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1 | #ifndef _LTTNG_UST_URCU_STATIC_H |
2 | #define _LTTNG_UST_URCU_STATIC_H | |
3 | ||
4 | /* | |
5 | * urcu-ust-static.h | |
6 | * | |
7 | * Userspace RCU 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 <unistd.h> | |
35 | ||
36 | #include <urcu/config.h> | |
37 | #include <urcu/compiler.h> | |
38 | #include <urcu/arch.h> | |
39 | #include <urcu/system.h> | |
40 | #include <urcu/uatomic.h> | |
41 | #include <urcu/list.h> | |
42 | #include <urcu/tls-compat.h> | |
43 | #include <urcu/debug.h> | |
44 | ||
45 | /* | |
46 | * This code section can only be included in LGPL 2.1 compatible source code. | |
47 | * See below for the function call wrappers which can be used in code meant to | |
48 | * be only linked with the Userspace RCU library. This comes with a small | |
49 | * performance degradation on the read-side due to the added function calls. | |
50 | * This is required to permit relinking with newer versions of the library. | |
51 | */ | |
52 | ||
53 | #ifdef __cplusplus | |
54 | extern "C" { | |
55 | #endif | |
56 | ||
57 | enum lttng_ust_urcu_state { | |
58 | LTTNG_UST_URCU_READER_ACTIVE_CURRENT, | |
59 | LTTNG_UST_URCU_READER_ACTIVE_OLD, | |
60 | LTTNG_UST_URCU_READER_INACTIVE, | |
61 | }; | |
62 | ||
63 | /* | |
64 | * The trick here is that LTTNG_UST_URCU_GP_CTR_PHASE must be a multiple of 8 so we can use a | |
65 | * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits. | |
66 | */ | |
67 | #define LTTNG_UST_URCU_GP_COUNT (1UL << 0) | |
68 | /* Use the amount of bits equal to half of the architecture long size */ | |
69 | #define LTTNG_UST_URCU_GP_CTR_PHASE (1UL << (sizeof(long) << 2)) | |
70 | #define LTTNG_UST_URCU_GP_CTR_NEST_MASK (LTTNG_UST_URCU_GP_CTR_PHASE - 1) | |
71 | ||
72 | /* | |
73 | * Used internally by _lttng_ust_urcu_read_lock. | |
74 | */ | |
75 | extern void lttng_ust_urcu_register(void); | |
76 | ||
77 | struct lttng_ust_urcu_gp { | |
78 | /* | |
79 | * Global grace period counter. | |
80 | * Contains the current LTTNG_UST_URCU_GP_CTR_PHASE. | |
81 | * Also has a LTTNG_UST_URCU_GP_COUNT of 1, to accelerate the reader fast path. | |
82 | * Written to only by writer with mutex taken. | |
83 | * Read by both writer and readers. | |
84 | */ | |
85 | unsigned long ctr; | |
86 | } __attribute__((aligned(CAA_CACHE_LINE_SIZE))); | |
87 | ||
88 | extern struct lttng_ust_urcu_gp lttng_ust_urcu_gp; | |
89 | ||
90 | struct lttng_ust_urcu_reader { | |
91 | /* Data used by both reader and lttng_ust_urcu_synchronize_rcu() */ | |
92 | unsigned long ctr; | |
93 | /* Data used for registry */ | |
94 | struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE))); | |
95 | pthread_t tid; | |
96 | int alloc; /* registry entry allocated */ | |
97 | }; | |
98 | ||
99 | /* | |
100 | * Bulletproof version keeps a pointer to a registry not part of the TLS. | |
101 | * Adds a pointer dereference on the read-side, but won't require to unregister | |
102 | * the reader thread. | |
103 | */ | |
104 | extern DECLARE_URCU_TLS(struct lttng_ust_urcu_reader *, lttng_ust_urcu_reader); | |
105 | ||
106 | #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER | |
107 | #define lttng_ust_urcu_has_sys_membarrier 1 | |
108 | #else | |
109 | extern int lttng_ust_urcu_has_sys_membarrier; | |
110 | #endif | |
111 | ||
112 | static inline void lttng_ust_urcu_smp_mb_slave(void) | |
113 | { | |
114 | if (caa_likely(lttng_ust_urcu_has_sys_membarrier)) | |
115 | cmm_barrier(); | |
116 | else | |
117 | cmm_smp_mb(); | |
118 | } | |
119 | ||
120 | static inline enum lttng_ust_urcu_state lttng_ust_urcu_reader_state(unsigned long *ctr) | |
121 | { | |
122 | unsigned long v; | |
123 | ||
124 | if (ctr == NULL) | |
125 | return LTTNG_UST_URCU_READER_INACTIVE; | |
126 | /* | |
127 | * Make sure both tests below are done on the same version of *value | |
128 | * to insure consistency. | |
129 | */ | |
130 | v = CMM_LOAD_SHARED(*ctr); | |
131 | if (!(v & LTTNG_UST_URCU_GP_CTR_NEST_MASK)) | |
132 | return LTTNG_UST_URCU_READER_INACTIVE; | |
133 | if (!((v ^ lttng_ust_urcu_gp.ctr) & LTTNG_UST_URCU_GP_CTR_PHASE)) | |
134 | return LTTNG_UST_URCU_READER_ACTIVE_CURRENT; | |
135 | return LTTNG_UST_URCU_READER_ACTIVE_OLD; | |
136 | } | |
137 | ||
138 | /* | |
139 | * Helper for _lttng_ust_urcu_read_lock(). The format of lttng_ust_urcu_gp.ctr (as well as | |
140 | * the per-thread rcu_reader.ctr) has the upper bits containing a count of | |
141 | * _lttng_ust_urcu_read_lock() nesting, and a lower-order bit that contains either zero | |
142 | * or LTTNG_UST_URCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in | |
143 | * _lttng_ust_urcu_read_lock() happen before the subsequent read-side critical section. | |
144 | */ | |
145 | static inline void _lttng_ust_urcu_read_lock_update(unsigned long tmp) | |
146 | { | |
147 | if (caa_likely(!(tmp & LTTNG_UST_URCU_GP_CTR_NEST_MASK))) { | |
148 | _CMM_STORE_SHARED(URCU_TLS(lttng_ust_urcu_reader)->ctr, _CMM_LOAD_SHARED(lttng_ust_urcu_gp.ctr)); | |
149 | lttng_ust_urcu_smp_mb_slave(); | |
150 | } else | |
151 | _CMM_STORE_SHARED(URCU_TLS(lttng_ust_urcu_reader)->ctr, tmp + LTTNG_UST_URCU_GP_COUNT); | |
152 | } | |
153 | ||
154 | /* | |
155 | * Enter an RCU read-side critical section. | |
156 | * | |
157 | * The first cmm_barrier() call ensures that the compiler does not reorder | |
158 | * the body of _lttng_ust_urcu_read_lock() with a mutex. | |
159 | * | |
160 | * This function and its helper are both less than 10 lines long. The | |
161 | * intent is that this function meets the 10-line criterion in LGPL, | |
162 | * allowing this function to be invoked directly from non-LGPL code. | |
163 | */ | |
164 | static inline void _lttng_ust_urcu_read_lock(void) | |
165 | { | |
166 | unsigned long tmp; | |
167 | ||
168 | if (caa_unlikely(!URCU_TLS(lttng_ust_urcu_reader))) | |
169 | lttng_ust_urcu_register(); /* If not yet registered. */ | |
170 | cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ | |
171 | tmp = URCU_TLS(lttng_ust_urcu_reader)->ctr; | |
172 | urcu_assert((tmp & LTTNG_UST_URCU_GP_CTR_NEST_MASK) != LTTNG_UST_URCU_GP_CTR_NEST_MASK); | |
173 | _lttng_ust_urcu_read_lock_update(tmp); | |
174 | } | |
175 | ||
176 | /* | |
177 | * Exit an RCU read-side critical section. This function is less than | |
178 | * 10 lines of code, and is intended to be usable by non-LGPL code, as | |
179 | * called out in LGPL. | |
180 | */ | |
181 | static inline void _lttng_ust_urcu_read_unlock(void) | |
182 | { | |
183 | unsigned long tmp; | |
184 | ||
185 | tmp = URCU_TLS(lttng_ust_urcu_reader)->ctr; | |
186 | urcu_assert(tmp & LTTNG_UST_URCU_GP_CTR_NEST_MASK); | |
187 | /* Finish using rcu before decrementing the pointer. */ | |
188 | lttng_ust_urcu_smp_mb_slave(); | |
189 | _CMM_STORE_SHARED(URCU_TLS(lttng_ust_urcu_reader)->ctr, tmp - LTTNG_UST_URCU_GP_COUNT); | |
190 | cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ | |
191 | } | |
192 | ||
193 | /* | |
194 | * Returns whether within a RCU read-side critical section. | |
195 | * | |
196 | * This function is less than 10 lines long. The intent is that this | |
197 | * function meets the 10-line criterion for LGPL, allowing this function | |
198 | * to be invoked directly from non-LGPL code. | |
199 | */ | |
200 | static inline int _lttng_ust_urcu_read_ongoing(void) | |
201 | { | |
202 | if (caa_unlikely(!URCU_TLS(lttng_ust_urcu_reader))) | |
203 | lttng_ust_urcu_register(); /* If not yet registered. */ | |
204 | return URCU_TLS(lttng_ust_urcu_reader)->ctr & LTTNG_UST_URCU_GP_CTR_NEST_MASK; | |
205 | } | |
206 | ||
207 | #ifdef __cplusplus | |
208 | } | |
209 | #endif | |
210 | ||
211 | #endif /* _LTTNG_UST_URCU_STATIC_H */ |