[urcu.git] / urcu-static.h

#ifndef _URCU_STATIC_H
#define _URCU_STATIC_H

/*
 * urcu-static.h
 *
 * Userspace RCU header.
 *
 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
 * dynamically with the userspace rcu library.
 *
 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
 */

#include <stdlib.h>
#include <pthread.h>
#include <syscall.h>
#include <unistd.h>

#include <urcu/compiler.h>
#include <urcu/arch.h>
#include <urcu/arch_uatomic.h>
#include <urcu/list.h>

/*
 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
 */
#define _LOAD_SHARED(p)	       ACCESS_ONCE(p)

/*
 * Load a data from shared memory, doing a cache flush if required.
 */
#define LOAD_SHARED(p)			\
	({				\
		smp_rmc();		\
		_LOAD_SHARED(p);	\
	})

/*
 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
 */
#define _STORE_SHARED(x, v)	({ ACCESS_ONCE(x) = (v); })

/*
 * Store v into x, where x is located in shared memory. Performs the required
 * cache flush after writing. Returns v.
 */
#define STORE_SHARED(x, v)		\
	({				\
		_STORE_SHARED(x, v);	\
		smp_wmc();		\
		(v);			\
	})

/**
 * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
 * into a RCU read-side critical section. The pointer can later be safely
 * dereferenced within the critical section.
 *
 * This ensures that the pointer copy is invariant thorough the whole critical
 * section.
 *
 * Inserts memory barriers on architectures that require them (currently only
 * Alpha) and documents which pointers are protected by RCU.
 *
 * The compiler memory barrier in LOAD_SHARED() ensures that value-speculative
 * optimizations (e.g. VSS: Value Speculation Scheduling) does not perform the
 * data read before the pointer read by speculating the value of the pointer.
 * Correct ordering is ensured because the pointer is read as a volatile access.
 * This acts as a global side-effect operation, which forbids reordering of
 * dependent memory operations. Note that such concern about dependency-breaking
 * optimizations will eventually be taken care of by the "memory_order_consume"
 * addition to forthcoming C++ standard.
 *
 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
 */

#define _rcu_dereference(p)     ({					\
				typeof(p) _________p1 = LOAD_SHARED(p); \
				smp_read_barrier_depends();		\
				(_________p1);				\
				})

#define futex(...)		syscall(__NR_futex, __VA_ARGS__)
#define FUTEX_WAIT		0
#define FUTEX_WAKE		1

/*
 * This code section can only be included in LGPL 2.1 compatible source code.
 * See below for the function call wrappers which can be used in code meant to
 * be only linked with the Userspace RCU library. This comes with a small
 * performance degradation on the read-side due to the added function calls.
 * This is required to permit relinking with newer versions of the library.
 */

/*
 * The signal number used by the RCU library can be overridden with
 * -DSIGURCU= when compiling the library.
 */
#ifndef SIGURCU
#define SIGURCU SIGUSR1
#endif

/*
 * If a reader is really non-cooperative and refuses to commit its
 * urcu_active_readers count to memory (there is no barrier in the reader
 * per-se), kick it after a few loops waiting for it.
 */
#define KICK_READER_LOOPS 10000

/*
 * Active attempts to check for reader Q.S. before calling futex().
 */
#define RCU_QS_ACTIVE_ATTEMPTS 100

#ifdef DEBUG_RCU
#define rcu_assert(args...)	assert(args)
#else
#define rcu_assert(args...)
#endif

#ifdef DEBUG_YIELD
#include <sched.h>
#include <time.h>
#include <pthread.h>
#include <unistd.h>

#define YIELD_READ 	(1 << 0)
#define YIELD_WRITE	(1 << 1)

/*
 * Updates without URCU_MB are much slower. Account this in
 * the delay.
 */
#ifdef URCU_MB
/* maximum sleep delay, in us */
#define MAX_SLEEP 50
#else
#define MAX_SLEEP 30000
#endif

extern unsigned int yield_active;
extern unsigned int __thread rand_yield;

static inline void debug_yield_read(void)
{
	if (yield_active & YIELD_READ)
		if (rand_r(&rand_yield) & 0x1)
			usleep(rand_r(&rand_yield) % MAX_SLEEP);
}

static inline void debug_yield_write(void)
{
	if (yield_active & YIELD_WRITE)
		if (rand_r(&rand_yield) & 0x1)
			usleep(rand_r(&rand_yield) % MAX_SLEEP);
}

static inline void debug_yield_init(void)
{
	rand_yield = time(NULL) ^ pthread_self();
}
#else
static inline void debug_yield_read(void)
{
}

static inline void debug_yield_write(void)
{
}

static inline void debug_yield_init(void)
{

}
#endif

#ifdef URCU_MB
static inline void reader_barrier()
{
	smp_mb();
}
#else
static inline void reader_barrier()
{
	barrier();
}
#endif

/*
 * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 */
#define RCU_GP_COUNT		(1UL << 0)
/* Use the amount of bits equal to half of the architecture long size */
#define RCU_GP_CTR_BIT		(1UL << (sizeof(long) << 2))
#define RCU_GP_CTR_NEST_MASK	(RCU_GP_CTR_BIT - 1)

/*
 * Global quiescent period counter with low-order bits unused.
 * Using a int rather than a char to eliminate false register dependencies
 * causing stalls on some architectures.
 */
extern long urcu_gp_ctr;

struct urcu_reader {
	/* Data used by both reader and synchronize_rcu() */
	long ctr;
	char need_mb;
	/* Data used for registry */
	struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
	pthread_t tid;
};

extern struct urcu_reader __thread urcu_reader;

extern int gp_futex;

/*
 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
 */
static inline void wake_up_gp(void)
{
	if (unlikely(uatomic_read(&gp_futex) == -1)) {
		uatomic_set(&gp_futex, 0);
		futex(&gp_futex, FUTEX_WAKE, 1,
		      NULL, NULL, 0);
	}
}

static inline int rcu_old_gp_ongoing(long *value)
{
	long v;

	if (value == NULL)
		return 0;
	/*
	 * Make sure both tests below are done on the same version of *value
	 * to insure consistency.
	 */
	v = LOAD_SHARED(*value);
	return (v & RCU_GP_CTR_NEST_MASK) &&
		 ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
}

static inline void _rcu_read_lock(void)
{
	long tmp;

	tmp = urcu_reader.ctr;
	/* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
	if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
		_STORE_SHARED(urcu_reader.ctr, _LOAD_SHARED(urcu_gp_ctr));
		/*
		 * Set active readers count for outermost nesting level before
		 * accessing the pointer. See force_mb_all_threads().
		 */
		reader_barrier();
	} else {
		_STORE_SHARED(urcu_reader.ctr, tmp + RCU_GP_COUNT);
	}
}

static inline void _rcu_read_unlock(void)
{
	long tmp;

	tmp = urcu_reader.ctr;
	/*
	 * Finish using rcu before decrementing the pointer.
	 * See force_mb_all_threads().
	 */
	if (likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
		reader_barrier();
		_STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT);
		/* write urcu_reader.ctr before read futex */
		reader_barrier();
		wake_up_gp();
	} else {
		_STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT);
	}
}

/**
 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
 * meant to be read by RCU read-side critical sections. Returns the assigned
 * value.
 *
 * Documents which pointers will be dereferenced by RCU read-side critical
 * sections and adds the required memory barriers on architectures requiring
 * them. It also makes sure the compiler does not reorder code initializing the
 * data structure before its publication.
 *
 * Should match rcu_dereference_pointer().
 */

#define _rcu_assign_pointer(p, v)			\
	({						\
		if (!__builtin_constant_p(v) || 	\
		    ((v) != NULL))			\
			wmb();				\
		STORE_SHARED(p, v);			\
	})

/**
 * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
 * is as expected by "old". If succeeds, returns the previous pointer to the
 * data structure, which can be safely freed after waiting for a quiescent state
 * using synchronize_rcu(). If fails (unexpected value), returns old (which
 * should not be freed !).
 */

#define _rcu_cmpxchg_pointer(p, old, _new)		\
	({						\
		if (!__builtin_constant_p(_new) ||	\
		    ((_new) != NULL))			\
			wmb();				\
		uatomic_cmpxchg(p, old, _new);		\
	})

/**
 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
 * pointer to the data structure, which can be safely freed after waiting for a
 * quiescent state using synchronize_rcu().
 */

#define _rcu_xchg_pointer(p, v)				\
	({						\
		if (!__builtin_constant_p(v) ||		\
		    ((v) != NULL))			\
			wmb();				\
		uatomic_xchg(p, v);			\
	})

/*
 * Exchanges the pointer and waits for quiescent state.
 * The pointer returned can be freed.
 */
#define _rcu_publish_content(p, v)			\
	({						\
		void *oldptr;				\
		oldptr = _rcu_xchg_pointer(p, v);	\
		synchronize_rcu();			\
		oldptr;					\
	})

#endif /* _URCU_STATIC_H */
Commit	Line	Data
adcfce54 MD	1	#ifndef _URCU_STATIC_H
	2	#define _URCU_STATIC_H
	3
	4	/*
	5	* urcu-static.h
	6	*
d2d23035	7	* Userspace RCU header.
adcfce54	8	*
d2d23035 MD	9	* TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
d2d23035 MD	10	* dynamically with the userspace rcu library.
adcfce54	11	*
d2d23035 MD	12	* Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
d2d23035 MD	13	* Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
adcfce54	14	*
d2d23035 MD	15	* This library is free software; you can redistribute it and/or
	16	* modify it under the terms of the GNU Lesser General Public
	17	* License as published by the Free Software Foundation; either
	18	* version 2.1 of the License, or (at your option) any later version.
	19	*
	20	* This library is distributed in the hope that it will be useful,
	21	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	22	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	23	* Lesser General Public License for more details.
	24	*
	25	* You should have received a copy of the GNU Lesser General Public
	26	* License along with this library; if not, write to the Free Software
	27	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
adcfce54 MD	28	*
	29	* IBM's contributions to this file may be relicensed under LGPLv2 or later.
	30	*/
	31
	32	#include <stdlib.h>
	33	#include <pthread.h>
bc6c15bb MD	34	#include <syscall.h>
bc6c15bb MD	35	#include <unistd.h>
adcfce54	36
ec4e58a3 MD	37	#include <urcu/compiler.h>
ec4e58a3 MD	38	#include <urcu/arch.h>
1ccf9cbe	39	#include <urcu/arch_uatomic.h>
e3b0cef0	40	#include <urcu/list.h>
adcfce54 MD	41
	42	/*
	43	* Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
	44	*/
	45	#define _LOAD_SHARED(p) ACCESS_ONCE(p)
	46
	47	/*
	48	* Load a data from shared memory, doing a cache flush if required.
	49	*/
	50	#define LOAD_SHARED(p) \
	51	({ \
	52	smp_rmc(); \
	53	_LOAD_SHARED(p); \
	54	})
	55
	56	/*
	57	* Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
	58	*/
	59	#define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
	60
	61	/*
	62	* Store v into x, where x is located in shared memory. Performs the required
	63	* cache flush after writing. Returns v.
	64	*/
	65	#define STORE_SHARED(x, v) \
	66	({ \
	67	_STORE_SHARED(x, v); \
	68	smp_wmc(); \
	69	(v); \
	70	})
	71
	72	/**
	73	* _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
	74	* into a RCU read-side critical section. The pointer can later be safely
	75	* dereferenced within the critical section.
	76	*
	77	* This ensures that the pointer copy is invariant thorough the whole critical
	78	* section.
	79	*
	80	* Inserts memory barriers on architectures that require them (currently only
	81	* Alpha) and documents which pointers are protected by RCU.
	82	*
809f4fde MD	83	* The compiler memory barrier in LOAD_SHARED() ensures that value-speculative
	84	* optimizations (e.g. VSS: Value Speculation Scheduling) does not perform the
	85	* data read before the pointer read by speculating the value of the pointer.
	86	* Correct ordering is ensured because the pointer is read as a volatile access.
	87	* This acts as a global side-effect operation, which forbids reordering of
015c702f MD	88	* dependent memory operations. Note that such concern about dependency-breaking
	89	* optimizations will eventually be taken care of by the "memory_order_consume"
	90	* addition to forthcoming C++ standard.
809f4fde	91	*
adcfce54 MD	92	* Should match rcu_assign_pointer() or rcu_xchg_pointer().
	93	*/
	94
	95	#define _rcu_dereference(p) ({ \
	96	typeof(p) _________p1 = LOAD_SHARED(p); \
	97	smp_read_barrier_depends(); \
	98	(_________p1); \
	99	})
	100
bc6c15bb MD	101	#define futex(...) syscall(__NR_futex, __VA_ARGS__)
	102	#define FUTEX_WAIT 0
	103	#define FUTEX_WAKE 1
	104
adcfce54 MD	105	/*
	106	* This code section can only be included in LGPL 2.1 compatible source code.
	107	* See below for the function call wrappers which can be used in code meant to
	108	* be only linked with the Userspace RCU library. This comes with a small
	109	* performance degradation on the read-side due to the added function calls.
	110	* This is required to permit relinking with newer versions of the library.
	111	*/
	112
	113	/*
	114	* The signal number used by the RCU library can be overridden with
	115	* -DSIGURCU= when compiling the library.
	116	*/
	117	#ifndef SIGURCU
	118	#define SIGURCU SIGUSR1
	119	#endif
	120
	121	/*
	122	* If a reader is really non-cooperative and refuses to commit its
	123	* urcu_active_readers count to memory (there is no barrier in the reader
	124	* per-se), kick it after a few loops waiting for it.
	125	*/
	126	#define KICK_READER_LOOPS 10000
	127
bc6c15bb MD	128	/*
	129	* Active attempts to check for reader Q.S. before calling futex().
	130	*/
	131	#define RCU_QS_ACTIVE_ATTEMPTS 100
	132
7ac06cef MD	133	#ifdef DEBUG_RCU
	134	#define rcu_assert(args...) assert(args)
	135	#else
	136	#define rcu_assert(args...)
	137	#endif
	138
adcfce54 MD	139	#ifdef DEBUG_YIELD
	140	#include <sched.h>
	141	#include <time.h>
	142	#include <pthread.h>
	143	#include <unistd.h>
	144
	145	#define YIELD_READ (1 << 0)
	146	#define YIELD_WRITE (1 << 1)
	147
b4ce1526	148	/*
0a1d290b	149	* Updates without URCU_MB are much slower. Account this in
b4ce1526 MD	150	* the delay.
b4ce1526 MD	151	*/
0a1d290b	152	#ifdef URCU_MB
adcfce54 MD	153	/* maximum sleep delay, in us */
	154	#define MAX_SLEEP 50
	155	#else
	156	#define MAX_SLEEP 30000
	157	#endif
	158
	159	extern unsigned int yield_active;
	160	extern unsigned int __thread rand_yield;
	161
	162	static inline void debug_yield_read(void)
	163	{
	164	if (yield_active & YIELD_READ)
	165	if (rand_r(&rand_yield) & 0x1)
	166	usleep(rand_r(&rand_yield) % MAX_SLEEP);
	167	}
	168
	169	static inline void debug_yield_write(void)
	170	{
	171	if (yield_active & YIELD_WRITE)
	172	if (rand_r(&rand_yield) & 0x1)
	173	usleep(rand_r(&rand_yield) % MAX_SLEEP);
	174	}
	175
	176	static inline void debug_yield_init(void)
	177	{
	178	rand_yield = time(NULL) ^ pthread_self();
	179	}
	180	#else
	181	static inline void debug_yield_read(void)
	182	{
	183	}
	184
	185	static inline void debug_yield_write(void)
	186	{
	187	}
	188
	189	static inline void debug_yield_init(void)
	190	{
	191
	192	}
	193	#endif
	194
0a1d290b	195	#ifdef URCU_MB
adcfce54 MD	196	static inline void reader_barrier()
	197	{
	198	smp_mb();
	199	}
	200	#else
	201	static inline void reader_barrier()
	202	{
	203	barrier();
	204	}
	205	#endif
	206
	207	/*
	208	* The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
	209	* full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
	210	*/
	211	#define RCU_GP_COUNT (1UL << 0)
	212	/* Use the amount of bits equal to half of the architecture long size */
	213	#define RCU_GP_CTR_BIT (1UL << (sizeof(long) << 2))
	214	#define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
	215
	216	/*
	217	* Global quiescent period counter with low-order bits unused.
	218	* Using a int rather than a char to eliminate false register dependencies
	219	* causing stalls on some architectures.
	220	*/
	221	extern long urcu_gp_ctr;
	222
e3b0cef0	223	struct urcu_reader {
bd1a5e15	224	/* Data used by both reader and synchronize_rcu() */
e3b0cef0	225	long ctr;
e3b0cef0	226	char need_mb;
bd1a5e15 MD	227	/* Data used for registry */
	228	struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
	229	pthread_t tid;
e3b0cef0 MD	230	};
	231
	232	extern struct urcu_reader __thread urcu_reader;
adcfce54	233
bc6c15bb MD	234	extern int gp_futex;
	235
	236	/*
	237	* Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
	238	*/
	239	static inline void wake_up_gp(void)
	240	{
ec4e58a3 MD	241	if (unlikely(uatomic_read(&gp_futex) == -1)) {
ec4e58a3 MD	242	uatomic_set(&gp_futex, 0);
bc6c15bb MD	243	futex(&gp_futex, FUTEX_WAKE, 1,
	244	NULL, NULL, 0);
	245	}
	246	}
	247
adcfce54 MD	248	static inline int rcu_old_gp_ongoing(long *value)
	249	{
	250	long v;
	251
	252	if (value == NULL)
	253	return 0;
	254	/*
	255	* Make sure both tests below are done on the same version of *value
	256	* to insure consistency.
	257	*/
	258	v = LOAD_SHARED(*value);
	259	return (v & RCU_GP_CTR_NEST_MASK) &&
	260	((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
	261	}
	262
	263	static inline void _rcu_read_lock(void)
	264	{
	265	long tmp;
	266
e3b0cef0	267	tmp = urcu_reader.ctr;
adcfce54	268	/* urcu_gp_ctr = RCU_GP_COUNT \| (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
67ef1a2c	269	if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
e3b0cef0	270	_STORE_SHARED(urcu_reader.ctr, _LOAD_SHARED(urcu_gp_ctr));
67ef1a2c MD	271	/*
	272	* Set active readers count for outermost nesting level before
	273	* accessing the pointer. See force_mb_all_threads().
	274	*/
	275	reader_barrier();
	276	} else {
e3b0cef0	277	_STORE_SHARED(urcu_reader.ctr, tmp + RCU_GP_COUNT);
67ef1a2c	278	}
adcfce54 MD	279	}
	280
	281	static inline void _rcu_read_unlock(void)
	282	{
bc6c15bb MD	283	long tmp;
bc6c15bb MD	284
e3b0cef0	285	tmp = urcu_reader.ctr;
adcfce54 MD	286	/*
	287	* Finish using rcu before decrementing the pointer.
	288	* See force_mb_all_threads().
	289	*/
bc6c15bb MD	290	if (likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
bc6c15bb MD	291	reader_barrier();
e3b0cef0 MD	292	_STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT);
e3b0cef0 MD	293	/* write urcu_reader.ctr before read futex */
bc6c15bb MD	294	reader_barrier();
	295	wake_up_gp();
	296	} else {
e3b0cef0	297	_STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT);
bc6c15bb	298	}
adcfce54 MD	299	}
	300
	301	/**
	302	* _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
	303	* meant to be read by RCU read-side critical sections. Returns the assigned
	304	* value.
	305	*
	306	* Documents which pointers will be dereferenced by RCU read-side critical
	307	* sections and adds the required memory barriers on architectures requiring
	308	* them. It also makes sure the compiler does not reorder code initializing the
	309	* data structure before its publication.
	310	*
	311	* Should match rcu_dereference_pointer().
	312	*/
	313
	314	#define _rcu_assign_pointer(p, v) \
	315	({ \
	316	if (!__builtin_constant_p(v) \|\| \
	317	((v) != NULL)) \
	318	wmb(); \
	319	STORE_SHARED(p, v); \
	320	})
	321
4d1ce26f MD	322	/**
	323	* _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
	324	* is as expected by "old". If succeeds, returns the previous pointer to the
	325	* data structure, which can be safely freed after waiting for a quiescent state
	326	* using synchronize_rcu(). If fails (unexpected value), returns old (which
	327	* should not be freed !).
	328	*/
	329
	330	#define _rcu_cmpxchg_pointer(p, old, _new) \
	331	({ \
	332	if (!__builtin_constant_p(_new) \|\| \
	333	((_new) != NULL)) \
	334	wmb(); \
ec4e58a3	335	uatomic_cmpxchg(p, old, _new); \
4d1ce26f MD	336	})
4d1ce26f MD	337
adcfce54 MD	338	/**
adcfce54 MD	339	* _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
67ef1a2c	340	* pointer to the data structure, which can be safely freed after waiting for a
adcfce54 MD	341	* quiescent state using synchronize_rcu().
	342	*/
	343
	344	#define _rcu_xchg_pointer(p, v) \
	345	({ \
	346	if (!__builtin_constant_p(v) \|\| \
	347	((v) != NULL)) \
	348	wmb(); \
ec4e58a3	349	uatomic_xchg(p, v); \
adcfce54 MD	350	})
	351
	352	/*
	353	* Exchanges the pointer and waits for quiescent state.
	354	* The pointer returned can be freed.
	355	*/
	356	#define _rcu_publish_content(p, v) \
	357	({ \
	358	void *oldptr; \
	359	oldptr = _rcu_xchg_pointer(p, v); \
	360	synchronize_rcu(); \
	361	oldptr; \
	362	})
	363
	364	#endif /* _URCU_STATIC_H */