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