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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 | ||
1da177e4 LT |
50 | /** |
51 | * struct rcu_head - callback structure for use with RCU | |
52 | * @next: next update requests in a list | |
53 | * @func: actual update function to call after the grace period. | |
54 | */ | |
55 | struct rcu_head { | |
56 | struct rcu_head *next; | |
57 | void (*func)(struct rcu_head *head); | |
58 | }; | |
59 | ||
03b042bf | 60 | /* Exported common interfaces */ |
03b042bf PM |
61 | extern void rcu_barrier(void); |
62 | extern void rcu_barrier_bh(void); | |
63 | extern void rcu_barrier_sched(void); | |
64 | extern void synchronize_sched_expedited(void); | |
65 | extern int sched_expedited_torture_stats(char *page); | |
66 | ||
67 | /* Internal to kernel */ | |
68 | extern void rcu_init(void); | |
a6826048 | 69 | |
f41d911f | 70 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
64db4cff | 71 | #include <linux/rcutree.h> |
2c28e245 | 72 | #elif defined(CONFIG_TINY_RCU) |
9b1d82fa | 73 | #include <linux/rcutiny.h> |
64db4cff PM |
74 | #else |
75 | #error "Unknown RCU implementation specified to kernel configuration" | |
6b3ef48a | 76 | #endif |
01c1c660 | 77 | |
3d76c082 | 78 | #define RCU_HEAD_INIT { .next = NULL, .func = NULL } |
8b6490e5 | 79 | #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT |
1da177e4 LT |
80 | #define INIT_RCU_HEAD(ptr) do { \ |
81 | (ptr)->next = NULL; (ptr)->func = NULL; \ | |
82 | } while (0) | |
83 | ||
551d55a9 MD |
84 | /* |
85 | * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic | |
86 | * initialization and destruction of rcu_head on the stack. rcu_head structures | |
87 | * allocated dynamically in the heap or defined statically don't need any | |
88 | * initialization. | |
89 | */ | |
90 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
91 | extern void init_rcu_head_on_stack(struct rcu_head *head); | |
92 | extern void destroy_rcu_head_on_stack(struct rcu_head *head); | |
93 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
4376030a MD |
94 | static inline void init_rcu_head_on_stack(struct rcu_head *head) |
95 | { | |
96 | } | |
97 | ||
98 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) | |
99 | { | |
100 | } | |
551d55a9 | 101 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
4376030a | 102 | |
bc33f24b | 103 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
632ee200 | 104 | |
bc33f24b | 105 | extern struct lockdep_map rcu_lock_map; |
632ee200 PM |
106 | # define rcu_read_acquire() \ |
107 | lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
bc33f24b | 108 | # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) |
632ee200 PM |
109 | |
110 | extern struct lockdep_map rcu_bh_lock_map; | |
111 | # define rcu_read_acquire_bh() \ | |
112 | lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
113 | # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) | |
114 | ||
115 | extern struct lockdep_map rcu_sched_lock_map; | |
116 | # define rcu_read_acquire_sched() \ | |
117 | lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
118 | # define rcu_read_release_sched() \ | |
119 | lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) | |
120 | ||
bc293d62 | 121 | extern int debug_lockdep_rcu_enabled(void); |
54dbf96c | 122 | |
632ee200 | 123 | /** |
ca5ecddf | 124 | * rcu_read_lock_held() - might we be in RCU read-side critical section? |
632ee200 | 125 | * |
d20200b5 PM |
126 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU |
127 | * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, | |
632ee200 | 128 | * this assumes we are in an RCU read-side critical section unless it can |
ca5ecddf PM |
129 | * prove otherwise. This is useful for debug checks in functions that |
130 | * require that they be called within an RCU read-side critical section. | |
54dbf96c | 131 | * |
ca5ecddf | 132 | * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot |
32c141a0 | 133 | * and while lockdep is disabled. |
632ee200 PM |
134 | */ |
135 | static inline int rcu_read_lock_held(void) | |
136 | { | |
54dbf96c PM |
137 | if (!debug_lockdep_rcu_enabled()) |
138 | return 1; | |
139 | return lock_is_held(&rcu_lock_map); | |
632ee200 PM |
140 | } |
141 | ||
e3818b8d PM |
142 | /* |
143 | * rcu_read_lock_bh_held() is defined out of line to avoid #include-file | |
144 | * hell. | |
632ee200 | 145 | */ |
e3818b8d | 146 | extern int rcu_read_lock_bh_held(void); |
632ee200 PM |
147 | |
148 | /** | |
ca5ecddf | 149 | * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? |
632ee200 | 150 | * |
d20200b5 PM |
151 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an |
152 | * RCU-sched read-side critical section. In absence of | |
153 | * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side | |
154 | * critical section unless it can prove otherwise. Note that disabling | |
155 | * of preemption (including disabling irqs) counts as an RCU-sched | |
ca5ecddf PM |
156 | * read-side critical section. This is useful for debug checks in functions |
157 | * that required that they be called within an RCU-sched read-side | |
158 | * critical section. | |
54dbf96c | 159 | * |
32c141a0 PM |
160 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot |
161 | * and while lockdep is disabled. | |
632ee200 | 162 | */ |
e6033e3b | 163 | #ifdef CONFIG_PREEMPT |
632ee200 PM |
164 | static inline int rcu_read_lock_sched_held(void) |
165 | { | |
166 | int lockdep_opinion = 0; | |
167 | ||
54dbf96c PM |
168 | if (!debug_lockdep_rcu_enabled()) |
169 | return 1; | |
632ee200 PM |
170 | if (debug_locks) |
171 | lockdep_opinion = lock_is_held(&rcu_sched_lock_map); | |
0cff810f | 172 | return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); |
632ee200 | 173 | } |
e6033e3b PM |
174 | #else /* #ifdef CONFIG_PREEMPT */ |
175 | static inline int rcu_read_lock_sched_held(void) | |
176 | { | |
177 | return 1; | |
632ee200 | 178 | } |
e6033e3b | 179 | #endif /* #else #ifdef CONFIG_PREEMPT */ |
632ee200 PM |
180 | |
181 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
182 | ||
183 | # define rcu_read_acquire() do { } while (0) | |
184 | # define rcu_read_release() do { } while (0) | |
185 | # define rcu_read_acquire_bh() do { } while (0) | |
186 | # define rcu_read_release_bh() do { } while (0) | |
187 | # define rcu_read_acquire_sched() do { } while (0) | |
188 | # define rcu_read_release_sched() do { } while (0) | |
189 | ||
190 | static inline int rcu_read_lock_held(void) | |
191 | { | |
192 | return 1; | |
193 | } | |
194 | ||
195 | static inline int rcu_read_lock_bh_held(void) | |
196 | { | |
197 | return 1; | |
198 | } | |
199 | ||
e6033e3b | 200 | #ifdef CONFIG_PREEMPT |
632ee200 PM |
201 | static inline int rcu_read_lock_sched_held(void) |
202 | { | |
bbad9379 | 203 | return preempt_count() != 0 || irqs_disabled(); |
632ee200 | 204 | } |
e6033e3b PM |
205 | #else /* #ifdef CONFIG_PREEMPT */ |
206 | static inline int rcu_read_lock_sched_held(void) | |
207 | { | |
208 | return 1; | |
632ee200 | 209 | } |
e6033e3b | 210 | #endif /* #else #ifdef CONFIG_PREEMPT */ |
632ee200 PM |
211 | |
212 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
213 | ||
214 | #ifdef CONFIG_PROVE_RCU | |
215 | ||
ee84b824 PM |
216 | extern int rcu_my_thread_group_empty(void); |
217 | ||
4221a991 TH |
218 | /** |
219 | * rcu_lockdep_assert - emit lockdep splat if specified condition not met | |
220 | * @c: condition to check | |
221 | */ | |
222 | #define rcu_lockdep_assert(c) \ | |
2b3fc35f LJ |
223 | do { \ |
224 | static bool __warned; \ | |
225 | if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ | |
226 | __warned = true; \ | |
227 | lockdep_rcu_dereference(__FILE__, __LINE__); \ | |
228 | } \ | |
229 | } while (0) | |
230 | ||
ca5ecddf PM |
231 | #else /* #ifdef CONFIG_PROVE_RCU */ |
232 | ||
4221a991 | 233 | #define rcu_lockdep_assert(c) do { } while (0) |
ca5ecddf PM |
234 | |
235 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
236 | ||
237 | /* | |
238 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() | |
239 | * and rcu_assign_pointer(). Some of these could be folded into their | |
240 | * callers, but they are left separate in order to ease introduction of | |
241 | * multiple flavors of pointers to match the multiple flavors of RCU | |
242 | * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in | |
243 | * the future. | |
244 | */ | |
245 | #define __rcu_access_pointer(p, space) \ | |
246 | ({ \ | |
247 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ | |
248 | (void) (((typeof (*p) space *)p) == p); \ | |
249 | ((typeof(*p) __force __kernel *)(_________p1)); \ | |
250 | }) | |
251 | #define __rcu_dereference_check(p, c, space) \ | |
252 | ({ \ | |
253 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ | |
4221a991 | 254 | rcu_lockdep_assert(c); \ |
ca5ecddf PM |
255 | (void) (((typeof (*p) space *)p) == p); \ |
256 | smp_read_barrier_depends(); \ | |
257 | ((typeof(*p) __force __kernel *)(_________p1)); \ | |
258 | }) | |
259 | #define __rcu_dereference_protected(p, c, space) \ | |
260 | ({ \ | |
4221a991 | 261 | rcu_lockdep_assert(c); \ |
ca5ecddf PM |
262 | (void) (((typeof (*p) space *)p) == p); \ |
263 | ((typeof(*p) __force __kernel *)(p)); \ | |
264 | }) | |
265 | ||
266 | #define __rcu_dereference_index_check(p, c) \ | |
267 | ({ \ | |
268 | typeof(p) _________p1 = ACCESS_ONCE(p); \ | |
4221a991 | 269 | rcu_lockdep_assert(c); \ |
ca5ecddf PM |
270 | smp_read_barrier_depends(); \ |
271 | (_________p1); \ | |
272 | }) | |
273 | #define __rcu_assign_pointer(p, v, space) \ | |
274 | ({ \ | |
275 | if (!__builtin_constant_p(v) || \ | |
276 | ((v) != NULL)) \ | |
277 | smp_wmb(); \ | |
278 | (p) = (typeof(*v) __force space *)(v); \ | |
279 | }) | |
280 | ||
281 | ||
282 | /** | |
283 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing | |
284 | * @p: The pointer to read | |
285 | * | |
286 | * Return the value of the specified RCU-protected pointer, but omit the | |
287 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful | |
288 | * when the value of this pointer is accessed, but the pointer is not | |
289 | * dereferenced, for example, when testing an RCU-protected pointer against | |
290 | * NULL. Although rcu_access_pointer() may also be used in cases where | |
291 | * update-side locks prevent the value of the pointer from changing, you | |
292 | * should instead use rcu_dereference_protected() for this use case. | |
293 | */ | |
294 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) | |
295 | ||
632ee200 | 296 | /** |
ca5ecddf | 297 | * rcu_dereference_check() - rcu_dereference with debug checking |
c08c68dd DH |
298 | * @p: The pointer to read, prior to dereferencing |
299 | * @c: The conditions under which the dereference will take place | |
632ee200 | 300 | * |
c08c68dd | 301 | * Do an rcu_dereference(), but check that the conditions under which the |
ca5ecddf PM |
302 | * dereference will take place are correct. Typically the conditions |
303 | * indicate the various locking conditions that should be held at that | |
304 | * point. The check should return true if the conditions are satisfied. | |
305 | * An implicit check for being in an RCU read-side critical section | |
306 | * (rcu_read_lock()) is included. | |
c08c68dd DH |
307 | * |
308 | * For example: | |
309 | * | |
ca5ecddf | 310 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
c08c68dd DH |
311 | * |
312 | * could be used to indicate to lockdep that foo->bar may only be dereferenced | |
ca5ecddf | 313 | * if either rcu_read_lock() is held, or that the lock required to replace |
c08c68dd DH |
314 | * the bar struct at foo->bar is held. |
315 | * | |
316 | * Note that the list of conditions may also include indications of when a lock | |
317 | * need not be held, for example during initialisation or destruction of the | |
318 | * target struct: | |
319 | * | |
ca5ecddf | 320 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
c08c68dd | 321 | * atomic_read(&foo->usage) == 0); |
ca5ecddf PM |
322 | * |
323 | * Inserts memory barriers on architectures that require them | |
324 | * (currently only the Alpha), prevents the compiler from refetching | |
325 | * (and from merging fetches), and, more importantly, documents exactly | |
326 | * which pointers are protected by RCU and checks that the pointer is | |
327 | * annotated as __rcu. | |
632ee200 PM |
328 | */ |
329 | #define rcu_dereference_check(p, c) \ | |
ca5ecddf PM |
330 | __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) |
331 | ||
332 | /** | |
333 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking | |
334 | * @p: The pointer to read, prior to dereferencing | |
335 | * @c: The conditions under which the dereference will take place | |
336 | * | |
337 | * This is the RCU-bh counterpart to rcu_dereference_check(). | |
338 | */ | |
339 | #define rcu_dereference_bh_check(p, c) \ | |
340 | __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) | |
632ee200 | 341 | |
b62730ba | 342 | /** |
ca5ecddf PM |
343 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
344 | * @p: The pointer to read, prior to dereferencing | |
345 | * @c: The conditions under which the dereference will take place | |
346 | * | |
347 | * This is the RCU-sched counterpart to rcu_dereference_check(). | |
348 | */ | |
349 | #define rcu_dereference_sched_check(p, c) \ | |
350 | __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ | |
351 | __rcu) | |
352 | ||
353 | #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ | |
354 | ||
355 | /** | |
356 | * rcu_dereference_index_check() - rcu_dereference for indices with debug checking | |
357 | * @p: The pointer to read, prior to dereferencing | |
358 | * @c: The conditions under which the dereference will take place | |
359 | * | |
360 | * Similar to rcu_dereference_check(), but omits the sparse checking. | |
361 | * This allows rcu_dereference_index_check() to be used on integers, | |
362 | * which can then be used as array indices. Attempting to use | |
363 | * rcu_dereference_check() on an integer will give compiler warnings | |
364 | * because the sparse address-space mechanism relies on dereferencing | |
365 | * the RCU-protected pointer. Dereferencing integers is not something | |
366 | * that even gcc will put up with. | |
367 | * | |
368 | * Note that this function does not implicitly check for RCU read-side | |
369 | * critical sections. If this function gains lots of uses, it might | |
370 | * make sense to provide versions for each flavor of RCU, but it does | |
371 | * not make sense as of early 2010. | |
372 | */ | |
373 | #define rcu_dereference_index_check(p, c) \ | |
374 | __rcu_dereference_index_check((p), (c)) | |
375 | ||
376 | /** | |
377 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented | |
378 | * @p: The pointer to read, prior to dereferencing | |
379 | * @c: The conditions under which the dereference will take place | |
b62730ba PM |
380 | * |
381 | * Return the value of the specified RCU-protected pointer, but omit | |
382 | * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This | |
383 | * is useful in cases where update-side locks prevent the value of the | |
384 | * pointer from changing. Please note that this primitive does -not- | |
385 | * prevent the compiler from repeating this reference or combining it | |
386 | * with other references, so it should not be used without protection | |
387 | * of appropriate locks. | |
ca5ecddf PM |
388 | * |
389 | * This function is only for update-side use. Using this function | |
390 | * when protected only by rcu_read_lock() will result in infrequent | |
391 | * but very ugly failures. | |
b62730ba PM |
392 | */ |
393 | #define rcu_dereference_protected(p, c) \ | |
ca5ecddf | 394 | __rcu_dereference_protected((p), (c), __rcu) |
b62730ba | 395 | |
ca5ecddf PM |
396 | /** |
397 | * rcu_dereference_bh_protected() - fetch RCU-bh pointer when updates prevented | |
398 | * @p: The pointer to read, prior to dereferencing | |
399 | * @c: The conditions under which the dereference will take place | |
400 | * | |
401 | * This is the RCU-bh counterpart to rcu_dereference_protected(). | |
402 | */ | |
403 | #define rcu_dereference_bh_protected(p, c) \ | |
404 | __rcu_dereference_protected((p), (c), __rcu) | |
632ee200 | 405 | |
ca5ecddf PM |
406 | /** |
407 | * rcu_dereference_sched_protected() - fetch RCU-sched pointer when updates prevented | |
408 | * @p: The pointer to read, prior to dereferencing | |
409 | * @c: The conditions under which the dereference will take place | |
410 | * | |
411 | * This is the RCU-sched counterpart to rcu_dereference_protected(). | |
412 | */ | |
413 | #define rcu_dereference_sched_protected(p, c) \ | |
414 | __rcu_dereference_protected((p), (c), __rcu) | |
632ee200 | 415 | |
bc33f24b | 416 | |
b62730ba | 417 | /** |
ca5ecddf PM |
418 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
419 | * @p: The pointer to read, prior to dereferencing | |
b62730ba | 420 | * |
ca5ecddf | 421 | * This is a simple wrapper around rcu_dereference_check(). |
b62730ba | 422 | */ |
ca5ecddf | 423 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
b62730ba | 424 | |
1da177e4 | 425 | /** |
ca5ecddf PM |
426 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
427 | * @p: The pointer to read, prior to dereferencing | |
428 | * | |
429 | * Makes rcu_dereference_check() do the dirty work. | |
430 | */ | |
431 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) | |
432 | ||
433 | /** | |
434 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing | |
435 | * @p: The pointer to read, prior to dereferencing | |
436 | * | |
437 | * Makes rcu_dereference_check() do the dirty work. | |
438 | */ | |
439 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) | |
440 | ||
441 | /** | |
442 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section | |
1da177e4 | 443 | * |
9b06e818 | 444 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 445 | * are within RCU read-side critical sections, then the |
9b06e818 | 446 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
447 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
448 | * on one CPU while other CPUs are within RCU read-side critical | |
449 | * sections, invocation of the corresponding RCU callback is deferred | |
450 | * until after the all the other CPUs exit their critical sections. | |
451 | * | |
452 | * Note, however, that RCU callbacks are permitted to run concurrently | |
453 | * with RCU read-side critical sections. One way that this can happen | |
454 | * is via the following sequence of events: (1) CPU 0 enters an RCU | |
455 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
456 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
457 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
458 | * callback is invoked. This is legal, because the RCU read-side critical | |
459 | * section that was running concurrently with the call_rcu() (and which | |
460 | * therefore might be referencing something that the corresponding RCU | |
461 | * callback would free up) has completed before the corresponding | |
462 | * RCU callback is invoked. | |
463 | * | |
464 | * RCU read-side critical sections may be nested. Any deferred actions | |
465 | * will be deferred until the outermost RCU read-side critical section | |
466 | * completes. | |
467 | * | |
468 | * It is illegal to block while in an RCU read-side critical section. | |
469 | */ | |
bc33f24b PM |
470 | static inline void rcu_read_lock(void) |
471 | { | |
472 | __rcu_read_lock(); | |
473 | __acquire(RCU); | |
474 | rcu_read_acquire(); | |
475 | } | |
1da177e4 | 476 | |
1da177e4 LT |
477 | /* |
478 | * So where is rcu_write_lock()? It does not exist, as there is no | |
479 | * way for writers to lock out RCU readers. This is a feature, not | |
480 | * a bug -- this property is what provides RCU's performance benefits. | |
481 | * Of course, writers must coordinate with each other. The normal | |
482 | * spinlock primitives work well for this, but any other technique may be | |
483 | * used as well. RCU does not care how the writers keep out of each | |
484 | * others' way, as long as they do so. | |
485 | */ | |
3d76c082 PM |
486 | |
487 | /** | |
ca5ecddf | 488 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
3d76c082 PM |
489 | * |
490 | * See rcu_read_lock() for more information. | |
491 | */ | |
bc33f24b PM |
492 | static inline void rcu_read_unlock(void) |
493 | { | |
494 | rcu_read_release(); | |
495 | __release(RCU); | |
496 | __rcu_read_unlock(); | |
497 | } | |
1da177e4 LT |
498 | |
499 | /** | |
ca5ecddf | 500 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
1da177e4 LT |
501 | * |
502 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
ca5ecddf PM |
503 | * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since |
504 | * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a | |
505 | * softirq handler to be a quiescent state, a process in RCU read-side | |
506 | * critical section must be protected by disabling softirqs. Read-side | |
507 | * critical sections in interrupt context can use just rcu_read_lock(), | |
508 | * though this should at least be commented to avoid confusing people | |
509 | * reading the code. | |
1da177e4 | 510 | */ |
bc33f24b PM |
511 | static inline void rcu_read_lock_bh(void) |
512 | { | |
513 | __rcu_read_lock_bh(); | |
514 | __acquire(RCU_BH); | |
632ee200 | 515 | rcu_read_acquire_bh(); |
bc33f24b | 516 | } |
1da177e4 LT |
517 | |
518 | /* | |
519 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
520 | * | |
521 | * See rcu_read_lock_bh() for more information. | |
522 | */ | |
bc33f24b PM |
523 | static inline void rcu_read_unlock_bh(void) |
524 | { | |
632ee200 | 525 | rcu_read_release_bh(); |
bc33f24b PM |
526 | __release(RCU_BH); |
527 | __rcu_read_unlock_bh(); | |
528 | } | |
1da177e4 | 529 | |
1c50b728 | 530 | /** |
ca5ecddf | 531 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
1c50b728 | 532 | * |
ca5ecddf PM |
533 | * This is equivalent of rcu_read_lock(), but to be used when updates |
534 | * are being done using call_rcu_sched() or synchronize_rcu_sched(). | |
535 | * Read-side critical sections can also be introduced by anything that | |
536 | * disables preemption, including local_irq_disable() and friends. | |
1c50b728 | 537 | */ |
d6714c22 PM |
538 | static inline void rcu_read_lock_sched(void) |
539 | { | |
540 | preempt_disable(); | |
bc33f24b | 541 | __acquire(RCU_SCHED); |
632ee200 | 542 | rcu_read_acquire_sched(); |
d6714c22 | 543 | } |
1eba8f84 PM |
544 | |
545 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 546 | static inline notrace void rcu_read_lock_sched_notrace(void) |
d6714c22 PM |
547 | { |
548 | preempt_disable_notrace(); | |
bc33f24b | 549 | __acquire(RCU_SCHED); |
d6714c22 | 550 | } |
1c50b728 MD |
551 | |
552 | /* | |
553 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section | |
554 | * | |
555 | * See rcu_read_lock_sched for more information. | |
556 | */ | |
d6714c22 PM |
557 | static inline void rcu_read_unlock_sched(void) |
558 | { | |
632ee200 | 559 | rcu_read_release_sched(); |
bc33f24b | 560 | __release(RCU_SCHED); |
d6714c22 PM |
561 | preempt_enable(); |
562 | } | |
1eba8f84 PM |
563 | |
564 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 565 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
d6714c22 | 566 | { |
bc33f24b | 567 | __release(RCU_SCHED); |
d6714c22 PM |
568 | preempt_enable_notrace(); |
569 | } | |
1c50b728 | 570 | |
1da177e4 | 571 | /** |
ca5ecddf PM |
572 | * rcu_assign_pointer() - assign to RCU-protected pointer |
573 | * @p: pointer to assign to | |
574 | * @v: value to assign (publish) | |
c26d34a5 | 575 | * |
ca5ecddf PM |
576 | * Assigns the specified value to the specified RCU-protected |
577 | * pointer, ensuring that any concurrent RCU readers will see | |
578 | * any prior initialization. Returns the value assigned. | |
1da177e4 LT |
579 | * |
580 | * Inserts memory barriers on architectures that require them | |
581 | * (pretty much all of them other than x86), and also prevents | |
582 | * the compiler from reordering the code that initializes the | |
583 | * structure after the pointer assignment. More importantly, this | |
584 | * call documents which pointers will be dereferenced by RCU read-side | |
585 | * code. | |
586 | */ | |
d99c4f6b | 587 | #define rcu_assign_pointer(p, v) \ |
ca5ecddf PM |
588 | __rcu_assign_pointer((p), (v), __rcu) |
589 | ||
590 | /** | |
591 | * RCU_INIT_POINTER() - initialize an RCU protected pointer | |
592 | * | |
593 | * Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep | |
594 | * splats. | |
595 | */ | |
596 | #define RCU_INIT_POINTER(p, v) \ | |
597 | p = (typeof(*v) __force __rcu *)(v) | |
1da177e4 | 598 | |
4446a36f PM |
599 | /* Infrastructure to implement the synchronize_() primitives. */ |
600 | ||
601 | struct rcu_synchronize { | |
602 | struct rcu_head head; | |
603 | struct completion completion; | |
604 | }; | |
605 | ||
606 | extern void wakeme_after_rcu(struct rcu_head *head); | |
607 | ||
01c1c660 | 608 | /** |
ca5ecddf | 609 | * call_rcu() - Queue an RCU callback for invocation after a grace period. |
01c1c660 PM |
610 | * @head: structure to be used for queueing the RCU updates. |
611 | * @func: actual update function to be invoked after the grace period | |
612 | * | |
613 | * The update function will be invoked some time after a full grace | |
614 | * period elapses, in other words after all currently executing RCU | |
615 | * read-side critical sections have completed. RCU read-side critical | |
616 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
617 | * and may be nested. | |
618 | */ | |
619 | extern void call_rcu(struct rcu_head *head, | |
620 | void (*func)(struct rcu_head *head)); | |
621 | ||
622 | /** | |
ca5ecddf | 623 | * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. |
01c1c660 PM |
624 | * @head: structure to be used for queueing the RCU updates. |
625 | * @func: actual update function to be invoked after the grace period | |
626 | * | |
627 | * The update function will be invoked some time after a full grace | |
628 | * period elapses, in other words after all currently executing RCU | |
629 | * read-side critical sections have completed. call_rcu_bh() assumes | |
630 | * that the read-side critical sections end on completion of a softirq | |
631 | * handler. This means that read-side critical sections in process | |
632 | * context must not be interrupted by softirqs. This interface is to be | |
633 | * used when most of the read-side critical sections are in softirq context. | |
634 | * RCU read-side critical sections are delimited by : | |
635 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. | |
636 | * OR | |
637 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. | |
638 | * These may be nested. | |
639 | */ | |
640 | extern void call_rcu_bh(struct rcu_head *head, | |
641 | void (*func)(struct rcu_head *head)); | |
642 | ||
551d55a9 MD |
643 | /* |
644 | * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally | |
645 | * by call_rcu() and rcu callback execution, and are therefore not part of the | |
646 | * RCU API. Leaving in rcupdate.h because they are used by all RCU flavors. | |
647 | */ | |
648 | ||
649 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
650 | # define STATE_RCU_HEAD_READY 0 | |
651 | # define STATE_RCU_HEAD_QUEUED 1 | |
652 | ||
653 | extern struct debug_obj_descr rcuhead_debug_descr; | |
654 | ||
655 | static inline void debug_rcu_head_queue(struct rcu_head *head) | |
656 | { | |
657 | debug_object_activate(head, &rcuhead_debug_descr); | |
658 | debug_object_active_state(head, &rcuhead_debug_descr, | |
659 | STATE_RCU_HEAD_READY, | |
660 | STATE_RCU_HEAD_QUEUED); | |
661 | } | |
662 | ||
663 | static inline void debug_rcu_head_unqueue(struct rcu_head *head) | |
664 | { | |
665 | debug_object_active_state(head, &rcuhead_debug_descr, | |
666 | STATE_RCU_HEAD_QUEUED, | |
667 | STATE_RCU_HEAD_READY); | |
668 | debug_object_deactivate(head, &rcuhead_debug_descr); | |
669 | } | |
670 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
671 | static inline void debug_rcu_head_queue(struct rcu_head *head) | |
672 | { | |
673 | } | |
674 | ||
675 | static inline void debug_rcu_head_unqueue(struct rcu_head *head) | |
676 | { | |
677 | } | |
678 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
679 | ||
1da177e4 | 680 | #endif /* __LINUX_RCUPDATE_H */ |