Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | /* |
Paul E. McKenney | a71fca5 | 2009-09-18 10:28:19 -0700 | [diff] [blame] | 2 | * Read-Copy Update mechanism for mutual exclusion |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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> |
Paul E. McKenney | a71fca5 | 2009-09-18 10:28:19 -0700 | [diff] [blame] | 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 - |
Paul E. McKenney | a71fca5 | 2009-09-18 10:28:19 -0700 | [diff] [blame] | 29 | * http://lse.sourceforge.net/locking/rcupdate.html |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 30 | * |
| 31 | */ |
| 32 | |
| 33 | #ifndef __LINUX_RCUPDATE_H |
| 34 | #define __LINUX_RCUPDATE_H |
| 35 | |
Paul E. McKenney | 9909875 | 2011-05-31 21:03:55 -0700 | [diff] [blame] | 36 | #include <linux/types.h> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 37 | #include <linux/cache.h> |
| 38 | #include <linux/spinlock.h> |
| 39 | #include <linux/threads.h> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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> |
Paul E. McKenney | 4446a36 | 2008-05-12 21:21:05 +0200 | [diff] [blame] | 43 | #include <linux/completion.h> |
Mathieu Desnoyers | 551d55a | 2010-04-17 08:48:42 -0400 | [diff] [blame] | 44 | #include <linux/debugobjects.h> |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 45 | #include <linux/compiler.h> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 46 | |
Dave Young | e5ab677 | 2010-03-10 15:24:05 -0800 | [diff] [blame] | 47 | #ifdef CONFIG_RCU_TORTURE_TEST |
| 48 | extern int rcutorture_runnable; /* for sysctl */ |
| 49 | #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ |
| 50 | |
Paul E. McKenney | 4a29865 | 2011-04-03 21:33:51 -0700 | [diff] [blame] | 51 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
| 52 | extern void rcutorture_record_test_transition(void); |
| 53 | extern void rcutorture_record_progress(unsigned long vernum); |
| 54 | #else |
| 55 | static inline void rcutorture_record_test_transition(void) |
| 56 | { |
| 57 | } |
| 58 | static inline void rcutorture_record_progress(unsigned long vernum) |
| 59 | { |
| 60 | } |
| 61 | #endif |
| 62 | |
Tejun Heo | e27fc96 | 2010-11-22 21:36:11 -0800 | [diff] [blame] | 63 | #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) |
| 64 | #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) |
Paul E. McKenney | a3dc3fb | 2010-08-13 16:16:25 -0700 | [diff] [blame] | 65 | #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) |
| 66 | #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) |
| 67 | |
Paul E. McKenney | 03b042b | 2009-06-25 09:08:16 -0700 | [diff] [blame] | 68 | /* Exported common interfaces */ |
Paul E. McKenney | 2c42818 | 2011-05-26 22:14:36 -0700 | [diff] [blame] | 69 | |
| 70 | #ifdef CONFIG_PREEMPT_RCU |
| 71 | |
| 72 | /** |
| 73 | * call_rcu() - Queue an RCU callback for invocation after a grace period. |
| 74 | * @head: structure to be used for queueing the RCU updates. |
| 75 | * @func: actual callback function to be invoked after the grace period |
| 76 | * |
| 77 | * The callback function will be invoked some time after a full grace |
| 78 | * period elapses, in other words after all pre-existing RCU read-side |
| 79 | * critical sections have completed. However, the callback function |
| 80 | * might well execute concurrently with RCU read-side critical sections |
| 81 | * that started after call_rcu() was invoked. RCU read-side critical |
| 82 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), |
| 83 | * and may be nested. |
| 84 | */ |
| 85 | extern void call_rcu(struct rcu_head *head, |
| 86 | void (*func)(struct rcu_head *head)); |
| 87 | |
| 88 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
| 89 | |
| 90 | /* In classic RCU, call_rcu() is just call_rcu_sched(). */ |
| 91 | #define call_rcu call_rcu_sched |
| 92 | |
| 93 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
| 94 | |
| 95 | /** |
| 96 | * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. |
| 97 | * @head: structure to be used for queueing the RCU updates. |
| 98 | * @func: actual callback function to be invoked after the grace period |
| 99 | * |
| 100 | * The callback function will be invoked some time after a full grace |
| 101 | * period elapses, in other words after all currently executing RCU |
| 102 | * read-side critical sections have completed. call_rcu_bh() assumes |
| 103 | * that the read-side critical sections end on completion of a softirq |
| 104 | * handler. This means that read-side critical sections in process |
| 105 | * context must not be interrupted by softirqs. This interface is to be |
| 106 | * used when most of the read-side critical sections are in softirq context. |
| 107 | * RCU read-side critical sections are delimited by : |
| 108 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. |
| 109 | * OR |
| 110 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. |
| 111 | * These may be nested. |
| 112 | */ |
| 113 | extern void call_rcu_bh(struct rcu_head *head, |
| 114 | void (*func)(struct rcu_head *head)); |
| 115 | |
| 116 | /** |
| 117 | * call_rcu_sched() - Queue an RCU for invocation after sched grace period. |
| 118 | * @head: structure to be used for queueing the RCU updates. |
| 119 | * @func: actual callback function to be invoked after the grace period |
| 120 | * |
| 121 | * The callback function will be invoked some time after a full grace |
| 122 | * period elapses, in other words after all currently executing RCU |
| 123 | * read-side critical sections have completed. call_rcu_sched() assumes |
| 124 | * that the read-side critical sections end on enabling of preemption |
| 125 | * or on voluntary preemption. |
| 126 | * RCU read-side critical sections are delimited by : |
| 127 | * - rcu_read_lock_sched() and rcu_read_unlock_sched(), |
| 128 | * OR |
| 129 | * anything that disables preemption. |
| 130 | * These may be nested. |
| 131 | */ |
Paul E. McKenney | 7b0b759 | 2010-08-17 14:18:46 -0700 | [diff] [blame] | 132 | extern void call_rcu_sched(struct rcu_head *head, |
| 133 | void (*func)(struct rcu_head *rcu)); |
Paul E. McKenney | 2c42818 | 2011-05-26 22:14:36 -0700 | [diff] [blame] | 134 | |
Paul E. McKenney | 7b0b759 | 2010-08-17 14:18:46 -0700 | [diff] [blame] | 135 | extern void synchronize_sched(void); |
Paul E. McKenney | 03b042b | 2009-06-25 09:08:16 -0700 | [diff] [blame] | 136 | |
Paul E. McKenney | 7b0b759 | 2010-08-17 14:18:46 -0700 | [diff] [blame] | 137 | static inline void __rcu_read_lock_bh(void) |
| 138 | { |
| 139 | local_bh_disable(); |
| 140 | } |
| 141 | |
| 142 | static inline void __rcu_read_unlock_bh(void) |
| 143 | { |
| 144 | local_bh_enable(); |
| 145 | } |
Paul E. McKenney | a682604 | 2009-02-25 18:03:42 -0800 | [diff] [blame] | 146 | |
Paul E. McKenney | a3dc3fb | 2010-08-13 16:16:25 -0700 | [diff] [blame] | 147 | #ifdef CONFIG_PREEMPT_RCU |
| 148 | |
Paul E. McKenney | 7b0b759 | 2010-08-17 14:18:46 -0700 | [diff] [blame] | 149 | extern void __rcu_read_lock(void); |
| 150 | extern void __rcu_read_unlock(void); |
| 151 | void synchronize_rcu(void); |
| 152 | |
Paul E. McKenney | a3dc3fb | 2010-08-13 16:16:25 -0700 | [diff] [blame] | 153 | /* |
| 154 | * Defined as a macro as it is a very low level header included from |
| 155 | * areas that don't even know about current. This gives the rcu_read_lock() |
| 156 | * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other |
| 157 | * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. |
| 158 | */ |
| 159 | #define rcu_preempt_depth() (current->rcu_read_lock_nesting) |
| 160 | |
Paul E. McKenney | 7b0b759 | 2010-08-17 14:18:46 -0700 | [diff] [blame] | 161 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
| 162 | |
| 163 | static inline void __rcu_read_lock(void) |
| 164 | { |
| 165 | preempt_disable(); |
| 166 | } |
| 167 | |
| 168 | static inline void __rcu_read_unlock(void) |
| 169 | { |
| 170 | preempt_enable(); |
| 171 | } |
| 172 | |
| 173 | static inline void synchronize_rcu(void) |
| 174 | { |
| 175 | synchronize_sched(); |
| 176 | } |
| 177 | |
| 178 | static inline int rcu_preempt_depth(void) |
| 179 | { |
| 180 | return 0; |
| 181 | } |
| 182 | |
| 183 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
| 184 | |
| 185 | /* Internal to kernel */ |
Paul E. McKenney | 7b0b759 | 2010-08-17 14:18:46 -0700 | [diff] [blame] | 186 | extern void rcu_sched_qs(int cpu); |
| 187 | extern void rcu_bh_qs(int cpu); |
| 188 | extern void rcu_check_callbacks(int cpu, int user); |
| 189 | struct notifier_block; |
| 190 | |
| 191 | #ifdef CONFIG_NO_HZ |
| 192 | |
| 193 | extern void rcu_enter_nohz(void); |
| 194 | extern void rcu_exit_nohz(void); |
| 195 | |
| 196 | #else /* #ifdef CONFIG_NO_HZ */ |
| 197 | |
| 198 | static inline void rcu_enter_nohz(void) |
| 199 | { |
| 200 | } |
| 201 | |
| 202 | static inline void rcu_exit_nohz(void) |
| 203 | { |
| 204 | } |
| 205 | |
| 206 | #endif /* #else #ifdef CONFIG_NO_HZ */ |
Paul E. McKenney | a3dc3fb | 2010-08-13 16:16:25 -0700 | [diff] [blame] | 207 | |
Paul E. McKenney | 2c42818 | 2011-05-26 22:14:36 -0700 | [diff] [blame] | 208 | /* |
| 209 | * Infrastructure to implement the synchronize_() primitives in |
| 210 | * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. |
| 211 | */ |
| 212 | |
| 213 | typedef void call_rcu_func_t(struct rcu_head *head, |
| 214 | void (*func)(struct rcu_head *head)); |
| 215 | void wait_rcu_gp(call_rcu_func_t crf); |
| 216 | |
Paul E. McKenney | f41d911 | 2009-08-22 13:56:52 -0700 | [diff] [blame] | 217 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
Paul E. McKenney | 64db4cf | 2008-12-18 21:55:32 +0100 | [diff] [blame] | 218 | #include <linux/rcutree.h> |
Paul E. McKenney | a57eb94 | 2010-06-29 16:49:16 -0700 | [diff] [blame] | 219 | #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) |
Paul E. McKenney | 9b1d82f | 2009-10-25 19:03:50 -0700 | [diff] [blame] | 220 | #include <linux/rcutiny.h> |
Paul E. McKenney | 64db4cf | 2008-12-18 21:55:32 +0100 | [diff] [blame] | 221 | #else |
| 222 | #error "Unknown RCU implementation specified to kernel configuration" |
Paul E. McKenney | 6b3ef48 | 2009-08-22 13:56:53 -0700 | [diff] [blame] | 223 | #endif |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 224 | |
Mathieu Desnoyers | 551d55a | 2010-04-17 08:48:42 -0400 | [diff] [blame] | 225 | /* |
| 226 | * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic |
| 227 | * initialization and destruction of rcu_head on the stack. rcu_head structures |
| 228 | * allocated dynamically in the heap or defined statically don't need any |
| 229 | * initialization. |
| 230 | */ |
| 231 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD |
| 232 | extern void init_rcu_head_on_stack(struct rcu_head *head); |
| 233 | extern void destroy_rcu_head_on_stack(struct rcu_head *head); |
| 234 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
Mathieu Desnoyers | 4376030 | 2010-04-17 08:48:39 -0400 | [diff] [blame] | 235 | static inline void init_rcu_head_on_stack(struct rcu_head *head) |
| 236 | { |
| 237 | } |
| 238 | |
| 239 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) |
| 240 | { |
| 241 | } |
Mathieu Desnoyers | 551d55a | 2010-04-17 08:48:42 -0400 | [diff] [blame] | 242 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
Mathieu Desnoyers | 4376030 | 2010-04-17 08:48:39 -0400 | [diff] [blame] | 243 | |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 244 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 245 | |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 246 | extern struct lockdep_map rcu_lock_map; |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 247 | # define rcu_read_acquire() \ |
| 248 | lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 249 | # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 250 | |
| 251 | extern struct lockdep_map rcu_bh_lock_map; |
| 252 | # define rcu_read_acquire_bh() \ |
| 253 | lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
| 254 | # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) |
| 255 | |
| 256 | extern struct lockdep_map rcu_sched_lock_map; |
| 257 | # define rcu_read_acquire_sched() \ |
| 258 | lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
| 259 | # define rcu_read_release_sched() \ |
| 260 | lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) |
| 261 | |
Paul E. McKenney | bc293d6 | 2010-04-15 12:50:39 -0700 | [diff] [blame] | 262 | extern int debug_lockdep_rcu_enabled(void); |
Paul E. McKenney | 54dbf96 | 2010-03-03 07:46:57 -0800 | [diff] [blame] | 263 | |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 264 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 265 | * rcu_read_lock_held() - might we be in RCU read-side critical section? |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 266 | * |
Paul E. McKenney | d20200b | 2010-03-30 10:52:21 -0700 | [diff] [blame] | 267 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU |
| 268 | * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 269 | * this assumes we are in an RCU read-side critical section unless it can |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 270 | * prove otherwise. This is useful for debug checks in functions that |
| 271 | * require that they be called within an RCU read-side critical section. |
Paul E. McKenney | 54dbf96 | 2010-03-03 07:46:57 -0800 | [diff] [blame] | 272 | * |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 273 | * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot |
Paul E. McKenney | 32c141a | 2010-03-30 10:59:28 -0700 | [diff] [blame] | 274 | * and while lockdep is disabled. |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 275 | */ |
| 276 | static inline int rcu_read_lock_held(void) |
| 277 | { |
Paul E. McKenney | 54dbf96 | 2010-03-03 07:46:57 -0800 | [diff] [blame] | 278 | if (!debug_lockdep_rcu_enabled()) |
| 279 | return 1; |
| 280 | return lock_is_held(&rcu_lock_map); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 281 | } |
| 282 | |
Paul E. McKenney | e3818b8 | 2010-03-15 17:03:43 -0700 | [diff] [blame] | 283 | /* |
| 284 | * rcu_read_lock_bh_held() is defined out of line to avoid #include-file |
| 285 | * hell. |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 286 | */ |
Paul E. McKenney | e3818b8 | 2010-03-15 17:03:43 -0700 | [diff] [blame] | 287 | extern int rcu_read_lock_bh_held(void); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 288 | |
| 289 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 290 | * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 291 | * |
Paul E. McKenney | d20200b | 2010-03-30 10:52:21 -0700 | [diff] [blame] | 292 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an |
| 293 | * RCU-sched read-side critical section. In absence of |
| 294 | * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side |
| 295 | * critical section unless it can prove otherwise. Note that disabling |
| 296 | * of preemption (including disabling irqs) counts as an RCU-sched |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 297 | * read-side critical section. This is useful for debug checks in functions |
| 298 | * that required that they be called within an RCU-sched read-side |
| 299 | * critical section. |
Paul E. McKenney | 54dbf96 | 2010-03-03 07:46:57 -0800 | [diff] [blame] | 300 | * |
Paul E. McKenney | 32c141a | 2010-03-30 10:59:28 -0700 | [diff] [blame] | 301 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot |
| 302 | * and while lockdep is disabled. |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 303 | */ |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 304 | #ifdef CONFIG_PREEMPT_COUNT |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 305 | static inline int rcu_read_lock_sched_held(void) |
| 306 | { |
| 307 | int lockdep_opinion = 0; |
| 308 | |
Paul E. McKenney | 54dbf96 | 2010-03-03 07:46:57 -0800 | [diff] [blame] | 309 | if (!debug_lockdep_rcu_enabled()) |
| 310 | return 1; |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 311 | if (debug_locks) |
| 312 | lockdep_opinion = lock_is_held(&rcu_sched_lock_map); |
Lai Jiangshan | 0cff810 | 2010-03-18 12:25:33 -0700 | [diff] [blame] | 313 | return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 314 | } |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 315 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
Paul E. McKenney | e6033e3 | 2010-03-03 17:50:16 -0800 | [diff] [blame] | 316 | static inline int rcu_read_lock_sched_held(void) |
| 317 | { |
| 318 | return 1; |
| 319 | } |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 320 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 321 | |
| 322 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
| 323 | |
| 324 | # define rcu_read_acquire() do { } while (0) |
| 325 | # define rcu_read_release() do { } while (0) |
| 326 | # define rcu_read_acquire_bh() do { } while (0) |
| 327 | # define rcu_read_release_bh() do { } while (0) |
| 328 | # define rcu_read_acquire_sched() do { } while (0) |
| 329 | # define rcu_read_release_sched() do { } while (0) |
| 330 | |
| 331 | static inline int rcu_read_lock_held(void) |
| 332 | { |
| 333 | return 1; |
| 334 | } |
| 335 | |
| 336 | static inline int rcu_read_lock_bh_held(void) |
| 337 | { |
| 338 | return 1; |
| 339 | } |
| 340 | |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 341 | #ifdef CONFIG_PREEMPT_COUNT |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 342 | static inline int rcu_read_lock_sched_held(void) |
| 343 | { |
Paul E. McKenney | bbad937 | 2010-04-02 16:17:17 -0700 | [diff] [blame] | 344 | return preempt_count() != 0 || irqs_disabled(); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 345 | } |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 346 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
Paul E. McKenney | e6033e3 | 2010-03-03 17:50:16 -0800 | [diff] [blame] | 347 | static inline int rcu_read_lock_sched_held(void) |
| 348 | { |
| 349 | return 1; |
| 350 | } |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 351 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 352 | |
| 353 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
| 354 | |
| 355 | #ifdef CONFIG_PROVE_RCU |
| 356 | |
Paul E. McKenney | ee84b82 | 2010-05-06 09:28:41 -0700 | [diff] [blame] | 357 | extern int rcu_my_thread_group_empty(void); |
| 358 | |
Tetsuo Handa | 4221a99 | 2010-06-26 01:08:19 +0900 | [diff] [blame] | 359 | /** |
| 360 | * rcu_lockdep_assert - emit lockdep splat if specified condition not met |
| 361 | * @c: condition to check |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 362 | * @s: informative message |
Tetsuo Handa | 4221a99 | 2010-06-26 01:08:19 +0900 | [diff] [blame] | 363 | */ |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 364 | #define rcu_lockdep_assert(c, s) \ |
Lai Jiangshan | 2b3fc35 | 2010-04-20 16:23:07 +0800 | [diff] [blame] | 365 | do { \ |
| 366 | static bool __warned; \ |
| 367 | if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ |
| 368 | __warned = true; \ |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 369 | lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ |
Lai Jiangshan | 2b3fc35 | 2010-04-20 16:23:07 +0800 | [diff] [blame] | 370 | } \ |
| 371 | } while (0) |
| 372 | |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 373 | #define rcu_sleep_check() \ |
| 374 | do { \ |
| 375 | rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \ |
| 376 | "Illegal context switch in RCU-bh" \ |
| 377 | " read-side critical section"); \ |
| 378 | rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \ |
| 379 | "Illegal context switch in RCU-sched"\ |
| 380 | " read-side critical section"); \ |
| 381 | } while (0) |
| 382 | |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 383 | #else /* #ifdef CONFIG_PROVE_RCU */ |
| 384 | |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 385 | #define rcu_lockdep_assert(c, s) do { } while (0) |
| 386 | #define rcu_sleep_check() do { } while (0) |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 387 | |
| 388 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ |
| 389 | |
| 390 | /* |
| 391 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() |
| 392 | * and rcu_assign_pointer(). Some of these could be folded into their |
| 393 | * callers, but they are left separate in order to ease introduction of |
| 394 | * multiple flavors of pointers to match the multiple flavors of RCU |
| 395 | * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in |
| 396 | * the future. |
| 397 | */ |
Paul E. McKenney | 53ecfba | 2010-09-13 17:24:21 -0700 | [diff] [blame] | 398 | |
| 399 | #ifdef __CHECKER__ |
| 400 | #define rcu_dereference_sparse(p, space) \ |
| 401 | ((void)(((typeof(*p) space *)p) == p)) |
| 402 | #else /* #ifdef __CHECKER__ */ |
| 403 | #define rcu_dereference_sparse(p, space) |
| 404 | #endif /* #else #ifdef __CHECKER__ */ |
| 405 | |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 406 | #define __rcu_access_pointer(p, space) \ |
| 407 | ({ \ |
| 408 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ |
Paul E. McKenney | 53ecfba | 2010-09-13 17:24:21 -0700 | [diff] [blame] | 409 | rcu_dereference_sparse(p, space); \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 410 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
| 411 | }) |
| 412 | #define __rcu_dereference_check(p, c, space) \ |
| 413 | ({ \ |
| 414 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 415 | rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \ |
| 416 | " usage"); \ |
Paul E. McKenney | 53ecfba | 2010-09-13 17:24:21 -0700 | [diff] [blame] | 417 | rcu_dereference_sparse(p, space); \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 418 | smp_read_barrier_depends(); \ |
| 419 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
| 420 | }) |
| 421 | #define __rcu_dereference_protected(p, c, space) \ |
| 422 | ({ \ |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 423 | rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \ |
| 424 | " usage"); \ |
Paul E. McKenney | 53ecfba | 2010-09-13 17:24:21 -0700 | [diff] [blame] | 425 | rcu_dereference_sparse(p, space); \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 426 | ((typeof(*p) __force __kernel *)(p)); \ |
| 427 | }) |
| 428 | |
Paul E. McKenney | a4dd992 | 2011-04-01 07:15:14 -0700 | [diff] [blame] | 429 | #define __rcu_access_index(p, space) \ |
| 430 | ({ \ |
| 431 | typeof(p) _________p1 = ACCESS_ONCE(p); \ |
| 432 | rcu_dereference_sparse(p, space); \ |
| 433 | (_________p1); \ |
| 434 | }) |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 435 | #define __rcu_dereference_index_check(p, c) \ |
| 436 | ({ \ |
| 437 | typeof(p) _________p1 = ACCESS_ONCE(p); \ |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 438 | rcu_lockdep_assert(c, \ |
| 439 | "suspicious rcu_dereference_index_check()" \ |
| 440 | " usage"); \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 441 | smp_read_barrier_depends(); \ |
| 442 | (_________p1); \ |
| 443 | }) |
| 444 | #define __rcu_assign_pointer(p, v, space) \ |
| 445 | ({ \ |
Eric Dumazet | d322f45 | 2011-07-31 22:09:25 -0700 | [diff] [blame] | 446 | smp_wmb(); \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 447 | (p) = (typeof(*v) __force space *)(v); \ |
| 448 | }) |
| 449 | |
| 450 | |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 451 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 452 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing |
| 453 | * @p: The pointer to read |
| 454 | * |
| 455 | * Return the value of the specified RCU-protected pointer, but omit the |
| 456 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful |
| 457 | * when the value of this pointer is accessed, but the pointer is not |
| 458 | * dereferenced, for example, when testing an RCU-protected pointer against |
| 459 | * NULL. Although rcu_access_pointer() may also be used in cases where |
| 460 | * update-side locks prevent the value of the pointer from changing, you |
| 461 | * should instead use rcu_dereference_protected() for this use case. |
| 462 | */ |
| 463 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) |
| 464 | |
| 465 | /** |
| 466 | * rcu_dereference_check() - rcu_dereference with debug checking |
David Howells | c08c68d | 2010-04-09 15:39:11 -0700 | [diff] [blame] | 467 | * @p: The pointer to read, prior to dereferencing |
| 468 | * @c: The conditions under which the dereference will take place |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 469 | * |
David Howells | c08c68d | 2010-04-09 15:39:11 -0700 | [diff] [blame] | 470 | * Do an rcu_dereference(), but check that the conditions under which the |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 471 | * dereference will take place are correct. Typically the conditions |
| 472 | * indicate the various locking conditions that should be held at that |
| 473 | * point. The check should return true if the conditions are satisfied. |
| 474 | * An implicit check for being in an RCU read-side critical section |
| 475 | * (rcu_read_lock()) is included. |
David Howells | c08c68d | 2010-04-09 15:39:11 -0700 | [diff] [blame] | 476 | * |
| 477 | * For example: |
| 478 | * |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 479 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
David Howells | c08c68d | 2010-04-09 15:39:11 -0700 | [diff] [blame] | 480 | * |
| 481 | * could be used to indicate to lockdep that foo->bar may only be dereferenced |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 482 | * if either rcu_read_lock() is held, or that the lock required to replace |
David Howells | c08c68d | 2010-04-09 15:39:11 -0700 | [diff] [blame] | 483 | * the bar struct at foo->bar is held. |
| 484 | * |
| 485 | * Note that the list of conditions may also include indications of when a lock |
| 486 | * need not be held, for example during initialisation or destruction of the |
| 487 | * target struct: |
| 488 | * |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 489 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
David Howells | c08c68d | 2010-04-09 15:39:11 -0700 | [diff] [blame] | 490 | * atomic_read(&foo->usage) == 0); |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 491 | * |
| 492 | * Inserts memory barriers on architectures that require them |
| 493 | * (currently only the Alpha), prevents the compiler from refetching |
| 494 | * (and from merging fetches), and, more importantly, documents exactly |
| 495 | * which pointers are protected by RCU and checks that the pointer is |
| 496 | * annotated as __rcu. |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 497 | */ |
| 498 | #define rcu_dereference_check(p, c) \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 499 | __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 500 | |
Paul E. McKenney | b62730b | 2010-04-09 15:39:10 -0700 | [diff] [blame] | 501 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 502 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking |
| 503 | * @p: The pointer to read, prior to dereferencing |
| 504 | * @c: The conditions under which the dereference will take place |
| 505 | * |
| 506 | * This is the RCU-bh counterpart to rcu_dereference_check(). |
| 507 | */ |
| 508 | #define rcu_dereference_bh_check(p, c) \ |
| 509 | __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) |
| 510 | |
| 511 | /** |
| 512 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
| 513 | * @p: The pointer to read, prior to dereferencing |
| 514 | * @c: The conditions under which the dereference will take place |
| 515 | * |
| 516 | * This is the RCU-sched counterpart to rcu_dereference_check(). |
| 517 | */ |
| 518 | #define rcu_dereference_sched_check(p, c) \ |
| 519 | __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ |
| 520 | __rcu) |
| 521 | |
| 522 | #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ |
| 523 | |
| 524 | /** |
Paul E. McKenney | a4dd992 | 2011-04-01 07:15:14 -0700 | [diff] [blame] | 525 | * rcu_access_index() - fetch RCU index with no dereferencing |
| 526 | * @p: The index to read |
| 527 | * |
| 528 | * Return the value of the specified RCU-protected index, but omit the |
| 529 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful |
| 530 | * when the value of this index is accessed, but the index is not |
| 531 | * dereferenced, for example, when testing an RCU-protected index against |
| 532 | * -1. Although rcu_access_index() may also be used in cases where |
| 533 | * update-side locks prevent the value of the index from changing, you |
| 534 | * should instead use rcu_dereference_index_protected() for this use case. |
| 535 | */ |
| 536 | #define rcu_access_index(p) __rcu_access_index((p), __rcu) |
| 537 | |
| 538 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 539 | * rcu_dereference_index_check() - rcu_dereference for indices with debug checking |
| 540 | * @p: The pointer to read, prior to dereferencing |
| 541 | * @c: The conditions under which the dereference will take place |
| 542 | * |
| 543 | * Similar to rcu_dereference_check(), but omits the sparse checking. |
| 544 | * This allows rcu_dereference_index_check() to be used on integers, |
| 545 | * which can then be used as array indices. Attempting to use |
| 546 | * rcu_dereference_check() on an integer will give compiler warnings |
| 547 | * because the sparse address-space mechanism relies on dereferencing |
| 548 | * the RCU-protected pointer. Dereferencing integers is not something |
| 549 | * that even gcc will put up with. |
| 550 | * |
| 551 | * Note that this function does not implicitly check for RCU read-side |
| 552 | * critical sections. If this function gains lots of uses, it might |
| 553 | * make sense to provide versions for each flavor of RCU, but it does |
| 554 | * not make sense as of early 2010. |
| 555 | */ |
| 556 | #define rcu_dereference_index_check(p, c) \ |
| 557 | __rcu_dereference_index_check((p), (c)) |
| 558 | |
| 559 | /** |
| 560 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented |
| 561 | * @p: The pointer to read, prior to dereferencing |
| 562 | * @c: The conditions under which the dereference will take place |
Paul E. McKenney | b62730b | 2010-04-09 15:39:10 -0700 | [diff] [blame] | 563 | * |
| 564 | * Return the value of the specified RCU-protected pointer, but omit |
| 565 | * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This |
| 566 | * is useful in cases where update-side locks prevent the value of the |
| 567 | * pointer from changing. Please note that this primitive does -not- |
| 568 | * prevent the compiler from repeating this reference or combining it |
| 569 | * with other references, so it should not be used without protection |
| 570 | * of appropriate locks. |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 571 | * |
| 572 | * This function is only for update-side use. Using this function |
| 573 | * when protected only by rcu_read_lock() will result in infrequent |
| 574 | * but very ugly failures. |
Paul E. McKenney | b62730b | 2010-04-09 15:39:10 -0700 | [diff] [blame] | 575 | */ |
| 576 | #define rcu_dereference_protected(p, c) \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 577 | __rcu_dereference_protected((p), (c), __rcu) |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 578 | |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 579 | |
| 580 | /** |
| 581 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
| 582 | * @p: The pointer to read, prior to dereferencing |
| 583 | * |
| 584 | * This is a simple wrapper around rcu_dereference_check(). |
| 585 | */ |
| 586 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
| 587 | |
| 588 | /** |
| 589 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
| 590 | * @p: The pointer to read, prior to dereferencing |
| 591 | * |
| 592 | * Makes rcu_dereference_check() do the dirty work. |
| 593 | */ |
| 594 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) |
| 595 | |
| 596 | /** |
| 597 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing |
| 598 | * @p: The pointer to read, prior to dereferencing |
| 599 | * |
| 600 | * Makes rcu_dereference_check() do the dirty work. |
| 601 | */ |
| 602 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) |
| 603 | |
| 604 | /** |
| 605 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 606 | * |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 607 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 608 | * are within RCU read-side critical sections, then the |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 609 | * synchronize_rcu() is guaranteed to block until after all the other |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 610 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
| 611 | * on one CPU while other CPUs are within RCU read-side critical |
| 612 | * sections, invocation of the corresponding RCU callback is deferred |
| 613 | * until after the all the other CPUs exit their critical sections. |
| 614 | * |
| 615 | * Note, however, that RCU callbacks are permitted to run concurrently |
Paul E. McKenney | 77d8485 | 2010-07-08 17:38:59 -0700 | [diff] [blame] | 616 | * with new RCU read-side critical sections. One way that this can happen |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 617 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
| 618 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register |
| 619 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, |
| 620 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU |
| 621 | * callback is invoked. This is legal, because the RCU read-side critical |
| 622 | * section that was running concurrently with the call_rcu() (and which |
| 623 | * therefore might be referencing something that the corresponding RCU |
| 624 | * callback would free up) has completed before the corresponding |
| 625 | * RCU callback is invoked. |
| 626 | * |
| 627 | * RCU read-side critical sections may be nested. Any deferred actions |
| 628 | * will be deferred until the outermost RCU read-side critical section |
| 629 | * completes. |
| 630 | * |
Paul E. McKenney | 9079fd7 | 2010-08-07 21:59:54 -0700 | [diff] [blame] | 631 | * You can avoid reading and understanding the next paragraph by |
| 632 | * following this rule: don't put anything in an rcu_read_lock() RCU |
| 633 | * read-side critical section that would block in a !PREEMPT kernel. |
| 634 | * But if you want the full story, read on! |
| 635 | * |
| 636 | * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it |
| 637 | * is illegal to block while in an RCU read-side critical section. In |
| 638 | * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) |
| 639 | * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may |
| 640 | * be preempted, but explicit blocking is illegal. Finally, in preemptible |
| 641 | * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, |
| 642 | * RCU read-side critical sections may be preempted and they may also |
| 643 | * block, but only when acquiring spinlocks that are subject to priority |
| 644 | * inheritance. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 645 | */ |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 646 | static inline void rcu_read_lock(void) |
| 647 | { |
| 648 | __rcu_read_lock(); |
| 649 | __acquire(RCU); |
| 650 | rcu_read_acquire(); |
| 651 | } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 652 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 653 | /* |
| 654 | * So where is rcu_write_lock()? It does not exist, as there is no |
| 655 | * way for writers to lock out RCU readers. This is a feature, not |
| 656 | * a bug -- this property is what provides RCU's performance benefits. |
| 657 | * Of course, writers must coordinate with each other. The normal |
| 658 | * spinlock primitives work well for this, but any other technique may be |
| 659 | * used as well. RCU does not care how the writers keep out of each |
| 660 | * others' way, as long as they do so. |
| 661 | */ |
Paul E. McKenney | 3d76c08 | 2009-09-28 07:46:32 -0700 | [diff] [blame] | 662 | |
| 663 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 664 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
Paul E. McKenney | 3d76c08 | 2009-09-28 07:46:32 -0700 | [diff] [blame] | 665 | * |
| 666 | * See rcu_read_lock() for more information. |
| 667 | */ |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 668 | static inline void rcu_read_unlock(void) |
| 669 | { |
| 670 | rcu_read_release(); |
| 671 | __release(RCU); |
| 672 | __rcu_read_unlock(); |
| 673 | } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 674 | |
| 675 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 676 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 677 | * |
| 678 | * This is equivalent of rcu_read_lock(), but to be used when updates |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 679 | * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since |
| 680 | * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a |
| 681 | * softirq handler to be a quiescent state, a process in RCU read-side |
| 682 | * critical section must be protected by disabling softirqs. Read-side |
| 683 | * critical sections in interrupt context can use just rcu_read_lock(), |
| 684 | * though this should at least be commented to avoid confusing people |
| 685 | * reading the code. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 686 | */ |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 687 | static inline void rcu_read_lock_bh(void) |
| 688 | { |
| 689 | __rcu_read_lock_bh(); |
| 690 | __acquire(RCU_BH); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 691 | rcu_read_acquire_bh(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 692 | } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 693 | |
| 694 | /* |
| 695 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section |
| 696 | * |
| 697 | * See rcu_read_lock_bh() for more information. |
| 698 | */ |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 699 | static inline void rcu_read_unlock_bh(void) |
| 700 | { |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 701 | rcu_read_release_bh(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 702 | __release(RCU_BH); |
| 703 | __rcu_read_unlock_bh(); |
| 704 | } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 705 | |
| 706 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 707 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
Mathieu Desnoyers | 1c50b72 | 2008-09-29 11:06:46 -0400 | [diff] [blame] | 708 | * |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 709 | * This is equivalent of rcu_read_lock(), but to be used when updates |
| 710 | * are being done using call_rcu_sched() or synchronize_rcu_sched(). |
| 711 | * Read-side critical sections can also be introduced by anything that |
| 712 | * disables preemption, including local_irq_disable() and friends. |
Mathieu Desnoyers | 1c50b72 | 2008-09-29 11:06:46 -0400 | [diff] [blame] | 713 | */ |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 714 | static inline void rcu_read_lock_sched(void) |
| 715 | { |
| 716 | preempt_disable(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 717 | __acquire(RCU_SCHED); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 718 | rcu_read_acquire_sched(); |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 719 | } |
Paul E. McKenney | 1eba8f8 | 2009-09-23 09:50:42 -0700 | [diff] [blame] | 720 | |
| 721 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
Paul E. McKenney | 7c614d6 | 2009-08-24 09:42:00 -0700 | [diff] [blame] | 722 | static inline notrace void rcu_read_lock_sched_notrace(void) |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 723 | { |
| 724 | preempt_disable_notrace(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 725 | __acquire(RCU_SCHED); |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 726 | } |
Mathieu Desnoyers | 1c50b72 | 2008-09-29 11:06:46 -0400 | [diff] [blame] | 727 | |
| 728 | /* |
| 729 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section |
| 730 | * |
| 731 | * See rcu_read_lock_sched for more information. |
| 732 | */ |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 733 | static inline void rcu_read_unlock_sched(void) |
| 734 | { |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 735 | rcu_read_release_sched(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 736 | __release(RCU_SCHED); |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 737 | preempt_enable(); |
| 738 | } |
Paul E. McKenney | 1eba8f8 | 2009-09-23 09:50:42 -0700 | [diff] [blame] | 739 | |
| 740 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
Paul E. McKenney | 7c614d6 | 2009-08-24 09:42:00 -0700 | [diff] [blame] | 741 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 742 | { |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 743 | __release(RCU_SCHED); |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 744 | preempt_enable_notrace(); |
| 745 | } |
Mathieu Desnoyers | 1c50b72 | 2008-09-29 11:06:46 -0400 | [diff] [blame] | 746 | |
Mathieu Desnoyers | 1c50b72 | 2008-09-29 11:06:46 -0400 | [diff] [blame] | 747 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 748 | * rcu_assign_pointer() - assign to RCU-protected pointer |
| 749 | * @p: pointer to assign to |
| 750 | * @v: value to assign (publish) |
Paul E. McKenney | c26d34a | 2010-02-22 17:04:46 -0800 | [diff] [blame] | 751 | * |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 752 | * Assigns the specified value to the specified RCU-protected |
| 753 | * pointer, ensuring that any concurrent RCU readers will see |
| 754 | * any prior initialization. Returns the value assigned. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 755 | * |
| 756 | * Inserts memory barriers on architectures that require them |
Paul E. McKenney | 6846c0c | 2011-07-31 22:33:02 -0700 | [diff] [blame^] | 757 | * (which is most of them), and also prevents the compiler from |
| 758 | * reordering the code that initializes the structure after the pointer |
| 759 | * assignment. More importantly, this call documents which pointers |
| 760 | * will be dereferenced by RCU read-side code. |
| 761 | * |
| 762 | * In some special cases, you may use RCU_INIT_POINTER() instead |
| 763 | * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due |
| 764 | * to the fact that it does not constrain either the CPU or the compiler. |
| 765 | * That said, using RCU_INIT_POINTER() when you should have used |
| 766 | * rcu_assign_pointer() is a very bad thing that results in |
| 767 | * impossible-to-diagnose memory corruption. So please be careful. |
| 768 | * See the RCU_INIT_POINTER() comment header for details. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 769 | */ |
Paul E. McKenney | d99c4f6 | 2008-02-06 01:37:25 -0800 | [diff] [blame] | 770 | #define rcu_assign_pointer(p, v) \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 771 | __rcu_assign_pointer((p), (v), __rcu) |
| 772 | |
| 773 | /** |
| 774 | * RCU_INIT_POINTER() - initialize an RCU protected pointer |
| 775 | * |
Paul E. McKenney | 6846c0c | 2011-07-31 22:33:02 -0700 | [diff] [blame^] | 776 | * Initialize an RCU-protected pointer in special cases where readers |
| 777 | * do not need ordering constraints on the CPU or the compiler. These |
| 778 | * special cases are: |
| 779 | * |
| 780 | * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or- |
| 781 | * 2. The caller has taken whatever steps are required to prevent |
| 782 | * RCU readers from concurrently accessing this pointer -or- |
| 783 | * 3. The referenced data structure has already been exposed to |
| 784 | * readers either at compile time or via rcu_assign_pointer() -and- |
| 785 | * a. You have not made -any- reader-visible changes to |
| 786 | * this structure since then -or- |
| 787 | * b. It is OK for readers accessing this structure from its |
| 788 | * new location to see the old state of the structure. (For |
| 789 | * example, the changes were to statistical counters or to |
| 790 | * other state where exact synchronization is not required.) |
| 791 | * |
| 792 | * Failure to follow these rules governing use of RCU_INIT_POINTER() will |
| 793 | * result in impossible-to-diagnose memory corruption. As in the structures |
| 794 | * will look OK in crash dumps, but any concurrent RCU readers might |
| 795 | * see pre-initialized values of the referenced data structure. So |
| 796 | * please be very careful how you use RCU_INIT_POINTER()!!! |
| 797 | * |
| 798 | * If you are creating an RCU-protected linked structure that is accessed |
| 799 | * by a single external-to-structure RCU-protected pointer, then you may |
| 800 | * use RCU_INIT_POINTER() to initialize the internal RCU-protected |
| 801 | * pointers, but you must use rcu_assign_pointer() to initialize the |
| 802 | * external-to-structure pointer -after- you have completely initialized |
| 803 | * the reader-accessible portions of the linked structure. |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 804 | */ |
| 805 | #define RCU_INIT_POINTER(p, v) \ |
| 806 | p = (typeof(*v) __force __rcu *)(v) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 807 | |
Lai Jiangshan | 9ab1544 | 2011-03-18 11:15:47 +0800 | [diff] [blame] | 808 | static __always_inline bool __is_kfree_rcu_offset(unsigned long offset) |
| 809 | { |
| 810 | return offset < 4096; |
| 811 | } |
| 812 | |
| 813 | static __always_inline |
| 814 | void __kfree_rcu(struct rcu_head *head, unsigned long offset) |
| 815 | { |
| 816 | typedef void (*rcu_callback)(struct rcu_head *); |
| 817 | |
| 818 | BUILD_BUG_ON(!__builtin_constant_p(offset)); |
| 819 | |
| 820 | /* See the kfree_rcu() header comment. */ |
| 821 | BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); |
| 822 | |
| 823 | call_rcu(head, (rcu_callback)offset); |
| 824 | } |
| 825 | |
Lai Jiangshan | 9ab1544 | 2011-03-18 11:15:47 +0800 | [diff] [blame] | 826 | /** |
| 827 | * kfree_rcu() - kfree an object after a grace period. |
| 828 | * @ptr: pointer to kfree |
| 829 | * @rcu_head: the name of the struct rcu_head within the type of @ptr. |
| 830 | * |
| 831 | * Many rcu callbacks functions just call kfree() on the base structure. |
| 832 | * These functions are trivial, but their size adds up, and furthermore |
| 833 | * when they are used in a kernel module, that module must invoke the |
| 834 | * high-latency rcu_barrier() function at module-unload time. |
| 835 | * |
| 836 | * The kfree_rcu() function handles this issue. Rather than encoding a |
| 837 | * function address in the embedded rcu_head structure, kfree_rcu() instead |
| 838 | * encodes the offset of the rcu_head structure within the base structure. |
| 839 | * Because the functions are not allowed in the low-order 4096 bytes of |
| 840 | * kernel virtual memory, offsets up to 4095 bytes can be accommodated. |
| 841 | * If the offset is larger than 4095 bytes, a compile-time error will |
| 842 | * be generated in __kfree_rcu(). If this error is triggered, you can |
| 843 | * either fall back to use of call_rcu() or rearrange the structure to |
| 844 | * position the rcu_head structure into the first 4096 bytes. |
| 845 | * |
| 846 | * Note that the allowable offset might decrease in the future, for example, |
| 847 | * to allow something like kmem_cache_free_rcu(). |
| 848 | */ |
| 849 | #define kfree_rcu(ptr, rcu_head) \ |
| 850 | __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) |
| 851 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 852 | #endif /* __LINUX_RCUPDATE_H */ |