Root/
1 | /* |
2 | * Read-Copy Update mechanism for mutual exclusion |
3 | * |
4 | * This program is free software; you can redistribute it and/or modify |
5 | * it under the terms of the GNU General Public License as published by |
6 | * the Free Software Foundation; either version 2 of the License, or |
7 | * (at your option) any later version. |
8 | * |
9 | * This program is distributed in the hope that it will be useful, |
10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
12 | * GNU General Public License for more details. |
13 | * |
14 | * You should have received a copy of the GNU General Public License |
15 | * along with this program; if not, write to the Free Software |
16 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
17 | * |
18 | * Copyright IBM Corporation, 2001 |
19 | * |
20 | * Author: Dipankar Sarma <dipankar@in.ibm.com> |
21 | * |
22 | * Based on the original work by Paul McKenney <paulmck@us.ibm.com> |
23 | * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. |
24 | * Papers: |
25 | * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf |
26 | * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) |
27 | * |
28 | * For detailed explanation of Read-Copy Update mechanism see - |
29 | * http://lse.sourceforge.net/locking/rcupdate.html |
30 | * |
31 | */ |
32 | |
33 | #ifndef __LINUX_RCUPDATE_H |
34 | #define __LINUX_RCUPDATE_H |
35 | |
36 | #include <linux/cache.h> |
37 | #include <linux/spinlock.h> |
38 | #include <linux/threads.h> |
39 | #include <linux/cpumask.h> |
40 | #include <linux/seqlock.h> |
41 | #include <linux/lockdep.h> |
42 | #include <linux/completion.h> |
43 | #include <linux/debugobjects.h> |
44 | #include <linux/compiler.h> |
45 | |
46 | #ifdef CONFIG_RCU_TORTURE_TEST |
47 | extern int rcutorture_runnable; /* for sysctl */ |
48 | #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ |
49 | |
50 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
51 | extern void rcutorture_record_test_transition(void); |
52 | extern void rcutorture_record_progress(unsigned long vernum); |
53 | #else |
54 | static inline void rcutorture_record_test_transition(void) |
55 | { |
56 | } |
57 | static inline void rcutorture_record_progress(unsigned long vernum) |
58 | { |
59 | } |
60 | #endif |
61 | |
62 | #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) |
63 | #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) |
64 | #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) |
65 | #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) |
66 | |
67 | /** |
68 | * struct rcu_head - callback structure for use with RCU |
69 | * @next: next update requests in a list |
70 | * @func: actual update function to call after the grace period. |
71 | */ |
72 | struct rcu_head { |
73 | struct rcu_head *next; |
74 | void (*func)(struct rcu_head *head); |
75 | }; |
76 | |
77 | /* Exported common interfaces */ |
78 | extern void call_rcu_sched(struct rcu_head *head, |
79 | void (*func)(struct rcu_head *rcu)); |
80 | extern void synchronize_sched(void); |
81 | extern void rcu_barrier_bh(void); |
82 | extern void rcu_barrier_sched(void); |
83 | |
84 | static inline void __rcu_read_lock_bh(void) |
85 | { |
86 | local_bh_disable(); |
87 | } |
88 | |
89 | static inline void __rcu_read_unlock_bh(void) |
90 | { |
91 | local_bh_enable(); |
92 | } |
93 | |
94 | #ifdef CONFIG_PREEMPT_RCU |
95 | |
96 | extern void __rcu_read_lock(void); |
97 | extern void __rcu_read_unlock(void); |
98 | void synchronize_rcu(void); |
99 | |
100 | /* |
101 | * Defined as a macro as it is a very low level header included from |
102 | * areas that don't even know about current. This gives the rcu_read_lock() |
103 | * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other |
104 | * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. |
105 | */ |
106 | #define rcu_preempt_depth() (current->rcu_read_lock_nesting) |
107 | |
108 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
109 | |
110 | static inline void __rcu_read_lock(void) |
111 | { |
112 | preempt_disable(); |
113 | } |
114 | |
115 | static inline void __rcu_read_unlock(void) |
116 | { |
117 | preempt_enable(); |
118 | } |
119 | |
120 | static inline void synchronize_rcu(void) |
121 | { |
122 | synchronize_sched(); |
123 | } |
124 | |
125 | static inline int rcu_preempt_depth(void) |
126 | { |
127 | return 0; |
128 | } |
129 | |
130 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
131 | |
132 | /* Internal to kernel */ |
133 | extern void rcu_sched_qs(int cpu); |
134 | extern void rcu_bh_qs(int cpu); |
135 | extern void rcu_check_callbacks(int cpu, int user); |
136 | struct notifier_block; |
137 | |
138 | #ifdef CONFIG_NO_HZ |
139 | |
140 | extern void rcu_enter_nohz(void); |
141 | extern void rcu_exit_nohz(void); |
142 | |
143 | #else /* #ifdef CONFIG_NO_HZ */ |
144 | |
145 | static inline void rcu_enter_nohz(void) |
146 | { |
147 | } |
148 | |
149 | static inline void rcu_exit_nohz(void) |
150 | { |
151 | } |
152 | |
153 | #endif /* #else #ifdef CONFIG_NO_HZ */ |
154 | |
155 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
156 | #include <linux/rcutree.h> |
157 | #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) |
158 | #include <linux/rcutiny.h> |
159 | #else |
160 | #error "Unknown RCU implementation specified to kernel configuration" |
161 | #endif |
162 | |
163 | /* |
164 | * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic |
165 | * initialization and destruction of rcu_head on the stack. rcu_head structures |
166 | * allocated dynamically in the heap or defined statically don't need any |
167 | * initialization. |
168 | */ |
169 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD |
170 | extern void init_rcu_head_on_stack(struct rcu_head *head); |
171 | extern void destroy_rcu_head_on_stack(struct rcu_head *head); |
172 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
173 | static inline void init_rcu_head_on_stack(struct rcu_head *head) |
174 | { |
175 | } |
176 | |
177 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) |
178 | { |
179 | } |
180 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
181 | |
182 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
183 | |
184 | extern struct lockdep_map rcu_lock_map; |
185 | # define rcu_read_acquire() \ |
186 | lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
187 | # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) |
188 | |
189 | extern struct lockdep_map rcu_bh_lock_map; |
190 | # define rcu_read_acquire_bh() \ |
191 | lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
192 | # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) |
193 | |
194 | extern struct lockdep_map rcu_sched_lock_map; |
195 | # define rcu_read_acquire_sched() \ |
196 | lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
197 | # define rcu_read_release_sched() \ |
198 | lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) |
199 | |
200 | extern int debug_lockdep_rcu_enabled(void); |
201 | |
202 | /** |
203 | * rcu_read_lock_held() - might we be in RCU read-side critical section? |
204 | * |
205 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU |
206 | * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, |
207 | * this assumes we are in an RCU read-side critical section unless it can |
208 | * prove otherwise. This is useful for debug checks in functions that |
209 | * require that they be called within an RCU read-side critical section. |
210 | * |
211 | * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot |
212 | * and while lockdep is disabled. |
213 | */ |
214 | static inline int rcu_read_lock_held(void) |
215 | { |
216 | if (!debug_lockdep_rcu_enabled()) |
217 | return 1; |
218 | return lock_is_held(&rcu_lock_map); |
219 | } |
220 | |
221 | /* |
222 | * rcu_read_lock_bh_held() is defined out of line to avoid #include-file |
223 | * hell. |
224 | */ |
225 | extern int rcu_read_lock_bh_held(void); |
226 | |
227 | /** |
228 | * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? |
229 | * |
230 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an |
231 | * RCU-sched read-side critical section. In absence of |
232 | * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side |
233 | * critical section unless it can prove otherwise. Note that disabling |
234 | * of preemption (including disabling irqs) counts as an RCU-sched |
235 | * read-side critical section. This is useful for debug checks in functions |
236 | * that required that they be called within an RCU-sched read-side |
237 | * critical section. |
238 | * |
239 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot |
240 | * and while lockdep is disabled. |
241 | */ |
242 | #ifdef CONFIG_PREEMPT |
243 | static inline int rcu_read_lock_sched_held(void) |
244 | { |
245 | int lockdep_opinion = 0; |
246 | |
247 | if (!debug_lockdep_rcu_enabled()) |
248 | return 1; |
249 | if (debug_locks) |
250 | lockdep_opinion = lock_is_held(&rcu_sched_lock_map); |
251 | return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); |
252 | } |
253 | #else /* #ifdef CONFIG_PREEMPT */ |
254 | static inline int rcu_read_lock_sched_held(void) |
255 | { |
256 | return 1; |
257 | } |
258 | #endif /* #else #ifdef CONFIG_PREEMPT */ |
259 | |
260 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
261 | |
262 | # define rcu_read_acquire() do { } while (0) |
263 | # define rcu_read_release() do { } while (0) |
264 | # define rcu_read_acquire_bh() do { } while (0) |
265 | # define rcu_read_release_bh() do { } while (0) |
266 | # define rcu_read_acquire_sched() do { } while (0) |
267 | # define rcu_read_release_sched() do { } while (0) |
268 | |
269 | static inline int rcu_read_lock_held(void) |
270 | { |
271 | return 1; |
272 | } |
273 | |
274 | static inline int rcu_read_lock_bh_held(void) |
275 | { |
276 | return 1; |
277 | } |
278 | |
279 | #ifdef CONFIG_PREEMPT |
280 | static inline int rcu_read_lock_sched_held(void) |
281 | { |
282 | return preempt_count() != 0 || irqs_disabled(); |
283 | } |
284 | #else /* #ifdef CONFIG_PREEMPT */ |
285 | static inline int rcu_read_lock_sched_held(void) |
286 | { |
287 | return 1; |
288 | } |
289 | #endif /* #else #ifdef CONFIG_PREEMPT */ |
290 | |
291 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
292 | |
293 | #ifdef CONFIG_PROVE_RCU |
294 | |
295 | extern int rcu_my_thread_group_empty(void); |
296 | |
297 | /** |
298 | * rcu_lockdep_assert - emit lockdep splat if specified condition not met |
299 | * @c: condition to check |
300 | */ |
301 | #define rcu_lockdep_assert(c) \ |
302 | do { \ |
303 | static bool __warned; \ |
304 | if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ |
305 | __warned = true; \ |
306 | lockdep_rcu_dereference(__FILE__, __LINE__); \ |
307 | } \ |
308 | } while (0) |
309 | |
310 | #else /* #ifdef CONFIG_PROVE_RCU */ |
311 | |
312 | #define rcu_lockdep_assert(c) do { } while (0) |
313 | |
314 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ |
315 | |
316 | /* |
317 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() |
318 | * and rcu_assign_pointer(). Some of these could be folded into their |
319 | * callers, but they are left separate in order to ease introduction of |
320 | * multiple flavors of pointers to match the multiple flavors of RCU |
321 | * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in |
322 | * the future. |
323 | */ |
324 | |
325 | #ifdef __CHECKER__ |
326 | #define rcu_dereference_sparse(p, space) \ |
327 | ((void)(((typeof(*p) space *)p) == p)) |
328 | #else /* #ifdef __CHECKER__ */ |
329 | #define rcu_dereference_sparse(p, space) |
330 | #endif /* #else #ifdef __CHECKER__ */ |
331 | |
332 | #define __rcu_access_pointer(p, space) \ |
333 | ({ \ |
334 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ |
335 | rcu_dereference_sparse(p, space); \ |
336 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
337 | }) |
338 | #define __rcu_dereference_check(p, c, space) \ |
339 | ({ \ |
340 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ |
341 | rcu_lockdep_assert(c); \ |
342 | rcu_dereference_sparse(p, space); \ |
343 | smp_read_barrier_depends(); \ |
344 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
345 | }) |
346 | #define __rcu_dereference_protected(p, c, space) \ |
347 | ({ \ |
348 | rcu_lockdep_assert(c); \ |
349 | rcu_dereference_sparse(p, space); \ |
350 | ((typeof(*p) __force __kernel *)(p)); \ |
351 | }) |
352 | |
353 | #define __rcu_access_index(p, space) \ |
354 | ({ \ |
355 | typeof(p) _________p1 = ACCESS_ONCE(p); \ |
356 | rcu_dereference_sparse(p, space); \ |
357 | (_________p1); \ |
358 | }) |
359 | #define __rcu_dereference_index_check(p, c) \ |
360 | ({ \ |
361 | typeof(p) _________p1 = ACCESS_ONCE(p); \ |
362 | rcu_lockdep_assert(c); \ |
363 | smp_read_barrier_depends(); \ |
364 | (_________p1); \ |
365 | }) |
366 | #define __rcu_assign_pointer(p, v, space) \ |
367 | ({ \ |
368 | if (!__builtin_constant_p(v) || \ |
369 | ((v) != NULL)) \ |
370 | smp_wmb(); \ |
371 | (p) = (typeof(*v) __force space *)(v); \ |
372 | }) |
373 | |
374 | |
375 | /** |
376 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing |
377 | * @p: The pointer to read |
378 | * |
379 | * Return the value of the specified RCU-protected pointer, but omit the |
380 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful |
381 | * when the value of this pointer is accessed, but the pointer is not |
382 | * dereferenced, for example, when testing an RCU-protected pointer against |
383 | * NULL. Although rcu_access_pointer() may also be used in cases where |
384 | * update-side locks prevent the value of the pointer from changing, you |
385 | * should instead use rcu_dereference_protected() for this use case. |
386 | */ |
387 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) |
388 | |
389 | /** |
390 | * rcu_dereference_check() - rcu_dereference with debug checking |
391 | * @p: The pointer to read, prior to dereferencing |
392 | * @c: The conditions under which the dereference will take place |
393 | * |
394 | * Do an rcu_dereference(), but check that the conditions under which the |
395 | * dereference will take place are correct. Typically the conditions |
396 | * indicate the various locking conditions that should be held at that |
397 | * point. The check should return true if the conditions are satisfied. |
398 | * An implicit check for being in an RCU read-side critical section |
399 | * (rcu_read_lock()) is included. |
400 | * |
401 | * For example: |
402 | * |
403 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
404 | * |
405 | * could be used to indicate to lockdep that foo->bar may only be dereferenced |
406 | * if either rcu_read_lock() is held, or that the lock required to replace |
407 | * the bar struct at foo->bar is held. |
408 | * |
409 | * Note that the list of conditions may also include indications of when a lock |
410 | * need not be held, for example during initialisation or destruction of the |
411 | * target struct: |
412 | * |
413 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
414 | * atomic_read(&foo->usage) == 0); |
415 | * |
416 | * Inserts memory barriers on architectures that require them |
417 | * (currently only the Alpha), prevents the compiler from refetching |
418 | * (and from merging fetches), and, more importantly, documents exactly |
419 | * which pointers are protected by RCU and checks that the pointer is |
420 | * annotated as __rcu. |
421 | */ |
422 | #define rcu_dereference_check(p, c) \ |
423 | __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) |
424 | |
425 | /** |
426 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking |
427 | * @p: The pointer to read, prior to dereferencing |
428 | * @c: The conditions under which the dereference will take place |
429 | * |
430 | * This is the RCU-bh counterpart to rcu_dereference_check(). |
431 | */ |
432 | #define rcu_dereference_bh_check(p, c) \ |
433 | __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) |
434 | |
435 | /** |
436 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
437 | * @p: The pointer to read, prior to dereferencing |
438 | * @c: The conditions under which the dereference will take place |
439 | * |
440 | * This is the RCU-sched counterpart to rcu_dereference_check(). |
441 | */ |
442 | #define rcu_dereference_sched_check(p, c) \ |
443 | __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ |
444 | __rcu) |
445 | |
446 | #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ |
447 | |
448 | /** |
449 | * rcu_access_index() - fetch RCU index with no dereferencing |
450 | * @p: The index to read |
451 | * |
452 | * Return the value of the specified RCU-protected index, but omit the |
453 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful |
454 | * when the value of this index is accessed, but the index is not |
455 | * dereferenced, for example, when testing an RCU-protected index against |
456 | * -1. Although rcu_access_index() may also be used in cases where |
457 | * update-side locks prevent the value of the index from changing, you |
458 | * should instead use rcu_dereference_index_protected() for this use case. |
459 | */ |
460 | #define rcu_access_index(p) __rcu_access_index((p), __rcu) |
461 | |
462 | /** |
463 | * rcu_dereference_index_check() - rcu_dereference for indices with debug checking |
464 | * @p: The pointer to read, prior to dereferencing |
465 | * @c: The conditions under which the dereference will take place |
466 | * |
467 | * Similar to rcu_dereference_check(), but omits the sparse checking. |
468 | * This allows rcu_dereference_index_check() to be used on integers, |
469 | * which can then be used as array indices. Attempting to use |
470 | * rcu_dereference_check() on an integer will give compiler warnings |
471 | * because the sparse address-space mechanism relies on dereferencing |
472 | * the RCU-protected pointer. Dereferencing integers is not something |
473 | * that even gcc will put up with. |
474 | * |
475 | * Note that this function does not implicitly check for RCU read-side |
476 | * critical sections. If this function gains lots of uses, it might |
477 | * make sense to provide versions for each flavor of RCU, but it does |
478 | * not make sense as of early 2010. |
479 | */ |
480 | #define rcu_dereference_index_check(p, c) \ |
481 | __rcu_dereference_index_check((p), (c)) |
482 | |
483 | /** |
484 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented |
485 | * @p: The pointer to read, prior to dereferencing |
486 | * @c: The conditions under which the dereference will take place |
487 | * |
488 | * Return the value of the specified RCU-protected pointer, but omit |
489 | * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This |
490 | * is useful in cases where update-side locks prevent the value of the |
491 | * pointer from changing. Please note that this primitive does -not- |
492 | * prevent the compiler from repeating this reference or combining it |
493 | * with other references, so it should not be used without protection |
494 | * of appropriate locks. |
495 | * |
496 | * This function is only for update-side use. Using this function |
497 | * when protected only by rcu_read_lock() will result in infrequent |
498 | * but very ugly failures. |
499 | */ |
500 | #define rcu_dereference_protected(p, c) \ |
501 | __rcu_dereference_protected((p), (c), __rcu) |
502 | |
503 | /** |
504 | * rcu_dereference_bh_protected() - fetch RCU-bh pointer when updates prevented |
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_protected(). |
509 | */ |
510 | #define rcu_dereference_bh_protected(p, c) \ |
511 | __rcu_dereference_protected((p), (c), __rcu) |
512 | |
513 | /** |
514 | * rcu_dereference_sched_protected() - fetch RCU-sched pointer when updates prevented |
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_protected(). |
519 | */ |
520 | #define rcu_dereference_sched_protected(p, c) \ |
521 | __rcu_dereference_protected((p), (c), __rcu) |
522 | |
523 | |
524 | /** |
525 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
526 | * @p: The pointer to read, prior to dereferencing |
527 | * |
528 | * This is a simple wrapper around rcu_dereference_check(). |
529 | */ |
530 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
531 | |
532 | /** |
533 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
534 | * @p: The pointer to read, prior to dereferencing |
535 | * |
536 | * Makes rcu_dereference_check() do the dirty work. |
537 | */ |
538 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) |
539 | |
540 | /** |
541 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing |
542 | * @p: The pointer to read, prior to dereferencing |
543 | * |
544 | * Makes rcu_dereference_check() do the dirty work. |
545 | */ |
546 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) |
547 | |
548 | /** |
549 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section |
550 | * |
551 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
552 | * are within RCU read-side critical sections, then the |
553 | * synchronize_rcu() is guaranteed to block until after all the other |
554 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
555 | * on one CPU while other CPUs are within RCU read-side critical |
556 | * sections, invocation of the corresponding RCU callback is deferred |
557 | * until after the all the other CPUs exit their critical sections. |
558 | * |
559 | * Note, however, that RCU callbacks are permitted to run concurrently |
560 | * with new RCU read-side critical sections. One way that this can happen |
561 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
562 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register |
563 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, |
564 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU |
565 | * callback is invoked. This is legal, because the RCU read-side critical |
566 | * section that was running concurrently with the call_rcu() (and which |
567 | * therefore might be referencing something that the corresponding RCU |
568 | * callback would free up) has completed before the corresponding |
569 | * RCU callback is invoked. |
570 | * |
571 | * RCU read-side critical sections may be nested. Any deferred actions |
572 | * will be deferred until the outermost RCU read-side critical section |
573 | * completes. |
574 | * |
575 | * You can avoid reading and understanding the next paragraph by |
576 | * following this rule: don't put anything in an rcu_read_lock() RCU |
577 | * read-side critical section that would block in a !PREEMPT kernel. |
578 | * But if you want the full story, read on! |
579 | * |
580 | * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it |
581 | * is illegal to block while in an RCU read-side critical section. In |
582 | * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) |
583 | * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may |
584 | * be preempted, but explicit blocking is illegal. Finally, in preemptible |
585 | * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, |
586 | * RCU read-side critical sections may be preempted and they may also |
587 | * block, but only when acquiring spinlocks that are subject to priority |
588 | * inheritance. |
589 | */ |
590 | static inline void rcu_read_lock(void) |
591 | { |
592 | __rcu_read_lock(); |
593 | __acquire(RCU); |
594 | rcu_read_acquire(); |
595 | } |
596 | |
597 | /* |
598 | * So where is rcu_write_lock()? It does not exist, as there is no |
599 | * way for writers to lock out RCU readers. This is a feature, not |
600 | * a bug -- this property is what provides RCU's performance benefits. |
601 | * Of course, writers must coordinate with each other. The normal |
602 | * spinlock primitives work well for this, but any other technique may be |
603 | * used as well. RCU does not care how the writers keep out of each |
604 | * others' way, as long as they do so. |
605 | */ |
606 | |
607 | /** |
608 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
609 | * |
610 | * See rcu_read_lock() for more information. |
611 | */ |
612 | static inline void rcu_read_unlock(void) |
613 | { |
614 | rcu_read_release(); |
615 | __release(RCU); |
616 | __rcu_read_unlock(); |
617 | } |
618 | |
619 | /** |
620 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
621 | * |
622 | * This is equivalent of rcu_read_lock(), but to be used when updates |
623 | * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since |
624 | * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a |
625 | * softirq handler to be a quiescent state, a process in RCU read-side |
626 | * critical section must be protected by disabling softirqs. Read-side |
627 | * critical sections in interrupt context can use just rcu_read_lock(), |
628 | * though this should at least be commented to avoid confusing people |
629 | * reading the code. |
630 | */ |
631 | static inline void rcu_read_lock_bh(void) |
632 | { |
633 | __rcu_read_lock_bh(); |
634 | __acquire(RCU_BH); |
635 | rcu_read_acquire_bh(); |
636 | } |
637 | |
638 | /* |
639 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section |
640 | * |
641 | * See rcu_read_lock_bh() for more information. |
642 | */ |
643 | static inline void rcu_read_unlock_bh(void) |
644 | { |
645 | rcu_read_release_bh(); |
646 | __release(RCU_BH); |
647 | __rcu_read_unlock_bh(); |
648 | } |
649 | |
650 | /** |
651 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
652 | * |
653 | * This is equivalent of rcu_read_lock(), but to be used when updates |
654 | * are being done using call_rcu_sched() or synchronize_rcu_sched(). |
655 | * Read-side critical sections can also be introduced by anything that |
656 | * disables preemption, including local_irq_disable() and friends. |
657 | */ |
658 | static inline void rcu_read_lock_sched(void) |
659 | { |
660 | preempt_disable(); |
661 | __acquire(RCU_SCHED); |
662 | rcu_read_acquire_sched(); |
663 | } |
664 | |
665 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
666 | static inline notrace void rcu_read_lock_sched_notrace(void) |
667 | { |
668 | preempt_disable_notrace(); |
669 | __acquire(RCU_SCHED); |
670 | } |
671 | |
672 | /* |
673 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section |
674 | * |
675 | * See rcu_read_lock_sched for more information. |
676 | */ |
677 | static inline void rcu_read_unlock_sched(void) |
678 | { |
679 | rcu_read_release_sched(); |
680 | __release(RCU_SCHED); |
681 | preempt_enable(); |
682 | } |
683 | |
684 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
685 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
686 | { |
687 | __release(RCU_SCHED); |
688 | preempt_enable_notrace(); |
689 | } |
690 | |
691 | /** |
692 | * rcu_assign_pointer() - assign to RCU-protected pointer |
693 | * @p: pointer to assign to |
694 | * @v: value to assign (publish) |
695 | * |
696 | * Assigns the specified value to the specified RCU-protected |
697 | * pointer, ensuring that any concurrent RCU readers will see |
698 | * any prior initialization. Returns the value assigned. |
699 | * |
700 | * Inserts memory barriers on architectures that require them |
701 | * (pretty much all of them other than x86), and also prevents |
702 | * the compiler from reordering the code that initializes the |
703 | * structure after the pointer assignment. More importantly, this |
704 | * call documents which pointers will be dereferenced by RCU read-side |
705 | * code. |
706 | */ |
707 | #define rcu_assign_pointer(p, v) \ |
708 | __rcu_assign_pointer((p), (v), __rcu) |
709 | |
710 | /** |
711 | * RCU_INIT_POINTER() - initialize an RCU protected pointer |
712 | * |
713 | * Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep |
714 | * splats. |
715 | */ |
716 | #define RCU_INIT_POINTER(p, v) \ |
717 | p = (typeof(*v) __force __rcu *)(v) |
718 | |
719 | /* Infrastructure to implement the synchronize_() primitives. */ |
720 | |
721 | struct rcu_synchronize { |
722 | struct rcu_head head; |
723 | struct completion completion; |
724 | }; |
725 | |
726 | extern void wakeme_after_rcu(struct rcu_head *head); |
727 | |
728 | #ifdef CONFIG_PREEMPT_RCU |
729 | |
730 | /** |
731 | * call_rcu() - Queue an RCU callback for invocation after a grace period. |
732 | * @head: structure to be used for queueing the RCU updates. |
733 | * @func: actual callback function to be invoked after the grace period |
734 | * |
735 | * The callback function will be invoked some time after a full grace |
736 | * period elapses, in other words after all pre-existing RCU read-side |
737 | * critical sections have completed. However, the callback function |
738 | * might well execute concurrently with RCU read-side critical sections |
739 | * that started after call_rcu() was invoked. RCU read-side critical |
740 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), |
741 | * and may be nested. |
742 | */ |
743 | extern void call_rcu(struct rcu_head *head, |
744 | void (*func)(struct rcu_head *head)); |
745 | |
746 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
747 | |
748 | /* In classic RCU, call_rcu() is just call_rcu_sched(). */ |
749 | #define call_rcu call_rcu_sched |
750 | |
751 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
752 | |
753 | /** |
754 | * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. |
755 | * @head: structure to be used for queueing the RCU updates. |
756 | * @func: actual callback function to be invoked after the grace period |
757 | * |
758 | * The callback function will be invoked some time after a full grace |
759 | * period elapses, in other words after all currently executing RCU |
760 | * read-side critical sections have completed. call_rcu_bh() assumes |
761 | * that the read-side critical sections end on completion of a softirq |
762 | * handler. This means that read-side critical sections in process |
763 | * context must not be interrupted by softirqs. This interface is to be |
764 | * used when most of the read-side critical sections are in softirq context. |
765 | * RCU read-side critical sections are delimited by : |
766 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. |
767 | * OR |
768 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. |
769 | * These may be nested. |
770 | */ |
771 | extern void call_rcu_bh(struct rcu_head *head, |
772 | void (*func)(struct rcu_head *head)); |
773 | |
774 | /* |
775 | * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally |
776 | * by call_rcu() and rcu callback execution, and are therefore not part of the |
777 | * RCU API. Leaving in rcupdate.h because they are used by all RCU flavors. |
778 | */ |
779 | |
780 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD |
781 | # define STATE_RCU_HEAD_READY 0 |
782 | # define STATE_RCU_HEAD_QUEUED 1 |
783 | |
784 | extern struct debug_obj_descr rcuhead_debug_descr; |
785 | |
786 | static inline void debug_rcu_head_queue(struct rcu_head *head) |
787 | { |
788 | WARN_ON_ONCE((unsigned long)head & 0x3); |
789 | debug_object_activate(head, &rcuhead_debug_descr); |
790 | debug_object_active_state(head, &rcuhead_debug_descr, |
791 | STATE_RCU_HEAD_READY, |
792 | STATE_RCU_HEAD_QUEUED); |
793 | } |
794 | |
795 | static inline void debug_rcu_head_unqueue(struct rcu_head *head) |
796 | { |
797 | debug_object_active_state(head, &rcuhead_debug_descr, |
798 | STATE_RCU_HEAD_QUEUED, |
799 | STATE_RCU_HEAD_READY); |
800 | debug_object_deactivate(head, &rcuhead_debug_descr); |
801 | } |
802 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
803 | static inline void debug_rcu_head_queue(struct rcu_head *head) |
804 | { |
805 | } |
806 | |
807 | static inline void debug_rcu_head_unqueue(struct rcu_head *head) |
808 | { |
809 | } |
810 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
811 | |
812 | static __always_inline bool __is_kfree_rcu_offset(unsigned long offset) |
813 | { |
814 | return offset < 4096; |
815 | } |
816 | |
817 | static __always_inline |
818 | void __kfree_rcu(struct rcu_head *head, unsigned long offset) |
819 | { |
820 | typedef void (*rcu_callback)(struct rcu_head *); |
821 | |
822 | BUILD_BUG_ON(!__builtin_constant_p(offset)); |
823 | |
824 | /* See the kfree_rcu() header comment. */ |
825 | BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); |
826 | |
827 | call_rcu(head, (rcu_callback)offset); |
828 | } |
829 | |
830 | extern void kfree(const void *); |
831 | |
832 | static inline void __rcu_reclaim(struct rcu_head *head) |
833 | { |
834 | unsigned long offset = (unsigned long)head->func; |
835 | |
836 | if (__is_kfree_rcu_offset(offset)) |
837 | kfree((void *)head - offset); |
838 | else |
839 | head->func(head); |
840 | } |
841 | |
842 | /** |
843 | * kfree_rcu() - kfree an object after a grace period. |
844 | * @ptr: pointer to kfree |
845 | * @rcu_head: the name of the struct rcu_head within the type of @ptr. |
846 | * |
847 | * Many rcu callbacks functions just call kfree() on the base structure. |
848 | * These functions are trivial, but their size adds up, and furthermore |
849 | * when they are used in a kernel module, that module must invoke the |
850 | * high-latency rcu_barrier() function at module-unload time. |
851 | * |
852 | * The kfree_rcu() function handles this issue. Rather than encoding a |
853 | * function address in the embedded rcu_head structure, kfree_rcu() instead |
854 | * encodes the offset of the rcu_head structure within the base structure. |
855 | * Because the functions are not allowed in the low-order 4096 bytes of |
856 | * kernel virtual memory, offsets up to 4095 bytes can be accommodated. |
857 | * If the offset is larger than 4095 bytes, a compile-time error will |
858 | * be generated in __kfree_rcu(). If this error is triggered, you can |
859 | * either fall back to use of call_rcu() or rearrange the structure to |
860 | * position the rcu_head structure into the first 4096 bytes. |
861 | * |
862 | * Note that the allowable offset might decrease in the future, for example, |
863 | * to allow something like kmem_cache_free_rcu(). |
864 | */ |
865 | #define kfree_rcu(ptr, rcu_head) \ |
866 | __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) |
867 | |
868 | #endif /* __LINUX_RCUPDATE_H */ |
869 |
Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master
Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9