linux/kernel/srcu.c
<<
>>
Prefs
   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        if (WARN_ON(srcu_readers_active(sp)))
 286                return; /* Leakage unless caller handles error. */
 287        free_percpu(sp->per_cpu_ref);
 288        sp->per_cpu_ref = NULL;
 289}
 290EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
 291
 292/*
 293 * Counts the new reader in the appropriate per-CPU element of the
 294 * srcu_struct.  Must be called from process context.
 295 * Returns an index that must be passed to the matching srcu_read_unlock().
 296 */
 297int __srcu_read_lock(struct srcu_struct *sp)
 298{
 299        int idx;
 300
 301        idx = ACCESS_ONCE(sp->completed) & 0x1;
 302        preempt_disable();
 303        ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1;
 304        smp_mb(); /* B */  /* Avoid leaking the critical section. */
 305        ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1;
 306        preempt_enable();
 307        return idx;
 308}
 309EXPORT_SYMBOL_GPL(__srcu_read_lock);
 310
 311/*
 312 * Removes the count for the old reader from the appropriate per-CPU
 313 * element of the srcu_struct.  Note that this may well be a different
 314 * CPU than that which was incremented by the corresponding srcu_read_lock().
 315 * Must be called from process context.
 316 */
 317void __srcu_read_unlock(struct srcu_struct *sp, int idx)
 318{
 319        smp_mb(); /* C */  /* Avoid leaking the critical section. */
 320        this_cpu_dec(sp->per_cpu_ref->c[idx]);
 321}
 322EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 323
 324/*
 325 * We use an adaptive strategy for synchronize_srcu() and especially for
 326 * synchronize_srcu_expedited().  We spin for a fixed time period
 327 * (defined below) to allow SRCU readers to exit their read-side critical
 328 * sections.  If there are still some readers after 10 microseconds,
 329 * we repeatedly block for 1-millisecond time periods.  This approach
 330 * has done well in testing, so there is no need for a config parameter.
 331 */
 332#define SRCU_RETRY_CHECK_DELAY          5
 333#define SYNCHRONIZE_SRCU_TRYCOUNT       2
 334#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT   12
 335
 336/*
 337 * @@@ Wait until all pre-existing readers complete.  Such readers
 338 * will have used the index specified by "idx".
 339 * the caller should ensures the ->completed is not changed while checking
 340 * and idx = (->completed & 1) ^ 1
 341 */
 342static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
 343{
 344        for (;;) {
 345                if (srcu_readers_active_idx_check(sp, idx))
 346                        return true;
 347                if (--trycount <= 0)
 348                        return false;
 349                udelay(SRCU_RETRY_CHECK_DELAY);
 350        }
 351}
 352
 353/*
 354 * Increment the ->completed counter so that future SRCU readers will
 355 * use the other rank of the ->c[] and ->seq[] arrays.  This allows
 356 * us to wait for pre-existing readers in a starvation-free manner.
 357 */
 358static void srcu_flip(struct srcu_struct *sp)
 359{
 360        sp->completed++;
 361}
 362
 363/*
 364 * Enqueue an SRCU callback on the specified srcu_struct structure,
 365 * initiating grace-period processing if it is not already running.
 366 */
 367void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 368                void (*func)(struct rcu_head *head))
 369{
 370        unsigned long flags;
 371
 372        head->next = NULL;
 373        head->func = func;
 374        spin_lock_irqsave(&sp->queue_lock, flags);
 375        rcu_batch_queue(&sp->batch_queue, head);
 376        if (!sp->running) {
 377                sp->running = true;
 378                schedule_delayed_work(&sp->work, 0);
 379        }
 380        spin_unlock_irqrestore(&sp->queue_lock, flags);
 381}
 382EXPORT_SYMBOL_GPL(call_srcu);
 383
 384struct rcu_synchronize {
 385        struct rcu_head head;
 386        struct completion completion;
 387};
 388
 389/*
 390 * Awaken the corresponding synchronize_srcu() instance now that a
 391 * grace period has elapsed.
 392 */
 393static void wakeme_after_rcu(struct rcu_head *head)
 394{
 395        struct rcu_synchronize *rcu;
 396
 397        rcu = container_of(head, struct rcu_synchronize, head);
 398        complete(&rcu->completion);
 399}
 400
 401static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
 402static void srcu_reschedule(struct srcu_struct *sp);
 403
 404/*
 405 * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
 406 */
 407static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 408{
 409        struct rcu_synchronize rcu;
 410        struct rcu_head *head = &rcu.head;
 411        bool done = false;
 412
 413        rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
 414                           !lock_is_held(&rcu_bh_lock_map) &&
 415                           !lock_is_held(&rcu_lock_map) &&
 416                           !lock_is_held(&rcu_sched_lock_map),
 417                           "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");
 418
 419        might_sleep();
 420        init_completion(&rcu.completion);
 421
 422        head->next = NULL;
 423        head->func = wakeme_after_rcu;
 424        spin_lock_irq(&sp->queue_lock);
 425        if (!sp->running) {
 426                /* steal the processing owner */
 427                sp->running = true;
 428                rcu_batch_queue(&sp->batch_check0, head);
 429                spin_unlock_irq(&sp->queue_lock);
 430
 431                srcu_advance_batches(sp, trycount);
 432                if (!rcu_batch_empty(&sp->batch_done)) {
 433                        BUG_ON(sp->batch_done.head != head);
 434                        rcu_batch_dequeue(&sp->batch_done);
 435                        done = true;
 436                }
 437                /* give the processing owner to work_struct */
 438                srcu_reschedule(sp);
 439        } else {
 440                rcu_batch_queue(&sp->batch_queue, head);
 441                spin_unlock_irq(&sp->queue_lock);
 442        }
 443
 444        if (!done)
 445                wait_for_completion(&rcu.completion);
 446}
 447
 448/**
 449 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
 450 * @sp: srcu_struct with which to synchronize.
 451 *
 452 * Wait for the count to drain to zero of both indexes. To avoid the
 453 * possible starvation of synchronize_srcu(), it waits for the count of
 454 * the index=((->completed & 1) ^ 1) to drain to zero at first,
 455 * and then flip the completed and wait for the count of the other index.
 456 *
 457 * Can block; must be called from process context.
 458 *
 459 * Note that it is illegal to call synchronize_srcu() from the corresponding
 460 * SRCU read-side critical section; doing so will result in deadlock.
 461 * However, it is perfectly legal to call synchronize_srcu() on one
 462 * srcu_struct from some other srcu_struct's read-side critical section.
 463 */
 464void synchronize_srcu(struct srcu_struct *sp)
 465{
 466        __synchronize_srcu(sp, rcu_expedited
 467                           ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
 468                           : SYNCHRONIZE_SRCU_TRYCOUNT);
 469}
 470EXPORT_SYMBOL_GPL(synchronize_srcu);
 471
 472/**
 473 * synchronize_srcu_expedited - Brute-force SRCU grace period
 474 * @sp: srcu_struct with which to synchronize.
 475 *
 476 * Wait for an SRCU grace period to elapse, but be more aggressive about
 477 * spinning rather than blocking when waiting.
 478 *
 479 * Note that it is also illegal to call synchronize_srcu_expedited()
 480 * from the corresponding SRCU read-side critical section;
 481 * doing so will result in deadlock.  However, it is perfectly legal
 482 * to call synchronize_srcu_expedited() on one srcu_struct from some
 483 * other srcu_struct's read-side critical section, as long as
 484 * the resulting graph of srcu_structs is acyclic.
 485 */
 486void synchronize_srcu_expedited(struct srcu_struct *sp)
 487{
 488        __synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
 489}
 490EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
 491
 492/**
 493 * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
 494 */
 495void srcu_barrier(struct srcu_struct *sp)
 496{
 497        synchronize_srcu(sp);
 498}
 499EXPORT_SYMBOL_GPL(srcu_barrier);
 500
 501/**
 502 * srcu_batches_completed - return batches completed.
 503 * @sp: srcu_struct on which to report batch completion.
 504 *
 505 * Report the number of batches, correlated with, but not necessarily
 506 * precisely the same as, the number of grace periods that have elapsed.
 507 */
 508long srcu_batches_completed(struct srcu_struct *sp)
 509{
 510        return sp->completed;
 511}
 512EXPORT_SYMBOL_GPL(srcu_batches_completed);
 513
 514#define SRCU_CALLBACK_BATCH     10
 515#define SRCU_INTERVAL           1
 516
 517/*
 518 * Move any new SRCU callbacks to the first stage of the SRCU grace
 519 * period pipeline.
 520 */
 521static void srcu_collect_new(struct srcu_struct *sp)
 522{
 523        if (!rcu_batch_empty(&sp->batch_queue)) {
 524                spin_lock_irq(&sp->queue_lock);
 525                rcu_batch_move(&sp->batch_check0, &sp->batch_queue);
 526                spin_unlock_irq(&sp->queue_lock);
 527        }
 528}
 529
 530/*
 531 * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
 532 * ->batch_check1 and then to ->batch_done as readers drain.
 533 */
 534static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 535{
 536        int idx = 1 ^ (sp->completed & 1);
 537
 538        /*
 539         * Because readers might be delayed for an extended period after
 540         * fetching ->completed for their index, at any point in time there
 541         * might well be readers using both idx=0 and idx=1.  We therefore
 542         * need to wait for readers to clear from both index values before
 543         * invoking a callback.
 544         */
 545
 546        if (rcu_batch_empty(&sp->batch_check0) &&
 547            rcu_batch_empty(&sp->batch_check1))
 548                return; /* no callbacks need to be advanced */
 549
 550        if (!try_check_zero(sp, idx, trycount))
 551                return; /* failed to advance, will try after SRCU_INTERVAL */
 552
 553        /*
 554         * The callbacks in ->batch_check1 have already done with their
 555         * first zero check and flip back when they were enqueued on
 556         * ->batch_check0 in a previous invocation of srcu_advance_batches().
 557         * (Presumably try_check_zero() returned false during that
 558         * invocation, leaving the callbacks stranded on ->batch_check1.)
 559         * They are therefore ready to invoke, so move them to ->batch_done.
 560         */
 561        rcu_batch_move(&sp->batch_done, &sp->batch_check1);
 562
 563        if (rcu_batch_empty(&sp->batch_check0))
 564                return; /* no callbacks need to be advanced */
 565        srcu_flip(sp);
 566
 567        /*
 568         * The callbacks in ->batch_check0 just finished their
 569         * first check zero and flip, so move them to ->batch_check1
 570         * for future checking on the other idx.
 571         */
 572        rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
 573
 574        /*
 575         * SRCU read-side critical sections are normally short, so check
 576         * at least twice in quick succession after a flip.
 577         */
 578        trycount = trycount < 2 ? 2 : trycount;
 579        if (!try_check_zero(sp, idx^1, trycount))
 580                return; /* failed to advance, will try after SRCU_INTERVAL */
 581
 582        /*
 583         * The callbacks in ->batch_check1 have now waited for all
 584         * pre-existing readers using both idx values.  They are therefore
 585         * ready to invoke, so move them to ->batch_done.
 586         */
 587        rcu_batch_move(&sp->batch_done, &sp->batch_check1);
 588}
 589
 590/*
 591 * Invoke a limited number of SRCU callbacks that have passed through
 592 * their grace period.  If there are more to do, SRCU will reschedule
 593 * the workqueue.
 594 */
 595static void srcu_invoke_callbacks(struct srcu_struct *sp)
 596{
 597        int i;
 598        struct rcu_head *head;
 599
 600        for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
 601                head = rcu_batch_dequeue(&sp->batch_done);
 602                if (!head)
 603                        break;
 604                local_bh_disable();
 605                head->func(head);
 606                local_bh_enable();
 607        }
 608}
 609
 610/*
 611 * Finished one round of SRCU grace period.  Start another if there are
 612 * more SRCU callbacks queued, otherwise put SRCU into not-running state.
 613 */
 614static void srcu_reschedule(struct srcu_struct *sp)
 615{
 616        bool pending = true;
 617
 618        if (rcu_batch_empty(&sp->batch_done) &&
 619            rcu_batch_empty(&sp->batch_check1) &&
 620            rcu_batch_empty(&sp->batch_check0) &&
 621            rcu_batch_empty(&sp->batch_queue)) {
 622                spin_lock_irq(&sp->queue_lock);
 623                if (rcu_batch_empty(&sp->batch_done) &&
 624                    rcu_batch_empty(&sp->batch_check1) &&
 625                    rcu_batch_empty(&sp->batch_check0) &&
 626                    rcu_batch_empty(&sp->batch_queue)) {
 627                        sp->running = false;
 628                        pending = false;
 629                }
 630                spin_unlock_irq(&sp->queue_lock);
 631        }
 632
 633        if (pending)
 634                schedule_delayed_work(&sp->work, SRCU_INTERVAL);
 635}
 636
 637/*
 638 * This is the work-queue function that handles SRCU grace periods.
 639 */
 640void process_srcu(struct work_struct *work)
 641{
 642        struct srcu_struct *sp;
 643
 644        sp = container_of(work, struct srcu_struct, work.work);
 645
 646        srcu_collect_new(sp);
 647        srcu_advance_batches(sp, 1);
 648        srcu_invoke_callbacks(sp);
 649        srcu_reschedule(sp);
 650}
 651EXPORT_SYMBOL_GPL(process_srcu);
 652
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.