| 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_QSBR_STATIC_H |
| 7 | #define _URCU_QSBR_STATIC_H |
| 8 | |
| 9 | /* |
| 10 | * Userspace RCU QSBR 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 <limits.h> |
| 21 | #include <unistd.h> |
| 22 | #include <stdint.h> |
| 23 | |
| 24 | #include <urcu/debug.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/futex.h> |
| 31 | #include <urcu/tls-compat.h> |
| 32 | #include <urcu/static/urcu-common.h> |
| 33 | |
| 34 | #ifdef __cplusplus |
| 35 | extern "C" { |
| 36 | #endif |
| 37 | |
| 38 | /* |
| 39 | * This code section can only be included in LGPL 2.1 compatible source code. |
| 40 | * See below for the function call wrappers which can be used in code meant to |
| 41 | * be only linked with the Userspace RCU library. This comes with a small |
| 42 | * performance degradation on the read-side due to the added function calls. |
| 43 | * This is required to permit relinking with newer versions of the library. |
| 44 | */ |
| 45 | |
| 46 | #define URCU_QSBR_GP_ONLINE (1UL << 0) |
| 47 | #define URCU_QSBR_GP_CTR (1UL << 1) |
| 48 | |
| 49 | extern struct urcu_gp urcu_qsbr_gp; |
| 50 | |
| 51 | struct urcu_qsbr_reader { |
| 52 | /* Data used by both reader and synchronize_rcu() */ |
| 53 | unsigned long ctr; |
| 54 | /* Data used for registry */ |
| 55 | struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE))); |
| 56 | int waiting; |
| 57 | pthread_t tid; |
| 58 | /* Reader registered flag, for internal checks. */ |
| 59 | unsigned int registered:1; |
| 60 | }; |
| 61 | |
| 62 | extern DECLARE_URCU_TLS(struct urcu_qsbr_reader, urcu_qsbr_reader); |
| 63 | |
| 64 | /* |
| 65 | * Wake-up waiting synchronize_rcu(). Called from many concurrent threads. |
| 66 | */ |
| 67 | static inline void urcu_qsbr_wake_up_gp(void) |
| 68 | { |
| 69 | if (caa_unlikely(_CMM_LOAD_SHARED(URCU_TLS(urcu_qsbr_reader).waiting))) { |
| 70 | _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).waiting, 0); |
| 71 | cmm_smp_mb(); |
| 72 | if (uatomic_read(&urcu_qsbr_gp.futex) != -1) |
| 73 | return; |
| 74 | uatomic_set(&urcu_qsbr_gp.futex, 0); |
| 75 | /* |
| 76 | * Ignoring return value until we can make this function |
| 77 | * return something (because urcu_die() is not publicly |
| 78 | * exposed). |
| 79 | */ |
| 80 | (void) futex_noasync(&urcu_qsbr_gp.futex, FUTEX_WAKE, 1, |
| 81 | NULL, NULL, 0); |
| 82 | } |
| 83 | } |
| 84 | |
| 85 | static inline enum urcu_state urcu_qsbr_reader_state(unsigned long *ctr) |
| 86 | { |
| 87 | unsigned long v; |
| 88 | |
| 89 | v = CMM_LOAD_SHARED(*ctr); |
| 90 | if (!v) |
| 91 | return URCU_READER_INACTIVE; |
| 92 | if (v == urcu_qsbr_gp.ctr) |
| 93 | return URCU_READER_ACTIVE_CURRENT; |
| 94 | return URCU_READER_ACTIVE_OLD; |
| 95 | } |
| 96 | |
| 97 | /* |
| 98 | * Enter an RCU read-side critical section. |
| 99 | * |
| 100 | * This function is less than 10 lines long. The intent is that this |
| 101 | * function meets the 10-line criterion for LGPL, allowing this function |
| 102 | * to be invoked directly from non-LGPL code. |
| 103 | */ |
| 104 | static inline void _urcu_qsbr_read_lock(void) |
| 105 | { |
| 106 | urcu_assert_debug(URCU_TLS(urcu_qsbr_reader).ctr); |
| 107 | } |
| 108 | |
| 109 | /* |
| 110 | * Exit an RCU read-side critical section. |
| 111 | * |
| 112 | * This function is less than 10 lines long. The intent is that this |
| 113 | * function meets the 10-line criterion for LGPL, allowing this function |
| 114 | * to be invoked directly from non-LGPL code. |
| 115 | */ |
| 116 | static inline void _urcu_qsbr_read_unlock(void) |
| 117 | { |
| 118 | urcu_assert_debug(URCU_TLS(urcu_qsbr_reader).ctr); |
| 119 | } |
| 120 | |
| 121 | /* |
| 122 | * Returns whether within a RCU read-side critical section. |
| 123 | * |
| 124 | * This function is less than 10 lines long. The intent is that this |
| 125 | * function meets the 10-line criterion for LGPL, allowing this function |
| 126 | * to be invoked directly from non-LGPL code. |
| 127 | */ |
| 128 | static inline int _urcu_qsbr_read_ongoing(void) |
| 129 | { |
| 130 | return URCU_TLS(urcu_qsbr_reader).ctr; |
| 131 | } |
| 132 | |
| 133 | /* |
| 134 | * This is a helper function for _rcu_quiescent_state(). |
| 135 | * The first cmm_smp_mb() ensures memory accesses in the prior read-side |
| 136 | * critical sections are not reordered with store to |
| 137 | * URCU_TLS(urcu_qsbr_reader).ctr, and ensures that mutexes held within an |
| 138 | * offline section that would happen to end with this |
| 139 | * urcu_qsbr_quiescent_state() call are not reordered with |
| 140 | * store to URCU_TLS(urcu_qsbr_reader).ctr. |
| 141 | */ |
| 142 | static inline void _urcu_qsbr_quiescent_state_update_and_wakeup(unsigned long gp_ctr) |
| 143 | { |
| 144 | cmm_smp_mb(); |
| 145 | _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).ctr, gp_ctr); |
| 146 | cmm_smp_mb(); /* write URCU_TLS(urcu_qsbr_reader).ctr before read futex */ |
| 147 | urcu_qsbr_wake_up_gp(); |
| 148 | cmm_smp_mb(); |
| 149 | } |
| 150 | |
| 151 | /* |
| 152 | * Inform RCU of a quiescent state. |
| 153 | * |
| 154 | * This function is less than 10 lines long. The intent is that this |
| 155 | * function meets the 10-line criterion for LGPL, allowing this function |
| 156 | * to be invoked directly from non-LGPL code. |
| 157 | * |
| 158 | * We skip the memory barriers and gp store if our local ctr already |
| 159 | * matches the global urcu_qsbr_gp.ctr value: this is OK because a prior |
| 160 | * _rcu_quiescent_state() or _rcu_thread_online() already updated it |
| 161 | * within our thread, so we have no quiescent state to report. |
| 162 | */ |
| 163 | static inline void _urcu_qsbr_quiescent_state(void) |
| 164 | { |
| 165 | unsigned long gp_ctr; |
| 166 | |
| 167 | urcu_assert_debug(URCU_TLS(urcu_qsbr_reader).registered); |
| 168 | if ((gp_ctr = CMM_LOAD_SHARED(urcu_qsbr_gp.ctr)) == URCU_TLS(urcu_qsbr_reader).ctr) |
| 169 | return; |
| 170 | _urcu_qsbr_quiescent_state_update_and_wakeup(gp_ctr); |
| 171 | } |
| 172 | |
| 173 | /* |
| 174 | * Take a thread offline, prohibiting it from entering further RCU |
| 175 | * read-side critical sections. |
| 176 | * |
| 177 | * This function is less than 10 lines long. The intent is that this |
| 178 | * function meets the 10-line criterion for LGPL, allowing this function |
| 179 | * to be invoked directly from non-LGPL code. |
| 180 | */ |
| 181 | static inline void _urcu_qsbr_thread_offline(void) |
| 182 | { |
| 183 | urcu_assert_debug(URCU_TLS(urcu_qsbr_reader).registered); |
| 184 | cmm_smp_mb(); |
| 185 | CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).ctr, 0); |
| 186 | cmm_smp_mb(); /* write URCU_TLS(urcu_qsbr_reader).ctr before read futex */ |
| 187 | urcu_qsbr_wake_up_gp(); |
| 188 | cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ |
| 189 | } |
| 190 | |
| 191 | /* |
| 192 | * Bring a thread online, allowing it to once again enter RCU |
| 193 | * read-side critical sections. |
| 194 | * |
| 195 | * This function is less than 10 lines long. The intent is that this |
| 196 | * function meets the 10-line criterion for LGPL, allowing this function |
| 197 | * to be invoked directly from non-LGPL code. |
| 198 | */ |
| 199 | static inline void _urcu_qsbr_thread_online(void) |
| 200 | { |
| 201 | urcu_assert_debug(URCU_TLS(urcu_qsbr_reader).registered); |
| 202 | cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ |
| 203 | _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).ctr, CMM_LOAD_SHARED(urcu_qsbr_gp.ctr)); |
| 204 | cmm_smp_mb(); |
| 205 | } |
| 206 | |
| 207 | #ifdef __cplusplus |
| 208 | } |
| 209 | #endif |
| 210 | |
| 211 | #endif /* _URCU_QSBR_STATIC_H */ |