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); |
Paul E. McKenney | 91afaf3 | 2011-10-02 07:44:32 -0700 | [diff] [blame^] | 54 | extern void do_trace_rcu_torture_read(char *rcutorturename, |
| 55 | struct rcu_head *rhp); |
Paul E. McKenney | 4a29865 | 2011-04-03 21:33:51 -0700 | [diff] [blame] | 56 | #else |
| 57 | static inline void rcutorture_record_test_transition(void) |
| 58 | { |
| 59 | } |
| 60 | static inline void rcutorture_record_progress(unsigned long vernum) |
| 61 | { |
| 62 | } |
Paul E. McKenney | 91afaf3 | 2011-10-02 07:44:32 -0700 | [diff] [blame^] | 63 | #ifdef CONFIG_RCU_TRACE |
| 64 | extern void do_trace_rcu_torture_read(char *rcutorturename, |
| 65 | struct rcu_head *rhp); |
| 66 | #else |
| 67 | #define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0) |
| 68 | #endif |
Paul E. McKenney | 4a29865 | 2011-04-03 21:33:51 -0700 | [diff] [blame] | 69 | #endif |
| 70 | |
Tejun Heo | e27fc96 | 2010-11-22 21:36:11 -0800 | [diff] [blame] | 71 | #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) |
| 72 | #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) |
Paul E. McKenney | a3dc3fb | 2010-08-13 16:16:25 -0700 | [diff] [blame] | 73 | #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) |
| 74 | #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) |
| 75 | |
Paul E. McKenney | 03b042b | 2009-06-25 09:08:16 -0700 | [diff] [blame] | 76 | /* Exported common interfaces */ |
Paul E. McKenney | 2c42818 | 2011-05-26 22:14:36 -0700 | [diff] [blame] | 77 | |
| 78 | #ifdef CONFIG_PREEMPT_RCU |
| 79 | |
| 80 | /** |
| 81 | * call_rcu() - Queue an RCU callback for invocation after a grace period. |
| 82 | * @head: structure to be used for queueing the RCU updates. |
| 83 | * @func: actual callback function to be invoked after the grace period |
| 84 | * |
| 85 | * The callback function will be invoked some time after a full grace |
| 86 | * period elapses, in other words after all pre-existing RCU read-side |
| 87 | * critical sections have completed. However, the callback function |
| 88 | * might well execute concurrently with RCU read-side critical sections |
| 89 | * that started after call_rcu() was invoked. RCU read-side critical |
| 90 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), |
| 91 | * and may be nested. |
| 92 | */ |
| 93 | extern void call_rcu(struct rcu_head *head, |
| 94 | void (*func)(struct rcu_head *head)); |
| 95 | |
| 96 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
| 97 | |
| 98 | /* In classic RCU, call_rcu() is just call_rcu_sched(). */ |
| 99 | #define call_rcu call_rcu_sched |
| 100 | |
| 101 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
| 102 | |
| 103 | /** |
| 104 | * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. |
| 105 | * @head: structure to be used for queueing the RCU updates. |
| 106 | * @func: actual callback function to be invoked after the grace period |
| 107 | * |
| 108 | * The callback function will be invoked some time after a full grace |
| 109 | * period elapses, in other words after all currently executing RCU |
| 110 | * read-side critical sections have completed. call_rcu_bh() assumes |
| 111 | * that the read-side critical sections end on completion of a softirq |
| 112 | * handler. This means that read-side critical sections in process |
| 113 | * context must not be interrupted by softirqs. This interface is to be |
| 114 | * used when most of the read-side critical sections are in softirq context. |
| 115 | * RCU read-side critical sections are delimited by : |
| 116 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. |
| 117 | * OR |
| 118 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. |
| 119 | * These may be nested. |
| 120 | */ |
| 121 | extern void call_rcu_bh(struct rcu_head *head, |
| 122 | void (*func)(struct rcu_head *head)); |
| 123 | |
| 124 | /** |
| 125 | * call_rcu_sched() - Queue an RCU for invocation after sched grace period. |
| 126 | * @head: structure to be used for queueing the RCU updates. |
| 127 | * @func: actual callback function to be invoked after the grace period |
| 128 | * |
| 129 | * The callback function will be invoked some time after a full grace |
| 130 | * period elapses, in other words after all currently executing RCU |
| 131 | * read-side critical sections have completed. call_rcu_sched() assumes |
| 132 | * that the read-side critical sections end on enabling of preemption |
| 133 | * or on voluntary preemption. |
| 134 | * RCU read-side critical sections are delimited by : |
| 135 | * - rcu_read_lock_sched() and rcu_read_unlock_sched(), |
| 136 | * OR |
| 137 | * anything that disables preemption. |
| 138 | * These may be nested. |
| 139 | */ |
Paul E. McKenney | 7b0b759 | 2010-08-17 14:18:46 -0700 | [diff] [blame] | 140 | extern void call_rcu_sched(struct rcu_head *head, |
| 141 | void (*func)(struct rcu_head *rcu)); |
Paul E. McKenney | 2c42818 | 2011-05-26 22:14:36 -0700 | [diff] [blame] | 142 | |
Paul E. McKenney | 7b0b759 | 2010-08-17 14:18:46 -0700 | [diff] [blame] | 143 | extern void synchronize_sched(void); |
Paul E. McKenney | 03b042b | 2009-06-25 09:08:16 -0700 | [diff] [blame] | 144 | |
Paul E. McKenney | a3dc3fb | 2010-08-13 16:16:25 -0700 | [diff] [blame] | 145 | #ifdef CONFIG_PREEMPT_RCU |
| 146 | |
Paul E. McKenney | 7b0b759 | 2010-08-17 14:18:46 -0700 | [diff] [blame] | 147 | extern void __rcu_read_lock(void); |
| 148 | extern void __rcu_read_unlock(void); |
| 149 | void synchronize_rcu(void); |
| 150 | |
Paul E. McKenney | a3dc3fb | 2010-08-13 16:16:25 -0700 | [diff] [blame] | 151 | /* |
| 152 | * Defined as a macro as it is a very low level header included from |
| 153 | * areas that don't even know about current. This gives the rcu_read_lock() |
| 154 | * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other |
| 155 | * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. |
| 156 | */ |
| 157 | #define rcu_preempt_depth() (current->rcu_read_lock_nesting) |
| 158 | |
Paul E. McKenney | 7b0b759 | 2010-08-17 14:18:46 -0700 | [diff] [blame] | 159 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
| 160 | |
| 161 | static inline void __rcu_read_lock(void) |
| 162 | { |
| 163 | preempt_disable(); |
| 164 | } |
| 165 | |
| 166 | static inline void __rcu_read_unlock(void) |
| 167 | { |
| 168 | preempt_enable(); |
| 169 | } |
| 170 | |
| 171 | static inline void synchronize_rcu(void) |
| 172 | { |
| 173 | synchronize_sched(); |
| 174 | } |
| 175 | |
| 176 | static inline int rcu_preempt_depth(void) |
| 177 | { |
| 178 | return 0; |
| 179 | } |
| 180 | |
| 181 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
| 182 | |
| 183 | /* Internal to kernel */ |
Paul E. McKenney | 7b0b759 | 2010-08-17 14:18:46 -0700 | [diff] [blame] | 184 | extern void rcu_sched_qs(int cpu); |
| 185 | extern void rcu_bh_qs(int cpu); |
| 186 | extern void rcu_check_callbacks(int cpu, int user); |
| 187 | struct notifier_block; |
Paul E. McKenney | 9b2e4f1 | 2011-09-30 12:10:22 -0700 | [diff] [blame] | 188 | extern void rcu_idle_enter(void); |
| 189 | extern void rcu_idle_exit(void); |
| 190 | extern void rcu_irq_enter(void); |
| 191 | extern void rcu_irq_exit(void); |
Paul E. McKenney | a3dc3fb | 2010-08-13 16:16:25 -0700 | [diff] [blame] | 192 | |
Paul E. McKenney | 2c42818 | 2011-05-26 22:14:36 -0700 | [diff] [blame] | 193 | /* |
| 194 | * Infrastructure to implement the synchronize_() primitives in |
| 195 | * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. |
| 196 | */ |
| 197 | |
| 198 | typedef void call_rcu_func_t(struct rcu_head *head, |
| 199 | void (*func)(struct rcu_head *head)); |
| 200 | void wait_rcu_gp(call_rcu_func_t crf); |
| 201 | |
Paul E. McKenney | f41d911 | 2009-08-22 13:56:52 -0700 | [diff] [blame] | 202 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
Paul E. McKenney | 64db4cf | 2008-12-18 21:55:32 +0100 | [diff] [blame] | 203 | #include <linux/rcutree.h> |
Paul E. McKenney | a57eb94 | 2010-06-29 16:49:16 -0700 | [diff] [blame] | 204 | #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) |
Paul E. McKenney | 9b1d82f | 2009-10-25 19:03:50 -0700 | [diff] [blame] | 205 | #include <linux/rcutiny.h> |
Paul E. McKenney | 64db4cf | 2008-12-18 21:55:32 +0100 | [diff] [blame] | 206 | #else |
| 207 | #error "Unknown RCU implementation specified to kernel configuration" |
Paul E. McKenney | 6b3ef48 | 2009-08-22 13:56:53 -0700 | [diff] [blame] | 208 | #endif |
Paul E. McKenney | 01c1c66 | 2008-01-25 21:08:24 +0100 | [diff] [blame] | 209 | |
Mathieu Desnoyers | 551d55a | 2010-04-17 08:48:42 -0400 | [diff] [blame] | 210 | /* |
| 211 | * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic |
| 212 | * initialization and destruction of rcu_head on the stack. rcu_head structures |
| 213 | * allocated dynamically in the heap or defined statically don't need any |
| 214 | * initialization. |
| 215 | */ |
| 216 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD |
| 217 | extern void init_rcu_head_on_stack(struct rcu_head *head); |
| 218 | extern void destroy_rcu_head_on_stack(struct rcu_head *head); |
| 219 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
Mathieu Desnoyers | 4376030 | 2010-04-17 08:48:39 -0400 | [diff] [blame] | 220 | static inline void init_rcu_head_on_stack(struct rcu_head *head) |
| 221 | { |
| 222 | } |
| 223 | |
| 224 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) |
| 225 | { |
| 226 | } |
Mathieu Desnoyers | 551d55a | 2010-04-17 08:48:42 -0400 | [diff] [blame] | 227 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
Mathieu Desnoyers | 4376030 | 2010-04-17 08:48:39 -0400 | [diff] [blame] | 228 | |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 229 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 230 | |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 231 | extern struct lockdep_map rcu_lock_map; |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 232 | # define rcu_read_acquire() \ |
| 233 | 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] | 234 | # 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] | 235 | |
| 236 | extern struct lockdep_map rcu_bh_lock_map; |
| 237 | # define rcu_read_acquire_bh() \ |
| 238 | lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
| 239 | # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) |
| 240 | |
| 241 | extern struct lockdep_map rcu_sched_lock_map; |
| 242 | # define rcu_read_acquire_sched() \ |
| 243 | lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
| 244 | # define rcu_read_release_sched() \ |
| 245 | lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) |
| 246 | |
Paul E. McKenney | bc293d6 | 2010-04-15 12:50:39 -0700 | [diff] [blame] | 247 | extern int debug_lockdep_rcu_enabled(void); |
Paul E. McKenney | 54dbf96 | 2010-03-03 07:46:57 -0800 | [diff] [blame] | 248 | |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 249 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 250 | * 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] | 251 | * |
Paul E. McKenney | d20200b | 2010-03-30 10:52:21 -0700 | [diff] [blame] | 252 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU |
| 253 | * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 254 | * 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] | 255 | * prove otherwise. This is useful for debug checks in functions that |
| 256 | * 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] | 257 | * |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 258 | * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot |
Paul E. McKenney | 32c141a | 2010-03-30 10:59:28 -0700 | [diff] [blame] | 259 | * and while lockdep is disabled. |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 260 | */ |
| 261 | static inline int rcu_read_lock_held(void) |
| 262 | { |
Paul E. McKenney | 54dbf96 | 2010-03-03 07:46:57 -0800 | [diff] [blame] | 263 | if (!debug_lockdep_rcu_enabled()) |
| 264 | return 1; |
| 265 | return lock_is_held(&rcu_lock_map); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 266 | } |
| 267 | |
Paul E. McKenney | e3818b8 | 2010-03-15 17:03:43 -0700 | [diff] [blame] | 268 | /* |
| 269 | * rcu_read_lock_bh_held() is defined out of line to avoid #include-file |
| 270 | * hell. |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 271 | */ |
Paul E. McKenney | e3818b8 | 2010-03-15 17:03:43 -0700 | [diff] [blame] | 272 | extern int rcu_read_lock_bh_held(void); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 273 | |
| 274 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 275 | * 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] | 276 | * |
Paul E. McKenney | d20200b | 2010-03-30 10:52:21 -0700 | [diff] [blame] | 277 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an |
| 278 | * RCU-sched read-side critical section. In absence of |
| 279 | * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side |
| 280 | * critical section unless it can prove otherwise. Note that disabling |
| 281 | * of preemption (including disabling irqs) counts as an RCU-sched |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 282 | * read-side critical section. This is useful for debug checks in functions |
| 283 | * that required that they be called within an RCU-sched read-side |
| 284 | * critical section. |
Paul E. McKenney | 54dbf96 | 2010-03-03 07:46:57 -0800 | [diff] [blame] | 285 | * |
Paul E. McKenney | 32c141a | 2010-03-30 10:59:28 -0700 | [diff] [blame] | 286 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot |
| 287 | * and while lockdep is disabled. |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 288 | */ |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 289 | #ifdef CONFIG_PREEMPT_COUNT |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 290 | static inline int rcu_read_lock_sched_held(void) |
| 291 | { |
| 292 | int lockdep_opinion = 0; |
| 293 | |
Paul E. McKenney | 54dbf96 | 2010-03-03 07:46:57 -0800 | [diff] [blame] | 294 | if (!debug_lockdep_rcu_enabled()) |
| 295 | return 1; |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 296 | if (debug_locks) |
| 297 | lockdep_opinion = lock_is_held(&rcu_sched_lock_map); |
Lai Jiangshan | 0cff810 | 2010-03-18 12:25:33 -0700 | [diff] [blame] | 298 | return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 299 | } |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 300 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
Paul E. McKenney | e6033e3 | 2010-03-03 17:50:16 -0800 | [diff] [blame] | 301 | static inline int rcu_read_lock_sched_held(void) |
| 302 | { |
| 303 | return 1; |
| 304 | } |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 305 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 306 | |
| 307 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
| 308 | |
| 309 | # define rcu_read_acquire() do { } while (0) |
| 310 | # define rcu_read_release() do { } while (0) |
| 311 | # define rcu_read_acquire_bh() do { } while (0) |
| 312 | # define rcu_read_release_bh() do { } while (0) |
| 313 | # define rcu_read_acquire_sched() do { } while (0) |
| 314 | # define rcu_read_release_sched() do { } while (0) |
| 315 | |
| 316 | static inline int rcu_read_lock_held(void) |
| 317 | { |
| 318 | return 1; |
| 319 | } |
| 320 | |
| 321 | static inline int rcu_read_lock_bh_held(void) |
| 322 | { |
| 323 | return 1; |
| 324 | } |
| 325 | |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 326 | #ifdef CONFIG_PREEMPT_COUNT |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 327 | static inline int rcu_read_lock_sched_held(void) |
| 328 | { |
Paul E. McKenney | bbad937 | 2010-04-02 16:17:17 -0700 | [diff] [blame] | 329 | return preempt_count() != 0 || irqs_disabled(); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 330 | } |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 331 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
Paul E. McKenney | e6033e3 | 2010-03-03 17:50:16 -0800 | [diff] [blame] | 332 | static inline int rcu_read_lock_sched_held(void) |
| 333 | { |
| 334 | return 1; |
| 335 | } |
Frederic Weisbecker | bdd4e85 | 2011-06-08 01:13:27 +0200 | [diff] [blame] | 336 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 337 | |
| 338 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
| 339 | |
| 340 | #ifdef CONFIG_PROVE_RCU |
| 341 | |
Paul E. McKenney | ee84b82 | 2010-05-06 09:28:41 -0700 | [diff] [blame] | 342 | extern int rcu_my_thread_group_empty(void); |
| 343 | |
Tetsuo Handa | 4221a99 | 2010-06-26 01:08:19 +0900 | [diff] [blame] | 344 | /** |
| 345 | * rcu_lockdep_assert - emit lockdep splat if specified condition not met |
| 346 | * @c: condition to check |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 347 | * @s: informative message |
Tetsuo Handa | 4221a99 | 2010-06-26 01:08:19 +0900 | [diff] [blame] | 348 | */ |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 349 | #define rcu_lockdep_assert(c, s) \ |
Lai Jiangshan | 2b3fc35 | 2010-04-20 16:23:07 +0800 | [diff] [blame] | 350 | do { \ |
| 351 | static bool __warned; \ |
| 352 | if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ |
| 353 | __warned = true; \ |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 354 | lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ |
Lai Jiangshan | 2b3fc35 | 2010-04-20 16:23:07 +0800 | [diff] [blame] | 355 | } \ |
| 356 | } while (0) |
| 357 | |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 358 | #define rcu_sleep_check() \ |
| 359 | do { \ |
| 360 | rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \ |
| 361 | "Illegal context switch in RCU-bh" \ |
| 362 | " read-side critical section"); \ |
| 363 | rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \ |
| 364 | "Illegal context switch in RCU-sched"\ |
| 365 | " read-side critical section"); \ |
| 366 | } while (0) |
| 367 | |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 368 | #else /* #ifdef CONFIG_PROVE_RCU */ |
| 369 | |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 370 | #define rcu_lockdep_assert(c, s) do { } while (0) |
| 371 | #define rcu_sleep_check() do { } while (0) |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 372 | |
| 373 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ |
| 374 | |
| 375 | /* |
| 376 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() |
| 377 | * and rcu_assign_pointer(). Some of these could be folded into their |
| 378 | * callers, but they are left separate in order to ease introduction of |
| 379 | * multiple flavors of pointers to match the multiple flavors of RCU |
| 380 | * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in |
| 381 | * the future. |
| 382 | */ |
Paul E. McKenney | 53ecfba | 2010-09-13 17:24:21 -0700 | [diff] [blame] | 383 | |
| 384 | #ifdef __CHECKER__ |
| 385 | #define rcu_dereference_sparse(p, space) \ |
| 386 | ((void)(((typeof(*p) space *)p) == p)) |
| 387 | #else /* #ifdef __CHECKER__ */ |
| 388 | #define rcu_dereference_sparse(p, space) |
| 389 | #endif /* #else #ifdef __CHECKER__ */ |
| 390 | |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 391 | #define __rcu_access_pointer(p, space) \ |
| 392 | ({ \ |
| 393 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ |
Paul E. McKenney | 53ecfba | 2010-09-13 17:24:21 -0700 | [diff] [blame] | 394 | rcu_dereference_sparse(p, space); \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 395 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
| 396 | }) |
| 397 | #define __rcu_dereference_check(p, c, space) \ |
| 398 | ({ \ |
| 399 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 400 | rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \ |
| 401 | " usage"); \ |
Paul E. McKenney | 53ecfba | 2010-09-13 17:24:21 -0700 | [diff] [blame] | 402 | rcu_dereference_sparse(p, space); \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 403 | smp_read_barrier_depends(); \ |
| 404 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
| 405 | }) |
| 406 | #define __rcu_dereference_protected(p, c, space) \ |
| 407 | ({ \ |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 408 | rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \ |
| 409 | " usage"); \ |
Paul E. McKenney | 53ecfba | 2010-09-13 17:24:21 -0700 | [diff] [blame] | 410 | rcu_dereference_sparse(p, space); \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 411 | ((typeof(*p) __force __kernel *)(p)); \ |
| 412 | }) |
| 413 | |
Paul E. McKenney | a4dd992 | 2011-04-01 07:15:14 -0700 | [diff] [blame] | 414 | #define __rcu_access_index(p, space) \ |
| 415 | ({ \ |
| 416 | typeof(p) _________p1 = ACCESS_ONCE(p); \ |
| 417 | rcu_dereference_sparse(p, space); \ |
| 418 | (_________p1); \ |
| 419 | }) |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 420 | #define __rcu_dereference_index_check(p, c) \ |
| 421 | ({ \ |
| 422 | typeof(p) _________p1 = ACCESS_ONCE(p); \ |
Paul E. McKenney | b3fbab0 | 2011-05-24 08:31:09 -0700 | [diff] [blame] | 423 | rcu_lockdep_assert(c, \ |
| 424 | "suspicious rcu_dereference_index_check()" \ |
| 425 | " usage"); \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 426 | smp_read_barrier_depends(); \ |
| 427 | (_________p1); \ |
| 428 | }) |
| 429 | #define __rcu_assign_pointer(p, v, space) \ |
| 430 | ({ \ |
Eric Dumazet | d322f45 | 2011-07-31 22:09:25 -0700 | [diff] [blame] | 431 | smp_wmb(); \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 432 | (p) = (typeof(*v) __force space *)(v); \ |
| 433 | }) |
| 434 | |
| 435 | |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 436 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 437 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing |
| 438 | * @p: The pointer to read |
| 439 | * |
| 440 | * Return the value of the specified RCU-protected pointer, but omit the |
| 441 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful |
| 442 | * when the value of this pointer is accessed, but the pointer is not |
| 443 | * dereferenced, for example, when testing an RCU-protected pointer against |
| 444 | * NULL. Although rcu_access_pointer() may also be used in cases where |
| 445 | * update-side locks prevent the value of the pointer from changing, you |
| 446 | * should instead use rcu_dereference_protected() for this use case. |
| 447 | */ |
| 448 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) |
| 449 | |
| 450 | /** |
| 451 | * rcu_dereference_check() - rcu_dereference with debug checking |
David Howells | c08c68d | 2010-04-09 15:39:11 -0700 | [diff] [blame] | 452 | * @p: The pointer to read, prior to dereferencing |
| 453 | * @c: The conditions under which the dereference will take place |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 454 | * |
David Howells | c08c68d | 2010-04-09 15:39:11 -0700 | [diff] [blame] | 455 | * 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] | 456 | * dereference will take place are correct. Typically the conditions |
| 457 | * indicate the various locking conditions that should be held at that |
| 458 | * point. The check should return true if the conditions are satisfied. |
| 459 | * An implicit check for being in an RCU read-side critical section |
| 460 | * (rcu_read_lock()) is included. |
David Howells | c08c68d | 2010-04-09 15:39:11 -0700 | [diff] [blame] | 461 | * |
| 462 | * For example: |
| 463 | * |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 464 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
David Howells | c08c68d | 2010-04-09 15:39:11 -0700 | [diff] [blame] | 465 | * |
| 466 | * 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] | 467 | * 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] | 468 | * the bar struct at foo->bar is held. |
| 469 | * |
| 470 | * Note that the list of conditions may also include indications of when a lock |
| 471 | * need not be held, for example during initialisation or destruction of the |
| 472 | * target struct: |
| 473 | * |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 474 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
David Howells | c08c68d | 2010-04-09 15:39:11 -0700 | [diff] [blame] | 475 | * atomic_read(&foo->usage) == 0); |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 476 | * |
| 477 | * Inserts memory barriers on architectures that require them |
| 478 | * (currently only the Alpha), prevents the compiler from refetching |
| 479 | * (and from merging fetches), and, more importantly, documents exactly |
| 480 | * which pointers are protected by RCU and checks that the pointer is |
| 481 | * annotated as __rcu. |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 482 | */ |
| 483 | #define rcu_dereference_check(p, c) \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 484 | __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 485 | |
Paul E. McKenney | b62730b | 2010-04-09 15:39:10 -0700 | [diff] [blame] | 486 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 487 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking |
| 488 | * @p: The pointer to read, prior to dereferencing |
| 489 | * @c: The conditions under which the dereference will take place |
| 490 | * |
| 491 | * This is the RCU-bh counterpart to rcu_dereference_check(). |
| 492 | */ |
| 493 | #define rcu_dereference_bh_check(p, c) \ |
| 494 | __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) |
| 495 | |
| 496 | /** |
| 497 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
| 498 | * @p: The pointer to read, prior to dereferencing |
| 499 | * @c: The conditions under which the dereference will take place |
| 500 | * |
| 501 | * This is the RCU-sched counterpart to rcu_dereference_check(). |
| 502 | */ |
| 503 | #define rcu_dereference_sched_check(p, c) \ |
| 504 | __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ |
| 505 | __rcu) |
| 506 | |
| 507 | #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ |
| 508 | |
| 509 | /** |
Paul E. McKenney | a4dd992 | 2011-04-01 07:15:14 -0700 | [diff] [blame] | 510 | * rcu_access_index() - fetch RCU index with no dereferencing |
| 511 | * @p: The index to read |
| 512 | * |
| 513 | * Return the value of the specified RCU-protected index, but omit the |
| 514 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful |
| 515 | * when the value of this index is accessed, but the index is not |
| 516 | * dereferenced, for example, when testing an RCU-protected index against |
| 517 | * -1. Although rcu_access_index() may also be used in cases where |
| 518 | * update-side locks prevent the value of the index from changing, you |
| 519 | * should instead use rcu_dereference_index_protected() for this use case. |
| 520 | */ |
| 521 | #define rcu_access_index(p) __rcu_access_index((p), __rcu) |
| 522 | |
| 523 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 524 | * rcu_dereference_index_check() - rcu_dereference for indices with debug checking |
| 525 | * @p: The pointer to read, prior to dereferencing |
| 526 | * @c: The conditions under which the dereference will take place |
| 527 | * |
| 528 | * Similar to rcu_dereference_check(), but omits the sparse checking. |
| 529 | * This allows rcu_dereference_index_check() to be used on integers, |
| 530 | * which can then be used as array indices. Attempting to use |
| 531 | * rcu_dereference_check() on an integer will give compiler warnings |
| 532 | * because the sparse address-space mechanism relies on dereferencing |
| 533 | * the RCU-protected pointer. Dereferencing integers is not something |
| 534 | * that even gcc will put up with. |
| 535 | * |
| 536 | * Note that this function does not implicitly check for RCU read-side |
| 537 | * critical sections. If this function gains lots of uses, it might |
| 538 | * make sense to provide versions for each flavor of RCU, but it does |
| 539 | * not make sense as of early 2010. |
| 540 | */ |
| 541 | #define rcu_dereference_index_check(p, c) \ |
| 542 | __rcu_dereference_index_check((p), (c)) |
| 543 | |
| 544 | /** |
| 545 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented |
| 546 | * @p: The pointer to read, prior to dereferencing |
| 547 | * @c: The conditions under which the dereference will take place |
Paul E. McKenney | b62730b | 2010-04-09 15:39:10 -0700 | [diff] [blame] | 548 | * |
| 549 | * Return the value of the specified RCU-protected pointer, but omit |
| 550 | * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This |
| 551 | * is useful in cases where update-side locks prevent the value of the |
| 552 | * pointer from changing. Please note that this primitive does -not- |
| 553 | * prevent the compiler from repeating this reference or combining it |
| 554 | * with other references, so it should not be used without protection |
| 555 | * of appropriate locks. |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 556 | * |
| 557 | * This function is only for update-side use. Using this function |
| 558 | * when protected only by rcu_read_lock() will result in infrequent |
| 559 | * but very ugly failures. |
Paul E. McKenney | b62730b | 2010-04-09 15:39:10 -0700 | [diff] [blame] | 560 | */ |
| 561 | #define rcu_dereference_protected(p, c) \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 562 | __rcu_dereference_protected((p), (c), __rcu) |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 563 | |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 564 | |
| 565 | /** |
| 566 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
| 567 | * @p: The pointer to read, prior to dereferencing |
| 568 | * |
| 569 | * This is a simple wrapper around rcu_dereference_check(). |
| 570 | */ |
| 571 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
| 572 | |
| 573 | /** |
| 574 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
| 575 | * @p: The pointer to read, prior to dereferencing |
| 576 | * |
| 577 | * Makes rcu_dereference_check() do the dirty work. |
| 578 | */ |
| 579 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) |
| 580 | |
| 581 | /** |
| 582 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing |
| 583 | * @p: The pointer to read, prior to dereferencing |
| 584 | * |
| 585 | * Makes rcu_dereference_check() do the dirty work. |
| 586 | */ |
| 587 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) |
| 588 | |
| 589 | /** |
| 590 | * 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] | 591 | * |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 592 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 593 | * are within RCU read-side critical sections, then the |
Paul E. McKenney | 9b06e81 | 2005-05-01 08:59:04 -0700 | [diff] [blame] | 594 | * synchronize_rcu() is guaranteed to block until after all the other |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 595 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
| 596 | * on one CPU while other CPUs are within RCU read-side critical |
| 597 | * sections, invocation of the corresponding RCU callback is deferred |
| 598 | * until after the all the other CPUs exit their critical sections. |
| 599 | * |
| 600 | * Note, however, that RCU callbacks are permitted to run concurrently |
Paul E. McKenney | 77d8485 | 2010-07-08 17:38:59 -0700 | [diff] [blame] | 601 | * 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] | 602 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
| 603 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register |
| 604 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, |
| 605 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU |
| 606 | * callback is invoked. This is legal, because the RCU read-side critical |
| 607 | * section that was running concurrently with the call_rcu() (and which |
| 608 | * therefore might be referencing something that the corresponding RCU |
| 609 | * callback would free up) has completed before the corresponding |
| 610 | * RCU callback is invoked. |
| 611 | * |
| 612 | * RCU read-side critical sections may be nested. Any deferred actions |
| 613 | * will be deferred until the outermost RCU read-side critical section |
| 614 | * completes. |
| 615 | * |
Paul E. McKenney | 9079fd7 | 2010-08-07 21:59:54 -0700 | [diff] [blame] | 616 | * You can avoid reading and understanding the next paragraph by |
| 617 | * following this rule: don't put anything in an rcu_read_lock() RCU |
| 618 | * read-side critical section that would block in a !PREEMPT kernel. |
| 619 | * But if you want the full story, read on! |
| 620 | * |
| 621 | * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it |
| 622 | * is illegal to block while in an RCU read-side critical section. In |
| 623 | * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) |
| 624 | * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may |
| 625 | * be preempted, but explicit blocking is illegal. Finally, in preemptible |
| 626 | * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, |
| 627 | * RCU read-side critical sections may be preempted and they may also |
| 628 | * block, but only when acquiring spinlocks that are subject to priority |
| 629 | * inheritance. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 630 | */ |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 631 | static inline void rcu_read_lock(void) |
| 632 | { |
| 633 | __rcu_read_lock(); |
| 634 | __acquire(RCU); |
| 635 | rcu_read_acquire(); |
| 636 | } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 637 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 638 | /* |
| 639 | * So where is rcu_write_lock()? It does not exist, as there is no |
| 640 | * way for writers to lock out RCU readers. This is a feature, not |
| 641 | * a bug -- this property is what provides RCU's performance benefits. |
| 642 | * Of course, writers must coordinate with each other. The normal |
| 643 | * spinlock primitives work well for this, but any other technique may be |
| 644 | * used as well. RCU does not care how the writers keep out of each |
| 645 | * others' way, as long as they do so. |
| 646 | */ |
Paul E. McKenney | 3d76c08 | 2009-09-28 07:46:32 -0700 | [diff] [blame] | 647 | |
| 648 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 649 | * 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] | 650 | * |
| 651 | * See rcu_read_lock() for more information. |
| 652 | */ |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 653 | static inline void rcu_read_unlock(void) |
| 654 | { |
| 655 | rcu_read_release(); |
| 656 | __release(RCU); |
| 657 | __rcu_read_unlock(); |
| 658 | } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 659 | |
| 660 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 661 | * 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] | 662 | * |
| 663 | * 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] | 664 | * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since |
| 665 | * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a |
| 666 | * softirq handler to be a quiescent state, a process in RCU read-side |
| 667 | * critical section must be protected by disabling softirqs. Read-side |
| 668 | * critical sections in interrupt context can use just rcu_read_lock(), |
| 669 | * though this should at least be commented to avoid confusing people |
| 670 | * reading the code. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 671 | */ |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 672 | static inline void rcu_read_lock_bh(void) |
| 673 | { |
Paul E. McKenney | 6206ab9 | 2011-08-01 06:22:11 -0700 | [diff] [blame] | 674 | local_bh_disable(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 675 | __acquire(RCU_BH); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 676 | rcu_read_acquire_bh(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 677 | } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 678 | |
| 679 | /* |
| 680 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section |
| 681 | * |
| 682 | * See rcu_read_lock_bh() for more information. |
| 683 | */ |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 684 | static inline void rcu_read_unlock_bh(void) |
| 685 | { |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 686 | rcu_read_release_bh(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 687 | __release(RCU_BH); |
Paul E. McKenney | 6206ab9 | 2011-08-01 06:22:11 -0700 | [diff] [blame] | 688 | local_bh_enable(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 689 | } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 690 | |
| 691 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 692 | * 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] | 693 | * |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 694 | * This is equivalent of rcu_read_lock(), but to be used when updates |
| 695 | * are being done using call_rcu_sched() or synchronize_rcu_sched(). |
| 696 | * Read-side critical sections can also be introduced by anything that |
| 697 | * disables preemption, including local_irq_disable() and friends. |
Mathieu Desnoyers | 1c50b72 | 2008-09-29 11:06:46 -0400 | [diff] [blame] | 698 | */ |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 699 | static inline void rcu_read_lock_sched(void) |
| 700 | { |
| 701 | preempt_disable(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 702 | __acquire(RCU_SCHED); |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 703 | rcu_read_acquire_sched(); |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 704 | } |
Paul E. McKenney | 1eba8f8 | 2009-09-23 09:50:42 -0700 | [diff] [blame] | 705 | |
| 706 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
Paul E. McKenney | 7c614d6 | 2009-08-24 09:42:00 -0700 | [diff] [blame] | 707 | static inline notrace void rcu_read_lock_sched_notrace(void) |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 708 | { |
| 709 | preempt_disable_notrace(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 710 | __acquire(RCU_SCHED); |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 711 | } |
Mathieu Desnoyers | 1c50b72 | 2008-09-29 11:06:46 -0400 | [diff] [blame] | 712 | |
| 713 | /* |
| 714 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section |
| 715 | * |
| 716 | * See rcu_read_lock_sched for more information. |
| 717 | */ |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 718 | static inline void rcu_read_unlock_sched(void) |
| 719 | { |
Paul E. McKenney | 632ee20 | 2010-02-22 17:04:45 -0800 | [diff] [blame] | 720 | rcu_read_release_sched(); |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 721 | __release(RCU_SCHED); |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 722 | preempt_enable(); |
| 723 | } |
Paul E. McKenney | 1eba8f8 | 2009-09-23 09:50:42 -0700 | [diff] [blame] | 724 | |
| 725 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
Paul E. McKenney | 7c614d6 | 2009-08-24 09:42:00 -0700 | [diff] [blame] | 726 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 727 | { |
Paul E. McKenney | bc33f24 | 2009-08-22 13:56:47 -0700 | [diff] [blame] | 728 | __release(RCU_SCHED); |
Paul E. McKenney | d6714c2 | 2009-08-22 13:56:46 -0700 | [diff] [blame] | 729 | preempt_enable_notrace(); |
| 730 | } |
Mathieu Desnoyers | 1c50b72 | 2008-09-29 11:06:46 -0400 | [diff] [blame] | 731 | |
Mathieu Desnoyers | 1c50b72 | 2008-09-29 11:06:46 -0400 | [diff] [blame] | 732 | /** |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 733 | * rcu_assign_pointer() - assign to RCU-protected pointer |
| 734 | * @p: pointer to assign to |
| 735 | * @v: value to assign (publish) |
Paul E. McKenney | c26d34a | 2010-02-22 17:04:46 -0800 | [diff] [blame] | 736 | * |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 737 | * Assigns the specified value to the specified RCU-protected |
| 738 | * pointer, ensuring that any concurrent RCU readers will see |
| 739 | * any prior initialization. Returns the value assigned. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 740 | * |
| 741 | * Inserts memory barriers on architectures that require them |
Paul E. McKenney | 6846c0c | 2011-07-31 22:33:02 -0700 | [diff] [blame] | 742 | * (which is most of them), and also prevents the compiler from |
| 743 | * reordering the code that initializes the structure after the pointer |
| 744 | * assignment. More importantly, this call documents which pointers |
| 745 | * will be dereferenced by RCU read-side code. |
| 746 | * |
| 747 | * In some special cases, you may use RCU_INIT_POINTER() instead |
| 748 | * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due |
| 749 | * to the fact that it does not constrain either the CPU or the compiler. |
| 750 | * That said, using RCU_INIT_POINTER() when you should have used |
| 751 | * rcu_assign_pointer() is a very bad thing that results in |
| 752 | * impossible-to-diagnose memory corruption. So please be careful. |
| 753 | * See the RCU_INIT_POINTER() comment header for details. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 754 | */ |
Paul E. McKenney | d99c4f6 | 2008-02-06 01:37:25 -0800 | [diff] [blame] | 755 | #define rcu_assign_pointer(p, v) \ |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 756 | __rcu_assign_pointer((p), (v), __rcu) |
| 757 | |
| 758 | /** |
| 759 | * RCU_INIT_POINTER() - initialize an RCU protected pointer |
| 760 | * |
Paul E. McKenney | 6846c0c | 2011-07-31 22:33:02 -0700 | [diff] [blame] | 761 | * Initialize an RCU-protected pointer in special cases where readers |
| 762 | * do not need ordering constraints on the CPU or the compiler. These |
| 763 | * special cases are: |
| 764 | * |
| 765 | * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or- |
| 766 | * 2. The caller has taken whatever steps are required to prevent |
| 767 | * RCU readers from concurrently accessing this pointer -or- |
| 768 | * 3. The referenced data structure has already been exposed to |
| 769 | * readers either at compile time or via rcu_assign_pointer() -and- |
| 770 | * a. You have not made -any- reader-visible changes to |
| 771 | * this structure since then -or- |
| 772 | * b. It is OK for readers accessing this structure from its |
| 773 | * new location to see the old state of the structure. (For |
| 774 | * example, the changes were to statistical counters or to |
| 775 | * other state where exact synchronization is not required.) |
| 776 | * |
| 777 | * Failure to follow these rules governing use of RCU_INIT_POINTER() will |
| 778 | * result in impossible-to-diagnose memory corruption. As in the structures |
| 779 | * will look OK in crash dumps, but any concurrent RCU readers might |
| 780 | * see pre-initialized values of the referenced data structure. So |
| 781 | * please be very careful how you use RCU_INIT_POINTER()!!! |
| 782 | * |
| 783 | * If you are creating an RCU-protected linked structure that is accessed |
| 784 | * by a single external-to-structure RCU-protected pointer, then you may |
| 785 | * use RCU_INIT_POINTER() to initialize the internal RCU-protected |
| 786 | * pointers, but you must use rcu_assign_pointer() to initialize the |
| 787 | * external-to-structure pointer -after- you have completely initialized |
| 788 | * the reader-accessible portions of the linked structure. |
Paul E. McKenney | ca5ecdd | 2010-04-28 14:39:09 -0700 | [diff] [blame] | 789 | */ |
| 790 | #define RCU_INIT_POINTER(p, v) \ |
| 791 | p = (typeof(*v) __force __rcu *)(v) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 792 | |
Lai Jiangshan | 9ab1544 | 2011-03-18 11:15:47 +0800 | [diff] [blame] | 793 | static __always_inline bool __is_kfree_rcu_offset(unsigned long offset) |
| 794 | { |
| 795 | return offset < 4096; |
| 796 | } |
| 797 | |
| 798 | static __always_inline |
| 799 | void __kfree_rcu(struct rcu_head *head, unsigned long offset) |
| 800 | { |
| 801 | typedef void (*rcu_callback)(struct rcu_head *); |
| 802 | |
| 803 | BUILD_BUG_ON(!__builtin_constant_p(offset)); |
| 804 | |
| 805 | /* See the kfree_rcu() header comment. */ |
| 806 | BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); |
| 807 | |
| 808 | call_rcu(head, (rcu_callback)offset); |
| 809 | } |
| 810 | |
Lai Jiangshan | 9ab1544 | 2011-03-18 11:15:47 +0800 | [diff] [blame] | 811 | /** |
| 812 | * kfree_rcu() - kfree an object after a grace period. |
| 813 | * @ptr: pointer to kfree |
| 814 | * @rcu_head: the name of the struct rcu_head within the type of @ptr. |
| 815 | * |
| 816 | * Many rcu callbacks functions just call kfree() on the base structure. |
| 817 | * These functions are trivial, but their size adds up, and furthermore |
| 818 | * when they are used in a kernel module, that module must invoke the |
| 819 | * high-latency rcu_barrier() function at module-unload time. |
| 820 | * |
| 821 | * The kfree_rcu() function handles this issue. Rather than encoding a |
| 822 | * function address in the embedded rcu_head structure, kfree_rcu() instead |
| 823 | * encodes the offset of the rcu_head structure within the base structure. |
| 824 | * Because the functions are not allowed in the low-order 4096 bytes of |
| 825 | * kernel virtual memory, offsets up to 4095 bytes can be accommodated. |
| 826 | * If the offset is larger than 4095 bytes, a compile-time error will |
| 827 | * be generated in __kfree_rcu(). If this error is triggered, you can |
| 828 | * either fall back to use of call_rcu() or rearrange the structure to |
| 829 | * position the rcu_head structure into the first 4096 bytes. |
| 830 | * |
| 831 | * Note that the allowable offset might decrease in the future, for example, |
| 832 | * to allow something like kmem_cache_free_rcu(). |
| 833 | */ |
| 834 | #define kfree_rcu(ptr, rcu_head) \ |
| 835 | __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) |
| 836 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 837 | #endif /* __LINUX_RCUPDATE_H */ |