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