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, write to the Free Software 16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. 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 36 struct srcu_struct_array { 37 unsigned long c[2]; 38 unsigned long seq[2]; 39 }; 40 41 struct rcu_batch { 42 struct rcu_head *head, **tail; 43 }; 44 45 #define RCU_BATCH_INIT(name) { NULL, &(name.head) } 46 47 struct srcu_struct { 48 unsigned completed; 49 struct srcu_struct_array __percpu *per_cpu_ref; 50 spinlock_t queue_lock; /* protect ->batch_queue, ->running */ 51 bool running; 52 /* callbacks just queued */ 53 struct rcu_batch batch_queue; 54 /* callbacks try to do the first check_zero */ 55 struct rcu_batch batch_check0; 56 /* callbacks done with the first check_zero and the flip */ 57 struct rcu_batch batch_check1; 58 struct rcu_batch batch_done; 59 struct delayed_work work; 60 #ifdef CONFIG_DEBUG_LOCK_ALLOC 61 struct lockdep_map dep_map; 62 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 63 }; 64 65 #ifdef CONFIG_DEBUG_LOCK_ALLOC 66 67 int __init_srcu_struct(struct srcu_struct *sp, const char *name, 68 struct lock_class_key *key); 69 70 #define init_srcu_struct(sp) \ 71 ({ \ 72 static struct lock_class_key __srcu_key; \ 73 \ 74 __init_srcu_struct((sp), #sp, &__srcu_key); \ 75 }) 76 77 #define __SRCU_DEP_MAP_INIT(srcu_name) .dep_map = { .name = #srcu_name }, 78 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 79 80 int init_srcu_struct(struct srcu_struct *sp); 81 82 #define __SRCU_DEP_MAP_INIT(srcu_name) 83 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 84 85 void process_srcu(struct work_struct *work); 86 87 #define __SRCU_STRUCT_INIT(name) \ 88 { \ 89 .completed = -300, \ 90 .per_cpu_ref = &name##_srcu_array, \ 91 .queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock), \ 92 .running = false, \ 93 .batch_queue = RCU_BATCH_INIT(name.batch_queue), \ 94 .batch_check0 = RCU_BATCH_INIT(name.batch_check0), \ 95 .batch_check1 = RCU_BATCH_INIT(name.batch_check1), \ 96 .batch_done = RCU_BATCH_INIT(name.batch_done), \ 97 .work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\ 98 __SRCU_DEP_MAP_INIT(name) \ 99 } 100 101 /* 102 * define and init a srcu struct at build time. 103 * dont't call init_srcu_struct() nor cleanup_srcu_struct() on it. 104 */ 105 #define DEFINE_SRCU(name) \ 106 static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\ 107 struct srcu_struct name = __SRCU_STRUCT_INIT(name); 108 109 #define DEFINE_STATIC_SRCU(name) \ 110 static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\ 111 static struct srcu_struct name = __SRCU_STRUCT_INIT(name); 112 113 /** 114 * call_srcu() - Queue a callback for invocation after an SRCU grace period 115 * @sp: srcu_struct in queue the callback 116 * @head: structure to be used for queueing the SRCU callback. 117 * @func: function to be invoked after the SRCU grace period 118 * 119 * The callback function will be invoked some time after a full SRCU 120 * grace period elapses, in other words after all pre-existing SRCU 121 * read-side critical sections have completed. However, the callback 122 * function might well execute concurrently with other SRCU read-side 123 * critical sections that started after call_srcu() was invoked. SRCU 124 * read-side critical sections are delimited by srcu_read_lock() and 125 * srcu_read_unlock(), and may be nested. 126 * 127 * The callback will be invoked from process context, but must nevertheless 128 * be fast and must not block. 129 */ 130 void call_srcu(struct srcu_struct *sp, struct rcu_head *head, 131 void (*func)(struct rcu_head *head)); 132 133 void cleanup_srcu_struct(struct srcu_struct *sp); 134 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp); 135 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp); 136 void synchronize_srcu(struct srcu_struct *sp); 137 void synchronize_srcu_expedited(struct srcu_struct *sp); 138 long srcu_batches_completed(struct srcu_struct *sp); 139 void srcu_barrier(struct srcu_struct *sp); 140 141 #ifdef CONFIG_DEBUG_LOCK_ALLOC 142 143 /** 144 * srcu_read_lock_held - might we be in SRCU read-side critical section? 145 * 146 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU 147 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, 148 * this assumes we are in an SRCU read-side critical section unless it can 149 * prove otherwise. 150 * 151 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot 152 * and while lockdep is disabled. 153 * 154 * Note that if the CPU is in the idle loop from an RCU point of view 155 * (ie: that we are in the section between rcu_idle_enter() and 156 * rcu_idle_exit()) then srcu_read_lock_held() returns false even if 157 * the CPU did an srcu_read_lock(). The reason for this is that RCU 158 * ignores CPUs that are in such a section, considering these as in 159 * extended quiescent state, so such a CPU is effectively never in an 160 * RCU read-side critical section regardless of what RCU primitives it 161 * invokes. This state of affairs is required --- we need to keep an 162 * RCU-free window in idle where the CPU may possibly enter into low 163 * power mode. This way we can notice an extended quiescent state to 164 * other CPUs that started a grace period. Otherwise we would delay any 165 * grace period as long as we run in the idle task. 166 * 167 * Similarly, we avoid claiming an SRCU read lock held if the current 168 * CPU is offline. 169 */ 170 static inline int srcu_read_lock_held(struct srcu_struct *sp) 171 { 172 if (!debug_lockdep_rcu_enabled()) 173 return 1; 174 if (rcu_is_cpu_idle()) 175 return 0; 176 if (!rcu_lockdep_current_cpu_online()) 177 return 0; 178 return lock_is_held(&sp->dep_map); 179 } 180 181 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 182 183 static inline int srcu_read_lock_held(struct srcu_struct *sp) 184 { 185 return 1; 186 } 187 188 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 189 190 /** 191 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing 192 * @p: the pointer to fetch and protect for later dereferencing 193 * @sp: pointer to the srcu_struct, which is used to check that we 194 * really are in an SRCU read-side critical section. 195 * @c: condition to check for update-side use 196 * 197 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side 198 * critical section will result in an RCU-lockdep splat, unless @c evaluates 199 * to 1. The @c argument will normally be a logical expression containing 200 * lockdep_is_held() calls. 201 */ 202 #define srcu_dereference_check(p, sp, c) \ 203 __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu) 204 205 /** 206 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing 207 * @p: the pointer to fetch and protect for later dereferencing 208 * @sp: pointer to the srcu_struct, which is used to check that we 209 * really are in an SRCU read-side critical section. 210 * 211 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU 212 * is enabled, invoking this outside of an RCU read-side critical 213 * section will result in an RCU-lockdep splat. 214 */ 215 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0) 216 217 /** 218 * srcu_read_lock - register a new reader for an SRCU-protected structure. 219 * @sp: srcu_struct in which to register the new reader. 220 * 221 * Enter an SRCU read-side critical section. Note that SRCU read-side 222 * critical sections may be nested. However, it is illegal to 223 * call anything that waits on an SRCU grace period for the same 224 * srcu_struct, whether directly or indirectly. Please note that 225 * one way to indirectly wait on an SRCU grace period is to acquire 226 * a mutex that is held elsewhere while calling synchronize_srcu() or 227 * synchronize_srcu_expedited(). 228 * 229 * Note that srcu_read_lock() and the matching srcu_read_unlock() must 230 * occur in the same context, for example, it is illegal to invoke 231 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock() 232 * was invoked in process context. 233 */ 234 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) 235 { 236 int retval = __srcu_read_lock(sp); 237 238 rcu_lock_acquire(&(sp)->dep_map); 239 rcu_lockdep_assert(!rcu_is_cpu_idle(), 240 "srcu_read_lock() used illegally while idle"); 241 return retval; 242 } 243 244 /** 245 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure. 246 * @sp: srcu_struct in which to unregister the old reader. 247 * @idx: return value from corresponding srcu_read_lock(). 248 * 249 * Exit an SRCU read-side critical section. 250 */ 251 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx) 252 __releases(sp) 253 { 254 rcu_lockdep_assert(!rcu_is_cpu_idle(), 255 "srcu_read_unlock() used illegally while idle"); 256 rcu_lock_release(&(sp)->dep_map); 257 __srcu_read_unlock(sp, idx); 258 } 259 260 /** 261 * srcu_read_lock_raw - register a new reader for an SRCU-protected structure. 262 * @sp: srcu_struct in which to register the new reader. 263 * 264 * Enter an SRCU read-side critical section. Similar to srcu_read_lock(), 265 * but avoids the RCU-lockdep checking. This means that it is legal to 266 * use srcu_read_lock_raw() in one context, for example, in an exception 267 * handler, and then have the matching srcu_read_unlock_raw() in another 268 * context, for example in the task that took the exception. 269 * 270 * However, the entire SRCU read-side critical section must reside within a 271 * single task. For example, beware of using srcu_read_lock_raw() in 272 * a device interrupt handler and srcu_read_unlock() in the interrupted 273 * task: This will not work if interrupts are threaded. 274 */ 275 static inline int srcu_read_lock_raw(struct srcu_struct *sp) 276 { 277 unsigned long flags; 278 int ret; 279 280 local_irq_save(flags); 281 ret = __srcu_read_lock(sp); 282 local_irq_restore(flags); 283 return ret; 284 } 285 286 /** 287 * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure. 288 * @sp: srcu_struct in which to unregister the old reader. 289 * @idx: return value from corresponding srcu_read_lock_raw(). 290 * 291 * Exit an SRCU read-side critical section without lockdep-RCU checking. 292 * See srcu_read_lock_raw() for more details. 293 */ 294 static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx) 295 { 296 unsigned long flags; 297 298 local_irq_save(flags); 299 __srcu_read_unlock(sp, idx); 300 local_irq_restore(flags); 301 } 302 303 #endif 304