[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/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 {
	long ctr;
	struct list_head head;
	pthread_t tid;
	char need_mb;
};

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