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Source at commit 2604e7f9a98c27be50a0c3ff7503b6a5ea8f6cfe created 12 years 7 months ago. By Maarten ter Huurne, cpufreq_stats: Support runtime changes to frequency table | |
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1 | /* |
2 | * Sleepable Read-Copy Update mechanism for mutual exclusion. |
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 | * |
18 | * Copyright (C) IBM Corporation, 2006 |
19 | * |
20 | * Author: Paul McKenney <paulmck@us.ibm.com> |
21 | * |
22 | * For detailed explanation of Read-Copy Update mechanism see - |
23 | * Documentation/RCU/ *.txt |
24 | * |
25 | */ |
26 | |
27 | #include <linux/export.h> |
28 | #include <linux/mutex.h> |
29 | #include <linux/percpu.h> |
30 | #include <linux/preempt.h> |
31 | #include <linux/rcupdate.h> |
32 | #include <linux/sched.h> |
33 | #include <linux/smp.h> |
34 | #include <linux/delay.h> |
35 | #include <linux/srcu.h> |
36 | |
37 | /* |
38 | * Initialize an rcu_batch structure to empty. |
39 | */ |
40 | static inline void rcu_batch_init(struct rcu_batch *b) |
41 | { |
42 | b->head = NULL; |
43 | b->tail = &b->head; |
44 | } |
45 | |
46 | /* |
47 | * Enqueue a callback onto the tail of the specified rcu_batch structure. |
48 | */ |
49 | static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head) |
50 | { |
51 | *b->tail = head; |
52 | b->tail = &head->next; |
53 | } |
54 | |
55 | /* |
56 | * Is the specified rcu_batch structure empty? |
57 | */ |
58 | static inline bool rcu_batch_empty(struct rcu_batch *b) |
59 | { |
60 | return b->tail == &b->head; |
61 | } |
62 | |
63 | /* |
64 | * Remove the callback at the head of the specified rcu_batch structure |
65 | * and return a pointer to it, or return NULL if the structure is empty. |
66 | */ |
67 | static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b) |
68 | { |
69 | struct rcu_head *head; |
70 | |
71 | if (rcu_batch_empty(b)) |
72 | return NULL; |
73 | |
74 | head = b->head; |
75 | b->head = head->next; |
76 | if (b->tail == &head->next) |
77 | rcu_batch_init(b); |
78 | |
79 | return head; |
80 | } |
81 | |
82 | /* |
83 | * Move all callbacks from the rcu_batch structure specified by "from" to |
84 | * the structure specified by "to". |
85 | */ |
86 | static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from) |
87 | { |
88 | if (!rcu_batch_empty(from)) { |
89 | *to->tail = from->head; |
90 | to->tail = from->tail; |
91 | rcu_batch_init(from); |
92 | } |
93 | } |
94 | |
95 | /* single-thread state-machine */ |
96 | static void process_srcu(struct work_struct *work); |
97 | |
98 | static int init_srcu_struct_fields(struct srcu_struct *sp) |
99 | { |
100 | sp->completed = 0; |
101 | spin_lock_init(&sp->queue_lock); |
102 | sp->running = false; |
103 | rcu_batch_init(&sp->batch_queue); |
104 | rcu_batch_init(&sp->batch_check0); |
105 | rcu_batch_init(&sp->batch_check1); |
106 | rcu_batch_init(&sp->batch_done); |
107 | INIT_DELAYED_WORK(&sp->work, process_srcu); |
108 | sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array); |
109 | return sp->per_cpu_ref ? 0 : -ENOMEM; |
110 | } |
111 | |
112 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
113 | |
114 | int __init_srcu_struct(struct srcu_struct *sp, const char *name, |
115 | struct lock_class_key *key) |
116 | { |
117 | /* Don't re-initialize a lock while it is held. */ |
118 | debug_check_no_locks_freed((void *)sp, sizeof(*sp)); |
119 | lockdep_init_map(&sp->dep_map, name, key, 0); |
120 | return init_srcu_struct_fields(sp); |
121 | } |
122 | EXPORT_SYMBOL_GPL(__init_srcu_struct); |
123 | |
124 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
125 | |
126 | /** |
127 | * init_srcu_struct - initialize a sleep-RCU structure |
128 | * @sp: structure to initialize. |
129 | * |
130 | * Must invoke this on a given srcu_struct before passing that srcu_struct |
131 | * to any other function. Each srcu_struct represents a separate domain |
132 | * of SRCU protection. |
133 | */ |
134 | int init_srcu_struct(struct srcu_struct *sp) |
135 | { |
136 | return init_srcu_struct_fields(sp); |
137 | } |
138 | EXPORT_SYMBOL_GPL(init_srcu_struct); |
139 | |
140 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
141 | |
142 | /* |
143 | * Returns approximate total of the readers' ->seq[] values for the |
144 | * rank of per-CPU counters specified by idx. |
145 | */ |
146 | static unsigned long srcu_readers_seq_idx(struct srcu_struct *sp, int idx) |
147 | { |
148 | int cpu; |
149 | unsigned long sum = 0; |
150 | unsigned long t; |
151 | |
152 | for_each_possible_cpu(cpu) { |
153 | t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->seq[idx]); |
154 | sum += t; |
155 | } |
156 | return sum; |
157 | } |
158 | |
159 | /* |
160 | * Returns approximate number of readers active on the specified rank |
161 | * of the per-CPU ->c[] counters. |
162 | */ |
163 | static unsigned long srcu_readers_active_idx(struct srcu_struct *sp, int idx) |
164 | { |
165 | int cpu; |
166 | unsigned long sum = 0; |
167 | unsigned long t; |
168 | |
169 | for_each_possible_cpu(cpu) { |
170 | t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx]); |
171 | sum += t; |
172 | } |
173 | return sum; |
174 | } |
175 | |
176 | /* |
177 | * Return true if the number of pre-existing readers is determined to |
178 | * be stably zero. An example unstable zero can occur if the call |
179 | * to srcu_readers_active_idx() misses an __srcu_read_lock() increment, |
180 | * but due to task migration, sees the corresponding __srcu_read_unlock() |
181 | * decrement. This can happen because srcu_readers_active_idx() takes |
182 | * time to sum the array, and might in fact be interrupted or preempted |
183 | * partway through the summation. |
184 | */ |
185 | static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx) |
186 | { |
187 | unsigned long seq; |
188 | |
189 | seq = srcu_readers_seq_idx(sp, idx); |
190 | |
191 | /* |
192 | * The following smp_mb() A pairs with the smp_mb() B located in |
193 | * __srcu_read_lock(). This pairing ensures that if an |
194 | * __srcu_read_lock() increments its counter after the summation |
195 | * in srcu_readers_active_idx(), then the corresponding SRCU read-side |
196 | * critical section will see any changes made prior to the start |
197 | * of the current SRCU grace period. |
198 | * |
199 | * Also, if the above call to srcu_readers_seq_idx() saw the |
200 | * increment of ->seq[], then the call to srcu_readers_active_idx() |
201 | * must see the increment of ->c[]. |
202 | */ |
203 | smp_mb(); /* A */ |
204 | |
205 | /* |
206 | * Note that srcu_readers_active_idx() can incorrectly return |
207 | * zero even though there is a pre-existing reader throughout. |
208 | * To see this, suppose that task A is in a very long SRCU |
209 | * read-side critical section that started on CPU 0, and that |
210 | * no other reader exists, so that the sum of the counters |
211 | * is equal to one. Then suppose that task B starts executing |
212 | * srcu_readers_active_idx(), summing up to CPU 1, and then that |
213 | * task C starts reading on CPU 0, so that its increment is not |
214 | * summed, but finishes reading on CPU 2, so that its decrement |
215 | * -is- summed. Then when task B completes its sum, it will |
216 | * incorrectly get zero, despite the fact that task A has been |
217 | * in its SRCU read-side critical section the whole time. |
218 | * |
219 | * We therefore do a validation step should srcu_readers_active_idx() |
220 | * return zero. |
221 | */ |
222 | if (srcu_readers_active_idx(sp, idx) != 0) |
223 | return false; |
224 | |
225 | /* |
226 | * The remainder of this function is the validation step. |
227 | * The following smp_mb() D pairs with the smp_mb() C in |
228 | * __srcu_read_unlock(). If the __srcu_read_unlock() was seen |
229 | * by srcu_readers_active_idx() above, then any destructive |
230 | * operation performed after the grace period will happen after |
231 | * the corresponding SRCU read-side critical section. |
232 | * |
233 | * Note that there can be at most NR_CPUS worth of readers using |
234 | * the old index, which is not enough to overflow even a 32-bit |
235 | * integer. (Yes, this does mean that systems having more than |
236 | * a billion or so CPUs need to be 64-bit systems.) Therefore, |
237 | * the sum of the ->seq[] counters cannot possibly overflow. |
238 | * Therefore, the only way that the return values of the two |
239 | * calls to srcu_readers_seq_idx() can be equal is if there were |
240 | * no increments of the corresponding rank of ->seq[] counts |
241 | * in the interim. But the missed-increment scenario laid out |
242 | * above includes an increment of the ->seq[] counter by |
243 | * the corresponding __srcu_read_lock(). Therefore, if this |
244 | * scenario occurs, the return values from the two calls to |
245 | * srcu_readers_seq_idx() will differ, and thus the validation |
246 | * step below suffices. |
247 | */ |
248 | smp_mb(); /* D */ |
249 | |
250 | return srcu_readers_seq_idx(sp, idx) == seq; |
251 | } |
252 | |
253 | /** |
254 | * srcu_readers_active - returns approximate number of readers. |
255 | * @sp: which srcu_struct to count active readers (holding srcu_read_lock). |
256 | * |
257 | * Note that this is not an atomic primitive, and can therefore suffer |
258 | * severe errors when invoked on an active srcu_struct. That said, it |
259 | * can be useful as an error check at cleanup time. |
260 | */ |
261 | static int srcu_readers_active(struct srcu_struct *sp) |
262 | { |
263 | int cpu; |
264 | unsigned long sum = 0; |
265 | |
266 | for_each_possible_cpu(cpu) { |
267 | sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[0]); |
268 | sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[1]); |
269 | } |
270 | return sum; |
271 | } |
272 | |
273 | /** |
274 | * cleanup_srcu_struct - deconstruct a sleep-RCU structure |
275 | * @sp: structure to clean up. |
276 | * |
277 | * Must invoke this after you are finished using a given srcu_struct that |
278 | * was initialized via init_srcu_struct(), else you leak memory. |
279 | */ |
280 | void cleanup_srcu_struct(struct srcu_struct *sp) |
281 | { |
282 | int sum; |
283 | |
284 | sum = srcu_readers_active(sp); |
285 | WARN_ON(sum); /* Leakage unless caller handles error. */ |
286 | if (sum != 0) |
287 | return; |
288 | free_percpu(sp->per_cpu_ref); |
289 | sp->per_cpu_ref = NULL; |
290 | } |
291 | EXPORT_SYMBOL_GPL(cleanup_srcu_struct); |
292 | |
293 | /* |
294 | * Counts the new reader in the appropriate per-CPU element of the |
295 | * srcu_struct. Must be called from process context. |
296 | * Returns an index that must be passed to the matching srcu_read_unlock(). |
297 | */ |
298 | int __srcu_read_lock(struct srcu_struct *sp) |
299 | { |
300 | int idx; |
301 | |
302 | preempt_disable(); |
303 | idx = rcu_dereference_index_check(sp->completed, |
304 | rcu_read_lock_sched_held()) & 0x1; |
305 | ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1; |
306 | smp_mb(); /* B */ /* Avoid leaking the critical section. */ |
307 | ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1; |
308 | preempt_enable(); |
309 | return idx; |
310 | } |
311 | EXPORT_SYMBOL_GPL(__srcu_read_lock); |
312 | |
313 | /* |
314 | * Removes the count for the old reader from the appropriate per-CPU |
315 | * element of the srcu_struct. Note that this may well be a different |
316 | * CPU than that which was incremented by the corresponding srcu_read_lock(). |
317 | * Must be called from process context. |
318 | */ |
319 | void __srcu_read_unlock(struct srcu_struct *sp, int idx) |
320 | { |
321 | preempt_disable(); |
322 | smp_mb(); /* C */ /* Avoid leaking the critical section. */ |
323 | ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) -= 1; |
324 | preempt_enable(); |
325 | } |
326 | EXPORT_SYMBOL_GPL(__srcu_read_unlock); |
327 | |
328 | /* |
329 | * We use an adaptive strategy for synchronize_srcu() and especially for |
330 | * synchronize_srcu_expedited(). We spin for a fixed time period |
331 | * (defined below) to allow SRCU readers to exit their read-side critical |
332 | * sections. If there are still some readers after 10 microseconds, |
333 | * we repeatedly block for 1-millisecond time periods. This approach |
334 | * has done well in testing, so there is no need for a config parameter. |
335 | */ |
336 | #define SRCU_RETRY_CHECK_DELAY 5 |
337 | #define SYNCHRONIZE_SRCU_TRYCOUNT 2 |
338 | #define SYNCHRONIZE_SRCU_EXP_TRYCOUNT 12 |
339 | |
340 | /* |
341 | * @@@ Wait until all pre-existing readers complete. Such readers |
342 | * will have used the index specified by "idx". |
343 | * the caller should ensures the ->completed is not changed while checking |
344 | * and idx = (->completed & 1) ^ 1 |
345 | */ |
346 | static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount) |
347 | { |
348 | for (;;) { |
349 | if (srcu_readers_active_idx_check(sp, idx)) |
350 | return true; |
351 | if (--trycount <= 0) |
352 | return false; |
353 | udelay(SRCU_RETRY_CHECK_DELAY); |
354 | } |
355 | } |
356 | |
357 | /* |
358 | * Increment the ->completed counter so that future SRCU readers will |
359 | * use the other rank of the ->c[] and ->seq[] arrays. This allows |
360 | * us to wait for pre-existing readers in a starvation-free manner. |
361 | */ |
362 | static void srcu_flip(struct srcu_struct *sp) |
363 | { |
364 | sp->completed++; |
365 | } |
366 | |
367 | /* |
368 | * Enqueue an SRCU callback on the specified srcu_struct structure, |
369 | * initiating grace-period processing if it is not already running. |
370 | */ |
371 | void call_srcu(struct srcu_struct *sp, struct rcu_head *head, |
372 | void (*func)(struct rcu_head *head)) |
373 | { |
374 | unsigned long flags; |
375 | |
376 | head->next = NULL; |
377 | head->func = func; |
378 | spin_lock_irqsave(&sp->queue_lock, flags); |
379 | rcu_batch_queue(&sp->batch_queue, head); |
380 | if (!sp->running) { |
381 | sp->running = true; |
382 | queue_delayed_work(system_nrt_wq, &sp->work, 0); |
383 | } |
384 | spin_unlock_irqrestore(&sp->queue_lock, flags); |
385 | } |
386 | EXPORT_SYMBOL_GPL(call_srcu); |
387 | |
388 | struct rcu_synchronize { |
389 | struct rcu_head head; |
390 | struct completion completion; |
391 | }; |
392 | |
393 | /* |
394 | * Awaken the corresponding synchronize_srcu() instance now that a |
395 | * grace period has elapsed. |
396 | */ |
397 | static void wakeme_after_rcu(struct rcu_head *head) |
398 | { |
399 | struct rcu_synchronize *rcu; |
400 | |
401 | rcu = container_of(head, struct rcu_synchronize, head); |
402 | complete(&rcu->completion); |
403 | } |
404 | |
405 | static void srcu_advance_batches(struct srcu_struct *sp, int trycount); |
406 | static void srcu_reschedule(struct srcu_struct *sp); |
407 | |
408 | /* |
409 | * Helper function for synchronize_srcu() and synchronize_srcu_expedited(). |
410 | */ |
411 | static void __synchronize_srcu(struct srcu_struct *sp, int trycount) |
412 | { |
413 | struct rcu_synchronize rcu; |
414 | struct rcu_head *head = &rcu.head; |
415 | bool done = false; |
416 | |
417 | rcu_lockdep_assert(!lock_is_held(&sp->dep_map) && |
418 | !lock_is_held(&rcu_bh_lock_map) && |
419 | !lock_is_held(&rcu_lock_map) && |
420 | !lock_is_held(&rcu_sched_lock_map), |
421 | "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section"); |
422 | |
423 | init_completion(&rcu.completion); |
424 | |
425 | head->next = NULL; |
426 | head->func = wakeme_after_rcu; |
427 | spin_lock_irq(&sp->queue_lock); |
428 | if (!sp->running) { |
429 | /* steal the processing owner */ |
430 | sp->running = true; |
431 | rcu_batch_queue(&sp->batch_check0, head); |
432 | spin_unlock_irq(&sp->queue_lock); |
433 | |
434 | srcu_advance_batches(sp, trycount); |
435 | if (!rcu_batch_empty(&sp->batch_done)) { |
436 | BUG_ON(sp->batch_done.head != head); |
437 | rcu_batch_dequeue(&sp->batch_done); |
438 | done = true; |
439 | } |
440 | /* give the processing owner to work_struct */ |
441 | srcu_reschedule(sp); |
442 | } else { |
443 | rcu_batch_queue(&sp->batch_queue, head); |
444 | spin_unlock_irq(&sp->queue_lock); |
445 | } |
446 | |
447 | if (!done) |
448 | wait_for_completion(&rcu.completion); |
449 | } |
450 | |
451 | /** |
452 | * synchronize_srcu - wait for prior SRCU read-side critical-section completion |
453 | * @sp: srcu_struct with which to synchronize. |
454 | * |
455 | * Flip the completed counter, and wait for the old count to drain to zero. |
456 | * As with classic RCU, the updater must use some separate means of |
457 | * synchronizing concurrent updates. Can block; must be called from |
458 | * process context. |
459 | * |
460 | * Note that it is illegal to call synchronize_srcu() from the corresponding |
461 | * SRCU read-side critical section; doing so will result in deadlock. |
462 | * However, it is perfectly legal to call synchronize_srcu() on one |
463 | * srcu_struct from some other srcu_struct's read-side critical section. |
464 | */ |
465 | void synchronize_srcu(struct srcu_struct *sp) |
466 | { |
467 | __synchronize_srcu(sp, SYNCHRONIZE_SRCU_TRYCOUNT); |
468 | } |
469 | EXPORT_SYMBOL_GPL(synchronize_srcu); |
470 | |
471 | /** |
472 | * synchronize_srcu_expedited - Brute-force SRCU grace period |
473 | * @sp: srcu_struct with which to synchronize. |
474 | * |
475 | * Wait for an SRCU grace period to elapse, but be more aggressive about |
476 | * spinning rather than blocking when waiting. |
477 | * |
478 | * Note that it is illegal to call this function while holding any lock |
479 | * that is acquired by a CPU-hotplug notifier. It is also illegal to call |
480 | * synchronize_srcu_expedited() from the corresponding SRCU read-side |
481 | * critical section; doing so will result in deadlock. However, it is |
482 | * perfectly legal to call synchronize_srcu_expedited() on one srcu_struct |
483 | * from some other srcu_struct's read-side critical section, as long as |
484 | * the resulting graph of srcu_structs is acyclic. |
485 | */ |
486 | void synchronize_srcu_expedited(struct srcu_struct *sp) |
487 | { |
488 | __synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT); |
489 | } |
490 | EXPORT_SYMBOL_GPL(synchronize_srcu_expedited); |
491 | |
492 | /** |
493 | * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete. |
494 | */ |
495 | void srcu_barrier(struct srcu_struct *sp) |
496 | { |
497 | synchronize_srcu(sp); |
498 | } |
499 | EXPORT_SYMBOL_GPL(srcu_barrier); |
500 | |
501 | /** |
502 | * srcu_batches_completed - return batches completed. |
503 | * @sp: srcu_struct on which to report batch completion. |
504 | * |
505 | * Report the number of batches, correlated with, but not necessarily |
506 | * precisely the same as, the number of grace periods that have elapsed. |
507 | */ |
508 | long srcu_batches_completed(struct srcu_struct *sp) |
509 | { |
510 | return sp->completed; |
511 | } |
512 | EXPORT_SYMBOL_GPL(srcu_batches_completed); |
513 | |
514 | #define SRCU_CALLBACK_BATCH 10 |
515 | #define SRCU_INTERVAL 1 |
516 | |
517 | /* |
518 | * Move any new SRCU callbacks to the first stage of the SRCU grace |
519 | * period pipeline. |
520 | */ |
521 | static void srcu_collect_new(struct srcu_struct *sp) |
522 | { |
523 | if (!rcu_batch_empty(&sp->batch_queue)) { |
524 | spin_lock_irq(&sp->queue_lock); |
525 | rcu_batch_move(&sp->batch_check0, &sp->batch_queue); |
526 | spin_unlock_irq(&sp->queue_lock); |
527 | } |
528 | } |
529 | |
530 | /* |
531 | * Core SRCU state machine. Advance callbacks from ->batch_check0 to |
532 | * ->batch_check1 and then to ->batch_done as readers drain. |
533 | */ |
534 | static void srcu_advance_batches(struct srcu_struct *sp, int trycount) |
535 | { |
536 | int idx = 1 ^ (sp->completed & 1); |
537 | |
538 | /* |
539 | * Because readers might be delayed for an extended period after |
540 | * fetching ->completed for their index, at any point in time there |
541 | * might well be readers using both idx=0 and idx=1. We therefore |
542 | * need to wait for readers to clear from both index values before |
543 | * invoking a callback. |
544 | */ |
545 | |
546 | if (rcu_batch_empty(&sp->batch_check0) && |
547 | rcu_batch_empty(&sp->batch_check1)) |
548 | return; /* no callbacks need to be advanced */ |
549 | |
550 | if (!try_check_zero(sp, idx, trycount)) |
551 | return; /* failed to advance, will try after SRCU_INTERVAL */ |
552 | |
553 | /* |
554 | * The callbacks in ->batch_check1 have already done with their |
555 | * first zero check and flip back when they were enqueued on |
556 | * ->batch_check0 in a previous invocation of srcu_advance_batches(). |
557 | * (Presumably try_check_zero() returned false during that |
558 | * invocation, leaving the callbacks stranded on ->batch_check1.) |
559 | * They are therefore ready to invoke, so move them to ->batch_done. |
560 | */ |
561 | rcu_batch_move(&sp->batch_done, &sp->batch_check1); |
562 | |
563 | if (rcu_batch_empty(&sp->batch_check0)) |
564 | return; /* no callbacks need to be advanced */ |
565 | srcu_flip(sp); |
566 | |
567 | /* |
568 | * The callbacks in ->batch_check0 just finished their |
569 | * first check zero and flip, so move them to ->batch_check1 |
570 | * for future checking on the other idx. |
571 | */ |
572 | rcu_batch_move(&sp->batch_check1, &sp->batch_check0); |
573 | |
574 | /* |
575 | * SRCU read-side critical sections are normally short, so check |
576 | * at least twice in quick succession after a flip. |
577 | */ |
578 | trycount = trycount < 2 ? 2 : trycount; |
579 | if (!try_check_zero(sp, idx^1, trycount)) |
580 | return; /* failed to advance, will try after SRCU_INTERVAL */ |
581 | |
582 | /* |
583 | * The callbacks in ->batch_check1 have now waited for all |
584 | * pre-existing readers using both idx values. They are therefore |
585 | * ready to invoke, so move them to ->batch_done. |
586 | */ |
587 | rcu_batch_move(&sp->batch_done, &sp->batch_check1); |
588 | } |
589 | |
590 | /* |
591 | * Invoke a limited number of SRCU callbacks that have passed through |
592 | * their grace period. If there are more to do, SRCU will reschedule |
593 | * the workqueue. |
594 | */ |
595 | static void srcu_invoke_callbacks(struct srcu_struct *sp) |
596 | { |
597 | int i; |
598 | struct rcu_head *head; |
599 | |
600 | for (i = 0; i < SRCU_CALLBACK_BATCH; i++) { |
601 | head = rcu_batch_dequeue(&sp->batch_done); |
602 | if (!head) |
603 | break; |
604 | local_bh_disable(); |
605 | head->func(head); |
606 | local_bh_enable(); |
607 | } |
608 | } |
609 | |
610 | /* |
611 | * Finished one round of SRCU grace period. Start another if there are |
612 | * more SRCU callbacks queued, otherwise put SRCU into not-running state. |
613 | */ |
614 | static void srcu_reschedule(struct srcu_struct *sp) |
615 | { |
616 | bool pending = true; |
617 | |
618 | if (rcu_batch_empty(&sp->batch_done) && |
619 | rcu_batch_empty(&sp->batch_check1) && |
620 | rcu_batch_empty(&sp->batch_check0) && |
621 | rcu_batch_empty(&sp->batch_queue)) { |
622 | spin_lock_irq(&sp->queue_lock); |
623 | if (rcu_batch_empty(&sp->batch_done) && |
624 | rcu_batch_empty(&sp->batch_check1) && |
625 | rcu_batch_empty(&sp->batch_check0) && |
626 | rcu_batch_empty(&sp->batch_queue)) { |
627 | sp->running = false; |
628 | pending = false; |
629 | } |
630 | spin_unlock_irq(&sp->queue_lock); |
631 | } |
632 | |
633 | if (pending) |
634 | queue_delayed_work(system_nrt_wq, &sp->work, SRCU_INTERVAL); |
635 | } |
636 | |
637 | /* |
638 | * This is the work-queue function that handles SRCU grace periods. |
639 | */ |
640 | static void process_srcu(struct work_struct *work) |
641 | { |
642 | struct srcu_struct *sp; |
643 | |
644 | sp = container_of(work, struct srcu_struct, work.work); |
645 | |
646 | srcu_collect_new(sp); |
647 | srcu_advance_batches(sp, 1); |
648 | srcu_invoke_callbacks(sp); |
649 | srcu_reschedule(sp); |
650 | } |
651 |
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od-2011-09-04
od-2011-09-18
v2.6.34-rc5
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