Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 | * |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 18 | * Copyright IBM Corporation, 2001 |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 19 | * |
| 20 | * Author: Dipankar Sarma <dipankar@in.ibm.com> |
| 21 | * |
Josh Triplett | 595182b | 2006-10-04 02:17:21 -0700 | [diff] [blame] | 22 | * Based on the original work by Paul McKenney <paulmck@us.ibm.com> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 36 | #include <linux/cache.h> |
| 37 | #include <linux/spinlock.h> |
| 38 | #include <linux/threads.h> |
| 39 | #include <linux/percpu.h> |
| 40 | #include <linux/cpumask.h> |
| 41 | #include <linux/seqlock.h> |
Peter Zijlstra | 851a67b | 2007-10-11 22:11:12 +0200 | [diff] [blame] | 42 | #include <linux/lockdep.h> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 | |
Paul E. McKenney | e260be6 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 54 | #ifdef CONFIG_CLASSIC_RCU |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 55 | #include <linux/rcuclassic.h> |
Paul E. McKenney | e260be6 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 56 | #else /* #ifdef CONFIG_CLASSIC_RCU */ |
| 57 | #include <linux/rcupreempt.h> |
| 58 | #endif /* #else #ifdef CONFIG_CLASSIC_RCU */ |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 59 | |
Dipankar Sarma | 8b6490e | 2005-09-09 13:04:07 -0700 | [diff] [blame] | 60 | #define RCU_HEAD_INIT { .next = NULL, .func = NULL } |
| 61 | #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 62 | #define INIT_RCU_HEAD(ptr) do { \ |
| 63 | (ptr)->next = NULL; (ptr)->func = NULL; \ |
| 64 | } while (0) |
| 65 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 66 | /** |
| 67 | * rcu_read_lock - mark the beginning of an RCU read-side critical section. |
| 68 | * |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 69 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 70 | * are within RCU read-side critical sections, then the |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 71 | * synchronize_rcu() is guaranteed to block until after all the other |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 72 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
| 73 | * on one CPU while other CPUs are within RCU read-side critical |
| 74 | * sections, invocation of the corresponding RCU callback is deferred |
| 75 | * until after the all the other CPUs exit their critical sections. |
| 76 | * |
| 77 | * Note, however, that RCU callbacks are permitted to run concurrently |
| 78 | * with RCU read-side critical sections. One way that this can happen |
| 79 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
| 80 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register |
| 81 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, |
| 82 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU |
| 83 | * callback is invoked. This is legal, because the RCU read-side critical |
| 84 | * section that was running concurrently with the call_rcu() (and which |
| 85 | * therefore might be referencing something that the corresponding RCU |
| 86 | * callback would free up) has completed before the corresponding |
| 87 | * RCU callback is invoked. |
| 88 | * |
| 89 | * RCU read-side critical sections may be nested. Any deferred actions |
| 90 | * will be deferred until the outermost RCU read-side critical section |
| 91 | * completes. |
| 92 | * |
| 93 | * It is illegal to block while in an RCU read-side critical section. |
| 94 | */ |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 95 | #define rcu_read_lock() __rcu_read_lock() |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 96 | |
| 97 | /** |
| 98 | * rcu_read_unlock - marks the end of an RCU read-side critical section. |
| 99 | * |
| 100 | * See rcu_read_lock() for more information. |
| 101 | */ |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 102 | |
| 103 | /* |
| 104 | * So where is rcu_write_lock()? It does not exist, as there is no |
| 105 | * way for writers to lock out RCU readers. This is a feature, not |
| 106 | * a bug -- this property is what provides RCU's performance benefits. |
| 107 | * Of course, writers must coordinate with each other. The normal |
| 108 | * spinlock primitives work well for this, but any other technique may be |
| 109 | * used as well. RCU does not care how the writers keep out of each |
| 110 | * others' way, as long as they do so. |
| 111 | */ |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 112 | #define rcu_read_unlock() __rcu_read_unlock() |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 113 | |
| 114 | /** |
| 115 | * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section |
| 116 | * |
| 117 | * This is equivalent of rcu_read_lock(), but to be used when updates |
| 118 | * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks |
| 119 | * consider completion of a softirq handler to be a quiescent state, |
| 120 | * a process in RCU read-side critical section must be protected by |
| 121 | * disabling softirqs. Read-side critical sections in interrupt context |
| 122 | * can use just rcu_read_lock(). |
| 123 | * |
| 124 | */ |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 125 | #define rcu_read_lock_bh() __rcu_read_lock_bh() |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 126 | |
| 127 | /* |
| 128 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section |
| 129 | * |
| 130 | * See rcu_read_lock_bh() for more information. |
| 131 | */ |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 132 | #define rcu_read_unlock_bh() __rcu_read_unlock_bh() |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 133 | |
Paul E. McKenney | 97b4303 | 2007-10-16 23:26:04 -0700 | [diff] [blame] | 134 | /* |
| 135 | * Prevent the compiler from merging or refetching accesses. The compiler |
| 136 | * is also forbidden from reordering successive instances of ACCESS_ONCE(), |
| 137 | * but only when the compiler is aware of some particular ordering. One way |
| 138 | * to make the compiler aware of ordering is to put the two invocations of |
| 139 | * ACCESS_ONCE() in different C statements. |
| 140 | * |
| 141 | * This macro does absolutely -nothing- to prevent the CPU from reordering, |
| 142 | * merging, or refetching absolutely anything at any time. |
| 143 | */ |
| 144 | #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) |
| 145 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 146 | /** |
| 147 | * rcu_dereference - fetch an RCU-protected pointer in an |
| 148 | * RCU read-side critical section. This pointer may later |
| 149 | * be safely dereferenced. |
| 150 | * |
| 151 | * Inserts memory barriers on architectures that require them |
| 152 | * (currently only the Alpha), and, more importantly, documents |
| 153 | * exactly which pointers are protected by RCU. |
| 154 | */ |
| 155 | |
| 156 | #define rcu_dereference(p) ({ \ |
Paul E. McKenney | 97b4303 | 2007-10-16 23:26:04 -0700 | [diff] [blame] | 157 | typeof(p) _________p1 = ACCESS_ONCE(p); \ |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 158 | smp_read_barrier_depends(); \ |
| 159 | (_________p1); \ |
| 160 | }) |
| 161 | |
| 162 | /** |
| 163 | * rcu_assign_pointer - assign (publicize) a pointer to a newly |
| 164 | * initialized structure that will be dereferenced by RCU read-side |
| 165 | * critical sections. Returns the value assigned. |
| 166 | * |
| 167 | * Inserts memory barriers on architectures that require them |
| 168 | * (pretty much all of them other than x86), and also prevents |
| 169 | * the compiler from reordering the code that initializes the |
| 170 | * structure after the pointer assignment. More importantly, this |
| 171 | * call documents which pointers will be dereferenced by RCU read-side |
| 172 | * code. |
| 173 | */ |
| 174 | |
Paul E. McKenney | d99c4f6 | 2008-02-06 01:37:25 -0800 | [diff] [blame] | 175 | #define rcu_assign_pointer(p, v) \ |
| 176 | ({ \ |
| 177 | if (!__builtin_constant_p(v) || \ |
| 178 | ((v) != NULL)) \ |
| 179 | smp_wmb(); \ |
| 180 | (p) = (v); \ |
| 181 | }) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 182 | |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 183 | /** |
| 184 | * synchronize_sched - block until all CPUs have exited any non-preemptive |
| 185 | * kernel code sequences. |
| 186 | * |
| 187 | * This means that all preempt_disable code sequences, including NMI and |
| 188 | * hardware-interrupt handlers, in progress on entry will have completed |
| 189 | * before this primitive returns. However, this does not guarantee that |
Paul E. McKenney | bb3b9cf1 | 2006-02-03 03:04:38 -0800 | [diff] [blame] | 190 | * softirq handlers will have completed, since in some kernels, these |
| 191 | * handlers can run in process context, and can block. |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 192 | * |
Paul E. McKenney | d83015b | 2006-06-23 02:05:51 -0700 | [diff] [blame] | 193 | * This primitive provides the guarantees made by the (now removed) |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 194 | * synchronize_kernel() API. In contrast, synchronize_rcu() only |
| 195 | * guarantees that rcu_read_lock() sections will have completed. |
Paul E. McKenney | bb3b9cf1 | 2006-02-03 03:04:38 -0800 | [diff] [blame] | 196 | * In "classic RCU", these two guarantees happen to be one and |
| 197 | * the same, but can differ in realtime RCU implementations. |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 198 | */ |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 199 | #define synchronize_sched() __synchronize_sched() |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 200 | |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 201 | /** |
| 202 | * call_rcu - Queue an RCU callback for invocation after a grace period. |
| 203 | * @head: structure to be used for queueing the RCU updates. |
| 204 | * @func: actual update function to be invoked after the grace period |
| 205 | * |
| 206 | * The update function will be invoked some time after a full grace |
| 207 | * period elapses, in other words after all currently executing RCU |
| 208 | * read-side critical sections have completed. RCU read-side critical |
| 209 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), |
| 210 | * and may be nested. |
| 211 | */ |
| 212 | extern void call_rcu(struct rcu_head *head, |
| 213 | void (*func)(struct rcu_head *head)); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 214 | |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 215 | /** |
| 216 | * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. |
| 217 | * @head: structure to be used for queueing the RCU updates. |
| 218 | * @func: actual update function to be invoked after the grace period |
| 219 | * |
| 220 | * The update function will be invoked some time after a full grace |
| 221 | * period elapses, in other words after all currently executing RCU |
| 222 | * read-side critical sections have completed. call_rcu_bh() assumes |
| 223 | * that the read-side critical sections end on completion of a softirq |
| 224 | * handler. This means that read-side critical sections in process |
| 225 | * context must not be interrupted by softirqs. This interface is to be |
| 226 | * used when most of the read-side critical sections are in softirq context. |
| 227 | * RCU read-side critical sections are delimited by : |
| 228 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. |
| 229 | * OR |
| 230 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. |
| 231 | * These may be nested. |
| 232 | */ |
| 233 | extern void call_rcu_bh(struct rcu_head *head, |
| 234 | void (*func)(struct rcu_head *head)); |
| 235 | |
| 236 | /* Exported common interfaces */ |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 237 | extern void synchronize_rcu(void); |
Dipankar Sarma | ab4720e | 2005-12-12 00:37:05 -0800 | [diff] [blame] | 238 | extern void rcu_barrier(void); |
Paul E. McKenney | e260be6 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 239 | extern long rcu_batches_completed(void); |
| 240 | extern long rcu_batches_completed_bh(void); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 241 | |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 242 | /* Internal to kernel */ |
| 243 | extern void rcu_init(void); |
Paul E. McKenney | e260be6 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 244 | extern int rcu_needs_cpu(int cpu); |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 245 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 246 | #endif /* __LINUX_RCUPDATE_H */ |