Add cmm_emit_legacy_smp_mb()
[urcu.git] / include / urcu / static / urcu-bp.h
1 // SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
2 // SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation.
3 //
4 // SPDX-License-Identifier: LGPL-2.1-or-later
5
6 #ifndef _URCU_BP_STATIC_H
7 #define _URCU_BP_STATIC_H
8
9 /*
10 * Userspace RCU header.
11 *
12 * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
13 * RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
14 *
15 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
16 */
17
18 #include <stdlib.h>
19 #include <pthread.h>
20 #include <unistd.h>
21
22 #include <urcu/annotate.h>
23 #include <urcu/debug.h>
24 #include <urcu/config.h>
25 #include <urcu/compiler.h>
26 #include <urcu/arch.h>
27 #include <urcu/system.h>
28 #include <urcu/uatomic.h>
29 #include <urcu/list.h>
30 #include <urcu/tls-compat.h>
31
32 /*
33 * This code section can only be included in LGPL 2.1 compatible source code.
34 * See below for the function call wrappers which can be used in code meant to
35 * be only linked with the Userspace RCU library. This comes with a small
36 * performance degradation on the read-side due to the added function calls.
37 * This is required to permit relinking with newer versions of the library.
38 */
39
40 #ifdef __cplusplus
41 extern "C" {
42 #endif
43
44 enum urcu_bp_state {
45 URCU_BP_READER_ACTIVE_CURRENT,
46 URCU_BP_READER_ACTIVE_OLD,
47 URCU_BP_READER_INACTIVE,
48 };
49
50 /*
51 * The trick here is that URCU_BP_GP_CTR_PHASE must be a multiple of 8 so we can use a
52 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
53 */
54 #define URCU_BP_GP_COUNT (1UL << 0)
55 /* Use the amount of bits equal to half of the architecture long size */
56 #define URCU_BP_GP_CTR_PHASE (1UL << (sizeof(long) << 2))
57 #define URCU_BP_GP_CTR_NEST_MASK (URCU_BP_GP_CTR_PHASE - 1)
58
59 /*
60 * Used internally by _urcu_bp_read_lock.
61 */
62 extern void urcu_bp_register(void);
63
64 struct urcu_bp_gp {
65 /*
66 * Global grace period counter.
67 * Contains the current URCU_BP_GP_CTR_PHASE.
68 * Also has a URCU_BP_GP_COUNT of 1, to accelerate the reader fast path.
69 * Written to only by writer with mutex taken.
70 * Read by both writer and readers.
71 */
72 unsigned long ctr;
73 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
74
75 extern struct urcu_bp_gp urcu_bp_gp;
76
77 struct urcu_bp_reader {
78 /* Data used by both reader and urcu_bp_synchronize_rcu() */
79 unsigned long ctr;
80 /* Data used for registry */
81 struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
82 pthread_t tid;
83 int alloc; /* registry entry allocated */
84 };
85
86 /*
87 * Bulletproof version keeps a pointer to a registry not part of the TLS.
88 * Adds a pointer dereference on the read-side, but won't require to unregister
89 * the reader thread.
90 */
91 extern DECLARE_URCU_TLS(struct urcu_bp_reader *, urcu_bp_reader);
92
93 #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
94 #define urcu_bp_has_sys_membarrier 1
95 #else
96 extern int urcu_bp_has_sys_membarrier;
97 #endif
98
99 static inline void urcu_bp_smp_mb_slave(void)
100 {
101 if (caa_likely(urcu_bp_has_sys_membarrier))
102 cmm_barrier();
103 else
104 cmm_smp_mb();
105 }
106
107 static inline enum urcu_bp_state urcu_bp_reader_state(unsigned long *ctr,
108 cmm_annotate_t *group)
109 {
110 unsigned long v;
111
112 if (ctr == NULL)
113 return URCU_BP_READER_INACTIVE;
114 /*
115 * Make sure both tests below are done on the same version of *value
116 * to insure consistency.
117 */
118 v = uatomic_load(ctr, CMM_RELAXED);
119 cmm_annotate_group_mem_acquire(group, ctr);
120
121 if (!(v & URCU_BP_GP_CTR_NEST_MASK))
122 return URCU_BP_READER_INACTIVE;
123 if (!((v ^ urcu_bp_gp.ctr) & URCU_BP_GP_CTR_PHASE))
124 return URCU_BP_READER_ACTIVE_CURRENT;
125 return URCU_BP_READER_ACTIVE_OLD;
126 }
127
128 /*
129 * Helper for _urcu_bp_read_lock(). The format of urcu_bp_gp.ctr (as well as
130 * the per-thread rcu_reader.ctr) has the lower-order bits containing a count of
131 * _urcu_bp_read_lock() nesting, and a single high-order URCU_BP_GP_CTR_PHASE bit
132 * that contains either zero or one. The smp_mb_slave() ensures that the accesses in
133 * _urcu_bp_read_lock() happen before the subsequent read-side critical section.
134 */
135 static inline void _urcu_bp_read_lock_update(unsigned long tmp)
136 {
137 if (caa_likely(!(tmp & URCU_BP_GP_CTR_NEST_MASK))) {
138 _CMM_STORE_SHARED(URCU_TLS(urcu_bp_reader)->ctr, _CMM_LOAD_SHARED(urcu_bp_gp.ctr));
139 urcu_bp_smp_mb_slave();
140 } else
141 _CMM_STORE_SHARED(URCU_TLS(urcu_bp_reader)->ctr, tmp + URCU_BP_GP_COUNT);
142 }
143
144 /*
145 * Enter an RCU read-side critical section.
146 *
147 * The first cmm_barrier() call ensures that the compiler does not reorder
148 * the body of _urcu_bp_read_lock() with a mutex.
149 *
150 * This function and its helper are both less than 10 lines long. The
151 * intent is that this function meets the 10-line criterion in LGPL,
152 * allowing this function to be invoked directly from non-LGPL code.
153 */
154 static inline void _urcu_bp_read_lock(void)
155 {
156 unsigned long tmp;
157
158 if (caa_unlikely(!URCU_TLS(urcu_bp_reader)))
159 urcu_bp_register(); /* If not yet registered. */
160 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
161 tmp = URCU_TLS(urcu_bp_reader)->ctr;
162 urcu_assert_debug((tmp & URCU_BP_GP_CTR_NEST_MASK) != URCU_BP_GP_CTR_NEST_MASK);
163 _urcu_bp_read_lock_update(tmp);
164 }
165
166 /*
167 * Exit an RCU read-side critical section. This function is less than
168 * 10 lines of code, and is intended to be usable by non-LGPL code, as
169 * called out in LGPL.
170 */
171 static inline void _urcu_bp_read_unlock(void)
172 {
173 unsigned long tmp;
174 unsigned long *ctr = &URCU_TLS(urcu_bp_reader)->ctr;
175
176 tmp = URCU_TLS(urcu_bp_reader)->ctr;
177 urcu_assert_debug(tmp & URCU_BP_GP_CTR_NEST_MASK);
178 /* Finish using rcu before decrementing the pointer. */
179 urcu_bp_smp_mb_slave();
180 cmm_annotate_mem_release(ctr);
181 uatomic_store(ctr, tmp - URCU_BP_GP_COUNT, CMM_RELAXED);
182 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
183 }
184
185 /*
186 * Returns whether within a RCU read-side critical section.
187 *
188 * This function is less than 10 lines long. The intent is that this
189 * function meets the 10-line criterion for LGPL, allowing this function
190 * to be invoked directly from non-LGPL code.
191 */
192 static inline int _urcu_bp_read_ongoing(void)
193 {
194 if (caa_unlikely(!URCU_TLS(urcu_bp_reader)))
195 urcu_bp_register(); /* If not yet registered. */
196 return URCU_TLS(urcu_bp_reader)->ctr & URCU_BP_GP_CTR_NEST_MASK;
197 }
198
199 #ifdef __cplusplus
200 }
201 #endif
202
203 #endif /* _URCU_BP_STATIC_H */
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