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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 | ||
99098751 | 36 | #include <linux/types.h> |
1da177e4 LT |
37 | #include <linux/cache.h> |
38 | #include <linux/spinlock.h> | |
39 | #include <linux/threads.h> | |
1da177e4 LT |
40 | #include <linux/cpumask.h> |
41 | #include <linux/seqlock.h> | |
851a67b8 | 42 | #include <linux/lockdep.h> |
4446a36f | 43 | #include <linux/completion.h> |
551d55a9 | 44 | #include <linux/debugobjects.h> |
ca5ecddf | 45 | #include <linux/compiler.h> |
1da177e4 | 46 | |
e5ab6772 DY |
47 | #ifdef CONFIG_RCU_TORTURE_TEST |
48 | extern int rcutorture_runnable; /* for sysctl */ | |
49 | #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ | |
50 | ||
4a298656 PM |
51 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
52 | extern void rcutorture_record_test_transition(void); | |
53 | extern void rcutorture_record_progress(unsigned long vernum); | |
54 | #else | |
55 | static inline void rcutorture_record_test_transition(void) | |
56 | { | |
57 | } | |
58 | static inline void rcutorture_record_progress(unsigned long vernum) | |
59 | { | |
60 | } | |
61 | #endif | |
62 | ||
e27fc964 TH |
63 | #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) |
64 | #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) | |
a3dc3fb1 PM |
65 | #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) |
66 | #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) | |
67 | ||
03b042bf | 68 | /* Exported common interfaces */ |
2c42818e PM |
69 | |
70 | #ifdef CONFIG_PREEMPT_RCU | |
71 | ||
72 | /** | |
73 | * call_rcu() - Queue an RCU callback for invocation after a grace period. | |
74 | * @head: structure to be used for queueing the RCU updates. | |
75 | * @func: actual callback function to be invoked after the grace period | |
76 | * | |
77 | * The callback function will be invoked some time after a full grace | |
78 | * period elapses, in other words after all pre-existing RCU read-side | |
79 | * critical sections have completed. However, the callback function | |
80 | * might well execute concurrently with RCU read-side critical sections | |
81 | * that started after call_rcu() was invoked. RCU read-side critical | |
82 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
83 | * and may be nested. | |
84 | */ | |
85 | extern void call_rcu(struct rcu_head *head, | |
86 | void (*func)(struct rcu_head *head)); | |
87 | ||
88 | #else /* #ifdef CONFIG_PREEMPT_RCU */ | |
89 | ||
90 | /* In classic RCU, call_rcu() is just call_rcu_sched(). */ | |
91 | #define call_rcu call_rcu_sched | |
92 | ||
93 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ | |
94 | ||
95 | /** | |
96 | * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. | |
97 | * @head: structure to be used for queueing the RCU updates. | |
98 | * @func: actual callback function to be invoked after the grace period | |
99 | * | |
100 | * The callback function will be invoked some time after a full grace | |
101 | * period elapses, in other words after all currently executing RCU | |
102 | * read-side critical sections have completed. call_rcu_bh() assumes | |
103 | * that the read-side critical sections end on completion of a softirq | |
104 | * handler. This means that read-side critical sections in process | |
105 | * context must not be interrupted by softirqs. This interface is to be | |
106 | * used when most of the read-side critical sections are in softirq context. | |
107 | * RCU read-side critical sections are delimited by : | |
108 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. | |
109 | * OR | |
110 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. | |
111 | * These may be nested. | |
112 | */ | |
113 | extern void call_rcu_bh(struct rcu_head *head, | |
114 | void (*func)(struct rcu_head *head)); | |
115 | ||
116 | /** | |
117 | * call_rcu_sched() - Queue an RCU for invocation after sched grace period. | |
118 | * @head: structure to be used for queueing the RCU updates. | |
119 | * @func: actual callback function to be invoked after the grace period | |
120 | * | |
121 | * The callback function will be invoked some time after a full grace | |
122 | * period elapses, in other words after all currently executing RCU | |
123 | * read-side critical sections have completed. call_rcu_sched() assumes | |
124 | * that the read-side critical sections end on enabling of preemption | |
125 | * or on voluntary preemption. | |
126 | * RCU read-side critical sections are delimited by : | |
127 | * - rcu_read_lock_sched() and rcu_read_unlock_sched(), | |
128 | * OR | |
129 | * anything that disables preemption. | |
130 | * These may be nested. | |
131 | */ | |
7b0b759b PM |
132 | extern void call_rcu_sched(struct rcu_head *head, |
133 | void (*func)(struct rcu_head *rcu)); | |
2c42818e | 134 | |
7b0b759b | 135 | extern void synchronize_sched(void); |
03b042bf | 136 | |
a3dc3fb1 PM |
137 | #ifdef CONFIG_PREEMPT_RCU |
138 | ||
7b0b759b PM |
139 | extern void __rcu_read_lock(void); |
140 | extern void __rcu_read_unlock(void); | |
141 | void synchronize_rcu(void); | |
142 | ||
a3dc3fb1 PM |
143 | /* |
144 | * Defined as a macro as it is a very low level header included from | |
145 | * areas that don't even know about current. This gives the rcu_read_lock() | |
146 | * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other | |
147 | * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. | |
148 | */ | |
149 | #define rcu_preempt_depth() (current->rcu_read_lock_nesting) | |
150 | ||
7b0b759b PM |
151 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
152 | ||
153 | static inline void __rcu_read_lock(void) | |
154 | { | |
155 | preempt_disable(); | |
156 | } | |
157 | ||
158 | static inline void __rcu_read_unlock(void) | |
159 | { | |
160 | preempt_enable(); | |
161 | } | |
162 | ||
163 | static inline void synchronize_rcu(void) | |
164 | { | |
165 | synchronize_sched(); | |
166 | } | |
167 | ||
168 | static inline int rcu_preempt_depth(void) | |
169 | { | |
170 | return 0; | |
171 | } | |
172 | ||
173 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ | |
174 | ||
175 | /* Internal to kernel */ | |
7b0b759b PM |
176 | extern void rcu_sched_qs(int cpu); |
177 | extern void rcu_bh_qs(int cpu); | |
178 | extern void rcu_check_callbacks(int cpu, int user); | |
179 | struct notifier_block; | |
180 | ||
181 | #ifdef CONFIG_NO_HZ | |
182 | ||
183 | extern void rcu_enter_nohz(void); | |
184 | extern void rcu_exit_nohz(void); | |
185 | ||
186 | #else /* #ifdef CONFIG_NO_HZ */ | |
187 | ||
188 | static inline void rcu_enter_nohz(void) | |
189 | { | |
190 | } | |
191 | ||
192 | static inline void rcu_exit_nohz(void) | |
193 | { | |
194 | } | |
195 | ||
196 | #endif /* #else #ifdef CONFIG_NO_HZ */ | |
a3dc3fb1 | 197 | |
2c42818e PM |
198 | /* |
199 | * Infrastructure to implement the synchronize_() primitives in | |
200 | * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. | |
201 | */ | |
202 | ||
203 | typedef void call_rcu_func_t(struct rcu_head *head, | |
204 | void (*func)(struct rcu_head *head)); | |
205 | void wait_rcu_gp(call_rcu_func_t crf); | |
206 | ||
f41d911f | 207 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
64db4cff | 208 | #include <linux/rcutree.h> |
a57eb940 | 209 | #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) |
9b1d82fa | 210 | #include <linux/rcutiny.h> |
64db4cff PM |
211 | #else |
212 | #error "Unknown RCU implementation specified to kernel configuration" | |
6b3ef48a | 213 | #endif |
01c1c660 | 214 | |
551d55a9 MD |
215 | /* |
216 | * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic | |
217 | * initialization and destruction of rcu_head on the stack. rcu_head structures | |
218 | * allocated dynamically in the heap or defined statically don't need any | |
219 | * initialization. | |
220 | */ | |
221 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
222 | extern void init_rcu_head_on_stack(struct rcu_head *head); | |
223 | extern void destroy_rcu_head_on_stack(struct rcu_head *head); | |
224 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
4376030a MD |
225 | static inline void init_rcu_head_on_stack(struct rcu_head *head) |
226 | { | |
227 | } | |
228 | ||
229 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) | |
230 | { | |
231 | } | |
551d55a9 | 232 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
4376030a | 233 | |
bc33f24b | 234 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
632ee200 | 235 | |
bc33f24b | 236 | extern struct lockdep_map rcu_lock_map; |
632ee200 PM |
237 | # define rcu_read_acquire() \ |
238 | lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
bc33f24b | 239 | # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) |
632ee200 PM |
240 | |
241 | extern struct lockdep_map rcu_bh_lock_map; | |
242 | # define rcu_read_acquire_bh() \ | |
243 | lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
244 | # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) | |
245 | ||
246 | extern struct lockdep_map rcu_sched_lock_map; | |
247 | # define rcu_read_acquire_sched() \ | |
248 | lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
249 | # define rcu_read_release_sched() \ | |
250 | lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) | |
251 | ||
bc293d62 | 252 | extern int debug_lockdep_rcu_enabled(void); |
54dbf96c | 253 | |
632ee200 | 254 | /** |
ca5ecddf | 255 | * rcu_read_lock_held() - might we be in RCU read-side critical section? |
632ee200 | 256 | * |
d20200b5 PM |
257 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU |
258 | * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, | |
632ee200 | 259 | * this assumes we are in an RCU read-side critical section unless it can |
ca5ecddf PM |
260 | * prove otherwise. This is useful for debug checks in functions that |
261 | * require that they be called within an RCU read-side critical section. | |
54dbf96c | 262 | * |
ca5ecddf | 263 | * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot |
32c141a0 | 264 | * and while lockdep is disabled. |
632ee200 PM |
265 | */ |
266 | static inline int rcu_read_lock_held(void) | |
267 | { | |
54dbf96c PM |
268 | if (!debug_lockdep_rcu_enabled()) |
269 | return 1; | |
270 | return lock_is_held(&rcu_lock_map); | |
632ee200 PM |
271 | } |
272 | ||
e3818b8d PM |
273 | /* |
274 | * rcu_read_lock_bh_held() is defined out of line to avoid #include-file | |
275 | * hell. | |
632ee200 | 276 | */ |
e3818b8d | 277 | extern int rcu_read_lock_bh_held(void); |
632ee200 PM |
278 | |
279 | /** | |
ca5ecddf | 280 | * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? |
632ee200 | 281 | * |
d20200b5 PM |
282 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an |
283 | * RCU-sched read-side critical section. In absence of | |
284 | * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side | |
285 | * critical section unless it can prove otherwise. Note that disabling | |
286 | * of preemption (including disabling irqs) counts as an RCU-sched | |
ca5ecddf PM |
287 | * read-side critical section. This is useful for debug checks in functions |
288 | * that required that they be called within an RCU-sched read-side | |
289 | * critical section. | |
54dbf96c | 290 | * |
32c141a0 PM |
291 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot |
292 | * and while lockdep is disabled. | |
632ee200 | 293 | */ |
bdd4e85d | 294 | #ifdef CONFIG_PREEMPT_COUNT |
632ee200 PM |
295 | static inline int rcu_read_lock_sched_held(void) |
296 | { | |
297 | int lockdep_opinion = 0; | |
298 | ||
54dbf96c PM |
299 | if (!debug_lockdep_rcu_enabled()) |
300 | return 1; | |
632ee200 PM |
301 | if (debug_locks) |
302 | lockdep_opinion = lock_is_held(&rcu_sched_lock_map); | |
0cff810f | 303 | return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); |
632ee200 | 304 | } |
bdd4e85d | 305 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
e6033e3b PM |
306 | static inline int rcu_read_lock_sched_held(void) |
307 | { | |
308 | return 1; | |
632ee200 | 309 | } |
bdd4e85d | 310 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
632ee200 PM |
311 | |
312 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
313 | ||
314 | # define rcu_read_acquire() do { } while (0) | |
315 | # define rcu_read_release() do { } while (0) | |
316 | # define rcu_read_acquire_bh() do { } while (0) | |
317 | # define rcu_read_release_bh() do { } while (0) | |
318 | # define rcu_read_acquire_sched() do { } while (0) | |
319 | # define rcu_read_release_sched() do { } while (0) | |
320 | ||
321 | static inline int rcu_read_lock_held(void) | |
322 | { | |
323 | return 1; | |
324 | } | |
325 | ||
326 | static inline int rcu_read_lock_bh_held(void) | |
327 | { | |
328 | return 1; | |
329 | } | |
330 | ||
bdd4e85d | 331 | #ifdef CONFIG_PREEMPT_COUNT |
632ee200 PM |
332 | static inline int rcu_read_lock_sched_held(void) |
333 | { | |
bbad9379 | 334 | return preempt_count() != 0 || irqs_disabled(); |
632ee200 | 335 | } |
bdd4e85d | 336 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
e6033e3b PM |
337 | static inline int rcu_read_lock_sched_held(void) |
338 | { | |
339 | return 1; | |
632ee200 | 340 | } |
bdd4e85d | 341 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
632ee200 PM |
342 | |
343 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
344 | ||
345 | #ifdef CONFIG_PROVE_RCU | |
346 | ||
ee84b824 PM |
347 | extern int rcu_my_thread_group_empty(void); |
348 | ||
4221a991 TH |
349 | /** |
350 | * rcu_lockdep_assert - emit lockdep splat if specified condition not met | |
351 | * @c: condition to check | |
b3fbab05 | 352 | * @s: informative message |
4221a991 | 353 | */ |
b3fbab05 | 354 | #define rcu_lockdep_assert(c, s) \ |
2b3fc35f LJ |
355 | do { \ |
356 | static bool __warned; \ | |
357 | if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ | |
358 | __warned = true; \ | |
b3fbab05 | 359 | lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ |
2b3fc35f LJ |
360 | } \ |
361 | } while (0) | |
362 | ||
b3fbab05 PM |
363 | #define rcu_sleep_check() \ |
364 | do { \ | |
365 | rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \ | |
366 | "Illegal context switch in RCU-bh" \ | |
367 | " read-side critical section"); \ | |
368 | rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \ | |
369 | "Illegal context switch in RCU-sched"\ | |
370 | " read-side critical section"); \ | |
371 | } while (0) | |
372 | ||
ca5ecddf PM |
373 | #else /* #ifdef CONFIG_PROVE_RCU */ |
374 | ||
b3fbab05 PM |
375 | #define rcu_lockdep_assert(c, s) do { } while (0) |
376 | #define rcu_sleep_check() do { } while (0) | |
ca5ecddf PM |
377 | |
378 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
379 | ||
380 | /* | |
381 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() | |
382 | * and rcu_assign_pointer(). Some of these could be folded into their | |
383 | * callers, but they are left separate in order to ease introduction of | |
384 | * multiple flavors of pointers to match the multiple flavors of RCU | |
385 | * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in | |
386 | * the future. | |
387 | */ | |
53ecfba2 PM |
388 | |
389 | #ifdef __CHECKER__ | |
390 | #define rcu_dereference_sparse(p, space) \ | |
391 | ((void)(((typeof(*p) space *)p) == p)) | |
392 | #else /* #ifdef __CHECKER__ */ | |
393 | #define rcu_dereference_sparse(p, space) | |
394 | #endif /* #else #ifdef __CHECKER__ */ | |
395 | ||
ca5ecddf PM |
396 | #define __rcu_access_pointer(p, space) \ |
397 | ({ \ | |
398 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ | |
53ecfba2 | 399 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
400 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
401 | }) | |
402 | #define __rcu_dereference_check(p, c, space) \ | |
403 | ({ \ | |
404 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ | |
b3fbab05 PM |
405 | rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \ |
406 | " usage"); \ | |
53ecfba2 | 407 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
408 | smp_read_barrier_depends(); \ |
409 | ((typeof(*p) __force __kernel *)(_________p1)); \ | |
410 | }) | |
411 | #define __rcu_dereference_protected(p, c, space) \ | |
412 | ({ \ | |
b3fbab05 PM |
413 | rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \ |
414 | " usage"); \ | |
53ecfba2 | 415 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
416 | ((typeof(*p) __force __kernel *)(p)); \ |
417 | }) | |
418 | ||
a4dd9925 PM |
419 | #define __rcu_access_index(p, space) \ |
420 | ({ \ | |
421 | typeof(p) _________p1 = ACCESS_ONCE(p); \ | |
422 | rcu_dereference_sparse(p, space); \ | |
423 | (_________p1); \ | |
424 | }) | |
ca5ecddf PM |
425 | #define __rcu_dereference_index_check(p, c) \ |
426 | ({ \ | |
427 | typeof(p) _________p1 = ACCESS_ONCE(p); \ | |
b3fbab05 PM |
428 | rcu_lockdep_assert(c, \ |
429 | "suspicious rcu_dereference_index_check()" \ | |
430 | " usage"); \ | |
ca5ecddf PM |
431 | smp_read_barrier_depends(); \ |
432 | (_________p1); \ | |
433 | }) | |
434 | #define __rcu_assign_pointer(p, v, space) \ | |
435 | ({ \ | |
d322f45c | 436 | smp_wmb(); \ |
ca5ecddf PM |
437 | (p) = (typeof(*v) __force space *)(v); \ |
438 | }) | |
439 | ||
440 | ||
441 | /** | |
442 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing | |
443 | * @p: The pointer to read | |
444 | * | |
445 | * Return the value of the specified RCU-protected pointer, but omit the | |
446 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful | |
447 | * when the value of this pointer is accessed, but the pointer is not | |
448 | * dereferenced, for example, when testing an RCU-protected pointer against | |
449 | * NULL. Although rcu_access_pointer() may also be used in cases where | |
450 | * update-side locks prevent the value of the pointer from changing, you | |
451 | * should instead use rcu_dereference_protected() for this use case. | |
452 | */ | |
453 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) | |
454 | ||
632ee200 | 455 | /** |
ca5ecddf | 456 | * rcu_dereference_check() - rcu_dereference with debug checking |
c08c68dd DH |
457 | * @p: The pointer to read, prior to dereferencing |
458 | * @c: The conditions under which the dereference will take place | |
632ee200 | 459 | * |
c08c68dd | 460 | * Do an rcu_dereference(), but check that the conditions under which the |
ca5ecddf PM |
461 | * dereference will take place are correct. Typically the conditions |
462 | * indicate the various locking conditions that should be held at that | |
463 | * point. The check should return true if the conditions are satisfied. | |
464 | * An implicit check for being in an RCU read-side critical section | |
465 | * (rcu_read_lock()) is included. | |
c08c68dd DH |
466 | * |
467 | * For example: | |
468 | * | |
ca5ecddf | 469 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
c08c68dd DH |
470 | * |
471 | * could be used to indicate to lockdep that foo->bar may only be dereferenced | |
ca5ecddf | 472 | * if either rcu_read_lock() is held, or that the lock required to replace |
c08c68dd DH |
473 | * the bar struct at foo->bar is held. |
474 | * | |
475 | * Note that the list of conditions may also include indications of when a lock | |
476 | * need not be held, for example during initialisation or destruction of the | |
477 | * target struct: | |
478 | * | |
ca5ecddf | 479 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
c08c68dd | 480 | * atomic_read(&foo->usage) == 0); |
ca5ecddf PM |
481 | * |
482 | * Inserts memory barriers on architectures that require them | |
483 | * (currently only the Alpha), prevents the compiler from refetching | |
484 | * (and from merging fetches), and, more importantly, documents exactly | |
485 | * which pointers are protected by RCU and checks that the pointer is | |
486 | * annotated as __rcu. | |
632ee200 PM |
487 | */ |
488 | #define rcu_dereference_check(p, c) \ | |
ca5ecddf PM |
489 | __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) |
490 | ||
491 | /** | |
492 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking | |
493 | * @p: The pointer to read, prior to dereferencing | |
494 | * @c: The conditions under which the dereference will take place | |
495 | * | |
496 | * This is the RCU-bh counterpart to rcu_dereference_check(). | |
497 | */ | |
498 | #define rcu_dereference_bh_check(p, c) \ | |
499 | __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) | |
632ee200 | 500 | |
b62730ba | 501 | /** |
ca5ecddf PM |
502 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
503 | * @p: The pointer to read, prior to dereferencing | |
504 | * @c: The conditions under which the dereference will take place | |
505 | * | |
506 | * This is the RCU-sched counterpart to rcu_dereference_check(). | |
507 | */ | |
508 | #define rcu_dereference_sched_check(p, c) \ | |
509 | __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ | |
510 | __rcu) | |
511 | ||
512 | #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ | |
513 | ||
a4dd9925 PM |
514 | /** |
515 | * rcu_access_index() - fetch RCU index with no dereferencing | |
516 | * @p: The index to read | |
517 | * | |
518 | * Return the value of the specified RCU-protected index, but omit the | |
519 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful | |
520 | * when the value of this index is accessed, but the index is not | |
521 | * dereferenced, for example, when testing an RCU-protected index against | |
522 | * -1. Although rcu_access_index() may also be used in cases where | |
523 | * update-side locks prevent the value of the index from changing, you | |
524 | * should instead use rcu_dereference_index_protected() for this use case. | |
525 | */ | |
526 | #define rcu_access_index(p) __rcu_access_index((p), __rcu) | |
527 | ||
ca5ecddf PM |
528 | /** |
529 | * rcu_dereference_index_check() - rcu_dereference for indices with debug checking | |
530 | * @p: The pointer to read, prior to dereferencing | |
531 | * @c: The conditions under which the dereference will take place | |
532 | * | |
533 | * Similar to rcu_dereference_check(), but omits the sparse checking. | |
534 | * This allows rcu_dereference_index_check() to be used on integers, | |
535 | * which can then be used as array indices. Attempting to use | |
536 | * rcu_dereference_check() on an integer will give compiler warnings | |
537 | * because the sparse address-space mechanism relies on dereferencing | |
538 | * the RCU-protected pointer. Dereferencing integers is not something | |
539 | * that even gcc will put up with. | |
540 | * | |
541 | * Note that this function does not implicitly check for RCU read-side | |
542 | * critical sections. If this function gains lots of uses, it might | |
543 | * make sense to provide versions for each flavor of RCU, but it does | |
544 | * not make sense as of early 2010. | |
545 | */ | |
546 | #define rcu_dereference_index_check(p, c) \ | |
547 | __rcu_dereference_index_check((p), (c)) | |
548 | ||
549 | /** | |
550 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented | |
551 | * @p: The pointer to read, prior to dereferencing | |
552 | * @c: The conditions under which the dereference will take place | |
b62730ba PM |
553 | * |
554 | * Return the value of the specified RCU-protected pointer, but omit | |
555 | * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This | |
556 | * is useful in cases where update-side locks prevent the value of the | |
557 | * pointer from changing. Please note that this primitive does -not- | |
558 | * prevent the compiler from repeating this reference or combining it | |
559 | * with other references, so it should not be used without protection | |
560 | * of appropriate locks. | |
ca5ecddf PM |
561 | * |
562 | * This function is only for update-side use. Using this function | |
563 | * when protected only by rcu_read_lock() will result in infrequent | |
564 | * but very ugly failures. | |
b62730ba PM |
565 | */ |
566 | #define rcu_dereference_protected(p, c) \ | |
ca5ecddf | 567 | __rcu_dereference_protected((p), (c), __rcu) |
b62730ba | 568 | |
bc33f24b | 569 | |
b62730ba | 570 | /** |
ca5ecddf PM |
571 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
572 | * @p: The pointer to read, prior to dereferencing | |
b62730ba | 573 | * |
ca5ecddf | 574 | * This is a simple wrapper around rcu_dereference_check(). |
b62730ba | 575 | */ |
ca5ecddf | 576 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
b62730ba | 577 | |
1da177e4 | 578 | /** |
ca5ecddf PM |
579 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
580 | * @p: The pointer to read, prior to dereferencing | |
581 | * | |
582 | * Makes rcu_dereference_check() do the dirty work. | |
583 | */ | |
584 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) | |
585 | ||
586 | /** | |
587 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing | |
588 | * @p: The pointer to read, prior to dereferencing | |
589 | * | |
590 | * Makes rcu_dereference_check() do the dirty work. | |
591 | */ | |
592 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) | |
593 | ||
594 | /** | |
595 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section | |
1da177e4 | 596 | * |
9b06e818 | 597 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 598 | * are within RCU read-side critical sections, then the |
9b06e818 | 599 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
600 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
601 | * on one CPU while other CPUs are within RCU read-side critical | |
602 | * sections, invocation of the corresponding RCU callback is deferred | |
603 | * until after the all the other CPUs exit their critical sections. | |
604 | * | |
605 | * Note, however, that RCU callbacks are permitted to run concurrently | |
77d8485a | 606 | * with new RCU read-side critical sections. One way that this can happen |
1da177e4 LT |
607 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
608 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
609 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
610 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
611 | * callback is invoked. This is legal, because the RCU read-side critical | |
612 | * section that was running concurrently with the call_rcu() (and which | |
613 | * therefore might be referencing something that the corresponding RCU | |
614 | * callback would free up) has completed before the corresponding | |
615 | * RCU callback is invoked. | |
616 | * | |
617 | * RCU read-side critical sections may be nested. Any deferred actions | |
618 | * will be deferred until the outermost RCU read-side critical section | |
619 | * completes. | |
620 | * | |
9079fd7c PM |
621 | * You can avoid reading and understanding the next paragraph by |
622 | * following this rule: don't put anything in an rcu_read_lock() RCU | |
623 | * read-side critical section that would block in a !PREEMPT kernel. | |
624 | * But if you want the full story, read on! | |
625 | * | |
626 | * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it | |
627 | * is illegal to block while in an RCU read-side critical section. In | |
628 | * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) | |
629 | * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may | |
630 | * be preempted, but explicit blocking is illegal. Finally, in preemptible | |
631 | * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, | |
632 | * RCU read-side critical sections may be preempted and they may also | |
633 | * block, but only when acquiring spinlocks that are subject to priority | |
634 | * inheritance. | |
1da177e4 | 635 | */ |
bc33f24b PM |
636 | static inline void rcu_read_lock(void) |
637 | { | |
638 | __rcu_read_lock(); | |
639 | __acquire(RCU); | |
640 | rcu_read_acquire(); | |
641 | } | |
1da177e4 | 642 | |
1da177e4 LT |
643 | /* |
644 | * So where is rcu_write_lock()? It does not exist, as there is no | |
645 | * way for writers to lock out RCU readers. This is a feature, not | |
646 | * a bug -- this property is what provides RCU's performance benefits. | |
647 | * Of course, writers must coordinate with each other. The normal | |
648 | * spinlock primitives work well for this, but any other technique may be | |
649 | * used as well. RCU does not care how the writers keep out of each | |
650 | * others' way, as long as they do so. | |
651 | */ | |
3d76c082 PM |
652 | |
653 | /** | |
ca5ecddf | 654 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
3d76c082 PM |
655 | * |
656 | * See rcu_read_lock() for more information. | |
657 | */ | |
bc33f24b PM |
658 | static inline void rcu_read_unlock(void) |
659 | { | |
660 | rcu_read_release(); | |
661 | __release(RCU); | |
662 | __rcu_read_unlock(); | |
663 | } | |
1da177e4 LT |
664 | |
665 | /** | |
ca5ecddf | 666 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
1da177e4 LT |
667 | * |
668 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
ca5ecddf PM |
669 | * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since |
670 | * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a | |
671 | * softirq handler to be a quiescent state, a process in RCU read-side | |
672 | * critical section must be protected by disabling softirqs. Read-side | |
673 | * critical sections in interrupt context can use just rcu_read_lock(), | |
674 | * though this should at least be commented to avoid confusing people | |
675 | * reading the code. | |
1da177e4 | 676 | */ |
bc33f24b PM |
677 | static inline void rcu_read_lock_bh(void) |
678 | { | |
6206ab9b | 679 | local_bh_disable(); |
bc33f24b | 680 | __acquire(RCU_BH); |
632ee200 | 681 | rcu_read_acquire_bh(); |
bc33f24b | 682 | } |
1da177e4 LT |
683 | |
684 | /* | |
685 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
686 | * | |
687 | * See rcu_read_lock_bh() for more information. | |
688 | */ | |
bc33f24b PM |
689 | static inline void rcu_read_unlock_bh(void) |
690 | { | |
632ee200 | 691 | rcu_read_release_bh(); |
bc33f24b | 692 | __release(RCU_BH); |
6206ab9b | 693 | local_bh_enable(); |
bc33f24b | 694 | } |
1da177e4 | 695 | |
1c50b728 | 696 | /** |
ca5ecddf | 697 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
1c50b728 | 698 | * |
ca5ecddf PM |
699 | * This is equivalent of rcu_read_lock(), but to be used when updates |
700 | * are being done using call_rcu_sched() or synchronize_rcu_sched(). | |
701 | * Read-side critical sections can also be introduced by anything that | |
702 | * disables preemption, including local_irq_disable() and friends. | |
1c50b728 | 703 | */ |
d6714c22 PM |
704 | static inline void rcu_read_lock_sched(void) |
705 | { | |
706 | preempt_disable(); | |
bc33f24b | 707 | __acquire(RCU_SCHED); |
632ee200 | 708 | rcu_read_acquire_sched(); |
d6714c22 | 709 | } |
1eba8f84 PM |
710 | |
711 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 712 | static inline notrace void rcu_read_lock_sched_notrace(void) |
d6714c22 PM |
713 | { |
714 | preempt_disable_notrace(); | |
bc33f24b | 715 | __acquire(RCU_SCHED); |
d6714c22 | 716 | } |
1c50b728 MD |
717 | |
718 | /* | |
719 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section | |
720 | * | |
721 | * See rcu_read_lock_sched for more information. | |
722 | */ | |
d6714c22 PM |
723 | static inline void rcu_read_unlock_sched(void) |
724 | { | |
632ee200 | 725 | rcu_read_release_sched(); |
bc33f24b | 726 | __release(RCU_SCHED); |
d6714c22 PM |
727 | preempt_enable(); |
728 | } | |
1eba8f84 PM |
729 | |
730 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 731 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
d6714c22 | 732 | { |
bc33f24b | 733 | __release(RCU_SCHED); |
d6714c22 PM |
734 | preempt_enable_notrace(); |
735 | } | |
1c50b728 | 736 | |
1da177e4 | 737 | /** |
ca5ecddf PM |
738 | * rcu_assign_pointer() - assign to RCU-protected pointer |
739 | * @p: pointer to assign to | |
740 | * @v: value to assign (publish) | |
c26d34a5 | 741 | * |
ca5ecddf PM |
742 | * Assigns the specified value to the specified RCU-protected |
743 | * pointer, ensuring that any concurrent RCU readers will see | |
744 | * any prior initialization. Returns the value assigned. | |
1da177e4 LT |
745 | * |
746 | * Inserts memory barriers on architectures that require them | |
6846c0c5 PM |
747 | * (which is most of them), and also prevents the compiler from |
748 | * reordering the code that initializes the structure after the pointer | |
749 | * assignment. More importantly, this call documents which pointers | |
750 | * will be dereferenced by RCU read-side code. | |
751 | * | |
752 | * In some special cases, you may use RCU_INIT_POINTER() instead | |
753 | * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due | |
754 | * to the fact that it does not constrain either the CPU or the compiler. | |
755 | * That said, using RCU_INIT_POINTER() when you should have used | |
756 | * rcu_assign_pointer() is a very bad thing that results in | |
757 | * impossible-to-diagnose memory corruption. So please be careful. | |
758 | * See the RCU_INIT_POINTER() comment header for details. | |
1da177e4 | 759 | */ |
d99c4f6b | 760 | #define rcu_assign_pointer(p, v) \ |
ca5ecddf PM |
761 | __rcu_assign_pointer((p), (v), __rcu) |
762 | ||
763 | /** | |
764 | * RCU_INIT_POINTER() - initialize an RCU protected pointer | |
765 | * | |
6846c0c5 PM |
766 | * Initialize an RCU-protected pointer in special cases where readers |
767 | * do not need ordering constraints on the CPU or the compiler. These | |
768 | * special cases are: | |
769 | * | |
770 | * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or- | |
771 | * 2. The caller has taken whatever steps are required to prevent | |
772 | * RCU readers from concurrently accessing this pointer -or- | |
773 | * 3. The referenced data structure has already been exposed to | |
774 | * readers either at compile time or via rcu_assign_pointer() -and- | |
775 | * a. You have not made -any- reader-visible changes to | |
776 | * this structure since then -or- | |
777 | * b. It is OK for readers accessing this structure from its | |
778 | * new location to see the old state of the structure. (For | |
779 | * example, the changes were to statistical counters or to | |
780 | * other state where exact synchronization is not required.) | |
781 | * | |
782 | * Failure to follow these rules governing use of RCU_INIT_POINTER() will | |
783 | * result in impossible-to-diagnose memory corruption. As in the structures | |
784 | * will look OK in crash dumps, but any concurrent RCU readers might | |
785 | * see pre-initialized values of the referenced data structure. So | |
786 | * please be very careful how you use RCU_INIT_POINTER()!!! | |
787 | * | |
788 | * If you are creating an RCU-protected linked structure that is accessed | |
789 | * by a single external-to-structure RCU-protected pointer, then you may | |
790 | * use RCU_INIT_POINTER() to initialize the internal RCU-protected | |
791 | * pointers, but you must use rcu_assign_pointer() to initialize the | |
792 | * external-to-structure pointer -after- you have completely initialized | |
793 | * the reader-accessible portions of the linked structure. | |
ca5ecddf PM |
794 | */ |
795 | #define RCU_INIT_POINTER(p, v) \ | |
796 | p = (typeof(*v) __force __rcu *)(v) | |
1da177e4 | 797 | |
9ab1544e LJ |
798 | static __always_inline bool __is_kfree_rcu_offset(unsigned long offset) |
799 | { | |
800 | return offset < 4096; | |
801 | } | |
802 | ||
803 | static __always_inline | |
804 | void __kfree_rcu(struct rcu_head *head, unsigned long offset) | |
805 | { | |
806 | typedef void (*rcu_callback)(struct rcu_head *); | |
807 | ||
808 | BUILD_BUG_ON(!__builtin_constant_p(offset)); | |
809 | ||
810 | /* See the kfree_rcu() header comment. */ | |
811 | BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); | |
812 | ||
813 | call_rcu(head, (rcu_callback)offset); | |
814 | } | |
815 | ||
9ab1544e LJ |
816 | /** |
817 | * kfree_rcu() - kfree an object after a grace period. | |
818 | * @ptr: pointer to kfree | |
819 | * @rcu_head: the name of the struct rcu_head within the type of @ptr. | |
820 | * | |
821 | * Many rcu callbacks functions just call kfree() on the base structure. | |
822 | * These functions are trivial, but their size adds up, and furthermore | |
823 | * when they are used in a kernel module, that module must invoke the | |
824 | * high-latency rcu_barrier() function at module-unload time. | |
825 | * | |
826 | * The kfree_rcu() function handles this issue. Rather than encoding a | |
827 | * function address in the embedded rcu_head structure, kfree_rcu() instead | |
828 | * encodes the offset of the rcu_head structure within the base structure. | |
829 | * Because the functions are not allowed in the low-order 4096 bytes of | |
830 | * kernel virtual memory, offsets up to 4095 bytes can be accommodated. | |
831 | * If the offset is larger than 4095 bytes, a compile-time error will | |
832 | * be generated in __kfree_rcu(). If this error is triggered, you can | |
833 | * either fall back to use of call_rcu() or rearrange the structure to | |
834 | * position the rcu_head structure into the first 4096 bytes. | |
835 | * | |
836 | * Note that the allowable offset might decrease in the future, for example, | |
837 | * to allow something like kmem_cache_free_rcu(). | |
838 | */ | |
839 | #define kfree_rcu(ptr, rcu_head) \ | |
840 | __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) | |
841 | ||
1da177e4 | 842 | #endif /* __LINUX_RCUPDATE_H */ |