1 /* 2 * 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 IBM Corporation, 2001 19 * 20 * Author: Dipankar Sarma <[email protected]> 21 * 22 * Based on the original work by Paul McKenney <[email protected]> 23 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. 24 * Papers: 25 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf 26 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) 27 * 28 * For detailed explanation of Read-Copy Update mechanism see - 29 * http://lse.sourceforge.net/locking/rcupdate.html 30 * 31 */ 32 33 #ifndef __LINUX_RCUPDATE_H 34 #define __LINUX_RCUPDATE_H 35 36 #include <linux/cache.h> 37 #include <linux/spinlock.h> 38 #include <linux/threads.h> 39 #include <linux/cpumask.h> 40 #include <linux/seqlock.h> 41 #include <linux/lockdep.h> 42 #include <linux/completion.h> 43 44 /** 45 * struct rcu_head - callback structure for use with RCU 46 * @next: next update requests in a list 47 * @func: actual update function to call after the grace period. 48 */ 49 struct rcu_head { 50 struct rcu_head *next; 51 void (*func)(struct rcu_head *head); 52 }; 53 54 /* Exported common interfaces */ 55 #ifdef CONFIG_TREE_PREEMPT_RCU 56 extern void synchronize_rcu(void); 57 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ 58 #define synchronize_rcu synchronize_sched 59 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ 60 extern void synchronize_rcu_bh(void); 61 extern void synchronize_sched(void); 62 extern void rcu_barrier(void); 63 extern void rcu_barrier_bh(void); 64 extern void rcu_barrier_sched(void); 65 extern void synchronize_sched_expedited(void); 66 extern int sched_expedited_torture_stats(char *page); 67 68 /* Internal to kernel */ 69 extern void rcu_init(void); 70 extern void rcu_scheduler_starting(void); 71 extern int rcu_needs_cpu(int cpu); 72 extern int rcu_scheduler_active; 73 74 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) 75 #include <linux/rcutree.h> 76 #else 77 #error "Unknown RCU implementation specified to kernel configuration" 78 #endif 79 80 #define RCU_HEAD_INIT { .next = NULL, .func = NULL } 81 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT 82 #define INIT_RCU_HEAD(ptr) do { \ 83 (ptr)->next = NULL; (ptr)->func = NULL; \ 84 } while (0) 85 86 #ifdef CONFIG_DEBUG_LOCK_ALLOC 87 extern struct lockdep_map rcu_lock_map; 88 # define rcu_read_acquire() \ 89 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) 90 # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) 91 #else 92 # define rcu_read_acquire() do { } while (0) 93 # define rcu_read_release() do { } while (0) 94 #endif 95 96 /** 97 * rcu_read_lock - mark the beginning of an RCU read-side critical section. 98 * 99 * When synchronize_rcu() is invoked on one CPU while other CPUs 100 * are within RCU read-side critical sections, then the 101 * synchronize_rcu() is guaranteed to block until after all the other 102 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked 103 * on one CPU while other CPUs are within RCU read-side critical 104 * sections, invocation of the corresponding RCU callback is deferred 105 * until after the all the other CPUs exit their critical sections. 106 * 107 * Note, however, that RCU callbacks are permitted to run concurrently 108 * with RCU read-side critical sections. One way that this can happen 109 * is via the following sequence of events: (1) CPU 0 enters an RCU 110 * read-side critical section, (2) CPU 1 invokes call_rcu() to register 111 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, 112 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU 113 * callback is invoked. This is legal, because the RCU read-side critical 114 * section that was running concurrently with the call_rcu() (and which 115 * therefore might be referencing something that the corresponding RCU 116 * callback would free up) has completed before the corresponding 117 * RCU callback is invoked. 118 * 119 * RCU read-side critical sections may be nested. Any deferred actions 120 * will be deferred until the outermost RCU read-side critical section 121 * completes. 122 * 123 * It is illegal to block while in an RCU read-side critical section. 124 */ 125 static inline void rcu_read_lock(void) 126 { 127 __rcu_read_lock(); 128 __acquire(RCU); 129 rcu_read_acquire(); 130 } 131 132 /* 133 * So where is rcu_write_lock()? It does not exist, as there is no 134 * way for writers to lock out RCU readers. This is a feature, not 135 * a bug -- this property is what provides RCU's performance benefits. 136 * Of course, writers must coordinate with each other. The normal 137 * spinlock primitives work well for this, but any other technique may be 138 * used as well. RCU does not care how the writers keep out of each 139 * others' way, as long as they do so. 140 */ 141 142 /** 143 * rcu_read_unlock - marks the end of an RCU read-side critical section. 144 * 145 * See rcu_read_lock() for more information. 146 */ 147 static inline void rcu_read_unlock(void) 148 { 149 rcu_read_release(); 150 __release(RCU); 151 __rcu_read_unlock(); 152 } 153 154 /** 155 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section 156 * 157 * This is equivalent of rcu_read_lock(), but to be used when updates 158 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks 159 * consider completion of a softirq handler to be a quiescent state, 160 * a process in RCU read-side critical section must be protected by 161 * disabling softirqs. Read-side critical sections in interrupt context 162 * can use just rcu_read_lock(). 163 * 164 */ 165 static inline void rcu_read_lock_bh(void) 166 { 167 __rcu_read_lock_bh(); 168 __acquire(RCU_BH); 169 rcu_read_acquire(); 170 } 171 172 /* 173 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section 174 * 175 * See rcu_read_lock_bh() for more information. 176 */ 177 static inline void rcu_read_unlock_bh(void) 178 { 179 rcu_read_release(); 180 __release(RCU_BH); 181 __rcu_read_unlock_bh(); 182 } 183 184 /** 185 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section 186 * 187 * Should be used with either 188 * - synchronize_sched() 189 * or 190 * - call_rcu_sched() and rcu_barrier_sched() 191 * on the write-side to insure proper synchronization. 192 */ 193 static inline void rcu_read_lock_sched(void) 194 { 195 preempt_disable(); 196 __acquire(RCU_SCHED); 197 rcu_read_acquire(); 198 } 199 200 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 201 static inline notrace void rcu_read_lock_sched_notrace(void) 202 { 203 preempt_disable_notrace(); 204 __acquire(RCU_SCHED); 205 } 206 207 /* 208 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section 209 * 210 * See rcu_read_lock_sched for more information. 211 */ 212 static inline void rcu_read_unlock_sched(void) 213 { 214 rcu_read_release(); 215 __release(RCU_SCHED); 216 preempt_enable(); 217 } 218 219 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 220 static inline notrace void rcu_read_unlock_sched_notrace(void) 221 { 222 __release(RCU_SCHED); 223 preempt_enable_notrace(); 224 } 225 226 227 /** 228 * rcu_dereference - fetch an RCU-protected pointer in an 229 * RCU read-side critical section. This pointer may later 230 * be safely dereferenced. 231 * 232 * Inserts memory barriers on architectures that require them 233 * (currently only the Alpha), and, more importantly, documents 234 * exactly which pointers are protected by RCU. 235 */ 236 237 #define rcu_dereference(p) ({ \ 238 typeof(p) _________p1 = ACCESS_ONCE(p); \ 239 smp_read_barrier_depends(); \ 240 (_________p1); \ 241 }) 242 243 /** 244 * rcu_assign_pointer - assign (publicize) a pointer to a newly 245 * initialized structure that will be dereferenced by RCU read-side 246 * critical sections. Returns the value assigned. 247 * 248 * Inserts memory barriers on architectures that require them 249 * (pretty much all of them other than x86), and also prevents 250 * the compiler from reordering the code that initializes the 251 * structure after the pointer assignment. More importantly, this 252 * call documents which pointers will be dereferenced by RCU read-side 253 * code. 254 */ 255 256 #define rcu_assign_pointer(p, v) \ 257 ({ \ 258 if (!__builtin_constant_p(v) || \ 259 ((v) != NULL)) \ 260 smp_wmb(); \ 261 (p) = (v); \ 262 }) 263 264 /* Infrastructure to implement the synchronize_() primitives. */ 265 266 struct rcu_synchronize { 267 struct rcu_head head; 268 struct completion completion; 269 }; 270 271 extern void wakeme_after_rcu(struct rcu_head *head); 272 273 /** 274 * call_rcu - Queue an RCU callback for invocation after a grace period. 275 * @head: structure to be used for queueing the RCU updates. 276 * @func: actual update function to be invoked after the grace period 277 * 278 * The update function will be invoked some time after a full grace 279 * period elapses, in other words after all currently executing RCU 280 * read-side critical sections have completed. RCU read-side critical 281 * sections are delimited by rcu_read_lock() and rcu_read_unlock(), 282 * and may be nested. 283 */ 284 extern void call_rcu(struct rcu_head *head, 285 void (*func)(struct rcu_head *head)); 286 287 /** 288 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. 289 * @head: structure to be used for queueing the RCU updates. 290 * @func: actual update function to be invoked after the grace period 291 * 292 * The update function will be invoked some time after a full grace 293 * period elapses, in other words after all currently executing RCU 294 * read-side critical sections have completed. call_rcu_bh() assumes 295 * that the read-side critical sections end on completion of a softirq 296 * handler. This means that read-side critical sections in process 297 * context must not be interrupted by softirqs. This interface is to be 298 * used when most of the read-side critical sections are in softirq context. 299 * RCU read-side critical sections are delimited by : 300 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. 301 * OR 302 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. 303 * These may be nested. 304 */ 305 extern void call_rcu_bh(struct rcu_head *head, 306 void (*func)(struct rcu_head *head)); 307 308 #endif /* __LINUX_RCUPDATE_H */ 309