diff options
author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2013-10-08 23:23:47 -0400 |
---|---|---|
committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2013-10-15 15:53:31 -0400 |
commit | 4102adab9189c8ea2f0cdd2f88345fd25d2790f1 (patch) | |
tree | 235964cfd9c09a5c642a2d0d8745a651a0d4bcfa /kernel/srcu.c | |
parent | 252997330908cb8ee3d5714539ed967b977c2eae (diff) |
rcu: Move RCU-related source code to kernel/rcu directory
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/srcu.c')
-rw-r--r-- | kernel/srcu.c | 651 |
1 files changed, 0 insertions, 651 deletions
diff --git a/kernel/srcu.c b/kernel/srcu.c deleted file mode 100644 index 01d5ccb8bfe3..000000000000 --- a/kernel/srcu.c +++ /dev/null | |||
@@ -1,651 +0,0 @@ | |||
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 | * Copyright (C) Fujitsu, 2012 | ||
20 | * | ||
21 | * Author: Paul McKenney <paulmck@us.ibm.com> | ||
22 | * Lai Jiangshan <laijs@cn.fujitsu.com> | ||
23 | * | ||
24 | * For detailed explanation of Read-Copy Update mechanism see - | ||
25 | * Documentation/RCU/ *.txt | ||
26 | * | ||
27 | */ | ||
28 | |||
29 | #include <linux/export.h> | ||
30 | #include <linux/mutex.h> | ||
31 | #include <linux/percpu.h> | ||
32 | #include <linux/preempt.h> | ||
33 | #include <linux/rcupdate.h> | ||
34 | #include <linux/sched.h> | ||
35 | #include <linux/smp.h> | ||
36 | #include <linux/delay.h> | ||
37 | #include <linux/srcu.h> | ||
38 | |||
39 | #include <trace/events/rcu.h> | ||
40 | |||
41 | #include "rcu.h" | ||
42 | |||
43 | /* | ||
44 | * Initialize an rcu_batch structure to empty. | ||
45 | */ | ||
46 | static inline void rcu_batch_init(struct rcu_batch *b) | ||
47 | { | ||
48 | b->head = NULL; | ||
49 | b->tail = &b->head; | ||
50 | } | ||
51 | |||
52 | /* | ||
53 | * Enqueue a callback onto the tail of the specified rcu_batch structure. | ||
54 | */ | ||
55 | static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head) | ||
56 | { | ||
57 | *b->tail = head; | ||
58 | b->tail = &head->next; | ||
59 | } | ||
60 | |||
61 | /* | ||
62 | * Is the specified rcu_batch structure empty? | ||
63 | */ | ||
64 | static inline bool rcu_batch_empty(struct rcu_batch *b) | ||
65 | { | ||
66 | return b->tail == &b->head; | ||
67 | } | ||
68 | |||
69 | /* | ||
70 | * Remove the callback at the head of the specified rcu_batch structure | ||
71 | * and return a pointer to it, or return NULL if the structure is empty. | ||
72 | */ | ||
73 | static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b) | ||
74 | { | ||
75 | struct rcu_head *head; | ||
76 | |||
77 | if (rcu_batch_empty(b)) | ||
78 | return NULL; | ||
79 | |||
80 | head = b->head; | ||
81 | b->head = head->next; | ||
82 | if (b->tail == &head->next) | ||
83 | rcu_batch_init(b); | ||
84 | |||
85 | return head; | ||
86 | } | ||
87 | |||
88 | /* | ||
89 | * Move all callbacks from the rcu_batch structure specified by "from" to | ||
90 | * the structure specified by "to". | ||
91 | */ | ||
92 | static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from) | ||
93 | { | ||
94 | if (!rcu_batch_empty(from)) { | ||
95 | *to->tail = from->head; | ||
96 | to->tail = from->tail; | ||
97 | rcu_batch_init(from); | ||
98 | } | ||
99 | } | ||
100 | |||
101 | static int init_srcu_struct_fields(struct srcu_struct *sp) | ||
102 | { | ||
103 | sp->completed = 0; | ||
104 | spin_lock_init(&sp->queue_lock); | ||
105 | sp->running = false; | ||
106 | rcu_batch_init(&sp->batch_queue); | ||
107 | rcu_batch_init(&sp->batch_check0); | ||
108 | rcu_batch_init(&sp->batch_check1); | ||
109 | rcu_batch_init(&sp->batch_done); | ||
110 | INIT_DELAYED_WORK(&sp->work, process_srcu); | ||
111 | sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array); | ||
112 | return sp->per_cpu_ref ? 0 : -ENOMEM; | ||
113 | } | ||
114 | |||
115 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | ||
116 | |||
117 | int __init_srcu_struct(struct srcu_struct *sp, const char *name, | ||
118 | struct lock_class_key *key) | ||
119 | { | ||
120 | /* Don't re-initialize a lock while it is held. */ | ||
121 | debug_check_no_locks_freed((void *)sp, sizeof(*sp)); | ||
122 | lockdep_init_map(&sp->dep_map, name, key, 0); | ||
123 | return init_srcu_struct_fields(sp); | ||
124 | } | ||
125 | EXPORT_SYMBOL_GPL(__init_srcu_struct); | ||
126 | |||
127 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | ||
128 | |||
129 | /** | ||
130 | * init_srcu_struct - initialize a sleep-RCU structure | ||
131 | * @sp: structure to initialize. | ||
132 | * | ||
133 | * Must invoke this on a given srcu_struct before passing that srcu_struct | ||
134 | * to any other function. Each srcu_struct represents a separate domain | ||
135 | * of SRCU protection. | ||
136 | */ | ||
137 | int init_srcu_struct(struct srcu_struct *sp) | ||
138 | { | ||
139 | return init_srcu_struct_fields(sp); | ||
140 | } | ||
141 | EXPORT_SYMBOL_GPL(init_srcu_struct); | ||
142 | |||
143 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | ||
144 | |||
145 | /* | ||
146 | * Returns approximate total of the readers' ->seq[] values for the | ||
147 | * rank of per-CPU counters specified by idx. | ||
148 | */ | ||
149 | static unsigned long srcu_readers_seq_idx(struct srcu_struct *sp, int idx) | ||
150 | { | ||
151 | int cpu; | ||
152 | unsigned long sum = 0; | ||
153 | unsigned long t; | ||
154 | |||
155 | for_each_possible_cpu(cpu) { | ||
156 | t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->seq[idx]); | ||
157 | sum += t; | ||
158 | } | ||
159 | return sum; | ||
160 | } | ||
161 | |||
162 | /* | ||
163 | * Returns approximate number of readers active on the specified rank | ||
164 | * of the per-CPU ->c[] counters. | ||
165 | */ | ||
166 | static unsigned long srcu_readers_active_idx(struct srcu_struct *sp, int idx) | ||
167 | { | ||
168 | int cpu; | ||
169 | unsigned long sum = 0; | ||
170 | unsigned long t; | ||
171 | |||
172 | for_each_possible_cpu(cpu) { | ||
173 | t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx]); | ||
174 | sum += t; | ||
175 | } | ||
176 | return sum; | ||
177 | } | ||
178 | |||
179 | /* | ||
180 | * Return true if the number of pre-existing readers is determined to | ||
181 | * be stably zero. An example unstable zero can occur if the call | ||
182 | * to srcu_readers_active_idx() misses an __srcu_read_lock() increment, | ||
183 | * but due to task migration, sees the corresponding __srcu_read_unlock() | ||
184 | * decrement. This can happen because srcu_readers_active_idx() takes | ||
185 | * time to sum the array, and might in fact be interrupted or preempted | ||
186 | * partway through the summation. | ||
187 | */ | ||
188 | static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx) | ||
189 | { | ||
190 | unsigned long seq; | ||
191 | |||
192 | seq = srcu_readers_seq_idx(sp, idx); | ||
193 | |||
194 | /* | ||
195 | * The following smp_mb() A pairs with the smp_mb() B located in | ||
196 | * __srcu_read_lock(). This pairing ensures that if an | ||
197 | * __srcu_read_lock() increments its counter after the summation | ||
198 | * in srcu_readers_active_idx(), then the corresponding SRCU read-side | ||
199 | * critical section will see any changes made prior to the start | ||
200 | * of the current SRCU grace period. | ||
201 | * | ||
202 | * Also, if the above call to srcu_readers_seq_idx() saw the | ||
203 | * increment of ->seq[], then the call to srcu_readers_active_idx() | ||
204 | * must see the increment of ->c[]. | ||
205 | */ | ||
206 | smp_mb(); /* A */ | ||
207 | |||
208 | /* | ||
209 | * Note that srcu_readers_active_idx() can incorrectly return | ||
210 | * zero even though there is a pre-existing reader throughout. | ||
211 | * To see this, suppose that task A is in a very long SRCU | ||
212 | * read-side critical section that started on CPU 0, and that | ||
213 | * no other reader exists, so that the sum of the counters | ||
214 | * is equal to one. Then suppose that task B starts executing | ||
215 | * srcu_readers_active_idx(), summing up to CPU 1, and then that | ||
216 | * task C starts reading on CPU 0, so that its increment is not | ||
217 | * summed, but finishes reading on CPU 2, so that its decrement | ||
218 | * -is- summed. Then when task B completes its sum, it will | ||
219 | * incorrectly get zero, despite the fact that task A has been | ||
220 | * in its SRCU read-side critical section the whole time. | ||
221 | * | ||
222 | * We therefore do a validation step should srcu_readers_active_idx() | ||
223 | * return zero. | ||
224 | */ | ||
225 | if (srcu_readers_active_idx(sp, idx) != 0) | ||
226 | return false; | ||
227 | |||
228 | /* | ||
229 | * The remainder of this function is the validation step. | ||
230 | * The following smp_mb() D pairs with the smp_mb() C in | ||
231 | * __srcu_read_unlock(). If the __srcu_read_unlock() was seen | ||
232 | * by srcu_readers_active_idx() above, then any destructive | ||
233 | * operation performed after the grace period will happen after | ||
234 | * the corresponding SRCU read-side critical section. | ||
235 | * | ||
236 | * Note that there can be at most NR_CPUS worth of readers using | ||
237 | * the old index, which is not enough to overflow even a 32-bit | ||
238 | * integer. (Yes, this does mean that systems having more than | ||
239 | * a billion or so CPUs need to be 64-bit systems.) Therefore, | ||
240 | * the sum of the ->seq[] counters cannot possibly overflow. | ||
241 | * Therefore, the only way that the return values of the two | ||
242 | * calls to srcu_readers_seq_idx() can be equal is if there were | ||
243 | * no increments of the corresponding rank of ->seq[] counts | ||
244 | * in the interim. But the missed-increment scenario laid out | ||
245 | * above includes an increment of the ->seq[] counter by | ||
246 | * the corresponding __srcu_read_lock(). Therefore, if this | ||
247 | * scenario occurs, the return values from the two calls to | ||
248 | * srcu_readers_seq_idx() will differ, and thus the validation | ||
249 | * step below suffices. | ||
250 | */ | ||
251 | smp_mb(); /* D */ | ||
252 | |||
253 | return srcu_readers_seq_idx(sp, idx) == seq; | ||
254 | } | ||
255 | |||
256 | /** | ||
257 | * srcu_readers_active - returns approximate number of readers. | ||
258 | * @sp: which srcu_struct to count active readers (holding srcu_read_lock). | ||
259 | * | ||
260 | * Note that this is not an atomic primitive, and can therefore suffer | ||
261 | * severe errors when invoked on an active srcu_struct. That said, it | ||
262 | * can be useful as an error check at cleanup time. | ||
263 | */ | ||
264 | static int srcu_readers_active(struct srcu_struct *sp) | ||
265 | { | ||
266 | int cpu; | ||
267 | unsigned long sum = 0; | ||
268 | |||
269 | for_each_possible_cpu(cpu) { | ||
270 | sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[0]); | ||
271 | sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[1]); | ||
272 | } | ||
273 | return sum; | ||
274 | } | ||
275 | |||
276 | /** | ||
277 | * cleanup_srcu_struct - deconstruct a sleep-RCU structure | ||
278 | * @sp: structure to clean up. | ||
279 | * | ||
280 | * Must invoke this after you are finished using a given srcu_struct that | ||
281 | * was initialized via init_srcu_struct(), else you leak memory. | ||
282 | */ | ||
283 | void cleanup_srcu_struct(struct srcu_struct *sp) | ||
284 | { | ||
285 | if (WARN_ON(srcu_readers_active(sp))) | ||
286 | return; /* Leakage unless caller handles error. */ | ||
287 | free_percpu(sp->per_cpu_ref); | ||
288 | sp->per_cpu_ref = NULL; | ||
289 | } | ||
290 | EXPORT_SYMBOL_GPL(cleanup_srcu_struct); | ||
291 | |||
292 | /* | ||
293 | * Counts the new reader in the appropriate per-CPU element of the | ||
294 | * srcu_struct. Must be called from process context. | ||
295 | * Returns an index that must be passed to the matching srcu_read_unlock(). | ||
296 | */ | ||
297 | int __srcu_read_lock(struct srcu_struct *sp) | ||
298 | { | ||
299 | int idx; | ||
300 | |||
301 | idx = ACCESS_ONCE(sp->completed) & 0x1; | ||
302 | preempt_disable(); | ||
303 | ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1; | ||
304 | smp_mb(); /* B */ /* Avoid leaking the critical section. */ | ||
305 | ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1; | ||
306 | preempt_enable(); | ||
307 | return idx; | ||
308 | } | ||
309 | EXPORT_SYMBOL_GPL(__srcu_read_lock); | ||
310 | |||
311 | /* | ||
312 | * Removes the count for the old reader from the appropriate per-CPU | ||
313 | * element of the srcu_struct. Note that this may well be a different | ||
314 | * CPU than that which was incremented by the corresponding srcu_read_lock(). | ||
315 | * Must be called from process context. | ||
316 | */ | ||
317 | void __srcu_read_unlock(struct srcu_struct *sp, int idx) | ||
318 | { | ||
319 | smp_mb(); /* C */ /* Avoid leaking the critical section. */ | ||
320 | this_cpu_dec(sp->per_cpu_ref->c[idx]); | ||
321 | } | ||
322 | EXPORT_SYMBOL_GPL(__srcu_read_unlock); | ||
323 | |||
324 | /* | ||
325 | * We use an adaptive strategy for synchronize_srcu() and especially for | ||
326 | * synchronize_srcu_expedited(). We spin for a fixed time period | ||
327 | * (defined below) to allow SRCU readers to exit their read-side critical | ||
328 | * sections. If there are still some readers after 10 microseconds, | ||
329 | * we repeatedly block for 1-millisecond time periods. This approach | ||
330 | * has done well in testing, so there is no need for a config parameter. | ||
331 | */ | ||
332 | #define SRCU_RETRY_CHECK_DELAY 5 | ||
333 | #define SYNCHRONIZE_SRCU_TRYCOUNT 2 | ||
334 | #define SYNCHRONIZE_SRCU_EXP_TRYCOUNT 12 | ||
335 | |||
336 | /* | ||
337 | * @@@ Wait until all pre-existing readers complete. Such readers | ||
338 | * will have used the index specified by "idx". | ||
339 | * the caller should ensures the ->completed is not changed while checking | ||
340 | * and idx = (->completed & 1) ^ 1 | ||
341 | */ | ||
342 | static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount) | ||
343 | { | ||
344 | for (;;) { | ||
345 | if (srcu_readers_active_idx_check(sp, idx)) | ||
346 | return true; | ||
347 | if (--trycount <= 0) | ||
348 | return false; | ||
349 | udelay(SRCU_RETRY_CHECK_DELAY); | ||
350 | } | ||
351 | } | ||
352 | |||
353 | /* | ||
354 | * Increment the ->completed counter so that future SRCU readers will | ||
355 | * use the other rank of the ->c[] and ->seq[] arrays. This allows | ||
356 | * us to wait for pre-existing readers in a starvation-free manner. | ||
357 | */ | ||
358 | static void srcu_flip(struct srcu_struct *sp) | ||
359 | { | ||
360 | sp->completed++; | ||
361 | } | ||
362 | |||
363 | /* | ||
364 | * Enqueue an SRCU callback on the specified srcu_struct structure, | ||
365 | * initiating grace-period processing if it is not already running. | ||
366 | */ | ||
367 | void call_srcu(struct srcu_struct *sp, struct rcu_head *head, | ||
368 | void (*func)(struct rcu_head *head)) | ||
369 | { | ||
370 | unsigned long flags; | ||
371 | |||
372 | head->next = NULL; | ||
373 | head->func = func; | ||
374 | spin_lock_irqsave(&sp->queue_lock, flags); | ||
375 | rcu_batch_queue(&sp->batch_queue, head); | ||
376 | if (!sp->running) { | ||
377 | sp->running = true; | ||
378 | schedule_delayed_work(&sp->work, 0); | ||
379 | } | ||
380 | spin_unlock_irqrestore(&sp->queue_lock, flags); | ||
381 | } | ||
382 | EXPORT_SYMBOL_GPL(call_srcu); | ||
383 | |||
384 | struct rcu_synchronize { | ||
385 | struct rcu_head head; | ||
386 | struct completion completion; | ||
387 | }; | ||
388 | |||
389 | /* | ||
390 | * Awaken the corresponding synchronize_srcu() instance now that a | ||
391 | * grace period has elapsed. | ||
392 | */ | ||
393 | static void wakeme_after_rcu(struct rcu_head *head) | ||
394 | { | ||
395 | struct rcu_synchronize *rcu; | ||
396 | |||
397 | rcu = container_of(head, struct rcu_synchronize, head); | ||
398 | complete(&rcu->completion); | ||
399 | } | ||
400 | |||
401 | static void srcu_advance_batches(struct srcu_struct *sp, int trycount); | ||
402 | static void srcu_reschedule(struct srcu_struct *sp); | ||
403 | |||
404 | /* | ||
405 | * Helper function for synchronize_srcu() and synchronize_srcu_expedited(). | ||
406 | */ | ||
407 | static void __synchronize_srcu(struct srcu_struct *sp, int trycount) | ||
408 | { | ||
409 | struct rcu_synchronize rcu; | ||
410 | struct rcu_head *head = &rcu.head; | ||
411 | bool done = false; | ||
412 | |||
413 | rcu_lockdep_assert(!lock_is_held(&sp->dep_map) && | ||
414 | !lock_is_held(&rcu_bh_lock_map) && | ||
415 | !lock_is_held(&rcu_lock_map) && | ||
416 | !lock_is_held(&rcu_sched_lock_map), | ||
417 | "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section"); | ||
418 | |||
419 | might_sleep(); | ||
420 | init_completion(&rcu.completion); | ||
421 | |||
422 | head->next = NULL; | ||
423 | head->func = wakeme_after_rcu; | ||
424 | spin_lock_irq(&sp->queue_lock); | ||
425 | if (!sp->running) { | ||
426 | /* steal the processing owner */ | ||
427 | sp->running = true; | ||
428 | rcu_batch_queue(&sp->batch_check0, head); | ||
429 | spin_unlock_irq(&sp->queue_lock); | ||
430 | |||
431 | srcu_advance_batches(sp, trycount); | ||
432 | if (!rcu_batch_empty(&sp->batch_done)) { | ||
433 | BUG_ON(sp->batch_done.head != head); | ||
434 | rcu_batch_dequeue(&sp->batch_done); | ||
435 | done = true; | ||
436 | } | ||
437 | /* give the processing owner to work_struct */ | ||
438 | srcu_reschedule(sp); | ||
439 | } else { | ||
440 | rcu_batch_queue(&sp->batch_queue, head); | ||
441 | spin_unlock_irq(&sp->queue_lock); | ||
442 | } | ||
443 | |||
444 | if (!done) | ||
445 | wait_for_completion(&rcu.completion); | ||
446 | } | ||
447 | |||
448 | /** | ||
449 | * synchronize_srcu - wait for prior SRCU read-side critical-section completion | ||
450 | * @sp: srcu_struct with which to synchronize. | ||
451 | * | ||
452 | * Wait for the count to drain to zero of both indexes. To avoid the | ||
453 | * possible starvation of synchronize_srcu(), it waits for the count of | ||
454 | * the index=((->completed & 1) ^ 1) to drain to zero at first, | ||
455 | * and then flip the completed and wait for the count of the other index. | ||
456 | * | ||
457 | * Can block; must be called from process context. | ||
458 | * | ||
459 | * Note that it is illegal to call synchronize_srcu() from the corresponding | ||
460 | * SRCU read-side critical section; doing so will result in deadlock. | ||
461 | * However, it is perfectly legal to call synchronize_srcu() on one | ||
462 | * srcu_struct from some other srcu_struct's read-side critical section. | ||
463 | */ | ||
464 | void synchronize_srcu(struct srcu_struct *sp) | ||
465 | { | ||
466 | __synchronize_srcu(sp, rcu_expedited | ||
467 | ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT | ||
468 | : SYNCHRONIZE_SRCU_TRYCOUNT); | ||
469 | } | ||
470 | EXPORT_SYMBOL_GPL(synchronize_srcu); | ||
471 | |||
472 | /** | ||
473 | * synchronize_srcu_expedited - Brute-force SRCU grace period | ||
474 | * @sp: srcu_struct with which to synchronize. | ||
475 | * | ||
476 | * Wait for an SRCU grace period to elapse, but be more aggressive about | ||
477 | * spinning rather than blocking when waiting. | ||
478 | * | ||
479 | * Note that it is also illegal to call synchronize_srcu_expedited() | ||
480 | * from the corresponding SRCU read-side critical section; | ||
481 | * doing so will result in deadlock. However, it is perfectly legal | ||
482 | * to call synchronize_srcu_expedited() on one srcu_struct from some | ||
483 | * 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 | schedule_delayed_work(&sp->work, SRCU_INTERVAL); | ||
635 | } | ||
636 | |||
637 | /* | ||
638 | * This is the work-queue function that handles SRCU grace periods. | ||
639 | */ | ||
640 | 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 | EXPORT_SYMBOL_GPL(process_srcu); | ||