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