Fix: compat_futex.c: *uaddr should be read as volatile
[urcu.git] / urcu / static / urcu-qsbr.h
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CommitLineData
1#ifndef _URCU_QSBR_STATIC_H
2#define _URCU_QSBR_STATIC_H
3
4/*
5 * urcu-qsbr-static.h
6 *
7 * Userspace RCU QSBR header.
8 *
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.
11 *
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
14 *
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
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>
34#include <assert.h>
35#include <limits.h>
36#include <unistd.h>
37#include <stdint.h>
38
39#include <urcu/compiler.h>
40#include <urcu/arch.h>
41#include <urcu/system.h>
42#include <urcu/uatomic.h>
43#include <urcu/list.h>
44#include <urcu/futex.h>
45#include <urcu/tls-compat.h>
46
47#ifdef __cplusplus
48extern "C" {
49#endif
50
51/*
52 * This code section can only be included in LGPL 2.1 compatible source code.
53 * See below for the function call wrappers which can be used in code meant to
54 * be only linked with the Userspace RCU library. This comes with a small
55 * performance degradation on the read-side due to the added function calls.
56 * This is required to permit relinking with newer versions of the library.
57 */
58
59#ifdef DEBUG_RCU
60#define rcu_assert(args...) assert(args)
61#else
62#define rcu_assert(args...)
63#endif
64
65enum rcu_state {
66 RCU_READER_ACTIVE_CURRENT,
67 RCU_READER_ACTIVE_OLD,
68 RCU_READER_INACTIVE,
69};
70
71#define RCU_GP_ONLINE (1UL << 0)
72#define RCU_GP_CTR (1UL << 1)
73
74struct rcu_gp {
75 /*
76 * Global quiescent period counter with low-order bits unused.
77 * Using a int rather than a char to eliminate false register
78 * dependencies causing stalls on some architectures.
79 */
80 unsigned long ctr;
81
82 int32_t futex;
83} __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
84
85extern struct rcu_gp rcu_gp;
86
87struct rcu_reader {
88 /* Data used by both reader and synchronize_rcu() */
89 unsigned long ctr;
90 /* Data used for registry */
91 struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
92 int waiting;
93 pthread_t tid;
94};
95
96extern DECLARE_URCU_TLS(struct rcu_reader, rcu_reader);
97
98/*
99 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
100 */
101static inline void wake_up_gp(void)
102{
103 if (caa_unlikely(_CMM_LOAD_SHARED(URCU_TLS(rcu_reader).waiting))) {
104 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).waiting, 0);
105 cmm_smp_mb();
106 if (uatomic_read(&rcu_gp.futex) != -1)
107 return;
108 uatomic_set(&rcu_gp.futex, 0);
109 futex_noasync(&rcu_gp.futex, FUTEX_WAKE, 1,
110 NULL, NULL, 0);
111 }
112}
113
114static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
115{
116 unsigned long v;
117
118 v = CMM_LOAD_SHARED(*ctr);
119 if (!v)
120 return RCU_READER_INACTIVE;
121 if (v == rcu_gp.ctr)
122 return RCU_READER_ACTIVE_CURRENT;
123 return RCU_READER_ACTIVE_OLD;
124}
125
126/*
127 * Enter an RCU read-side critical section.
128 *
129 * This function is less than 10 lines long. The intent is that this
130 * function meets the 10-line criterion for LGPL, allowing this function
131 * to be invoked directly from non-LGPL code.
132 */
133static inline void _rcu_read_lock(void)
134{
135 rcu_assert(URCU_TLS(rcu_reader).ctr);
136}
137
138/*
139 * Exit an RCU read-side critical section.
140 *
141 * This function is less than 10 lines long. The intent is that this
142 * function meets the 10-line criterion for LGPL, allowing this function
143 * to be invoked directly from non-LGPL code.
144 */
145static inline void _rcu_read_unlock(void)
146{
147}
148
149/*
150 * Returns whether within a RCU read-side critical section.
151 *
152 * This function is less than 10 lines long. The intent is that this
153 * function meets the 10-line criterion for LGPL, allowing this function
154 * to be invoked directly from non-LGPL code.
155 */
156static inline int _rcu_read_ongoing(void)
157{
158 return URCU_TLS(rcu_reader).ctr;
159}
160
161/*
162 * This is a helper function for _rcu_quiescent_state().
163 * The first cmm_smp_mb() ensures memory accesses in the prior read-side
164 * critical sections are not reordered with store to
165 * URCU_TLS(rcu_reader).ctr, and ensures that mutexes held within an
166 * offline section that would happen to end with this
167 * rcu_quiescent_state() call are not reordered with
168 * store to URCU_TLS(rcu_reader).ctr.
169 */
170static inline void _rcu_quiescent_state_update_and_wakeup(unsigned long gp_ctr)
171{
172 cmm_smp_mb();
173 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, gp_ctr);
174 cmm_smp_mb(); /* write URCU_TLS(rcu_reader).ctr before read futex */
175 wake_up_gp();
176 cmm_smp_mb();
177}
178
179/*
180 * Inform RCU of a quiescent state.
181 *
182 * This function is less than 10 lines long. The intent is that this
183 * function meets the 10-line criterion for LGPL, allowing this function
184 * to be invoked directly from non-LGPL code.
185 *
186 * We skip the memory barriers and gp store if our local ctr already
187 * matches the global rcu_gp.ctr value: this is OK because a prior
188 * _rcu_quiescent_state() or _rcu_thread_online() already updated it
189 * within our thread, so we have no quiescent state to report.
190 */
191static inline void _rcu_quiescent_state(void)
192{
193 unsigned long gp_ctr;
194
195 if ((gp_ctr = CMM_LOAD_SHARED(rcu_gp.ctr)) == URCU_TLS(rcu_reader).ctr)
196 return;
197 _rcu_quiescent_state_update_and_wakeup(gp_ctr);
198}
199
200/*
201 * Take a thread offline, prohibiting it from entering further RCU
202 * read-side critical sections.
203 *
204 * This function is less than 10 lines long. The intent is that this
205 * function meets the 10-line criterion for LGPL, allowing this function
206 * to be invoked directly from non-LGPL code.
207 */
208static inline void _rcu_thread_offline(void)
209{
210 cmm_smp_mb();
211 CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, 0);
212 cmm_smp_mb(); /* write URCU_TLS(rcu_reader).ctr before read futex */
213 wake_up_gp();
214 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
215}
216
217/*
218 * Bring a thread online, allowing it to once again enter RCU
219 * read-side critical sections.
220 *
221 * This function is less than 10 lines long. The intent is that this
222 * function meets the 10-line criterion for LGPL, allowing this function
223 * to be invoked directly from non-LGPL code.
224 */
225static inline void _rcu_thread_online(void)
226{
227 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
228 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, CMM_LOAD_SHARED(rcu_gp.ctr));
229 cmm_smp_mb();
230}
231
232#ifdef __cplusplus
233}
234#endif
235
236#endif /* _URCU_QSBR_STATIC_H */
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