7 * Userspace RCU header.
9 * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
10 * RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
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.
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.
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
29 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
37 #include <urcu/config.h>
38 #include <urcu/compiler.h>
39 #include <urcu/arch.h>
40 #include <urcu/system.h>
41 #include <urcu/uatomic.h>
42 #include <urcu/list.h>
43 #include <urcu/futex.h>
44 #include <urcu/tls-compat.h>
45 #include <urcu/debug.h>
46 #include <urcu/static/urcu-signal.h>
52 /* Default is RCU_MEMBARRIER */
53 #if !defined(RCU_MEMBARRIER) && !defined(RCU_MB) && !defined(RCU_SIGNAL)
54 #define RCU_MEMBARRIER
58 * This code section can only be included in LGPL 2.1 compatible source code.
59 * See below for the function call wrappers which can be used in code meant to
60 * be only linked with the Userspace RCU library. This comes with a small
61 * performance degradation on the read-side due to the added function calls.
62 * This is required to permit relinking with newer versions of the library.
66 RCU_READER_ACTIVE_CURRENT
,
67 RCU_READER_ACTIVE_OLD
,
72 * Slave barriers are only guaranteed to be ordered wrt master barriers.
74 * The pair ordering is detailed as (O: ordered, X: not ordered) :
81 #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
82 #define rcu_has_sys_membarrier_memb 1
84 extern int rcu_has_sys_membarrier_memb
;
87 static inline void smp_mb_slave(void)
89 if (caa_likely(rcu_has_sys_membarrier_memb
))
97 static inline void smp_mb_slave(void)
104 static inline void smp_mb_slave(void)
111 * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use
112 * a full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
114 #define RCU_GP_COUNT (1UL << 0)
115 /* Use the amount of bits equal to half of the architecture long size */
116 #define RCU_GP_CTR_PHASE (1UL << (sizeof(unsigned long) << 2))
117 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_PHASE - 1)
121 * Global grace period counter.
122 * Contains the current RCU_GP_CTR_PHASE.
123 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
124 * Written to only by writer with mutex taken.
125 * Read by both writer and readers.
130 } __attribute__((aligned(CAA_CACHE_LINE_SIZE
)));
132 extern struct rcu_gp rcu_gp
;
135 /* Data used by both reader and synchronize_rcu() */
138 /* Data used for registry */
139 struct cds_list_head node
__attribute__((aligned(CAA_CACHE_LINE_SIZE
)));
141 /* Reader registered flag, for internal checks. */
142 unsigned int registered
:1;
145 extern DECLARE_URCU_TLS(struct rcu_reader
, rcu_reader
);
148 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
150 static inline void wake_up_gp(void)
152 if (caa_unlikely(uatomic_read(&rcu_gp
.futex
) == -1)) {
153 uatomic_set(&rcu_gp
.futex
, 0);
155 * Ignoring return value until we can make this function
156 * return something (because urcu_die() is not publicly
159 (void) futex_async(&rcu_gp
.futex
, FUTEX_WAKE
, 1,
164 static inline enum rcu_state
rcu_reader_state(unsigned long *ctr
)
169 * Make sure both tests below are done on the same version of *value
170 * to insure consistency.
172 v
= CMM_LOAD_SHARED(*ctr
);
173 if (!(v
& RCU_GP_CTR_NEST_MASK
))
174 return RCU_READER_INACTIVE
;
175 if (!((v
^ rcu_gp
.ctr
) & RCU_GP_CTR_PHASE
))
176 return RCU_READER_ACTIVE_CURRENT
;
177 return RCU_READER_ACTIVE_OLD
;
181 * Helper for _rcu_read_lock(). The format of rcu_gp.ctr (as well as
182 * the per-thread rcu_reader.ctr) has the upper bits containing a count of
183 * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
184 * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in
185 * _rcu_read_lock() happen before the subsequent read-side critical section.
187 static inline void _rcu_read_lock_update(unsigned long tmp
)
189 if (caa_likely(!(tmp
& RCU_GP_CTR_NEST_MASK
))) {
190 _CMM_STORE_SHARED(URCU_TLS(rcu_reader
).ctr
, _CMM_LOAD_SHARED(rcu_gp
.ctr
));
193 _CMM_STORE_SHARED(URCU_TLS(rcu_reader
).ctr
, tmp
+ RCU_GP_COUNT
);
197 * Enter an RCU read-side critical section.
199 * The first cmm_barrier() call ensures that the compiler does not reorder
200 * the body of _rcu_read_lock() with a mutex.
202 * This function and its helper are both less than 10 lines long. The
203 * intent is that this function meets the 10-line criterion in LGPL,
204 * allowing this function to be invoked directly from non-LGPL code.
206 static inline void _rcu_read_lock(void)
210 urcu_assert(URCU_TLS(rcu_reader
).registered
);
212 tmp
= URCU_TLS(rcu_reader
).ctr
;
213 urcu_assert((tmp
& RCU_GP_CTR_NEST_MASK
) != RCU_GP_CTR_NEST_MASK
);
214 _rcu_read_lock_update(tmp
);
218 * This is a helper function for _rcu_read_unlock().
220 * The first smp_mb_slave() call ensures that the critical section is
221 * seen to precede the store to rcu_reader.ctr.
222 * The second smp_mb_slave() call ensures that we write to rcu_reader.ctr
223 * before reading the update-side futex.
225 static inline void _rcu_read_unlock_update_and_wakeup(unsigned long tmp
)
227 if (caa_likely((tmp
& RCU_GP_CTR_NEST_MASK
) == RCU_GP_COUNT
)) {
229 _CMM_STORE_SHARED(URCU_TLS(rcu_reader
).ctr
, tmp
- RCU_GP_COUNT
);
233 _CMM_STORE_SHARED(URCU_TLS(rcu_reader
).ctr
, tmp
- RCU_GP_COUNT
);
237 * Exit an RCU read-side crtical section. Both this function and its
238 * helper are smaller than 10 lines of code, and are intended to be
239 * usable by non-LGPL code, as called out in LGPL.
241 static inline void _rcu_read_unlock(void)
245 urcu_assert(URCU_TLS(rcu_reader
).registered
);
246 tmp
= URCU_TLS(rcu_reader
).ctr
;
247 urcu_assert(tmp
& RCU_GP_CTR_NEST_MASK
);
248 _rcu_read_unlock_update_and_wakeup(tmp
);
249 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
253 * Returns whether within a RCU read-side critical section.
255 * This function is less than 10 lines long. The intent is that this
256 * function meets the 10-line criterion for LGPL, allowing this function
257 * to be invoked directly from non-LGPL code.
259 static inline int _rcu_read_ongoing(void)
261 return URCU_TLS(rcu_reader
).ctr
& RCU_GP_CTR_NEST_MASK
;
268 #endif /* _URCU_STATIC_H */