing something that the corresponding RCU
	166	* callback would free up) has completed before the corresponding
	167	* RCU callback is invoked.
	168	*
	169	* RCU read-side critical sections may be nested. Any deferred actions
	170	* will be deferred until the outermost RCU read-side critical section
	171	* completes.
	172	*
	173	* It is illegal to block while in an RCU read-side critical section.
	174	*/
7f04ac06 JT	175	#define rcu_read_lock() \
	176	do { \
	177	preempt_disable(); \
	178	__acquire(RCU); \
851a67b8	179	rcu_read_acquire(); \
7f04ac06	180	} while(0)
1da177e4 LT	181
	182	/**
	183	* rcu_read_unlock - marks the end of an RCU read-side critical section.
	184	*
	185	* See rcu_read_lock() for more information.
	186	*/
7f04ac06 JT	187	#define rcu_read_unlock() \
7f04ac06 JT	188	do { \
851a67b8	189	rcu_read_release(); \
7f04ac06 JT	190	__release(RCU); \
	191	preempt_enable(); \
	192	} while(0)
1da177e4 LT	193
	194	/*
	195	* So where is rcu_write_lock()? It does not exist, as there is no
	196	* way for writers to lock out RCU readers. This is a feature, not
	197	* a bug -- this property is what provides RCU's performance benefits.
	198	* Of course, writers must coordinate with each other. The normal
	199	* spinlock primitives work well for this, but any other technique may be
	200	* used as well. RCU does not care how the writers keep out of each
	201	* others' way, as long as they do so.
	202	*/
	203
	204	/**
	205	* rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
	206	*
	207	* This is equivalent of rcu_read_lock(), but to be used when updates
	208	* are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
	209	* consider completion of a softirq handler to be a quiescent state,
	210	* a process in RCU read-side critical section must be protected by
	211	* disabling softirqs. Read-side critical sections in interrupt context
	212	* can use just rcu_read_lock().
	213	*
	214	*/
7f04ac06 JT	215	#define rcu_read_lock_bh() \
	216	do { \
	217	local_bh_disable(); \
	218	__acquire(RCU_BH); \
851a67b8	219	rcu_read_acquire(); \
7f04ac06	220	} while(0)
1da177e4 LT	221
	222	/*
	223	* rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
	224	*
	225	* See rcu_read_lock_bh() for more information.
	226	*/
7f04ac06 JT	227	#define rcu_read_unlock_bh() \
7f04ac06 JT	228	do { \
851a67b8	229	rcu_read_release(); \
7f04ac06 JT	230	__release(RCU_BH); \
	231	local_bh_enable(); \
	232	} while(0)
1da177e4 LT	233
	234	/**
	235	* rcu_dereference - fetch an RCU-protected pointer in an
	236	* RCU read-side critical section. This pointer may later
	237	* be safely dereferenced.
	238	*
	239	* Inserts memory barriers on architectures that require them
	240	* (currently only the Alpha), and, more importantly, documents
	241	* exactly which pointers are protected by RCU.
	242	*/
	243
	244	#define rcu_dereference(p) ({ \
	245	typeof(p) _________p1 = p; \
	246	smp_read_barrier_depends(); \
	247	(_________p1); \
	248	})
	249
	250	/**
	251	* rcu_assign_pointer - assign (publicize) a pointer to a newly
	252	* initialized structure that will be dereferenced by RCU read-side
	253	* critical sections. Returns the value assigned.
	254	*
	255	* Inserts memory barriers on architectures that require them
	256	* (pretty much all of them other than x86), and also prevents
	257	* the compiler from reordering the code that initializes the
	258	* structure after the pointer assignment. More importantly, this
	259	* call documents which pointers will be dereferenced by RCU read-side
	260	* code.
	261	*/
	262
	263	#define rcu_assign_pointer(p, v) ({ \
	264	smp_wmb(); \
	265	(p) = (v); \
	266	})
	267
9b06e818 PM	268	/**
	269	* synchronize_sched - block until all CPUs have exited any non-preemptive
	270	* kernel code sequences.
	271	*
	272	* This means that all preempt_disable code sequences, including NMI and
	273	* hardware-interrupt handlers, in progress on entry will have completed
	274	* before this primitive returns. However, this does not guarantee that
bb3b9cf1 PM	275	* softirq handlers will have completed, since in some kernels, these
bb3b9cf1 PM	276	* handlers can run in process context, and can block.
9b06e818	277	*
d83015b8	278	* This primitive provides the guarantees made by the (now removed)
9b06e818 PM	279	* synchronize_kernel() API. In contrast, synchronize_rcu() only
9b06e818 PM	280	* guarantees that rcu_read_lock() sections will have completed.
bb3b9cf1 PM	281	* In "classic RCU", these two guarantees happen to be one and
bb3b9cf1 PM	282	* the same, but can differ in realtime RCU implementations.
9b06e818 PM	283	*/
	284	#define synchronize_sched() synchronize_rcu()
	285
1da177e4 LT	286	extern void rcu_init(void);
	287	extern void rcu_check_callbacks(int cpu, int user);
	288	extern void rcu_restart_cpu(int cpu);
a241ec65	289	extern long rcu_batches_completed(void);
c32e0660	290	extern long rcu_batches_completed_bh(void);
1da177e4 LT	291
	292	/* Exported interfaces */
	293	extern void FASTCALL(call_rcu(struct rcu_head *head,
	294	void (func)(struct rcu_head head)));
	295	extern void FASTCALL(call_rcu_bh(struct rcu_head *head,
	296	void (func)(struct rcu_head head)));
9b06e818	297	extern void synchronize_rcu(void);
ab4720ec	298	extern void rcu_barrier(void);
1da177e4 LT	299
	300	#endif /* __KERNEL__ */
	301	#endif /* __LINUX_RCUPDATE_H */