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10544ee8 | 1 | /* |
c0c0989a | 2 | * SPDX-License-Identifier: LGPL-2.1-or-later |
10544ee8 MD |
3 | * |
4 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
5 | * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. | |
6 | * | |
c0c0989a | 7 | * Userspace RCU header. |
10544ee8 | 8 | * |
c0c0989a MJ |
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. | |
10544ee8 MD |
11 | */ |
12 | ||
c0c0989a MJ |
13 | #ifndef _LTTNG_UST_URCU_STATIC_H |
14 | #define _LTTNG_UST_URCU_STATIC_H | |
15 | ||
10544ee8 MD |
16 | #include <stdlib.h> |
17 | #include <pthread.h> | |
18 | #include <unistd.h> | |
19 | ||
20 | #include <urcu/config.h> | |
21 | #include <urcu/compiler.h> | |
22 | #include <urcu/arch.h> | |
23 | #include <urcu/system.h> | |
24 | #include <urcu/uatomic.h> | |
25 | #include <urcu/list.h> | |
26 | #include <urcu/tls-compat.h> | |
27 | #include <urcu/debug.h> | |
28 | ||
29 | /* | |
30 | * This code section can only be included in LGPL 2.1 compatible source code. | |
31 | * See below for the function call wrappers which can be used in code meant to | |
32 | * be only linked with the Userspace RCU library. This comes with a small | |
33 | * performance degradation on the read-side due to the added function calls. | |
34 | * This is required to permit relinking with newer versions of the library. | |
35 | */ | |
36 | ||
37 | #ifdef __cplusplus | |
38 | extern "C" { | |
39 | #endif | |
40 | ||
41 | enum lttng_ust_urcu_state { | |
42 | LTTNG_UST_URCU_READER_ACTIVE_CURRENT, | |
43 | LTTNG_UST_URCU_READER_ACTIVE_OLD, | |
44 | LTTNG_UST_URCU_READER_INACTIVE, | |
45 | }; | |
46 | ||
47 | /* | |
48 | * The trick here is that LTTNG_UST_URCU_GP_CTR_PHASE must be a multiple of 8 so we can use a | |
49 | * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits. | |
50 | */ | |
51 | #define LTTNG_UST_URCU_GP_COUNT (1UL << 0) | |
52 | /* Use the amount of bits equal to half of the architecture long size */ | |
53 | #define LTTNG_UST_URCU_GP_CTR_PHASE (1UL << (sizeof(long) << 2)) | |
54 | #define LTTNG_UST_URCU_GP_CTR_NEST_MASK (LTTNG_UST_URCU_GP_CTR_PHASE - 1) | |
55 | ||
56 | /* | |
57 | * Used internally by _lttng_ust_urcu_read_lock. | |
58 | */ | |
59 | extern void lttng_ust_urcu_register(void); | |
60 | ||
61 | struct lttng_ust_urcu_gp { | |
62 | /* | |
63 | * Global grace period counter. | |
64 | * Contains the current LTTNG_UST_URCU_GP_CTR_PHASE. | |
65 | * Also has a LTTNG_UST_URCU_GP_COUNT of 1, to accelerate the reader fast path. | |
66 | * Written to only by writer with mutex taken. | |
67 | * Read by both writer and readers. | |
68 | */ | |
69 | unsigned long ctr; | |
70 | } __attribute__((aligned(CAA_CACHE_LINE_SIZE))); | |
71 | ||
72 | extern struct lttng_ust_urcu_gp lttng_ust_urcu_gp; | |
73 | ||
74 | struct lttng_ust_urcu_reader { | |
75 | /* Data used by both reader and lttng_ust_urcu_synchronize_rcu() */ | |
76 | unsigned long ctr; | |
77 | /* Data used for registry */ | |
78 | struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE))); | |
79 | pthread_t tid; | |
80 | int alloc; /* registry entry allocated */ | |
81 | }; | |
82 | ||
83 | /* | |
84 | * Bulletproof version keeps a pointer to a registry not part of the TLS. | |
85 | * Adds a pointer dereference on the read-side, but won't require to unregister | |
86 | * the reader thread. | |
87 | */ | |
88 | extern DECLARE_URCU_TLS(struct lttng_ust_urcu_reader *, lttng_ust_urcu_reader); | |
89 | ||
90 | #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER | |
91 | #define lttng_ust_urcu_has_sys_membarrier 1 | |
92 | #else | |
93 | extern int lttng_ust_urcu_has_sys_membarrier; | |
94 | #endif | |
95 | ||
96 | static inline void lttng_ust_urcu_smp_mb_slave(void) | |
97 | { | |
98 | if (caa_likely(lttng_ust_urcu_has_sys_membarrier)) | |
99 | cmm_barrier(); | |
100 | else | |
101 | cmm_smp_mb(); | |
102 | } | |
103 | ||
104 | static inline enum lttng_ust_urcu_state lttng_ust_urcu_reader_state(unsigned long *ctr) | |
105 | { | |
106 | unsigned long v; | |
107 | ||
108 | if (ctr == NULL) | |
109 | return LTTNG_UST_URCU_READER_INACTIVE; | |
110 | /* | |
111 | * Make sure both tests below are done on the same version of *value | |
112 | * to insure consistency. | |
113 | */ | |
114 | v = CMM_LOAD_SHARED(*ctr); | |
115 | if (!(v & LTTNG_UST_URCU_GP_CTR_NEST_MASK)) | |
116 | return LTTNG_UST_URCU_READER_INACTIVE; | |
117 | if (!((v ^ lttng_ust_urcu_gp.ctr) & LTTNG_UST_URCU_GP_CTR_PHASE)) | |
118 | return LTTNG_UST_URCU_READER_ACTIVE_CURRENT; | |
119 | return LTTNG_UST_URCU_READER_ACTIVE_OLD; | |
120 | } | |
121 | ||
122 | /* | |
123 | * Helper for _lttng_ust_urcu_read_lock(). The format of lttng_ust_urcu_gp.ctr (as well as | |
124 | * the per-thread rcu_reader.ctr) has the upper bits containing a count of | |
125 | * _lttng_ust_urcu_read_lock() nesting, and a lower-order bit that contains either zero | |
126 | * or LTTNG_UST_URCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in | |
127 | * _lttng_ust_urcu_read_lock() happen before the subsequent read-side critical section. | |
128 | */ | |
129 | static inline void _lttng_ust_urcu_read_lock_update(unsigned long tmp) | |
130 | { | |
131 | if (caa_likely(!(tmp & LTTNG_UST_URCU_GP_CTR_NEST_MASK))) { | |
132 | _CMM_STORE_SHARED(URCU_TLS(lttng_ust_urcu_reader)->ctr, _CMM_LOAD_SHARED(lttng_ust_urcu_gp.ctr)); | |
133 | lttng_ust_urcu_smp_mb_slave(); | |
134 | } else | |
135 | _CMM_STORE_SHARED(URCU_TLS(lttng_ust_urcu_reader)->ctr, tmp + LTTNG_UST_URCU_GP_COUNT); | |
136 | } | |
137 | ||
138 | /* | |
139 | * Enter an RCU read-side critical section. | |
140 | * | |
141 | * The first cmm_barrier() call ensures that the compiler does not reorder | |
142 | * the body of _lttng_ust_urcu_read_lock() with a mutex. | |
143 | * | |
144 | * This function and its helper are both less than 10 lines long. The | |
145 | * intent is that this function meets the 10-line criterion in LGPL, | |
146 | * allowing this function to be invoked directly from non-LGPL code. | |
147 | */ | |
148 | static inline void _lttng_ust_urcu_read_lock(void) | |
149 | { | |
150 | unsigned long tmp; | |
151 | ||
152 | if (caa_unlikely(!URCU_TLS(lttng_ust_urcu_reader))) | |
153 | lttng_ust_urcu_register(); /* If not yet registered. */ | |
154 | cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ | |
155 | tmp = URCU_TLS(lttng_ust_urcu_reader)->ctr; | |
156 | urcu_assert((tmp & LTTNG_UST_URCU_GP_CTR_NEST_MASK) != LTTNG_UST_URCU_GP_CTR_NEST_MASK); | |
157 | _lttng_ust_urcu_read_lock_update(tmp); | |
158 | } | |
159 | ||
160 | /* | |
161 | * Exit an RCU read-side critical section. This function is less than | |
162 | * 10 lines of code, and is intended to be usable by non-LGPL code, as | |
163 | * called out in LGPL. | |
164 | */ | |
165 | static inline void _lttng_ust_urcu_read_unlock(void) | |
166 | { | |
167 | unsigned long tmp; | |
168 | ||
169 | tmp = URCU_TLS(lttng_ust_urcu_reader)->ctr; | |
170 | urcu_assert(tmp & LTTNG_UST_URCU_GP_CTR_NEST_MASK); | |
171 | /* Finish using rcu before decrementing the pointer. */ | |
172 | lttng_ust_urcu_smp_mb_slave(); | |
173 | _CMM_STORE_SHARED(URCU_TLS(lttng_ust_urcu_reader)->ctr, tmp - LTTNG_UST_URCU_GP_COUNT); | |
174 | cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ | |
175 | } | |
176 | ||
177 | /* | |
178 | * Returns whether within a RCU read-side critical section. | |
179 | * | |
180 | * This function is less than 10 lines long. The intent is that this | |
181 | * function meets the 10-line criterion for LGPL, allowing this function | |
182 | * to be invoked directly from non-LGPL code. | |
183 | */ | |
184 | static inline int _lttng_ust_urcu_read_ongoing(void) | |
185 | { | |
186 | if (caa_unlikely(!URCU_TLS(lttng_ust_urcu_reader))) | |
187 | lttng_ust_urcu_register(); /* If not yet registered. */ | |
188 | return URCU_TLS(lttng_ust_urcu_reader)->ctr & LTTNG_UST_URCU_GP_CTR_NEST_MASK; | |
189 | } | |
190 | ||
191 | #ifdef __cplusplus | |
192 | } | |
193 | #endif | |
194 | ||
195 | #endif /* _LTTNG_UST_URCU_STATIC_H */ |