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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 | ||
1da177e4 LT |
36 | #include <linux/cache.h> |
37 | #include <linux/spinlock.h> | |
38 | #include <linux/threads.h> | |
1da177e4 LT |
39 | #include <linux/cpumask.h> |
40 | #include <linux/seqlock.h> | |
851a67b8 | 41 | #include <linux/lockdep.h> |
4446a36f | 42 | #include <linux/completion.h> |
551d55a9 | 43 | #include <linux/debugobjects.h> |
ca5ecddf | 44 | #include <linux/compiler.h> |
1da177e4 | 45 | |
e5ab6772 DY |
46 | #ifdef CONFIG_RCU_TORTURE_TEST |
47 | extern int rcutorture_runnable; /* for sysctl */ | |
48 | #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ | |
49 | ||
e27fc964 TH |
50 | #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) |
51 | #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) | |
a3dc3fb1 PM |
52 | #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) |
53 | #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) | |
54 | ||
1da177e4 LT |
55 | /** |
56 | * struct rcu_head - callback structure for use with RCU | |
57 | * @next: next update requests in a list | |
58 | * @func: actual update function to call after the grace period. | |
59 | */ | |
60 | struct rcu_head { | |
61 | struct rcu_head *next; | |
62 | void (*func)(struct rcu_head *head); | |
63 | }; | |
64 | ||
03b042bf | 65 | /* Exported common interfaces */ |
7b0b759b PM |
66 | extern void call_rcu_sched(struct rcu_head *head, |
67 | void (*func)(struct rcu_head *rcu)); | |
68 | extern void synchronize_sched(void); | |
03b042bf PM |
69 | extern void rcu_barrier_bh(void); |
70 | extern void rcu_barrier_sched(void); | |
03b042bf PM |
71 | extern int sched_expedited_torture_stats(char *page); |
72 | ||
7b0b759b PM |
73 | static inline void __rcu_read_lock_bh(void) |
74 | { | |
75 | local_bh_disable(); | |
76 | } | |
77 | ||
78 | static inline void __rcu_read_unlock_bh(void) | |
79 | { | |
80 | local_bh_enable(); | |
81 | } | |
a6826048 | 82 | |
a3dc3fb1 PM |
83 | #ifdef CONFIG_PREEMPT_RCU |
84 | ||
7b0b759b PM |
85 | extern void __rcu_read_lock(void); |
86 | extern void __rcu_read_unlock(void); | |
87 | void synchronize_rcu(void); | |
88 | ||
a3dc3fb1 PM |
89 | /* |
90 | * Defined as a macro as it is a very low level header included from | |
91 | * areas that don't even know about current. This gives the rcu_read_lock() | |
92 | * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other | |
93 | * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. | |
94 | */ | |
95 | #define rcu_preempt_depth() (current->rcu_read_lock_nesting) | |
96 | ||
7b0b759b PM |
97 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
98 | ||
99 | static inline void __rcu_read_lock(void) | |
100 | { | |
101 | preempt_disable(); | |
102 | } | |
103 | ||
104 | static inline void __rcu_read_unlock(void) | |
105 | { | |
106 | preempt_enable(); | |
107 | } | |
108 | ||
109 | static inline void synchronize_rcu(void) | |
110 | { | |
111 | synchronize_sched(); | |
112 | } | |
113 | ||
114 | static inline int rcu_preempt_depth(void) | |
115 | { | |
116 | return 0; | |
117 | } | |
118 | ||
119 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ | |
120 | ||
121 | /* Internal to kernel */ | |
7b0b759b PM |
122 | extern void rcu_sched_qs(int cpu); |
123 | extern void rcu_bh_qs(int cpu); | |
124 | extern void rcu_check_callbacks(int cpu, int user); | |
125 | struct notifier_block; | |
126 | ||
127 | #ifdef CONFIG_NO_HZ | |
128 | ||
129 | extern void rcu_enter_nohz(void); | |
130 | extern void rcu_exit_nohz(void); | |
131 | ||
132 | #else /* #ifdef CONFIG_NO_HZ */ | |
133 | ||
134 | static inline void rcu_enter_nohz(void) | |
135 | { | |
136 | } | |
137 | ||
138 | static inline void rcu_exit_nohz(void) | |
139 | { | |
140 | } | |
141 | ||
142 | #endif /* #else #ifdef CONFIG_NO_HZ */ | |
a3dc3fb1 | 143 | |
f41d911f | 144 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
64db4cff | 145 | #include <linux/rcutree.h> |
a57eb940 | 146 | #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) |
9b1d82fa | 147 | #include <linux/rcutiny.h> |
64db4cff PM |
148 | #else |
149 | #error "Unknown RCU implementation specified to kernel configuration" | |
6b3ef48a | 150 | #endif |
01c1c660 | 151 | |
551d55a9 MD |
152 | /* |
153 | * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic | |
154 | * initialization and destruction of rcu_head on the stack. rcu_head structures | |
155 | * allocated dynamically in the heap or defined statically don't need any | |
156 | * initialization. | |
157 | */ | |
158 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
159 | extern void init_rcu_head_on_stack(struct rcu_head *head); | |
160 | extern void destroy_rcu_head_on_stack(struct rcu_head *head); | |
161 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
4376030a MD |
162 | static inline void init_rcu_head_on_stack(struct rcu_head *head) |
163 | { | |
164 | } | |
165 | ||
166 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) | |
167 | { | |
168 | } | |
551d55a9 | 169 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
4376030a | 170 | |
bc33f24b | 171 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
632ee200 | 172 | |
bc33f24b | 173 | extern struct lockdep_map rcu_lock_map; |
632ee200 PM |
174 | # define rcu_read_acquire() \ |
175 | lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
bc33f24b | 176 | # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) |
632ee200 PM |
177 | |
178 | extern struct lockdep_map rcu_bh_lock_map; | |
179 | # define rcu_read_acquire_bh() \ | |
180 | lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
181 | # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) | |
182 | ||
183 | extern struct lockdep_map rcu_sched_lock_map; | |
184 | # define rcu_read_acquire_sched() \ | |
185 | lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
186 | # define rcu_read_release_sched() \ | |
187 | lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) | |
188 | ||
bc293d62 | 189 | extern int debug_lockdep_rcu_enabled(void); |
54dbf96c | 190 | |
632ee200 | 191 | /** |
ca5ecddf | 192 | * rcu_read_lock_held() - might we be in RCU read-side critical section? |
632ee200 | 193 | * |
d20200b5 PM |
194 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU |
195 | * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, | |
632ee200 | 196 | * this assumes we are in an RCU read-side critical section unless it can |
ca5ecddf PM |
197 | * prove otherwise. This is useful for debug checks in functions that |
198 | * require that they be called within an RCU read-side critical section. | |
54dbf96c | 199 | * |
ca5ecddf | 200 | * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot |
32c141a0 | 201 | * and while lockdep is disabled. |
632ee200 PM |
202 | */ |
203 | static inline int rcu_read_lock_held(void) | |
204 | { | |
54dbf96c PM |
205 | if (!debug_lockdep_rcu_enabled()) |
206 | return 1; | |
207 | return lock_is_held(&rcu_lock_map); | |
632ee200 PM |
208 | } |
209 | ||
e3818b8d PM |
210 | /* |
211 | * rcu_read_lock_bh_held() is defined out of line to avoid #include-file | |
212 | * hell. | |
632ee200 | 213 | */ |
e3818b8d | 214 | extern int rcu_read_lock_bh_held(void); |
632ee200 PM |
215 | |
216 | /** | |
ca5ecddf | 217 | * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? |
632ee200 | 218 | * |
d20200b5 PM |
219 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an |
220 | * RCU-sched read-side critical section. In absence of | |
221 | * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side | |
222 | * critical section unless it can prove otherwise. Note that disabling | |
223 | * of preemption (including disabling irqs) counts as an RCU-sched | |
ca5ecddf PM |
224 | * read-side critical section. This is useful for debug checks in functions |
225 | * that required that they be called within an RCU-sched read-side | |
226 | * critical section. | |
54dbf96c | 227 | * |
32c141a0 PM |
228 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot |
229 | * and while lockdep is disabled. | |
632ee200 | 230 | */ |
e6033e3b | 231 | #ifdef CONFIG_PREEMPT |
632ee200 PM |
232 | static inline int rcu_read_lock_sched_held(void) |
233 | { | |
234 | int lockdep_opinion = 0; | |
235 | ||
54dbf96c PM |
236 | if (!debug_lockdep_rcu_enabled()) |
237 | return 1; | |
632ee200 PM |
238 | if (debug_locks) |
239 | lockdep_opinion = lock_is_held(&rcu_sched_lock_map); | |
0cff810f | 240 | return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); |
632ee200 | 241 | } |
e6033e3b PM |
242 | #else /* #ifdef CONFIG_PREEMPT */ |
243 | static inline int rcu_read_lock_sched_held(void) | |
244 | { | |
245 | return 1; | |
632ee200 | 246 | } |
e6033e3b | 247 | #endif /* #else #ifdef CONFIG_PREEMPT */ |
632ee200 PM |
248 | |
249 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
250 | ||
251 | # define rcu_read_acquire() do { } while (0) | |
252 | # define rcu_read_release() do { } while (0) | |
253 | # define rcu_read_acquire_bh() do { } while (0) | |
254 | # define rcu_read_release_bh() do { } while (0) | |
255 | # define rcu_read_acquire_sched() do { } while (0) | |
256 | # define rcu_read_release_sched() do { } while (0) | |
257 | ||
258 | static inline int rcu_read_lock_held(void) | |
259 | { | |
260 | return 1; | |
261 | } | |
262 | ||
263 | static inline int rcu_read_lock_bh_held(void) | |
264 | { | |
265 | return 1; | |
266 | } | |
267 | ||
e6033e3b | 268 | #ifdef CONFIG_PREEMPT |
632ee200 PM |
269 | static inline int rcu_read_lock_sched_held(void) |
270 | { | |
bbad9379 | 271 | return preempt_count() != 0 || irqs_disabled(); |
632ee200 | 272 | } |
e6033e3b PM |
273 | #else /* #ifdef CONFIG_PREEMPT */ |
274 | static inline int rcu_read_lock_sched_held(void) | |
275 | { | |
276 | return 1; | |
632ee200 | 277 | } |
e6033e3b | 278 | #endif /* #else #ifdef CONFIG_PREEMPT */ |
632ee200 PM |
279 | |
280 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
281 | ||
282 | #ifdef CONFIG_PROVE_RCU | |
283 | ||
ee84b824 PM |
284 | extern int rcu_my_thread_group_empty(void); |
285 | ||
4221a991 TH |
286 | /** |
287 | * rcu_lockdep_assert - emit lockdep splat if specified condition not met | |
288 | * @c: condition to check | |
289 | */ | |
290 | #define rcu_lockdep_assert(c) \ | |
2b3fc35f LJ |
291 | do { \ |
292 | static bool __warned; \ | |
293 | if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ | |
294 | __warned = true; \ | |
295 | lockdep_rcu_dereference(__FILE__, __LINE__); \ | |
296 | } \ | |
297 | } while (0) | |
298 | ||
ca5ecddf PM |
299 | #else /* #ifdef CONFIG_PROVE_RCU */ |
300 | ||
4221a991 | 301 | #define rcu_lockdep_assert(c) do { } while (0) |
ca5ecddf PM |
302 | |
303 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
304 | ||
305 | /* | |
306 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() | |
307 | * and rcu_assign_pointer(). Some of these could be folded into their | |
308 | * callers, but they are left separate in order to ease introduction of | |
309 | * multiple flavors of pointers to match the multiple flavors of RCU | |
310 | * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in | |
311 | * the future. | |
312 | */ | |
53ecfba2 PM |
313 | |
314 | #ifdef __CHECKER__ | |
315 | #define rcu_dereference_sparse(p, space) \ | |
316 | ((void)(((typeof(*p) space *)p) == p)) | |
317 | #else /* #ifdef __CHECKER__ */ | |
318 | #define rcu_dereference_sparse(p, space) | |
319 | #endif /* #else #ifdef __CHECKER__ */ | |
320 | ||
ca5ecddf PM |
321 | #define __rcu_access_pointer(p, space) \ |
322 | ({ \ | |
323 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ | |
53ecfba2 | 324 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
325 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
326 | }) | |
327 | #define __rcu_dereference_check(p, c, space) \ | |
328 | ({ \ | |
329 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ | |
4221a991 | 330 | rcu_lockdep_assert(c); \ |
53ecfba2 | 331 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
332 | smp_read_barrier_depends(); \ |
333 | ((typeof(*p) __force __kernel *)(_________p1)); \ | |
334 | }) | |
335 | #define __rcu_dereference_protected(p, c, space) \ | |
336 | ({ \ | |
4221a991 | 337 | rcu_lockdep_assert(c); \ |
53ecfba2 | 338 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
339 | ((typeof(*p) __force __kernel *)(p)); \ |
340 | }) | |
341 | ||
342 | #define __rcu_dereference_index_check(p, c) \ | |
343 | ({ \ | |
344 | typeof(p) _________p1 = ACCESS_ONCE(p); \ | |
4221a991 | 345 | rcu_lockdep_assert(c); \ |
ca5ecddf PM |
346 | smp_read_barrier_depends(); \ |
347 | (_________p1); \ | |
348 | }) | |
349 | #define __rcu_assign_pointer(p, v, space) \ | |
350 | ({ \ | |
351 | if (!__builtin_constant_p(v) || \ | |
352 | ((v) != NULL)) \ | |
353 | smp_wmb(); \ | |
354 | (p) = (typeof(*v) __force space *)(v); \ | |
355 | }) | |
356 | ||
357 | ||
358 | /** | |
359 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing | |
360 | * @p: The pointer to read | |
361 | * | |
362 | * Return the value of the specified RCU-protected pointer, but omit the | |
363 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful | |
364 | * when the value of this pointer is accessed, but the pointer is not | |
365 | * dereferenced, for example, when testing an RCU-protected pointer against | |
366 | * NULL. Although rcu_access_pointer() may also be used in cases where | |
367 | * update-side locks prevent the value of the pointer from changing, you | |
368 | * should instead use rcu_dereference_protected() for this use case. | |
369 | */ | |
370 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) | |
371 | ||
632ee200 | 372 | /** |
ca5ecddf | 373 | * rcu_dereference_check() - rcu_dereference with debug checking |
c08c68dd DH |
374 | * @p: The pointer to read, prior to dereferencing |
375 | * @c: The conditions under which the dereference will take place | |
632ee200 | 376 | * |
c08c68dd | 377 | * Do an rcu_dereference(), but check that the conditions under which the |
ca5ecddf PM |
378 | * dereference will take place are correct. Typically the conditions |
379 | * indicate the various locking conditions that should be held at that | |
380 | * point. The check should return true if the conditions are satisfied. | |
381 | * An implicit check for being in an RCU read-side critical section | |
382 | * (rcu_read_lock()) is included. | |
c08c68dd DH |
383 | * |
384 | * For example: | |
385 | * | |
ca5ecddf | 386 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
c08c68dd DH |
387 | * |
388 | * could be used to indicate to lockdep that foo->bar may only be dereferenced | |
ca5ecddf | 389 | * if either rcu_read_lock() is held, or that the lock required to replace |
c08c68dd DH |
390 | * the bar struct at foo->bar is held. |
391 | * | |
392 | * Note that the list of conditions may also include indications of when a lock | |
393 | * need not be held, for example during initialisation or destruction of the | |
394 | * target struct: | |
395 | * | |
ca5ecddf | 396 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
c08c68dd | 397 | * atomic_read(&foo->usage) == 0); |
ca5ecddf PM |
398 | * |
399 | * Inserts memory barriers on architectures that require them | |
400 | * (currently only the Alpha), prevents the compiler from refetching | |
401 | * (and from merging fetches), and, more importantly, documents exactly | |
402 | * which pointers are protected by RCU and checks that the pointer is | |
403 | * annotated as __rcu. | |
632ee200 PM |
404 | */ |
405 | #define rcu_dereference_check(p, c) \ | |
ca5ecddf PM |
406 | __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) |
407 | ||
408 | /** | |
409 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking | |
410 | * @p: The pointer to read, prior to dereferencing | |
411 | * @c: The conditions under which the dereference will take place | |
412 | * | |
413 | * This is the RCU-bh counterpart to rcu_dereference_check(). | |
414 | */ | |
415 | #define rcu_dereference_bh_check(p, c) \ | |
416 | __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) | |
632ee200 | 417 | |
b62730ba | 418 | /** |
ca5ecddf PM |
419 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
420 | * @p: The pointer to read, prior to dereferencing | |
421 | * @c: The conditions under which the dereference will take place | |
422 | * | |
423 | * This is the RCU-sched counterpart to rcu_dereference_check(). | |
424 | */ | |
425 | #define rcu_dereference_sched_check(p, c) \ | |
426 | __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ | |
427 | __rcu) | |
428 | ||
429 | #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ | |
430 | ||
431 | /** | |
432 | * rcu_dereference_index_check() - rcu_dereference for indices with debug checking | |
433 | * @p: The pointer to read, prior to dereferencing | |
434 | * @c: The conditions under which the dereference will take place | |
435 | * | |
436 | * Similar to rcu_dereference_check(), but omits the sparse checking. | |
437 | * This allows rcu_dereference_index_check() to be used on integers, | |
438 | * which can then be used as array indices. Attempting to use | |
439 | * rcu_dereference_check() on an integer will give compiler warnings | |
440 | * because the sparse address-space mechanism relies on dereferencing | |
441 | * the RCU-protected pointer. Dereferencing integers is not something | |
442 | * that even gcc will put up with. | |
443 | * | |
444 | * Note that this function does not implicitly check for RCU read-side | |
445 | * critical sections. If this function gains lots of uses, it might | |
446 | * make sense to provide versions for each flavor of RCU, but it does | |
447 | * not make sense as of early 2010. | |
448 | */ | |
449 | #define rcu_dereference_index_check(p, c) \ | |
450 | __rcu_dereference_index_check((p), (c)) | |
451 | ||
452 | /** | |
453 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented | |
454 | * @p: The pointer to read, prior to dereferencing | |
455 | * @c: The conditions under which the dereference will take place | |
b62730ba PM |
456 | * |
457 | * Return the value of the specified RCU-protected pointer, but omit | |
458 | * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This | |
459 | * is useful in cases where update-side locks prevent the value of the | |
460 | * pointer from changing. Please note that this primitive does -not- | |
461 | * prevent the compiler from repeating this reference or combining it | |
462 | * with other references, so it should not be used without protection | |
463 | * of appropriate locks. | |
ca5ecddf PM |
464 | * |
465 | * This function is only for update-side use. Using this function | |
466 | * when protected only by rcu_read_lock() will result in infrequent | |
467 | * but very ugly failures. | |
b62730ba PM |
468 | */ |
469 | #define rcu_dereference_protected(p, c) \ | |
ca5ecddf | 470 | __rcu_dereference_protected((p), (c), __rcu) |
b62730ba | 471 | |
ca5ecddf PM |
472 | /** |
473 | * rcu_dereference_bh_protected() - fetch RCU-bh pointer when updates prevented | |
474 | * @p: The pointer to read, prior to dereferencing | |
475 | * @c: The conditions under which the dereference will take place | |
476 | * | |
477 | * This is the RCU-bh counterpart to rcu_dereference_protected(). | |
478 | */ | |
479 | #define rcu_dereference_bh_protected(p, c) \ | |
480 | __rcu_dereference_protected((p), (c), __rcu) | |
632ee200 | 481 | |
ca5ecddf PM |
482 | /** |
483 | * rcu_dereference_sched_protected() - fetch RCU-sched pointer when updates prevented | |
484 | * @p: The pointer to read, prior to dereferencing | |
485 | * @c: The conditions under which the dereference will take place | |
486 | * | |
487 | * This is the RCU-sched counterpart to rcu_dereference_protected(). | |
488 | */ | |
489 | #define rcu_dereference_sched_protected(p, c) \ | |
490 | __rcu_dereference_protected((p), (c), __rcu) | |
632ee200 | 491 | |
bc33f24b | 492 | |
b62730ba | 493 | /** |
ca5ecddf PM |
494 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
495 | * @p: The pointer to read, prior to dereferencing | |
b62730ba | 496 | * |
ca5ecddf | 497 | * This is a simple wrapper around rcu_dereference_check(). |
b62730ba | 498 | */ |
ca5ecddf | 499 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
b62730ba | 500 | |
1da177e4 | 501 | /** |
ca5ecddf PM |
502 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
503 | * @p: The pointer to read, prior to dereferencing | |
504 | * | |
505 | * Makes rcu_dereference_check() do the dirty work. | |
506 | */ | |
507 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) | |
508 | ||
509 | /** | |
510 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing | |
511 | * @p: The pointer to read, prior to dereferencing | |
512 | * | |
513 | * Makes rcu_dereference_check() do the dirty work. | |
514 | */ | |
515 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) | |
516 | ||
517 | /** | |
518 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section | |
1da177e4 | 519 | * |
9b06e818 | 520 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 521 | * are within RCU read-side critical sections, then the |
9b06e818 | 522 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
523 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
524 | * on one CPU while other CPUs are within RCU read-side critical | |
525 | * sections, invocation of the corresponding RCU callback is deferred | |
526 | * until after the all the other CPUs exit their critical sections. | |
527 | * | |
528 | * Note, however, that RCU callbacks are permitted to run concurrently | |
77d8485a | 529 | * with new RCU read-side critical sections. One way that this can happen |
1da177e4 LT |
530 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
531 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
532 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
533 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
534 | * callback is invoked. This is legal, because the RCU read-side critical | |
535 | * section that was running concurrently with the call_rcu() (and which | |
536 | * therefore might be referencing something that the corresponding RCU | |
537 | * callback would free up) has completed before the corresponding | |
538 | * RCU callback is invoked. | |
539 | * | |
540 | * RCU read-side critical sections may be nested. Any deferred actions | |
541 | * will be deferred until the outermost RCU read-side critical section | |
542 | * completes. | |
543 | * | |
9079fd7c PM |
544 | * You can avoid reading and understanding the next paragraph by |
545 | * following this rule: don't put anything in an rcu_read_lock() RCU | |
546 | * read-side critical section that would block in a !PREEMPT kernel. | |
547 | * But if you want the full story, read on! | |
548 | * | |
549 | * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it | |
550 | * is illegal to block while in an RCU read-side critical section. In | |
551 | * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) | |
552 | * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may | |
553 | * be preempted, but explicit blocking is illegal. Finally, in preemptible | |
554 | * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, | |
555 | * RCU read-side critical sections may be preempted and they may also | |
556 | * block, but only when acquiring spinlocks that are subject to priority | |
557 | * inheritance. | |
1da177e4 | 558 | */ |
bc33f24b PM |
559 | static inline void rcu_read_lock(void) |
560 | { | |
561 | __rcu_read_lock(); | |
562 | __acquire(RCU); | |
563 | rcu_read_acquire(); | |
564 | } | |
1da177e4 | 565 | |
1da177e4 LT |
566 | /* |
567 | * So where is rcu_write_lock()? It does not exist, as there is no | |
568 | * way for writers to lock out RCU readers. This is a feature, not | |
569 | * a bug -- this property is what provides RCU's performance benefits. | |
570 | * Of course, writers must coordinate with each other. The normal | |
571 | * spinlock primitives work well for this, but any other technique may be | |
572 | * used as well. RCU does not care how the writers keep out of each | |
573 | * others' way, as long as they do so. | |
574 | */ | |
3d76c082 PM |
575 | |
576 | /** | |
ca5ecddf | 577 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
3d76c082 PM |
578 | * |
579 | * See rcu_read_lock() for more information. | |
580 | */ | |
bc33f24b PM |
581 | static inline void rcu_read_unlock(void) |
582 | { | |
583 | rcu_read_release(); | |
584 | __release(RCU); | |
585 | __rcu_read_unlock(); | |
586 | } | |
1da177e4 LT |
587 | |
588 | /** | |
ca5ecddf | 589 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
1da177e4 LT |
590 | * |
591 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
ca5ecddf PM |
592 | * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since |
593 | * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a | |
594 | * softirq handler to be a quiescent state, a process in RCU read-side | |
595 | * critical section must be protected by disabling softirqs. Read-side | |
596 | * critical sections in interrupt context can use just rcu_read_lock(), | |
597 | * though this should at least be commented to avoid confusing people | |
598 | * reading the code. | |
1da177e4 | 599 | */ |
bc33f24b PM |
600 | static inline void rcu_read_lock_bh(void) |
601 | { | |
602 | __rcu_read_lock_bh(); | |
603 | __acquire(RCU_BH); | |
632ee200 | 604 | rcu_read_acquire_bh(); |
bc33f24b | 605 | } |
1da177e4 LT |
606 | |
607 | /* | |
608 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
609 | * | |
610 | * See rcu_read_lock_bh() for more information. | |
611 | */ | |
bc33f24b PM |
612 | static inline void rcu_read_unlock_bh(void) |
613 | { | |
632ee200 | 614 | rcu_read_release_bh(); |
bc33f24b PM |
615 | __release(RCU_BH); |
616 | __rcu_read_unlock_bh(); | |
617 | } | |
1da177e4 | 618 | |
1c50b728 | 619 | /** |
ca5ecddf | 620 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
1c50b728 | 621 | * |
ca5ecddf PM |
622 | * This is equivalent of rcu_read_lock(), but to be used when updates |
623 | * are being done using call_rcu_sched() or synchronize_rcu_sched(). | |
624 | * Read-side critical sections can also be introduced by anything that | |
625 | * disables preemption, including local_irq_disable() and friends. | |
1c50b728 | 626 | */ |
d6714c22 PM |
627 | static inline void rcu_read_lock_sched(void) |
628 | { | |
629 | preempt_disable(); | |
bc33f24b | 630 | __acquire(RCU_SCHED); |
632ee200 | 631 | rcu_read_acquire_sched(); |
d6714c22 | 632 | } |
1eba8f84 PM |
633 | |
634 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 635 | static inline notrace void rcu_read_lock_sched_notrace(void) |
d6714c22 PM |
636 | { |
637 | preempt_disable_notrace(); | |
bc33f24b | 638 | __acquire(RCU_SCHED); |
d6714c22 | 639 | } |
1c50b728 MD |
640 | |
641 | /* | |
642 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section | |
643 | * | |
644 | * See rcu_read_lock_sched for more information. | |
645 | */ | |
d6714c22 PM |
646 | static inline void rcu_read_unlock_sched(void) |
647 | { | |
632ee200 | 648 | rcu_read_release_sched(); |
bc33f24b | 649 | __release(RCU_SCHED); |
d6714c22 PM |
650 | preempt_enable(); |
651 | } | |
1eba8f84 PM |
652 | |
653 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 654 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
d6714c22 | 655 | { |
bc33f24b | 656 | __release(RCU_SCHED); |
d6714c22 PM |
657 | preempt_enable_notrace(); |
658 | } | |
1c50b728 | 659 | |
1da177e4 | 660 | /** |
ca5ecddf PM |
661 | * rcu_assign_pointer() - assign to RCU-protected pointer |
662 | * @p: pointer to assign to | |
663 | * @v: value to assign (publish) | |
c26d34a5 | 664 | * |
ca5ecddf PM |
665 | * Assigns the specified value to the specified RCU-protected |
666 | * pointer, ensuring that any concurrent RCU readers will see | |
667 | * any prior initialization. Returns the value assigned. | |
1da177e4 LT |
668 | * |
669 | * Inserts memory barriers on architectures that require them | |
670 | * (pretty much all of them other than x86), and also prevents | |
671 | * the compiler from reordering the code that initializes the | |
672 | * structure after the pointer assignment. More importantly, this | |
673 | * call documents which pointers will be dereferenced by RCU read-side | |
674 | * code. | |
675 | */ | |
d99c4f6b | 676 | #define rcu_assign_pointer(p, v) \ |
ca5ecddf PM |
677 | __rcu_assign_pointer((p), (v), __rcu) |
678 | ||
679 | /** | |
680 | * RCU_INIT_POINTER() - initialize an RCU protected pointer | |
681 | * | |
682 | * Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep | |
683 | * splats. | |
684 | */ | |
685 | #define RCU_INIT_POINTER(p, v) \ | |
686 | p = (typeof(*v) __force __rcu *)(v) | |
1da177e4 | 687 | |
4446a36f PM |
688 | /* Infrastructure to implement the synchronize_() primitives. */ |
689 | ||
690 | struct rcu_synchronize { | |
691 | struct rcu_head head; | |
692 | struct completion completion; | |
693 | }; | |
694 | ||
695 | extern void wakeme_after_rcu(struct rcu_head *head); | |
696 | ||
7b0b759b PM |
697 | #ifdef CONFIG_PREEMPT_RCU |
698 | ||
01c1c660 | 699 | /** |
ca5ecddf | 700 | * call_rcu() - Queue an RCU callback for invocation after a grace period. |
01c1c660 | 701 | * @head: structure to be used for queueing the RCU updates. |
77d8485a | 702 | * @func: actual callback function to be invoked after the grace period |
01c1c660 | 703 | * |
77d8485a PM |
704 | * The callback function will be invoked some time after a full grace |
705 | * period elapses, in other words after all pre-existing RCU read-side | |
706 | * critical sections have completed. However, the callback function | |
707 | * might well execute concurrently with RCU read-side critical sections | |
708 | * that started after call_rcu() was invoked. RCU read-side critical | |
01c1c660 PM |
709 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), |
710 | * and may be nested. | |
711 | */ | |
712 | extern void call_rcu(struct rcu_head *head, | |
713 | void (*func)(struct rcu_head *head)); | |
714 | ||
7b0b759b PM |
715 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
716 | ||
717 | /* In classic RCU, call_rcu() is just call_rcu_sched(). */ | |
718 | #define call_rcu call_rcu_sched | |
719 | ||
720 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ | |
721 | ||
01c1c660 | 722 | /** |
ca5ecddf | 723 | * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. |
01c1c660 | 724 | * @head: structure to be used for queueing the RCU updates. |
77d8485a | 725 | * @func: actual callback function to be invoked after the grace period |
01c1c660 | 726 | * |
77d8485a | 727 | * The callback function will be invoked some time after a full grace |
01c1c660 PM |
728 | * period elapses, in other words after all currently executing RCU |
729 | * read-side critical sections have completed. call_rcu_bh() assumes | |
730 | * that the read-side critical sections end on completion of a softirq | |
731 | * handler. This means that read-side critical sections in process | |
732 | * context must not be interrupted by softirqs. This interface is to be | |
733 | * used when most of the read-side critical sections are in softirq context. | |
734 | * RCU read-side critical sections are delimited by : | |
735 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. | |
736 | * OR | |
737 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. | |
738 | * These may be nested. | |
739 | */ | |
740 | extern void call_rcu_bh(struct rcu_head *head, | |
741 | void (*func)(struct rcu_head *head)); | |
742 | ||
551d55a9 MD |
743 | /* |
744 | * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally | |
745 | * by call_rcu() and rcu callback execution, and are therefore not part of the | |
746 | * RCU API. Leaving in rcupdate.h because they are used by all RCU flavors. | |
747 | */ | |
748 | ||
749 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
750 | # define STATE_RCU_HEAD_READY 0 | |
751 | # define STATE_RCU_HEAD_QUEUED 1 | |
752 | ||
753 | extern struct debug_obj_descr rcuhead_debug_descr; | |
754 | ||
755 | static inline void debug_rcu_head_queue(struct rcu_head *head) | |
756 | { | |
757 | debug_object_activate(head, &rcuhead_debug_descr); | |
758 | debug_object_active_state(head, &rcuhead_debug_descr, | |
759 | STATE_RCU_HEAD_READY, | |
760 | STATE_RCU_HEAD_QUEUED); | |
761 | } | |
762 | ||
763 | static inline void debug_rcu_head_unqueue(struct rcu_head *head) | |
764 | { | |
765 | debug_object_active_state(head, &rcuhead_debug_descr, | |
766 | STATE_RCU_HEAD_QUEUED, | |
767 | STATE_RCU_HEAD_READY); | |
768 | debug_object_deactivate(head, &rcuhead_debug_descr); | |
769 | } | |
770 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
771 | static inline void debug_rcu_head_queue(struct rcu_head *head) | |
772 | { | |
773 | } | |
774 | ||
775 | static inline void debug_rcu_head_unqueue(struct rcu_head *head) | |
776 | { | |
777 | } | |
778 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
779 | ||
1da177e4 | 780 | #endif /* __LINUX_RCUPDATE_H */ |