1 /* 2 * Sleepable Read-Copy Update mechanism for mutual exclusion 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License as published by 6 * the Free Software Foundation; either version 2 of the License, or 7 * (at your option) any later version. 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * GNU General Public License for more details. 13 * 14 * You should have received a copy of the GNU General Public License 15 * along with this program; if not, you can access it online at 16 * http://www.gnu.org/licenses/gpl-2.0.html. 17 * 18 * Copyright (C) IBM Corporation, 2006 19 * Copyright (C) Fujitsu, 2012 20 * 21 * Author: Paul McKenney <[email protected]> 22 * Lai Jiangshan <[email protected]> 23 * 24 * For detailed explanation of Read-Copy Update mechanism see - 25 * Documentation/RCU/ *.txt 26 * 27 */ 28 29 #ifndef _LINUX_SRCU_H 30 #define _LINUX_SRCU_H 31 32 #include <linux/mutex.h> 33 #include <linux/rcupdate.h> 34 #include <linux/workqueue.h> 35 #include <linux/rcu_segcblist.h> 36 37 struct srcu_struct; 38 39 #ifdef CONFIG_DEBUG_LOCK_ALLOC 40 41 int __init_srcu_struct(struct srcu_struct *sp, const char *name, 42 struct lock_class_key *key); 43 44 #define init_srcu_struct(sp) \ 45 ({ \ 46 static struct lock_class_key __srcu_key; \ 47 \ 48 __init_srcu_struct((sp), #sp, &__srcu_key); \ 49 }) 50 51 #define __SRCU_DEP_MAP_INIT(srcu_name) .dep_map = { .name = #srcu_name }, 52 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 53 54 int init_srcu_struct(struct srcu_struct *sp); 55 56 #define __SRCU_DEP_MAP_INIT(srcu_name) 57 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 58 59 #ifdef CONFIG_TINY_SRCU 60 #include <linux/srcutiny.h> 61 #elif defined(CONFIG_TREE_SRCU) 62 #include <linux/srcutree.h> 63 #elif defined(CONFIG_SRCU) 64 #error "Unknown SRCU implementation specified to kernel configuration" 65 #else 66 /* Dummy definition for things like notifiers. Actual use gets link error. */ 67 struct srcu_struct { }; 68 #endif 69 70 void call_srcu(struct srcu_struct *sp, struct rcu_head *head, 71 void (*func)(struct rcu_head *head)); 72 void cleanup_srcu_struct(struct srcu_struct *sp); 73 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp); 74 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp); 75 void synchronize_srcu(struct srcu_struct *sp); 76 77 #ifdef CONFIG_DEBUG_LOCK_ALLOC 78 79 /** 80 * srcu_read_lock_held - might we be in SRCU read-side critical section? 81 * @sp: The srcu_struct structure to check 82 * 83 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU 84 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, 85 * this assumes we are in an SRCU read-side critical section unless it can 86 * prove otherwise. 87 * 88 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot 89 * and while lockdep is disabled. 90 * 91 * Note that SRCU is based on its own statemachine and it doesn't 92 * relies on normal RCU, it can be called from the CPU which 93 * is in the idle loop from an RCU point of view or offline. 94 */ 95 static inline int srcu_read_lock_held(const struct srcu_struct *sp) 96 { 97 if (!debug_lockdep_rcu_enabled()) 98 return 1; 99 return lock_is_held(&sp->dep_map); 100 } 101 102 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 103 104 static inline int srcu_read_lock_held(const struct srcu_struct *sp) 105 { 106 return 1; 107 } 108 109 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 110 111 /** 112 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing 113 * @p: the pointer to fetch and protect for later dereferencing 114 * @sp: pointer to the srcu_struct, which is used to check that we 115 * really are in an SRCU read-side critical section. 116 * @c: condition to check for update-side use 117 * 118 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side 119 * critical section will result in an RCU-lockdep splat, unless @c evaluates 120 * to 1. The @c argument will normally be a logical expression containing 121 * lockdep_is_held() calls. 122 */ 123 #define srcu_dereference_check(p, sp, c) \ 124 __rcu_dereference_check((p), (c) || srcu_read_lock_held(sp), __rcu) 125 126 /** 127 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing 128 * @p: the pointer to fetch and protect for later dereferencing 129 * @sp: pointer to the srcu_struct, which is used to check that we 130 * really are in an SRCU read-side critical section. 131 * 132 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU 133 * is enabled, invoking this outside of an RCU read-side critical 134 * section will result in an RCU-lockdep splat. 135 */ 136 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0) 137 138 /** 139 * srcu_read_lock - register a new reader for an SRCU-protected structure. 140 * @sp: srcu_struct in which to register the new reader. 141 * 142 * Enter an SRCU read-side critical section. Note that SRCU read-side 143 * critical sections may be nested. However, it is illegal to 144 * call anything that waits on an SRCU grace period for the same 145 * srcu_struct, whether directly or indirectly. Please note that 146 * one way to indirectly wait on an SRCU grace period is to acquire 147 * a mutex that is held elsewhere while calling synchronize_srcu() or 148 * synchronize_srcu_expedited(). 149 * 150 * Note that srcu_read_lock() and the matching srcu_read_unlock() must 151 * occur in the same context, for example, it is illegal to invoke 152 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock() 153 * was invoked in process context. 154 */ 155 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) 156 { 157 int retval; 158 159 retval = __srcu_read_lock(sp); 160 rcu_lock_acquire(&(sp)->dep_map); 161 return retval; 162 } 163 164 /** 165 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure. 166 * @sp: srcu_struct in which to unregister the old reader. 167 * @idx: return value from corresponding srcu_read_lock(). 168 * 169 * Exit an SRCU read-side critical section. 170 */ 171 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx) 172 __releases(sp) 173 { 174 rcu_lock_release(&(sp)->dep_map); 175 __srcu_read_unlock(sp, idx); 176 } 177 178 /** 179 * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock 180 * 181 * Converts the preceding srcu_read_unlock into a two-way memory barrier. 182 * 183 * Call this after srcu_read_unlock, to guarantee that all memory operations 184 * that occur after smp_mb__after_srcu_read_unlock will appear to happen after 185 * the preceding srcu_read_unlock. 186 */ 187 static inline void smp_mb__after_srcu_read_unlock(void) 188 { 189 /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */ 190 } 191 192 #endif 193