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1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Sleepable Read-Copy Update mechanism for mutual exclusion.
4 *
5 * Copyright (C) IBM Corporation, 2006
6 * Copyright (C) Fujitsu, 2012
7 *
8 * Author: Paul McKenney <paulmck@linux.ibm.com>
9 * Lai Jiangshan <laijs@cn.fujitsu.com>
10 *
11 * For detailed explanation of Read-Copy Update mechanism see -
12 * Documentation/RCU/ *.txt
13 *
14 */
15
16#define pr_fmt(fmt) "rcu: " fmt
17
18#include <linux/export.h>
19#include <linux/mutex.h>
20#include <linux/percpu.h>
21#include <linux/preempt.h>
22#include <linux/rcupdate_wait.h>
23#include <linux/sched.h>
24#include <linux/smp.h>
25#include <linux/delay.h>
26#include <linux/module.h>
27#include <linux/srcu.h>
28
29#include "rcu.h"
30#include "rcu_segcblist.h"
31
32/* Holdoff in nanoseconds for auto-expediting. */
33#define DEFAULT_SRCU_EXP_HOLDOFF (25 * 1000)
34static ulong exp_holdoff = DEFAULT_SRCU_EXP_HOLDOFF;
35module_param(exp_holdoff, ulong, 0444);
36
37/* Overflow-check frequency. N bits roughly says every 2**N grace periods. */
38static ulong counter_wrap_check = (ULONG_MAX >> 2);
39module_param(counter_wrap_check, ulong, 0444);
40
41/* Early-boot callback-management, so early that no lock is required! */
42static LIST_HEAD(srcu_boot_list);
43static bool __read_mostly srcu_init_done;
44
45static void srcu_invoke_callbacks(struct work_struct *work);
46static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay);
47static void process_srcu(struct work_struct *work);
48static void srcu_delay_timer(struct timer_list *t);
49
50/* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */
51#define spin_lock_rcu_node(p) \
52do { \
53 spin_lock(&ACCESS_PRIVATE(p, lock)); \
54 smp_mb__after_unlock_lock(); \
55} while (0)
56
57#define spin_unlock_rcu_node(p) spin_unlock(&ACCESS_PRIVATE(p, lock))
58
59#define spin_lock_irq_rcu_node(p) \
60do { \
61 spin_lock_irq(&ACCESS_PRIVATE(p, lock)); \
62 smp_mb__after_unlock_lock(); \
63} while (0)
64
65#define spin_unlock_irq_rcu_node(p) \
66 spin_unlock_irq(&ACCESS_PRIVATE(p, lock))
67
68#define spin_lock_irqsave_rcu_node(p, flags) \
69do { \
70 spin_lock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \
71 smp_mb__after_unlock_lock(); \
72} while (0)
73
74#define spin_unlock_irqrestore_rcu_node(p, flags) \
75 spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) \
76
77/*
78 * Initialize SRCU combining tree. Note that statically allocated
79 * srcu_struct structures might already have srcu_read_lock() and
80 * srcu_read_unlock() running against them. So if the is_static parameter
81 * is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[].
82 */
83static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static)
84{
85 int cpu;
86 int i;
87 int level = 0;
88 int levelspread[RCU_NUM_LVLS];
89 struct srcu_data *sdp;
90 struct srcu_node *snp;
91 struct srcu_node *snp_first;
92
93 /* Work out the overall tree geometry. */
94 ssp->level[0] = &ssp->node[0];
95 for (i = 1; i < rcu_num_lvls; i++)
96 ssp->level[i] = ssp->level[i - 1] + num_rcu_lvl[i - 1];
97 rcu_init_levelspread(levelspread, num_rcu_lvl);
98
99 /* Each pass through this loop initializes one srcu_node structure. */
100 srcu_for_each_node_breadth_first(ssp, snp) {
101 spin_lock_init(&ACCESS_PRIVATE(snp, lock));
102 WARN_ON_ONCE(ARRAY_SIZE(snp->srcu_have_cbs) !=
103 ARRAY_SIZE(snp->srcu_data_have_cbs));
104 for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++) {
105 snp->srcu_have_cbs[i] = 0;
106 snp->srcu_data_have_cbs[i] = 0;
107 }
108 snp->srcu_gp_seq_needed_exp = 0;
109 snp->grplo = -1;
110 snp->grphi = -1;
111 if (snp == &ssp->node[0]) {
112 /* Root node, special case. */
113 snp->srcu_parent = NULL;
114 continue;
115 }
116
117 /* Non-root node. */
118 if (snp == ssp->level[level + 1])
119 level++;
120 snp->srcu_parent = ssp->level[level - 1] +
121 (snp - ssp->level[level]) /
122 levelspread[level - 1];
123 }
124
125 /*
126 * Initialize the per-CPU srcu_data array, which feeds into the
127 * leaves of the srcu_node tree.
128 */
129 WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) !=
130 ARRAY_SIZE(sdp->srcu_unlock_count));
131 level = rcu_num_lvls - 1;
132 snp_first = ssp->level[level];
133 for_each_possible_cpu(cpu) {
134 sdp = per_cpu_ptr(ssp->sda, cpu);
135 spin_lock_init(&ACCESS_PRIVATE(sdp, lock));
136 rcu_segcblist_init(&sdp->srcu_cblist);
137 sdp->srcu_cblist_invoking = false;
138 sdp->srcu_gp_seq_needed = ssp->srcu_gp_seq;
139 sdp->srcu_gp_seq_needed_exp = ssp->srcu_gp_seq;
140 sdp->mynode = &snp_first[cpu / levelspread[level]];
141 for (snp = sdp->mynode; snp != NULL; snp = snp->srcu_parent) {
142 if (snp->grplo < 0)
143 snp->grplo = cpu;
144 snp->grphi = cpu;
145 }
146 sdp->cpu = cpu;
147 INIT_WORK(&sdp->work, srcu_invoke_callbacks);
148 timer_setup(&sdp->delay_work, srcu_delay_timer, 0);
149 sdp->ssp = ssp;
150 sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
151 if (is_static)
152 continue;
153
154 /* Dynamically allocated, better be no srcu_read_locks()! */
155 for (i = 0; i < ARRAY_SIZE(sdp->srcu_lock_count); i++) {
156 sdp->srcu_lock_count[i] = 0;
157 sdp->srcu_unlock_count[i] = 0;
158 }
159 }
160}
161
162/*
163 * Initialize non-compile-time initialized fields, including the
164 * associated srcu_node and srcu_data structures. The is_static
165 * parameter is passed through to init_srcu_struct_nodes(), and
166 * also tells us that ->sda has already been wired up to srcu_data.
167 */
168static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
169{
170 mutex_init(&ssp->srcu_cb_mutex);
171 mutex_init(&ssp->srcu_gp_mutex);
172 ssp->srcu_idx = 0;
173 ssp->srcu_gp_seq = 0;
174 ssp->srcu_barrier_seq = 0;
175 mutex_init(&ssp->srcu_barrier_mutex);
176 atomic_set(&ssp->srcu_barrier_cpu_cnt, 0);
177 INIT_DELAYED_WORK(&ssp->work, process_srcu);
178 if (!is_static)
179 ssp->sda = alloc_percpu(struct srcu_data);
180 init_srcu_struct_nodes(ssp, is_static);
181 ssp->srcu_gp_seq_needed_exp = 0;
182 ssp->srcu_last_gp_end = ktime_get_mono_fast_ns();
183 smp_store_release(&ssp->srcu_gp_seq_needed, 0); /* Init done. */
184 return ssp->sda ? 0 : -ENOMEM;
185}
186
187#ifdef CONFIG_DEBUG_LOCK_ALLOC
188
189int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
190 struct lock_class_key *key)
191{
192 /* Don't re-initialize a lock while it is held. */
193 debug_check_no_locks_freed((void *)ssp, sizeof(*ssp));
194 lockdep_init_map(&ssp->dep_map, name, key, 0);
195 spin_lock_init(&ACCESS_PRIVATE(ssp, lock));
196 return init_srcu_struct_fields(ssp, false);
197}
198EXPORT_SYMBOL_GPL(__init_srcu_struct);
199
200#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
201
202/**
203 * init_srcu_struct - initialize a sleep-RCU structure
204 * @ssp: structure to initialize.
205 *
206 * Must invoke this on a given srcu_struct before passing that srcu_struct
207 * to any other function. Each srcu_struct represents a separate domain
208 * of SRCU protection.
209 */
210int init_srcu_struct(struct srcu_struct *ssp)
211{
212 spin_lock_init(&ACCESS_PRIVATE(ssp, lock));
213 return init_srcu_struct_fields(ssp, false);
214}
215EXPORT_SYMBOL_GPL(init_srcu_struct);
216
217#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
218
219/*
220 * First-use initialization of statically allocated srcu_struct
221 * structure. Wiring up the combining tree is more than can be
222 * done with compile-time initialization, so this check is added
223 * to each update-side SRCU primitive. Use ssp->lock, which -is-
224 * compile-time initialized, to resolve races involving multiple
225 * CPUs trying to garner first-use privileges.
226 */
227static void check_init_srcu_struct(struct srcu_struct *ssp)
228{
229 unsigned long flags;
230
231 /* The smp_load_acquire() pairs with the smp_store_release(). */
232 if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_gp_seq_needed))) /*^^^*/
233 return; /* Already initialized. */
234 spin_lock_irqsave_rcu_node(ssp, flags);
235 if (!rcu_seq_state(ssp->srcu_gp_seq_needed)) {
236 spin_unlock_irqrestore_rcu_node(ssp, flags);
237 return;
238 }
239 init_srcu_struct_fields(ssp, true);
240 spin_unlock_irqrestore_rcu_node(ssp, flags);
241}
242
243/*
244 * Returns approximate total of the readers' ->srcu_lock_count[] values
245 * for the rank of per-CPU counters specified by idx.
246 */
247static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx)
248{
249 int cpu;
250 unsigned long sum = 0;
251
252 for_each_possible_cpu(cpu) {
253 struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
254
255 sum += READ_ONCE(cpuc->srcu_lock_count[idx]);
256 }
257 return sum;
258}
259
260/*
261 * Returns approximate total of the readers' ->srcu_unlock_count[] values
262 * for the rank of per-CPU counters specified by idx.
263 */
264static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx)
265{
266 int cpu;
267 unsigned long sum = 0;
268
269 for_each_possible_cpu(cpu) {
270 struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
271
272 sum += READ_ONCE(cpuc->srcu_unlock_count[idx]);
273 }
274 return sum;
275}
276
277/*
278 * Return true if the number of pre-existing readers is determined to
279 * be zero.
280 */
281static bool srcu_readers_active_idx_check(struct srcu_struct *ssp, int idx)
282{
283 unsigned long unlocks;
284
285 unlocks = srcu_readers_unlock_idx(ssp, idx);
286
287 /*
288 * Make sure that a lock is always counted if the corresponding
289 * unlock is counted. Needs to be a smp_mb() as the read side may
290 * contain a read from a variable that is written to before the
291 * synchronize_srcu() in the write side. In this case smp_mb()s
292 * A and B act like the store buffering pattern.
293 *
294 * This smp_mb() also pairs with smp_mb() C to prevent accesses
295 * after the synchronize_srcu() from being executed before the
296 * grace period ends.
297 */
298 smp_mb(); /* A */
299
300 /*
301 * If the locks are the same as the unlocks, then there must have
302 * been no readers on this index at some time in between. This does
303 * not mean that there are no more readers, as one could have read
304 * the current index but not have incremented the lock counter yet.
305 *
306 * So suppose that the updater is preempted here for so long
307 * that more than ULONG_MAX non-nested readers come and go in
308 * the meantime. It turns out that this cannot result in overflow
309 * because if a reader modifies its unlock count after we read it
310 * above, then that reader's next load of ->srcu_idx is guaranteed
311 * to get the new value, which will cause it to operate on the
312 * other bank of counters, where it cannot contribute to the
313 * overflow of these counters. This means that there is a maximum
314 * of 2*NR_CPUS increments, which cannot overflow given current
315 * systems, especially not on 64-bit systems.
316 *
317 * OK, how about nesting? This does impose a limit on nesting
318 * of floor(ULONG_MAX/NR_CPUS/2), which should be sufficient,
319 * especially on 64-bit systems.
320 */
321 return srcu_readers_lock_idx(ssp, idx) == unlocks;
322}
323
324/**
325 * srcu_readers_active - returns true if there are readers. and false
326 * otherwise
327 * @ssp: which srcu_struct to count active readers (holding srcu_read_lock).
328 *
329 * Note that this is not an atomic primitive, and can therefore suffer
330 * severe errors when invoked on an active srcu_struct. That said, it
331 * can be useful as an error check at cleanup time.
332 */
333static bool srcu_readers_active(struct srcu_struct *ssp)
334{
335 int cpu;
336 unsigned long sum = 0;
337
338 for_each_possible_cpu(cpu) {
339 struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
340
341 sum += READ_ONCE(cpuc->srcu_lock_count[0]);
342 sum += READ_ONCE(cpuc->srcu_lock_count[1]);
343 sum -= READ_ONCE(cpuc->srcu_unlock_count[0]);
344 sum -= READ_ONCE(cpuc->srcu_unlock_count[1]);
345 }
346 return sum;
347}
348
349#define SRCU_INTERVAL 1
350
351/*
352 * Return grace-period delay, zero if there are expedited grace
353 * periods pending, SRCU_INTERVAL otherwise.
354 */
355static unsigned long srcu_get_delay(struct srcu_struct *ssp)
356{
357 if (ULONG_CMP_LT(READ_ONCE(ssp->srcu_gp_seq),
358 READ_ONCE(ssp->srcu_gp_seq_needed_exp)))
359 return 0;
360 return SRCU_INTERVAL;
361}
362
363/**
364 * cleanup_srcu_struct - deconstruct a sleep-RCU structure
365 * @ssp: structure to clean up.
366 *
367 * Must invoke this after you are finished using a given srcu_struct that
368 * was initialized via init_srcu_struct(), else you leak memory.
369 */
370void cleanup_srcu_struct(struct srcu_struct *ssp)
371{
372 int cpu;
373
374 if (WARN_ON(!srcu_get_delay(ssp)))
375 return; /* Just leak it! */
376 if (WARN_ON(srcu_readers_active(ssp)))
377 return; /* Just leak it! */
378 flush_delayed_work(&ssp->work);
379 for_each_possible_cpu(cpu) {
380 struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
381
382 del_timer_sync(&sdp->delay_work);
383 flush_work(&sdp->work);
384 if (WARN_ON(rcu_segcblist_n_cbs(&sdp->srcu_cblist)))
385 return; /* Forgot srcu_barrier(), so just leak it! */
386 }
387 if (WARN_ON(rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
388 WARN_ON(srcu_readers_active(ssp))) {
389 pr_info("%s: Active srcu_struct %p state: %d\n",
390 __func__, ssp, rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)));
391 return; /* Caller forgot to stop doing call_srcu()? */
392 }
393 free_percpu(ssp->sda);
394 ssp->sda = NULL;
395}
396EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
397
398/*
399 * Counts the new reader in the appropriate per-CPU element of the
400 * srcu_struct.
401 * Returns an index that must be passed to the matching srcu_read_unlock().
402 */
403int __srcu_read_lock(struct srcu_struct *ssp)
404{
405 int idx;
406
407 idx = READ_ONCE(ssp->srcu_idx) & 0x1;
408 this_cpu_inc(ssp->sda->srcu_lock_count[idx]);
409 smp_mb(); /* B */ /* Avoid leaking the critical section. */
410 return idx;
411}
412EXPORT_SYMBOL_GPL(__srcu_read_lock);
413
414/*
415 * Removes the count for the old reader from the appropriate per-CPU
416 * element of the srcu_struct. Note that this may well be a different
417 * CPU than that which was incremented by the corresponding srcu_read_lock().
418 */
419void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
420{
421 smp_mb(); /* C */ /* Avoid leaking the critical section. */
422 this_cpu_inc(ssp->sda->srcu_unlock_count[idx]);
423}
424EXPORT_SYMBOL_GPL(__srcu_read_unlock);
425
426/*
427 * We use an adaptive strategy for synchronize_srcu() and especially for
428 * synchronize_srcu_expedited(). We spin for a fixed time period
429 * (defined below) to allow SRCU readers to exit their read-side critical
430 * sections. If there are still some readers after a few microseconds,
431 * we repeatedly block for 1-millisecond time periods.
432 */
433#define SRCU_RETRY_CHECK_DELAY 5
434
435/*
436 * Start an SRCU grace period.
437 */
438static void srcu_gp_start(struct srcu_struct *ssp)
439{
440 struct srcu_data *sdp = this_cpu_ptr(ssp->sda);
441 int state;
442
443 lockdep_assert_held(&ACCESS_PRIVATE(ssp, lock));
444 WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed));
445 spin_lock_rcu_node(sdp); /* Interrupts already disabled. */
446 rcu_segcblist_advance(&sdp->srcu_cblist,
447 rcu_seq_current(&ssp->srcu_gp_seq));
448 (void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
449 rcu_seq_snap(&ssp->srcu_gp_seq));
450 spin_unlock_rcu_node(sdp); /* Interrupts remain disabled. */
451 smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
452 rcu_seq_start(&ssp->srcu_gp_seq);
453 state = rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq));
454 WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
455}
456
457
458static void srcu_delay_timer(struct timer_list *t)
459{
460 struct srcu_data *sdp = container_of(t, struct srcu_data, delay_work);
461
462 queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
463}
464
465static void srcu_queue_delayed_work_on(struct srcu_data *sdp,
466 unsigned long delay)
467{
468 if (!delay) {
469 queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
470 return;
471 }
472
473 timer_reduce(&sdp->delay_work, jiffies + delay);
474}
475
476/*
477 * Schedule callback invocation for the specified srcu_data structure,
478 * if possible, on the corresponding CPU.
479 */
480static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay)
481{
482 srcu_queue_delayed_work_on(sdp, delay);
483}
484
485/*
486 * Schedule callback invocation for all srcu_data structures associated
487 * with the specified srcu_node structure that have callbacks for the
488 * just-completed grace period, the one corresponding to idx. If possible,
489 * schedule this invocation on the corresponding CPUs.
490 */
491static void srcu_schedule_cbs_snp(struct srcu_struct *ssp, struct srcu_node *snp,
492 unsigned long mask, unsigned long delay)
493{
494 int cpu;
495
496 for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
497 if (!(mask & (1 << (cpu - snp->grplo))))
498 continue;
499 srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, cpu), delay);
500 }
501}
502
503/*
504 * Note the end of an SRCU grace period. Initiates callback invocation
505 * and starts a new grace period if needed.
506 *
507 * The ->srcu_cb_mutex acquisition does not protect any data, but
508 * instead prevents more than one grace period from starting while we
509 * are initiating callback invocation. This allows the ->srcu_have_cbs[]
510 * array to have a finite number of elements.
511 */
512static void srcu_gp_end(struct srcu_struct *ssp)
513{
514 unsigned long cbdelay;
515 bool cbs;
516 bool last_lvl;
517 int cpu;
518 unsigned long flags;
519 unsigned long gpseq;
520 int idx;
521 unsigned long mask;
522 struct srcu_data *sdp;
523 struct srcu_node *snp;
524
525 /* Prevent more than one additional grace period. */
526 mutex_lock(&ssp->srcu_cb_mutex);
527
528 /* End the current grace period. */
529 spin_lock_irq_rcu_node(ssp);
530 idx = rcu_seq_state(ssp->srcu_gp_seq);
531 WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);
532 cbdelay = srcu_get_delay(ssp);
533 ssp->srcu_last_gp_end = ktime_get_mono_fast_ns();
534 rcu_seq_end(&ssp->srcu_gp_seq);
535 gpseq = rcu_seq_current(&ssp->srcu_gp_seq);
536 if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq))
537 ssp->srcu_gp_seq_needed_exp = gpseq;
538 spin_unlock_irq_rcu_node(ssp);
539 mutex_unlock(&ssp->srcu_gp_mutex);
540 /* A new grace period can start at this point. But only one. */
541
542 /* Initiate callback invocation as needed. */
543 idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs);
544 srcu_for_each_node_breadth_first(ssp, snp) {
545 spin_lock_irq_rcu_node(snp);
546 cbs = false;
547 last_lvl = snp >= ssp->level[rcu_num_lvls - 1];
548 if (last_lvl)
549 cbs = snp->srcu_have_cbs[idx] == gpseq;
550 snp->srcu_have_cbs[idx] = gpseq;
551 rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
552 if (ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, gpseq))
553 snp->srcu_gp_seq_needed_exp = gpseq;
554 mask = snp->srcu_data_have_cbs[idx];
555 snp->srcu_data_have_cbs[idx] = 0;
556 spin_unlock_irq_rcu_node(snp);
557 if (cbs)
558 srcu_schedule_cbs_snp(ssp, snp, mask, cbdelay);
559
560 /* Occasionally prevent srcu_data counter wrap. */
561 if (!(gpseq & counter_wrap_check) && last_lvl)
562 for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
563 sdp = per_cpu_ptr(ssp->sda, cpu);
564 spin_lock_irqsave_rcu_node(sdp, flags);
565 if (ULONG_CMP_GE(gpseq,
566 sdp->srcu_gp_seq_needed + 100))
567 sdp->srcu_gp_seq_needed = gpseq;
568 if (ULONG_CMP_GE(gpseq,
569 sdp->srcu_gp_seq_needed_exp + 100))
570 sdp->srcu_gp_seq_needed_exp = gpseq;
571 spin_unlock_irqrestore_rcu_node(sdp, flags);
572 }
573 }
574
575 /* Callback initiation done, allow grace periods after next. */
576 mutex_unlock(&ssp->srcu_cb_mutex);
577
578 /* Start a new grace period if needed. */
579 spin_lock_irq_rcu_node(ssp);
580 gpseq = rcu_seq_current(&ssp->srcu_gp_seq);
581 if (!rcu_seq_state(gpseq) &&
582 ULONG_CMP_LT(gpseq, ssp->srcu_gp_seq_needed)) {
583 srcu_gp_start(ssp);
584 spin_unlock_irq_rcu_node(ssp);
585 srcu_reschedule(ssp, 0);
586 } else {
587 spin_unlock_irq_rcu_node(ssp);
588 }
589}
590
591/*
592 * Funnel-locking scheme to scalably mediate many concurrent expedited
593 * grace-period requests. This function is invoked for the first known
594 * expedited request for a grace period that has already been requested,
595 * but without expediting. To start a completely new grace period,
596 * whether expedited or not, use srcu_funnel_gp_start() instead.
597 */
598static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp,
599 unsigned long s)
600{
601 unsigned long flags;
602
603 for (; snp != NULL; snp = snp->srcu_parent) {
604 if (rcu_seq_done(&ssp->srcu_gp_seq, s) ||
605 ULONG_CMP_GE(READ_ONCE(snp->srcu_gp_seq_needed_exp), s))
606 return;
607 spin_lock_irqsave_rcu_node(snp, flags);
608 if (ULONG_CMP_GE(snp->srcu_gp_seq_needed_exp, s)) {
609 spin_unlock_irqrestore_rcu_node(snp, flags);
610 return;
611 }
612 WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
613 spin_unlock_irqrestore_rcu_node(snp, flags);
614 }
615 spin_lock_irqsave_rcu_node(ssp, flags);
616 if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s))
617 ssp->srcu_gp_seq_needed_exp = s;
618 spin_unlock_irqrestore_rcu_node(ssp, flags);
619}
620
621/*
622 * Funnel-locking scheme to scalably mediate many concurrent grace-period
623 * requests. The winner has to do the work of actually starting grace
624 * period s. Losers must either ensure that their desired grace-period
625 * number is recorded on at least their leaf srcu_node structure, or they
626 * must take steps to invoke their own callbacks.
627 *
628 * Note that this function also does the work of srcu_funnel_exp_start(),
629 * in some cases by directly invoking it.
630 */
631static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
632 unsigned long s, bool do_norm)
633{
634 unsigned long flags;
635 int idx = rcu_seq_ctr(s) % ARRAY_SIZE(sdp->mynode->srcu_have_cbs);
636 struct srcu_node *snp = sdp->mynode;
637 unsigned long snp_seq;
638
639 /* Each pass through the loop does one level of the srcu_node tree. */
640 for (; snp != NULL; snp = snp->srcu_parent) {
641 if (rcu_seq_done(&ssp->srcu_gp_seq, s) && snp != sdp->mynode)
642 return; /* GP already done and CBs recorded. */
643 spin_lock_irqsave_rcu_node(snp, flags);
644 if (ULONG_CMP_GE(snp->srcu_have_cbs[idx], s)) {
645 snp_seq = snp->srcu_have_cbs[idx];
646 if (snp == sdp->mynode && snp_seq == s)
647 snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
648 spin_unlock_irqrestore_rcu_node(snp, flags);
649 if (snp == sdp->mynode && snp_seq != s) {
650 srcu_schedule_cbs_sdp(sdp, do_norm
651 ? SRCU_INTERVAL
652 : 0);
653 return;
654 }
655 if (!do_norm)
656 srcu_funnel_exp_start(ssp, snp, s);
657 return;
658 }
659 snp->srcu_have_cbs[idx] = s;
660 if (snp == sdp->mynode)
661 snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
662 if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s))
663 snp->srcu_gp_seq_needed_exp = s;
664 spin_unlock_irqrestore_rcu_node(snp, flags);
665 }
666
667 /* Top of tree, must ensure the grace period will be started. */
668 spin_lock_irqsave_rcu_node(ssp, flags);
669 if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed, s)) {
670 /*
671 * Record need for grace period s. Pair with load
672 * acquire setting up for initialization.
673 */
674 smp_store_release(&ssp->srcu_gp_seq_needed, s); /*^^^*/
675 }
676 if (!do_norm && ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s))
677 ssp->srcu_gp_seq_needed_exp = s;
678
679 /* If grace period not already done and none in progress, start it. */
680 if (!rcu_seq_done(&ssp->srcu_gp_seq, s) &&
681 rcu_seq_state(ssp->srcu_gp_seq) == SRCU_STATE_IDLE) {
682 WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed));
683 srcu_gp_start(ssp);
684 if (likely(srcu_init_done))
685 queue_delayed_work(rcu_gp_wq, &ssp->work,
686 srcu_get_delay(ssp));
687 else if (list_empty(&ssp->work.work.entry))
688 list_add(&ssp->work.work.entry, &srcu_boot_list);
689 }
690 spin_unlock_irqrestore_rcu_node(ssp, flags);
691}
692
693/*
694 * Wait until all readers counted by array index idx complete, but
695 * loop an additional time if there is an expedited grace period pending.
696 * The caller must ensure that ->srcu_idx is not changed while checking.
697 */
698static bool try_check_zero(struct srcu_struct *ssp, int idx, int trycount)
699{
700 for (;;) {
701 if (srcu_readers_active_idx_check(ssp, idx))
702 return true;
703 if (--trycount + !srcu_get_delay(ssp) <= 0)
704 return false;
705 udelay(SRCU_RETRY_CHECK_DELAY);
706 }
707}
708
709/*
710 * Increment the ->srcu_idx counter so that future SRCU readers will
711 * use the other rank of the ->srcu_(un)lock_count[] arrays. This allows
712 * us to wait for pre-existing readers in a starvation-free manner.
713 */
714static void srcu_flip(struct srcu_struct *ssp)
715{
716 /*
717 * Ensure that if this updater saw a given reader's increment
718 * from __srcu_read_lock(), that reader was using an old value
719 * of ->srcu_idx. Also ensure that if a given reader sees the
720 * new value of ->srcu_idx, this updater's earlier scans cannot
721 * have seen that reader's increments (which is OK, because this
722 * grace period need not wait on that reader).
723 */
724 smp_mb(); /* E */ /* Pairs with B and C. */
725
726 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
727
728 /*
729 * Ensure that if the updater misses an __srcu_read_unlock()
730 * increment, that task's next __srcu_read_lock() will see the
731 * above counter update. Note that both this memory barrier
732 * and the one in srcu_readers_active_idx_check() provide the
733 * guarantee for __srcu_read_lock().
734 */
735 smp_mb(); /* D */ /* Pairs with C. */
736}
737
738/*
739 * If SRCU is likely idle, return true, otherwise return false.
740 *
741 * Note that it is OK for several current from-idle requests for a new
742 * grace period from idle to specify expediting because they will all end
743 * up requesting the same grace period anyhow. So no loss.
744 *
745 * Note also that if any CPU (including the current one) is still invoking
746 * callbacks, this function will nevertheless say "idle". This is not
747 * ideal, but the overhead of checking all CPUs' callback lists is even
748 * less ideal, especially on large systems. Furthermore, the wakeup
749 * can happen before the callback is fully removed, so we have no choice
750 * but to accept this type of error.
751 *
752 * This function is also subject to counter-wrap errors, but let's face
753 * it, if this function was preempted for enough time for the counters
754 * to wrap, it really doesn't matter whether or not we expedite the grace
755 * period. The extra overhead of a needlessly expedited grace period is
756 * negligible when amoritized over that time period, and the extra latency
757 * of a needlessly non-expedited grace period is similarly negligible.
758 */
759static bool srcu_might_be_idle(struct srcu_struct *ssp)
760{
761 unsigned long curseq;
762 unsigned long flags;
763 struct srcu_data *sdp;
764 unsigned long t;
765
766 /* If the local srcu_data structure has callbacks, not idle. */
767 local_irq_save(flags);
768 sdp = this_cpu_ptr(ssp->sda);
769 if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) {
770 local_irq_restore(flags);
771 return false; /* Callbacks already present, so not idle. */
772 }
773 local_irq_restore(flags);
774
775 /*
776 * No local callbacks, so probabalistically probe global state.
777 * Exact information would require acquiring locks, which would
778 * kill scalability, hence the probabalistic nature of the probe.
779 */
780
781 /* First, see if enough time has passed since the last GP. */
782 t = ktime_get_mono_fast_ns();
783 if (exp_holdoff == 0 ||
784 time_in_range_open(t, ssp->srcu_last_gp_end,
785 ssp->srcu_last_gp_end + exp_holdoff))
786 return false; /* Too soon after last GP. */
787
788 /* Next, check for probable idleness. */
789 curseq = rcu_seq_current(&ssp->srcu_gp_seq);
790 smp_mb(); /* Order ->srcu_gp_seq with ->srcu_gp_seq_needed. */
791 if (ULONG_CMP_LT(curseq, READ_ONCE(ssp->srcu_gp_seq_needed)))
792 return false; /* Grace period in progress, so not idle. */
793 smp_mb(); /* Order ->srcu_gp_seq with prior access. */
794 if (curseq != rcu_seq_current(&ssp->srcu_gp_seq))
795 return false; /* GP # changed, so not idle. */
796 return true; /* With reasonable probability, idle! */
797}
798
799/*
800 * SRCU callback function to leak a callback.
801 */
802static void srcu_leak_callback(struct rcu_head *rhp)
803{
804}
805
806/*
807 * Enqueue an SRCU callback on the srcu_data structure associated with
808 * the current CPU and the specified srcu_struct structure, initiating
809 * grace-period processing if it is not already running.
810 *
811 * Note that all CPUs must agree that the grace period extended beyond
812 * all pre-existing SRCU read-side critical section. On systems with
813 * more than one CPU, this means that when "func()" is invoked, each CPU
814 * is guaranteed to have executed a full memory barrier since the end of
815 * its last corresponding SRCU read-side critical section whose beginning
816 * preceded the call to call_srcu(). It also means that each CPU executing
817 * an SRCU read-side critical section that continues beyond the start of
818 * "func()" must have executed a memory barrier after the call_srcu()
819 * but before the beginning of that SRCU read-side critical section.
820 * Note that these guarantees include CPUs that are offline, idle, or
821 * executing in user mode, as well as CPUs that are executing in the kernel.
822 *
823 * Furthermore, if CPU A invoked call_srcu() and CPU B invoked the
824 * resulting SRCU callback function "func()", then both CPU A and CPU
825 * B are guaranteed to execute a full memory barrier during the time
826 * interval between the call to call_srcu() and the invocation of "func()".
827 * This guarantee applies even if CPU A and CPU B are the same CPU (but
828 * again only if the system has more than one CPU).
829 *
830 * Of course, these guarantees apply only for invocations of call_srcu(),
831 * srcu_read_lock(), and srcu_read_unlock() that are all passed the same
832 * srcu_struct structure.
833 */
834static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
835 rcu_callback_t func, bool do_norm)
836{
837 unsigned long flags;
838 int idx;
839 bool needexp = false;
840 bool needgp = false;
841 unsigned long s;
842 struct srcu_data *sdp;
843
844 check_init_srcu_struct(ssp);
845 if (debug_rcu_head_queue(rhp)) {
846 /* Probable double call_srcu(), so leak the callback. */
847 WRITE_ONCE(rhp->func, srcu_leak_callback);
848 WARN_ONCE(1, "call_srcu(): Leaked duplicate callback\n");
849 return;
850 }
851 rhp->func = func;
852 idx = srcu_read_lock(ssp);
853 local_irq_save(flags);
854 sdp = this_cpu_ptr(ssp->sda);
855 spin_lock_rcu_node(sdp);
856 rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp, false);
857 rcu_segcblist_advance(&sdp->srcu_cblist,
858 rcu_seq_current(&ssp->srcu_gp_seq));
859 s = rcu_seq_snap(&ssp->srcu_gp_seq);
860 (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
861 if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
862 sdp->srcu_gp_seq_needed = s;
863 needgp = true;
864 }
865 if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
866 sdp->srcu_gp_seq_needed_exp = s;
867 needexp = true;
868 }
869 spin_unlock_irqrestore_rcu_node(sdp, flags);
870 if (needgp)
871 srcu_funnel_gp_start(ssp, sdp, s, do_norm);
872 else if (needexp)
873 srcu_funnel_exp_start(ssp, sdp->mynode, s);
874 srcu_read_unlock(ssp, idx);
875}
876
877/**
878 * call_srcu() - Queue a callback for invocation after an SRCU grace period
879 * @ssp: srcu_struct in queue the callback
880 * @rhp: structure to be used for queueing the SRCU callback.
881 * @func: function to be invoked after the SRCU grace period
882 *
883 * The callback function will be invoked some time after a full SRCU
884 * grace period elapses, in other words after all pre-existing SRCU
885 * read-side critical sections have completed. However, the callback
886 * function might well execute concurrently with other SRCU read-side
887 * critical sections that started after call_srcu() was invoked. SRCU
888 * read-side critical sections are delimited by srcu_read_lock() and
889 * srcu_read_unlock(), and may be nested.
890 *
891 * The callback will be invoked from process context, but must nevertheless
892 * be fast and must not block.
893 */
894void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
895 rcu_callback_t func)
896{
897 __call_srcu(ssp, rhp, func, true);
898}
899EXPORT_SYMBOL_GPL(call_srcu);
900
901/*
902 * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
903 */
904static void __synchronize_srcu(struct srcu_struct *ssp, bool do_norm)
905{
906 struct rcu_synchronize rcu;
907
908 RCU_LOCKDEP_WARN(lock_is_held(&ssp->dep_map) ||
909 lock_is_held(&rcu_bh_lock_map) ||
910 lock_is_held(&rcu_lock_map) ||
911 lock_is_held(&rcu_sched_lock_map),
912 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
913
914 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
915 return;
916 might_sleep();
917 check_init_srcu_struct(ssp);
918 init_completion(&rcu.completion);
919 init_rcu_head_on_stack(&rcu.head);
920 __call_srcu(ssp, &rcu.head, wakeme_after_rcu, do_norm);
921 wait_for_completion(&rcu.completion);
922 destroy_rcu_head_on_stack(&rcu.head);
923
924 /*
925 * Make sure that later code is ordered after the SRCU grace
926 * period. This pairs with the spin_lock_irq_rcu_node()
927 * in srcu_invoke_callbacks(). Unlike Tree RCU, this is needed
928 * because the current CPU might have been totally uninvolved with
929 * (and thus unordered against) that grace period.
930 */
931 smp_mb();
932}
933
934/**
935 * synchronize_srcu_expedited - Brute-force SRCU grace period
936 * @ssp: srcu_struct with which to synchronize.
937 *
938 * Wait for an SRCU grace period to elapse, but be more aggressive about
939 * spinning rather than blocking when waiting.
940 *
941 * Note that synchronize_srcu_expedited() has the same deadlock and
942 * memory-ordering properties as does synchronize_srcu().
943 */
944void synchronize_srcu_expedited(struct srcu_struct *ssp)
945{
946 __synchronize_srcu(ssp, rcu_gp_is_normal());
947}
948EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
949
950/**
951 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
952 * @ssp: srcu_struct with which to synchronize.
953 *
954 * Wait for the count to drain to zero of both indexes. To avoid the
955 * possible starvation of synchronize_srcu(), it waits for the count of
956 * the index=((->srcu_idx & 1) ^ 1) to drain to zero at first,
957 * and then flip the srcu_idx and wait for the count of the other index.
958 *
959 * Can block; must be called from process context.
960 *
961 * Note that it is illegal to call synchronize_srcu() from the corresponding
962 * SRCU read-side critical section; doing so will result in deadlock.
963 * However, it is perfectly legal to call synchronize_srcu() on one
964 * srcu_struct from some other srcu_struct's read-side critical section,
965 * as long as the resulting graph of srcu_structs is acyclic.
966 *
967 * There are memory-ordering constraints implied by synchronize_srcu().
968 * On systems with more than one CPU, when synchronize_srcu() returns,
969 * each CPU is guaranteed to have executed a full memory barrier since
970 * the end of its last corresponding SRCU read-side critical section
971 * whose beginning preceded the call to synchronize_srcu(). In addition,
972 * each CPU having an SRCU read-side critical section that extends beyond
973 * the return from synchronize_srcu() is guaranteed to have executed a
974 * full memory barrier after the beginning of synchronize_srcu() and before
975 * the beginning of that SRCU read-side critical section. Note that these
976 * guarantees include CPUs that are offline, idle, or executing in user mode,
977 * as well as CPUs that are executing in the kernel.
978 *
979 * Furthermore, if CPU A invoked synchronize_srcu(), which returned
980 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
981 * to have executed a full memory barrier during the execution of
982 * synchronize_srcu(). This guarantee applies even if CPU A and CPU B
983 * are the same CPU, but again only if the system has more than one CPU.
984 *
985 * Of course, these memory-ordering guarantees apply only when
986 * synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are
987 * passed the same srcu_struct structure.
988 *
989 * If SRCU is likely idle, expedite the first request. This semantic
990 * was provided by Classic SRCU, and is relied upon by its users, so TREE
991 * SRCU must also provide it. Note that detecting idleness is heuristic
992 * and subject to both false positives and negatives.
993 */
994void synchronize_srcu(struct srcu_struct *ssp)
995{
996 if (srcu_might_be_idle(ssp) || rcu_gp_is_expedited())
997 synchronize_srcu_expedited(ssp);
998 else
999 __synchronize_srcu(ssp, true);
1000}
1001EXPORT_SYMBOL_GPL(synchronize_srcu);
1002
1003/*
1004 * Callback function for srcu_barrier() use.
1005 */
1006static void srcu_barrier_cb(struct rcu_head *rhp)
1007{
1008 struct srcu_data *sdp;
1009 struct srcu_struct *ssp;
1010
1011 sdp = container_of(rhp, struct srcu_data, srcu_barrier_head);
1012 ssp = sdp->ssp;
1013 if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt))
1014 complete(&ssp->srcu_barrier_completion);
1015}
1016
1017/**
1018 * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
1019 * @ssp: srcu_struct on which to wait for in-flight callbacks.
1020 */
1021void srcu_barrier(struct srcu_struct *ssp)
1022{
1023 int cpu;
1024 struct srcu_data *sdp;
1025 unsigned long s = rcu_seq_snap(&ssp->srcu_barrier_seq);
1026
1027 check_init_srcu_struct(ssp);
1028 mutex_lock(&ssp->srcu_barrier_mutex);
1029 if (rcu_seq_done(&ssp->srcu_barrier_seq, s)) {
1030 smp_mb(); /* Force ordering following return. */
1031 mutex_unlock(&ssp->srcu_barrier_mutex);
1032 return; /* Someone else did our work for us. */
1033 }
1034 rcu_seq_start(&ssp->srcu_barrier_seq);
1035 init_completion(&ssp->srcu_barrier_completion);
1036
1037 /* Initial count prevents reaching zero until all CBs are posted. */
1038 atomic_set(&ssp->srcu_barrier_cpu_cnt, 1);
1039
1040 /*
1041 * Each pass through this loop enqueues a callback, but only
1042 * on CPUs already having callbacks enqueued. Note that if
1043 * a CPU already has callbacks enqueue, it must have already
1044 * registered the need for a future grace period, so all we
1045 * need do is enqueue a callback that will use the same
1046 * grace period as the last callback already in the queue.
1047 */
1048 for_each_possible_cpu(cpu) {
1049 sdp = per_cpu_ptr(ssp->sda, cpu);
1050 spin_lock_irq_rcu_node(sdp);
1051 atomic_inc(&ssp->srcu_barrier_cpu_cnt);
1052 sdp->srcu_barrier_head.func = srcu_barrier_cb;
1053 debug_rcu_head_queue(&sdp->srcu_barrier_head);
1054 if (!rcu_segcblist_entrain(&sdp->srcu_cblist,
1055 &sdp->srcu_barrier_head, 0)) {
1056 debug_rcu_head_unqueue(&sdp->srcu_barrier_head);
1057 atomic_dec(&ssp->srcu_barrier_cpu_cnt);
1058 }
1059 spin_unlock_irq_rcu_node(sdp);
1060 }
1061
1062 /* Remove the initial count, at which point reaching zero can happen. */
1063 if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt))
1064 complete(&ssp->srcu_barrier_completion);
1065 wait_for_completion(&ssp->srcu_barrier_completion);
1066
1067 rcu_seq_end(&ssp->srcu_barrier_seq);
1068 mutex_unlock(&ssp->srcu_barrier_mutex);
1069}
1070EXPORT_SYMBOL_GPL(srcu_barrier);
1071
1072/**
1073 * srcu_batches_completed - return batches completed.
1074 * @ssp: srcu_struct on which to report batch completion.
1075 *
1076 * Report the number of batches, correlated with, but not necessarily
1077 * precisely the same as, the number of grace periods that have elapsed.
1078 */
1079unsigned long srcu_batches_completed(struct srcu_struct *ssp)
1080{
1081 return ssp->srcu_idx;
1082}
1083EXPORT_SYMBOL_GPL(srcu_batches_completed);
1084
1085/*
1086 * Core SRCU state machine. Push state bits of ->srcu_gp_seq
1087 * to SRCU_STATE_SCAN2, and invoke srcu_gp_end() when scan has
1088 * completed in that state.
1089 */
1090static void srcu_advance_state(struct srcu_struct *ssp)
1091{
1092 int idx;
1093
1094 mutex_lock(&ssp->srcu_gp_mutex);
1095
1096 /*
1097 * Because readers might be delayed for an extended period after
1098 * fetching ->srcu_idx for their index, at any point in time there
1099 * might well be readers using both idx=0 and idx=1. We therefore
1100 * need to wait for readers to clear from both index values before
1101 * invoking a callback.
1102 *
1103 * The load-acquire ensures that we see the accesses performed
1104 * by the prior grace period.
1105 */
1106 idx = rcu_seq_state(smp_load_acquire(&ssp->srcu_gp_seq)); /* ^^^ */
1107 if (idx == SRCU_STATE_IDLE) {
1108 spin_lock_irq_rcu_node(ssp);
1109 if (ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)) {
1110 WARN_ON_ONCE(rcu_seq_state(ssp->srcu_gp_seq));
1111 spin_unlock_irq_rcu_node(ssp);
1112 mutex_unlock(&ssp->srcu_gp_mutex);
1113 return;
1114 }
1115 idx = rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq));
1116 if (idx == SRCU_STATE_IDLE)
1117 srcu_gp_start(ssp);
1118 spin_unlock_irq_rcu_node(ssp);
1119 if (idx != SRCU_STATE_IDLE) {
1120 mutex_unlock(&ssp->srcu_gp_mutex);
1121 return; /* Someone else started the grace period. */
1122 }
1123 }
1124
1125 if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
1126 idx = 1 ^ (ssp->srcu_idx & 1);
1127 if (!try_check_zero(ssp, idx, 1)) {
1128 mutex_unlock(&ssp->srcu_gp_mutex);
1129 return; /* readers present, retry later. */
1130 }
1131 srcu_flip(ssp);
1132 rcu_seq_set_state(&ssp->srcu_gp_seq, SRCU_STATE_SCAN2);
1133 }
1134
1135 if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
1136
1137 /*
1138 * SRCU read-side critical sections are normally short,
1139 * so check at least twice in quick succession after a flip.
1140 */
1141 idx = 1 ^ (ssp->srcu_idx & 1);
1142 if (!try_check_zero(ssp, idx, 2)) {
1143 mutex_unlock(&ssp->srcu_gp_mutex);
1144 return; /* readers present, retry later. */
1145 }
1146 srcu_gp_end(ssp); /* Releases ->srcu_gp_mutex. */
1147 }
1148}
1149
1150/*
1151 * Invoke a limited number of SRCU callbacks that have passed through
1152 * their grace period. If there are more to do, SRCU will reschedule
1153 * the workqueue. Note that needed memory barriers have been executed
1154 * in this task's context by srcu_readers_active_idx_check().
1155 */
1156static void srcu_invoke_callbacks(struct work_struct *work)
1157{
1158 bool more;
1159 struct rcu_cblist ready_cbs;
1160 struct rcu_head *rhp;
1161 struct srcu_data *sdp;
1162 struct srcu_struct *ssp;
1163
1164 sdp = container_of(work, struct srcu_data, work);
1165
1166 ssp = sdp->ssp;
1167 rcu_cblist_init(&ready_cbs);
1168 spin_lock_irq_rcu_node(sdp);
1169 rcu_segcblist_advance(&sdp->srcu_cblist,
1170 rcu_seq_current(&ssp->srcu_gp_seq));
1171 if (sdp->srcu_cblist_invoking ||
1172 !rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) {
1173 spin_unlock_irq_rcu_node(sdp);
1174 return; /* Someone else on the job or nothing to do. */
1175 }
1176
1177 /* We are on the job! Extract and invoke ready callbacks. */
1178 sdp->srcu_cblist_invoking = true;
1179 rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs);
1180 spin_unlock_irq_rcu_node(sdp);
1181 rhp = rcu_cblist_dequeue(&ready_cbs);
1182 for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
1183 debug_rcu_head_unqueue(rhp);
1184 local_bh_disable();
1185 rhp->func(rhp);
1186 local_bh_enable();
1187 }
1188
1189 /*
1190 * Update counts, accelerate new callbacks, and if needed,
1191 * schedule another round of callback invocation.
1192 */
1193 spin_lock_irq_rcu_node(sdp);
1194 rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs);
1195 (void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
1196 rcu_seq_snap(&ssp->srcu_gp_seq));
1197 sdp->srcu_cblist_invoking = false;
1198 more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);
1199 spin_unlock_irq_rcu_node(sdp);
1200 if (more)
1201 srcu_schedule_cbs_sdp(sdp, 0);
1202}
1203
1204/*
1205 * Finished one round of SRCU grace period. Start another if there are
1206 * more SRCU callbacks queued, otherwise put SRCU into not-running state.
1207 */
1208static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay)
1209{
1210 bool pushgp = true;
1211
1212 spin_lock_irq_rcu_node(ssp);
1213 if (ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)) {
1214 if (!WARN_ON_ONCE(rcu_seq_state(ssp->srcu_gp_seq))) {
1215 /* All requests fulfilled, time to go idle. */
1216 pushgp = false;
1217 }
1218 } else if (!rcu_seq_state(ssp->srcu_gp_seq)) {
1219 /* Outstanding request and no GP. Start one. */
1220 srcu_gp_start(ssp);
1221 }
1222 spin_unlock_irq_rcu_node(ssp);
1223
1224 if (pushgp)
1225 queue_delayed_work(rcu_gp_wq, &ssp->work, delay);
1226}
1227
1228/*
1229 * This is the work-queue function that handles SRCU grace periods.
1230 */
1231static void process_srcu(struct work_struct *work)
1232{
1233 struct srcu_struct *ssp;
1234
1235 ssp = container_of(work, struct srcu_struct, work.work);
1236
1237 srcu_advance_state(ssp);
1238 srcu_reschedule(ssp, srcu_get_delay(ssp));
1239}
1240
1241void srcutorture_get_gp_data(enum rcutorture_type test_type,
1242 struct srcu_struct *ssp, int *flags,
1243 unsigned long *gp_seq)
1244{
1245 if (test_type != SRCU_FLAVOR)
1246 return;
1247 *flags = 0;
1248 *gp_seq = rcu_seq_current(&ssp->srcu_gp_seq);
1249}
1250EXPORT_SYMBOL_GPL(srcutorture_get_gp_data);
1251
1252void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
1253{
1254 int cpu;
1255 int idx;
1256 unsigned long s0 = 0, s1 = 0;
1257
1258 idx = ssp->srcu_idx & 0x1;
1259 pr_alert("%s%s Tree SRCU g%ld per-CPU(idx=%d):",
1260 tt, tf, rcu_seq_current(&ssp->srcu_gp_seq), idx);
1261 for_each_possible_cpu(cpu) {
1262 unsigned long l0, l1;
1263 unsigned long u0, u1;
1264 long c0, c1;
1265 struct srcu_data *sdp;
1266
1267 sdp = per_cpu_ptr(ssp->sda, cpu);
1268 u0 = sdp->srcu_unlock_count[!idx];
1269 u1 = sdp->srcu_unlock_count[idx];
1270
1271 /*
1272 * Make sure that a lock is always counted if the corresponding
1273 * unlock is counted.
1274 */
1275 smp_rmb();
1276
1277 l0 = sdp->srcu_lock_count[!idx];
1278 l1 = sdp->srcu_lock_count[idx];
1279
1280 c0 = l0 - u0;
1281 c1 = l1 - u1;
1282 pr_cont(" %d(%ld,%ld %c)",
1283 cpu, c0, c1,
1284 "C."[rcu_segcblist_empty(&sdp->srcu_cblist)]);
1285 s0 += c0;
1286 s1 += c1;
1287 }
1288 pr_cont(" T(%ld,%ld)\n", s0, s1);
1289}
1290EXPORT_SYMBOL_GPL(srcu_torture_stats_print);
1291
1292static int __init srcu_bootup_announce(void)
1293{
1294 pr_info("Hierarchical SRCU implementation.\n");
1295 if (exp_holdoff != DEFAULT_SRCU_EXP_HOLDOFF)
1296 pr_info("\tNon-default auto-expedite holdoff of %lu ns.\n", exp_holdoff);
1297 return 0;
1298}
1299early_initcall(srcu_bootup_announce);
1300
1301void __init srcu_init(void)
1302{
1303 struct srcu_struct *ssp;
1304
1305 srcu_init_done = true;
1306 while (!list_empty(&srcu_boot_list)) {
1307 ssp = list_first_entry(&srcu_boot_list, struct srcu_struct,
1308 work.work.entry);
1309 check_init_srcu_struct(ssp);
1310 list_del_init(&ssp->work.work.entry);
1311 queue_work(rcu_gp_wq, &ssp->work.work);
1312 }
1313}
1314
1315#ifdef CONFIG_MODULES
1316
1317/* Initialize any global-scope srcu_struct structures used by this module. */
1318static int srcu_module_coming(struct module *mod)
1319{
1320 int i;
1321 struct srcu_struct **sspp = mod->srcu_struct_ptrs;
1322 int ret;
1323
1324 for (i = 0; i < mod->num_srcu_structs; i++) {
1325 ret = init_srcu_struct(*(sspp++));
1326 if (WARN_ON_ONCE(ret))
1327 return ret;
1328 }
1329 return 0;
1330}
1331
1332/* Clean up any global-scope srcu_struct structures used by this module. */
1333static void srcu_module_going(struct module *mod)
1334{
1335 int i;
1336 struct srcu_struct **sspp = mod->srcu_struct_ptrs;
1337
1338 for (i = 0; i < mod->num_srcu_structs; i++)
1339 cleanup_srcu_struct(*(sspp++));
1340}
1341
1342/* Handle one module, either coming or going. */
1343static int srcu_module_notify(struct notifier_block *self,
1344 unsigned long val, void *data)
1345{
1346 struct module *mod = data;
1347 int ret = 0;
1348
1349 switch (val) {
1350 case MODULE_STATE_COMING:
1351 ret = srcu_module_coming(mod);
1352 break;
1353 case MODULE_STATE_GOING:
1354 srcu_module_going(mod);
1355 break;
1356 default:
1357 break;
1358 }
1359 return ret;
1360}
1361
1362static struct notifier_block srcu_module_nb = {
1363 .notifier_call = srcu_module_notify,
1364 .priority = 0,
1365};
1366
1367static __init int init_srcu_module_notifier(void)
1368{
1369 int ret;
1370
1371 ret = register_module_notifier(&srcu_module_nb);
1372 if (ret)
1373 pr_warn("Failed to register srcu module notifier\n");
1374 return ret;
1375}
1376late_initcall(init_srcu_module_notifier);
1377
1378#endif /* #ifdef CONFIG_MODULES */
1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Sleepable Read-Copy Update mechanism for mutual exclusion.
4 *
5 * Copyright (C) IBM Corporation, 2006
6 * Copyright (C) Fujitsu, 2012
7 *
8 * Authors: Paul McKenney <paulmck@linux.ibm.com>
9 * Lai Jiangshan <laijs@cn.fujitsu.com>
10 *
11 * For detailed explanation of Read-Copy Update mechanism see -
12 * Documentation/RCU/ *.txt
13 *
14 */
15
16#define pr_fmt(fmt) "rcu: " fmt
17
18#include <linux/export.h>
19#include <linux/mutex.h>
20#include <linux/percpu.h>
21#include <linux/preempt.h>
22#include <linux/rcupdate_wait.h>
23#include <linux/sched.h>
24#include <linux/smp.h>
25#include <linux/delay.h>
26#include <linux/module.h>
27#include <linux/slab.h>
28#include <linux/srcu.h>
29
30#include "rcu.h"
31#include "rcu_segcblist.h"
32
33/* Holdoff in nanoseconds for auto-expediting. */
34#define DEFAULT_SRCU_EXP_HOLDOFF (25 * 1000)
35static ulong exp_holdoff = DEFAULT_SRCU_EXP_HOLDOFF;
36module_param(exp_holdoff, ulong, 0444);
37
38/* Overflow-check frequency. N bits roughly says every 2**N grace periods. */
39static ulong counter_wrap_check = (ULONG_MAX >> 2);
40module_param(counter_wrap_check, ulong, 0444);
41
42/*
43 * Control conversion to SRCU_SIZE_BIG:
44 * 0: Don't convert at all.
45 * 1: Convert at init_srcu_struct() time.
46 * 2: Convert when rcutorture invokes srcu_torture_stats_print().
47 * 3: Decide at boot time based on system shape (default).
48 * 0x1x: Convert when excessive contention encountered.
49 */
50#define SRCU_SIZING_NONE 0
51#define SRCU_SIZING_INIT 1
52#define SRCU_SIZING_TORTURE 2
53#define SRCU_SIZING_AUTO 3
54#define SRCU_SIZING_CONTEND 0x10
55#define SRCU_SIZING_IS(x) ((convert_to_big & ~SRCU_SIZING_CONTEND) == x)
56#define SRCU_SIZING_IS_NONE() (SRCU_SIZING_IS(SRCU_SIZING_NONE))
57#define SRCU_SIZING_IS_INIT() (SRCU_SIZING_IS(SRCU_SIZING_INIT))
58#define SRCU_SIZING_IS_TORTURE() (SRCU_SIZING_IS(SRCU_SIZING_TORTURE))
59#define SRCU_SIZING_IS_CONTEND() (convert_to_big & SRCU_SIZING_CONTEND)
60static int convert_to_big = SRCU_SIZING_AUTO;
61module_param(convert_to_big, int, 0444);
62
63/* Number of CPUs to trigger init_srcu_struct()-time transition to big. */
64static int big_cpu_lim __read_mostly = 128;
65module_param(big_cpu_lim, int, 0444);
66
67/* Contention events per jiffy to initiate transition to big. */
68static int small_contention_lim __read_mostly = 100;
69module_param(small_contention_lim, int, 0444);
70
71/* Early-boot callback-management, so early that no lock is required! */
72static LIST_HEAD(srcu_boot_list);
73static bool __read_mostly srcu_init_done;
74
75static void srcu_invoke_callbacks(struct work_struct *work);
76static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay);
77static void process_srcu(struct work_struct *work);
78static void srcu_delay_timer(struct timer_list *t);
79
80/* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */
81#define spin_lock_rcu_node(p) \
82do { \
83 spin_lock(&ACCESS_PRIVATE(p, lock)); \
84 smp_mb__after_unlock_lock(); \
85} while (0)
86
87#define spin_unlock_rcu_node(p) spin_unlock(&ACCESS_PRIVATE(p, lock))
88
89#define spin_lock_irq_rcu_node(p) \
90do { \
91 spin_lock_irq(&ACCESS_PRIVATE(p, lock)); \
92 smp_mb__after_unlock_lock(); \
93} while (0)
94
95#define spin_unlock_irq_rcu_node(p) \
96 spin_unlock_irq(&ACCESS_PRIVATE(p, lock))
97
98#define spin_lock_irqsave_rcu_node(p, flags) \
99do { \
100 spin_lock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \
101 smp_mb__after_unlock_lock(); \
102} while (0)
103
104#define spin_trylock_irqsave_rcu_node(p, flags) \
105({ \
106 bool ___locked = spin_trylock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \
107 \
108 if (___locked) \
109 smp_mb__after_unlock_lock(); \
110 ___locked; \
111})
112
113#define spin_unlock_irqrestore_rcu_node(p, flags) \
114 spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) \
115
116/*
117 * Initialize SRCU per-CPU data. Note that statically allocated
118 * srcu_struct structures might already have srcu_read_lock() and
119 * srcu_read_unlock() running against them. So if the is_static parameter
120 * is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[].
121 */
122static void init_srcu_struct_data(struct srcu_struct *ssp)
123{
124 int cpu;
125 struct srcu_data *sdp;
126
127 /*
128 * Initialize the per-CPU srcu_data array, which feeds into the
129 * leaves of the srcu_node tree.
130 */
131 WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) !=
132 ARRAY_SIZE(sdp->srcu_unlock_count));
133 for_each_possible_cpu(cpu) {
134 sdp = per_cpu_ptr(ssp->sda, cpu);
135 spin_lock_init(&ACCESS_PRIVATE(sdp, lock));
136 rcu_segcblist_init(&sdp->srcu_cblist);
137 sdp->srcu_cblist_invoking = false;
138 sdp->srcu_gp_seq_needed = ssp->srcu_sup->srcu_gp_seq;
139 sdp->srcu_gp_seq_needed_exp = ssp->srcu_sup->srcu_gp_seq;
140 sdp->mynode = NULL;
141 sdp->cpu = cpu;
142 INIT_WORK(&sdp->work, srcu_invoke_callbacks);
143 timer_setup(&sdp->delay_work, srcu_delay_timer, 0);
144 sdp->ssp = ssp;
145 }
146}
147
148/* Invalid seq state, used during snp node initialization */
149#define SRCU_SNP_INIT_SEQ 0x2
150
151/*
152 * Check whether sequence number corresponding to snp node,
153 * is invalid.
154 */
155static inline bool srcu_invl_snp_seq(unsigned long s)
156{
157 return s == SRCU_SNP_INIT_SEQ;
158}
159
160/*
161 * Allocated and initialize SRCU combining tree. Returns @true if
162 * allocation succeeded and @false otherwise.
163 */
164static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags)
165{
166 int cpu;
167 int i;
168 int level = 0;
169 int levelspread[RCU_NUM_LVLS];
170 struct srcu_data *sdp;
171 struct srcu_node *snp;
172 struct srcu_node *snp_first;
173
174 /* Initialize geometry if it has not already been initialized. */
175 rcu_init_geometry();
176 ssp->srcu_sup->node = kcalloc(rcu_num_nodes, sizeof(*ssp->srcu_sup->node), gfp_flags);
177 if (!ssp->srcu_sup->node)
178 return false;
179
180 /* Work out the overall tree geometry. */
181 ssp->srcu_sup->level[0] = &ssp->srcu_sup->node[0];
182 for (i = 1; i < rcu_num_lvls; i++)
183 ssp->srcu_sup->level[i] = ssp->srcu_sup->level[i - 1] + num_rcu_lvl[i - 1];
184 rcu_init_levelspread(levelspread, num_rcu_lvl);
185
186 /* Each pass through this loop initializes one srcu_node structure. */
187 srcu_for_each_node_breadth_first(ssp, snp) {
188 spin_lock_init(&ACCESS_PRIVATE(snp, lock));
189 WARN_ON_ONCE(ARRAY_SIZE(snp->srcu_have_cbs) !=
190 ARRAY_SIZE(snp->srcu_data_have_cbs));
191 for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++) {
192 snp->srcu_have_cbs[i] = SRCU_SNP_INIT_SEQ;
193 snp->srcu_data_have_cbs[i] = 0;
194 }
195 snp->srcu_gp_seq_needed_exp = SRCU_SNP_INIT_SEQ;
196 snp->grplo = -1;
197 snp->grphi = -1;
198 if (snp == &ssp->srcu_sup->node[0]) {
199 /* Root node, special case. */
200 snp->srcu_parent = NULL;
201 continue;
202 }
203
204 /* Non-root node. */
205 if (snp == ssp->srcu_sup->level[level + 1])
206 level++;
207 snp->srcu_parent = ssp->srcu_sup->level[level - 1] +
208 (snp - ssp->srcu_sup->level[level]) /
209 levelspread[level - 1];
210 }
211
212 /*
213 * Initialize the per-CPU srcu_data array, which feeds into the
214 * leaves of the srcu_node tree.
215 */
216 level = rcu_num_lvls - 1;
217 snp_first = ssp->srcu_sup->level[level];
218 for_each_possible_cpu(cpu) {
219 sdp = per_cpu_ptr(ssp->sda, cpu);
220 sdp->mynode = &snp_first[cpu / levelspread[level]];
221 for (snp = sdp->mynode; snp != NULL; snp = snp->srcu_parent) {
222 if (snp->grplo < 0)
223 snp->grplo = cpu;
224 snp->grphi = cpu;
225 }
226 sdp->grpmask = 1UL << (cpu - sdp->mynode->grplo);
227 }
228 smp_store_release(&ssp->srcu_sup->srcu_size_state, SRCU_SIZE_WAIT_BARRIER);
229 return true;
230}
231
232/*
233 * Initialize non-compile-time initialized fields, including the
234 * associated srcu_node and srcu_data structures. The is_static parameter
235 * tells us that ->sda has already been wired up to srcu_data.
236 */
237static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
238{
239 if (!is_static)
240 ssp->srcu_sup = kzalloc(sizeof(*ssp->srcu_sup), GFP_KERNEL);
241 if (!ssp->srcu_sup)
242 return -ENOMEM;
243 if (!is_static)
244 spin_lock_init(&ACCESS_PRIVATE(ssp->srcu_sup, lock));
245 ssp->srcu_sup->srcu_size_state = SRCU_SIZE_SMALL;
246 ssp->srcu_sup->node = NULL;
247 mutex_init(&ssp->srcu_sup->srcu_cb_mutex);
248 mutex_init(&ssp->srcu_sup->srcu_gp_mutex);
249 ssp->srcu_idx = 0;
250 ssp->srcu_sup->srcu_gp_seq = 0;
251 ssp->srcu_sup->srcu_barrier_seq = 0;
252 mutex_init(&ssp->srcu_sup->srcu_barrier_mutex);
253 atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0);
254 INIT_DELAYED_WORK(&ssp->srcu_sup->work, process_srcu);
255 ssp->srcu_sup->sda_is_static = is_static;
256 if (!is_static)
257 ssp->sda = alloc_percpu(struct srcu_data);
258 if (!ssp->sda)
259 goto err_free_sup;
260 init_srcu_struct_data(ssp);
261 ssp->srcu_sup->srcu_gp_seq_needed_exp = 0;
262 ssp->srcu_sup->srcu_last_gp_end = ktime_get_mono_fast_ns();
263 if (READ_ONCE(ssp->srcu_sup->srcu_size_state) == SRCU_SIZE_SMALL && SRCU_SIZING_IS_INIT()) {
264 if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC))
265 goto err_free_sda;
266 WRITE_ONCE(ssp->srcu_sup->srcu_size_state, SRCU_SIZE_BIG);
267 }
268 ssp->srcu_sup->srcu_ssp = ssp;
269 smp_store_release(&ssp->srcu_sup->srcu_gp_seq_needed, 0); /* Init done. */
270 return 0;
271
272err_free_sda:
273 if (!is_static) {
274 free_percpu(ssp->sda);
275 ssp->sda = NULL;
276 }
277err_free_sup:
278 if (!is_static) {
279 kfree(ssp->srcu_sup);
280 ssp->srcu_sup = NULL;
281 }
282 return -ENOMEM;
283}
284
285#ifdef CONFIG_DEBUG_LOCK_ALLOC
286
287int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
288 struct lock_class_key *key)
289{
290 /* Don't re-initialize a lock while it is held. */
291 debug_check_no_locks_freed((void *)ssp, sizeof(*ssp));
292 lockdep_init_map(&ssp->dep_map, name, key, 0);
293 return init_srcu_struct_fields(ssp, false);
294}
295EXPORT_SYMBOL_GPL(__init_srcu_struct);
296
297#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
298
299/**
300 * init_srcu_struct - initialize a sleep-RCU structure
301 * @ssp: structure to initialize.
302 *
303 * Must invoke this on a given srcu_struct before passing that srcu_struct
304 * to any other function. Each srcu_struct represents a separate domain
305 * of SRCU protection.
306 */
307int init_srcu_struct(struct srcu_struct *ssp)
308{
309 return init_srcu_struct_fields(ssp, false);
310}
311EXPORT_SYMBOL_GPL(init_srcu_struct);
312
313#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
314
315/*
316 * Initiate a transition to SRCU_SIZE_BIG with lock held.
317 */
318static void __srcu_transition_to_big(struct srcu_struct *ssp)
319{
320 lockdep_assert_held(&ACCESS_PRIVATE(ssp->srcu_sup, lock));
321 smp_store_release(&ssp->srcu_sup->srcu_size_state, SRCU_SIZE_ALLOC);
322}
323
324/*
325 * Initiate an idempotent transition to SRCU_SIZE_BIG.
326 */
327static void srcu_transition_to_big(struct srcu_struct *ssp)
328{
329 unsigned long flags;
330
331 /* Double-checked locking on ->srcu_size-state. */
332 if (smp_load_acquire(&ssp->srcu_sup->srcu_size_state) != SRCU_SIZE_SMALL)
333 return;
334 spin_lock_irqsave_rcu_node(ssp->srcu_sup, flags);
335 if (smp_load_acquire(&ssp->srcu_sup->srcu_size_state) != SRCU_SIZE_SMALL) {
336 spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags);
337 return;
338 }
339 __srcu_transition_to_big(ssp);
340 spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags);
341}
342
343/*
344 * Check to see if the just-encountered contention event justifies
345 * a transition to SRCU_SIZE_BIG.
346 */
347static void spin_lock_irqsave_check_contention(struct srcu_struct *ssp)
348{
349 unsigned long j;
350
351 if (!SRCU_SIZING_IS_CONTEND() || ssp->srcu_sup->srcu_size_state)
352 return;
353 j = jiffies;
354 if (ssp->srcu_sup->srcu_size_jiffies != j) {
355 ssp->srcu_sup->srcu_size_jiffies = j;
356 ssp->srcu_sup->srcu_n_lock_retries = 0;
357 }
358 if (++ssp->srcu_sup->srcu_n_lock_retries <= small_contention_lim)
359 return;
360 __srcu_transition_to_big(ssp);
361}
362
363/*
364 * Acquire the specified srcu_data structure's ->lock, but check for
365 * excessive contention, which results in initiation of a transition
366 * to SRCU_SIZE_BIG. But only if the srcutree.convert_to_big module
367 * parameter permits this.
368 */
369static void spin_lock_irqsave_sdp_contention(struct srcu_data *sdp, unsigned long *flags)
370{
371 struct srcu_struct *ssp = sdp->ssp;
372
373 if (spin_trylock_irqsave_rcu_node(sdp, *flags))
374 return;
375 spin_lock_irqsave_rcu_node(ssp->srcu_sup, *flags);
376 spin_lock_irqsave_check_contention(ssp);
377 spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, *flags);
378 spin_lock_irqsave_rcu_node(sdp, *flags);
379}
380
381/*
382 * Acquire the specified srcu_struct structure's ->lock, but check for
383 * excessive contention, which results in initiation of a transition
384 * to SRCU_SIZE_BIG. But only if the srcutree.convert_to_big module
385 * parameter permits this.
386 */
387static void spin_lock_irqsave_ssp_contention(struct srcu_struct *ssp, unsigned long *flags)
388{
389 if (spin_trylock_irqsave_rcu_node(ssp->srcu_sup, *flags))
390 return;
391 spin_lock_irqsave_rcu_node(ssp->srcu_sup, *flags);
392 spin_lock_irqsave_check_contention(ssp);
393}
394
395/*
396 * First-use initialization of statically allocated srcu_struct
397 * structure. Wiring up the combining tree is more than can be
398 * done with compile-time initialization, so this check is added
399 * to each update-side SRCU primitive. Use ssp->lock, which -is-
400 * compile-time initialized, to resolve races involving multiple
401 * CPUs trying to garner first-use privileges.
402 */
403static void check_init_srcu_struct(struct srcu_struct *ssp)
404{
405 unsigned long flags;
406
407 /* The smp_load_acquire() pairs with the smp_store_release(). */
408 if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_sup->srcu_gp_seq_needed))) /*^^^*/
409 return; /* Already initialized. */
410 spin_lock_irqsave_rcu_node(ssp->srcu_sup, flags);
411 if (!rcu_seq_state(ssp->srcu_sup->srcu_gp_seq_needed)) {
412 spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags);
413 return;
414 }
415 init_srcu_struct_fields(ssp, true);
416 spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags);
417}
418
419/*
420 * Returns approximate total of the readers' ->srcu_lock_count[] values
421 * for the rank of per-CPU counters specified by idx.
422 */
423static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx)
424{
425 int cpu;
426 unsigned long sum = 0;
427
428 for_each_possible_cpu(cpu) {
429 struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
430
431 sum += atomic_long_read(&cpuc->srcu_lock_count[idx]);
432 }
433 return sum;
434}
435
436/*
437 * Returns approximate total of the readers' ->srcu_unlock_count[] values
438 * for the rank of per-CPU counters specified by idx.
439 */
440static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx)
441{
442 int cpu;
443 unsigned long mask = 0;
444 unsigned long sum = 0;
445
446 for_each_possible_cpu(cpu) {
447 struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
448
449 sum += atomic_long_read(&cpuc->srcu_unlock_count[idx]);
450 if (IS_ENABLED(CONFIG_PROVE_RCU))
451 mask = mask | READ_ONCE(cpuc->srcu_nmi_safety);
452 }
453 WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask >> 1)),
454 "Mixed NMI-safe readers for srcu_struct at %ps.\n", ssp);
455 return sum;
456}
457
458/*
459 * Return true if the number of pre-existing readers is determined to
460 * be zero.
461 */
462static bool srcu_readers_active_idx_check(struct srcu_struct *ssp, int idx)
463{
464 unsigned long unlocks;
465
466 unlocks = srcu_readers_unlock_idx(ssp, idx);
467
468 /*
469 * Make sure that a lock is always counted if the corresponding
470 * unlock is counted. Needs to be a smp_mb() as the read side may
471 * contain a read from a variable that is written to before the
472 * synchronize_srcu() in the write side. In this case smp_mb()s
473 * A and B act like the store buffering pattern.
474 *
475 * This smp_mb() also pairs with smp_mb() C to prevent accesses
476 * after the synchronize_srcu() from being executed before the
477 * grace period ends.
478 */
479 smp_mb(); /* A */
480
481 /*
482 * If the locks are the same as the unlocks, then there must have
483 * been no readers on this index at some point in this function.
484 * But there might be more readers, as a task might have read
485 * the current ->srcu_idx but not yet have incremented its CPU's
486 * ->srcu_lock_count[idx] counter. In fact, it is possible
487 * that most of the tasks have been preempted between fetching
488 * ->srcu_idx and incrementing ->srcu_lock_count[idx]. And there
489 * could be almost (ULONG_MAX / sizeof(struct task_struct)) tasks
490 * in a system whose address space was fully populated with memory.
491 * Call this quantity Nt.
492 *
493 * So suppose that the updater is preempted at this point in the
494 * code for a long time. That now-preempted updater has already
495 * flipped ->srcu_idx (possibly during the preceding grace period),
496 * done an smp_mb() (again, possibly during the preceding grace
497 * period), and summed up the ->srcu_unlock_count[idx] counters.
498 * How many times can a given one of the aforementioned Nt tasks
499 * increment the old ->srcu_idx value's ->srcu_lock_count[idx]
500 * counter, in the absence of nesting?
501 *
502 * It can clearly do so once, given that it has already fetched
503 * the old value of ->srcu_idx and is just about to use that value
504 * to index its increment of ->srcu_lock_count[idx]. But as soon as
505 * it leaves that SRCU read-side critical section, it will increment
506 * ->srcu_unlock_count[idx], which must follow the updater's above
507 * read from that same value. Thus, as soon the reading task does
508 * an smp_mb() and a later fetch from ->srcu_idx, that task will be
509 * guaranteed to get the new index. Except that the increment of
510 * ->srcu_unlock_count[idx] in __srcu_read_unlock() is after the
511 * smp_mb(), and the fetch from ->srcu_idx in __srcu_read_lock()
512 * is before the smp_mb(). Thus, that task might not see the new
513 * value of ->srcu_idx until the -second- __srcu_read_lock(),
514 * which in turn means that this task might well increment
515 * ->srcu_lock_count[idx] for the old value of ->srcu_idx twice,
516 * not just once.
517 *
518 * However, it is important to note that a given smp_mb() takes
519 * effect not just for the task executing it, but also for any
520 * later task running on that same CPU.
521 *
522 * That is, there can be almost Nt + Nc further increments of
523 * ->srcu_lock_count[idx] for the old index, where Nc is the number
524 * of CPUs. But this is OK because the size of the task_struct
525 * structure limits the value of Nt and current systems limit Nc
526 * to a few thousand.
527 *
528 * OK, but what about nesting? This does impose a limit on
529 * nesting of half of the size of the task_struct structure
530 * (measured in bytes), which should be sufficient. A late 2022
531 * TREE01 rcutorture run reported this size to be no less than
532 * 9408 bytes, allowing up to 4704 levels of nesting, which is
533 * comfortably beyond excessive. Especially on 64-bit systems,
534 * which are unlikely to be configured with an address space fully
535 * populated with memory, at least not anytime soon.
536 */
537 return srcu_readers_lock_idx(ssp, idx) == unlocks;
538}
539
540/**
541 * srcu_readers_active - returns true if there are readers. and false
542 * otherwise
543 * @ssp: which srcu_struct to count active readers (holding srcu_read_lock).
544 *
545 * Note that this is not an atomic primitive, and can therefore suffer
546 * severe errors when invoked on an active srcu_struct. That said, it
547 * can be useful as an error check at cleanup time.
548 */
549static bool srcu_readers_active(struct srcu_struct *ssp)
550{
551 int cpu;
552 unsigned long sum = 0;
553
554 for_each_possible_cpu(cpu) {
555 struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
556
557 sum += atomic_long_read(&cpuc->srcu_lock_count[0]);
558 sum += atomic_long_read(&cpuc->srcu_lock_count[1]);
559 sum -= atomic_long_read(&cpuc->srcu_unlock_count[0]);
560 sum -= atomic_long_read(&cpuc->srcu_unlock_count[1]);
561 }
562 return sum;
563}
564
565/*
566 * We use an adaptive strategy for synchronize_srcu() and especially for
567 * synchronize_srcu_expedited(). We spin for a fixed time period
568 * (defined below, boot time configurable) to allow SRCU readers to exit
569 * their read-side critical sections. If there are still some readers
570 * after one jiffy, we repeatedly block for one jiffy time periods.
571 * The blocking time is increased as the grace-period age increases,
572 * with max blocking time capped at 10 jiffies.
573 */
574#define SRCU_DEFAULT_RETRY_CHECK_DELAY 5
575
576static ulong srcu_retry_check_delay = SRCU_DEFAULT_RETRY_CHECK_DELAY;
577module_param(srcu_retry_check_delay, ulong, 0444);
578
579#define SRCU_INTERVAL 1 // Base delay if no expedited GPs pending.
580#define SRCU_MAX_INTERVAL 10 // Maximum incremental delay from slow readers.
581
582#define SRCU_DEFAULT_MAX_NODELAY_PHASE_LO 3UL // Lowmark on default per-GP-phase
583 // no-delay instances.
584#define SRCU_DEFAULT_MAX_NODELAY_PHASE_HI 1000UL // Highmark on default per-GP-phase
585 // no-delay instances.
586
587#define SRCU_UL_CLAMP_LO(val, low) ((val) > (low) ? (val) : (low))
588#define SRCU_UL_CLAMP_HI(val, high) ((val) < (high) ? (val) : (high))
589#define SRCU_UL_CLAMP(val, low, high) SRCU_UL_CLAMP_HI(SRCU_UL_CLAMP_LO((val), (low)), (high))
590// per-GP-phase no-delay instances adjusted to allow non-sleeping poll upto
591// one jiffies time duration. Mult by 2 is done to factor in the srcu_get_delay()
592// called from process_srcu().
593#define SRCU_DEFAULT_MAX_NODELAY_PHASE_ADJUSTED \
594 (2UL * USEC_PER_SEC / HZ / SRCU_DEFAULT_RETRY_CHECK_DELAY)
595
596// Maximum per-GP-phase consecutive no-delay instances.
597#define SRCU_DEFAULT_MAX_NODELAY_PHASE \
598 SRCU_UL_CLAMP(SRCU_DEFAULT_MAX_NODELAY_PHASE_ADJUSTED, \
599 SRCU_DEFAULT_MAX_NODELAY_PHASE_LO, \
600 SRCU_DEFAULT_MAX_NODELAY_PHASE_HI)
601
602static ulong srcu_max_nodelay_phase = SRCU_DEFAULT_MAX_NODELAY_PHASE;
603module_param(srcu_max_nodelay_phase, ulong, 0444);
604
605// Maximum consecutive no-delay instances.
606#define SRCU_DEFAULT_MAX_NODELAY (SRCU_DEFAULT_MAX_NODELAY_PHASE > 100 ? \
607 SRCU_DEFAULT_MAX_NODELAY_PHASE : 100)
608
609static ulong srcu_max_nodelay = SRCU_DEFAULT_MAX_NODELAY;
610module_param(srcu_max_nodelay, ulong, 0444);
611
612/*
613 * Return grace-period delay, zero if there are expedited grace
614 * periods pending, SRCU_INTERVAL otherwise.
615 */
616static unsigned long srcu_get_delay(struct srcu_struct *ssp)
617{
618 unsigned long gpstart;
619 unsigned long j;
620 unsigned long jbase = SRCU_INTERVAL;
621 struct srcu_usage *sup = ssp->srcu_sup;
622
623 if (ULONG_CMP_LT(READ_ONCE(sup->srcu_gp_seq), READ_ONCE(sup->srcu_gp_seq_needed_exp)))
624 jbase = 0;
625 if (rcu_seq_state(READ_ONCE(sup->srcu_gp_seq))) {
626 j = jiffies - 1;
627 gpstart = READ_ONCE(sup->srcu_gp_start);
628 if (time_after(j, gpstart))
629 jbase += j - gpstart;
630 if (!jbase) {
631 WRITE_ONCE(sup->srcu_n_exp_nodelay, READ_ONCE(sup->srcu_n_exp_nodelay) + 1);
632 if (READ_ONCE(sup->srcu_n_exp_nodelay) > srcu_max_nodelay_phase)
633 jbase = 1;
634 }
635 }
636 return jbase > SRCU_MAX_INTERVAL ? SRCU_MAX_INTERVAL : jbase;
637}
638
639/**
640 * cleanup_srcu_struct - deconstruct a sleep-RCU structure
641 * @ssp: structure to clean up.
642 *
643 * Must invoke this after you are finished using a given srcu_struct that
644 * was initialized via init_srcu_struct(), else you leak memory.
645 */
646void cleanup_srcu_struct(struct srcu_struct *ssp)
647{
648 int cpu;
649 struct srcu_usage *sup = ssp->srcu_sup;
650
651 if (WARN_ON(!srcu_get_delay(ssp)))
652 return; /* Just leak it! */
653 if (WARN_ON(srcu_readers_active(ssp)))
654 return; /* Just leak it! */
655 flush_delayed_work(&sup->work);
656 for_each_possible_cpu(cpu) {
657 struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
658
659 del_timer_sync(&sdp->delay_work);
660 flush_work(&sdp->work);
661 if (WARN_ON(rcu_segcblist_n_cbs(&sdp->srcu_cblist)))
662 return; /* Forgot srcu_barrier(), so just leak it! */
663 }
664 if (WARN_ON(rcu_seq_state(READ_ONCE(sup->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
665 WARN_ON(rcu_seq_current(&sup->srcu_gp_seq) != sup->srcu_gp_seq_needed) ||
666 WARN_ON(srcu_readers_active(ssp))) {
667 pr_info("%s: Active srcu_struct %p read state: %d gp state: %lu/%lu\n",
668 __func__, ssp, rcu_seq_state(READ_ONCE(sup->srcu_gp_seq)),
669 rcu_seq_current(&sup->srcu_gp_seq), sup->srcu_gp_seq_needed);
670 return; /* Caller forgot to stop doing call_srcu()? */
671 }
672 kfree(sup->node);
673 sup->node = NULL;
674 sup->srcu_size_state = SRCU_SIZE_SMALL;
675 if (!sup->sda_is_static) {
676 free_percpu(ssp->sda);
677 ssp->sda = NULL;
678 kfree(sup);
679 ssp->srcu_sup = NULL;
680 }
681}
682EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
683
684#ifdef CONFIG_PROVE_RCU
685/*
686 * Check for consistent NMI safety.
687 */
688void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe)
689{
690 int nmi_safe_mask = 1 << nmi_safe;
691 int old_nmi_safe_mask;
692 struct srcu_data *sdp;
693
694 /* NMI-unsafe use in NMI is a bad sign */
695 WARN_ON_ONCE(!nmi_safe && in_nmi());
696 sdp = raw_cpu_ptr(ssp->sda);
697 old_nmi_safe_mask = READ_ONCE(sdp->srcu_nmi_safety);
698 if (!old_nmi_safe_mask) {
699 WRITE_ONCE(sdp->srcu_nmi_safety, nmi_safe_mask);
700 return;
701 }
702 WARN_ONCE(old_nmi_safe_mask != nmi_safe_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_nmi_safe_mask, nmi_safe_mask);
703}
704EXPORT_SYMBOL_GPL(srcu_check_nmi_safety);
705#endif /* CONFIG_PROVE_RCU */
706
707/*
708 * Counts the new reader in the appropriate per-CPU element of the
709 * srcu_struct.
710 * Returns an index that must be passed to the matching srcu_read_unlock().
711 */
712int __srcu_read_lock(struct srcu_struct *ssp)
713{
714 int idx;
715
716 idx = READ_ONCE(ssp->srcu_idx) & 0x1;
717 this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter);
718 smp_mb(); /* B */ /* Avoid leaking the critical section. */
719 return idx;
720}
721EXPORT_SYMBOL_GPL(__srcu_read_lock);
722
723/*
724 * Removes the count for the old reader from the appropriate per-CPU
725 * element of the srcu_struct. Note that this may well be a different
726 * CPU than that which was incremented by the corresponding srcu_read_lock().
727 */
728void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
729{
730 smp_mb(); /* C */ /* Avoid leaking the critical section. */
731 this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter);
732}
733EXPORT_SYMBOL_GPL(__srcu_read_unlock);
734
735#ifdef CONFIG_NEED_SRCU_NMI_SAFE
736
737/*
738 * Counts the new reader in the appropriate per-CPU element of the
739 * srcu_struct, but in an NMI-safe manner using RMW atomics.
740 * Returns an index that must be passed to the matching srcu_read_unlock().
741 */
742int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
743{
744 int idx;
745 struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);
746
747 idx = READ_ONCE(ssp->srcu_idx) & 0x1;
748 atomic_long_inc(&sdp->srcu_lock_count[idx]);
749 smp_mb__after_atomic(); /* B */ /* Avoid leaking the critical section. */
750 return idx;
751}
752EXPORT_SYMBOL_GPL(__srcu_read_lock_nmisafe);
753
754/*
755 * Removes the count for the old reader from the appropriate per-CPU
756 * element of the srcu_struct. Note that this may well be a different
757 * CPU than that which was incremented by the corresponding srcu_read_lock().
758 */
759void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
760{
761 struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);
762
763 smp_mb__before_atomic(); /* C */ /* Avoid leaking the critical section. */
764 atomic_long_inc(&sdp->srcu_unlock_count[idx]);
765}
766EXPORT_SYMBOL_GPL(__srcu_read_unlock_nmisafe);
767
768#endif // CONFIG_NEED_SRCU_NMI_SAFE
769
770/*
771 * Start an SRCU grace period.
772 */
773static void srcu_gp_start(struct srcu_struct *ssp)
774{
775 int state;
776
777 lockdep_assert_held(&ACCESS_PRIVATE(ssp->srcu_sup, lock));
778 WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed));
779 WRITE_ONCE(ssp->srcu_sup->srcu_gp_start, jiffies);
780 WRITE_ONCE(ssp->srcu_sup->srcu_n_exp_nodelay, 0);
781 smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
782 rcu_seq_start(&ssp->srcu_sup->srcu_gp_seq);
783 state = rcu_seq_state(ssp->srcu_sup->srcu_gp_seq);
784 WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
785}
786
787
788static void srcu_delay_timer(struct timer_list *t)
789{
790 struct srcu_data *sdp = container_of(t, struct srcu_data, delay_work);
791
792 queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
793}
794
795static void srcu_queue_delayed_work_on(struct srcu_data *sdp,
796 unsigned long delay)
797{
798 if (!delay) {
799 queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
800 return;
801 }
802
803 timer_reduce(&sdp->delay_work, jiffies + delay);
804}
805
806/*
807 * Schedule callback invocation for the specified srcu_data structure,
808 * if possible, on the corresponding CPU.
809 */
810static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay)
811{
812 srcu_queue_delayed_work_on(sdp, delay);
813}
814
815/*
816 * Schedule callback invocation for all srcu_data structures associated
817 * with the specified srcu_node structure that have callbacks for the
818 * just-completed grace period, the one corresponding to idx. If possible,
819 * schedule this invocation on the corresponding CPUs.
820 */
821static void srcu_schedule_cbs_snp(struct srcu_struct *ssp, struct srcu_node *snp,
822 unsigned long mask, unsigned long delay)
823{
824 int cpu;
825
826 for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
827 if (!(mask & (1UL << (cpu - snp->grplo))))
828 continue;
829 srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, cpu), delay);
830 }
831}
832
833/*
834 * Note the end of an SRCU grace period. Initiates callback invocation
835 * and starts a new grace period if needed.
836 *
837 * The ->srcu_cb_mutex acquisition does not protect any data, but
838 * instead prevents more than one grace period from starting while we
839 * are initiating callback invocation. This allows the ->srcu_have_cbs[]
840 * array to have a finite number of elements.
841 */
842static void srcu_gp_end(struct srcu_struct *ssp)
843{
844 unsigned long cbdelay = 1;
845 bool cbs;
846 bool last_lvl;
847 int cpu;
848 unsigned long flags;
849 unsigned long gpseq;
850 int idx;
851 unsigned long mask;
852 struct srcu_data *sdp;
853 unsigned long sgsne;
854 struct srcu_node *snp;
855 int ss_state;
856 struct srcu_usage *sup = ssp->srcu_sup;
857
858 /* Prevent more than one additional grace period. */
859 mutex_lock(&sup->srcu_cb_mutex);
860
861 /* End the current grace period. */
862 spin_lock_irq_rcu_node(sup);
863 idx = rcu_seq_state(sup->srcu_gp_seq);
864 WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);
865 if (ULONG_CMP_LT(READ_ONCE(sup->srcu_gp_seq), READ_ONCE(sup->srcu_gp_seq_needed_exp)))
866 cbdelay = 0;
867
868 WRITE_ONCE(sup->srcu_last_gp_end, ktime_get_mono_fast_ns());
869 rcu_seq_end(&sup->srcu_gp_seq);
870 gpseq = rcu_seq_current(&sup->srcu_gp_seq);
871 if (ULONG_CMP_LT(sup->srcu_gp_seq_needed_exp, gpseq))
872 WRITE_ONCE(sup->srcu_gp_seq_needed_exp, gpseq);
873 spin_unlock_irq_rcu_node(sup);
874 mutex_unlock(&sup->srcu_gp_mutex);
875 /* A new grace period can start at this point. But only one. */
876
877 /* Initiate callback invocation as needed. */
878 ss_state = smp_load_acquire(&sup->srcu_size_state);
879 if (ss_state < SRCU_SIZE_WAIT_BARRIER) {
880 srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, get_boot_cpu_id()),
881 cbdelay);
882 } else {
883 idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs);
884 srcu_for_each_node_breadth_first(ssp, snp) {
885 spin_lock_irq_rcu_node(snp);
886 cbs = false;
887 last_lvl = snp >= sup->level[rcu_num_lvls - 1];
888 if (last_lvl)
889 cbs = ss_state < SRCU_SIZE_BIG || snp->srcu_have_cbs[idx] == gpseq;
890 snp->srcu_have_cbs[idx] = gpseq;
891 rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
892 sgsne = snp->srcu_gp_seq_needed_exp;
893 if (srcu_invl_snp_seq(sgsne) || ULONG_CMP_LT(sgsne, gpseq))
894 WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq);
895 if (ss_state < SRCU_SIZE_BIG)
896 mask = ~0;
897 else
898 mask = snp->srcu_data_have_cbs[idx];
899 snp->srcu_data_have_cbs[idx] = 0;
900 spin_unlock_irq_rcu_node(snp);
901 if (cbs)
902 srcu_schedule_cbs_snp(ssp, snp, mask, cbdelay);
903 }
904 }
905
906 /* Occasionally prevent srcu_data counter wrap. */
907 if (!(gpseq & counter_wrap_check))
908 for_each_possible_cpu(cpu) {
909 sdp = per_cpu_ptr(ssp->sda, cpu);
910 spin_lock_irqsave_rcu_node(sdp, flags);
911 if (ULONG_CMP_GE(gpseq, sdp->srcu_gp_seq_needed + 100))
912 sdp->srcu_gp_seq_needed = gpseq;
913 if (ULONG_CMP_GE(gpseq, sdp->srcu_gp_seq_needed_exp + 100))
914 sdp->srcu_gp_seq_needed_exp = gpseq;
915 spin_unlock_irqrestore_rcu_node(sdp, flags);
916 }
917
918 /* Callback initiation done, allow grace periods after next. */
919 mutex_unlock(&sup->srcu_cb_mutex);
920
921 /* Start a new grace period if needed. */
922 spin_lock_irq_rcu_node(sup);
923 gpseq = rcu_seq_current(&sup->srcu_gp_seq);
924 if (!rcu_seq_state(gpseq) &&
925 ULONG_CMP_LT(gpseq, sup->srcu_gp_seq_needed)) {
926 srcu_gp_start(ssp);
927 spin_unlock_irq_rcu_node(sup);
928 srcu_reschedule(ssp, 0);
929 } else {
930 spin_unlock_irq_rcu_node(sup);
931 }
932
933 /* Transition to big if needed. */
934 if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) {
935 if (ss_state == SRCU_SIZE_ALLOC)
936 init_srcu_struct_nodes(ssp, GFP_KERNEL);
937 else
938 smp_store_release(&sup->srcu_size_state, ss_state + 1);
939 }
940}
941
942/*
943 * Funnel-locking scheme to scalably mediate many concurrent expedited
944 * grace-period requests. This function is invoked for the first known
945 * expedited request for a grace period that has already been requested,
946 * but without expediting. To start a completely new grace period,
947 * whether expedited or not, use srcu_funnel_gp_start() instead.
948 */
949static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp,
950 unsigned long s)
951{
952 unsigned long flags;
953 unsigned long sgsne;
954
955 if (snp)
956 for (; snp != NULL; snp = snp->srcu_parent) {
957 sgsne = READ_ONCE(snp->srcu_gp_seq_needed_exp);
958 if (WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_sup->srcu_gp_seq, s)) ||
959 (!srcu_invl_snp_seq(sgsne) && ULONG_CMP_GE(sgsne, s)))
960 return;
961 spin_lock_irqsave_rcu_node(snp, flags);
962 sgsne = snp->srcu_gp_seq_needed_exp;
963 if (!srcu_invl_snp_seq(sgsne) && ULONG_CMP_GE(sgsne, s)) {
964 spin_unlock_irqrestore_rcu_node(snp, flags);
965 return;
966 }
967 WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
968 spin_unlock_irqrestore_rcu_node(snp, flags);
969 }
970 spin_lock_irqsave_ssp_contention(ssp, &flags);
971 if (ULONG_CMP_LT(ssp->srcu_sup->srcu_gp_seq_needed_exp, s))
972 WRITE_ONCE(ssp->srcu_sup->srcu_gp_seq_needed_exp, s);
973 spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags);
974}
975
976/*
977 * Funnel-locking scheme to scalably mediate many concurrent grace-period
978 * requests. The winner has to do the work of actually starting grace
979 * period s. Losers must either ensure that their desired grace-period
980 * number is recorded on at least their leaf srcu_node structure, or they
981 * must take steps to invoke their own callbacks.
982 *
983 * Note that this function also does the work of srcu_funnel_exp_start(),
984 * in some cases by directly invoking it.
985 *
986 * The srcu read lock should be hold around this function. And s is a seq snap
987 * after holding that lock.
988 */
989static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
990 unsigned long s, bool do_norm)
991{
992 unsigned long flags;
993 int idx = rcu_seq_ctr(s) % ARRAY_SIZE(sdp->mynode->srcu_have_cbs);
994 unsigned long sgsne;
995 struct srcu_node *snp;
996 struct srcu_node *snp_leaf;
997 unsigned long snp_seq;
998 struct srcu_usage *sup = ssp->srcu_sup;
999
1000 /* Ensure that snp node tree is fully initialized before traversing it */
1001 if (smp_load_acquire(&sup->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
1002 snp_leaf = NULL;
1003 else
1004 snp_leaf = sdp->mynode;
1005
1006 if (snp_leaf)
1007 /* Each pass through the loop does one level of the srcu_node tree. */
1008 for (snp = snp_leaf; snp != NULL; snp = snp->srcu_parent) {
1009 if (WARN_ON_ONCE(rcu_seq_done(&sup->srcu_gp_seq, s)) && snp != snp_leaf)
1010 return; /* GP already done and CBs recorded. */
1011 spin_lock_irqsave_rcu_node(snp, flags);
1012 snp_seq = snp->srcu_have_cbs[idx];
1013 if (!srcu_invl_snp_seq(snp_seq) && ULONG_CMP_GE(snp_seq, s)) {
1014 if (snp == snp_leaf && snp_seq == s)
1015 snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
1016 spin_unlock_irqrestore_rcu_node(snp, flags);
1017 if (snp == snp_leaf && snp_seq != s) {
1018 srcu_schedule_cbs_sdp(sdp, do_norm ? SRCU_INTERVAL : 0);
1019 return;
1020 }
1021 if (!do_norm)
1022 srcu_funnel_exp_start(ssp, snp, s);
1023 return;
1024 }
1025 snp->srcu_have_cbs[idx] = s;
1026 if (snp == snp_leaf)
1027 snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
1028 sgsne = snp->srcu_gp_seq_needed_exp;
1029 if (!do_norm && (srcu_invl_snp_seq(sgsne) || ULONG_CMP_LT(sgsne, s)))
1030 WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
1031 spin_unlock_irqrestore_rcu_node(snp, flags);
1032 }
1033
1034 /* Top of tree, must ensure the grace period will be started. */
1035 spin_lock_irqsave_ssp_contention(ssp, &flags);
1036 if (ULONG_CMP_LT(sup->srcu_gp_seq_needed, s)) {
1037 /*
1038 * Record need for grace period s. Pair with load
1039 * acquire setting up for initialization.
1040 */
1041 smp_store_release(&sup->srcu_gp_seq_needed, s); /*^^^*/
1042 }
1043 if (!do_norm && ULONG_CMP_LT(sup->srcu_gp_seq_needed_exp, s))
1044 WRITE_ONCE(sup->srcu_gp_seq_needed_exp, s);
1045
1046 /* If grace period not already in progress, start it. */
1047 if (!WARN_ON_ONCE(rcu_seq_done(&sup->srcu_gp_seq, s)) &&
1048 rcu_seq_state(sup->srcu_gp_seq) == SRCU_STATE_IDLE) {
1049 WARN_ON_ONCE(ULONG_CMP_GE(sup->srcu_gp_seq, sup->srcu_gp_seq_needed));
1050 srcu_gp_start(ssp);
1051
1052 // And how can that list_add() in the "else" clause
1053 // possibly be safe for concurrent execution? Well,
1054 // it isn't. And it does not have to be. After all, it
1055 // can only be executed during early boot when there is only
1056 // the one boot CPU running with interrupts still disabled.
1057 if (likely(srcu_init_done))
1058 queue_delayed_work(rcu_gp_wq, &sup->work,
1059 !!srcu_get_delay(ssp));
1060 else if (list_empty(&sup->work.work.entry))
1061 list_add(&sup->work.work.entry, &srcu_boot_list);
1062 }
1063 spin_unlock_irqrestore_rcu_node(sup, flags);
1064}
1065
1066/*
1067 * Wait until all readers counted by array index idx complete, but
1068 * loop an additional time if there is an expedited grace period pending.
1069 * The caller must ensure that ->srcu_idx is not changed while checking.
1070 */
1071static bool try_check_zero(struct srcu_struct *ssp, int idx, int trycount)
1072{
1073 unsigned long curdelay;
1074
1075 curdelay = !srcu_get_delay(ssp);
1076
1077 for (;;) {
1078 if (srcu_readers_active_idx_check(ssp, idx))
1079 return true;
1080 if ((--trycount + curdelay) <= 0)
1081 return false;
1082 udelay(srcu_retry_check_delay);
1083 }
1084}
1085
1086/*
1087 * Increment the ->srcu_idx counter so that future SRCU readers will
1088 * use the other rank of the ->srcu_(un)lock_count[] arrays. This allows
1089 * us to wait for pre-existing readers in a starvation-free manner.
1090 */
1091static void srcu_flip(struct srcu_struct *ssp)
1092{
1093 /*
1094 * Because the flip of ->srcu_idx is executed only if the
1095 * preceding call to srcu_readers_active_idx_check() found that
1096 * the ->srcu_unlock_count[] and ->srcu_lock_count[] sums matched
1097 * and because that summing uses atomic_long_read(), there is
1098 * ordering due to a control dependency between that summing and
1099 * the WRITE_ONCE() in this call to srcu_flip(). This ordering
1100 * ensures that if this updater saw a given reader's increment from
1101 * __srcu_read_lock(), that reader was using a value of ->srcu_idx
1102 * from before the previous call to srcu_flip(), which should be
1103 * quite rare. This ordering thus helps forward progress because
1104 * the grace period could otherwise be delayed by additional
1105 * calls to __srcu_read_lock() using that old (soon to be new)
1106 * value of ->srcu_idx.
1107 *
1108 * This sum-equality check and ordering also ensures that if
1109 * a given call to __srcu_read_lock() uses the new value of
1110 * ->srcu_idx, this updater's earlier scans cannot have seen
1111 * that reader's increments, which is all to the good, because
1112 * this grace period need not wait on that reader. After all,
1113 * if those earlier scans had seen that reader, there would have
1114 * been a sum mismatch and this code would not be reached.
1115 *
1116 * This means that the following smp_mb() is redundant, but
1117 * it stays until either (1) Compilers learn about this sort of
1118 * control dependency or (2) Some production workload running on
1119 * a production system is unduly delayed by this slowpath smp_mb().
1120 */
1121 smp_mb(); /* E */ /* Pairs with B and C. */
1122
1123 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); // Flip the counter.
1124
1125 /*
1126 * Ensure that if the updater misses an __srcu_read_unlock()
1127 * increment, that task's __srcu_read_lock() following its next
1128 * __srcu_read_lock() or __srcu_read_unlock() will see the above
1129 * counter update. Note that both this memory barrier and the
1130 * one in srcu_readers_active_idx_check() provide the guarantee
1131 * for __srcu_read_lock().
1132 */
1133 smp_mb(); /* D */ /* Pairs with C. */
1134}
1135
1136/*
1137 * If SRCU is likely idle, return true, otherwise return false.
1138 *
1139 * Note that it is OK for several current from-idle requests for a new
1140 * grace period from idle to specify expediting because they will all end
1141 * up requesting the same grace period anyhow. So no loss.
1142 *
1143 * Note also that if any CPU (including the current one) is still invoking
1144 * callbacks, this function will nevertheless say "idle". This is not
1145 * ideal, but the overhead of checking all CPUs' callback lists is even
1146 * less ideal, especially on large systems. Furthermore, the wakeup
1147 * can happen before the callback is fully removed, so we have no choice
1148 * but to accept this type of error.
1149 *
1150 * This function is also subject to counter-wrap errors, but let's face
1151 * it, if this function was preempted for enough time for the counters
1152 * to wrap, it really doesn't matter whether or not we expedite the grace
1153 * period. The extra overhead of a needlessly expedited grace period is
1154 * negligible when amortized over that time period, and the extra latency
1155 * of a needlessly non-expedited grace period is similarly negligible.
1156 */
1157static bool srcu_might_be_idle(struct srcu_struct *ssp)
1158{
1159 unsigned long curseq;
1160 unsigned long flags;
1161 struct srcu_data *sdp;
1162 unsigned long t;
1163 unsigned long tlast;
1164
1165 check_init_srcu_struct(ssp);
1166 /* If the local srcu_data structure has callbacks, not idle. */
1167 sdp = raw_cpu_ptr(ssp->sda);
1168 spin_lock_irqsave_rcu_node(sdp, flags);
1169 if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) {
1170 spin_unlock_irqrestore_rcu_node(sdp, flags);
1171 return false; /* Callbacks already present, so not idle. */
1172 }
1173 spin_unlock_irqrestore_rcu_node(sdp, flags);
1174
1175 /*
1176 * No local callbacks, so probabilistically probe global state.
1177 * Exact information would require acquiring locks, which would
1178 * kill scalability, hence the probabilistic nature of the probe.
1179 */
1180
1181 /* First, see if enough time has passed since the last GP. */
1182 t = ktime_get_mono_fast_ns();
1183 tlast = READ_ONCE(ssp->srcu_sup->srcu_last_gp_end);
1184 if (exp_holdoff == 0 ||
1185 time_in_range_open(t, tlast, tlast + exp_holdoff))
1186 return false; /* Too soon after last GP. */
1187
1188 /* Next, check for probable idleness. */
1189 curseq = rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq);
1190 smp_mb(); /* Order ->srcu_gp_seq with ->srcu_gp_seq_needed. */
1191 if (ULONG_CMP_LT(curseq, READ_ONCE(ssp->srcu_sup->srcu_gp_seq_needed)))
1192 return false; /* Grace period in progress, so not idle. */
1193 smp_mb(); /* Order ->srcu_gp_seq with prior access. */
1194 if (curseq != rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq))
1195 return false; /* GP # changed, so not idle. */
1196 return true; /* With reasonable probability, idle! */
1197}
1198
1199/*
1200 * SRCU callback function to leak a callback.
1201 */
1202static void srcu_leak_callback(struct rcu_head *rhp)
1203{
1204}
1205
1206/*
1207 * Start an SRCU grace period, and also queue the callback if non-NULL.
1208 */
1209static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
1210 struct rcu_head *rhp, bool do_norm)
1211{
1212 unsigned long flags;
1213 int idx;
1214 bool needexp = false;
1215 bool needgp = false;
1216 unsigned long s;
1217 struct srcu_data *sdp;
1218 struct srcu_node *sdp_mynode;
1219 int ss_state;
1220
1221 check_init_srcu_struct(ssp);
1222 /*
1223 * While starting a new grace period, make sure we are in an
1224 * SRCU read-side critical section so that the grace-period
1225 * sequence number cannot wrap around in the meantime.
1226 */
1227 idx = __srcu_read_lock_nmisafe(ssp);
1228 ss_state = smp_load_acquire(&ssp->srcu_sup->srcu_size_state);
1229 if (ss_state < SRCU_SIZE_WAIT_CALL)
1230 sdp = per_cpu_ptr(ssp->sda, get_boot_cpu_id());
1231 else
1232 sdp = raw_cpu_ptr(ssp->sda);
1233 spin_lock_irqsave_sdp_contention(sdp, &flags);
1234 if (rhp)
1235 rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
1236 /*
1237 * It's crucial to capture the snapshot 's' for acceleration before
1238 * reading the current gp_seq that is used for advancing. This is
1239 * essential because if the acceleration snapshot is taken after a
1240 * failed advancement attempt, there's a risk that a grace period may
1241 * conclude and a new one may start in the interim. If the snapshot is
1242 * captured after this sequence of events, the acceleration snapshot 's'
1243 * could be excessively advanced, leading to acceleration failure.
1244 * In such a scenario, an 'acceleration leak' can occur, where new
1245 * callbacks become indefinitely stuck in the RCU_NEXT_TAIL segment.
1246 * Also note that encountering advancing failures is a normal
1247 * occurrence when the grace period for RCU_WAIT_TAIL is in progress.
1248 *
1249 * To see this, consider the following events which occur if
1250 * rcu_seq_snap() were to be called after advance:
1251 *
1252 * 1) The RCU_WAIT_TAIL segment has callbacks (gp_num = X + 4) and the
1253 * RCU_NEXT_READY_TAIL also has callbacks (gp_num = X + 8).
1254 *
1255 * 2) The grace period for RCU_WAIT_TAIL is seen as started but not
1256 * completed so rcu_seq_current() returns X + SRCU_STATE_SCAN1.
1257 *
1258 * 3) This value is passed to rcu_segcblist_advance() which can't move
1259 * any segment forward and fails.
1260 *
1261 * 4) srcu_gp_start_if_needed() still proceeds with callback acceleration.
1262 * But then the call to rcu_seq_snap() observes the grace period for the
1263 * RCU_WAIT_TAIL segment as completed and the subsequent one for the
1264 * RCU_NEXT_READY_TAIL segment as started (ie: X + 4 + SRCU_STATE_SCAN1)
1265 * so it returns a snapshot of the next grace period, which is X + 12.
1266 *
1267 * 5) The value of X + 12 is passed to rcu_segcblist_accelerate() but the
1268 * freshly enqueued callback in RCU_NEXT_TAIL can't move to
1269 * RCU_NEXT_READY_TAIL which already has callbacks for a previous grace
1270 * period (gp_num = X + 8). So acceleration fails.
1271 */
1272 s = rcu_seq_snap(&ssp->srcu_sup->srcu_gp_seq);
1273 if (rhp) {
1274 rcu_segcblist_advance(&sdp->srcu_cblist,
1275 rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
1276 /*
1277 * Acceleration can never fail because the base current gp_seq
1278 * used for acceleration is <= the value of gp_seq used for
1279 * advancing. This means that RCU_NEXT_TAIL segment will
1280 * always be able to be emptied by the acceleration into the
1281 * RCU_NEXT_READY_TAIL or RCU_WAIT_TAIL segments.
1282 */
1283 WARN_ON_ONCE(!rcu_segcblist_accelerate(&sdp->srcu_cblist, s));
1284 }
1285 if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
1286 sdp->srcu_gp_seq_needed = s;
1287 needgp = true;
1288 }
1289 if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
1290 sdp->srcu_gp_seq_needed_exp = s;
1291 needexp = true;
1292 }
1293 spin_unlock_irqrestore_rcu_node(sdp, flags);
1294
1295 /* Ensure that snp node tree is fully initialized before traversing it */
1296 if (ss_state < SRCU_SIZE_WAIT_BARRIER)
1297 sdp_mynode = NULL;
1298 else
1299 sdp_mynode = sdp->mynode;
1300
1301 if (needgp)
1302 srcu_funnel_gp_start(ssp, sdp, s, do_norm);
1303 else if (needexp)
1304 srcu_funnel_exp_start(ssp, sdp_mynode, s);
1305 __srcu_read_unlock_nmisafe(ssp, idx);
1306 return s;
1307}
1308
1309/*
1310 * Enqueue an SRCU callback on the srcu_data structure associated with
1311 * the current CPU and the specified srcu_struct structure, initiating
1312 * grace-period processing if it is not already running.
1313 *
1314 * Note that all CPUs must agree that the grace period extended beyond
1315 * all pre-existing SRCU read-side critical section. On systems with
1316 * more than one CPU, this means that when "func()" is invoked, each CPU
1317 * is guaranteed to have executed a full memory barrier since the end of
1318 * its last corresponding SRCU read-side critical section whose beginning
1319 * preceded the call to call_srcu(). It also means that each CPU executing
1320 * an SRCU read-side critical section that continues beyond the start of
1321 * "func()" must have executed a memory barrier after the call_srcu()
1322 * but before the beginning of that SRCU read-side critical section.
1323 * Note that these guarantees include CPUs that are offline, idle, or
1324 * executing in user mode, as well as CPUs that are executing in the kernel.
1325 *
1326 * Furthermore, if CPU A invoked call_srcu() and CPU B invoked the
1327 * resulting SRCU callback function "func()", then both CPU A and CPU
1328 * B are guaranteed to execute a full memory barrier during the time
1329 * interval between the call to call_srcu() and the invocation of "func()".
1330 * This guarantee applies even if CPU A and CPU B are the same CPU (but
1331 * again only if the system has more than one CPU).
1332 *
1333 * Of course, these guarantees apply only for invocations of call_srcu(),
1334 * srcu_read_lock(), and srcu_read_unlock() that are all passed the same
1335 * srcu_struct structure.
1336 */
1337static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
1338 rcu_callback_t func, bool do_norm)
1339{
1340 if (debug_rcu_head_queue(rhp)) {
1341 /* Probable double call_srcu(), so leak the callback. */
1342 WRITE_ONCE(rhp->func, srcu_leak_callback);
1343 WARN_ONCE(1, "call_srcu(): Leaked duplicate callback\n");
1344 return;
1345 }
1346 rhp->func = func;
1347 (void)srcu_gp_start_if_needed(ssp, rhp, do_norm);
1348}
1349
1350/**
1351 * call_srcu() - Queue a callback for invocation after an SRCU grace period
1352 * @ssp: srcu_struct in queue the callback
1353 * @rhp: structure to be used for queueing the SRCU callback.
1354 * @func: function to be invoked after the SRCU grace period
1355 *
1356 * The callback function will be invoked some time after a full SRCU
1357 * grace period elapses, in other words after all pre-existing SRCU
1358 * read-side critical sections have completed. However, the callback
1359 * function might well execute concurrently with other SRCU read-side
1360 * critical sections that started after call_srcu() was invoked. SRCU
1361 * read-side critical sections are delimited by srcu_read_lock() and
1362 * srcu_read_unlock(), and may be nested.
1363 *
1364 * The callback will be invoked from process context, but must nevertheless
1365 * be fast and must not block.
1366 */
1367void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
1368 rcu_callback_t func)
1369{
1370 __call_srcu(ssp, rhp, func, true);
1371}
1372EXPORT_SYMBOL_GPL(call_srcu);
1373
1374/*
1375 * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
1376 */
1377static void __synchronize_srcu(struct srcu_struct *ssp, bool do_norm)
1378{
1379 struct rcu_synchronize rcu;
1380
1381 srcu_lock_sync(&ssp->dep_map);
1382
1383 RCU_LOCKDEP_WARN(lockdep_is_held(ssp) ||
1384 lock_is_held(&rcu_bh_lock_map) ||
1385 lock_is_held(&rcu_lock_map) ||
1386 lock_is_held(&rcu_sched_lock_map),
1387 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
1388
1389 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
1390 return;
1391 might_sleep();
1392 check_init_srcu_struct(ssp);
1393 init_completion(&rcu.completion);
1394 init_rcu_head_on_stack(&rcu.head);
1395 __call_srcu(ssp, &rcu.head, wakeme_after_rcu, do_norm);
1396 wait_for_completion(&rcu.completion);
1397 destroy_rcu_head_on_stack(&rcu.head);
1398
1399 /*
1400 * Make sure that later code is ordered after the SRCU grace
1401 * period. This pairs with the spin_lock_irq_rcu_node()
1402 * in srcu_invoke_callbacks(). Unlike Tree RCU, this is needed
1403 * because the current CPU might have been totally uninvolved with
1404 * (and thus unordered against) that grace period.
1405 */
1406 smp_mb();
1407}
1408
1409/**
1410 * synchronize_srcu_expedited - Brute-force SRCU grace period
1411 * @ssp: srcu_struct with which to synchronize.
1412 *
1413 * Wait for an SRCU grace period to elapse, but be more aggressive about
1414 * spinning rather than blocking when waiting.
1415 *
1416 * Note that synchronize_srcu_expedited() has the same deadlock and
1417 * memory-ordering properties as does synchronize_srcu().
1418 */
1419void synchronize_srcu_expedited(struct srcu_struct *ssp)
1420{
1421 __synchronize_srcu(ssp, rcu_gp_is_normal());
1422}
1423EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
1424
1425/**
1426 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
1427 * @ssp: srcu_struct with which to synchronize.
1428 *
1429 * Wait for the count to drain to zero of both indexes. To avoid the
1430 * possible starvation of synchronize_srcu(), it waits for the count of
1431 * the index=((->srcu_idx & 1) ^ 1) to drain to zero at first,
1432 * and then flip the srcu_idx and wait for the count of the other index.
1433 *
1434 * Can block; must be called from process context.
1435 *
1436 * Note that it is illegal to call synchronize_srcu() from the corresponding
1437 * SRCU read-side critical section; doing so will result in deadlock.
1438 * However, it is perfectly legal to call synchronize_srcu() on one
1439 * srcu_struct from some other srcu_struct's read-side critical section,
1440 * as long as the resulting graph of srcu_structs is acyclic.
1441 *
1442 * There are memory-ordering constraints implied by synchronize_srcu().
1443 * On systems with more than one CPU, when synchronize_srcu() returns,
1444 * each CPU is guaranteed to have executed a full memory barrier since
1445 * the end of its last corresponding SRCU read-side critical section
1446 * whose beginning preceded the call to synchronize_srcu(). In addition,
1447 * each CPU having an SRCU read-side critical section that extends beyond
1448 * the return from synchronize_srcu() is guaranteed to have executed a
1449 * full memory barrier after the beginning of synchronize_srcu() and before
1450 * the beginning of that SRCU read-side critical section. Note that these
1451 * guarantees include CPUs that are offline, idle, or executing in user mode,
1452 * as well as CPUs that are executing in the kernel.
1453 *
1454 * Furthermore, if CPU A invoked synchronize_srcu(), which returned
1455 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
1456 * to have executed a full memory barrier during the execution of
1457 * synchronize_srcu(). This guarantee applies even if CPU A and CPU B
1458 * are the same CPU, but again only if the system has more than one CPU.
1459 *
1460 * Of course, these memory-ordering guarantees apply only when
1461 * synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are
1462 * passed the same srcu_struct structure.
1463 *
1464 * Implementation of these memory-ordering guarantees is similar to
1465 * that of synchronize_rcu().
1466 *
1467 * If SRCU is likely idle, expedite the first request. This semantic
1468 * was provided by Classic SRCU, and is relied upon by its users, so TREE
1469 * SRCU must also provide it. Note that detecting idleness is heuristic
1470 * and subject to both false positives and negatives.
1471 */
1472void synchronize_srcu(struct srcu_struct *ssp)
1473{
1474 if (srcu_might_be_idle(ssp) || rcu_gp_is_expedited())
1475 synchronize_srcu_expedited(ssp);
1476 else
1477 __synchronize_srcu(ssp, true);
1478}
1479EXPORT_SYMBOL_GPL(synchronize_srcu);
1480
1481/**
1482 * get_state_synchronize_srcu - Provide an end-of-grace-period cookie
1483 * @ssp: srcu_struct to provide cookie for.
1484 *
1485 * This function returns a cookie that can be passed to
1486 * poll_state_synchronize_srcu(), which will return true if a full grace
1487 * period has elapsed in the meantime. It is the caller's responsibility
1488 * to make sure that grace period happens, for example, by invoking
1489 * call_srcu() after return from get_state_synchronize_srcu().
1490 */
1491unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
1492{
1493 // Any prior manipulation of SRCU-protected data must happen
1494 // before the load from ->srcu_gp_seq.
1495 smp_mb();
1496 return rcu_seq_snap(&ssp->srcu_sup->srcu_gp_seq);
1497}
1498EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
1499
1500/**
1501 * start_poll_synchronize_srcu - Provide cookie and start grace period
1502 * @ssp: srcu_struct to provide cookie for.
1503 *
1504 * This function returns a cookie that can be passed to
1505 * poll_state_synchronize_srcu(), which will return true if a full grace
1506 * period has elapsed in the meantime. Unlike get_state_synchronize_srcu(),
1507 * this function also ensures that any needed SRCU grace period will be
1508 * started. This convenience does come at a cost in terms of CPU overhead.
1509 */
1510unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
1511{
1512 return srcu_gp_start_if_needed(ssp, NULL, true);
1513}
1514EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
1515
1516/**
1517 * poll_state_synchronize_srcu - Has cookie's grace period ended?
1518 * @ssp: srcu_struct to provide cookie for.
1519 * @cookie: Return value from get_state_synchronize_srcu() or start_poll_synchronize_srcu().
1520 *
1521 * This function takes the cookie that was returned from either
1522 * get_state_synchronize_srcu() or start_poll_synchronize_srcu(), and
1523 * returns @true if an SRCU grace period elapsed since the time that the
1524 * cookie was created.
1525 *
1526 * Because cookies are finite in size, wrapping/overflow is possible.
1527 * This is more pronounced on 32-bit systems where cookies are 32 bits,
1528 * where in theory wrapping could happen in about 14 hours assuming
1529 * 25-microsecond expedited SRCU grace periods. However, a more likely
1530 * overflow lower bound is on the order of 24 days in the case of
1531 * one-millisecond SRCU grace periods. Of course, wrapping in a 64-bit
1532 * system requires geologic timespans, as in more than seven million years
1533 * even for expedited SRCU grace periods.
1534 *
1535 * Wrapping/overflow is much more of an issue for CONFIG_SMP=n systems
1536 * that also have CONFIG_PREEMPTION=n, which selects Tiny SRCU. This uses
1537 * a 16-bit cookie, which rcutorture routinely wraps in a matter of a
1538 * few minutes. If this proves to be a problem, this counter will be
1539 * expanded to the same size as for Tree SRCU.
1540 */
1541bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
1542{
1543 if (!rcu_seq_done(&ssp->srcu_sup->srcu_gp_seq, cookie))
1544 return false;
1545 // Ensure that the end of the SRCU grace period happens before
1546 // any subsequent code that the caller might execute.
1547 smp_mb(); // ^^^
1548 return true;
1549}
1550EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
1551
1552/*
1553 * Callback function for srcu_barrier() use.
1554 */
1555static void srcu_barrier_cb(struct rcu_head *rhp)
1556{
1557 struct srcu_data *sdp;
1558 struct srcu_struct *ssp;
1559
1560 sdp = container_of(rhp, struct srcu_data, srcu_barrier_head);
1561 ssp = sdp->ssp;
1562 if (atomic_dec_and_test(&ssp->srcu_sup->srcu_barrier_cpu_cnt))
1563 complete(&ssp->srcu_sup->srcu_barrier_completion);
1564}
1565
1566/*
1567 * Enqueue an srcu_barrier() callback on the specified srcu_data
1568 * structure's ->cblist. but only if that ->cblist already has at least one
1569 * callback enqueued. Note that if a CPU already has callbacks enqueue,
1570 * it must have already registered the need for a future grace period,
1571 * so all we need do is enqueue a callback that will use the same grace
1572 * period as the last callback already in the queue.
1573 */
1574static void srcu_barrier_one_cpu(struct srcu_struct *ssp, struct srcu_data *sdp)
1575{
1576 spin_lock_irq_rcu_node(sdp);
1577 atomic_inc(&ssp->srcu_sup->srcu_barrier_cpu_cnt);
1578 sdp->srcu_barrier_head.func = srcu_barrier_cb;
1579 debug_rcu_head_queue(&sdp->srcu_barrier_head);
1580 if (!rcu_segcblist_entrain(&sdp->srcu_cblist,
1581 &sdp->srcu_barrier_head)) {
1582 debug_rcu_head_unqueue(&sdp->srcu_barrier_head);
1583 atomic_dec(&ssp->srcu_sup->srcu_barrier_cpu_cnt);
1584 }
1585 spin_unlock_irq_rcu_node(sdp);
1586}
1587
1588/**
1589 * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
1590 * @ssp: srcu_struct on which to wait for in-flight callbacks.
1591 */
1592void srcu_barrier(struct srcu_struct *ssp)
1593{
1594 int cpu;
1595 int idx;
1596 unsigned long s = rcu_seq_snap(&ssp->srcu_sup->srcu_barrier_seq);
1597
1598 check_init_srcu_struct(ssp);
1599 mutex_lock(&ssp->srcu_sup->srcu_barrier_mutex);
1600 if (rcu_seq_done(&ssp->srcu_sup->srcu_barrier_seq, s)) {
1601 smp_mb(); /* Force ordering following return. */
1602 mutex_unlock(&ssp->srcu_sup->srcu_barrier_mutex);
1603 return; /* Someone else did our work for us. */
1604 }
1605 rcu_seq_start(&ssp->srcu_sup->srcu_barrier_seq);
1606 init_completion(&ssp->srcu_sup->srcu_barrier_completion);
1607
1608 /* Initial count prevents reaching zero until all CBs are posted. */
1609 atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 1);
1610
1611 idx = __srcu_read_lock_nmisafe(ssp);
1612 if (smp_load_acquire(&ssp->srcu_sup->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
1613 srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, get_boot_cpu_id()));
1614 else
1615 for_each_possible_cpu(cpu)
1616 srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, cpu));
1617 __srcu_read_unlock_nmisafe(ssp, idx);
1618
1619 /* Remove the initial count, at which point reaching zero can happen. */
1620 if (atomic_dec_and_test(&ssp->srcu_sup->srcu_barrier_cpu_cnt))
1621 complete(&ssp->srcu_sup->srcu_barrier_completion);
1622 wait_for_completion(&ssp->srcu_sup->srcu_barrier_completion);
1623
1624 rcu_seq_end(&ssp->srcu_sup->srcu_barrier_seq);
1625 mutex_unlock(&ssp->srcu_sup->srcu_barrier_mutex);
1626}
1627EXPORT_SYMBOL_GPL(srcu_barrier);
1628
1629/**
1630 * srcu_batches_completed - return batches completed.
1631 * @ssp: srcu_struct on which to report batch completion.
1632 *
1633 * Report the number of batches, correlated with, but not necessarily
1634 * precisely the same as, the number of grace periods that have elapsed.
1635 */
1636unsigned long srcu_batches_completed(struct srcu_struct *ssp)
1637{
1638 return READ_ONCE(ssp->srcu_idx);
1639}
1640EXPORT_SYMBOL_GPL(srcu_batches_completed);
1641
1642/*
1643 * Core SRCU state machine. Push state bits of ->srcu_gp_seq
1644 * to SRCU_STATE_SCAN2, and invoke srcu_gp_end() when scan has
1645 * completed in that state.
1646 */
1647static void srcu_advance_state(struct srcu_struct *ssp)
1648{
1649 int idx;
1650
1651 mutex_lock(&ssp->srcu_sup->srcu_gp_mutex);
1652
1653 /*
1654 * Because readers might be delayed for an extended period after
1655 * fetching ->srcu_idx for their index, at any point in time there
1656 * might well be readers using both idx=0 and idx=1. We therefore
1657 * need to wait for readers to clear from both index values before
1658 * invoking a callback.
1659 *
1660 * The load-acquire ensures that we see the accesses performed
1661 * by the prior grace period.
1662 */
1663 idx = rcu_seq_state(smp_load_acquire(&ssp->srcu_sup->srcu_gp_seq)); /* ^^^ */
1664 if (idx == SRCU_STATE_IDLE) {
1665 spin_lock_irq_rcu_node(ssp->srcu_sup);
1666 if (ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed)) {
1667 WARN_ON_ONCE(rcu_seq_state(ssp->srcu_sup->srcu_gp_seq));
1668 spin_unlock_irq_rcu_node(ssp->srcu_sup);
1669 mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
1670 return;
1671 }
1672 idx = rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq));
1673 if (idx == SRCU_STATE_IDLE)
1674 srcu_gp_start(ssp);
1675 spin_unlock_irq_rcu_node(ssp->srcu_sup);
1676 if (idx != SRCU_STATE_IDLE) {
1677 mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
1678 return; /* Someone else started the grace period. */
1679 }
1680 }
1681
1682 if (rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
1683 idx = 1 ^ (ssp->srcu_idx & 1);
1684 if (!try_check_zero(ssp, idx, 1)) {
1685 mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
1686 return; /* readers present, retry later. */
1687 }
1688 srcu_flip(ssp);
1689 spin_lock_irq_rcu_node(ssp->srcu_sup);
1690 rcu_seq_set_state(&ssp->srcu_sup->srcu_gp_seq, SRCU_STATE_SCAN2);
1691 ssp->srcu_sup->srcu_n_exp_nodelay = 0;
1692 spin_unlock_irq_rcu_node(ssp->srcu_sup);
1693 }
1694
1695 if (rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
1696
1697 /*
1698 * SRCU read-side critical sections are normally short,
1699 * so check at least twice in quick succession after a flip.
1700 */
1701 idx = 1 ^ (ssp->srcu_idx & 1);
1702 if (!try_check_zero(ssp, idx, 2)) {
1703 mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
1704 return; /* readers present, retry later. */
1705 }
1706 ssp->srcu_sup->srcu_n_exp_nodelay = 0;
1707 srcu_gp_end(ssp); /* Releases ->srcu_gp_mutex. */
1708 }
1709}
1710
1711/*
1712 * Invoke a limited number of SRCU callbacks that have passed through
1713 * their grace period. If there are more to do, SRCU will reschedule
1714 * the workqueue. Note that needed memory barriers have been executed
1715 * in this task's context by srcu_readers_active_idx_check().
1716 */
1717static void srcu_invoke_callbacks(struct work_struct *work)
1718{
1719 long len;
1720 bool more;
1721 struct rcu_cblist ready_cbs;
1722 struct rcu_head *rhp;
1723 struct srcu_data *sdp;
1724 struct srcu_struct *ssp;
1725
1726 sdp = container_of(work, struct srcu_data, work);
1727
1728 ssp = sdp->ssp;
1729 rcu_cblist_init(&ready_cbs);
1730 spin_lock_irq_rcu_node(sdp);
1731 WARN_ON_ONCE(!rcu_segcblist_segempty(&sdp->srcu_cblist, RCU_NEXT_TAIL));
1732 rcu_segcblist_advance(&sdp->srcu_cblist,
1733 rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
1734 /*
1735 * Although this function is theoretically re-entrant, concurrent
1736 * callbacks invocation is disallowed to avoid executing an SRCU barrier
1737 * too early.
1738 */
1739 if (sdp->srcu_cblist_invoking ||
1740 !rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) {
1741 spin_unlock_irq_rcu_node(sdp);
1742 return; /* Someone else on the job or nothing to do. */
1743 }
1744
1745 /* We are on the job! Extract and invoke ready callbacks. */
1746 sdp->srcu_cblist_invoking = true;
1747 rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs);
1748 len = ready_cbs.len;
1749 spin_unlock_irq_rcu_node(sdp);
1750 rhp = rcu_cblist_dequeue(&ready_cbs);
1751 for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
1752 debug_rcu_head_unqueue(rhp);
1753 debug_rcu_head_callback(rhp);
1754 local_bh_disable();
1755 rhp->func(rhp);
1756 local_bh_enable();
1757 }
1758 WARN_ON_ONCE(ready_cbs.len);
1759
1760 /*
1761 * Update counts, accelerate new callbacks, and if needed,
1762 * schedule another round of callback invocation.
1763 */
1764 spin_lock_irq_rcu_node(sdp);
1765 rcu_segcblist_add_len(&sdp->srcu_cblist, -len);
1766 sdp->srcu_cblist_invoking = false;
1767 more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);
1768 spin_unlock_irq_rcu_node(sdp);
1769 /* An SRCU barrier or callbacks from previous nesting work pending */
1770 if (more)
1771 srcu_schedule_cbs_sdp(sdp, 0);
1772}
1773
1774/*
1775 * Finished one round of SRCU grace period. Start another if there are
1776 * more SRCU callbacks queued, otherwise put SRCU into not-running state.
1777 */
1778static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay)
1779{
1780 bool pushgp = true;
1781
1782 spin_lock_irq_rcu_node(ssp->srcu_sup);
1783 if (ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed)) {
1784 if (!WARN_ON_ONCE(rcu_seq_state(ssp->srcu_sup->srcu_gp_seq))) {
1785 /* All requests fulfilled, time to go idle. */
1786 pushgp = false;
1787 }
1788 } else if (!rcu_seq_state(ssp->srcu_sup->srcu_gp_seq)) {
1789 /* Outstanding request and no GP. Start one. */
1790 srcu_gp_start(ssp);
1791 }
1792 spin_unlock_irq_rcu_node(ssp->srcu_sup);
1793
1794 if (pushgp)
1795 queue_delayed_work(rcu_gp_wq, &ssp->srcu_sup->work, delay);
1796}
1797
1798/*
1799 * This is the work-queue function that handles SRCU grace periods.
1800 */
1801static void process_srcu(struct work_struct *work)
1802{
1803 unsigned long curdelay;
1804 unsigned long j;
1805 struct srcu_struct *ssp;
1806 struct srcu_usage *sup;
1807
1808 sup = container_of(work, struct srcu_usage, work.work);
1809 ssp = sup->srcu_ssp;
1810
1811 srcu_advance_state(ssp);
1812 curdelay = srcu_get_delay(ssp);
1813 if (curdelay) {
1814 WRITE_ONCE(sup->reschedule_count, 0);
1815 } else {
1816 j = jiffies;
1817 if (READ_ONCE(sup->reschedule_jiffies) == j) {
1818 WRITE_ONCE(sup->reschedule_count, READ_ONCE(sup->reschedule_count) + 1);
1819 if (READ_ONCE(sup->reschedule_count) > srcu_max_nodelay)
1820 curdelay = 1;
1821 } else {
1822 WRITE_ONCE(sup->reschedule_count, 1);
1823 WRITE_ONCE(sup->reschedule_jiffies, j);
1824 }
1825 }
1826 srcu_reschedule(ssp, curdelay);
1827}
1828
1829void srcutorture_get_gp_data(enum rcutorture_type test_type,
1830 struct srcu_struct *ssp, int *flags,
1831 unsigned long *gp_seq)
1832{
1833 if (test_type != SRCU_FLAVOR)
1834 return;
1835 *flags = 0;
1836 *gp_seq = rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq);
1837}
1838EXPORT_SYMBOL_GPL(srcutorture_get_gp_data);
1839
1840static const char * const srcu_size_state_name[] = {
1841 "SRCU_SIZE_SMALL",
1842 "SRCU_SIZE_ALLOC",
1843 "SRCU_SIZE_WAIT_BARRIER",
1844 "SRCU_SIZE_WAIT_CALL",
1845 "SRCU_SIZE_WAIT_CBS1",
1846 "SRCU_SIZE_WAIT_CBS2",
1847 "SRCU_SIZE_WAIT_CBS3",
1848 "SRCU_SIZE_WAIT_CBS4",
1849 "SRCU_SIZE_BIG",
1850 "SRCU_SIZE_???",
1851};
1852
1853void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
1854{
1855 int cpu;
1856 int idx;
1857 unsigned long s0 = 0, s1 = 0;
1858 int ss_state = READ_ONCE(ssp->srcu_sup->srcu_size_state);
1859 int ss_state_idx = ss_state;
1860
1861 idx = ssp->srcu_idx & 0x1;
1862 if (ss_state < 0 || ss_state >= ARRAY_SIZE(srcu_size_state_name))
1863 ss_state_idx = ARRAY_SIZE(srcu_size_state_name) - 1;
1864 pr_alert("%s%s Tree SRCU g%ld state %d (%s)",
1865 tt, tf, rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq), ss_state,
1866 srcu_size_state_name[ss_state_idx]);
1867 if (!ssp->sda) {
1868 // Called after cleanup_srcu_struct(), perhaps.
1869 pr_cont(" No per-CPU srcu_data structures (->sda == NULL).\n");
1870 } else {
1871 pr_cont(" per-CPU(idx=%d):", idx);
1872 for_each_possible_cpu(cpu) {
1873 unsigned long l0, l1;
1874 unsigned long u0, u1;
1875 long c0, c1;
1876 struct srcu_data *sdp;
1877
1878 sdp = per_cpu_ptr(ssp->sda, cpu);
1879 u0 = data_race(atomic_long_read(&sdp->srcu_unlock_count[!idx]));
1880 u1 = data_race(atomic_long_read(&sdp->srcu_unlock_count[idx]));
1881
1882 /*
1883 * Make sure that a lock is always counted if the corresponding
1884 * unlock is counted.
1885 */
1886 smp_rmb();
1887
1888 l0 = data_race(atomic_long_read(&sdp->srcu_lock_count[!idx]));
1889 l1 = data_race(atomic_long_read(&sdp->srcu_lock_count[idx]));
1890
1891 c0 = l0 - u0;
1892 c1 = l1 - u1;
1893 pr_cont(" %d(%ld,%ld %c)",
1894 cpu, c0, c1,
1895 "C."[rcu_segcblist_empty(&sdp->srcu_cblist)]);
1896 s0 += c0;
1897 s1 += c1;
1898 }
1899 pr_cont(" T(%ld,%ld)\n", s0, s1);
1900 }
1901 if (SRCU_SIZING_IS_TORTURE())
1902 srcu_transition_to_big(ssp);
1903}
1904EXPORT_SYMBOL_GPL(srcu_torture_stats_print);
1905
1906static int __init srcu_bootup_announce(void)
1907{
1908 pr_info("Hierarchical SRCU implementation.\n");
1909 if (exp_holdoff != DEFAULT_SRCU_EXP_HOLDOFF)
1910 pr_info("\tNon-default auto-expedite holdoff of %lu ns.\n", exp_holdoff);
1911 if (srcu_retry_check_delay != SRCU_DEFAULT_RETRY_CHECK_DELAY)
1912 pr_info("\tNon-default retry check delay of %lu us.\n", srcu_retry_check_delay);
1913 if (srcu_max_nodelay != SRCU_DEFAULT_MAX_NODELAY)
1914 pr_info("\tNon-default max no-delay of %lu.\n", srcu_max_nodelay);
1915 pr_info("\tMax phase no-delay instances is %lu.\n", srcu_max_nodelay_phase);
1916 return 0;
1917}
1918early_initcall(srcu_bootup_announce);
1919
1920void __init srcu_init(void)
1921{
1922 struct srcu_usage *sup;
1923
1924 /* Decide on srcu_struct-size strategy. */
1925 if (SRCU_SIZING_IS(SRCU_SIZING_AUTO)) {
1926 if (nr_cpu_ids >= big_cpu_lim) {
1927 convert_to_big = SRCU_SIZING_INIT; // Don't bother waiting for contention.
1928 pr_info("%s: Setting srcu_struct sizes to big.\n", __func__);
1929 } else {
1930 convert_to_big = SRCU_SIZING_NONE | SRCU_SIZING_CONTEND;
1931 pr_info("%s: Setting srcu_struct sizes based on contention.\n", __func__);
1932 }
1933 }
1934
1935 /*
1936 * Once that is set, call_srcu() can follow the normal path and
1937 * queue delayed work. This must follow RCU workqueues creation
1938 * and timers initialization.
1939 */
1940 srcu_init_done = true;
1941 while (!list_empty(&srcu_boot_list)) {
1942 sup = list_first_entry(&srcu_boot_list, struct srcu_usage,
1943 work.work.entry);
1944 list_del_init(&sup->work.work.entry);
1945 if (SRCU_SIZING_IS(SRCU_SIZING_INIT) &&
1946 sup->srcu_size_state == SRCU_SIZE_SMALL)
1947 sup->srcu_size_state = SRCU_SIZE_ALLOC;
1948 queue_work(rcu_gp_wq, &sup->work.work);
1949 }
1950}
1951
1952#ifdef CONFIG_MODULES
1953
1954/* Initialize any global-scope srcu_struct structures used by this module. */
1955static int srcu_module_coming(struct module *mod)
1956{
1957 int i;
1958 struct srcu_struct *ssp;
1959 struct srcu_struct **sspp = mod->srcu_struct_ptrs;
1960
1961 for (i = 0; i < mod->num_srcu_structs; i++) {
1962 ssp = *(sspp++);
1963 ssp->sda = alloc_percpu(struct srcu_data);
1964 if (WARN_ON_ONCE(!ssp->sda))
1965 return -ENOMEM;
1966 }
1967 return 0;
1968}
1969
1970/* Clean up any global-scope srcu_struct structures used by this module. */
1971static void srcu_module_going(struct module *mod)
1972{
1973 int i;
1974 struct srcu_struct *ssp;
1975 struct srcu_struct **sspp = mod->srcu_struct_ptrs;
1976
1977 for (i = 0; i < mod->num_srcu_structs; i++) {
1978 ssp = *(sspp++);
1979 if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_sup->srcu_gp_seq_needed)) &&
1980 !WARN_ON_ONCE(!ssp->srcu_sup->sda_is_static))
1981 cleanup_srcu_struct(ssp);
1982 if (!WARN_ON(srcu_readers_active(ssp)))
1983 free_percpu(ssp->sda);
1984 }
1985}
1986
1987/* Handle one module, either coming or going. */
1988static int srcu_module_notify(struct notifier_block *self,
1989 unsigned long val, void *data)
1990{
1991 struct module *mod = data;
1992 int ret = 0;
1993
1994 switch (val) {
1995 case MODULE_STATE_COMING:
1996 ret = srcu_module_coming(mod);
1997 break;
1998 case MODULE_STATE_GOING:
1999 srcu_module_going(mod);
2000 break;
2001 default:
2002 break;
2003 }
2004 return ret;
2005}
2006
2007static struct notifier_block srcu_module_nb = {
2008 .notifier_call = srcu_module_notify,
2009 .priority = 0,
2010};
2011
2012static __init int init_srcu_module_notifier(void)
2013{
2014 int ret;
2015
2016 ret = register_module_notifier(&srcu_module_nb);
2017 if (ret)
2018 pr_warn("Failed to register srcu module notifier\n");
2019 return ret;
2020}
2021late_initcall(init_srcu_module_notifier);
2022
2023#endif /* #ifdef CONFIG_MODULES */