linux/lib/lru_cache.c
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   1/*
   2   lru_cache.c
   3
   4   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
   5
   6   Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
   7   Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
   8   Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
   9
  10   drbd is free software; you can redistribute it and/or modify
  11   it under the terms of the GNU General Public License as published by
  12   the Free Software Foundation; either version 2, or (at your option)
  13   any later version.
  14
  15   drbd is distributed in the hope that it will be useful,
  16   but WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18   GNU General Public License for more details.
  19
  20   You should have received a copy of the GNU General Public License
  21   along with drbd; see the file COPYING.  If not, write to
  22   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
  23
  24 */
  25
  26#include <linux/module.h>
  27#include <linux/bitops.h>
  28#include <linux/slab.h>
  29#include <linux/string.h> /* for memset */
  30#include <linux/seq_file.h> /* for seq_printf */
  31#include <linux/lru_cache.h>
  32
  33MODULE_AUTHOR("Philipp Reisner <phil@linbit.com>, "
  34              "Lars Ellenberg <lars@linbit.com>");
  35MODULE_DESCRIPTION("lru_cache - Track sets of hot objects");
  36MODULE_LICENSE("GPL");
  37
  38/* this is developers aid only.
  39 * it catches concurrent access (lack of locking on the users part) */
  40#define PARANOIA_ENTRY() do {           \
  41        BUG_ON(!lc);                    \
  42        BUG_ON(!lc->nr_elements);       \
  43        BUG_ON(test_and_set_bit(__LC_PARANOIA, &lc->flags)); \
  44} while (0)
  45
  46#define RETURN(x...)     do { \
  47        clear_bit_unlock(__LC_PARANOIA, &lc->flags); \
  48        return x ; } while (0)
  49
  50/* BUG() if e is not one of the elements tracked by lc */
  51#define PARANOIA_LC_ELEMENT(lc, e) do { \
  52        struct lru_cache *lc_ = (lc);   \
  53        struct lc_element *e_ = (e);    \
  54        unsigned i = e_->lc_index;      \
  55        BUG_ON(i >= lc_->nr_elements);  \
  56        BUG_ON(lc_->lc_element[i] != e_); } while (0)
  57
  58
  59/* We need to atomically
  60 *  - try to grab the lock (set LC_LOCKED)
  61 *  - only if there is no pending transaction
  62 *    (neither LC_DIRTY nor LC_STARVING is set)
  63 * Because of PARANOIA_ENTRY() above abusing lc->flags as well,
  64 * it is not sufficient to just say
  65 *      return 0 == cmpxchg(&lc->flags, 0, LC_LOCKED);
  66 */
  67int lc_try_lock(struct lru_cache *lc)
  68{
  69        unsigned long val;
  70        do {
  71                val = cmpxchg(&lc->flags, 0, LC_LOCKED);
  72        } while (unlikely (val == LC_PARANOIA));
  73        /* Spin until no-one is inside a PARANOIA_ENTRY()/RETURN() section. */
  74        return 0 == val;
  75#if 0
  76        /* Alternative approach, spin in case someone enters or leaves a
  77         * PARANOIA_ENTRY()/RETURN() section. */
  78        unsigned long old, new, val;
  79        do {
  80                old = lc->flags & LC_PARANOIA;
  81                new = old | LC_LOCKED;
  82                val = cmpxchg(&lc->flags, old, new);
  83        } while (unlikely (val == (old ^ LC_PARANOIA)));
  84        return old == val;
  85#endif
  86}
  87
  88/**
  89 * lc_create - prepares to track objects in an active set
  90 * @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
  91 * @max_pending_changes: maximum changes to accumulate until a transaction is required
  92 * @e_count: number of elements allowed to be active simultaneously
  93 * @e_size: size of the tracked objects
  94 * @e_off: offset to the &struct lc_element member in a tracked object
  95 *
  96 * Returns a pointer to a newly initialized struct lru_cache on success,
  97 * or NULL on (allocation) failure.
  98 */
  99struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
 100                unsigned max_pending_changes,
 101                unsigned e_count, size_t e_size, size_t e_off)
 102{
 103        struct hlist_head *slot = NULL;
 104        struct lc_element **element = NULL;
 105        struct lru_cache *lc;
 106        struct lc_element *e;
 107        unsigned cache_obj_size = kmem_cache_size(cache);
 108        unsigned i;
 109
 110        WARN_ON(cache_obj_size < e_size);
 111        if (cache_obj_size < e_size)
 112                return NULL;
 113
 114        /* e_count too big; would probably fail the allocation below anyways.
 115         * for typical use cases, e_count should be few thousand at most. */
 116        if (e_count > LC_MAX_ACTIVE)
 117                return NULL;
 118
 119        slot = kcalloc(e_count, sizeof(struct hlist_head), GFP_KERNEL);
 120        if (!slot)
 121                goto out_fail;
 122        element = kzalloc(e_count * sizeof(struct lc_element *), GFP_KERNEL);
 123        if (!element)
 124                goto out_fail;
 125
 126        lc = kzalloc(sizeof(*lc), GFP_KERNEL);
 127        if (!lc)
 128                goto out_fail;
 129
 130        INIT_LIST_HEAD(&lc->in_use);
 131        INIT_LIST_HEAD(&lc->lru);
 132        INIT_LIST_HEAD(&lc->free);
 133        INIT_LIST_HEAD(&lc->to_be_changed);
 134
 135        lc->name = name;
 136        lc->element_size = e_size;
 137        lc->element_off = e_off;
 138        lc->nr_elements = e_count;
 139        lc->max_pending_changes = max_pending_changes;
 140        lc->lc_cache = cache;
 141        lc->lc_element = element;
 142        lc->lc_slot = slot;
 143
 144        /* preallocate all objects */
 145        for (i = 0; i < e_count; i++) {
 146                void *p = kmem_cache_alloc(cache, GFP_KERNEL);
 147                if (!p)
 148                        break;
 149                memset(p, 0, lc->element_size);
 150                e = p + e_off;
 151                e->lc_index = i;
 152                e->lc_number = LC_FREE;
 153                e->lc_new_number = LC_FREE;
 154                list_add(&e->list, &lc->free);
 155                element[i] = e;
 156        }
 157        if (i == e_count)
 158                return lc;
 159
 160        /* else: could not allocate all elements, give up */
 161        for (i--; i; i--) {
 162                void *p = element[i];
 163                kmem_cache_free(cache, p - e_off);
 164        }
 165        kfree(lc);
 166out_fail:
 167        kfree(element);
 168        kfree(slot);
 169        return NULL;
 170}
 171
 172void lc_free_by_index(struct lru_cache *lc, unsigned i)
 173{
 174        void *p = lc->lc_element[i];
 175        WARN_ON(!p);
 176        if (p) {
 177                p -= lc->element_off;
 178                kmem_cache_free(lc->lc_cache, p);
 179        }
 180}
 181
 182/**
 183 * lc_destroy - frees memory allocated by lc_create()
 184 * @lc: the lru cache to destroy
 185 */
 186void lc_destroy(struct lru_cache *lc)
 187{
 188        unsigned i;
 189        if (!lc)
 190                return;
 191        for (i = 0; i < lc->nr_elements; i++)
 192                lc_free_by_index(lc, i);
 193        kfree(lc->lc_element);
 194        kfree(lc->lc_slot);
 195        kfree(lc);
 196}
 197
 198/**
 199 * lc_reset - does a full reset for @lc and the hash table slots.
 200 * @lc: the lru cache to operate on
 201 *
 202 * It is roughly the equivalent of re-allocating a fresh lru_cache object,
 203 * basically a short cut to lc_destroy(lc); lc = lc_create(...);
 204 */
 205void lc_reset(struct lru_cache *lc)
 206{
 207        unsigned i;
 208
 209        INIT_LIST_HEAD(&lc->in_use);
 210        INIT_LIST_HEAD(&lc->lru);
 211        INIT_LIST_HEAD(&lc->free);
 212        INIT_LIST_HEAD(&lc->to_be_changed);
 213        lc->used = 0;
 214        lc->hits = 0;
 215        lc->misses = 0;
 216        lc->starving = 0;
 217        lc->locked = 0;
 218        lc->changed = 0;
 219        lc->pending_changes = 0;
 220        lc->flags = 0;
 221        memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);
 222
 223        for (i = 0; i < lc->nr_elements; i++) {
 224                struct lc_element *e = lc->lc_element[i];
 225                void *p = e;
 226                p -= lc->element_off;
 227                memset(p, 0, lc->element_size);
 228                /* re-init it */
 229                e->lc_index = i;
 230                e->lc_number = LC_FREE;
 231                e->lc_new_number = LC_FREE;
 232                list_add(&e->list, &lc->free);
 233        }
 234}
 235
 236/**
 237 * lc_seq_printf_stats - print stats about @lc into @seq
 238 * @seq: the seq_file to print into
 239 * @lc: the lru cache to print statistics of
 240 */
 241size_t lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc)
 242{
 243        /* NOTE:
 244         * total calls to lc_get are
 245         * (starving + hits + misses)
 246         * misses include "locked" count (update from an other thread in
 247         * progress) and "changed", when this in fact lead to an successful
 248         * update of the cache.
 249         */
 250        return seq_printf(seq, "\t%s: used:%u/%u "
 251                "hits:%lu misses:%lu starving:%lu locked:%lu changed:%lu\n",
 252                lc->name, lc->used, lc->nr_elements,
 253                lc->hits, lc->misses, lc->starving, lc->locked, lc->changed);
 254}
 255
 256static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
 257{
 258        return  lc->lc_slot + (enr % lc->nr_elements);
 259}
 260
 261
 262static struct lc_element *__lc_find(struct lru_cache *lc, unsigned int enr,
 263                bool include_changing)
 264{
 265        struct lc_element *e;
 266
 267        BUG_ON(!lc);
 268        BUG_ON(!lc->nr_elements);
 269        hlist_for_each_entry(e, lc_hash_slot(lc, enr), colision) {
 270                /* "about to be changed" elements, pending transaction commit,
 271                 * are hashed by their "new number". "Normal" elements have
 272                 * lc_number == lc_new_number. */
 273                if (e->lc_new_number != enr)
 274                        continue;
 275                if (e->lc_new_number == e->lc_number || include_changing)
 276                        return e;
 277                break;
 278        }
 279        return NULL;
 280}
 281
 282/**
 283 * lc_find - find element by label, if present in the hash table
 284 * @lc: The lru_cache object
 285 * @enr: element number
 286 *
 287 * Returns the pointer to an element, if the element with the requested
 288 * "label" or element number is present in the hash table,
 289 * or NULL if not found. Does not change the refcnt.
 290 * Ignores elements that are "about to be used", i.e. not yet in the active
 291 * set, but still pending transaction commit.
 292 */
 293struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
 294{
 295        return __lc_find(lc, enr, 0);
 296}
 297
 298/**
 299 * lc_is_used - find element by label
 300 * @lc: The lru_cache object
 301 * @enr: element number
 302 *
 303 * Returns true, if the element with the requested "label" or element number is
 304 * present in the hash table, and is used (refcnt > 0).
 305 * Also finds elements that are not _currently_ used but only "about to be
 306 * used", i.e. on the "to_be_changed" list, pending transaction commit.
 307 */
 308bool lc_is_used(struct lru_cache *lc, unsigned int enr)
 309{
 310        struct lc_element *e = __lc_find(lc, enr, 1);
 311        return e && e->refcnt;
 312}
 313
 314/**
 315 * lc_del - removes an element from the cache
 316 * @lc: The lru_cache object
 317 * @e: The element to remove
 318 *
 319 * @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
 320 * sets @e->enr to %LC_FREE.
 321 */
 322void lc_del(struct lru_cache *lc, struct lc_element *e)
 323{
 324        PARANOIA_ENTRY();
 325        PARANOIA_LC_ELEMENT(lc, e);
 326        BUG_ON(e->refcnt);
 327
 328        e->lc_number = e->lc_new_number = LC_FREE;
 329        hlist_del_init(&e->colision);
 330        list_move(&e->list, &lc->free);
 331        RETURN();
 332}
 333
 334static struct lc_element *lc_prepare_for_change(struct lru_cache *lc, unsigned new_number)
 335{
 336        struct list_head *n;
 337        struct lc_element *e;
 338
 339        if (!list_empty(&lc->free))
 340                n = lc->free.next;
 341        else if (!list_empty(&lc->lru))
 342                n = lc->lru.prev;
 343        else
 344                return NULL;
 345
 346        e = list_entry(n, struct lc_element, list);
 347        PARANOIA_LC_ELEMENT(lc, e);
 348
 349        e->lc_new_number = new_number;
 350        if (!hlist_unhashed(&e->colision))
 351                __hlist_del(&e->colision);
 352        hlist_add_head(&e->colision, lc_hash_slot(lc, new_number));
 353        list_move(&e->list, &lc->to_be_changed);
 354
 355        return e;
 356}
 357
 358static int lc_unused_element_available(struct lru_cache *lc)
 359{
 360        if (!list_empty(&lc->free))
 361                return 1; /* something on the free list */
 362        if (!list_empty(&lc->lru))
 363                return 1;  /* something to evict */
 364
 365        return 0;
 366}
 367
 368static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, bool may_change)
 369{
 370        struct lc_element *e;
 371
 372        PARANOIA_ENTRY();
 373        if (lc->flags & LC_STARVING) {
 374                ++lc->starving;
 375                RETURN(NULL);
 376        }
 377
 378        e = __lc_find(lc, enr, 1);
 379        /* if lc_new_number != lc_number,
 380         * this enr is currently being pulled in already,
 381         * and will be available once the pending transaction
 382         * has been committed. */
 383        if (e && e->lc_new_number == e->lc_number) {
 384                ++lc->hits;
 385                if (e->refcnt++ == 0)
 386                        lc->used++;
 387                list_move(&e->list, &lc->in_use); /* Not evictable... */
 388                RETURN(e);
 389        }
 390
 391        ++lc->misses;
 392        if (!may_change)
 393                RETURN(NULL);
 394
 395        /* It has been found above, but on the "to_be_changed" list, not yet
 396         * committed.  Don't pull it in twice, wait for the transaction, then
 397         * try again */
 398        if (e)
 399                RETURN(NULL);
 400
 401        /* To avoid races with lc_try_lock(), first, mark us dirty
 402         * (using test_and_set_bit, as it implies memory barriers), ... */
 403        test_and_set_bit(__LC_DIRTY, &lc->flags);
 404
 405        /* ... only then check if it is locked anyways. If lc_unlock clears
 406         * the dirty bit again, that's not a problem, we will come here again.
 407         */
 408        if (test_bit(__LC_LOCKED, &lc->flags)) {
 409                ++lc->locked;
 410                RETURN(NULL);
 411        }
 412
 413        /* In case there is nothing available and we can not kick out
 414         * the LRU element, we have to wait ...
 415         */
 416        if (!lc_unused_element_available(lc)) {
 417                __set_bit(__LC_STARVING, &lc->flags);
 418                RETURN(NULL);
 419        }
 420
 421        /* It was not present in the active set.  We are going to recycle an
 422         * unused (or even "free") element, but we won't accumulate more than
 423         * max_pending_changes changes.  */
 424        if (lc->pending_changes >= lc->max_pending_changes)
 425                RETURN(NULL);
 426
 427        e = lc_prepare_for_change(lc, enr);
 428        BUG_ON(!e);
 429
 430        clear_bit(__LC_STARVING, &lc->flags);
 431        BUG_ON(++e->refcnt != 1);
 432        lc->used++;
 433        lc->pending_changes++;
 434
 435        RETURN(e);
 436}
 437
 438/**
 439 * lc_get - get element by label, maybe change the active set
 440 * @lc: the lru cache to operate on
 441 * @enr: the label to look up
 442 *
 443 * Finds an element in the cache, increases its usage count,
 444 * "touches" and returns it.
 445 *
 446 * In case the requested number is not present, it needs to be added to the
 447 * cache. Therefore it is possible that an other element becomes evicted from
 448 * the cache. In either case, the user is notified so he is able to e.g. keep
 449 * a persistent log of the cache changes, and therefore the objects in use.
 450 *
 451 * Return values:
 452 *  NULL
 453 *     The cache was marked %LC_STARVING,
 454 *     or the requested label was not in the active set
 455 *     and a changing transaction is still pending (@lc was marked %LC_DIRTY).
 456 *     Or no unused or free element could be recycled (@lc will be marked as
 457 *     %LC_STARVING, blocking further lc_get() operations).
 458 *
 459 *  pointer to the element with the REQUESTED element number.
 460 *     In this case, it can be used right away
 461 *
 462 *  pointer to an UNUSED element with some different element number,
 463 *          where that different number may also be %LC_FREE.
 464 *
 465 *          In this case, the cache is marked %LC_DIRTY,
 466 *          so lc_try_lock() will no longer succeed.
 467 *          The returned element pointer is moved to the "to_be_changed" list,
 468 *          and registered with the new element number on the hash collision chains,
 469 *          so it is possible to pick it up from lc_is_used().
 470 *          Up to "max_pending_changes" (see lc_create()) can be accumulated.
 471 *          The user now should do whatever housekeeping is necessary,
 472 *          typically serialize on lc_try_lock_for_transaction(), then call
 473 *          lc_committed(lc) and lc_unlock(), to finish the change.
 474 *
 475 * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
 476 *       any cache set change.
 477 */
 478struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
 479{
 480        return __lc_get(lc, enr, 1);
 481}
 482
 483/**
 484 * lc_try_get - get element by label, if present; do not change the active set
 485 * @lc: the lru cache to operate on
 486 * @enr: the label to look up
 487 *
 488 * Finds an element in the cache, increases its usage count,
 489 * "touches" and returns it.
 490 *
 491 * Return values:
 492 *  NULL
 493 *     The cache was marked %LC_STARVING,
 494 *     or the requested label was not in the active set
 495 *
 496 *  pointer to the element with the REQUESTED element number.
 497 *     In this case, it can be used right away
 498 */
 499struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
 500{
 501        return __lc_get(lc, enr, 0);
 502}
 503
 504/**
 505 * lc_committed - tell @lc that pending changes have been recorded
 506 * @lc: the lru cache to operate on
 507 *
 508 * User is expected to serialize on explicit lc_try_lock_for_transaction()
 509 * before the transaction is started, and later needs to lc_unlock() explicitly
 510 * as well.
 511 */
 512void lc_committed(struct lru_cache *lc)
 513{
 514        struct lc_element *e, *tmp;
 515
 516        PARANOIA_ENTRY();
 517        list_for_each_entry_safe(e, tmp, &lc->to_be_changed, list) {
 518                /* count number of changes, not number of transactions */
 519                ++lc->changed;
 520                e->lc_number = e->lc_new_number;
 521                list_move(&e->list, &lc->in_use);
 522        }
 523        lc->pending_changes = 0;
 524        RETURN();
 525}
 526
 527
 528/**
 529 * lc_put - give up refcnt of @e
 530 * @lc: the lru cache to operate on
 531 * @e: the element to put
 532 *
 533 * If refcnt reaches zero, the element is moved to the lru list,
 534 * and a %LC_STARVING (if set) is cleared.
 535 * Returns the new (post-decrement) refcnt.
 536 */
 537unsigned int lc_put(struct lru_cache *lc, struct lc_element *e)
 538{
 539        PARANOIA_ENTRY();
 540        PARANOIA_LC_ELEMENT(lc, e);
 541        BUG_ON(e->refcnt == 0);
 542        BUG_ON(e->lc_number != e->lc_new_number);
 543        if (--e->refcnt == 0) {
 544                /* move it to the front of LRU. */
 545                list_move(&e->list, &lc->lru);
 546                lc->used--;
 547                clear_bit_unlock(__LC_STARVING, &lc->flags);
 548        }
 549        RETURN(e->refcnt);
 550}
 551
 552/**
 553 * lc_element_by_index
 554 * @lc: the lru cache to operate on
 555 * @i: the index of the element to return
 556 */
 557struct lc_element *lc_element_by_index(struct lru_cache *lc, unsigned i)
 558{
 559        BUG_ON(i >= lc->nr_elements);
 560        BUG_ON(lc->lc_element[i] == NULL);
 561        BUG_ON(lc->lc_element[i]->lc_index != i);
 562        return lc->lc_element[i];
 563}
 564
 565/**
 566 * lc_index_of
 567 * @lc: the lru cache to operate on
 568 * @e: the element to query for its index position in lc->element
 569 */
 570unsigned int lc_index_of(struct lru_cache *lc, struct lc_element *e)
 571{
 572        PARANOIA_LC_ELEMENT(lc, e);
 573        return e->lc_index;
 574}
 575
 576/**
 577 * lc_set - associate index with label
 578 * @lc: the lru cache to operate on
 579 * @enr: the label to set
 580 * @index: the element index to associate label with.
 581 *
 582 * Used to initialize the active set to some previously recorded state.
 583 */
 584void lc_set(struct lru_cache *lc, unsigned int enr, int index)
 585{
 586        struct lc_element *e;
 587        struct list_head *lh;
 588
 589        if (index < 0 || index >= lc->nr_elements)
 590                return;
 591
 592        e = lc_element_by_index(lc, index);
 593        BUG_ON(e->lc_number != e->lc_new_number);
 594        BUG_ON(e->refcnt != 0);
 595
 596        e->lc_number = e->lc_new_number = enr;
 597        hlist_del_init(&e->colision);
 598        if (enr == LC_FREE)
 599                lh = &lc->free;
 600        else {
 601                hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
 602                lh = &lc->lru;
 603        }
 604        list_move(&e->list, lh);
 605}
 606
 607/**
 608 * lc_dump - Dump a complete LRU cache to seq in textual form.
 609 * @lc: the lru cache to operate on
 610 * @seq: the &struct seq_file pointer to seq_printf into
 611 * @utext: user supplied "heading" or other info
 612 * @detail: function pointer the user may provide to dump further details
 613 * of the object the lc_element is embedded in.
 614 */
 615void lc_seq_dump_details(struct seq_file *seq, struct lru_cache *lc, char *utext,
 616             void (*detail) (struct seq_file *, struct lc_element *))
 617{
 618        unsigned int nr_elements = lc->nr_elements;
 619        struct lc_element *e;
 620        int i;
 621
 622        seq_printf(seq, "\tnn: lc_number refcnt %s\n ", utext);
 623        for (i = 0; i < nr_elements; i++) {
 624                e = lc_element_by_index(lc, i);
 625                if (e->lc_number == LC_FREE) {
 626                        seq_printf(seq, "\t%2d: FREE\n", i);
 627                } else {
 628                        seq_printf(seq, "\t%2d: %4u %4u    ", i,
 629                                   e->lc_number, e->refcnt);
 630                        detail(seq, e);
 631                }
 632        }
 633}
 634
 635EXPORT_SYMBOL(lc_create);
 636EXPORT_SYMBOL(lc_reset);
 637EXPORT_SYMBOL(lc_destroy);
 638EXPORT_SYMBOL(lc_set);
 639EXPORT_SYMBOL(lc_del);
 640EXPORT_SYMBOL(lc_try_get);
 641EXPORT_SYMBOL(lc_find);
 642EXPORT_SYMBOL(lc_get);
 643EXPORT_SYMBOL(lc_put);
 644EXPORT_SYMBOL(lc_committed);
 645EXPORT_SYMBOL(lc_element_by_index);
 646EXPORT_SYMBOL(lc_index_of);
 647EXPORT_SYMBOL(lc_seq_printf_stats);
 648EXPORT_SYMBOL(lc_seq_dump_details);
 649EXPORT_SYMBOL(lc_try_lock);
 650EXPORT_SYMBOL(lc_is_used);
 651
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