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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> |
1da177e4 LT |
43 | |
44 | /** | |
45 | * struct rcu_head - callback structure for use with RCU | |
46 | * @next: next update requests in a list | |
47 | * @func: actual update function to call after the grace period. | |
48 | */ | |
49 | struct rcu_head { | |
50 | struct rcu_head *next; | |
51 | void (*func)(struct rcu_head *head); | |
52 | }; | |
53 | ||
03b042bf | 54 | /* Exported common interfaces */ |
03b042bf | 55 | extern void synchronize_rcu_bh(void); |
16e30811 | 56 | extern void synchronize_sched(void); |
03b042bf PM |
57 | extern void rcu_barrier(void); |
58 | extern void rcu_barrier_bh(void); | |
59 | extern void rcu_barrier_sched(void); | |
60 | extern void synchronize_sched_expedited(void); | |
61 | extern int sched_expedited_torture_stats(char *page); | |
62 | ||
63 | /* Internal to kernel */ | |
64 | extern void rcu_init(void); | |
a6826048 | 65 | |
f41d911f | 66 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
64db4cff | 67 | #include <linux/rcutree.h> |
2c28e245 | 68 | #elif defined(CONFIG_TINY_RCU) |
9b1d82fa | 69 | #include <linux/rcutiny.h> |
64db4cff PM |
70 | #else |
71 | #error "Unknown RCU implementation specified to kernel configuration" | |
6b3ef48a | 72 | #endif |
01c1c660 | 73 | |
3d76c082 | 74 | #define RCU_HEAD_INIT { .next = NULL, .func = NULL } |
8b6490e5 | 75 | #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT |
1da177e4 LT |
76 | #define INIT_RCU_HEAD(ptr) do { \ |
77 | (ptr)->next = NULL; (ptr)->func = NULL; \ | |
78 | } while (0) | |
79 | ||
bc33f24b | 80 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
632ee200 | 81 | |
bc33f24b | 82 | extern struct lockdep_map rcu_lock_map; |
632ee200 PM |
83 | # define rcu_read_acquire() \ |
84 | lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
bc33f24b | 85 | # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) |
632ee200 PM |
86 | |
87 | extern struct lockdep_map rcu_bh_lock_map; | |
88 | # define rcu_read_acquire_bh() \ | |
89 | lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
90 | # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) | |
91 | ||
92 | extern struct lockdep_map rcu_sched_lock_map; | |
93 | # define rcu_read_acquire_sched() \ | |
94 | lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
95 | # define rcu_read_release_sched() \ | |
96 | lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) | |
97 | ||
98 | /** | |
99 | * rcu_read_lock_held - might we be in RCU read-side critical section? | |
100 | * | |
101 | * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in | |
102 | * an RCU read-side critical section. In absence of CONFIG_PROVE_LOCKING, | |
103 | * this assumes we are in an RCU read-side critical section unless it can | |
104 | * prove otherwise. | |
105 | */ | |
106 | static inline int rcu_read_lock_held(void) | |
107 | { | |
108 | if (debug_locks) | |
109 | return lock_is_held(&rcu_lock_map); | |
110 | return 1; | |
111 | } | |
112 | ||
113 | /** | |
114 | * rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section? | |
115 | * | |
116 | * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in | |
117 | * an RCU-bh read-side critical section. In absence of CONFIG_PROVE_LOCKING, | |
118 | * this assumes we are in an RCU-bh read-side critical section unless it can | |
119 | * prove otherwise. | |
120 | */ | |
121 | static inline int rcu_read_lock_bh_held(void) | |
122 | { | |
123 | if (debug_locks) | |
124 | return lock_is_held(&rcu_bh_lock_map); | |
125 | return 1; | |
126 | } | |
127 | ||
128 | /** | |
129 | * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section? | |
130 | * | |
131 | * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in an | |
132 | * RCU-sched read-side critical section. In absence of CONFIG_PROVE_LOCKING, | |
133 | * this assumes we are in an RCU-sched read-side critical section unless it | |
134 | * can prove otherwise. Note that disabling of preemption (including | |
135 | * disabling irqs) counts as an RCU-sched read-side critical section. | |
136 | */ | |
137 | static inline int rcu_read_lock_sched_held(void) | |
138 | { | |
139 | int lockdep_opinion = 0; | |
140 | ||
141 | if (debug_locks) | |
142 | lockdep_opinion = lock_is_held(&rcu_sched_lock_map); | |
143 | return lockdep_opinion || preempt_count() != 0; | |
144 | } | |
145 | ||
146 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
147 | ||
148 | # define rcu_read_acquire() do { } while (0) | |
149 | # define rcu_read_release() do { } while (0) | |
150 | # define rcu_read_acquire_bh() do { } while (0) | |
151 | # define rcu_read_release_bh() do { } while (0) | |
152 | # define rcu_read_acquire_sched() do { } while (0) | |
153 | # define rcu_read_release_sched() do { } while (0) | |
154 | ||
155 | static inline int rcu_read_lock_held(void) | |
156 | { | |
157 | return 1; | |
158 | } | |
159 | ||
160 | static inline int rcu_read_lock_bh_held(void) | |
161 | { | |
162 | return 1; | |
163 | } | |
164 | ||
165 | static inline int rcu_read_lock_sched_held(void) | |
166 | { | |
167 | return preempt_count() != 0; | |
168 | } | |
169 | ||
170 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
171 | ||
172 | #ifdef CONFIG_PROVE_RCU | |
173 | ||
174 | /** | |
175 | * rcu_dereference_check - rcu_dereference with debug checking | |
176 | * | |
177 | * Do an rcu_dereference(), but check that the context is correct. | |
178 | * For example, rcu_dereference_check(gp, rcu_read_lock_held()) to | |
179 | * ensure that the rcu_dereference_check() executes within an RCU | |
180 | * read-side critical section. It is also possible to check for | |
181 | * locks being held, for example, by using lockdep_is_held(). | |
182 | */ | |
183 | #define rcu_dereference_check(p, c) \ | |
184 | ({ \ | |
185 | if (debug_locks) \ | |
186 | WARN_ON_ONCE(!(c)); \ | |
c26d34a5 | 187 | rcu_dereference_raw(p); \ |
632ee200 PM |
188 | }) |
189 | ||
190 | #else /* #ifdef CONFIG_PROVE_RCU */ | |
191 | ||
c26d34a5 | 192 | #define rcu_dereference_check(p, c) rcu_dereference_raw(p) |
632ee200 PM |
193 | |
194 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
bc33f24b | 195 | |
1da177e4 LT |
196 | /** |
197 | * rcu_read_lock - mark the beginning of an RCU read-side critical section. | |
198 | * | |
9b06e818 | 199 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 200 | * are within RCU read-side critical sections, then the |
9b06e818 | 201 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
202 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
203 | * on one CPU while other CPUs are within RCU read-side critical | |
204 | * sections, invocation of the corresponding RCU callback is deferred | |
205 | * until after the all the other CPUs exit their critical sections. | |
206 | * | |
207 | * Note, however, that RCU callbacks are permitted to run concurrently | |
208 | * with RCU read-side critical sections. One way that this can happen | |
209 | * is via the following sequence of events: (1) CPU 0 enters an RCU | |
210 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
211 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
212 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
213 | * callback is invoked. This is legal, because the RCU read-side critical | |
214 | * section that was running concurrently with the call_rcu() (and which | |
215 | * therefore might be referencing something that the corresponding RCU | |
216 | * callback would free up) has completed before the corresponding | |
217 | * RCU callback is invoked. | |
218 | * | |
219 | * RCU read-side critical sections may be nested. Any deferred actions | |
220 | * will be deferred until the outermost RCU read-side critical section | |
221 | * completes. | |
222 | * | |
223 | * It is illegal to block while in an RCU read-side critical section. | |
224 | */ | |
bc33f24b PM |
225 | static inline void rcu_read_lock(void) |
226 | { | |
227 | __rcu_read_lock(); | |
228 | __acquire(RCU); | |
229 | rcu_read_acquire(); | |
230 | } | |
1da177e4 | 231 | |
1da177e4 LT |
232 | /* |
233 | * So where is rcu_write_lock()? It does not exist, as there is no | |
234 | * way for writers to lock out RCU readers. This is a feature, not | |
235 | * a bug -- this property is what provides RCU's performance benefits. | |
236 | * Of course, writers must coordinate with each other. The normal | |
237 | * spinlock primitives work well for this, but any other technique may be | |
238 | * used as well. RCU does not care how the writers keep out of each | |
239 | * others' way, as long as they do so. | |
240 | */ | |
3d76c082 PM |
241 | |
242 | /** | |
243 | * rcu_read_unlock - marks the end of an RCU read-side critical section. | |
244 | * | |
245 | * See rcu_read_lock() for more information. | |
246 | */ | |
bc33f24b PM |
247 | static inline void rcu_read_unlock(void) |
248 | { | |
249 | rcu_read_release(); | |
250 | __release(RCU); | |
251 | __rcu_read_unlock(); | |
252 | } | |
1da177e4 LT |
253 | |
254 | /** | |
255 | * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section | |
256 | * | |
257 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
258 | * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks | |
259 | * consider completion of a softirq handler to be a quiescent state, | |
260 | * a process in RCU read-side critical section must be protected by | |
261 | * disabling softirqs. Read-side critical sections in interrupt context | |
262 | * can use just rcu_read_lock(). | |
263 | * | |
264 | */ | |
bc33f24b PM |
265 | static inline void rcu_read_lock_bh(void) |
266 | { | |
267 | __rcu_read_lock_bh(); | |
268 | __acquire(RCU_BH); | |
632ee200 | 269 | rcu_read_acquire_bh(); |
bc33f24b | 270 | } |
1da177e4 LT |
271 | |
272 | /* | |
273 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
274 | * | |
275 | * See rcu_read_lock_bh() for more information. | |
276 | */ | |
bc33f24b PM |
277 | static inline void rcu_read_unlock_bh(void) |
278 | { | |
632ee200 | 279 | rcu_read_release_bh(); |
bc33f24b PM |
280 | __release(RCU_BH); |
281 | __rcu_read_unlock_bh(); | |
282 | } | |
1da177e4 | 283 | |
1c50b728 MD |
284 | /** |
285 | * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section | |
286 | * | |
287 | * Should be used with either | |
288 | * - synchronize_sched() | |
289 | * or | |
290 | * - call_rcu_sched() and rcu_barrier_sched() | |
291 | * on the write-side to insure proper synchronization. | |
292 | */ | |
d6714c22 PM |
293 | static inline void rcu_read_lock_sched(void) |
294 | { | |
295 | preempt_disable(); | |
bc33f24b | 296 | __acquire(RCU_SCHED); |
632ee200 | 297 | rcu_read_acquire_sched(); |
d6714c22 | 298 | } |
1eba8f84 PM |
299 | |
300 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 301 | static inline notrace void rcu_read_lock_sched_notrace(void) |
d6714c22 PM |
302 | { |
303 | preempt_disable_notrace(); | |
bc33f24b | 304 | __acquire(RCU_SCHED); |
d6714c22 | 305 | } |
1c50b728 MD |
306 | |
307 | /* | |
308 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section | |
309 | * | |
310 | * See rcu_read_lock_sched for more information. | |
311 | */ | |
d6714c22 PM |
312 | static inline void rcu_read_unlock_sched(void) |
313 | { | |
632ee200 | 314 | rcu_read_release_sched(); |
bc33f24b | 315 | __release(RCU_SCHED); |
d6714c22 PM |
316 | preempt_enable(); |
317 | } | |
1eba8f84 PM |
318 | |
319 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 320 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
d6714c22 | 321 | { |
bc33f24b | 322 | __release(RCU_SCHED); |
d6714c22 PM |
323 | preempt_enable_notrace(); |
324 | } | |
1c50b728 MD |
325 | |
326 | ||
1da177e4 | 327 | /** |
c26d34a5 PM |
328 | * rcu_dereference_raw - fetch an RCU-protected pointer |
329 | * | |
330 | * The caller must be within some flavor of RCU read-side critical | |
331 | * section, or must be otherwise preventing the pointer from changing, | |
332 | * for example, by holding an appropriate lock. This pointer may later | |
333 | * be safely dereferenced. It is the caller's responsibility to have | |
334 | * done the right thing, as this primitive does no checking of any kind. | |
1da177e4 LT |
335 | * |
336 | * Inserts memory barriers on architectures that require them | |
337 | * (currently only the Alpha), and, more importantly, documents | |
338 | * exactly which pointers are protected by RCU. | |
339 | */ | |
c26d34a5 | 340 | #define rcu_dereference_raw(p) ({ \ |
97b43032 | 341 | typeof(p) _________p1 = ACCESS_ONCE(p); \ |
1da177e4 LT |
342 | smp_read_barrier_depends(); \ |
343 | (_________p1); \ | |
344 | }) | |
345 | ||
c26d34a5 PM |
346 | /** |
347 | * rcu_dereference - fetch an RCU-protected pointer, checking for RCU | |
348 | * | |
349 | * Makes rcu_dereference_check() do the dirty work. | |
350 | */ | |
351 | #define rcu_dereference(p) \ | |
352 | rcu_dereference_check(p, rcu_read_lock_held()) | |
353 | ||
354 | /** | |
355 | * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh | |
356 | * | |
357 | * Makes rcu_dereference_check() do the dirty work. | |
358 | */ | |
359 | #define rcu_dereference_bh(p) \ | |
360 | rcu_dereference_check(p, rcu_read_lock_bh_held()) | |
361 | ||
362 | /** | |
363 | * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched | |
364 | * | |
365 | * Makes rcu_dereference_check() do the dirty work. | |
366 | */ | |
367 | #define rcu_dereference_sched(p) \ | |
368 | rcu_dereference_check(p, rcu_read_lock_sched_held()) | |
369 | ||
1da177e4 LT |
370 | /** |
371 | * rcu_assign_pointer - assign (publicize) a pointer to a newly | |
372 | * initialized structure that will be dereferenced by RCU read-side | |
373 | * critical sections. Returns the value assigned. | |
374 | * | |
375 | * Inserts memory barriers on architectures that require them | |
376 | * (pretty much all of them other than x86), and also prevents | |
377 | * the compiler from reordering the code that initializes the | |
378 | * structure after the pointer assignment. More importantly, this | |
379 | * call documents which pointers will be dereferenced by RCU read-side | |
380 | * code. | |
381 | */ | |
382 | ||
d99c4f6b PM |
383 | #define rcu_assign_pointer(p, v) \ |
384 | ({ \ | |
385 | if (!__builtin_constant_p(v) || \ | |
386 | ((v) != NULL)) \ | |
387 | smp_wmb(); \ | |
388 | (p) = (v); \ | |
389 | }) | |
1da177e4 | 390 | |
4446a36f PM |
391 | /* Infrastructure to implement the synchronize_() primitives. */ |
392 | ||
393 | struct rcu_synchronize { | |
394 | struct rcu_head head; | |
395 | struct completion completion; | |
396 | }; | |
397 | ||
398 | extern void wakeme_after_rcu(struct rcu_head *head); | |
399 | ||
01c1c660 PM |
400 | /** |
401 | * call_rcu - Queue an RCU callback for invocation after a grace period. | |
402 | * @head: structure to be used for queueing the RCU updates. | |
403 | * @func: actual update function to be invoked after the grace period | |
404 | * | |
405 | * The update function will be invoked some time after a full grace | |
406 | * period elapses, in other words after all currently executing RCU | |
407 | * read-side critical sections have completed. RCU read-side critical | |
408 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
409 | * and may be nested. | |
410 | */ | |
411 | extern void call_rcu(struct rcu_head *head, | |
412 | void (*func)(struct rcu_head *head)); | |
413 | ||
414 | /** | |
415 | * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. | |
416 | * @head: structure to be used for queueing the RCU updates. | |
417 | * @func: actual update function to be invoked after the grace period | |
418 | * | |
419 | * The update function will be invoked some time after a full grace | |
420 | * period elapses, in other words after all currently executing RCU | |
421 | * read-side critical sections have completed. call_rcu_bh() assumes | |
422 | * that the read-side critical sections end on completion of a softirq | |
423 | * handler. This means that read-side critical sections in process | |
424 | * context must not be interrupted by softirqs. This interface is to be | |
425 | * used when most of the read-side critical sections are in softirq context. | |
426 | * RCU read-side critical sections are delimited by : | |
427 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. | |
428 | * OR | |
429 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. | |
430 | * These may be nested. | |
431 | */ | |
432 | extern void call_rcu_bh(struct rcu_head *head, | |
433 | void (*func)(struct rcu_head *head)); | |
434 | ||
1da177e4 | 435 | #endif /* __LINUX_RCUPDATE_H */ |