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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 : : * 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 : 33 : b->head = NULL;
49 : 33 : 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 : 11 : *b->tail = head;
58 : 11 : 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 : 143 : 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 [ # # ][ + - ]: 11 : if (rcu_batch_empty(b))
78 : : return NULL;
79 : :
80 : 0 : head = b->head;
81 : 11 : b->head = head->next;
82 [ # # ][ + - ]: 11 : 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 [ - + ][ + - ]: 33 : if (!rcu_batch_empty(from)) {
[ + - # # ]
95 : 22 : *to->tail = from->head;
96 : 22 : to->tail = from->tail;
97 : : rcu_batch_init(from);
98 : : }
99 : : }
100 : :
101 : 0 : static int init_srcu_struct_fields(struct srcu_struct *sp)
102 : : {
103 : 0 : sp->completed = 0;
104 : 0 : spin_lock_init(&sp->queue_lock);
105 : 0 : 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 : 0 : INIT_DELAYED_WORK(&sp->work, process_srcu);
111 : 0 : sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
112 [ # # ]: 0 : 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 : 0 : int init_srcu_struct(struct srcu_struct *sp)
138 : : {
139 : 0 : 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 : 44 : 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 [ + + ]: 264 : for_each_possible_cpu(cpu) {
156 : 220 : t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->seq[idx]);
157 : 220 : sum += t;
158 : : }
159 : 44 : 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 : 22 : 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 [ + + ]: 132 : for_each_possible_cpu(cpu) {
173 : 110 : t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx]);
174 : 110 : sum += t;
175 : : }
176 : 22 : 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 : 0 : static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
189 : : {
190 : : unsigned long seq;
191 : :
192 : 22 : 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 : 22 : 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 [ + - ]: 22 : 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 : 22 : smp_mb(); /* D */
252 : :
253 : 22 : 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 : 0 : static int srcu_readers_active(struct srcu_struct *sp)
265 : : {
266 : : int cpu;
267 : : unsigned long sum = 0;
268 : :
269 [ # # ]: 0 : for_each_possible_cpu(cpu) {
270 : 0 : sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[0]);
271 : 0 : sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[1]);
272 : : }
273 : 0 : 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 : 0 : void cleanup_srcu_struct(struct srcu_struct *sp)
284 : : {
285 [ # # ][ # # ]: 0 : if (WARN_ON(srcu_readers_active(sp)))
286 : 0 : return; /* Leakage unless caller handles error. */
287 : 0 : free_percpu(sp->per_cpu_ref);
288 : 0 : 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 : 0 : int __srcu_read_lock(struct srcu_struct *sp)
298 : : {
299 : : int idx;
300 : :
301 : 5637434 : idx = ACCESS_ONCE(sp->completed) & 0x1;
302 : 5637434 : preempt_disable();
303 : 11274420 : ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1;
304 : 5637210 : smp_mb(); /* B */ /* Avoid leaking the critical section. */
305 : 11274378 : ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1;
306 : 5637189 : preempt_enable();
307 : 5637213 : 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 : 0 : void __srcu_read_unlock(struct srcu_struct *sp, int idx)
318 : : {
319 : 5637157 : smp_mb(); /* C */ /* Avoid leaking the critical section. */
320 : 11275394 : this_cpu_dec(sp->per_cpu_ref->c[idx]);
321 : 5637770 : }
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 : 22 : static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
343 : : {
344 : : for (;;) {
345 [ - + ]: 22 : if (srcu_readers_active_idx_check(sp, idx))
346 : : return true;
347 [ # # ]: 0 : if (--trycount <= 0)
348 : : return false;
349 : 0 : udelay(SRCU_RETRY_CHECK_DELAY);
350 : 0 : }
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 : 11 : 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 : 0 : 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 : 0 : head->next = NULL;
373 : 0 : head->func = func;
374 : 0 : spin_lock_irqsave(&sp->queue_lock, flags);
375 : : rcu_batch_queue(&sp->batch_queue, head);
376 [ # # ]: 0 : if (!sp->running) {
377 : 0 : sp->running = true;
378 : 0 : schedule_delayed_work(&sp->work, 0);
379 : : }
380 : : spin_unlock_irqrestore(&sp->queue_lock, flags);
381 : 0 : }
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 : 0 : 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 : 0 : complete(&rcu->completion);
399 : 0 : }
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 : 0 : 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 : 11 : head->next = NULL;
423 : 11 : head->func = wakeme_after_rcu;
424 : : spin_lock_irq(&sp->queue_lock);
425 [ + - ]: 11 : if (!sp->running) {
426 : : /* steal the processing owner */
427 : 11 : sp->running = true;
428 : : rcu_batch_queue(&sp->batch_check0, head);
429 : : spin_unlock_irq(&sp->queue_lock);
430 : :
431 : 11 : srcu_advance_batches(sp, trycount);
432 [ + - ]: 11 : if (!rcu_batch_empty(&sp->batch_done)) {
433 [ - + ]: 11 : 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 : 11 : srcu_reschedule(sp);
439 : : } else {
440 : : rcu_batch_queue(&sp->batch_queue, head);
441 : : spin_unlock_irq(&sp->queue_lock);
442 : : }
443 : :
444 [ - + ]: 11 : if (!done)
445 : 0 : wait_for_completion(&rcu.completion);
446 : 11 : }
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 : 0 : void synchronize_srcu(struct srcu_struct *sp)
465 : : {
466 [ # # ][ + - ]: 11 : __synchronize_srcu(sp, rcu_expedited
467 : 11 : ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
468 : : : SYNCHRONIZE_SRCU_TRYCOUNT);
469 : 11 : }
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 : 0 : void synchronize_srcu_expedited(struct srcu_struct *sp)
487 : : {
488 : 0 : __synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
489 : 0 : }
490 : : EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
491 : :
492 : : /**
493 : : * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
494 : : */
495 : 0 : void srcu_barrier(struct srcu_struct *sp)
496 : : {
497 : : synchronize_srcu(sp);
498 : 0 : }
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 : 0 : long srcu_batches_completed(struct srcu_struct *sp)
509 : : {
510 : 0 : 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 : 0 : static void srcu_collect_new(struct srcu_struct *sp)
522 : : {
523 [ # # ]: 0 : 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 : 0 : }
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 : 0 : static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
535 : : {
536 : 11 : 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 [ - + ][ # # ]: 11 : if (rcu_batch_empty(&sp->batch_check0) &&
547 : : rcu_batch_empty(&sp->batch_check1))
548 : : return; /* no callbacks need to be advanced */
549 : :
550 [ + - ]: 11 : 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 [ + - ]: 11 : 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 : 11 : trycount = trycount < 2 ? 2 : trycount;
579 [ + - ]: 11 : 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 : 0 : static void srcu_invoke_callbacks(struct srcu_struct *sp)
596 : : {
597 : : int i;
598 : : struct rcu_head *head;
599 : :
600 [ # # ]: 0 : for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
601 : : head = rcu_batch_dequeue(&sp->batch_done);
602 [ # # ]: 0 : if (!head)
603 : : break;
604 : 0 : local_bh_disable();
605 : 0 : head->func(head);
606 : 0 : local_bh_enable();
607 : : }
608 : 0 : }
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 : 0 : static void srcu_reschedule(struct srcu_struct *sp)
615 : : {
616 : : bool pending = true;
617 : :
618 [ + - ][ + - ]: 11 : if (rcu_batch_empty(&sp->batch_done) &&
619 [ + - ]: 11 : rcu_batch_empty(&sp->batch_check1) &&
620 [ + - ]: 11 : rcu_batch_empty(&sp->batch_check0) &&
621 : : rcu_batch_empty(&sp->batch_queue)) {
622 : : spin_lock_irq(&sp->queue_lock);
623 [ + - ][ + - ]: 11 : if (rcu_batch_empty(&sp->batch_done) &&
624 [ + - ]: 11 : rcu_batch_empty(&sp->batch_check1) &&
625 [ + - ]: 11 : rcu_batch_empty(&sp->batch_check0) &&
626 : : rcu_batch_empty(&sp->batch_queue)) {
627 : 11 : sp->running = false;
628 : : pending = false;
629 : : }
630 : : spin_unlock_irq(&sp->queue_lock);
631 : : }
632 : :
633 [ - + ]: 11 : if (pending)
634 : 0 : schedule_delayed_work(&sp->work, SRCU_INTERVAL);
635 : 11 : }
636 : :
637 : : /*
638 : : * This is the work-queue function that handles SRCU grace periods.
639 : : */
640 : 0 : void process_srcu(struct work_struct *work)
641 : : {
642 : : struct srcu_struct *sp;
643 : :
644 : 0 : sp = container_of(work, struct srcu_struct, work.work);
645 : :
646 : 0 : srcu_collect_new(sp);
647 : 0 : srcu_advance_batches(sp, 1);
648 : 0 : srcu_invoke_callbacks(sp);
649 : 0 : srcu_reschedule(sp);
650 : 0 : }
651 : : EXPORT_SYMBOL_GPL(process_srcu);
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