fs/fscache/cookie.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* netfs cookie management
   3  *
   4  * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  *
   7  * See Documentation/filesystems/caching/netfs-api.rst for more information on
   8  * the netfs API.
   9  */
  10
  11 #define FSCACHE_DEBUG_LEVEL COOKIE
  12 #include <linux/module.h>
  13 #include <linux/slab.h>
  14 #include "internal.h"
  15
  16 struct kmem_cache *fscache_cookie_jar;
  17
  18 static void fscache_cookie_lru_timed_out(struct timer_list *timer);
  19 static void fscache_cookie_lru_worker(struct work_struct *work);
  20 static void fscache_cookie_worker(struct work_struct *work);
  21 static void fscache_unhash_cookie(struct fscache_cookie *cookie);
  22 static void fscache_perform_invalidation(struct fscache_cookie *cookie);
  23
  24 #define fscache_cookie_hash_shift 15
  25 static struct hlist_bl_head fscache_cookie_hash[1 << fscache_cookie_hash_shift];
  26 static LIST_HEAD(fscache_cookies);
  27 static DEFINE_RWLOCK(fscache_cookies_lock);
  28 static LIST_HEAD(fscache_cookie_lru);
  29 static DEFINE_SPINLOCK(fscache_cookie_lru_lock);
  30 DEFINE_TIMER(fscache_cookie_lru_timer, fscache_cookie_lru_timed_out);
  31 static DECLARE_WORK(fscache_cookie_lru_work, fscache_cookie_lru_worker);
  32 static const char fscache_cookie_states[FSCACHE_COOKIE_STATE__NR] = "-LCAIFUWRD";
  33 static unsigned int fscache_lru_cookie_timeout = 10 * HZ;
  34
  35 void fscache_print_cookie(struct fscache_cookie *cookie, char prefix)
  36 {
  37         const u8 *k;
  38
  39         pr_err("%c-cookie c=%08x [fl=%lx na=%u nA=%u s=%c]\n",
  40                prefix,
  41                cookie->debug_id,
  42                cookie->flags,
  43                atomic_read(&cookie->n_active),
  44                atomic_read(&cookie->n_accesses),
  45                fscache_cookie_states[cookie->state]);
  46         pr_err("%c-cookie V=%08x [%s]\n",
  47                prefix,
  48                cookie->volume->debug_id,
  49                cookie->volume->key);
  50
  51         k = (cookie->key_len <= sizeof(cookie->inline_key)) ?
  52                 cookie->inline_key : cookie->key;
  53         pr_err("%c-key=[%u] '%*phN'\n", prefix, cookie->key_len, cookie->key_len, k);
  54 }
  55
  56 static void fscache_free_cookie(struct fscache_cookie *cookie)
  57 {
  58         if (WARN_ON_ONCE(!list_empty(&cookie->commit_link))) {
  59                 spin_lock(&fscache_cookie_lru_lock);
  60                 list_del_init(&cookie->commit_link);
  61                 spin_unlock(&fscache_cookie_lru_lock);
  62                 fscache_stat_d(&fscache_n_cookies_lru);
  63                 fscache_stat(&fscache_n_cookies_lru_removed);
  64         }
  65
  66         if (WARN_ON_ONCE(test_bit(FSCACHE_COOKIE_IS_HASHED, &cookie->flags))) {
  67                 fscache_print_cookie(cookie, 'F');
  68                 return;
  69         }
  70
  71         write_lock(&fscache_cookies_lock);
  72         list_del(&cookie->proc_link);
  73         write_unlock(&fscache_cookies_lock);
  74         if (cookie->aux_len > sizeof(cookie->inline_aux))
  75                 kfree(cookie->aux);
  76         if (cookie->key_len > sizeof(cookie->inline_key))
  77                 kfree(cookie->key);
  78         fscache_stat_d(&fscache_n_cookies);
  79         kmem_cache_free(fscache_cookie_jar, cookie);
  80 }
  81
  82 static void __fscache_queue_cookie(struct fscache_cookie *cookie)
  83 {
  84         if (!queue_work(fscache_wq, &cookie->work))
  85                 fscache_put_cookie(cookie, fscache_cookie_put_over_queued);
  86 }
  87
  88 static void fscache_queue_cookie(struct fscache_cookie *cookie,
  89                                  enum fscache_cookie_trace where)
  90 {
  91         fscache_get_cookie(cookie, where);
  92         __fscache_queue_cookie(cookie);
  93 }
  94
  95 /*
  96  * Initialise the access gate on a cookie by setting a flag to prevent the
  97  * state machine from being queued when the access counter transitions to 0.
  98  * We're only interested in this when we withdraw caching services from the
  99  * cookie.
 100  */
 101 static void fscache_init_access_gate(struct fscache_cookie *cookie)
 102 {
 103         int n_accesses;
 104
 105         n_accesses = atomic_read(&cookie->n_accesses);
 106         trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
 107                              n_accesses, fscache_access_cache_pin);
 108         set_bit(FSCACHE_COOKIE_NO_ACCESS_WAKE, &cookie->flags);
 109 }
 110
 111 /**
 112  * fscache_end_cookie_access - Unpin a cache at the end of an access.
 113  * @cookie: A data file cookie
 114  * @why: An indication of the circumstances of the access for tracing
 115  *
 116  * Unpin a cache cookie after we've accessed it and bring a deferred
 117  * relinquishment or withdrawal state into effect.
 118  *
 119  * The @why indicator is provided for tracing purposes.
 120  */
 121 void fscache_end_cookie_access(struct fscache_cookie *cookie,
 122                                enum fscache_access_trace why)
 123 {
 124         int n_accesses;
 125
 126         smp_mb__before_atomic();
 127         n_accesses = atomic_dec_return(&cookie->n_accesses);
 128         trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
 129                              n_accesses, why);
 130         if (n_accesses == 0 &&
 131             !test_bit(FSCACHE_COOKIE_NO_ACCESS_WAKE, &cookie->flags))
 132                 fscache_queue_cookie(cookie, fscache_cookie_get_end_access);
 133 }
 134 EXPORT_SYMBOL(fscache_end_cookie_access);
 135
 136 /*
 137  * Pin the cache behind a cookie so that we can access it.
 138  */
 139 static void __fscache_begin_cookie_access(struct fscache_cookie *cookie,
 140                                           enum fscache_access_trace why)
 141 {
 142         int n_accesses;
 143
 144         n_accesses = atomic_inc_return(&cookie->n_accesses);
 145         smp_mb__after_atomic(); /* (Future) read state after is-caching.
 146                                  * Reread n_accesses after is-caching
 147                                  */
 148         trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
 149                              n_accesses, why);
 150 }
 151
 152 /**
 153  * fscache_begin_cookie_access - Pin a cache so data can be accessed
 154  * @cookie: A data file cookie
 155  * @why: An indication of the circumstances of the access for tracing
 156  *
 157  * Attempt to pin the cache to prevent it from going away whilst we're
 158  * accessing data and returns true if successful.  This works as follows:
 159  *
 160  *  (1) If the cookie is not being cached (ie. FSCACHE_COOKIE_IS_CACHING is not
 161  *      set), we return false to indicate access was not permitted.
 162  *
 163  *  (2) If the cookie is being cached, we increment its n_accesses count and
 164  *      then recheck the IS_CACHING flag, ending the access if it got cleared.
 165  *
 166  *  (3) When we end the access, we decrement the cookie's n_accesses and wake
 167  *      up the any waiters if it reaches 0.
 168  *
 169  *  (4) Whilst the cookie is actively being cached, its n_accesses is kept
 170  *      artificially incremented to prevent wakeups from happening.
 171  *
 172  *  (5) When the cache is taken offline or if the cookie is culled, the flag is
 173  *      cleared to prevent new accesses, the cookie's n_accesses is decremented
 174  *      and we wait for it to become 0.
 175  *
 176  * The @why indicator are merely provided for tracing purposes.
 177  */
 178 bool fscache_begin_cookie_access(struct fscache_cookie *cookie,
 179                                  enum fscache_access_trace why)
 180 {
 181         if (!test_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags))
 182                 return false;
 183         __fscache_begin_cookie_access(cookie, why);
 184         if (!test_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags) ||
 185             !fscache_cache_is_live(cookie->volume->cache)) {
 186                 fscache_end_cookie_access(cookie, fscache_access_unlive);
 187                 return false;
 188         }
 189         return true;
 190 }
 191
 192 static inline void wake_up_cookie_state(struct fscache_cookie *cookie)
 193 {
 194         /* Use a barrier to ensure that waiters see the state variable
 195          * change, as spin_unlock doesn't guarantee a barrier.
 196          *
 197          * See comments over wake_up_bit() and waitqueue_active().
 198          */
 199         smp_mb();
 200         wake_up_var(&cookie->state);
 201 }
 202
 203 /*
 204  * Change the state a cookie is at and wake up anyone waiting for that.  Impose
 205  * an ordering between the stuff stored in the cookie and the state member.
 206  * Paired with fscache_cookie_state().
 207  */
 208 static void __fscache_set_cookie_state(struct fscache_cookie *cookie,
 209                                        enum fscache_cookie_state state)
 210 {
 211         smp_store_release(&cookie->state, state);
 212 }
 213
 214 static void fscache_set_cookie_state(struct fscache_cookie *cookie,
 215                                      enum fscache_cookie_state state)
 216 {
 217         spin_lock(&cookie->lock);
 218         __fscache_set_cookie_state(cookie, state);
 219         spin_unlock(&cookie->lock);
 220         wake_up_cookie_state(cookie);
 221 }
 222
 223 /**
 224  * fscache_cookie_lookup_negative - Note negative lookup
 225  * @cookie: The cookie that was being looked up
 226  *
 227  * Note that some part of the metadata path in the cache doesn't exist and so
 228  * we can release any waiting readers in the certain knowledge that there's
 229  * nothing for them to actually read.
 230  *
 231  * This function uses no locking and must only be called from the state machine.
 232  */
 233 void fscache_cookie_lookup_negative(struct fscache_cookie *cookie)
 234 {
 235         set_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags);
 236         fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_CREATING);
 237 }
 238 EXPORT_SYMBOL(fscache_cookie_lookup_negative);
 239
 240 /**
 241  * fscache_resume_after_invalidation - Allow I/O to resume after invalidation
 242  * @cookie: The cookie that was invalidated
 243  *
 244  * Tell fscache that invalidation is sufficiently complete that I/O can be
 245  * allowed again.
 246  */
 247 void fscache_resume_after_invalidation(struct fscache_cookie *cookie)
 248 {
 249         fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_ACTIVE);
 250 }
 251 EXPORT_SYMBOL(fscache_resume_after_invalidation);
 252
 253 /**
 254  * fscache_caching_failed - Report that a failure stopped caching on a cookie
 255  * @cookie: The cookie that was affected
 256  *
 257  * Tell fscache that caching on a cookie needs to be stopped due to some sort
 258  * of failure.
 259  *
 260  * This function uses no locking and must only be called from the state machine.
 261  */
 262 void fscache_caching_failed(struct fscache_cookie *cookie)
 263 {
 264         clear_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags);
 265         fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_FAILED);
 266 }
 267 EXPORT_SYMBOL(fscache_caching_failed);
 268
 269 /*
 270  * Set the index key in a cookie.  The cookie struct has space for a 16-byte
 271  * key plus length and hash, but if that's not big enough, it's instead a
 272  * pointer to a buffer containing 3 bytes of hash, 1 byte of length and then
 273  * the key data.
 274  */
 275 static int fscache_set_key(struct fscache_cookie *cookie,
 276                            const void *index_key, size_t index_key_len)
 277 {
 278         void *buf;
 279         size_t buf_size;
 280
 281         buf_size = round_up(index_key_len, sizeof(__le32));
 282
 283         if (index_key_len > sizeof(cookie->inline_key)) {
 284                 buf = kzalloc(buf_size, GFP_KERNEL);
 285                 if (!buf)
 286                         return -ENOMEM;
 287                 cookie->key = buf;
 288         } else {
 289                 buf = cookie->inline_key;
 290         }
 291
 292         memcpy(buf, index_key, index_key_len);
 293         cookie->key_hash = fscache_hash(cookie->volume->key_hash,
 294                                         buf, buf_size);
 295         return 0;
 296 }
 297
 298 static bool fscache_cookie_same(const struct fscache_cookie *a,
 299                                 const struct fscache_cookie *b)
 300 {
 301         const void *ka, *kb;
 302
 303         if (a->key_hash != b->key_hash ||
 304             a->volume   != b->volume ||
 305             a->key_len  != b->key_len)
 306                 return false;
 307
 308         if (a->key_len <= sizeof(a->inline_key)) {
 309                 ka = &a->inline_key;
 310                 kb = &b->inline_key;
 311         } else {
 312                 ka = a->key;
 313                 kb = b->key;
 314         }
 315         return memcmp(ka, kb, a->key_len) == 0;
 316 }
 317
 318 static atomic_t fscache_cookie_debug_id = ATOMIC_INIT(1);
 319
 320 /*
 321  * Allocate a cookie.
 322  */
 323 static struct fscache_cookie *fscache_alloc_cookie(
 324         struct fscache_volume *volume,
 325         u8 advice,
 326         const void *index_key, size_t index_key_len,
 327         const void *aux_data, size_t aux_data_len,
 328         loff_t object_size)
 329 {
 330         struct fscache_cookie *cookie;
 331
 332         /* allocate and initialise a cookie */
 333         cookie = kmem_cache_zalloc(fscache_cookie_jar, GFP_KERNEL);
 334         if (!cookie)
 335                 return NULL;
 336         fscache_stat(&fscache_n_cookies);
 337
 338         cookie->volume          = volume;
 339         cookie->advice          = advice;
 340         cookie->key_len         = index_key_len;
 341         cookie->aux_len         = aux_data_len;
 342         cookie->object_size     = object_size;
 343         if (object_size == 0)
 344                 __set_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags);
 345
 346         if (fscache_set_key(cookie, index_key, index_key_len) < 0)
 347                 goto nomem;
 348
 349         if (cookie->aux_len <= sizeof(cookie->inline_aux)) {
 350                 memcpy(cookie->inline_aux, aux_data, cookie->aux_len);
 351         } else {
 352                 cookie->aux = kmemdup(aux_data, cookie->aux_len, GFP_KERNEL);
 353                 if (!cookie->aux)
 354                         goto nomem;
 355         }
 356
 357         refcount_set(&cookie->ref, 1);
 358         cookie->debug_id = atomic_inc_return(&fscache_cookie_debug_id);
 359         spin_lock_init(&cookie->lock);
 360         INIT_LIST_HEAD(&cookie->commit_link);
 361         INIT_WORK(&cookie->work, fscache_cookie_worker);
 362         __fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_QUIESCENT);
 363
 364         write_lock(&fscache_cookies_lock);
 365         list_add_tail(&cookie->proc_link, &fscache_cookies);
 366         write_unlock(&fscache_cookies_lock);
 367         fscache_see_cookie(cookie, fscache_cookie_new_acquire);
 368         return cookie;
 369
 370 nomem:
 371         fscache_free_cookie(cookie);
 372         return NULL;
 373 }
 374
 375 static inline bool fscache_cookie_is_dropped(struct fscache_cookie *cookie)
 376 {
 377         return READ_ONCE(cookie->state) == FSCACHE_COOKIE_STATE_DROPPED;
 378 }
 379
 380 static void fscache_wait_on_collision(struct fscache_cookie *candidate,
 381                                       struct fscache_cookie *wait_for)
 382 {
 383         enum fscache_cookie_state *statep = &wait_for->state;
 384
 385         wait_var_event_timeout(statep, fscache_cookie_is_dropped(wait_for),
 386                                20 * HZ);
 387         if (!fscache_cookie_is_dropped(wait_for)) {
 388                 pr_notice("Potential collision c=%08x old: c=%08x",
 389                           candidate->debug_id, wait_for->debug_id);
 390                 wait_var_event(statep, fscache_cookie_is_dropped(wait_for));
 391         }
 392 }
 393
 394 /*
 395  * Attempt to insert the new cookie into the hash.  If there's a collision, we
 396  * wait for the old cookie to complete if it's being relinquished and an error
 397  * otherwise.
 398  */
 399 static bool fscache_hash_cookie(struct fscache_cookie *candidate)
 400 {
 401         struct fscache_cookie *cursor, *wait_for = NULL;
 402         struct hlist_bl_head *h;
 403         struct hlist_bl_node *p;
 404         unsigned int bucket;
 405
 406         bucket = candidate->key_hash & (ARRAY_SIZE(fscache_cookie_hash) - 1);
 407         h = &fscache_cookie_hash[bucket];
 408
 409         hlist_bl_lock(h);
 410         hlist_bl_for_each_entry(cursor, p, h, hash_link) {
 411                 if (fscache_cookie_same(candidate, cursor)) {
 412                         if (!test_bit(FSCACHE_COOKIE_RELINQUISHED, &cursor->flags))
 413                                 goto collision;
 414                         wait_for = fscache_get_cookie(cursor,
 415                                                       fscache_cookie_get_hash_collision);
 416                         break;
 417                 }
 418         }
 419
 420         fscache_get_volume(candidate->volume, fscache_volume_get_cookie);
 421         atomic_inc(&candidate->volume->n_cookies);
 422         hlist_bl_add_head(&candidate->hash_link, h);
 423         set_bit(FSCACHE_COOKIE_IS_HASHED, &candidate->flags);
 424         hlist_bl_unlock(h);
 425
 426         if (wait_for) {
 427                 fscache_wait_on_collision(candidate, wait_for);
 428                 fscache_put_cookie(wait_for, fscache_cookie_put_hash_collision);
 429         }
 430         return true;
 431
 432 collision:
 433         trace_fscache_cookie(cursor->debug_id, refcount_read(&cursor->ref),
 434                              fscache_cookie_collision);
 435         pr_err("Duplicate cookie detected\n");
 436         fscache_print_cookie(cursor, 'O');
 437         fscache_print_cookie(candidate, 'N');
 438         hlist_bl_unlock(h);
 439         return false;
 440 }
 441
 442 /*
 443  * Request a cookie to represent a data storage object within a volume.
 444  *
 445  * We never let on to the netfs about errors.  We may set a negative cookie
 446  * pointer, but that's okay
 447  */
 448 struct fscache_cookie *__fscache_acquire_cookie(
 449         struct fscache_volume *volume,
 450         u8 advice,
 451         const void *index_key, size_t index_key_len,
 452         const void *aux_data, size_t aux_data_len,
 453         loff_t object_size)
 454 {
 455         struct fscache_cookie *cookie;
 456
 457         _enter("V=%x", volume->debug_id);
 458
 459         if (!index_key || !index_key_len || index_key_len > 255 || aux_data_len > 255)
 460                 return NULL;
 461         if (!aux_data || !aux_data_len) {
 462                 aux_data = NULL;
 463                 aux_data_len = 0;
 464         }
 465
 466         fscache_stat(&fscache_n_acquires);
 467
 468         cookie = fscache_alloc_cookie(volume, advice,
 469                                       index_key, index_key_len,
 470                                       aux_data, aux_data_len,
 471                                       object_size);
 472         if (!cookie) {
 473                 fscache_stat(&fscache_n_acquires_oom);
 474                 return NULL;
 475         }
 476
 477         if (!fscache_hash_cookie(cookie)) {
 478                 fscache_see_cookie(cookie, fscache_cookie_discard);
 479                 fscache_free_cookie(cookie);
 480                 return NULL;
 481         }
 482
 483         trace_fscache_acquire(cookie);
 484         fscache_stat(&fscache_n_acquires_ok);
 485         _leave(" = c=%08x", cookie->debug_id);
 486         return cookie;
 487 }
 488 EXPORT_SYMBOL(__fscache_acquire_cookie);
 489
 490 /*
 491  * Prepare a cache object to be written to.
 492  */
 493 static void fscache_prepare_to_write(struct fscache_cookie *cookie)
 494 {
 495         cookie->volume->cache->ops->prepare_to_write(cookie);
 496 }
 497
 498 /*
 499  * Look up a cookie in the cache.
 500  */
 501 static void fscache_perform_lookup(struct fscache_cookie *cookie)
 502 {
 503         enum fscache_access_trace trace = fscache_access_lookup_cookie_end_failed;
 504         bool need_withdraw = false;
 505
 506         _enter("");
 507
 508         if (!cookie->volume->cache_priv) {
 509                 fscache_create_volume(cookie->volume, true);
 510                 if (!cookie->volume->cache_priv) {
 511                         fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_QUIESCENT);
 512                         goto out;
 513                 }
 514         }
 515
 516         if (!cookie->volume->cache->ops->lookup_cookie(cookie)) {
 517                 if (cookie->state != FSCACHE_COOKIE_STATE_FAILED)
 518                         fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_QUIESCENT);
 519                 need_withdraw = true;
 520                 _leave(" [fail]");
 521                 goto out;
 522         }
 523
 524         fscache_see_cookie(cookie, fscache_cookie_see_active);
 525         spin_lock(&cookie->lock);
 526         if (test_and_clear_bit(FSCACHE_COOKIE_DO_INVALIDATE, &cookie->flags))
 527                 __fscache_set_cookie_state(cookie,
 528                                            FSCACHE_COOKIE_STATE_INVALIDATING);
 529         else
 530                 __fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_ACTIVE);
 531         spin_unlock(&cookie->lock);
 532         wake_up_cookie_state(cookie);
 533         trace = fscache_access_lookup_cookie_end;
 534
 535 out:
 536         fscache_end_cookie_access(cookie, trace);
 537         if (need_withdraw)
 538                 fscache_withdraw_cookie(cookie);
 539         fscache_end_volume_access(cookie->volume, cookie, trace);
 540 }
 541
 542 /*
 543  * Begin the process of looking up a cookie.  We offload the actual process to
 544  * a worker thread.
 545  */
 546 static bool fscache_begin_lookup(struct fscache_cookie *cookie, bool will_modify)
 547 {
 548         if (will_modify) {
 549                 set_bit(FSCACHE_COOKIE_LOCAL_WRITE, &cookie->flags);
 550                 set_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags);
 551         }
 552         if (!fscache_begin_volume_access(cookie->volume, cookie,
 553                                          fscache_access_lookup_cookie))
 554                 return false;
 555
 556         __fscache_begin_cookie_access(cookie, fscache_access_lookup_cookie);
 557         __fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_LOOKING_UP);
 558         set_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags);
 559         set_bit(FSCACHE_COOKIE_HAS_BEEN_CACHED, &cookie->flags);
 560         return true;
 561 }
 562
 563 /*
 564  * Start using the cookie for I/O.  This prevents the backing object from being
 565  * reaped by VM pressure.
 566  */
 567 void __fscache_use_cookie(struct fscache_cookie *cookie, bool will_modify)
 568 {
 569         enum fscache_cookie_state state;
 570         bool queue = false;
 571         int n_active;
 572
 573         _enter("c=%08x", cookie->debug_id);
 574
 575         if (WARN(test_bit(FSCACHE_COOKIE_RELINQUISHED, &cookie->flags),
 576                  "Trying to use relinquished cookie\n"))
 577                 return;
 578
 579         spin_lock(&cookie->lock);
 580
 581         n_active = atomic_inc_return(&cookie->n_active);
 582         trace_fscache_active(cookie->debug_id, refcount_read(&cookie->ref),
 583                              n_active, atomic_read(&cookie->n_accesses),
 584                              will_modify ?
 585                              fscache_active_use_modify : fscache_active_use);
 586
 587 again:
 588         state = fscache_cookie_state(cookie);
 589         switch (state) {
 590         case FSCACHE_COOKIE_STATE_QUIESCENT:
 591                 queue = fscache_begin_lookup(cookie, will_modify);
 592                 break;
 593
 594         case FSCACHE_COOKIE_STATE_LOOKING_UP:
 595         case FSCACHE_COOKIE_STATE_CREATING:
 596                 if (will_modify)
 597                         set_bit(FSCACHE_COOKIE_LOCAL_WRITE, &cookie->flags);
 598                 break;
 599         case FSCACHE_COOKIE_STATE_ACTIVE:
 600         case FSCACHE_COOKIE_STATE_INVALIDATING:
 601                 if (will_modify &&
 602                     !test_and_set_bit(FSCACHE_COOKIE_LOCAL_WRITE, &cookie->flags)) {
 603                         set_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags);
 604                         queue = true;
 605                 }
 606                 break;
 607
 608         case FSCACHE_COOKIE_STATE_FAILED:
 609         case FSCACHE_COOKIE_STATE_WITHDRAWING:
 610                 break;
 611
 612         case FSCACHE_COOKIE_STATE_LRU_DISCARDING:
 613                 spin_unlock(&cookie->lock);
 614                 wait_var_event(&cookie->state,
 615                                fscache_cookie_state(cookie) !=
 616                                FSCACHE_COOKIE_STATE_LRU_DISCARDING);
 617                 spin_lock(&cookie->lock);
 618                 goto again;
 619
 620         case FSCACHE_COOKIE_STATE_DROPPED:
 621         case FSCACHE_COOKIE_STATE_RELINQUISHING:
 622                 WARN(1, "Can't use cookie in state %u\n", state);
 623                 break;
 624         }
 625
 626         spin_unlock(&cookie->lock);
 627         if (queue)
 628                 fscache_queue_cookie(cookie, fscache_cookie_get_use_work);
 629         _leave("");
 630 }
 631 EXPORT_SYMBOL(__fscache_use_cookie);
 632
 633 static void fscache_unuse_cookie_locked(struct fscache_cookie *cookie)
 634 {
 635         clear_bit(FSCACHE_COOKIE_DISABLED, &cookie->flags);
 636         if (!test_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags))
 637                 return;
 638
 639         cookie->unused_at = jiffies;
 640         spin_lock(&fscache_cookie_lru_lock);
 641         if (list_empty(&cookie->commit_link)) {
 642                 fscache_get_cookie(cookie, fscache_cookie_get_lru);
 643                 fscache_stat(&fscache_n_cookies_lru);
 644         }
 645         list_move_tail(&cookie->commit_link, &fscache_cookie_lru);
 646
 647         spin_unlock(&fscache_cookie_lru_lock);
 648         timer_reduce(&fscache_cookie_lru_timer,
 649                      jiffies + fscache_lru_cookie_timeout);
 650 }
 651
 652 /*
 653  * Stop using the cookie for I/O.
 654  */
 655 void __fscache_unuse_cookie(struct fscache_cookie *cookie,
 656                             const void *aux_data, const loff_t *object_size)
 657 {
 658         unsigned int debug_id = cookie->debug_id;
 659         unsigned int r = refcount_read(&cookie->ref);
 660         unsigned int a = atomic_read(&cookie->n_accesses);
 661         unsigned int c;
 662
 663         if (aux_data || object_size)
 664                 __fscache_update_cookie(cookie, aux_data, object_size);
 665
 666         /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
 667         c = atomic_fetch_add_unless(&cookie->n_active, -1, 1);
 668         if (c != 1) {
 669                 trace_fscache_active(debug_id, r, c - 1, a, fscache_active_unuse);
 670                 return;
 671         }
 672
 673         spin_lock(&cookie->lock);
 674         r = refcount_read(&cookie->ref);
 675         a = atomic_read(&cookie->n_accesses);
 676         c = atomic_dec_return(&cookie->n_active);
 677         trace_fscache_active(debug_id, r, c, a, fscache_active_unuse);
 678         if (c == 0)
 679                 fscache_unuse_cookie_locked(cookie);
 680         spin_unlock(&cookie->lock);
 681 }
 682 EXPORT_SYMBOL(__fscache_unuse_cookie);
 683
 684 /*
 685  * Perform work upon the cookie, such as committing its cache state,
 686  * relinquishing it or withdrawing the backing cache.  We're protected from the
 687  * cache going away under us as object withdrawal must come through this
 688  * non-reentrant work item.
 689  */
 690 static void fscache_cookie_state_machine(struct fscache_cookie *cookie)
 691 {
 692         enum fscache_cookie_state state;
 693         bool wake = false;
 694
 695         _enter("c=%x", cookie->debug_id);
 696
 697 again:
 698         spin_lock(&cookie->lock);
 699 again_locked:
 700         state = cookie->state;
 701         switch (state) {
 702         case FSCACHE_COOKIE_STATE_QUIESCENT:
 703                 /* The QUIESCENT state is jumped to the LOOKING_UP state by
 704                  * fscache_use_cookie().
 705                  */
 706
 707                 if (atomic_read(&cookie->n_accesses) == 0 &&
 708                     test_bit(FSCACHE_COOKIE_DO_RELINQUISH, &cookie->flags)) {
 709                         __fscache_set_cookie_state(cookie,
 710                                                    FSCACHE_COOKIE_STATE_RELINQUISHING);
 711                         wake = true;
 712                         goto again_locked;
 713                 }
 714                 break;
 715
 716         case FSCACHE_COOKIE_STATE_LOOKING_UP:
 717                 spin_unlock(&cookie->lock);
 718                 fscache_init_access_gate(cookie);
 719                 fscache_perform_lookup(cookie);
 720                 goto again;
 721
 722         case FSCACHE_COOKIE_STATE_INVALIDATING:
 723                 spin_unlock(&cookie->lock);
 724                 fscache_perform_invalidation(cookie);
 725                 goto again;
 726
 727         case FSCACHE_COOKIE_STATE_ACTIVE:
 728                 if (test_and_clear_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags)) {
 729                         spin_unlock(&cookie->lock);
 730                         fscache_prepare_to_write(cookie);
 731                         spin_lock(&cookie->lock);
 732                 }
 733                 if (test_bit(FSCACHE_COOKIE_DO_LRU_DISCARD, &cookie->flags)) {
 734                         __fscache_set_cookie_state(cookie,
 735                                                    FSCACHE_COOKIE_STATE_LRU_DISCARDING);
 736                         wake = true;
 737                         goto again_locked;
 738                 }
 739                 fallthrough;
 740
 741         case FSCACHE_COOKIE_STATE_FAILED:
 742                 if (atomic_read(&cookie->n_accesses) != 0)
 743                         break;
 744                 if (test_bit(FSCACHE_COOKIE_DO_RELINQUISH, &cookie->flags)) {
 745                         __fscache_set_cookie_state(cookie,
 746                                                    FSCACHE_COOKIE_STATE_RELINQUISHING);
 747                         wake = true;
 748                         goto again_locked;
 749                 }
 750                 if (test_bit(FSCACHE_COOKIE_DO_WITHDRAW, &cookie->flags)) {
 751                         __fscache_set_cookie_state(cookie,
 752                                                    FSCACHE_COOKIE_STATE_WITHDRAWING);
 753                         wake = true;
 754                         goto again_locked;
 755                 }
 756                 break;
 757
 758         case FSCACHE_COOKIE_STATE_LRU_DISCARDING:
 759         case FSCACHE_COOKIE_STATE_RELINQUISHING:
 760         case FSCACHE_COOKIE_STATE_WITHDRAWING:
 761                 if (cookie->cache_priv) {
 762                         spin_unlock(&cookie->lock);
 763                         cookie->volume->cache->ops->withdraw_cookie(cookie);
 764                         spin_lock(&cookie->lock);
 765                 }
 766
 767                 if (test_and_clear_bit(FSCACHE_COOKIE_DO_INVALIDATE, &cookie->flags))
 768                         fscache_end_cookie_access(cookie, fscache_access_invalidate_cookie_end);
 769
 770                 switch (state) {
 771                 case FSCACHE_COOKIE_STATE_RELINQUISHING:
 772                         fscache_see_cookie(cookie, fscache_cookie_see_relinquish);
 773                         fscache_unhash_cookie(cookie);
 774                         __fscache_set_cookie_state(cookie,
 775                                                    FSCACHE_COOKIE_STATE_DROPPED);
 776                         wake = true;
 777                         goto out;
 778                 case FSCACHE_COOKIE_STATE_LRU_DISCARDING:
 779                         fscache_see_cookie(cookie, fscache_cookie_see_lru_discard);
 780                         break;
 781                 case FSCACHE_COOKIE_STATE_WITHDRAWING:
 782                         fscache_see_cookie(cookie, fscache_cookie_see_withdraw);
 783                         break;
 784                 default:
 785                         BUG();
 786                 }
 787
 788                 clear_bit(FSCACHE_COOKIE_NEEDS_UPDATE, &cookie->flags);
 789                 clear_bit(FSCACHE_COOKIE_DO_WITHDRAW, &cookie->flags);
 790                 clear_bit(FSCACHE_COOKIE_DO_LRU_DISCARD, &cookie->flags);
 791                 clear_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags);
 792                 set_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags);
 793                 __fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_QUIESCENT);
 794                 wake = true;
 795                 goto again_locked;
 796
 797         case FSCACHE_COOKIE_STATE_DROPPED:
 798                 break;
 799
 800         default:
 801                 WARN_ONCE(1, "Cookie %x in unexpected state %u\n",
 802                           cookie->debug_id, state);
 803                 break;
 804         }
 805
 806 out:
 807         spin_unlock(&cookie->lock);
 808         if (wake)
 809                 wake_up_cookie_state(cookie);
 810         _leave("");
 811 }
 812
 813 static void fscache_cookie_worker(struct work_struct *work)
 814 {
 815         struct fscache_cookie *cookie = container_of(work, struct fscache_cookie, work);
 816
 817         fscache_see_cookie(cookie, fscache_cookie_see_work);
 818         fscache_cookie_state_machine(cookie);
 819         fscache_put_cookie(cookie, fscache_cookie_put_work);
 820 }
 821
 822 /*
 823  * Wait for the object to become inactive.  The cookie's work item will be
 824  * scheduled when someone transitions n_accesses to 0 - but if someone's
 825  * already done that, schedule it anyway.
 826  */
 827 static void __fscache_withdraw_cookie(struct fscache_cookie *cookie)
 828 {
 829         int n_accesses;
 830         bool unpinned;
 831
 832         unpinned = test_and_clear_bit(FSCACHE_COOKIE_NO_ACCESS_WAKE, &cookie->flags);
 833
 834         /* Need to read the access count after unpinning */
 835         n_accesses = atomic_read(&cookie->n_accesses);
 836         if (unpinned)
 837                 trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
 838                                      n_accesses, fscache_access_cache_unpin);
 839         if (n_accesses == 0)
 840                 fscache_queue_cookie(cookie, fscache_cookie_get_end_access);
 841 }
 842
 843 static void fscache_cookie_lru_do_one(struct fscache_cookie *cookie)
 844 {
 845         fscache_see_cookie(cookie, fscache_cookie_see_lru_do_one);
 846
 847         spin_lock(&cookie->lock);
 848         if (cookie->state != FSCACHE_COOKIE_STATE_ACTIVE ||
 849             time_before(jiffies, cookie->unused_at + fscache_lru_cookie_timeout) ||
 850             atomic_read(&cookie->n_active) > 0) {
 851                 spin_unlock(&cookie->lock);
 852                 fscache_stat(&fscache_n_cookies_lru_removed);
 853         } else {
 854                 set_bit(FSCACHE_COOKIE_DO_LRU_DISCARD, &cookie->flags);
 855                 spin_unlock(&cookie->lock);
 856                 fscache_stat(&fscache_n_cookies_lru_expired);
 857                 _debug("lru c=%x", cookie->debug_id);
 858                 __fscache_withdraw_cookie(cookie);
 859         }
 860
 861         fscache_put_cookie(cookie, fscache_cookie_put_lru);
 862 }
 863
 864 static void fscache_cookie_lru_worker(struct work_struct *work)
 865 {
 866         struct fscache_cookie *cookie;
 867         unsigned long unused_at;
 868
 869         spin_lock(&fscache_cookie_lru_lock);
 870
 871         while (!list_empty(&fscache_cookie_lru)) {
 872                 cookie = list_first_entry(&fscache_cookie_lru,
 873                                           struct fscache_cookie, commit_link);
 874                 unused_at = cookie->unused_at + fscache_lru_cookie_timeout;
 875                 if (time_before(jiffies, unused_at)) {
 876                         timer_reduce(&fscache_cookie_lru_timer, unused_at);
 877                         break;
 878                 }
 879
 880                 list_del_init(&cookie->commit_link);
 881                 fscache_stat_d(&fscache_n_cookies_lru);
 882                 spin_unlock(&fscache_cookie_lru_lock);
 883                 fscache_cookie_lru_do_one(cookie);
 884                 spin_lock(&fscache_cookie_lru_lock);
 885         }
 886
 887         spin_unlock(&fscache_cookie_lru_lock);
 888 }
 889
 890 static void fscache_cookie_lru_timed_out(struct timer_list *timer)
 891 {
 892         queue_work(fscache_wq, &fscache_cookie_lru_work);
 893 }
 894
 895 static void fscache_cookie_drop_from_lru(struct fscache_cookie *cookie)
 896 {
 897         bool need_put = false;
 898
 899         if (!list_empty(&cookie->commit_link)) {
 900                 spin_lock(&fscache_cookie_lru_lock);
 901                 if (!list_empty(&cookie->commit_link)) {
 902                         list_del_init(&cookie->commit_link);
 903                         fscache_stat_d(&fscache_n_cookies_lru);
 904                         fscache_stat(&fscache_n_cookies_lru_dropped);
 905                         need_put = true;
 906                 }
 907                 spin_unlock(&fscache_cookie_lru_lock);
 908                 if (need_put)
 909                         fscache_put_cookie(cookie, fscache_cookie_put_lru);
 910         }
 911 }
 912
 913 /*
 914  * Remove a cookie from the hash table.
 915  */
 916 static void fscache_unhash_cookie(struct fscache_cookie *cookie)
 917 {
 918         struct hlist_bl_head *h;
 919         unsigned int bucket;
 920
 921         bucket = cookie->key_hash & (ARRAY_SIZE(fscache_cookie_hash) - 1);
 922         h = &fscache_cookie_hash[bucket];
 923
 924         hlist_bl_lock(h);
 925         hlist_bl_del(&cookie->hash_link);
 926         clear_bit(FSCACHE_COOKIE_IS_HASHED, &cookie->flags);
 927         hlist_bl_unlock(h);
 928         fscache_stat(&fscache_n_relinquishes_dropped);
 929 }
 930
 931 static void fscache_drop_withdraw_cookie(struct fscache_cookie *cookie)
 932 {
 933         fscache_cookie_drop_from_lru(cookie);
 934         __fscache_withdraw_cookie(cookie);
 935 }
 936
 937 /**
 938  * fscache_withdraw_cookie - Mark a cookie for withdrawal
 939  * @cookie: The cookie to be withdrawn.
 940  *
 941  * Allow the cache backend to withdraw the backing for a cookie for its own
 942  * reasons, even if that cookie is in active use.
 943  */
 944 void fscache_withdraw_cookie(struct fscache_cookie *cookie)
 945 {
 946         set_bit(FSCACHE_COOKIE_DO_WITHDRAW, &cookie->flags);
 947         fscache_drop_withdraw_cookie(cookie);
 948 }
 949 EXPORT_SYMBOL(fscache_withdraw_cookie);
 950
 951 /*
 952  * Allow the netfs to release a cookie back to the cache.
 953  * - the object will be marked as recyclable on disk if retire is true
 954  */
 955 void __fscache_relinquish_cookie(struct fscache_cookie *cookie, bool retire)
 956 {
 957         fscache_stat(&fscache_n_relinquishes);
 958         if (retire)
 959                 fscache_stat(&fscache_n_relinquishes_retire);
 960
 961         _enter("c=%08x{%d},%d",
 962                cookie->debug_id, atomic_read(&cookie->n_active), retire);
 963
 964         if (WARN(test_and_set_bit(FSCACHE_COOKIE_RELINQUISHED, &cookie->flags),
 965                  "Cookie c=%x already relinquished\n", cookie->debug_id))
 966                 return;
 967
 968         if (retire)
 969                 set_bit(FSCACHE_COOKIE_RETIRED, &cookie->flags);
 970         trace_fscache_relinquish(cookie, retire);
 971
 972         ASSERTCMP(atomic_read(&cookie->n_active), ==, 0);
 973         ASSERTCMP(atomic_read(&cookie->volume->n_cookies), >, 0);
 974         atomic_dec(&cookie->volume->n_cookies);
 975
 976         if (test_bit(FSCACHE_COOKIE_HAS_BEEN_CACHED, &cookie->flags)) {
 977                 set_bit(FSCACHE_COOKIE_DO_RELINQUISH, &cookie->flags);
 978                 fscache_drop_withdraw_cookie(cookie);
 979         } else {
 980                 fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_DROPPED);
 981                 fscache_unhash_cookie(cookie);
 982         }
 983         fscache_put_cookie(cookie, fscache_cookie_put_relinquish);
 984 }
 985 EXPORT_SYMBOL(__fscache_relinquish_cookie);
 986
 987 /*
 988  * Drop a reference to a cookie.
 989  */
 990 void fscache_put_cookie(struct fscache_cookie *cookie,
 991                         enum fscache_cookie_trace where)
 992 {
 993         struct fscache_volume *volume = cookie->volume;
 994         unsigned int cookie_debug_id = cookie->debug_id;
 995         bool zero;
 996         int ref;
 997
 998         zero = __refcount_dec_and_test(&cookie->ref, &ref);
 999         trace_fscache_cookie(cookie_debug_id, ref - 1, where);
1000         if (zero) {
1001                 fscache_free_cookie(cookie);
1002                 fscache_put_volume(volume, fscache_volume_put_cookie);
1003         }
1004 }
1005 EXPORT_SYMBOL(fscache_put_cookie);
1006
1007 /*
1008  * Get a reference to a cookie.
1009  */
1010 struct fscache_cookie *fscache_get_cookie(struct fscache_cookie *cookie,
1011                                           enum fscache_cookie_trace where)
1012 {
1013         int ref;
1014
1015         __refcount_inc(&cookie->ref, &ref);
1016         trace_fscache_cookie(cookie->debug_id, ref + 1, where);
1017         return cookie;
1018 }
1019 EXPORT_SYMBOL(fscache_get_cookie);
1020
1021 /*
1022  * Ask the cache to effect invalidation of a cookie.
1023  */
1024 static void fscache_perform_invalidation(struct fscache_cookie *cookie)
1025 {
1026         if (!cookie->volume->cache->ops->invalidate_cookie(cookie))
1027                 fscache_caching_failed(cookie);
1028         fscache_end_cookie_access(cookie, fscache_access_invalidate_cookie_end);
1029 }
1030
1031 /*
1032  * Invalidate an object.
1033  */
1034 void __fscache_invalidate(struct fscache_cookie *cookie,
1035                           const void *aux_data, loff_t new_size,
1036                           unsigned int flags)
1037 {
1038         bool is_caching;
1039
1040         _enter("c=%x", cookie->debug_id);
1041
1042         fscache_stat(&fscache_n_invalidates);
1043
1044         if (WARN(test_bit(FSCACHE_COOKIE_RELINQUISHED, &cookie->flags),
1045                  "Trying to invalidate relinquished cookie\n"))
1046                 return;
1047
1048         if ((flags & FSCACHE_INVAL_DIO_WRITE) &&
1049             test_and_set_bit(FSCACHE_COOKIE_DISABLED, &cookie->flags))
1050                 return;
1051
1052         spin_lock(&cookie->lock);
1053         set_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags);
1054         fscache_update_aux(cookie, aux_data, &new_size);
1055         cookie->inval_counter++;
1056         trace_fscache_invalidate(cookie, new_size);
1057
1058         switch (cookie->state) {
1059         case FSCACHE_COOKIE_STATE_INVALIDATING: /* is_still_valid will catch it */
1060         default:
1061                 spin_unlock(&cookie->lock);
1062                 _leave(" [no %u]", cookie->state);
1063                 return;
1064
1065         case FSCACHE_COOKIE_STATE_LOOKING_UP:
1066                 __fscache_begin_cookie_access(cookie, fscache_access_invalidate_cookie);
1067                 set_bit(FSCACHE_COOKIE_DO_INVALIDATE, &cookie->flags);
1068                 fallthrough;
1069         case FSCACHE_COOKIE_STATE_CREATING:
1070                 spin_unlock(&cookie->lock);
1071                 _leave(" [look %x]", cookie->inval_counter);
1072                 return;
1073
1074         case FSCACHE_COOKIE_STATE_ACTIVE:
1075                 is_caching = fscache_begin_cookie_access(
1076                         cookie, fscache_access_invalidate_cookie);
1077                 if (is_caching)
1078                         __fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_INVALIDATING);
1079                 spin_unlock(&cookie->lock);
1080                 wake_up_cookie_state(cookie);
1081
1082                 if (is_caching)
1083                         fscache_queue_cookie(cookie, fscache_cookie_get_inval_work);
1084                 _leave(" [inv]");
1085                 return;
1086         }
1087 }
1088 EXPORT_SYMBOL(__fscache_invalidate);
1089
1090 #ifdef CONFIG_PROC_FS
1091 /*
1092  * Generate a list of extant cookies in /proc/fs/fscache/cookies
1093  */
1094 static int fscache_cookies_seq_show(struct seq_file *m, void *v)
1095 {
1096         struct fscache_cookie *cookie;
1097         unsigned int keylen = 0, auxlen = 0;
1098         u8 *p;
1099
1100         if (v == &fscache_cookies) {
1101                 seq_puts(m,
1102                          "COOKIE   VOLUME   REF ACT ACC S FL DEF             \n"
1103                          "======== ======== === === === = == ================\n"
1104                          );
1105                 return 0;
1106         }
1107
1108         cookie = list_entry(v, struct fscache_cookie, proc_link);
1109
1110         seq_printf(m,
1111                    "%08x %08x %3d %3d %3d %c %02lx",
1112                    cookie->debug_id,
1113                    cookie->volume->debug_id,
1114                    refcount_read(&cookie->ref),
1115                    atomic_read(&cookie->n_active),
1116                    atomic_read(&cookie->n_accesses),
1117                    fscache_cookie_states[cookie->state],
1118                    cookie->flags);
1119
1120         keylen = cookie->key_len;
1121         auxlen = cookie->aux_len;
1122
1123         if (keylen > 0 || auxlen > 0) {
1124                 seq_puts(m, " ");
1125                 p = keylen <= sizeof(cookie->inline_key) ?
1126                         cookie->inline_key : cookie->key;
1127                 for (; keylen > 0; keylen--)
1128                         seq_printf(m, "%02x", *p++);
1129                 if (auxlen > 0) {
1130                         seq_puts(m, ", ");
1131                         p = auxlen <= sizeof(cookie->inline_aux) ?
1132                                 cookie->inline_aux : cookie->aux;
1133                         for (; auxlen > 0; auxlen--)
1134                                 seq_printf(m, "%02x", *p++);
1135                 }
1136         }
1137
1138         seq_puts(m, "\n");
1139         return 0;
1140 }
1141
1142 static void *fscache_cookies_seq_start(struct seq_file *m, loff_t *_pos)
1143         __acquires(fscache_cookies_lock)
1144 {
1145         read_lock(&fscache_cookies_lock);
1146         return seq_list_start_head(&fscache_cookies, *_pos);
1147 }
1148
1149 static void *fscache_cookies_seq_next(struct seq_file *m, void *v, loff_t *_pos)
1150 {
1151         return seq_list_next(v, &fscache_cookies, _pos);
1152 }
1153
1154 static void fscache_cookies_seq_stop(struct seq_file *m, void *v)
1155         __releases(rcu)
1156 {
1157         read_unlock(&fscache_cookies_lock);
1158 }
1159
1160
1161 const struct seq_operations fscache_cookies_seq_ops = {
1162         .start  = fscache_cookies_seq_start,
1163         .next   = fscache_cookies_seq_next,
1164         .stop   = fscache_cookies_seq_stop,
1165         .show   = fscache_cookies_seq_show,
1166 };
1167 #endif