aboutsummaryrefslogtreecommitdiffstats
path: root/kernel/srcu.c
blob: 2b859828cdc327d811627fbf877318de8dbc5595 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
/*
 * Sleepable Read-Copy Update mechanism for mutual exclusion.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (C) IBM Corporation, 2006
 * Copyright (C) Fujitsu, 2012
 *
 * Author: Paul McKenney <paulmck@us.ibm.com>
 *	   Lai Jiangshan <laijs@cn.fujitsu.com>
 *
 * For detailed explanation of Read-Copy Update mechanism see -
 * 		Documentation/RCU/ *.txt
 *
 */

#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/percpu.h>
#include <linux/preempt.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/delay.h>
#include <linux/srcu.h>

#include <trace/events/rcu.h>

#include "rcu.h"

/*
 * Initialize an rcu_batch structure to empty.
 */
static inline void rcu_batch_init(struct rcu_batch *b)
{
	b->head = NULL;
	b->tail = &b->head;
}

/*
 * Enqueue a callback onto the tail of the specified rcu_batch structure.
 */
static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
{
	*b->tail = head;
	b->tail = &head->next;
}

/*
 * Is the specified rcu_batch structure empty?
 */
static inline bool rcu_batch_empty(struct rcu_batch *b)
{
	return b->tail == &b->head;
}

/*
 * Remove the callback at the head of the specified rcu_batch structure
 * and return a pointer to it, or return NULL if the structure is empty.
 */
static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
{
	struct rcu_head *head;

	if (rcu_batch_empty(b))
		return NULL;

	head = b->head;
	b->head = head->next;
	if (b->tail == &head->next)
		rcu_batch_init(b);

	return head;
}

/*
 * Move all callbacks from the rcu_batch structure specified by "from" to
 * the structure specified by "to".
 */
static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
{
	if (!rcu_batch_empty(from)) {
		*to->tail = from->head;
		to->tail = from->tail;
		rcu_batch_init(from);
	}
}

static int init_srcu_struct_fields(struct srcu_struct *sp)
{
	sp->completed = 0;
	spin_lock_init(&sp->queue_lock);
	sp->running = false;
	rcu_batch_init(&sp->batch_queue);
	rcu_batch_init(&sp->batch_check0);
	rcu_batch_init(&sp->batch_check1);
	rcu_batch_init(&sp->batch_done);
	INIT_DELAYED_WORK(&sp->work, process_srcu);
	sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
	return sp->per_cpu_ref ? 0 : -ENOMEM;
}

#ifdef CONFIG_DEBUG_LOCK_ALLOC

int __init_srcu_struct(struct srcu_struct *sp, const char *name,
		       struct lock_class_key *key)
{
	/* Don't re-initialize a lock while it is held. */
	debug_check_no_locks_freed((void *)sp, sizeof(*sp));
	lockdep_init_map(&sp->dep_map, name, key, 0);
	return init_srcu_struct_fields(sp);
}
EXPORT_SYMBOL_GPL(__init_srcu_struct);

#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

/**
 * init_srcu_struct - initialize a sleep-RCU structure
 * @sp: structure to initialize.
 *
 * Must invoke this on a given srcu_struct before passing that srcu_struct
 * to any other function.  Each srcu_struct represents a separate domain
 * of SRCU protection.
 */
int init_srcu_struct(struct srcu_struct *sp)
{
	return init_srcu_struct_fields(sp);
}
EXPORT_SYMBOL_GPL(init_srcu_struct);

#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

/*
 * Returns approximate total of the readers' ->seq[] values for the
 * rank of per-CPU counters specified by idx.
 */
static unsigned long srcu_readers_seq_idx(struct srcu_struct *sp, int idx)
{
	int cpu;
	unsigned long sum = 0;
	unsigned long t;

	for_each_possible_cpu(cpu) {
		t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->seq[idx]);
		sum += t;
	}
	return sum;
}

/*
 * Returns approximate number of readers active on the specified rank
 * of the per-CPU ->c[] counters.
 */
static unsigned long srcu_readers_active_idx(struct srcu_struct *sp, int idx)
{
	int cpu;
	unsigned long sum = 0;
	unsigned long t;

	for_each_possible_cpu(cpu) {
		t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx]);
		sum += t;
	}
	return sum;
}

/*
 * Return true if the number of pre-existing readers is determined to
 * be stably zero.  An example unstable zero can occur if the call
 * to srcu_readers_active_idx() misses an __srcu_read_lock() increment,
 * but due to task migration, sees the corresponding __srcu_read_unlock()
 * decrement.  This can happen because srcu_readers_active_idx() takes
 * time to sum the array, and might in fact be interrupted or preempted
 * partway through the summation.
 */
static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
{
	unsigned long seq;

	seq = srcu_readers_seq_idx(sp, idx);

	/*
	 * The following smp_mb() A pairs with the smp_mb() B located in
	 * __srcu_read_lock().  This pairing ensures that if an
	 * __srcu_read_lock() increments its counter after the summation
	 * in srcu_readers_active_idx(), then the corresponding SRCU read-side
	 * critical section will see any changes made prior to the start
	 * of the current SRCU grace period.
	 *
	 * Also, if the above call to srcu_readers_seq_idx() saw the
	 * increment of ->seq[], then the call to srcu_readers_active_idx()
	 * must see the increment of ->c[].
	 */
	smp_mb(); /* A */

	/*
	 * Note that srcu_readers_active_idx() can incorrectly return
	 * zero even though there is a pre-existing reader throughout.
	 * To see this, suppose that task A is in a very long SRCU
	 * read-side critical section that started on CPU 0, and that
	 * no other reader exists, so that the sum of the counters
	 * is equal to one.  Then suppose that task B starts executing
	 * srcu_readers_active_idx(), summing up to CPU 1, and then that
	 * task C starts reading on CPU 0, so that its increment is not
	 * summed, but finishes reading on CPU 2, so that its decrement
	 * -is- summed.  Then when task B completes its sum, it will
	 * incorrectly get zero, despite the fact that task A has been
	 * in its SRCU read-side critical section the whole time.
	 *
	 * We therefore do a validation step should srcu_readers_active_idx()
	 * return zero.
	 */
	if (srcu_readers_active_idx(sp, idx) != 0)
		return false;

	/*
	 * The remainder of this function is the validation step.
	 * The following smp_mb() D pairs with the smp_mb() C in
	 * __srcu_read_unlock().  If the __srcu_read_unlock() was seen
	 * by srcu_readers_active_idx() above, then any destructive
	 * operation performed after the grace period will happen after
	 * the corresponding SRCU read-side critical section.
	 *
	 * Note that there can be at most NR_CPUS worth of readers using
	 * the old index, which is not enough to overflow even a 32-bit
	 * integer.  (Yes, this does mean that systems having more than
	 * a billion or so CPUs need to be 64-bit systems.)  Therefore,
	 * the sum of the ->seq[] counters cannot possibly overflow.
	 * Therefore, the only way that the return values of the two
	 * calls to srcu_readers_seq_idx() can be equal is if there were
	 * no increments of the corresponding rank of ->seq[] counts
	 * in the interim.  But the missed-increment scenario laid out
	 * above includes an increment of the ->seq[] counter by
	 * the corresponding __srcu_read_lock().  Therefore, if this
	 * scenario occurs, the return values from the two calls to
	 * srcu_readers_seq_idx() will differ, and thus the validation
	 * step below suffices.
	 */
	smp_mb(); /* D */

	return srcu_readers_seq_idx(sp, idx) == seq;
}

/**
 * srcu_readers_active - returns approximate number of readers.
 * @sp: which srcu_struct to count active readers (holding srcu_read_lock).
 *
 * Note that this is not an atomic primitive, and can therefore suffer
 * severe errors when invoked on an active srcu_struct.  That said, it
 * can be useful as an error check at cleanup time.
 */
static int srcu_readers_active(struct srcu_struct *sp)
{
	int cpu;
	unsigned long sum = 0;

	for_each_possible_cpu(cpu) {
		sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[0]);
		sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[1]);
	}
	return sum;
}

/**
 * cleanup_srcu_struct - deconstruct a sleep-RCU structure
 * @sp: structure to clean up.
 *
 * Must invoke this after you are finished using a given srcu_struct that
 * was initialized via init_srcu_struct(), else you leak memory.
 */
void cleanup_srcu_struct(struct srcu_struct *sp)
{
	int sum;

	sum = srcu_readers_active(sp);
	WARN_ON(sum);  /* Leakage unless caller handles error. */
	if (sum != 0)
		return;
	free_percpu(sp->per_cpu_ref);
	sp->per_cpu_ref = NULL;
}
EXPORT_SYMBOL_GPL(cleanup_srcu_struct);

/*
 * Counts the new reader in the appropriate per-CPU element of the
 * srcu_struct.  Must be called from process context.
 * Returns an index that must be passed to the matching srcu_read_unlock().
 */
int __srcu_read_lock(struct srcu_struct *sp)
{
	int idx;

	preempt_disable();
	idx = rcu_dereference_index_check(sp->completed,
					  rcu_read_lock_sched_held()) & 0x1;
	ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1;
	smp_mb(); /* B */  /* Avoid leaking the critical section. */
	ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1;
	preempt_enable();
	return idx;
}
EXPORT_SYMBOL_GPL(__srcu_read_lock);

/*
 * Removes the count for the old reader from the appropriate per-CPU
 * element of the srcu_struct.  Note that this may well be a different
 * CPU than that which was incremented by the corresponding srcu_read_lock().
 * Must be called from process context.
 */
void __srcu_read_unlock(struct srcu_struct *sp, int idx)
{
	preempt_disable();
	smp_mb(); /* C */  /* Avoid leaking the critical section. */
	ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) -= 1;
	preempt_enable();
}
EXPORT_SYMBOL_GPL(__srcu_read_unlock);

/*
 * We use an adaptive strategy for synchronize_srcu() and especially for
 * synchronize_srcu_expedited().  We spin for a fixed time period
 * (defined below) to allow SRCU readers to exit their read-side critical
 * sections.  If there are still some readers after 10 microseconds,
 * we repeatedly block for 1-millisecond time periods.  This approach
 * has done well in testing, so there is no need for a config parameter.
 */
#define SRCU_RETRY_CHECK_DELAY		5
#define SYNCHRONIZE_SRCU_TRYCOUNT	2
#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT	12

/*
 * @@@ Wait until all pre-existing readers complete.  Such readers
 * will have used the index specified by "idx".
 * the caller should ensures the ->completed is not changed while checking
 * and idx = (->completed & 1) ^ 1
 */
static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
{
	for (;;) {
		if (srcu_readers_active_idx_check(sp, idx))
			return true;
		if (--trycount <= 0)
			return false;
		udelay(SRCU_RETRY_CHECK_DELAY);
	}
}

/*
 * Increment the ->completed counter so that future SRCU readers will
 * use the other rank of the ->c[] and ->seq[] arrays.  This allows
 * us to wait for pre-existing readers in a starvation-free manner.
 */
static void srcu_flip(struct srcu_struct *sp)
{
	sp->completed++;
}

/*
 * Enqueue an SRCU callback on the specified srcu_struct structure,
 * initiating grace-period processing if it is not already running.
 */
void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
		void (*func)(struct rcu_head *head))
{
	unsigned long flags;

	head->next = NULL;
	head->func = func;
	spin_lock_irqsave(&sp->queue_lock, flags);
	rcu_batch_queue(&sp->batch_queue, head);
	if (!sp->running) {
		sp->running = true;
		schedule_delayed_work(&sp->work, 0);
	}
	spin_unlock_irqrestore(&sp->queue_lock, flags);
}
EXPORT_SYMBOL_GPL(call_srcu);

struct rcu_synchronize {
	struct rcu_head head;
	struct completion completion;
};

/*
 * Awaken the corresponding synchronize_srcu() instance now that a
 * grace period has elapsed.
 */
static void wakeme_after_rcu(struct rcu_head *head)
{
	struct rcu_synchronize *rcu;

	rcu = container_of(head, struct rcu_synchronize, head);
	complete(&rcu->completion);
}

static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
static void srcu_reschedule(struct srcu_struct *sp);

/*
 * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
 */
static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
{
	struct rcu_synchronize rcu;
	struct rcu_head *head = &rcu.head;
	bool done = false;

	rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
			   !lock_is_held(&rcu_bh_lock_map) &&
			   !lock_is_held(&rcu_lock_map) &&
			   !lock_is_held(&rcu_sched_lock_map),
			   "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");

	init_completion(&rcu.completion);

	head->next = NULL;
	head->func = wakeme_after_rcu;
	spin_lock_irq(&sp->queue_lock);
	if (!sp->running) {
		/* steal the processing owner */
		sp->running = true;
		rcu_batch_queue(&sp->batch_check0, head);
		spin_unlock_irq(&sp->queue_lock);

		srcu_advance_batches(sp, trycount);
		if (!rcu_batch_empty(&sp->batch_done)) {
			BUG_ON(sp->batch_done.head != head);
			rcu_batch_dequeue(&sp->batch_done);
			done = true;
		}
		/* give the processing owner to work_struct */
		srcu_reschedule(sp);
	} else {
		rcu_batch_queue(&sp->batch_queue, head);
		spin_unlock_irq(&sp->queue_lock);
	}

	if (!done)
		wait_for_completion(&rcu.completion);
}

/**
 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
 * @sp: srcu_struct with which to synchronize.
 *
 * Flip the completed counter, and wait for the old count to drain to zero.
 * As with classic RCU, the updater must use some separate means of
 * synchronizing concurrent updates.  Can block; must be called from
 * process context.
 *
 * Note that it is illegal to call synchronize_srcu() from the corresponding
 * SRCU read-side critical section; doing so will result in deadlock.
 * However, it is perfectly legal to call synchronize_srcu() on one
 * srcu_struct from some other srcu_struct's read-side critical section.
 */
void synchronize_srcu(struct srcu_struct *sp)
{
	__synchronize_srcu(sp, rcu_expedited
			   ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
			   : SYNCHRONIZE_SRCU_TRYCOUNT);
}
EXPORT_SYMBOL_GPL(synchronize_srcu);

/**
 * synchronize_srcu_expedited - Brute-force SRCU grace period
 * @sp: srcu_struct with which to synchronize.
 *
 * Wait for an SRCU grace period to elapse, but be more aggressive about
 * spinning rather than blocking when waiting.
 *
 * Note that it is illegal to call this function while holding any lock
 * that is acquired by a CPU-hotplug notifier.  It is also illegal to call
 * synchronize_srcu_expedited() from the corresponding SRCU read-side
 * critical section; doing so will result in deadlock.  However, it is
 * perfectly legal to call synchronize_srcu_expedited() on one srcu_struct
 * from some other srcu_struct's read-side critical section, as long as
 * the resulting graph of srcu_structs is acyclic.
 */
void synchronize_srcu_expedited(struct srcu_struct *sp)
{
	__synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
}
EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);

/**
 * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
 */
void srcu_barrier(struct srcu_struct *sp)
{
	synchronize_srcu(sp);
}
EXPORT_SYMBOL_GPL(srcu_barrier);

/**
 * srcu_batches_completed - return batches completed.
 * @sp: srcu_struct on which to report batch completion.
 *
 * Report the number of batches, correlated with, but not necessarily
 * precisely the same as, the number of grace periods that have elapsed.
 */
long srcu_batches_completed(struct srcu_struct *sp)
{
	return sp->completed;
}
EXPORT_SYMBOL_GPL(srcu_batches_completed);

#define SRCU_CALLBACK_BATCH	10
#define SRCU_INTERVAL		1

/*
 * Move any new SRCU callbacks to the first stage of the SRCU grace
 * period pipeline.
 */
static void srcu_collect_new(struct srcu_struct *sp)
{
	if (!rcu_batch_empty(&sp->batch_queue)) {
		spin_lock_irq(&sp->queue_lock);
		rcu_batch_move(&sp->batch_check0, &sp->batch_queue);
		spin_unlock_irq(&sp->queue_lock);
	}
}

/*
 * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
 * ->batch_check1 and then to ->batch_done as readers drain.
 */
static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
{
	int idx = 1 ^ (sp->completed & 1);

	/*
	 * Because readers might be delayed for an extended period after
	 * fetching ->completed for their index, at any point in time there
	 * might well be readers using both idx=0 and idx=1.  We therefore
	 * need to wait for readers to clear from both index values before
	 * invoking a callback.
	 */

	if (rcu_batch_empty(&sp->batch_check0) &&
	    rcu_batch_empty(&sp->batch_check1))
		return; /* no callbacks need to be advanced */

	if (!try_check_zero(sp, idx, trycount))
		return; /* failed to advance, will try after SRCU_INTERVAL */

	/*
	 * The callbacks in ->batch_check1 have already done with their
	 * first zero check and flip back when they were enqueued on
	 * ->batch_check0 in a previous invocation of srcu_advance_batches().
	 * (Presumably try_check_zero() returned false during that
	 * invocation, leaving the callbacks stranded on ->batch_check1.)
	 * They are therefore ready to invoke, so move them to ->batch_done.
	 */
	rcu_batch_move(&sp->batch_done, &sp->batch_check1);

	if (rcu_batch_empty(&sp->batch_check0))
		return; /* no callbacks need to be advanced */
	srcu_flip(sp);

	/*
	 * The callbacks in ->batch_check0 just finished their
	 * first check zero and flip, so move them to ->batch_check1
	 * for future checking on the other idx.
	 */
	rcu_batch_move(&sp->batch_check1, &sp->batch_check0);

	/*
	 * SRCU read-side critical sections are normally short, so check
	 * at least twice in quick succession after a flip.
	 */
	trycount = trycount < 2 ? 2 : trycount;
	if (!try_check_zero(sp, idx^1, trycount))
		return; /* failed to advance, will try after SRCU_INTERVAL */

	/*
	 * The callbacks in ->batch_check1 have now waited for all
	 * pre-existing readers using both idx values.  They are therefore
	 * ready to invoke, so move them to ->batch_done.
	 */
	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
}

/*
 * Invoke a limited number of SRCU callbacks that have passed through
 * their grace period.  If there are more to do, SRCU will reschedule
 * the workqueue.
 */
static void srcu_invoke_callbacks(struct srcu_struct *sp)
{
	int i;
	struct rcu_head *head;

	for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
		head = rcu_batch_dequeue(&sp->batch_done);
		if (!head)
			break;
		local_bh_disable();
		head->func(head);
		local_bh_enable();
	}
}

/*
 * Finished one round of SRCU grace period.  Start another if there are
 * more SRCU callbacks queued, otherwise put SRCU into not-running state.
 */
static void srcu_reschedule(struct srcu_struct *sp)
{
	bool pending = true;

	if (rcu_batch_empty(&sp->batch_done) &&
	    rcu_batch_empty(&sp->batch_check1) &&
	    rcu_batch_empty(&sp->batch_check0) &&
	    rcu_batch_empty(&sp->batch_queue)) {
		spin_lock_irq(&sp->queue_lock);
		if (rcu_batch_empty(&sp->batch_done) &&
		    rcu_batch_empty(&sp->batch_check1) &&
		    rcu_batch_empty(&sp->batch_check0) &&
		    rcu_batch_empty(&sp->batch_queue)) {
			sp->running = false;
			pending = false;
		}
		spin_unlock_irq(&sp->queue_lock);
	}

	if (pending)
		schedule_delayed_work(&sp->work, SRCU_INTERVAL);
}

/*
 * This is the work-queue function that handles SRCU grace periods.
 */
void process_srcu(struct work_struct *work)
{
	struct srcu_struct *sp;

	sp = container_of(work, struct srcu_struct, work.work);

	srcu_collect_new(sp);
	srcu_advance_batches(sp, 1);
	srcu_invoke_callbacks(sp);
	srcu_reschedule(sp);
}
EXPORT_SYMBOL_GPL(process_srcu);