linux/kernel/srcu.c
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   1/*
   2 * Sleepable Read-Copy Update mechanism for mutual exclusion.
   3 *
   4 * This program is free software; you can redistribute it and/or modify
   5 * it under the terms of the GNU General Public License as published by
   6 * the Free Software Foundation; either version 2 of the License, or
   7 * (at your option) any later version.
   8 *
   9 * This program is distributed in the hope that it will be useful,
  10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 * GNU General Public License for more details.
  13 *
  14 * You should have received a copy of the GNU General Public License
  15 * along with this program; if not, write to the Free Software
  16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17 *
  18 * Copyright (C) IBM Corporation, 2006
  19 * Copyright (C) Fujitsu, 2012
  20 *
  21 * Author: Paul McKenney <paulmck@us.ibm.com>
  22 *         Lai Jiangshan <laijs@cn.fujitsu.com>
  23 *
  24 * For detailed explanation of Read-Copy Update mechanism see -
  25 *              Documentation/RCU/ *.txt
  26 *
  27 */
  28
  29#include <linux/export.h>
  30#include <linux/mutex.h>
  31#include <linux/percpu.h>
  32#include <linux/preempt.h>
  33#include <linux/rcupdate.h>
  34#include <linux/sched.h>
  35#include <linux/smp.h>
  36#include <linux/delay.h>
  37#include <linux/srcu.h>
  38
  39#include <trace/events/rcu.h>
  40
  41#include "rcu.h"
  42
  43/*
  44 * Initialize an rcu_batch structure to empty.
  45 */
  46static inline void rcu_batch_init(struct rcu_batch *b)
  47{
  48        b->head = NULL;
  49        b->tail = &b->head;
  50}
  51
  52/*
  53 * Enqueue a callback onto the tail of the specified rcu_batch structure.
  54 */
  55static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
  56{
  57        *b->tail = head;
  58        b->tail = &head->next;
  59}
  60
  61/*
  62 * Is the specified rcu_batch structure empty?
  63 */
  64static inline bool rcu_batch_empty(struct rcu_batch *b)
  65{
  66        return b->tail == &b->head;
  67}
  68
  69/*
  70 * Remove the callback at the head of the specified rcu_batch structure
  71 * and return a pointer to it, or return NULL if the structure is empty.
  72 */
  73static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
  74{
  75        struct rcu_head *head;
  76
  77        if (rcu_batch_empty(b))
  78                return NULL;
  79
  80        head = b->head;
  81        b->head = head->next;
  82        if (b->tail == &head->next)
  83                rcu_batch_init(b);
  84
  85        return head;
  86}
  87
  88/*
  89 * Move all callbacks from the rcu_batch structure specified by "from" to
  90 * the structure specified by "to".
  91 */
  92static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
  93{
  94        if (!rcu_batch_empty(from)) {
  95                *to->tail = from->head;
  96                to->tail = from->tail;
  97                rcu_batch_init(from);
  98        }
  99}
 100
 101static int init_srcu_struct_fields(struct srcu_struct *sp)
 102{
 103        sp->completed = 0;
 104        spin_lock_init(&sp->queue_lock);
 105        sp->running = false;
 106        rcu_batch_init(&sp->batch_queue);
 107        rcu_batch_init(&sp->batch_check0);
 108        rcu_batch_init(&sp->batch_check1);
 109        rcu_batch_init(&sp->batch_done);
 110        INIT_DELAYED_WORK(&sp->work, process_srcu);
 111        sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
 112        return sp->per_cpu_ref ? 0 : -ENOMEM;
 113}
 114
 115#ifdef CONFIG_DEBUG_LOCK_ALLOC
 116
 117int __init_srcu_struct(struct srcu_struct *sp, const char *name,
 118                       struct lock_class_key *key)
 119{
 120        /* Don't re-initialize a lock while it is held. */
 121        debug_check_no_locks_freed((void *)sp, sizeof(*sp));
 122        lockdep_init_map(&sp->dep_map, name, key, 0);
 123        return init_srcu_struct_fields(sp);
 124}
 125EXPORT_SYMBOL_GPL(__init_srcu_struct);
 126
 127#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 128
 129/**
 130 * init_srcu_struct - initialize a sleep-RCU structure
 131 * @sp: structure to initialize.
 132 *
 133 * Must invoke this on a given srcu_struct before passing that srcu_struct
 134 * to any other function.  Each srcu_struct represents a separate domain
 135 * of SRCU protection.
 136 */
 137int init_srcu_struct(struct srcu_struct *sp)
 138{
 139        return init_srcu_struct_fields(sp);
 140}
 141EXPORT_SYMBOL_GPL(init_srcu_struct);
 142
 143#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 144
 145/*
 146 * Returns approximate total of the readers' ->seq[] values for the
 147 * rank of per-CPU counters specified by idx.
 148 */
 149static unsigned long srcu_readers_seq_idx(struct srcu_struct *sp, int idx)
 150{
 151        int cpu;
 152        unsigned long sum = 0;
 153        unsigned long t;
 154
 155        for_each_possible_cpu(cpu) {
 156                t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->seq[idx]);
 157                sum += t;
 158        }
 159        return sum;
 160}
 161
 162/*
 163 * Returns approximate number of readers active on the specified rank
 164 * of the per-CPU ->c[] counters.
 165 */
 166static unsigned long srcu_readers_active_idx(struct srcu_struct *sp, int idx)
 167{
 168        int cpu;
 169        unsigned long sum = 0;
 170        unsigned long t;
 171
 172        for_each_possible_cpu(cpu) {
 173                t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx]);
 174                sum += t;
 175        }
 176        return sum;
 177}
 178
 179/*
 180 * Return true if the number of pre-existing readers is determined to
 181 * be stably zero.  An example unstable zero can occur if the call
 182 * to srcu_readers_active_idx() misses an __srcu_read_lock() increment,
 183 * but due to task migration, sees the corresponding __srcu_read_unlock()
 184 * decrement.  This can happen because srcu_readers_active_idx() takes
 185 * time to sum the array, and might in fact be interrupted or preempted
 186 * partway through the summation.
 187 */
 188static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
 189{
 190        unsigned long seq;
 191
 192        seq = srcu_readers_seq_idx(sp, idx);
 193
 194        /*
 195         * The following smp_mb() A pairs with the smp_mb() B located in
 196         * __srcu_read_lock().  This pairing ensures that if an
 197         * __srcu_read_lock() increments its counter after the summation
 198         * in srcu_readers_active_idx(), then the corresponding SRCU read-side
 199         * critical section will see any changes made prior to the start
 200         * of the current SRCU grace period.
 201         *
 202         * Also, if the above call to srcu_readers_seq_idx() saw the
 203         * increment of ->seq[], then the call to srcu_readers_active_idx()
 204         * must see the increment of ->c[].
 205         */
 206        smp_mb(); /* A */
 207
 208        /*
 209         * Note that srcu_readers_active_idx() can incorrectly return
 210         * zero even though there is a pre-existing reader throughout.
 211         * To see this, suppose that task A is in a very long SRCU
 212         * read-side critical section that started on CPU 0, and that
 213         * no other reader exists, so that the sum of the counters
 214         * is equal to one.  Then suppose that task B starts executing
 215         * srcu_readers_active_idx(), summing up to CPU 1, and then that
 216         * task C starts reading on CPU 0, so that its increment is not
 217         * summed, but finishes reading on CPU 2, so that its decrement
 218         * -is- summed.  Then when task B completes its sum, it will
 219         * incorrectly get zero, despite the fact that task A has been
 220         * in its SRCU read-side critical section the whole time.
 221         *
 222         * We therefore do a validation step should srcu_readers_active_idx()
 223         * return zero.
 224         */
 225        if (srcu_readers_active_idx(sp, idx) != 0)
 226                return false;
 227
 228        /*
 229         * The remainder of this function is the validation step.
 230         * The following smp_mb() D pairs with the smp_mb() C in
 231         * __srcu_read_unlock().  If the __srcu_read_unlock() was seen
 232         * by srcu_readers_active_idx() above, then any destructive
 233         * operation performed after the grace period will happen after
 234         * the corresponding SRCU read-side critical section.
 235         *
 236         * Note that there can be at most NR_CPUS worth of readers using
 237         * the old index, which is not enough to overflow even a 32-bit
 238         * integer.  (Yes, this does mean that systems having more than
 239         * a billion or so CPUs need to be 64-bit systems.)  Therefore,
 240         * the sum of the ->seq[] counters cannot possibly overflow.
 241         * Therefore, the only way that the return values of the two
 242         * calls to srcu_readers_seq_idx() can be equal is if there were
 243         * no increments of the corresponding rank of ->seq[] counts
 244         * in the interim.  But the missed-increment scenario laid out
 245         * above includes an increment of the ->seq[] counter by
 246         * the corresponding __srcu_read_lock().  Therefore, if this
 247         * scenario occurs, the return values from the two calls to
 248         * srcu_readers_seq_idx() will differ, and thus the validation
 249         * step below suffices.
 250         */
 251        smp_mb(); /* D */
 252
 253        return srcu_readers_seq_idx(sp, idx) == seq;
 254}
 255
 256/**
 257 * srcu_readers_active - returns approximate number of readers.
 258 * @sp: which srcu_struct to count active readers (holding srcu_read_lock).
 259 *
 260 * Note that this is not an atomic primitive, and can therefore suffer
 261 * severe errors when invoked on an active srcu_struct.  That said, it
 262 * can be useful as an error check at cleanup time.
 263 */
 264static int srcu_readers_active(struct srcu_struct *sp)
 265{
 266        int cpu;
 267        unsigned long sum = 0;
 268
 269        for_each_possible_cpu(cpu) {
 270                sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[0]);
 271                sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[1]);
 272        }
 273        return sum;
 274}
 275
 276/**
 277 * cleanup_srcu_struct - deconstruct a sleep-RCU structure
 278 * @sp: structure to clean up.
 279 *
 280 * Must invoke this after you are finished using a given srcu_struct that
 281 * was initialized via init_srcu_struct(), else you leak memory.
 282 */
 283void cleanup_srcu_struct(struct srcu_struct *sp)
 284{
 285        int sum;
 286
 287        sum = srcu_readers_active(sp);
 288        WARN_ON(sum);  /* Leakage unless caller handles error. */
 289        if (sum != 0)
 290                return;
 291        free_percpu(sp->per_cpu_ref);
 292        sp->per_cpu_ref = NULL;
 293}
 294EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
 295
 296/*
 297 * Counts the new reader in the appropriate per-CPU element of the
 298 * srcu_struct.  Must be called from process context.
 299 * Returns an index that must be passed to the matching srcu_read_unlock().
 300 */
 301int __srcu_read_lock(struct srcu_struct *sp)
 302{
 303        int idx;
 304
 305        preempt_disable();
 306        idx = rcu_dereference_index_check(sp->completed,
 307                                          rcu_read_lock_sched_held()) & 0x1;
 308        ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1;
 309        smp_mb(); /* B */  /* Avoid leaking the critical section. */
 310        ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1;
 311        preempt_enable();
 312        return idx;
 313}
 314EXPORT_SYMBOL_GPL(__srcu_read_lock);
 315
 316/*
 317 * Removes the count for the old reader from the appropriate per-CPU
 318 * element of the srcu_struct.  Note that this may well be a different
 319 * CPU than that which was incremented by the corresponding srcu_read_lock().
 320 * Must be called from process context.
 321 */
 322void __srcu_read_unlock(struct srcu_struct *sp, int idx)
 323{
 324        preempt_disable();
 325        smp_mb(); /* C */  /* Avoid leaking the critical section. */
 326        ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) -= 1;
 327        preempt_enable();
 328}
 329EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 330
 331/*
 332 * We use an adaptive strategy for synchronize_srcu() and especially for
 333 * synchronize_srcu_expedited().  We spin for a fixed time period
 334 * (defined below) to allow SRCU readers to exit their read-side critical
 335 * sections.  If there are still some readers after 10 microseconds,
 336 * we repeatedly block for 1-millisecond time periods.  This approach
 337 * has done well in testing, so there is no need for a config parameter.
 338 */
 339#define SRCU_RETRY_CHECK_DELAY          5
 340#define SYNCHRONIZE_SRCU_TRYCOUNT       2
 341#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT   12
 342
 343/*
 344 * @@@ Wait until all pre-existing readers complete.  Such readers
 345 * will have used the index specified by "idx".
 346 * the caller should ensures the ->completed is not changed while checking
 347 * and idx = (->completed & 1) ^ 1
 348 */
 349static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
 350{
 351        for (;;) {
 352                if (srcu_readers_active_idx_check(sp, idx))
 353                        return true;
 354                if (--trycount <= 0)
 355                        return false;
 356                udelay(SRCU_RETRY_CHECK_DELAY);
 357        }
 358}
 359
 360/*
 361 * Increment the ->completed counter so that future SRCU readers will
 362 * use the other rank of the ->c[] and ->seq[] arrays.  This allows
 363 * us to wait for pre-existing readers in a starvation-free manner.
 364 */
 365static void srcu_flip(struct srcu_struct *sp)
 366{
 367        sp->completed++;
 368}
 369
 370/*
 371 * Enqueue an SRCU callback on the specified srcu_struct structure,
 372 * initiating grace-period processing if it is not already running.
 373 */
 374void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 375                void (*func)(struct rcu_head *head))
 376{
 377        unsigned long flags;
 378
 379        head->next = NULL;
 380        head->func = func;
 381        spin_lock_irqsave(&sp->queue_lock, flags);
 382        rcu_batch_queue(&sp->batch_queue, head);
 383        if (!sp->running) {
 384                sp->running = true;
 385                schedule_delayed_work(&sp->work, 0);
 386        }
 387        spin_unlock_irqrestore(&sp->queue_lock, flags);
 388}
 389EXPORT_SYMBOL_GPL(call_srcu);
 390
 391struct rcu_synchronize {
 392        struct rcu_head head;
 393        struct completion completion;
 394};
 395
 396/*
 397 * Awaken the corresponding synchronize_srcu() instance now that a
 398 * grace period has elapsed.
 399 */
 400static void wakeme_after_rcu(struct rcu_head *head)
 401{
 402        struct rcu_synchronize *rcu;
 403
 404        rcu = container_of(head, struct rcu_synchronize, head);
 405        complete(&rcu->completion);
 406}
 407
 408static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
 409static void srcu_reschedule(struct srcu_struct *sp);
 410
 411/*
 412 * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
 413 */
 414static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 415{
 416        struct rcu_synchronize rcu;
 417        struct rcu_head *head = &rcu.head;
 418        bool done = false;
 419
 420        rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
 421                           !lock_is_held(&rcu_bh_lock_map) &&
 422                           !lock_is_held(&rcu_lock_map) &&
 423                           !lock_is_held(&rcu_sched_lock_map),
 424                           "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");
 425
 426        init_completion(&rcu.completion);
 427
 428        head->next = NULL;
 429        head->func = wakeme_after_rcu;
 430        spin_lock_irq(&sp->queue_lock);
 431        if (!sp->running) {
 432                /* steal the processing owner */
 433                sp->running = true;
 434                rcu_batch_queue(&sp->batch_check0, head);
 435                spin_unlock_irq(&sp->queue_lock);
 436
 437                srcu_advance_batches(sp, trycount);
 438                if (!rcu_batch_empty(&sp->batch_done)) {
 439                        BUG_ON(sp->batch_done.head != head);
 440                        rcu_batch_dequeue(&sp->batch_done);
 441                        done = true;
 442                }
 443                /* give the processing owner to work_struct */
 444                srcu_reschedule(sp);
 445        } else {
 446                rcu_batch_queue(&sp->batch_queue, head);
 447                spin_unlock_irq(&sp->queue_lock);
 448        }
 449
 450        if (!done)
 451                wait_for_completion(&rcu.completion);
 452}
 453
 454/**
 455 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
 456 * @sp: srcu_struct with which to synchronize.
 457 *
 458 * Flip the completed counter, and wait for the old count to drain to zero.
 459 * As with classic RCU, the updater must use some separate means of
 460 * synchronizing concurrent updates.  Can block; must be called from
 461 * process context.
 462 *
 463 * Note that it is illegal to call synchronize_srcu() from the corresponding
 464 * SRCU read-side critical section; doing so will result in deadlock.
 465 * However, it is perfectly legal to call synchronize_srcu() on one
 466 * srcu_struct from some other srcu_struct's read-side critical section.
 467 */
 468void synchronize_srcu(struct srcu_struct *sp)
 469{
 470        __synchronize_srcu(sp, rcu_expedited
 471                           ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
 472                           : SYNCHRONIZE_SRCU_TRYCOUNT);
 473}
 474EXPORT_SYMBOL_GPL(synchronize_srcu);
 475
 476/**
 477 * synchronize_srcu_expedited - Brute-force SRCU grace period
 478 * @sp: srcu_struct with which to synchronize.
 479 *
 480 * Wait for an SRCU grace period to elapse, but be more aggressive about
 481 * spinning rather than blocking when waiting.
 482 *
 483 * Note that it is illegal to call this function while holding any lock
 484 * that is acquired by a CPU-hotplug notifier.  It is also illegal to call
 485 * synchronize_srcu_expedited() from the corresponding SRCU read-side
 486 * critical section; doing so will result in deadlock.  However, it is
 487 * perfectly legal to call synchronize_srcu_expedited() on one srcu_struct
 488 * from some other srcu_struct's read-side critical section, as long as
 489 * the resulting graph of srcu_structs is acyclic.
 490 */
 491void synchronize_srcu_expedited(struct srcu_struct *sp)
 492{
 493        __synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
 494}
 495EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
 496
 497/**
 498 * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
 499 */
 500void srcu_barrier(struct srcu_struct *sp)
 501{
 502        synchronize_srcu(sp);
 503}
 504EXPORT_SYMBOL_GPL(srcu_barrier);
 505
 506/**
 507 * srcu_batches_completed - return batches completed.
 508 * @sp: srcu_struct on which to report batch completion.
 509 *
 510 * Report the number of batches, correlated with, but not necessarily
 511 * precisely the same as, the number of grace periods that have elapsed.
 512 */
 513long srcu_batches_completed(struct srcu_struct *sp)
 514{
 515        return sp->completed;
 516}
 517EXPORT_SYMBOL_GPL(srcu_batches_completed);
 518
 519#define SRCU_CALLBACK_BATCH     10
 520#define SRCU_INTERVAL           1
 521
 522/*
 523 * Move any new SRCU callbacks to the first stage of the SRCU grace
 524 * period pipeline.
 525 */
 526static void srcu_collect_new(struct srcu_struct *sp)
 527{
 528        if (!rcu_batch_empty(&sp->batch_queue)) {
 529                spin_lock_irq(&sp->queue_lock);
 530                rcu_batch_move(&sp->batch_check0, &sp->batch_queue);
 531                spin_unlock_irq(&sp->queue_lock);
 532        }
 533}
 534
 535/*
 536 * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
 537 * ->batch_check1 and then to ->batch_done as readers drain.
 538 */
 539static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 540{
 541        int idx = 1 ^ (sp->completed & 1);
 542
 543        /*
 544         * Because readers might be delayed for an extended period after
 545         * fetching ->completed for their index, at any point in time there
 546         * might well be readers using both idx=0 and idx=1.  We therefore
 547         * need to wait for readers to clear from both index values before
 548         * invoking a callback.
 549         */
 550
 551        if (rcu_batch_empty(&sp->batch_check0) &&
 552            rcu_batch_empty(&sp->batch_check1))
 553                return; /* no callbacks need to be advanced */
 554
 555        if (!try_check_zero(sp, idx, trycount))
 556                return; /* failed to advance, will try after SRCU_INTERVAL */
 557
 558        /*
 559         * The callbacks in ->batch_check1 have already done with their
 560         * first zero check and flip back when they were enqueued on
 561         * ->batch_check0 in a previous invocation of srcu_advance_batches().
 562         * (Presumably try_check_zero() returned false during that
 563         * invocation, leaving the callbacks stranded on ->batch_check1.)
 564         * They are therefore ready to invoke, so move them to ->batch_done.
 565         */
 566        rcu_batch_move(&sp->batch_done, &sp->batch_check1);
 567
 568        if (rcu_batch_empty(&sp->batch_check0))
 569                return; /* no callbacks need to be advanced */
 570        srcu_flip(sp);
 571
 572        /*
 573         * The callbacks in ->batch_check0 just finished their
 574         * first check zero and flip, so move them to ->batch_check1
 575         * for future checking on the other idx.
 576         */
 577        rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
 578
 579        /*
 580         * SRCU read-side critical sections are normally short, so check
 581         * at least twice in quick succession after a flip.
 582         */
 583        trycount = trycount < 2 ? 2 : trycount;
 584        if (!try_check_zero(sp, idx^1, trycount))
 585                return; /* failed to advance, will try after SRCU_INTERVAL */
 586
 587        /*
 588         * The callbacks in ->batch_check1 have now waited for all
 589         * pre-existing readers using both idx values.  They are therefore
 590         * ready to invoke, so move them to ->batch_done.
 591         */
 592        rcu_batch_move(&sp->batch_done, &sp->batch_check1);
 593}
 594
 595/*
 596 * Invoke a limited number of SRCU callbacks that have passed through
 597 * their grace period.  If there are more to do, SRCU will reschedule
 598 * the workqueue.
 599 */
 600static void srcu_invoke_callbacks(struct srcu_struct *sp)
 601{
 602        int i;
 603        struct rcu_head *head;
 604
 605        for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
 606                head = rcu_batch_dequeue(&sp->batch_done);
 607                if (!head)
 608                        break;
 609                local_bh_disable();
 610                head->func(head);
 611                local_bh_enable();
 612        }
 613}
 614
 615/*
 616 * Finished one round of SRCU grace period.  Start another if there are
 617 * more SRCU callbacks queued, otherwise put SRCU into not-running state.
 618 */
 619static void srcu_reschedule(struct srcu_struct *sp)
 620{
 621        bool pending = true;
 622
 623        if (rcu_batch_empty(&sp->batch_done) &&
 624            rcu_batch_empty(&sp->batch_check1) &&
 625            rcu_batch_empty(&sp->batch_check0) &&
 626            rcu_batch_empty(&sp->batch_queue)) {
 627                spin_lock_irq(&sp->queue_lock);
 628                if (rcu_batch_empty(&sp->batch_done) &&
 629                    rcu_batch_empty(&sp->batch_check1) &&
 630                    rcu_batch_empty(&sp->batch_check0) &&
 631                    rcu_batch_empty(&sp->batch_queue)) {
 632                        sp->running = false;
 633                        pending = false;
 634                }
 635                spin_unlock_irq(&sp->queue_lock);
 636        }
 637
 638        if (pending)
 639                schedule_delayed_work(&sp->work, SRCU_INTERVAL);
 640}
 641
 642/*
 643 * This is the work-queue function that handles SRCU grace periods.
 644 */
 645void process_srcu(struct work_struct *work)
 646{
 647        struct srcu_struct *sp;
 648
 649        sp = container_of(work, struct srcu_struct, work.work);
 650
 651        srcu_collect_new(sp);
 652        srcu_advance_batches(sp, 1);
 653        srcu_invoke_callbacks(sp);
 654        srcu_reschedule(sp);
 655}
 656EXPORT_SYMBOL_GPL(process_srcu);
 657
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