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1da177e4 | 1 | /* |
a71fca58 | 2 | * Read-Copy Update mechanism for mutual exclusion |
1da177e4 LT |
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 | * | |
01c1c660 | 18 | * Copyright IBM Corporation, 2001 |
1da177e4 LT |
19 | * |
20 | * Author: Dipankar Sarma <dipankar@in.ibm.com> | |
a71fca58 | 21 | * |
595182bc | 22 | * Based on the original work by Paul McKenney <paulmck@us.ibm.com> |
1da177e4 LT |
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 - | |
a71fca58 | 29 | * http://lse.sourceforge.net/locking/rcupdate.html |
1da177e4 LT |
30 | * |
31 | */ | |
32 | ||
33 | #ifndef __LINUX_RCUPDATE_H | |
34 | #define __LINUX_RCUPDATE_H | |
35 | ||
99098751 | 36 | #include <linux/types.h> |
1da177e4 LT |
37 | #include <linux/cache.h> |
38 | #include <linux/spinlock.h> | |
39 | #include <linux/threads.h> | |
1da177e4 LT |
40 | #include <linux/cpumask.h> |
41 | #include <linux/seqlock.h> | |
851a67b8 | 42 | #include <linux/lockdep.h> |
4446a36f | 43 | #include <linux/completion.h> |
551d55a9 | 44 | #include <linux/debugobjects.h> |
ca5ecddf | 45 | #include <linux/compiler.h> |
1da177e4 | 46 | |
e5ab6772 DY |
47 | #ifdef CONFIG_RCU_TORTURE_TEST |
48 | extern int rcutorture_runnable; /* for sysctl */ | |
49 | #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ | |
50 | ||
4a298656 PM |
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 | ||
e27fc964 TH |
63 | #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) |
64 | #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) | |
a3dc3fb1 PM |
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 | ||
03b042bf | 68 | /* Exported common interfaces */ |
2c42818e PM |
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 | */ | |
7b0b759b PM |
132 | extern void call_rcu_sched(struct rcu_head *head, |
133 | void (*func)(struct rcu_head *rcu)); | |
2c42818e | 134 | |
7b0b759b | 135 | extern void synchronize_sched(void); |
03b042bf | 136 | |
7b0b759b PM |
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 | } | |
a6826048 | 146 | |
a3dc3fb1 PM |
147 | #ifdef CONFIG_PREEMPT_RCU |
148 | ||
7b0b759b PM |
149 | extern void __rcu_read_lock(void); |
150 | extern void __rcu_read_unlock(void); | |
151 | void synchronize_rcu(void); | |
152 | ||
a3dc3fb1 PM |
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 | ||
7b0b759b PM |
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 */ | |
7b0b759b PM |
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 */ | |
a3dc3fb1 | 207 | |
2c42818e PM |
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 | ||
f41d911f | 217 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
64db4cff | 218 | #include <linux/rcutree.h> |
a57eb940 | 219 | #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) |
9b1d82fa | 220 | #include <linux/rcutiny.h> |
64db4cff PM |
221 | #else |
222 | #error "Unknown RCU implementation specified to kernel configuration" | |
6b3ef48a | 223 | #endif |
01c1c660 | 224 | |
551d55a9 MD |
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 */ | |
4376030a MD |
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 | } | |
551d55a9 | 242 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
4376030a | 243 | |
bc33f24b | 244 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
632ee200 | 245 | |
bc33f24b | 246 | extern struct lockdep_map rcu_lock_map; |
632ee200 PM |
247 | # define rcu_read_acquire() \ |
248 | lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
bc33f24b | 249 | # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) |
632ee200 PM |
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 | ||
bc293d62 | 262 | extern int debug_lockdep_rcu_enabled(void); |
54dbf96c | 263 | |
632ee200 | 264 | /** |
ca5ecddf | 265 | * rcu_read_lock_held() - might we be in RCU read-side critical section? |
632ee200 | 266 | * |
d20200b5 PM |
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, | |
632ee200 | 269 | * this assumes we are in an RCU read-side critical section unless it can |
ca5ecddf PM |
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. | |
54dbf96c | 272 | * |
ca5ecddf | 273 | * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot |
32c141a0 | 274 | * and while lockdep is disabled. |
632ee200 PM |
275 | */ |
276 | static inline int rcu_read_lock_held(void) | |
277 | { | |
54dbf96c PM |
278 | if (!debug_lockdep_rcu_enabled()) |
279 | return 1; | |
280 | return lock_is_held(&rcu_lock_map); | |
632ee200 PM |
281 | } |
282 | ||
e3818b8d PM |
283 | /* |
284 | * rcu_read_lock_bh_held() is defined out of line to avoid #include-file | |
285 | * hell. | |
632ee200 | 286 | */ |
e3818b8d | 287 | extern int rcu_read_lock_bh_held(void); |
632ee200 PM |
288 | |
289 | /** | |
ca5ecddf | 290 | * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? |
632ee200 | 291 | * |
d20200b5 PM |
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 | |
ca5ecddf PM |
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. | |
54dbf96c | 300 | * |
32c141a0 PM |
301 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot |
302 | * and while lockdep is disabled. | |
632ee200 | 303 | */ |
bdd4e85d | 304 | #ifdef CONFIG_PREEMPT_COUNT |
632ee200 PM |
305 | static inline int rcu_read_lock_sched_held(void) |
306 | { | |
307 | int lockdep_opinion = 0; | |
308 | ||
54dbf96c PM |
309 | if (!debug_lockdep_rcu_enabled()) |
310 | return 1; | |
632ee200 PM |
311 | if (debug_locks) |
312 | lockdep_opinion = lock_is_held(&rcu_sched_lock_map); | |
0cff810f | 313 | return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); |
632ee200 | 314 | } |
bdd4e85d | 315 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
e6033e3b PM |
316 | static inline int rcu_read_lock_sched_held(void) |
317 | { | |
318 | return 1; | |
632ee200 | 319 | } |
bdd4e85d | 320 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
632ee200 PM |
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 | ||
bdd4e85d | 341 | #ifdef CONFIG_PREEMPT_COUNT |
632ee200 PM |
342 | static inline int rcu_read_lock_sched_held(void) |
343 | { | |
bbad9379 | 344 | return preempt_count() != 0 || irqs_disabled(); |
632ee200 | 345 | } |
bdd4e85d | 346 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
e6033e3b PM |
347 | static inline int rcu_read_lock_sched_held(void) |
348 | { | |
349 | return 1; | |
632ee200 | 350 | } |
bdd4e85d | 351 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
632ee200 PM |
352 | |
353 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
354 | ||
355 | #ifdef CONFIG_PROVE_RCU | |
356 | ||
ee84b824 PM |
357 | extern int rcu_my_thread_group_empty(void); |
358 | ||
4221a991 TH |
359 | /** |
360 | * rcu_lockdep_assert - emit lockdep splat if specified condition not met | |
361 | * @c: condition to check | |
b3fbab05 | 362 | * @s: informative message |
4221a991 | 363 | */ |
b3fbab05 | 364 | #define rcu_lockdep_assert(c, s) \ |
2b3fc35f LJ |
365 | do { \ |
366 | static bool __warned; \ | |
367 | if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ | |
368 | __warned = true; \ | |
b3fbab05 | 369 | lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ |
2b3fc35f LJ |
370 | } \ |
371 | } while (0) | |
372 | ||
b3fbab05 PM |
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 | ||
ca5ecddf PM |
383 | #else /* #ifdef CONFIG_PROVE_RCU */ |
384 | ||
b3fbab05 PM |
385 | #define rcu_lockdep_assert(c, s) do { } while (0) |
386 | #define rcu_sleep_check() do { } while (0) | |
ca5ecddf PM |
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 | */ | |
53ecfba2 PM |
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 | ||
ca5ecddf PM |
406 | #define __rcu_access_pointer(p, space) \ |
407 | ({ \ | |
408 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ | |
53ecfba2 | 409 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
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); \ | |
b3fbab05 PM |
415 | rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \ |
416 | " usage"); \ | |
53ecfba2 | 417 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
418 | smp_read_barrier_depends(); \ |
419 | ((typeof(*p) __force __kernel *)(_________p1)); \ | |
420 | }) | |
421 | #define __rcu_dereference_protected(p, c, space) \ | |
422 | ({ \ | |
b3fbab05 PM |
423 | rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \ |
424 | " usage"); \ | |
53ecfba2 | 425 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
426 | ((typeof(*p) __force __kernel *)(p)); \ |
427 | }) | |
428 | ||
a4dd9925 PM |
429 | #define __rcu_access_index(p, space) \ |
430 | ({ \ | |
431 | typeof(p) _________p1 = ACCESS_ONCE(p); \ | |
432 | rcu_dereference_sparse(p, space); \ | |
433 | (_________p1); \ | |
434 | }) | |
ca5ecddf PM |
435 | #define __rcu_dereference_index_check(p, c) \ |
436 | ({ \ | |
437 | typeof(p) _________p1 = ACCESS_ONCE(p); \ | |
b3fbab05 PM |
438 | rcu_lockdep_assert(c, \ |
439 | "suspicious rcu_dereference_index_check()" \ | |
440 | " usage"); \ | |
ca5ecddf PM |
441 | smp_read_barrier_depends(); \ |
442 | (_________p1); \ | |
443 | }) | |
444 | #define __rcu_assign_pointer(p, v, space) \ | |
445 | ({ \ | |
446 | if (!__builtin_constant_p(v) || \ | |
447 | ((v) != NULL)) \ | |
448 | smp_wmb(); \ | |
449 | (p) = (typeof(*v) __force space *)(v); \ | |
450 | }) | |
451 | ||
452 | ||
453 | /** | |
454 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing | |
455 | * @p: The pointer to read | |
456 | * | |
457 | * Return the value of the specified RCU-protected pointer, but omit the | |
458 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful | |
459 | * when the value of this pointer is accessed, but the pointer is not | |
460 | * dereferenced, for example, when testing an RCU-protected pointer against | |
461 | * NULL. Although rcu_access_pointer() may also be used in cases where | |
462 | * update-side locks prevent the value of the pointer from changing, you | |
463 | * should instead use rcu_dereference_protected() for this use case. | |
464 | */ | |
465 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) | |
466 | ||
632ee200 | 467 | /** |
ca5ecddf | 468 | * rcu_dereference_check() - rcu_dereference with debug checking |
c08c68dd DH |
469 | * @p: The pointer to read, prior to dereferencing |
470 | * @c: The conditions under which the dereference will take place | |
632ee200 | 471 | * |
c08c68dd | 472 | * Do an rcu_dereference(), but check that the conditions under which the |
ca5ecddf PM |
473 | * dereference will take place are correct. Typically the conditions |
474 | * indicate the various locking conditions that should be held at that | |
475 | * point. The check should return true if the conditions are satisfied. | |
476 | * An implicit check for being in an RCU read-side critical section | |
477 | * (rcu_read_lock()) is included. | |
c08c68dd DH |
478 | * |
479 | * For example: | |
480 | * | |
ca5ecddf | 481 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
c08c68dd DH |
482 | * |
483 | * could be used to indicate to lockdep that foo->bar may only be dereferenced | |
ca5ecddf | 484 | * if either rcu_read_lock() is held, or that the lock required to replace |
c08c68dd DH |
485 | * the bar struct at foo->bar is held. |
486 | * | |
487 | * Note that the list of conditions may also include indications of when a lock | |
488 | * need not be held, for example during initialisation or destruction of the | |
489 | * target struct: | |
490 | * | |
ca5ecddf | 491 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
c08c68dd | 492 | * atomic_read(&foo->usage) == 0); |
ca5ecddf PM |
493 | * |
494 | * Inserts memory barriers on architectures that require them | |
495 | * (currently only the Alpha), prevents the compiler from refetching | |
496 | * (and from merging fetches), and, more importantly, documents exactly | |
497 | * which pointers are protected by RCU and checks that the pointer is | |
498 | * annotated as __rcu. | |
632ee200 PM |
499 | */ |
500 | #define rcu_dereference_check(p, c) \ | |
ca5ecddf PM |
501 | __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) |
502 | ||
503 | /** | |
504 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking | |
505 | * @p: The pointer to read, prior to dereferencing | |
506 | * @c: The conditions under which the dereference will take place | |
507 | * | |
508 | * This is the RCU-bh counterpart to rcu_dereference_check(). | |
509 | */ | |
510 | #define rcu_dereference_bh_check(p, c) \ | |
511 | __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) | |
632ee200 | 512 | |
b62730ba | 513 | /** |
ca5ecddf PM |
514 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
515 | * @p: The pointer to read, prior to dereferencing | |
516 | * @c: The conditions under which the dereference will take place | |
517 | * | |
518 | * This is the RCU-sched counterpart to rcu_dereference_check(). | |
519 | */ | |
520 | #define rcu_dereference_sched_check(p, c) \ | |
521 | __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ | |
522 | __rcu) | |
523 | ||
524 | #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ | |
525 | ||
a4dd9925 PM |
526 | /** |
527 | * rcu_access_index() - fetch RCU index with no dereferencing | |
528 | * @p: The index to read | |
529 | * | |
530 | * Return the value of the specified RCU-protected index, but omit the | |
531 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful | |
532 | * when the value of this index is accessed, but the index is not | |
533 | * dereferenced, for example, when testing an RCU-protected index against | |
534 | * -1. Although rcu_access_index() may also be used in cases where | |
535 | * update-side locks prevent the value of the index from changing, you | |
536 | * should instead use rcu_dereference_index_protected() for this use case. | |
537 | */ | |
538 | #define rcu_access_index(p) __rcu_access_index((p), __rcu) | |
539 | ||
ca5ecddf PM |
540 | /** |
541 | * rcu_dereference_index_check() - rcu_dereference for indices with debug checking | |
542 | * @p: The pointer to read, prior to dereferencing | |
543 | * @c: The conditions under which the dereference will take place | |
544 | * | |
545 | * Similar to rcu_dereference_check(), but omits the sparse checking. | |
546 | * This allows rcu_dereference_index_check() to be used on integers, | |
547 | * which can then be used as array indices. Attempting to use | |
548 | * rcu_dereference_check() on an integer will give compiler warnings | |
549 | * because the sparse address-space mechanism relies on dereferencing | |
550 | * the RCU-protected pointer. Dereferencing integers is not something | |
551 | * that even gcc will put up with. | |
552 | * | |
553 | * Note that this function does not implicitly check for RCU read-side | |
554 | * critical sections. If this function gains lots of uses, it might | |
555 | * make sense to provide versions for each flavor of RCU, but it does | |
556 | * not make sense as of early 2010. | |
557 | */ | |
558 | #define rcu_dereference_index_check(p, c) \ | |
559 | __rcu_dereference_index_check((p), (c)) | |
560 | ||
561 | /** | |
562 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented | |
563 | * @p: The pointer to read, prior to dereferencing | |
564 | * @c: The conditions under which the dereference will take place | |
b62730ba PM |
565 | * |
566 | * Return the value of the specified RCU-protected pointer, but omit | |
567 | * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This | |
568 | * is useful in cases where update-side locks prevent the value of the | |
569 | * pointer from changing. Please note that this primitive does -not- | |
570 | * prevent the compiler from repeating this reference or combining it | |
571 | * with other references, so it should not be used without protection | |
572 | * of appropriate locks. | |
ca5ecddf PM |
573 | * |
574 | * This function is only for update-side use. Using this function | |
575 | * when protected only by rcu_read_lock() will result in infrequent | |
576 | * but very ugly failures. | |
b62730ba PM |
577 | */ |
578 | #define rcu_dereference_protected(p, c) \ | |
ca5ecddf | 579 | __rcu_dereference_protected((p), (c), __rcu) |
b62730ba | 580 | |
ca5ecddf PM |
581 | /** |
582 | * rcu_dereference_bh_protected() - fetch RCU-bh pointer when updates prevented | |
583 | * @p: The pointer to read, prior to dereferencing | |
584 | * @c: The conditions under which the dereference will take place | |
585 | * | |
586 | * This is the RCU-bh counterpart to rcu_dereference_protected(). | |
587 | */ | |
588 | #define rcu_dereference_bh_protected(p, c) \ | |
589 | __rcu_dereference_protected((p), (c), __rcu) | |
632ee200 | 590 | |
ca5ecddf PM |
591 | /** |
592 | * rcu_dereference_sched_protected() - fetch RCU-sched pointer when updates prevented | |
593 | * @p: The pointer to read, prior to dereferencing | |
594 | * @c: The conditions under which the dereference will take place | |
595 | * | |
596 | * This is the RCU-sched counterpart to rcu_dereference_protected(). | |
597 | */ | |
598 | #define rcu_dereference_sched_protected(p, c) \ | |
599 | __rcu_dereference_protected((p), (c), __rcu) | |
632ee200 | 600 | |
bc33f24b | 601 | |
b62730ba | 602 | /** |
ca5ecddf PM |
603 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
604 | * @p: The pointer to read, prior to dereferencing | |
b62730ba | 605 | * |
ca5ecddf | 606 | * This is a simple wrapper around rcu_dereference_check(). |
b62730ba | 607 | */ |
ca5ecddf | 608 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
b62730ba | 609 | |
1da177e4 | 610 | /** |
ca5ecddf PM |
611 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
612 | * @p: The pointer to read, prior to dereferencing | |
613 | * | |
614 | * Makes rcu_dereference_check() do the dirty work. | |
615 | */ | |
616 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) | |
617 | ||
618 | /** | |
619 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing | |
620 | * @p: The pointer to read, prior to dereferencing | |
621 | * | |
622 | * Makes rcu_dereference_check() do the dirty work. | |
623 | */ | |
624 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) | |
625 | ||
626 | /** | |
627 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section | |
1da177e4 | 628 | * |
9b06e818 | 629 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 630 | * are within RCU read-side critical sections, then the |
9b06e818 | 631 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
632 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
633 | * on one CPU while other CPUs are within RCU read-side critical | |
634 | * sections, invocation of the corresponding RCU callback is deferred | |
635 | * until after the all the other CPUs exit their critical sections. | |
636 | * | |
637 | * Note, however, that RCU callbacks are permitted to run concurrently | |
77d8485a | 638 | * with new RCU read-side critical sections. One way that this can happen |
1da177e4 LT |
639 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
640 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
641 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
642 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
643 | * callback is invoked. This is legal, because the RCU read-side critical | |
644 | * section that was running concurrently with the call_rcu() (and which | |
645 | * therefore might be referencing something that the corresponding RCU | |
646 | * callback would free up) has completed before the corresponding | |
647 | * RCU callback is invoked. | |
648 | * | |
649 | * RCU read-side critical sections may be nested. Any deferred actions | |
650 | * will be deferred until the outermost RCU read-side critical section | |
651 | * completes. | |
652 | * | |
9079fd7c PM |
653 | * You can avoid reading and understanding the next paragraph by |
654 | * following this rule: don't put anything in an rcu_read_lock() RCU | |
655 | * read-side critical section that would block in a !PREEMPT kernel. | |
656 | * But if you want the full story, read on! | |
657 | * | |
658 | * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it | |
659 | * is illegal to block while in an RCU read-side critical section. In | |
660 | * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) | |
661 | * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may | |
662 | * be preempted, but explicit blocking is illegal. Finally, in preemptible | |
663 | * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, | |
664 | * RCU read-side critical sections may be preempted and they may also | |
665 | * block, but only when acquiring spinlocks that are subject to priority | |
666 | * inheritance. | |
1da177e4 | 667 | */ |
bc33f24b PM |
668 | static inline void rcu_read_lock(void) |
669 | { | |
670 | __rcu_read_lock(); | |
671 | __acquire(RCU); | |
672 | rcu_read_acquire(); | |
673 | } | |
1da177e4 | 674 | |
1da177e4 LT |
675 | /* |
676 | * So where is rcu_write_lock()? It does not exist, as there is no | |
677 | * way for writers to lock out RCU readers. This is a feature, not | |
678 | * a bug -- this property is what provides RCU's performance benefits. | |
679 | * Of course, writers must coordinate with each other. The normal | |
680 | * spinlock primitives work well for this, but any other technique may be | |
681 | * used as well. RCU does not care how the writers keep out of each | |
682 | * others' way, as long as they do so. | |
683 | */ | |
3d76c082 PM |
684 | |
685 | /** | |
ca5ecddf | 686 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
3d76c082 PM |
687 | * |
688 | * See rcu_read_lock() for more information. | |
689 | */ | |
bc33f24b PM |
690 | static inline void rcu_read_unlock(void) |
691 | { | |
692 | rcu_read_release(); | |
693 | __release(RCU); | |
694 | __rcu_read_unlock(); | |
695 | } | |
1da177e4 LT |
696 | |
697 | /** | |
ca5ecddf | 698 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
1da177e4 LT |
699 | * |
700 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
ca5ecddf PM |
701 | * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since |
702 | * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a | |
703 | * softirq handler to be a quiescent state, a process in RCU read-side | |
704 | * critical section must be protected by disabling softirqs. Read-side | |
705 | * critical sections in interrupt context can use just rcu_read_lock(), | |
706 | * though this should at least be commented to avoid confusing people | |
707 | * reading the code. | |
1da177e4 | 708 | */ |
bc33f24b PM |
709 | static inline void rcu_read_lock_bh(void) |
710 | { | |
711 | __rcu_read_lock_bh(); | |
712 | __acquire(RCU_BH); | |
632ee200 | 713 | rcu_read_acquire_bh(); |
bc33f24b | 714 | } |
1da177e4 LT |
715 | |
716 | /* | |
717 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
718 | * | |
719 | * See rcu_read_lock_bh() for more information. | |
720 | */ | |
bc33f24b PM |
721 | static inline void rcu_read_unlock_bh(void) |
722 | { | |
632ee200 | 723 | rcu_read_release_bh(); |
bc33f24b PM |
724 | __release(RCU_BH); |
725 | __rcu_read_unlock_bh(); | |
726 | } | |
1da177e4 | 727 | |
1c50b728 | 728 | /** |
ca5ecddf | 729 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
1c50b728 | 730 | * |
ca5ecddf PM |
731 | * This is equivalent of rcu_read_lock(), but to be used when updates |
732 | * are being done using call_rcu_sched() or synchronize_rcu_sched(). | |
733 | * Read-side critical sections can also be introduced by anything that | |
734 | * disables preemption, including local_irq_disable() and friends. | |
1c50b728 | 735 | */ |
d6714c22 PM |
736 | static inline void rcu_read_lock_sched(void) |
737 | { | |
738 | preempt_disable(); | |
bc33f24b | 739 | __acquire(RCU_SCHED); |
632ee200 | 740 | rcu_read_acquire_sched(); |
d6714c22 | 741 | } |
1eba8f84 PM |
742 | |
743 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 744 | static inline notrace void rcu_read_lock_sched_notrace(void) |
d6714c22 PM |
745 | { |
746 | preempt_disable_notrace(); | |
bc33f24b | 747 | __acquire(RCU_SCHED); |
d6714c22 | 748 | } |
1c50b728 MD |
749 | |
750 | /* | |
751 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section | |
752 | * | |
753 | * See rcu_read_lock_sched for more information. | |
754 | */ | |
d6714c22 PM |
755 | static inline void rcu_read_unlock_sched(void) |
756 | { | |
632ee200 | 757 | rcu_read_release_sched(); |
bc33f24b | 758 | __release(RCU_SCHED); |
d6714c22 PM |
759 | preempt_enable(); |
760 | } | |
1eba8f84 PM |
761 | |
762 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 763 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
d6714c22 | 764 | { |
bc33f24b | 765 | __release(RCU_SCHED); |
d6714c22 PM |
766 | preempt_enable_notrace(); |
767 | } | |
1c50b728 | 768 | |
1da177e4 | 769 | /** |
ca5ecddf PM |
770 | * rcu_assign_pointer() - assign to RCU-protected pointer |
771 | * @p: pointer to assign to | |
772 | * @v: value to assign (publish) | |
c26d34a5 | 773 | * |
ca5ecddf PM |
774 | * Assigns the specified value to the specified RCU-protected |
775 | * pointer, ensuring that any concurrent RCU readers will see | |
776 | * any prior initialization. Returns the value assigned. | |
1da177e4 LT |
777 | * |
778 | * Inserts memory barriers on architectures that require them | |
779 | * (pretty much all of them other than x86), and also prevents | |
780 | * the compiler from reordering the code that initializes the | |
781 | * structure after the pointer assignment. More importantly, this | |
782 | * call documents which pointers will be dereferenced by RCU read-side | |
783 | * code. | |
784 | */ | |
d99c4f6b | 785 | #define rcu_assign_pointer(p, v) \ |
ca5ecddf PM |
786 | __rcu_assign_pointer((p), (v), __rcu) |
787 | ||
788 | /** | |
789 | * RCU_INIT_POINTER() - initialize an RCU protected pointer | |
790 | * | |
791 | * Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep | |
792 | * splats. | |
793 | */ | |
794 | #define RCU_INIT_POINTER(p, v) \ | |
795 | p = (typeof(*v) __force __rcu *)(v) | |
1da177e4 | 796 | |
9ab1544e LJ |
797 | static __always_inline bool __is_kfree_rcu_offset(unsigned long offset) |
798 | { | |
799 | return offset < 4096; | |
800 | } | |
801 | ||
802 | static __always_inline | |
803 | void __kfree_rcu(struct rcu_head *head, unsigned long offset) | |
804 | { | |
805 | typedef void (*rcu_callback)(struct rcu_head *); | |
806 | ||
807 | BUILD_BUG_ON(!__builtin_constant_p(offset)); | |
808 | ||
809 | /* See the kfree_rcu() header comment. */ | |
810 | BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); | |
811 | ||
812 | call_rcu(head, (rcu_callback)offset); | |
813 | } | |
814 | ||
9ab1544e LJ |
815 | /** |
816 | * kfree_rcu() - kfree an object after a grace period. | |
817 | * @ptr: pointer to kfree | |
818 | * @rcu_head: the name of the struct rcu_head within the type of @ptr. | |
819 | * | |
820 | * Many rcu callbacks functions just call kfree() on the base structure. | |
821 | * These functions are trivial, but their size adds up, and furthermore | |
822 | * when they are used in a kernel module, that module must invoke the | |
823 | * high-latency rcu_barrier() function at module-unload time. | |
824 | * | |
825 | * The kfree_rcu() function handles this issue. Rather than encoding a | |
826 | * function address in the embedded rcu_head structure, kfree_rcu() instead | |
827 | * encodes the offset of the rcu_head structure within the base structure. | |
828 | * Because the functions are not allowed in the low-order 4096 bytes of | |
829 | * kernel virtual memory, offsets up to 4095 bytes can be accommodated. | |
830 | * If the offset is larger than 4095 bytes, a compile-time error will | |
831 | * be generated in __kfree_rcu(). If this error is triggered, you can | |
832 | * either fall back to use of call_rcu() or rearrange the structure to | |
833 | * position the rcu_head structure into the first 4096 bytes. | |
834 | * | |
835 | * Note that the allowable offset might decrease in the future, for example, | |
836 | * to allow something like kmem_cache_free_rcu(). | |
837 | */ | |
838 | #define kfree_rcu(ptr, rcu_head) \ | |
839 | __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) | |
840 | ||
1da177e4 | 841 | #endif /* __LINUX_RCUPDATE_H */ |