fs/btrfs/delayed-ref.c

   1 /*
   2  * Copyright (C) 2009 Oracle.  All rights reserved.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public
   6  * License v2 as published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public
  14  * License along with this program; if not, write to the
  15  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  16  * Boston, MA 021110-1307, USA.
  17  */
  18
  19 #include <linux/sched.h>
  20 #include <linux/sort.h>
  21 #include <linux/ftrace.h>
  22 #include "ctree.h"
  23 #include "delayed-ref.h"
  24 #include "transaction.h"
  25
  26 /*
  27  * delayed back reference update tracking.  For subvolume trees
  28  * we queue up extent allocations and backref maintenance for
  29  * delayed processing.   This avoids deep call chains where we
  30  * add extents in the middle of btrfs_search_slot, and it allows
  31  * us to buffer up frequently modified backrefs in an rb tree instead
  32  * of hammering updates on the extent allocation tree.
  33  *
  34  * Right now this code is only used for reference counted trees, but
  35  * the long term goal is to get rid of the similar code for delayed
  36  * extent tree modifications.
  37  */
  38
  39 /*
  40  * entries in the rb tree are ordered by the byte number of the extent
  41  * and by the byte number of the parent block.
  42  */
  43 static int comp_entry(struct btrfs_delayed_ref_node *ref,
  44                       u64 bytenr, u64 parent)
  45 {
  46         if (bytenr < ref->bytenr)
  47                 return -1;
  48         if (bytenr > ref->bytenr)
  49                 return 1;
  50         if (parent < ref->parent)
  51                 return -1;
  52         if (parent > ref->parent)
  53                 return 1;
  54         return 0;
  55 }
  56
  57 /*
  58  * insert a new ref into the rbtree.  This returns any existing refs
  59  * for the same (bytenr,parent) tuple, or NULL if the new node was properly
  60  * inserted.
  61  */
  62 static struct btrfs_delayed_ref_node *tree_insert(struct rb_root *root,
  63                                                   u64 bytenr, u64 parent,
  64                                                   struct rb_node *node)
  65 {
  66         struct rb_node **p = &root->rb_node;
  67         struct rb_node *parent_node = NULL;
  68         struct btrfs_delayed_ref_node *entry;
  69         int cmp;
  70
  71         while (*p) {
  72                 parent_node = *p;
  73                 entry = rb_entry(parent_node, struct btrfs_delayed_ref_node,
  74                                  rb_node);
  75
  76                 cmp = comp_entry(entry, bytenr, parent);
  77                 if (cmp < 0)
  78                         p = &(*p)->rb_left;
  79                 else if (cmp > 0)
  80                         p = &(*p)->rb_right;
  81                 else
  82                         return entry;
  83         }
  84
  85         entry = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
  86         rb_link_node(node, parent_node, p);
  87         rb_insert_color(node, root);
  88         return NULL;
  89 }
  90
  91 /*
  92  * find an entry based on (bytenr,parent).  This returns the delayed
  93  * ref if it was able to find one, or NULL if nothing was in that spot
  94  */
  95 static struct btrfs_delayed_ref_node *tree_search(struct rb_root *root,
  96                                   u64 bytenr, u64 parent,
  97                                   struct btrfs_delayed_ref_node **last)
  98 {
  99         struct rb_node *n = root->rb_node;
 100         struct btrfs_delayed_ref_node *entry;
 101         int cmp;
 102
 103         while (n) {
 104                 entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
 105                 WARN_ON(!entry->in_tree);
 106                 if (last)
 107                         *last = entry;
 108
 109                 cmp = comp_entry(entry, bytenr, parent);
 110                 if (cmp < 0)
 111                         n = n->rb_left;
 112                 else if (cmp > 0)
 113                         n = n->rb_right;
 114                 else
 115                         return entry;
 116         }
 117         return NULL;
 118 }
 119
 120 int btrfs_delayed_ref_lock(struct btrfs_trans_handle *trans,
 121                            struct btrfs_delayed_ref_head *head)
 122 {
 123         struct btrfs_delayed_ref_root *delayed_refs;
 124
 125         delayed_refs = &trans->transaction->delayed_refs;
 126         assert_spin_locked(&delayed_refs->lock);
 127         if (mutex_trylock(&head->mutex))
 128                 return 0;
 129
 130         atomic_inc(&head->node.refs);
 131         spin_unlock(&delayed_refs->lock);
 132
 133         mutex_lock(&head->mutex);
 134         spin_lock(&delayed_refs->lock);
 135         if (!head->node.in_tree) {
 136                 mutex_unlock(&head->mutex);
 137                 btrfs_put_delayed_ref(&head->node);
 138                 return -EAGAIN;
 139         }
 140         btrfs_put_delayed_ref(&head->node);
 141         return 0;
 142 }
 143
 144 int btrfs_find_ref_cluster(struct btrfs_trans_handle *trans,
 145                            struct list_head *cluster, u64 start)
 146 {
 147         int count = 0;
 148         struct btrfs_delayed_ref_root *delayed_refs;
 149         struct rb_node *node;
 150         struct btrfs_delayed_ref_node *ref;
 151         struct btrfs_delayed_ref_head *head;
 152
 153         delayed_refs = &trans->transaction->delayed_refs;
 154         if (start == 0) {
 155                 node = rb_first(&delayed_refs->root);
 156         } else {
 157                 ref = NULL;
 158                 tree_search(&delayed_refs->root, start, (u64)-1, &ref);
 159                 if (ref) {
 160                         struct btrfs_delayed_ref_node *tmp;
 161
 162                         node = rb_prev(&ref->rb_node);
 163                         while (node) {
 164                                 tmp = rb_entry(node,
 165                                                struct btrfs_delayed_ref_node,
 166                                                rb_node);
 167                                 if (tmp->bytenr < start)
 168                                         break;
 169                                 ref = tmp;
 170                                 node = rb_prev(&ref->rb_node);
 171                         }
 172                         node = &ref->rb_node;
 173                 } else
 174                         node = rb_first(&delayed_refs->root);
 175         }
 176 again:
 177         while (node && count < 32) {
 178                 ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
 179                 if (btrfs_delayed_ref_is_head(ref)) {
 180                         head = btrfs_delayed_node_to_head(ref);
 181                         if (list_empty(&head->cluster)) {
 182                                 list_add_tail(&head->cluster, cluster);
 183                                 delayed_refs->run_delayed_start =
 184                                         head->node.bytenr;
 185                                 count++;
 186
 187                                 WARN_ON(delayed_refs->num_heads_ready == 0);
 188                                 delayed_refs->num_heads_ready--;
 189                         } else if (count) {
 190                                 /* the goal of the clustering is to find extents
 191                                  * that are likely to end up in the same extent
 192                                  * leaf on disk.  So, we don't want them spread
 193                                  * all over the tree.  Stop now if we've hit
 194                                  * a head that was already in use
 195                                  */
 196                                 break;
 197                         }
 198                 }
 199                 node = rb_next(node);
 200         }
 201         if (count) {
 202                 return 0;
 203         } else if (start) {
 204                 /*
 205                  * we've gone to the end of the rbtree without finding any
 206                  * clusters.  start from the beginning and try again
 207                  */
 208                 start = 0;
 209                 node = rb_first(&delayed_refs->root);
 210                 goto again;
 211         }
 212         return 1;
 213 }
 214
 215 /*
 216  * This checks to see if there are any delayed refs in the
 217  * btree for a given bytenr.  It returns one if it finds any
 218  * and zero otherwise.
 219  *
 220  * If it only finds a head node, it returns 0.
 221  *
 222  * The idea is to use this when deciding if you can safely delete an
 223  * extent from the extent allocation tree.  There may be a pending
 224  * ref in the rbtree that adds or removes references, so as long as this
 225  * returns one you need to leave the BTRFS_EXTENT_ITEM in the extent
 226  * allocation tree.
 227  */
 228 int btrfs_delayed_ref_pending(struct btrfs_trans_handle *trans, u64 bytenr)
 229 {
 230         struct btrfs_delayed_ref_node *ref;
 231         struct btrfs_delayed_ref_root *delayed_refs;
 232         struct rb_node *prev_node;
 233         int ret = 0;
 234
 235         delayed_refs = &trans->transaction->delayed_refs;
 236         spin_lock(&delayed_refs->lock);
 237
 238         ref = tree_search(&delayed_refs->root, bytenr, (u64)-1, NULL);
 239         if (ref) {
 240                 prev_node = rb_prev(&ref->rb_node);
 241                 if (!prev_node)
 242                         goto out;
 243                 ref = rb_entry(prev_node, struct btrfs_delayed_ref_node,
 244                                rb_node);
 245                 if (ref->bytenr == bytenr)
 246                         ret = 1;
 247         }
 248 out:
 249         spin_unlock(&delayed_refs->lock);
 250         return ret;
 251 }
 252
 253 /*
 254  * helper function to lookup reference count
 255  *
 256  * the head node for delayed ref is used to store the sum of all the
 257  * reference count modifications queued up in the rbtree.  This way you
 258  * can check to see what the reference count would be if all of the
 259  * delayed refs are processed.
 260  */
 261 int btrfs_lookup_extent_ref(struct btrfs_trans_handle *trans,
 262                             struct btrfs_root *root, u64 bytenr,
 263                             u64 num_bytes, u32 *refs)
 264 {
 265         struct btrfs_delayed_ref_node *ref;
 266         struct btrfs_delayed_ref_head *head;
 267         struct btrfs_delayed_ref_root *delayed_refs;
 268         struct btrfs_path *path;
 269         struct extent_buffer *leaf;
 270         struct btrfs_extent_item *ei;
 271         struct btrfs_key key;
 272         u32 num_refs;
 273         int ret;
 274
 275         path = btrfs_alloc_path();
 276         if (!path)
 277                 return -ENOMEM;
 278
 279         key.objectid = bytenr;
 280         key.type = BTRFS_EXTENT_ITEM_KEY;
 281         key.offset = num_bytes;
 282         delayed_refs = &trans->transaction->delayed_refs;
 283 again:
 284         ret = btrfs_search_slot(trans, root->fs_info->extent_root,
 285                                 &key, path, 0, 0);
 286         if (ret < 0)
 287                 goto out;
 288
 289         if (ret == 0) {
 290                 leaf = path->nodes[0];
 291                 ei = btrfs_item_ptr(leaf, path->slots[0],
 292                                     struct btrfs_extent_item);
 293                 num_refs = btrfs_extent_refs(leaf, ei);
 294         } else {
 295                 num_refs = 0;
 296                 ret = 0;
 297         }
 298
 299         spin_lock(&delayed_refs->lock);
 300         ref = tree_search(&delayed_refs->root, bytenr, (u64)-1, NULL);
 301         if (ref) {
 302                 head = btrfs_delayed_node_to_head(ref);
 303                 if (mutex_trylock(&head->mutex)) {
 304                         num_refs += ref->ref_mod;
 305                         mutex_unlock(&head->mutex);
 306                         *refs = num_refs;
 307                         goto out;
 308                 }
 309
 310                 atomic_inc(&ref->refs);
 311                 spin_unlock(&delayed_refs->lock);
 312
 313                 btrfs_release_path(root->fs_info->extent_root, path);
 314
 315                 mutex_lock(&head->mutex);
 316                 mutex_unlock(&head->mutex);
 317                 btrfs_put_delayed_ref(ref);
 318                 goto again;
 319         } else {
 320                 *refs = num_refs;
 321         }
 322 out:
 323         spin_unlock(&delayed_refs->lock);
 324         btrfs_free_path(path);
 325         return ret;
 326 }
 327
 328 /*
 329  * helper function to update an extent delayed ref in the
 330  * rbtree.  existing and update must both have the same
 331  * bytenr and parent
 332  *
 333  * This may free existing if the update cancels out whatever
 334  * operation it was doing.
 335  */
 336 static noinline void
 337 update_existing_ref(struct btrfs_trans_handle *trans,
 338                     struct btrfs_delayed_ref_root *delayed_refs,
 339                     struct btrfs_delayed_ref_node *existing,
 340                     struct btrfs_delayed_ref_node *update)
 341 {
 342         struct btrfs_delayed_ref *existing_ref;
 343         struct btrfs_delayed_ref *ref;
 344
 345         existing_ref = btrfs_delayed_node_to_ref(existing);
 346         ref = btrfs_delayed_node_to_ref(update);
 347
 348         if (ref->pin)
 349                 existing_ref->pin = 1;
 350
 351         if (ref->action != existing_ref->action) {
 352                 /*
 353                  * this is effectively undoing either an add or a
 354                  * drop.  We decrement the ref_mod, and if it goes
 355                  * down to zero we just delete the entry without
 356                  * every changing the extent allocation tree.
 357                  */
 358                 existing->ref_mod--;
 359                 if (existing->ref_mod == 0) {
 360                         rb_erase(&existing->rb_node,
 361                                  &delayed_refs->root);
 362                         existing->in_tree = 0;
 363                         btrfs_put_delayed_ref(existing);
 364                         delayed_refs->num_entries--;
 365                         if (trans->delayed_ref_updates)
 366                                 trans->delayed_ref_updates--;
 367                 }
 368         } else {
 369                 if (existing_ref->action == BTRFS_ADD_DELAYED_REF) {
 370                         /* if we're adding refs, make sure all the
 371                          * details match up.  The extent could
 372                          * have been totally freed and reallocated
 373                          * by a different owner before the delayed
 374                          * ref entries were removed.
 375                          */
 376                         existing_ref->owner_objectid = ref->owner_objectid;
 377                         existing_ref->generation = ref->generation;
 378                         existing_ref->root = ref->root;
 379                         existing->num_bytes = update->num_bytes;
 380                 }
 381                 /*
 382                  * the action on the existing ref matches
 383                  * the action on the ref we're trying to add.
 384                  * Bump the ref_mod by one so the backref that
 385                  * is eventually added/removed has the correct
 386                  * reference count
 387                  */
 388                 existing->ref_mod += update->ref_mod;
 389         }
 390 }
 391
 392 /*
 393  * helper function to update the accounting in the head ref
 394  * existing and update must have the same bytenr
 395  */
 396 static noinline void
 397 update_existing_head_ref(struct btrfs_delayed_ref_node *existing,
 398                          struct btrfs_delayed_ref_node *update)
 399 {
 400         struct btrfs_delayed_ref_head *existing_ref;
 401         struct btrfs_delayed_ref_head *ref;
 402
 403         existing_ref = btrfs_delayed_node_to_head(existing);
 404         ref = btrfs_delayed_node_to_head(update);
 405
 406         if (ref->must_insert_reserved) {
 407                 /* if the extent was freed and then
 408                  * reallocated before the delayed ref
 409                  * entries were processed, we can end up
 410                  * with an existing head ref without
 411                  * the must_insert_reserved flag set.
 412                  * Set it again here
 413                  */
 414                 existing_ref->must_insert_reserved = ref->must_insert_reserved;
 415
 416                 /*
 417                  * update the num_bytes so we make sure the accounting
 418                  * is done correctly
 419                  */
 420                 existing->num_bytes = update->num_bytes;
 421
 422         }
 423
 424         /*
 425          * update the reference mod on the head to reflect this new operation
 426          */
 427         existing->ref_mod += update->ref_mod;
 428 }
 429
 430 /*
 431  * helper function to actually insert a delayed ref into the rbtree.
 432  * this does all the dirty work in terms of maintaining the correct
 433  * overall modification count in the head node and properly dealing
 434  * with updating existing nodes as new modifications are queued.
 435  */
 436 static noinline int __btrfs_add_delayed_ref(struct btrfs_trans_handle *trans,
 437                           struct btrfs_delayed_ref_node *ref,
 438                           u64 bytenr, u64 num_bytes, u64 parent, u64 ref_root,
 439                           u64 ref_generation, u64 owner_objectid, int action,
 440                           int pin)
 441 {
 442         struct btrfs_delayed_ref_node *existing;
 443         struct btrfs_delayed_ref *full_ref;
 444         struct btrfs_delayed_ref_head *head_ref = NULL;
 445         struct btrfs_delayed_ref_root *delayed_refs;
 446         int count_mod = 1;
 447         int must_insert_reserved = 0;
 448
 449         /*
 450          * the head node stores the sum of all the mods, so dropping a ref
 451          * should drop the sum in the head node by one.
 452          */
 453         if (parent == (u64)-1) {
 454                 if (action == BTRFS_DROP_DELAYED_REF)
 455                         count_mod = -1;
 456                 else if (action == BTRFS_UPDATE_DELAYED_HEAD)
 457                         count_mod = 0;
 458         }
 459
 460         /*
 461          * BTRFS_ADD_DELAYED_EXTENT means that we need to update
 462          * the reserved accounting when the extent is finally added, or
 463          * if a later modification deletes the delayed ref without ever
 464          * inserting the extent into the extent allocation tree.
 465          * ref->must_insert_reserved is the flag used to record
 466          * that accounting mods are required.
 467          *
 468          * Once we record must_insert_reserved, switch the action to
 469          * BTRFS_ADD_DELAYED_REF because other special casing is not required.
 470          */
 471         if (action == BTRFS_ADD_DELAYED_EXTENT) {
 472                 must_insert_reserved = 1;
 473                 action = BTRFS_ADD_DELAYED_REF;
 474         } else {
 475                 must_insert_reserved = 0;
 476         }
 477
 478
 479         delayed_refs = &trans->transaction->delayed_refs;
 480
 481         /* first set the basic ref node struct up */
 482         atomic_set(&ref->refs, 1);
 483         ref->bytenr = bytenr;
 484         ref->parent = parent;
 485         ref->ref_mod = count_mod;
 486         ref->in_tree = 1;
 487         ref->num_bytes = num_bytes;
 488
 489         if (btrfs_delayed_ref_is_head(ref)) {
 490                 head_ref = btrfs_delayed_node_to_head(ref);
 491                 head_ref->must_insert_reserved = must_insert_reserved;
 492                 INIT_LIST_HEAD(&head_ref->cluster);
 493                 mutex_init(&head_ref->mutex);
 494         } else {
 495                 full_ref = btrfs_delayed_node_to_ref(ref);
 496                 full_ref->root = ref_root;
 497                 full_ref->generation = ref_generation;
 498                 full_ref->owner_objectid = owner_objectid;
 499                 full_ref->pin = pin;
 500                 full_ref->action = action;
 501         }
 502
 503         existing = tree_insert(&delayed_refs->root, bytenr,
 504                                parent, &ref->rb_node);
 505
 506         if (existing) {
 507                 if (btrfs_delayed_ref_is_head(ref))
 508                         update_existing_head_ref(existing, ref);
 509                 else
 510                         update_existing_ref(trans, delayed_refs, existing, ref);
 511
 512                 /*
 513                  * we've updated the existing ref, free the newly
 514                  * allocated ref
 515                  */
 516                 kfree(ref);
 517         } else {
 518                 if (btrfs_delayed_ref_is_head(ref)) {
 519                         delayed_refs->num_heads++;
 520                         delayed_refs->num_heads_ready++;
 521                 }
 522                 delayed_refs->num_entries++;
 523                 trans->delayed_ref_updates++;
 524         }
 525         return 0;
 526 }
 527
 528 /*
 529  * add a delayed ref to the tree.  This does all of the accounting required
 530  * to make sure the delayed ref is eventually processed before this
 531  * transaction commits.
 532  */
 533 int btrfs_add_delayed_ref(struct btrfs_trans_handle *trans,
 534                           u64 bytenr, u64 num_bytes, u64 parent, u64 ref_root,
 535                           u64 ref_generation, u64 owner_objectid, int action,
 536                           int pin)
 537 {
 538         struct btrfs_delayed_ref *ref;
 539         struct btrfs_delayed_ref_head *head_ref;
 540         struct btrfs_delayed_ref_root *delayed_refs;
 541         int ret;
 542
 543         ref = kmalloc(sizeof(*ref), GFP_NOFS);
 544         if (!ref)
 545                 return -ENOMEM;
 546
 547         /*
 548          * the parent = 0 case comes from cases where we don't actually
 549          * know the parent yet.  It will get updated later via a add/drop
 550          * pair.
 551          */
 552         if (parent == 0)
 553                 parent = bytenr;
 554
 555         head_ref = kmalloc(sizeof(*head_ref), GFP_NOFS);
 556         if (!head_ref) {
 557                 kfree(ref);
 558                 return -ENOMEM;
 559         }
 560         delayed_refs = &trans->transaction->delayed_refs;
 561         spin_lock(&delayed_refs->lock);
 562
 563         /*
 564          * insert both the head node and the new ref without dropping
 565          * the spin lock
 566          */
 567         ret = __btrfs_add_delayed_ref(trans, &head_ref->node, bytenr, num_bytes,
 568                                       (u64)-1, 0, 0, 0, action, pin);
 569         BUG_ON(ret);
 570
 571         ret = __btrfs_add_delayed_ref(trans, &ref->node, bytenr, num_bytes,
 572                                       parent, ref_root, ref_generation,
 573                                       owner_objectid, action, pin);
 574         BUG_ON(ret);
 575         spin_unlock(&delayed_refs->lock);
 576         return 0;
 577 }
 578
 579 /*
 580  * this does a simple search for the head node for a given extent.
 581  * It must be called with the delayed ref spinlock held, and it returns
 582  * the head node if any where found, or NULL if not.
 583  */
 584 struct btrfs_delayed_ref_head *
 585 btrfs_find_delayed_ref_head(struct btrfs_trans_handle *trans, u64 bytenr)
 586 {
 587         struct btrfs_delayed_ref_node *ref;
 588         struct btrfs_delayed_ref_root *delayed_refs;
 589
 590         delayed_refs = &trans->transaction->delayed_refs;
 591         ref = tree_search(&delayed_refs->root, bytenr, (u64)-1, NULL);
 592         if (ref)
 593                 return btrfs_delayed_node_to_head(ref);
 594         return NULL;
 595 }
 596
 597 /*
 598  * add a delayed ref to the tree.  This does all of the accounting required
 599  * to make sure the delayed ref is eventually processed before this
 600  * transaction commits.
 601  *
 602  * The main point of this call is to add and remove a backreference in a single
 603  * shot, taking the lock only once, and only searching for the head node once.
 604  *
 605  * It is the same as doing a ref add and delete in two separate calls.
 606  */
 607 int btrfs_update_delayed_ref(struct btrfs_trans_handle *trans,
 608                           u64 bytenr, u64 num_bytes, u64 orig_parent,
 609                           u64 parent, u64 orig_ref_root, u64 ref_root,
 610                           u64 orig_ref_generation, u64 ref_generation,
 611                           u64 owner_objectid, int pin)
 612 {
 613         struct btrfs_delayed_ref *ref;
 614         struct btrfs_delayed_ref *old_ref;
 615         struct btrfs_delayed_ref_head *head_ref;
 616         struct btrfs_delayed_ref_root *delayed_refs;
 617         int ret;
 618
 619         ref = kmalloc(sizeof(*ref), GFP_NOFS);
 620         if (!ref)
 621                 return -ENOMEM;
 622
 623         old_ref = kmalloc(sizeof(*old_ref), GFP_NOFS);
 624         if (!old_ref) {
 625                 kfree(ref);
 626                 return -ENOMEM;
 627         }
 628
 629         /*
 630          * the parent = 0 case comes from cases where we don't actually
 631          * know the parent yet.  It will get updated later via a add/drop
 632          * pair.
 633          */
 634         if (parent == 0)
 635                 parent = bytenr;
 636         if (orig_parent == 0)
 637                 orig_parent = bytenr;
 638
 639         head_ref = kmalloc(sizeof(*head_ref), GFP_NOFS);
 640         if (!head_ref) {
 641                 kfree(ref);
 642                 kfree(old_ref);
 643                 return -ENOMEM;
 644         }
 645         delayed_refs = &trans->transaction->delayed_refs;
 646         spin_lock(&delayed_refs->lock);
 647
 648         /*
 649          * insert both the head node and the new ref without dropping
 650          * the spin lock
 651          */
 652         ret = __btrfs_add_delayed_ref(trans, &head_ref->node, bytenr, num_bytes,
 653                                       (u64)-1, 0, 0, 0,
 654                                       BTRFS_UPDATE_DELAYED_HEAD, 0);
 655         BUG_ON(ret);
 656
 657         ret = __btrfs_add_delayed_ref(trans, &ref->node, bytenr, num_bytes,
 658                                       parent, ref_root, ref_generation,
 659                                       owner_objectid, BTRFS_ADD_DELAYED_REF, 0);
 660         BUG_ON(ret);
 661
 662         ret = __btrfs_add_delayed_ref(trans, &old_ref->node, bytenr, num_bytes,
 663                                       orig_parent, orig_ref_root,
 664                                       orig_ref_generation, owner_objectid,
 665                                       BTRFS_DROP_DELAYED_REF, pin);
 666         BUG_ON(ret);
 667         spin_unlock(&delayed_refs->lock);
 668         return 0;
 669 }