fs/fscache/object.c

   1 /* FS-Cache object state machine handler
   2  *
   3  * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  *
  11  * See Documentation/filesystems/caching/object.txt for a description of the
  12  * object state machine and the in-kernel representations.
  13  */
  14
  15 #define FSCACHE_DEBUG_LEVEL COOKIE
  16 #include <linux/module.h>
  17 #include <linux/seq_file.h>
  18 #include "internal.h"
  19
  20 const char *fscache_object_states[FSCACHE_OBJECT__NSTATES] = {
  21         [FSCACHE_OBJECT_INIT]           = "OBJECT_INIT",
  22         [FSCACHE_OBJECT_LOOKING_UP]     = "OBJECT_LOOKING_UP",
  23         [FSCACHE_OBJECT_CREATING]       = "OBJECT_CREATING",
  24         [FSCACHE_OBJECT_AVAILABLE]      = "OBJECT_AVAILABLE",
  25         [FSCACHE_OBJECT_ACTIVE]         = "OBJECT_ACTIVE",
  26         [FSCACHE_OBJECT_UPDATING]       = "OBJECT_UPDATING",
  27         [FSCACHE_OBJECT_DYING]          = "OBJECT_DYING",
  28         [FSCACHE_OBJECT_LC_DYING]       = "OBJECT_LC_DYING",
  29         [FSCACHE_OBJECT_ABORT_INIT]     = "OBJECT_ABORT_INIT",
  30         [FSCACHE_OBJECT_RELEASING]      = "OBJECT_RELEASING",
  31         [FSCACHE_OBJECT_RECYCLING]      = "OBJECT_RECYCLING",
  32         [FSCACHE_OBJECT_WITHDRAWING]    = "OBJECT_WITHDRAWING",
  33         [FSCACHE_OBJECT_DEAD]           = "OBJECT_DEAD",
  34 };
  35 EXPORT_SYMBOL(fscache_object_states);
  36
  37 const char fscache_object_states_short[FSCACHE_OBJECT__NSTATES][5] = {
  38         [FSCACHE_OBJECT_INIT]           = "INIT",
  39         [FSCACHE_OBJECT_LOOKING_UP]     = "LOOK",
  40         [FSCACHE_OBJECT_CREATING]       = "CRTN",
  41         [FSCACHE_OBJECT_AVAILABLE]      = "AVBL",
  42         [FSCACHE_OBJECT_ACTIVE]         = "ACTV",
  43         [FSCACHE_OBJECT_UPDATING]       = "UPDT",
  44         [FSCACHE_OBJECT_DYING]          = "DYNG",
  45         [FSCACHE_OBJECT_LC_DYING]       = "LCDY",
  46         [FSCACHE_OBJECT_ABORT_INIT]     = "ABTI",
  47         [FSCACHE_OBJECT_RELEASING]      = "RELS",
  48         [FSCACHE_OBJECT_RECYCLING]      = "RCYC",
  49         [FSCACHE_OBJECT_WITHDRAWING]    = "WTHD",
  50         [FSCACHE_OBJECT_DEAD]           = "DEAD",
  51 };
  52
  53 static void fscache_object_slow_work_put_ref(struct slow_work *);
  54 static int  fscache_object_slow_work_get_ref(struct slow_work *);
  55 static void fscache_object_slow_work_execute(struct slow_work *);
  56 #ifdef CONFIG_SLOW_WORK_PROC
  57 static void fscache_object_slow_work_desc(struct slow_work *, struct seq_file *);
  58 #endif
  59 static void fscache_initialise_object(struct fscache_object *);
  60 static void fscache_lookup_object(struct fscache_object *);
  61 static void fscache_object_available(struct fscache_object *);
  62 static void fscache_release_object(struct fscache_object *);
  63 static void fscache_withdraw_object(struct fscache_object *);
  64 static void fscache_enqueue_dependents(struct fscache_object *);
  65 static void fscache_dequeue_object(struct fscache_object *);
  66
  67 const struct slow_work_ops fscache_object_slow_work_ops = {
  68         .owner          = THIS_MODULE,
  69         .get_ref        = fscache_object_slow_work_get_ref,
  70         .put_ref        = fscache_object_slow_work_put_ref,
  71         .execute        = fscache_object_slow_work_execute,
  72 #ifdef CONFIG_SLOW_WORK_PROC
  73         .desc           = fscache_object_slow_work_desc,
  74 #endif
  75 };
  76 EXPORT_SYMBOL(fscache_object_slow_work_ops);
  77
  78 /*
  79  * we need to notify the parent when an op completes that we had outstanding
  80  * upon it
  81  */
  82 static inline void fscache_done_parent_op(struct fscache_object *object)
  83 {
  84         struct fscache_object *parent = object->parent;
  85
  86         _enter("OBJ%x {OBJ%x,%x}",
  87                object->debug_id, parent->debug_id, parent->n_ops);
  88
  89         spin_lock_nested(&parent->lock, 1);
  90         parent->n_ops--;
  91         parent->n_obj_ops--;
  92         if (parent->n_ops == 0)
  93                 fscache_raise_event(parent, FSCACHE_OBJECT_EV_CLEARED);
  94         spin_unlock(&parent->lock);
  95 }
  96
  97 /*
  98  * process events that have been sent to an object's state machine
  99  * - initiates parent lookup
 100  * - does object lookup
 101  * - does object creation
 102  * - does object recycling and retirement
 103  * - does object withdrawal
 104  */
 105 static void fscache_object_state_machine(struct fscache_object *object)
 106 {
 107         enum fscache_object_state new_state;
 108         struct fscache_cookie *cookie;
 109
 110         ASSERT(object != NULL);
 111
 112         _enter("{OBJ%x,%s,%lx}",
 113                object->debug_id, fscache_object_states[object->state],
 114                object->events);
 115
 116         switch (object->state) {
 117                 /* wait for the parent object to become ready */
 118         case FSCACHE_OBJECT_INIT:
 119                 object->event_mask =
 120                         ULONG_MAX & ~(1 << FSCACHE_OBJECT_EV_CLEARED);
 121                 fscache_initialise_object(object);
 122                 goto done;
 123
 124                 /* look up the object metadata on disk */
 125         case FSCACHE_OBJECT_LOOKING_UP:
 126                 fscache_lookup_object(object);
 127                 goto lookup_transit;
 128
 129                 /* create the object metadata on disk */
 130         case FSCACHE_OBJECT_CREATING:
 131                 fscache_lookup_object(object);
 132                 goto lookup_transit;
 133
 134                 /* handle an object becoming available; start pending
 135                  * operations and queue dependent operations for processing */
 136         case FSCACHE_OBJECT_AVAILABLE:
 137                 fscache_object_available(object);
 138                 goto active_transit;
 139
 140                 /* normal running state */
 141         case FSCACHE_OBJECT_ACTIVE:
 142                 goto active_transit;
 143
 144                 /* update the object metadata on disk */
 145         case FSCACHE_OBJECT_UPDATING:
 146                 clear_bit(FSCACHE_OBJECT_EV_UPDATE, &object->events);
 147                 fscache_stat(&fscache_n_updates_run);
 148                 fscache_stat(&fscache_n_cop_update_object);
 149                 object->cache->ops->update_object(object);
 150                 fscache_stat_d(&fscache_n_cop_update_object);
 151                 goto active_transit;
 152
 153                 /* handle an object dying during lookup or creation */
 154         case FSCACHE_OBJECT_LC_DYING:
 155                 object->event_mask &= ~(1 << FSCACHE_OBJECT_EV_UPDATE);
 156                 fscache_stat(&fscache_n_cop_lookup_complete);
 157                 object->cache->ops->lookup_complete(object);
 158                 fscache_stat_d(&fscache_n_cop_lookup_complete);
 159
 160                 spin_lock(&object->lock);
 161                 object->state = FSCACHE_OBJECT_DYING;
 162                 cookie = object->cookie;
 163                 if (cookie) {
 164                         if (test_and_clear_bit(FSCACHE_COOKIE_LOOKING_UP,
 165                                                &cookie->flags))
 166                                 wake_up_bit(&cookie->flags,
 167                                             FSCACHE_COOKIE_LOOKING_UP);
 168                         if (test_and_clear_bit(FSCACHE_COOKIE_CREATING,
 169                                                &cookie->flags))
 170                                 wake_up_bit(&cookie->flags,
 171                                             FSCACHE_COOKIE_CREATING);
 172                 }
 173                 spin_unlock(&object->lock);
 174
 175                 fscache_done_parent_op(object);
 176
 177                 /* wait for completion of all active operations on this object
 178                  * and the death of all child objects of this object */
 179         case FSCACHE_OBJECT_DYING:
 180         dying:
 181                 clear_bit(FSCACHE_OBJECT_EV_CLEARED, &object->events);
 182                 spin_lock(&object->lock);
 183                 _debug("dying OBJ%x {%d,%d}",
 184                        object->debug_id, object->n_ops, object->n_children);
 185                 if (object->n_ops == 0 && object->n_children == 0) {
 186                         object->event_mask &=
 187                                 ~(1 << FSCACHE_OBJECT_EV_CLEARED);
 188                         object->event_mask |=
 189                                 (1 << FSCACHE_OBJECT_EV_WITHDRAW) |
 190                                 (1 << FSCACHE_OBJECT_EV_RETIRE) |
 191                                 (1 << FSCACHE_OBJECT_EV_RELEASE) |
 192                                 (1 << FSCACHE_OBJECT_EV_ERROR);
 193                 } else {
 194                         object->event_mask &=
 195                                 ~((1 << FSCACHE_OBJECT_EV_WITHDRAW) |
 196                                   (1 << FSCACHE_OBJECT_EV_RETIRE) |
 197                                   (1 << FSCACHE_OBJECT_EV_RELEASE) |
 198                                   (1 << FSCACHE_OBJECT_EV_ERROR));
 199                         object->event_mask |=
 200                                 1 << FSCACHE_OBJECT_EV_CLEARED;
 201                 }
 202                 spin_unlock(&object->lock);
 203                 fscache_enqueue_dependents(object);
 204                 goto terminal_transit;
 205
 206                 /* handle an abort during initialisation */
 207         case FSCACHE_OBJECT_ABORT_INIT:
 208                 _debug("handle abort init %lx", object->events);
 209                 object->event_mask &= ~(1 << FSCACHE_OBJECT_EV_UPDATE);
 210
 211                 spin_lock(&object->lock);
 212                 fscache_dequeue_object(object);
 213
 214                 object->state = FSCACHE_OBJECT_DYING;
 215                 if (test_and_clear_bit(FSCACHE_COOKIE_CREATING,
 216                                        &object->cookie->flags))
 217                         wake_up_bit(&object->cookie->flags,
 218                                     FSCACHE_COOKIE_CREATING);
 219                 spin_unlock(&object->lock);
 220                 goto dying;
 221
 222                 /* handle the netfs releasing an object and possibly marking it
 223                  * obsolete too */
 224         case FSCACHE_OBJECT_RELEASING:
 225         case FSCACHE_OBJECT_RECYCLING:
 226                 object->event_mask &=
 227                         ~((1 << FSCACHE_OBJECT_EV_WITHDRAW) |
 228                           (1 << FSCACHE_OBJECT_EV_RETIRE) |
 229                           (1 << FSCACHE_OBJECT_EV_RELEASE) |
 230                           (1 << FSCACHE_OBJECT_EV_ERROR));
 231                 fscache_release_object(object);
 232                 spin_lock(&object->lock);
 233                 object->state = FSCACHE_OBJECT_DEAD;
 234                 spin_unlock(&object->lock);
 235                 fscache_stat(&fscache_n_object_dead);
 236                 goto terminal_transit;
 237
 238                 /* handle the parent cache of this object being withdrawn from
 239                  * active service */
 240         case FSCACHE_OBJECT_WITHDRAWING:
 241                 object->event_mask &=
 242                         ~((1 << FSCACHE_OBJECT_EV_WITHDRAW) |
 243                           (1 << FSCACHE_OBJECT_EV_RETIRE) |
 244                           (1 << FSCACHE_OBJECT_EV_RELEASE) |
 245                           (1 << FSCACHE_OBJECT_EV_ERROR));
 246                 fscache_withdraw_object(object);
 247                 spin_lock(&object->lock);
 248                 object->state = FSCACHE_OBJECT_DEAD;
 249                 spin_unlock(&object->lock);
 250                 fscache_stat(&fscache_n_object_dead);
 251                 goto terminal_transit;
 252
 253                 /* complain about the object being woken up once it is
 254                  * deceased */
 255         case FSCACHE_OBJECT_DEAD:
 256                 printk(KERN_ERR "FS-Cache:"
 257                        " Unexpected event in dead state %lx\n",
 258                        object->events & object->event_mask);
 259                 BUG();
 260
 261         default:
 262                 printk(KERN_ERR "FS-Cache: Unknown object state %u\n",
 263                        object->state);
 264                 BUG();
 265         }
 266
 267         /* determine the transition from a lookup state */
 268 lookup_transit:
 269         switch (fls(object->events & object->event_mask) - 1) {
 270         case FSCACHE_OBJECT_EV_WITHDRAW:
 271         case FSCACHE_OBJECT_EV_RETIRE:
 272         case FSCACHE_OBJECT_EV_RELEASE:
 273         case FSCACHE_OBJECT_EV_ERROR:
 274                 new_state = FSCACHE_OBJECT_LC_DYING;
 275                 goto change_state;
 276         case FSCACHE_OBJECT_EV_REQUEUE:
 277                 goto done;
 278         case -1:
 279                 goto done; /* sleep until event */
 280         default:
 281                 goto unsupported_event;
 282         }
 283
 284         /* determine the transition from an active state */
 285 active_transit:
 286         switch (fls(object->events & object->event_mask) - 1) {
 287         case FSCACHE_OBJECT_EV_WITHDRAW:
 288         case FSCACHE_OBJECT_EV_RETIRE:
 289         case FSCACHE_OBJECT_EV_RELEASE:
 290         case FSCACHE_OBJECT_EV_ERROR:
 291                 new_state = FSCACHE_OBJECT_DYING;
 292                 goto change_state;
 293         case FSCACHE_OBJECT_EV_UPDATE:
 294                 new_state = FSCACHE_OBJECT_UPDATING;
 295                 goto change_state;
 296         case -1:
 297                 new_state = FSCACHE_OBJECT_ACTIVE;
 298                 goto change_state; /* sleep until event */
 299         default:
 300                 goto unsupported_event;
 301         }
 302
 303         /* determine the transition from a terminal state */
 304 terminal_transit:
 305         switch (fls(object->events & object->event_mask) - 1) {
 306         case FSCACHE_OBJECT_EV_WITHDRAW:
 307                 new_state = FSCACHE_OBJECT_WITHDRAWING;
 308                 goto change_state;
 309         case FSCACHE_OBJECT_EV_RETIRE:
 310                 new_state = FSCACHE_OBJECT_RECYCLING;
 311                 goto change_state;
 312         case FSCACHE_OBJECT_EV_RELEASE:
 313                 new_state = FSCACHE_OBJECT_RELEASING;
 314                 goto change_state;
 315         case FSCACHE_OBJECT_EV_ERROR:
 316                 new_state = FSCACHE_OBJECT_WITHDRAWING;
 317                 goto change_state;
 318         case FSCACHE_OBJECT_EV_CLEARED:
 319                 new_state = FSCACHE_OBJECT_DYING;
 320                 goto change_state;
 321         case -1:
 322                 goto done; /* sleep until event */
 323         default:
 324                 goto unsupported_event;
 325         }
 326
 327 change_state:
 328         spin_lock(&object->lock);
 329         object->state = new_state;
 330         spin_unlock(&object->lock);
 331
 332 done:
 333         _leave(" [->%s]", fscache_object_states[object->state]);
 334         return;
 335
 336 unsupported_event:
 337         printk(KERN_ERR "FS-Cache:"
 338                " Unsupported event %lx [mask %lx] in state %s\n",
 339                object->events, object->event_mask,
 340                fscache_object_states[object->state]);
 341         BUG();
 342 }
 343
 344 /*
 345  * execute an object
 346  */
 347 static void fscache_object_slow_work_execute(struct slow_work *work)
 348 {
 349         struct fscache_object *object =
 350                 container_of(work, struct fscache_object, work);
 351         unsigned long start;
 352
 353         _enter("{OBJ%x}", object->debug_id);
 354
 355         clear_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
 356
 357         start = jiffies;
 358         fscache_object_state_machine(object);
 359         fscache_hist(fscache_objs_histogram, start);
 360         if (object->events & object->event_mask)
 361                 fscache_enqueue_object(object);
 362 }
 363
 364 /*
 365  * describe an object for slow-work debugging
 366  */
 367 #ifdef CONFIG_SLOW_WORK_PROC
 368 static void fscache_object_slow_work_desc(struct slow_work *work,
 369                                           struct seq_file *m)
 370 {
 371         struct fscache_object *object =
 372                 container_of(work, struct fscache_object, work);
 373
 374         seq_printf(m, "FSC: OBJ%x: %s",
 375                    object->debug_id,
 376                    fscache_object_states_short[object->state]);
 377 }
 378 #endif
 379
 380 /*
 381  * initialise an object
 382  * - check the specified object's parent to see if we can make use of it
 383  *   immediately to do a creation
 384  * - we may need to start the process of creating a parent and we need to wait
 385  *   for the parent's lookup and creation to complete if it's not there yet
 386  * - an object's cookie is pinned until we clear FSCACHE_COOKIE_CREATING on the
 387  *   leaf-most cookies of the object and all its children
 388  */
 389 static void fscache_initialise_object(struct fscache_object *object)
 390 {
 391         struct fscache_object *parent;
 392
 393         _enter("");
 394         ASSERT(object->cookie != NULL);
 395         ASSERT(object->cookie->parent != NULL);
 396         ASSERT(list_empty(&object->work.link));
 397
 398         if (object->events & ((1 << FSCACHE_OBJECT_EV_ERROR) |
 399                               (1 << FSCACHE_OBJECT_EV_RELEASE) |
 400                               (1 << FSCACHE_OBJECT_EV_RETIRE) |
 401                               (1 << FSCACHE_OBJECT_EV_WITHDRAW))) {
 402                 _debug("abort init %lx", object->events);
 403                 spin_lock(&object->lock);
 404                 object->state = FSCACHE_OBJECT_ABORT_INIT;
 405                 spin_unlock(&object->lock);
 406                 return;
 407         }
 408
 409         spin_lock(&object->cookie->lock);
 410         spin_lock_nested(&object->cookie->parent->lock, 1);
 411
 412         parent = object->parent;
 413         if (!parent) {
 414                 _debug("no parent");
 415                 set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events);
 416         } else {
 417                 spin_lock(&object->lock);
 418                 spin_lock_nested(&parent->lock, 1);
 419                 _debug("parent %s", fscache_object_states[parent->state]);
 420
 421                 if (parent->state >= FSCACHE_OBJECT_DYING) {
 422                         _debug("bad parent");
 423                         set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events);
 424                 } else if (parent->state < FSCACHE_OBJECT_AVAILABLE) {
 425                         _debug("wait");
 426
 427                         /* we may get woken up in this state by child objects
 428                          * binding on to us, so we need to make sure we don't
 429                          * add ourself to the list multiple times */
 430                         if (list_empty(&object->dep_link)) {
 431                                 fscache_stat(&fscache_n_cop_grab_object);
 432                                 object->cache->ops->grab_object(object);
 433                                 fscache_stat_d(&fscache_n_cop_grab_object);
 434                                 list_add(&object->dep_link,
 435                                          &parent->dependents);
 436
 437                                 /* fscache_acquire_non_index_cookie() uses this
 438                                  * to wake the chain up */
 439                                 if (parent->state == FSCACHE_OBJECT_INIT)
 440                                         fscache_enqueue_object(parent);
 441                         }
 442                 } else {
 443                         _debug("go");
 444                         parent->n_ops++;
 445                         parent->n_obj_ops++;
 446                         object->lookup_jif = jiffies;
 447                         object->state = FSCACHE_OBJECT_LOOKING_UP;
 448                         set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
 449                 }
 450
 451                 spin_unlock(&parent->lock);
 452                 spin_unlock(&object->lock);
 453         }
 454
 455         spin_unlock(&object->cookie->parent->lock);
 456         spin_unlock(&object->cookie->lock);
 457         _leave("");
 458 }
 459
 460 /*
 461  * look an object up in the cache from which it was allocated
 462  * - we hold an "access lock" on the parent object, so the parent object cannot
 463  *   be withdrawn by either party till we've finished
 464  * - an object's cookie is pinned until we clear FSCACHE_COOKIE_CREATING on the
 465  *   leaf-most cookies of the object and all its children
 466  */
 467 static void fscache_lookup_object(struct fscache_object *object)
 468 {
 469         struct fscache_cookie *cookie = object->cookie;
 470         struct fscache_object *parent;
 471
 472         _enter("");
 473
 474         parent = object->parent;
 475         ASSERT(parent != NULL);
 476         ASSERTCMP(parent->n_ops, >, 0);
 477         ASSERTCMP(parent->n_obj_ops, >, 0);
 478
 479         /* make sure the parent is still available */
 480         ASSERTCMP(parent->state, >=, FSCACHE_OBJECT_AVAILABLE);
 481
 482         if (parent->state >= FSCACHE_OBJECT_DYING ||
 483             test_bit(FSCACHE_IOERROR, &object->cache->flags)) {
 484                 _debug("unavailable");
 485                 set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events);
 486                 _leave("");
 487                 return;
 488         }
 489
 490         _debug("LOOKUP \"%s/%s\" in \"%s\"",
 491                parent->cookie->def->name, cookie->def->name,
 492                object->cache->tag->name);
 493
 494         fscache_stat(&fscache_n_object_lookups);
 495         fscache_stat(&fscache_n_cop_lookup_object);
 496         object->cache->ops->lookup_object(object);
 497         fscache_stat_d(&fscache_n_cop_lookup_object);
 498
 499         if (test_bit(FSCACHE_OBJECT_EV_ERROR, &object->events))
 500                 set_bit(FSCACHE_COOKIE_UNAVAILABLE, &cookie->flags);
 501
 502         _leave("");
 503 }
 504
 505 /**
 506  * fscache_object_lookup_negative - Note negative cookie lookup
 507  * @object: Object pointing to cookie to mark
 508  *
 509  * Note negative lookup, permitting those waiting to read data from an already
 510  * existing backing object to continue as there's no data for them to read.
 511  */
 512 void fscache_object_lookup_negative(struct fscache_object *object)
 513 {
 514         struct fscache_cookie *cookie = object->cookie;
 515
 516         _enter("{OBJ%x,%s}",
 517                object->debug_id, fscache_object_states[object->state]);
 518
 519         spin_lock(&object->lock);
 520         if (object->state == FSCACHE_OBJECT_LOOKING_UP) {
 521                 fscache_stat(&fscache_n_object_lookups_negative);
 522
 523                 /* transit here to allow write requests to begin stacking up
 524                  * and read requests to begin returning ENODATA */
 525                 object->state = FSCACHE_OBJECT_CREATING;
 526                 spin_unlock(&object->lock);
 527
 528                 set_bit(FSCACHE_COOKIE_PENDING_FILL, &cookie->flags);
 529                 set_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);
 530
 531                 _debug("wake up lookup %p", &cookie->flags);
 532                 smp_mb__before_clear_bit();
 533                 clear_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags);
 534                 smp_mb__after_clear_bit();
 535                 wake_up_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP);
 536                 set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
 537         } else {
 538                 ASSERTCMP(object->state, ==, FSCACHE_OBJECT_CREATING);
 539                 spin_unlock(&object->lock);
 540         }
 541
 542         _leave("");
 543 }
 544 EXPORT_SYMBOL(fscache_object_lookup_negative);
 545
 546 /**
 547  * fscache_obtained_object - Note successful object lookup or creation
 548  * @object: Object pointing to cookie to mark
 549  *
 550  * Note successful lookup and/or creation, permitting those waiting to write
 551  * data to a backing object to continue.
 552  *
 553  * Note that after calling this, an object's cookie may be relinquished by the
 554  * netfs, and so must be accessed with object lock held.
 555  */
 556 void fscache_obtained_object(struct fscache_object *object)
 557 {
 558         struct fscache_cookie *cookie = object->cookie;
 559
 560         _enter("{OBJ%x,%s}",
 561                object->debug_id, fscache_object_states[object->state]);
 562
 563         /* if we were still looking up, then we must have a positive lookup
 564          * result, in which case there may be data available */
 565         spin_lock(&object->lock);
 566         if (object->state == FSCACHE_OBJECT_LOOKING_UP) {
 567                 fscache_stat(&fscache_n_object_lookups_positive);
 568
 569                 clear_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);
 570
 571                 object->state = FSCACHE_OBJECT_AVAILABLE;
 572                 spin_unlock(&object->lock);
 573
 574                 smp_mb__before_clear_bit();
 575                 clear_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags);
 576                 smp_mb__after_clear_bit();
 577                 wake_up_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP);
 578                 set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
 579         } else {
 580                 ASSERTCMP(object->state, ==, FSCACHE_OBJECT_CREATING);
 581                 fscache_stat(&fscache_n_object_created);
 582
 583                 object->state = FSCACHE_OBJECT_AVAILABLE;
 584                 spin_unlock(&object->lock);
 585                 set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
 586                 smp_wmb();
 587         }
 588
 589         if (test_and_clear_bit(FSCACHE_COOKIE_CREATING, &cookie->flags))
 590                 wake_up_bit(&cookie->flags, FSCACHE_COOKIE_CREATING);
 591
 592         _leave("");
 593 }
 594 EXPORT_SYMBOL(fscache_obtained_object);
 595
 596 /*
 597  * handle an object that has just become available
 598  */
 599 static void fscache_object_available(struct fscache_object *object)
 600 {
 601         _enter("{OBJ%x}", object->debug_id);
 602
 603         spin_lock(&object->lock);
 604
 605         if (object->cookie &&
 606             test_and_clear_bit(FSCACHE_COOKIE_CREATING, &object->cookie->flags))
 607                 wake_up_bit(&object->cookie->flags, FSCACHE_COOKIE_CREATING);
 608
 609         fscache_done_parent_op(object);
 610         if (object->n_in_progress == 0) {
 611                 if (object->n_ops > 0) {
 612                         ASSERTCMP(object->n_ops, >=, object->n_obj_ops);
 613                         ASSERTIF(object->n_ops > object->n_obj_ops,
 614                                  !list_empty(&object->pending_ops));
 615                         fscache_start_operations(object);
 616                 } else {
 617                         ASSERT(list_empty(&object->pending_ops));
 618                 }
 619         }
 620         spin_unlock(&object->lock);
 621
 622         fscache_stat(&fscache_n_cop_lookup_complete);
 623         object->cache->ops->lookup_complete(object);
 624         fscache_stat_d(&fscache_n_cop_lookup_complete);
 625         fscache_enqueue_dependents(object);
 626
 627         fscache_hist(fscache_obj_instantiate_histogram, object->lookup_jif);
 628         fscache_stat(&fscache_n_object_avail);
 629
 630         _leave("");
 631 }
 632
 633 /*
 634  * drop an object's attachments
 635  */
 636 static void fscache_drop_object(struct fscache_object *object)
 637 {
 638         struct fscache_object *parent = object->parent;
 639         struct fscache_cache *cache = object->cache;
 640
 641         _enter("{OBJ%x,%d}", object->debug_id, object->n_children);
 642
 643         ASSERTCMP(object->cookie, ==, NULL);
 644         ASSERT(hlist_unhashed(&object->cookie_link));
 645
 646         spin_lock(&cache->object_list_lock);
 647         list_del_init(&object->cache_link);
 648         spin_unlock(&cache->object_list_lock);
 649
 650         fscache_stat(&fscache_n_cop_drop_object);
 651         cache->ops->drop_object(object);
 652         fscache_stat_d(&fscache_n_cop_drop_object);
 653
 654         if (parent) {
 655                 _debug("release parent OBJ%x {%d}",
 656                        parent->debug_id, parent->n_children);
 657
 658                 spin_lock(&parent->lock);
 659                 parent->n_children--;
 660                 if (parent->n_children == 0)
 661                         fscache_raise_event(parent, FSCACHE_OBJECT_EV_CLEARED);
 662                 spin_unlock(&parent->lock);
 663                 object->parent = NULL;
 664         }
 665
 666         /* this just shifts the object release to the slow work processor */
 667         fscache_stat(&fscache_n_cop_put_object);
 668         object->cache->ops->put_object(object);
 669         fscache_stat_d(&fscache_n_cop_put_object);
 670
 671         _leave("");
 672 }
 673
 674 /*
 675  * release or recycle an object that the netfs has discarded
 676  */
 677 static void fscache_release_object(struct fscache_object *object)
 678 {
 679         _enter("");
 680
 681         fscache_drop_object(object);
 682 }
 683
 684 /*
 685  * withdraw an object from active service
 686  */
 687 static void fscache_withdraw_object(struct fscache_object *object)
 688 {
 689         struct fscache_cookie *cookie;
 690         bool detached;
 691
 692         _enter("");
 693
 694         spin_lock(&object->lock);
 695         cookie = object->cookie;
 696         if (cookie) {
 697                 /* need to get the cookie lock before the object lock, starting
 698                  * from the object pointer */
 699                 atomic_inc(&cookie->usage);
 700                 spin_unlock(&object->lock);
 701
 702                 detached = false;
 703                 spin_lock(&cookie->lock);
 704                 spin_lock(&object->lock);
 705
 706                 if (object->cookie == cookie) {
 707                         hlist_del_init(&object->cookie_link);
 708                         object->cookie = NULL;
 709                         detached = true;
 710                 }
 711                 spin_unlock(&cookie->lock);
 712                 fscache_cookie_put(cookie);
 713                 if (detached)
 714                         fscache_cookie_put(cookie);
 715         }
 716
 717         spin_unlock(&object->lock);
 718
 719         fscache_drop_object(object);
 720 }
 721
 722 /*
 723  * withdraw an object from active service at the behest of the cache
 724  * - need break the links to a cached object cookie
 725  * - called under two situations:
 726  *   (1) recycler decides to reclaim an in-use object
 727  *   (2) a cache is unmounted
 728  * - have to take care as the cookie can be being relinquished by the netfs
 729  *   simultaneously
 730  * - the object is pinned by the caller holding a refcount on it
 731  */
 732 void fscache_withdrawing_object(struct fscache_cache *cache,
 733                                 struct fscache_object *object)
 734 {
 735         bool enqueue = false;
 736
 737         _enter(",OBJ%x", object->debug_id);
 738
 739         spin_lock(&object->lock);
 740         if (object->state < FSCACHE_OBJECT_WITHDRAWING) {
 741                 object->state = FSCACHE_OBJECT_WITHDRAWING;
 742                 enqueue = true;
 743         }
 744         spin_unlock(&object->lock);
 745
 746         if (enqueue)
 747                 fscache_enqueue_object(object);
 748
 749         _leave("");
 750 }
 751
 752 /*
 753  * allow the slow work item processor to get a ref on an object
 754  */
 755 static int fscache_object_slow_work_get_ref(struct slow_work *work)
 756 {
 757         struct fscache_object *object =
 758                 container_of(work, struct fscache_object, work);
 759         int ret;
 760
 761         fscache_stat(&fscache_n_cop_grab_object);
 762         ret = object->cache->ops->grab_object(object) ? 0 : -EAGAIN;
 763         fscache_stat_d(&fscache_n_cop_grab_object);
 764         return ret;
 765 }
 766
 767 /*
 768  * allow the slow work item processor to discard a ref on a work item
 769  */
 770 static void fscache_object_slow_work_put_ref(struct slow_work *work)
 771 {
 772         struct fscache_object *object =
 773                 container_of(work, struct fscache_object, work);
 774
 775         fscache_stat(&fscache_n_cop_put_object);
 776         object->cache->ops->put_object(object);
 777         fscache_stat_d(&fscache_n_cop_put_object);
 778 }
 779
 780 /*
 781  * enqueue an object for metadata-type processing
 782  */
 783 void fscache_enqueue_object(struct fscache_object *object)
 784 {
 785         _enter("{OBJ%x}", object->debug_id);
 786
 787         slow_work_enqueue(&object->work);
 788 }
 789
 790 /*
 791  * enqueue the dependents of an object for metadata-type processing
 792  * - the caller must hold the object's lock
 793  * - this may cause an already locked object to wind up being processed again
 794  */
 795 static void fscache_enqueue_dependents(struct fscache_object *object)
 796 {
 797         struct fscache_object *dep;
 798
 799         _enter("{OBJ%x}", object->debug_id);
 800
 801         if (list_empty(&object->dependents))
 802                 return;
 803
 804         spin_lock(&object->lock);
 805
 806         while (!list_empty(&object->dependents)) {
 807                 dep = list_entry(object->dependents.next,
 808                                  struct fscache_object, dep_link);
 809                 list_del_init(&dep->dep_link);
 810
 811
 812                 /* sort onto appropriate lists */
 813                 fscache_enqueue_object(dep);
 814                 fscache_stat(&fscache_n_cop_put_object);
 815                 dep->cache->ops->put_object(dep);
 816                 fscache_stat_d(&fscache_n_cop_put_object);
 817
 818                 if (!list_empty(&object->dependents))
 819                         cond_resched_lock(&object->lock);
 820         }
 821
 822         spin_unlock(&object->lock);
 823 }
 824
 825 /*
 826  * remove an object from whatever queue it's waiting on
 827  * - the caller must hold object->lock
 828  */
 829 void fscache_dequeue_object(struct fscache_object *object)
 830 {
 831         _enter("{OBJ%x}", object->debug_id);
 832
 833         if (!list_empty(&object->dep_link)) {
 834                 spin_lock(&object->parent->lock);
 835                 list_del_init(&object->dep_link);
 836                 spin_unlock(&object->parent->lock);
 837         }
 838
 839         _leave("");
 840 }
 841
 842 /**
 843  * fscache_check_aux - Ask the netfs whether an object on disk is still valid
 844  * @object: The object to ask about
 845  * @data: The auxiliary data for the object
 846  * @datalen: The size of the auxiliary data
 847  *
 848  * This function consults the netfs about the coherency state of an object
 849  */
 850 enum fscache_checkaux fscache_check_aux(struct fscache_object *object,
 851                                         const void *data, uint16_t datalen)
 852 {
 853         enum fscache_checkaux result;
 854
 855         if (!object->cookie->def->check_aux) {
 856                 fscache_stat(&fscache_n_checkaux_none);
 857                 return FSCACHE_CHECKAUX_OKAY;
 858         }
 859
 860         result = object->cookie->def->check_aux(object->cookie->netfs_data,
 861                                                 data, datalen);
 862         switch (result) {
 863                 /* entry okay as is */
 864         case FSCACHE_CHECKAUX_OKAY:
 865                 fscache_stat(&fscache_n_checkaux_okay);
 866                 break;
 867
 868                 /* entry requires update */
 869         case FSCACHE_CHECKAUX_NEEDS_UPDATE:
 870                 fscache_stat(&fscache_n_checkaux_update);
 871                 break;
 872
 873                 /* entry requires deletion */
 874         case FSCACHE_CHECKAUX_OBSOLETE:
 875                 fscache_stat(&fscache_n_checkaux_obsolete);
 876                 break;
 877
 878         default:
 879                 BUG();
 880         }
 881
 882         return result;
 883 }
 884 EXPORT_SYMBOL(fscache_check_aux);