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TOMOYO Linux Cross Reference
Linux/fs/btrfs/transaction.c

Version: ~ [ linux-5.2-rc6 ] ~ [ linux-5.1.15 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.56 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.130 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.183 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.183 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.69 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.102 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ linux-2.6.39.4 ] ~ [ linux-2.6.38.8 ] ~ [ linux-2.6.37.6 ] ~ [ linux-2.6.36.4 ] ~ [ linux-2.6.35.14 ] ~ [ linux-2.6.34.15 ] ~ [ linux-2.6.33.20 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
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  1 /*
  2  * Copyright (C) 2007 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/fs.h>
 20 #include <linux/slab.h>
 21 #include <linux/sched.h>
 22 #include <linux/writeback.h>
 23 #include <linux/pagemap.h>
 24 #include <linux/blkdev.h>
 25 #include <linux/uuid.h>
 26 #include "ctree.h"
 27 #include "disk-io.h"
 28 #include "transaction.h"
 29 #include "locking.h"
 30 #include "tree-log.h"
 31 #include "inode-map.h"
 32 #include "volumes.h"
 33 #include "dev-replace.h"
 34 
 35 #define BTRFS_ROOT_TRANS_TAG 0
 36 
 37 static unsigned int btrfs_blocked_trans_types[TRANS_STATE_MAX] = {
 38         [TRANS_STATE_RUNNING]           = 0U,
 39         [TRANS_STATE_BLOCKED]           = (__TRANS_USERSPACE |
 40                                            __TRANS_START),
 41         [TRANS_STATE_COMMIT_START]      = (__TRANS_USERSPACE |
 42                                            __TRANS_START |
 43                                            __TRANS_ATTACH),
 44         [TRANS_STATE_COMMIT_DOING]      = (__TRANS_USERSPACE |
 45                                            __TRANS_START |
 46                                            __TRANS_ATTACH |
 47                                            __TRANS_JOIN),
 48         [TRANS_STATE_UNBLOCKED]         = (__TRANS_USERSPACE |
 49                                            __TRANS_START |
 50                                            __TRANS_ATTACH |
 51                                            __TRANS_JOIN |
 52                                            __TRANS_JOIN_NOLOCK),
 53         [TRANS_STATE_COMPLETED]         = (__TRANS_USERSPACE |
 54                                            __TRANS_START |
 55                                            __TRANS_ATTACH |
 56                                            __TRANS_JOIN |
 57                                            __TRANS_JOIN_NOLOCK),
 58 };
 59 
 60 static void put_transaction(struct btrfs_transaction *transaction)
 61 {
 62         WARN_ON(atomic_read(&transaction->use_count) == 0);
 63         if (atomic_dec_and_test(&transaction->use_count)) {
 64                 BUG_ON(!list_empty(&transaction->list));
 65                 WARN_ON(transaction->delayed_refs.root.rb_node);
 66                 while (!list_empty(&transaction->pending_chunks)) {
 67                         struct extent_map *em;
 68 
 69                         em = list_first_entry(&transaction->pending_chunks,
 70                                               struct extent_map, list);
 71                         list_del_init(&em->list);
 72                         free_extent_map(em);
 73                 }
 74                 kmem_cache_free(btrfs_transaction_cachep, transaction);
 75         }
 76 }
 77 
 78 static noinline void switch_commit_root(struct btrfs_root *root)
 79 {
 80         free_extent_buffer(root->commit_root);
 81         root->commit_root = btrfs_root_node(root);
 82 }
 83 
 84 static inline void extwriter_counter_inc(struct btrfs_transaction *trans,
 85                                          unsigned int type)
 86 {
 87         if (type & TRANS_EXTWRITERS)
 88                 atomic_inc(&trans->num_extwriters);
 89 }
 90 
 91 static inline void extwriter_counter_dec(struct btrfs_transaction *trans,
 92                                          unsigned int type)
 93 {
 94         if (type & TRANS_EXTWRITERS)
 95                 atomic_dec(&trans->num_extwriters);
 96 }
 97 
 98 static inline void extwriter_counter_init(struct btrfs_transaction *trans,
 99                                           unsigned int type)
100 {
101         atomic_set(&trans->num_extwriters, ((type & TRANS_EXTWRITERS) ? 1 : 0));
102 }
103 
104 static inline int extwriter_counter_read(struct btrfs_transaction *trans)
105 {
106         return atomic_read(&trans->num_extwriters);
107 }
108 
109 /*
110  * either allocate a new transaction or hop into the existing one
111  */
112 static noinline int join_transaction(struct btrfs_root *root, unsigned int type)
113 {
114         struct btrfs_transaction *cur_trans;
115         struct btrfs_fs_info *fs_info = root->fs_info;
116 
117         spin_lock(&fs_info->trans_lock);
118 loop:
119         /* The file system has been taken offline. No new transactions. */
120         if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {
121                 spin_unlock(&fs_info->trans_lock);
122                 return -EROFS;
123         }
124 
125         cur_trans = fs_info->running_transaction;
126         if (cur_trans) {
127                 if (cur_trans->aborted) {
128                         spin_unlock(&fs_info->trans_lock);
129                         return cur_trans->aborted;
130                 }
131                 if (btrfs_blocked_trans_types[cur_trans->state] & type) {
132                         spin_unlock(&fs_info->trans_lock);
133                         return -EBUSY;
134                 }
135                 atomic_inc(&cur_trans->use_count);
136                 atomic_inc(&cur_trans->num_writers);
137                 extwriter_counter_inc(cur_trans, type);
138                 spin_unlock(&fs_info->trans_lock);
139                 return 0;
140         }
141         spin_unlock(&fs_info->trans_lock);
142 
143         /*
144          * If we are ATTACH, we just want to catch the current transaction,
145          * and commit it. If there is no transaction, just return ENOENT.
146          */
147         if (type == TRANS_ATTACH)
148                 return -ENOENT;
149 
150         /*
151          * JOIN_NOLOCK only happens during the transaction commit, so
152          * it is impossible that ->running_transaction is NULL
153          */
154         BUG_ON(type == TRANS_JOIN_NOLOCK);
155 
156         cur_trans = kmem_cache_alloc(btrfs_transaction_cachep, GFP_NOFS);
157         if (!cur_trans)
158                 return -ENOMEM;
159 
160         spin_lock(&fs_info->trans_lock);
161         if (fs_info->running_transaction) {
162                 /*
163                  * someone started a transaction after we unlocked.  Make sure
164                  * to redo the checks above
165                  */
166                 kmem_cache_free(btrfs_transaction_cachep, cur_trans);
167                 goto loop;
168         } else if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {
169                 spin_unlock(&fs_info->trans_lock);
170                 kmem_cache_free(btrfs_transaction_cachep, cur_trans);
171                 return -EROFS;
172         }
173 
174         atomic_set(&cur_trans->num_writers, 1);
175         extwriter_counter_init(cur_trans, type);
176         init_waitqueue_head(&cur_trans->writer_wait);
177         init_waitqueue_head(&cur_trans->commit_wait);
178         cur_trans->state = TRANS_STATE_RUNNING;
179         /*
180          * One for this trans handle, one so it will live on until we
181          * commit the transaction.
182          */
183         atomic_set(&cur_trans->use_count, 2);
184         cur_trans->start_time = get_seconds();
185 
186         cur_trans->delayed_refs.root = RB_ROOT;
187         cur_trans->delayed_refs.num_entries = 0;
188         cur_trans->delayed_refs.num_heads_ready = 0;
189         cur_trans->delayed_refs.num_heads = 0;
190         cur_trans->delayed_refs.flushing = 0;
191         cur_trans->delayed_refs.run_delayed_start = 0;
192 
193         /*
194          * although the tree mod log is per file system and not per transaction,
195          * the log must never go across transaction boundaries.
196          */
197         smp_mb();
198         if (!list_empty(&fs_info->tree_mod_seq_list))
199                 WARN(1, KERN_ERR "btrfs: tree_mod_seq_list not empty when "
200                         "creating a fresh transaction\n");
201         if (!RB_EMPTY_ROOT(&fs_info->tree_mod_log))
202                 WARN(1, KERN_ERR "btrfs: tree_mod_log rb tree not empty when "
203                         "creating a fresh transaction\n");
204         atomic64_set(&fs_info->tree_mod_seq, 0);
205 
206         spin_lock_init(&cur_trans->delayed_refs.lock);
207         atomic_set(&cur_trans->delayed_refs.procs_running_refs, 0);
208         atomic_set(&cur_trans->delayed_refs.ref_seq, 0);
209         init_waitqueue_head(&cur_trans->delayed_refs.wait);
210 
211         INIT_LIST_HEAD(&cur_trans->pending_snapshots);
212         INIT_LIST_HEAD(&cur_trans->ordered_operations);
213         INIT_LIST_HEAD(&cur_trans->pending_chunks);
214         list_add_tail(&cur_trans->list, &fs_info->trans_list);
215         extent_io_tree_init(&cur_trans->dirty_pages,
216                              fs_info->btree_inode->i_mapping);
217         fs_info->generation++;
218         cur_trans->transid = fs_info->generation;
219         fs_info->running_transaction = cur_trans;
220         cur_trans->aborted = 0;
221         spin_unlock(&fs_info->trans_lock);
222 
223         return 0;
224 }
225 
226 /*
227  * this does all the record keeping required to make sure that a reference
228  * counted root is properly recorded in a given transaction.  This is required
229  * to make sure the old root from before we joined the transaction is deleted
230  * when the transaction commits
231  */
232 static int record_root_in_trans(struct btrfs_trans_handle *trans,
233                                struct btrfs_root *root)
234 {
235         if (root->ref_cows && root->last_trans < trans->transid) {
236                 WARN_ON(root == root->fs_info->extent_root);
237                 WARN_ON(root->commit_root != root->node);
238 
239                 /*
240                  * see below for in_trans_setup usage rules
241                  * we have the reloc mutex held now, so there
242                  * is only one writer in this function
243                  */
244                 root->in_trans_setup = 1;
245 
246                 /* make sure readers find in_trans_setup before
247                  * they find our root->last_trans update
248                  */
249                 smp_wmb();
250 
251                 spin_lock(&root->fs_info->fs_roots_radix_lock);
252                 if (root->last_trans == trans->transid) {
253                         spin_unlock(&root->fs_info->fs_roots_radix_lock);
254                         return 0;
255                 }
256                 radix_tree_tag_set(&root->fs_info->fs_roots_radix,
257                            (unsigned long)root->root_key.objectid,
258                            BTRFS_ROOT_TRANS_TAG);
259                 spin_unlock(&root->fs_info->fs_roots_radix_lock);
260                 root->last_trans = trans->transid;
261 
262                 /* this is pretty tricky.  We don't want to
263                  * take the relocation lock in btrfs_record_root_in_trans
264                  * unless we're really doing the first setup for this root in
265                  * this transaction.
266                  *
267                  * Normally we'd use root->last_trans as a flag to decide
268                  * if we want to take the expensive mutex.
269                  *
270                  * But, we have to set root->last_trans before we
271                  * init the relocation root, otherwise, we trip over warnings
272                  * in ctree.c.  The solution used here is to flag ourselves
273                  * with root->in_trans_setup.  When this is 1, we're still
274                  * fixing up the reloc trees and everyone must wait.
275                  *
276                  * When this is zero, they can trust root->last_trans and fly
277                  * through btrfs_record_root_in_trans without having to take the
278                  * lock.  smp_wmb() makes sure that all the writes above are
279                  * done before we pop in the zero below
280                  */
281                 btrfs_init_reloc_root(trans, root);
282                 smp_wmb();
283                 root->in_trans_setup = 0;
284         }
285         return 0;
286 }
287 
288 
289 int btrfs_record_root_in_trans(struct btrfs_trans_handle *trans,
290                                struct btrfs_root *root)
291 {
292         if (!root->ref_cows)
293                 return 0;
294 
295         /*
296          * see record_root_in_trans for comments about in_trans_setup usage
297          * and barriers
298          */
299         smp_rmb();
300         if (root->last_trans == trans->transid &&
301             !root->in_trans_setup)
302                 return 0;
303 
304         mutex_lock(&root->fs_info->reloc_mutex);
305         record_root_in_trans(trans, root);
306         mutex_unlock(&root->fs_info->reloc_mutex);
307 
308         return 0;
309 }
310 
311 static inline int is_transaction_blocked(struct btrfs_transaction *trans)
312 {
313         return (trans->state >= TRANS_STATE_BLOCKED &&
314                 trans->state < TRANS_STATE_UNBLOCKED &&
315                 !trans->aborted);
316 }
317 
318 /* wait for commit against the current transaction to become unblocked
319  * when this is done, it is safe to start a new transaction, but the current
320  * transaction might not be fully on disk.
321  */
322 static void wait_current_trans(struct btrfs_root *root)
323 {
324         struct btrfs_transaction *cur_trans;
325 
326         spin_lock(&root->fs_info->trans_lock);
327         cur_trans = root->fs_info->running_transaction;
328         if (cur_trans && is_transaction_blocked(cur_trans)) {
329                 atomic_inc(&cur_trans->use_count);
330                 spin_unlock(&root->fs_info->trans_lock);
331 
332                 wait_event(root->fs_info->transaction_wait,
333                            cur_trans->state >= TRANS_STATE_UNBLOCKED ||
334                            cur_trans->aborted);
335                 put_transaction(cur_trans);
336         } else {
337                 spin_unlock(&root->fs_info->trans_lock);
338         }
339 }
340 
341 static int may_wait_transaction(struct btrfs_root *root, int type)
342 {
343         if (root->fs_info->log_root_recovering)
344                 return 0;
345 
346         if (type == TRANS_USERSPACE)
347                 return 1;
348 
349         if (type == TRANS_START &&
350             !atomic_read(&root->fs_info->open_ioctl_trans))
351                 return 1;
352 
353         return 0;
354 }
355 
356 static struct btrfs_trans_handle *
357 start_transaction(struct btrfs_root *root, u64 num_items, unsigned int type,
358                   enum btrfs_reserve_flush_enum flush)
359 {
360         struct btrfs_trans_handle *h;
361         struct btrfs_transaction *cur_trans;
362         u64 num_bytes = 0;
363         int ret;
364         u64 qgroup_reserved = 0;
365 
366         if (test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state))
367                 return ERR_PTR(-EROFS);
368 
369         if (current->journal_info) {
370                 WARN_ON(type & TRANS_EXTWRITERS);
371                 h = current->journal_info;
372                 h->use_count++;
373                 WARN_ON(h->use_count > 2);
374                 h->orig_rsv = h->block_rsv;
375                 h->block_rsv = NULL;
376                 goto got_it;
377         }
378 
379         /*
380          * Do the reservation before we join the transaction so we can do all
381          * the appropriate flushing if need be.
382          */
383         if (num_items > 0 && root != root->fs_info->chunk_root) {
384                 if (root->fs_info->quota_enabled &&
385                     is_fstree(root->root_key.objectid)) {
386                         qgroup_reserved = num_items * root->leafsize;
387                         ret = btrfs_qgroup_reserve(root, qgroup_reserved);
388                         if (ret)
389                                 return ERR_PTR(ret);
390                 }
391 
392                 num_bytes = btrfs_calc_trans_metadata_size(root, num_items);
393                 ret = btrfs_block_rsv_add(root,
394                                           &root->fs_info->trans_block_rsv,
395                                           num_bytes, flush);
396                 if (ret)
397                         goto reserve_fail;
398         }
399 again:
400         h = kmem_cache_alloc(btrfs_trans_handle_cachep, GFP_NOFS);
401         if (!h) {
402                 ret = -ENOMEM;
403                 goto alloc_fail;
404         }
405 
406         /*
407          * If we are JOIN_NOLOCK we're already committing a transaction and
408          * waiting on this guy, so we don't need to do the sb_start_intwrite
409          * because we're already holding a ref.  We need this because we could
410          * have raced in and did an fsync() on a file which can kick a commit
411          * and then we deadlock with somebody doing a freeze.
412          *
413          * If we are ATTACH, it means we just want to catch the current
414          * transaction and commit it, so we needn't do sb_start_intwrite(). 
415          */
416         if (type & __TRANS_FREEZABLE)
417                 sb_start_intwrite(root->fs_info->sb);
418 
419         if (may_wait_transaction(root, type))
420                 wait_current_trans(root);
421 
422         do {
423                 ret = join_transaction(root, type);
424                 if (ret == -EBUSY) {
425                         wait_current_trans(root);
426                         if (unlikely(type == TRANS_ATTACH))
427                                 ret = -ENOENT;
428                 }
429         } while (ret == -EBUSY);
430 
431         if (ret < 0) {
432                 /* We must get the transaction if we are JOIN_NOLOCK. */
433                 BUG_ON(type == TRANS_JOIN_NOLOCK);
434                 goto join_fail;
435         }
436 
437         cur_trans = root->fs_info->running_transaction;
438 
439         h->transid = cur_trans->transid;
440         h->transaction = cur_trans;
441         h->blocks_used = 0;
442         h->bytes_reserved = 0;
443         h->root = root;
444         h->delayed_ref_updates = 0;
445         h->use_count = 1;
446         h->adding_csums = 0;
447         h->block_rsv = NULL;
448         h->orig_rsv = NULL;
449         h->aborted = 0;
450         h->qgroup_reserved = 0;
451         h->delayed_ref_elem.seq = 0;
452         h->type = type;
453         h->allocating_chunk = false;
454         INIT_LIST_HEAD(&h->qgroup_ref_list);
455         INIT_LIST_HEAD(&h->new_bgs);
456 
457         smp_mb();
458         if (cur_trans->state >= TRANS_STATE_BLOCKED &&
459             may_wait_transaction(root, type)) {
460                 btrfs_commit_transaction(h, root);
461                 goto again;
462         }
463 
464         if (num_bytes) {
465                 trace_btrfs_space_reservation(root->fs_info, "transaction",
466                                               h->transid, num_bytes, 1);
467                 h->block_rsv = &root->fs_info->trans_block_rsv;
468                 h->bytes_reserved = num_bytes;
469         }
470         h->qgroup_reserved = qgroup_reserved;
471 
472 got_it:
473         btrfs_record_root_in_trans(h, root);
474 
475         if (!current->journal_info && type != TRANS_USERSPACE)
476                 current->journal_info = h;
477         return h;
478 
479 join_fail:
480         if (type & __TRANS_FREEZABLE)
481                 sb_end_intwrite(root->fs_info->sb);
482         kmem_cache_free(btrfs_trans_handle_cachep, h);
483 alloc_fail:
484         if (num_bytes)
485                 btrfs_block_rsv_release(root, &root->fs_info->trans_block_rsv,
486                                         num_bytes);
487 reserve_fail:
488         if (qgroup_reserved)
489                 btrfs_qgroup_free(root, qgroup_reserved);
490         return ERR_PTR(ret);
491 }
492 
493 struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root,
494                                                    int num_items)
495 {
496         return start_transaction(root, num_items, TRANS_START,
497                                  BTRFS_RESERVE_FLUSH_ALL);
498 }
499 
500 struct btrfs_trans_handle *btrfs_start_transaction_lflush(
501                                         struct btrfs_root *root, int num_items)
502 {
503         return start_transaction(root, num_items, TRANS_START,
504                                  BTRFS_RESERVE_FLUSH_LIMIT);
505 }
506 
507 struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root)
508 {
509         return start_transaction(root, 0, TRANS_JOIN, 0);
510 }
511 
512 struct btrfs_trans_handle *btrfs_join_transaction_nolock(struct btrfs_root *root)
513 {
514         return start_transaction(root, 0, TRANS_JOIN_NOLOCK, 0);
515 }
516 
517 struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root)
518 {
519         return start_transaction(root, 0, TRANS_USERSPACE, 0);
520 }
521 
522 /*
523  * btrfs_attach_transaction() - catch the running transaction
524  *
525  * It is used when we want to commit the current the transaction, but
526  * don't want to start a new one.
527  *
528  * Note: If this function return -ENOENT, it just means there is no
529  * running transaction. But it is possible that the inactive transaction
530  * is still in the memory, not fully on disk. If you hope there is no
531  * inactive transaction in the fs when -ENOENT is returned, you should
532  * invoke
533  *     btrfs_attach_transaction_barrier()
534  */
535 struct btrfs_trans_handle *btrfs_attach_transaction(struct btrfs_root *root)
536 {
537         return start_transaction(root, 0, TRANS_ATTACH, 0);
538 }
539 
540 /*
541  * btrfs_attach_transaction_barrier() - catch the running transaction
542  *
543  * It is similar to the above function, the differentia is this one
544  * will wait for all the inactive transactions until they fully
545  * complete.
546  */
547 struct btrfs_trans_handle *
548 btrfs_attach_transaction_barrier(struct btrfs_root *root)
549 {
550         struct btrfs_trans_handle *trans;
551 
552         trans = start_transaction(root, 0, TRANS_ATTACH, 0);
553         if (IS_ERR(trans) && PTR_ERR(trans) == -ENOENT)
554                 btrfs_wait_for_commit(root, 0);
555 
556         return trans;
557 }
558 
559 /* wait for a transaction commit to be fully complete */
560 static noinline void wait_for_commit(struct btrfs_root *root,
561                                     struct btrfs_transaction *commit)
562 {
563         wait_event(commit->commit_wait, commit->state == TRANS_STATE_COMPLETED);
564 }
565 
566 int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid)
567 {
568         struct btrfs_transaction *cur_trans = NULL, *t;
569         int ret = 0;
570 
571         if (transid) {
572                 if (transid <= root->fs_info->last_trans_committed)
573                         goto out;
574 
575                 ret = -EINVAL;
576                 /* find specified transaction */
577                 spin_lock(&root->fs_info->trans_lock);
578                 list_for_each_entry(t, &root->fs_info->trans_list, list) {
579                         if (t->transid == transid) {
580                                 cur_trans = t;
581                                 atomic_inc(&cur_trans->use_count);
582                                 ret = 0;
583                                 break;
584                         }
585                         if (t->transid > transid) {
586                                 ret = 0;
587                                 break;
588                         }
589                 }
590                 spin_unlock(&root->fs_info->trans_lock);
591                 /* The specified transaction doesn't exist */
592                 if (!cur_trans)
593                         goto out;
594         } else {
595                 /* find newest transaction that is committing | committed */
596                 spin_lock(&root->fs_info->trans_lock);
597                 list_for_each_entry_reverse(t, &root->fs_info->trans_list,
598                                             list) {
599                         if (t->state >= TRANS_STATE_COMMIT_START) {
600                                 if (t->state == TRANS_STATE_COMPLETED)
601                                         break;
602                                 cur_trans = t;
603                                 atomic_inc(&cur_trans->use_count);
604                                 break;
605                         }
606                 }
607                 spin_unlock(&root->fs_info->trans_lock);
608                 if (!cur_trans)
609                         goto out;  /* nothing committing|committed */
610         }
611 
612         wait_for_commit(root, cur_trans);
613         put_transaction(cur_trans);
614 out:
615         return ret;
616 }
617 
618 void btrfs_throttle(struct btrfs_root *root)
619 {
620         if (!atomic_read(&root->fs_info->open_ioctl_trans))
621                 wait_current_trans(root);
622 }
623 
624 static int should_end_transaction(struct btrfs_trans_handle *trans,
625                                   struct btrfs_root *root)
626 {
627         if (root->fs_info->global_block_rsv.space_info->full &&
628             btrfs_should_throttle_delayed_refs(trans, root))
629                 return 1;
630 
631         return !!btrfs_block_rsv_check(root, &root->fs_info->global_block_rsv, 5);
632 }
633 
634 int btrfs_should_end_transaction(struct btrfs_trans_handle *trans,
635                                  struct btrfs_root *root)
636 {
637         struct btrfs_transaction *cur_trans = trans->transaction;
638         int updates;
639         int err;
640 
641         smp_mb();
642         if (cur_trans->state >= TRANS_STATE_BLOCKED ||
643             cur_trans->delayed_refs.flushing)
644                 return 1;
645 
646         updates = trans->delayed_ref_updates;
647         trans->delayed_ref_updates = 0;
648         if (updates) {
649                 err = btrfs_run_delayed_refs(trans, root, updates);
650                 if (err) /* Error code will also eval true */
651                         return err;
652         }
653 
654         return should_end_transaction(trans, root);
655 }
656 
657 static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
658                           struct btrfs_root *root, int throttle)
659 {
660         struct btrfs_transaction *cur_trans = trans->transaction;
661         struct btrfs_fs_info *info = root->fs_info;
662         unsigned long cur = trans->delayed_ref_updates;
663         int lock = (trans->type != TRANS_JOIN_NOLOCK);
664         int err = 0;
665 
666         if (--trans->use_count) {
667                 trans->block_rsv = trans->orig_rsv;
668                 return 0;
669         }
670 
671         /*
672          * do the qgroup accounting as early as possible
673          */
674         err = btrfs_delayed_refs_qgroup_accounting(trans, info);
675 
676         btrfs_trans_release_metadata(trans, root);
677         trans->block_rsv = NULL;
678 
679         if (trans->qgroup_reserved) {
680                 /*
681                  * the same root has to be passed here between start_transaction
682                  * and end_transaction. Subvolume quota depends on this.
683                  */
684                 btrfs_qgroup_free(trans->root, trans->qgroup_reserved);
685                 trans->qgroup_reserved = 0;
686         }
687 
688         if (!list_empty(&trans->new_bgs))
689                 btrfs_create_pending_block_groups(trans, root);
690 
691         trans->delayed_ref_updates = 0;
692         if (btrfs_should_throttle_delayed_refs(trans, root)) {
693                 cur = max_t(unsigned long, cur, 1);
694                 trans->delayed_ref_updates = 0;
695                 btrfs_run_delayed_refs(trans, root, cur);
696         }
697 
698         btrfs_trans_release_metadata(trans, root);
699         trans->block_rsv = NULL;
700 
701         if (!list_empty(&trans->new_bgs))
702                 btrfs_create_pending_block_groups(trans, root);
703 
704         if (lock && !atomic_read(&root->fs_info->open_ioctl_trans) &&
705             should_end_transaction(trans, root) &&
706             ACCESS_ONCE(cur_trans->state) == TRANS_STATE_RUNNING) {
707                 spin_lock(&info->trans_lock);
708                 if (cur_trans->state == TRANS_STATE_RUNNING)
709                         cur_trans->state = TRANS_STATE_BLOCKED;
710                 spin_unlock(&info->trans_lock);
711         }
712 
713         if (lock && ACCESS_ONCE(cur_trans->state) == TRANS_STATE_BLOCKED) {
714                 if (throttle) {
715                         /*
716                          * We may race with somebody else here so end up having
717                          * to call end_transaction on ourselves again, so inc
718                          * our use_count.
719                          */
720                         trans->use_count++;
721                         return btrfs_commit_transaction(trans, root);
722                 } else {
723                         wake_up_process(info->transaction_kthread);
724                 }
725         }
726 
727         if (trans->type & __TRANS_FREEZABLE)
728                 sb_end_intwrite(root->fs_info->sb);
729 
730         WARN_ON(cur_trans != info->running_transaction);
731         WARN_ON(atomic_read(&cur_trans->num_writers) < 1);
732         atomic_dec(&cur_trans->num_writers);
733         extwriter_counter_dec(cur_trans, trans->type);
734 
735         smp_mb();
736         if (waitqueue_active(&cur_trans->writer_wait))
737                 wake_up(&cur_trans->writer_wait);
738         put_transaction(cur_trans);
739 
740         if (current->journal_info == trans)
741                 current->journal_info = NULL;
742 
743         if (throttle)
744                 btrfs_run_delayed_iputs(root);
745 
746         if (trans->aborted ||
747             test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state))
748                 err = -EIO;
749         assert_qgroups_uptodate(trans);
750 
751         kmem_cache_free(btrfs_trans_handle_cachep, trans);
752         return err;
753 }
754 
755 int btrfs_end_transaction(struct btrfs_trans_handle *trans,
756                           struct btrfs_root *root)
757 {
758         return __btrfs_end_transaction(trans, root, 0);
759 }
760 
761 int btrfs_end_transaction_throttle(struct btrfs_trans_handle *trans,
762                                    struct btrfs_root *root)
763 {
764         return __btrfs_end_transaction(trans, root, 1);
765 }
766 
767 int btrfs_end_transaction_dmeta(struct btrfs_trans_handle *trans,
768                                 struct btrfs_root *root)
769 {
770         return __btrfs_end_transaction(trans, root, 1);
771 }
772 
773 /*
774  * when btree blocks are allocated, they have some corresponding bits set for
775  * them in one of two extent_io trees.  This is used to make sure all of
776  * those extents are sent to disk but does not wait on them
777  */
778 int btrfs_write_marked_extents(struct btrfs_root *root,
779                                struct extent_io_tree *dirty_pages, int mark)
780 {
781         int err = 0;
782         int werr = 0;
783         struct address_space *mapping = root->fs_info->btree_inode->i_mapping;
784         struct extent_state *cached_state = NULL;
785         u64 start = 0;
786         u64 end;
787 
788         while (!find_first_extent_bit(dirty_pages, start, &start, &end,
789                                       mark, &cached_state)) {
790                 convert_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
791                                    mark, &cached_state, GFP_NOFS);
792                 cached_state = NULL;
793                 err = filemap_fdatawrite_range(mapping, start, end);
794                 if (err)
795                         werr = err;
796                 cond_resched();
797                 start = end + 1;
798         }
799         if (err)
800                 werr = err;
801         return werr;
802 }
803 
804 /*
805  * when btree blocks are allocated, they have some corresponding bits set for
806  * them in one of two extent_io trees.  This is used to make sure all of
807  * those extents are on disk for transaction or log commit.  We wait
808  * on all the pages and clear them from the dirty pages state tree
809  */
810 int btrfs_wait_marked_extents(struct btrfs_root *root,
811                               struct extent_io_tree *dirty_pages, int mark)
812 {
813         int err = 0;
814         int werr = 0;
815         struct address_space *mapping = root->fs_info->btree_inode->i_mapping;
816         struct extent_state *cached_state = NULL;
817         u64 start = 0;
818         u64 end;
819 
820         while (!find_first_extent_bit(dirty_pages, start, &start, &end,
821                                       EXTENT_NEED_WAIT, &cached_state)) {
822                 clear_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
823                                  0, 0, &cached_state, GFP_NOFS);
824                 err = filemap_fdatawait_range(mapping, start, end);
825                 if (err)
826                         werr = err;
827                 cond_resched();
828                 start = end + 1;
829         }
830         if (err)
831                 werr = err;
832         return werr;
833 }
834 
835 /*
836  * when btree blocks are allocated, they have some corresponding bits set for
837  * them in one of two extent_io trees.  This is used to make sure all of
838  * those extents are on disk for transaction or log commit
839  */
840 int btrfs_write_and_wait_marked_extents(struct btrfs_root *root,
841                                 struct extent_io_tree *dirty_pages, int mark)
842 {
843         int ret;
844         int ret2;
845         struct blk_plug plug;
846 
847         blk_start_plug(&plug);
848         ret = btrfs_write_marked_extents(root, dirty_pages, mark);
849         blk_finish_plug(&plug);
850         ret2 = btrfs_wait_marked_extents(root, dirty_pages, mark);
851 
852         if (ret)
853                 return ret;
854         if (ret2)
855                 return ret2;
856         return 0;
857 }
858 
859 int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
860                                      struct btrfs_root *root)
861 {
862         if (!trans || !trans->transaction) {
863                 struct inode *btree_inode;
864                 btree_inode = root->fs_info->btree_inode;
865                 return filemap_write_and_wait(btree_inode->i_mapping);
866         }
867         return btrfs_write_and_wait_marked_extents(root,
868                                            &trans->transaction->dirty_pages,
869                                            EXTENT_DIRTY);
870 }
871 
872 /*
873  * this is used to update the root pointer in the tree of tree roots.
874  *
875  * But, in the case of the extent allocation tree, updating the root
876  * pointer may allocate blocks which may change the root of the extent
877  * allocation tree.
878  *
879  * So, this loops and repeats and makes sure the cowonly root didn't
880  * change while the root pointer was being updated in the metadata.
881  */
882 static int update_cowonly_root(struct btrfs_trans_handle *trans,
883                                struct btrfs_root *root)
884 {
885         int ret;
886         u64 old_root_bytenr;
887         u64 old_root_used;
888         struct btrfs_root *tree_root = root->fs_info->tree_root;
889 
890         old_root_used = btrfs_root_used(&root->root_item);
891         btrfs_write_dirty_block_groups(trans, root);
892 
893         while (1) {
894                 old_root_bytenr = btrfs_root_bytenr(&root->root_item);
895                 if (old_root_bytenr == root->node->start &&
896                     old_root_used == btrfs_root_used(&root->root_item))
897                         break;
898 
899                 btrfs_set_root_node(&root->root_item, root->node);
900                 ret = btrfs_update_root(trans, tree_root,
901                                         &root->root_key,
902                                         &root->root_item);
903                 if (ret)
904                         return ret;
905 
906                 old_root_used = btrfs_root_used(&root->root_item);
907                 ret = btrfs_write_dirty_block_groups(trans, root);
908                 if (ret)
909                         return ret;
910         }
911 
912         if (root != root->fs_info->extent_root)
913                 switch_commit_root(root);
914 
915         return 0;
916 }
917 
918 /*
919  * update all the cowonly tree roots on disk
920  *
921  * The error handling in this function may not be obvious. Any of the
922  * failures will cause the file system to go offline. We still need
923  * to clean up the delayed refs.
924  */
925 static noinline int commit_cowonly_roots(struct btrfs_trans_handle *trans,
926                                          struct btrfs_root *root)
927 {
928         struct btrfs_fs_info *fs_info = root->fs_info;
929         struct list_head *next;
930         struct extent_buffer *eb;
931         int ret;
932 
933         ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
934         if (ret)
935                 return ret;
936 
937         eb = btrfs_lock_root_node(fs_info->tree_root);
938         ret = btrfs_cow_block(trans, fs_info->tree_root, eb, NULL,
939                               0, &eb);
940         btrfs_tree_unlock(eb);
941         free_extent_buffer(eb);
942 
943         if (ret)
944                 return ret;
945 
946         ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
947         if (ret)
948                 return ret;
949 
950         ret = btrfs_run_dev_stats(trans, root->fs_info);
951         WARN_ON(ret);
952         ret = btrfs_run_dev_replace(trans, root->fs_info);
953         WARN_ON(ret);
954 
955         ret = btrfs_run_qgroups(trans, root->fs_info);
956         BUG_ON(ret);
957 
958         /* run_qgroups might have added some more refs */
959         ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
960         BUG_ON(ret);
961 
962         while (!list_empty(&fs_info->dirty_cowonly_roots)) {
963                 next = fs_info->dirty_cowonly_roots.next;
964                 list_del_init(next);
965                 root = list_entry(next, struct btrfs_root, dirty_list);
966 
967                 ret = update_cowonly_root(trans, root);
968                 if (ret)
969                         return ret;
970         }
971 
972         down_write(&fs_info->extent_commit_sem);
973         switch_commit_root(fs_info->extent_root);
974         up_write(&fs_info->extent_commit_sem);
975 
976         btrfs_after_dev_replace_commit(fs_info);
977 
978         return 0;
979 }
980 
981 /*
982  * dead roots are old snapshots that need to be deleted.  This allocates
983  * a dirty root struct and adds it into the list of dead roots that need to
984  * be deleted
985  */
986 void btrfs_add_dead_root(struct btrfs_root *root)
987 {
988         spin_lock(&root->fs_info->trans_lock);
989         if (list_empty(&root->root_list))
990                 list_add_tail(&root->root_list, &root->fs_info->dead_roots);
991         spin_unlock(&root->fs_info->trans_lock);
992 }
993 
994 /*
995  * update all the cowonly tree roots on disk
996  */
997 static noinline int commit_fs_roots(struct btrfs_trans_handle *trans,
998                                     struct btrfs_root *root)
999 {
1000         struct btrfs_root *gang[8];
1001         struct btrfs_fs_info *fs_info = root->fs_info;
1002         int i;
1003         int ret;
1004         int err = 0;
1005 
1006         spin_lock(&fs_info->fs_roots_radix_lock);
1007         while (1) {
1008                 ret = radix_tree_gang_lookup_tag(&fs_info->fs_roots_radix,
1009                                                  (void **)gang, 0,
1010                                                  ARRAY_SIZE(gang),
1011                                                  BTRFS_ROOT_TRANS_TAG);
1012                 if (ret == 0)
1013                         break;
1014                 for (i = 0; i < ret; i++) {
1015                         root = gang[i];
1016                         radix_tree_tag_clear(&fs_info->fs_roots_radix,
1017                                         (unsigned long)root->root_key.objectid,
1018                                         BTRFS_ROOT_TRANS_TAG);
1019                         spin_unlock(&fs_info->fs_roots_radix_lock);
1020 
1021                         btrfs_free_log(trans, root);
1022                         btrfs_update_reloc_root(trans, root);
1023                         btrfs_orphan_commit_root(trans, root);
1024 
1025                         btrfs_save_ino_cache(root, trans);
1026 
1027                         /* see comments in should_cow_block() */
1028                         root->force_cow = 0;
1029                         smp_wmb();
1030 
1031                         if (root->commit_root != root->node) {
1032                                 mutex_lock(&root->fs_commit_mutex);
1033                                 switch_commit_root(root);
1034                                 btrfs_unpin_free_ino(root);
1035                                 mutex_unlock(&root->fs_commit_mutex);
1036 
1037                                 btrfs_set_root_node(&root->root_item,
1038                                                     root->node);
1039                         }
1040 
1041                         err = btrfs_update_root(trans, fs_info->tree_root,
1042                                                 &root->root_key,
1043                                                 &root->root_item);
1044                         spin_lock(&fs_info->fs_roots_radix_lock);
1045                         if (err)
1046                                 break;
1047                 }
1048         }
1049         spin_unlock(&fs_info->fs_roots_radix_lock);
1050         return err;
1051 }
1052 
1053 /*
1054  * defrag a given btree.
1055  * Every leaf in the btree is read and defragged.
1056  */
1057 int btrfs_defrag_root(struct btrfs_root *root)
1058 {
1059         struct btrfs_fs_info *info = root->fs_info;
1060         struct btrfs_trans_handle *trans;
1061         int ret;
1062 
1063         if (xchg(&root->defrag_running, 1))
1064                 return 0;
1065 
1066         while (1) {
1067                 trans = btrfs_start_transaction(root, 0);
1068                 if (IS_ERR(trans))
1069                         return PTR_ERR(trans);
1070 
1071                 ret = btrfs_defrag_leaves(trans, root);
1072 
1073                 btrfs_end_transaction(trans, root);
1074                 btrfs_btree_balance_dirty(info->tree_root);
1075                 cond_resched();
1076 
1077                 if (btrfs_fs_closing(root->fs_info) || ret != -EAGAIN)
1078                         break;
1079 
1080                 if (btrfs_defrag_cancelled(root->fs_info)) {
1081                         printk(KERN_DEBUG "btrfs: defrag_root cancelled\n");
1082                         ret = -EAGAIN;
1083                         break;
1084                 }
1085         }
1086         root->defrag_running = 0;
1087         return ret;
1088 }
1089 
1090 /*
1091  * new snapshots need to be created at a very specific time in the
1092  * transaction commit.  This does the actual creation.
1093  *
1094  * Note:
1095  * If the error which may affect the commitment of the current transaction
1096  * happens, we should return the error number. If the error which just affect
1097  * the creation of the pending snapshots, just return 0.
1098  */
1099 static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
1100                                    struct btrfs_fs_info *fs_info,
1101                                    struct btrfs_pending_snapshot *pending)
1102 {
1103         struct btrfs_key key;
1104         struct btrfs_root_item *new_root_item;
1105         struct btrfs_root *tree_root = fs_info->tree_root;
1106         struct btrfs_root *root = pending->root;
1107         struct btrfs_root *parent_root;
1108         struct btrfs_block_rsv *rsv;
1109         struct inode *parent_inode;
1110         struct btrfs_path *path;
1111         struct btrfs_dir_item *dir_item;
1112         struct dentry *dentry;
1113         struct extent_buffer *tmp;
1114         struct extent_buffer *old;
1115         struct timespec cur_time = CURRENT_TIME;
1116         int ret = 0;
1117         u64 to_reserve = 0;
1118         u64 index = 0;
1119         u64 objectid;
1120         u64 root_flags;
1121         uuid_le new_uuid;
1122 
1123         path = btrfs_alloc_path();
1124         if (!path) {
1125                 pending->error = -ENOMEM;
1126                 return 0;
1127         }
1128 
1129         new_root_item = kmalloc(sizeof(*new_root_item), GFP_NOFS);
1130         if (!new_root_item) {
1131                 pending->error = -ENOMEM;
1132                 goto root_item_alloc_fail;
1133         }
1134 
1135         pending->error = btrfs_find_free_objectid(tree_root, &objectid);
1136         if (pending->error)
1137                 goto no_free_objectid;
1138 
1139         btrfs_reloc_pre_snapshot(trans, pending, &to_reserve);
1140 
1141         if (to_reserve > 0) {
1142                 pending->error = btrfs_block_rsv_add(root,
1143                                                      &pending->block_rsv,
1144                                                      to_reserve,
1145                                                      BTRFS_RESERVE_NO_FLUSH);
1146                 if (pending->error)
1147                         goto no_free_objectid;
1148         }
1149 
1150         pending->error = btrfs_qgroup_inherit(trans, fs_info,
1151                                               root->root_key.objectid,
1152                                               objectid, pending->inherit);
1153         if (pending->error)
1154                 goto no_free_objectid;
1155 
1156         key.objectid = objectid;
1157         key.offset = (u64)-1;
1158         key.type = BTRFS_ROOT_ITEM_KEY;
1159 
1160         rsv = trans->block_rsv;
1161         trans->block_rsv = &pending->block_rsv;
1162         trans->bytes_reserved = trans->block_rsv->reserved;
1163 
1164         dentry = pending->dentry;
1165         parent_inode = pending->dir;
1166         parent_root = BTRFS_I(parent_inode)->root;
1167         record_root_in_trans(trans, parent_root);
1168 
1169         /*
1170          * insert the directory item
1171          */
1172         ret = btrfs_set_inode_index(parent_inode, &index);
1173         BUG_ON(ret); /* -ENOMEM */
1174 
1175         /* check if there is a file/dir which has the same name. */
1176         dir_item = btrfs_lookup_dir_item(NULL, parent_root, path,
1177                                          btrfs_ino(parent_inode),
1178                                          dentry->d_name.name,
1179                                          dentry->d_name.len, 0);
1180         if (dir_item != NULL && !IS_ERR(dir_item)) {
1181                 pending->error = -EEXIST;
1182                 goto dir_item_existed;
1183         } else if (IS_ERR(dir_item)) {
1184                 ret = PTR_ERR(dir_item);
1185                 btrfs_abort_transaction(trans, root, ret);
1186                 goto fail;
1187         }
1188         btrfs_release_path(path);
1189 
1190         /*
1191          * pull in the delayed directory update
1192          * and the delayed inode item
1193          * otherwise we corrupt the FS during
1194          * snapshot
1195          */
1196         ret = btrfs_run_delayed_items(trans, root);
1197         if (ret) {      /* Transaction aborted */
1198                 btrfs_abort_transaction(trans, root, ret);
1199                 goto fail;
1200         }
1201 
1202         record_root_in_trans(trans, root);
1203         btrfs_set_root_last_snapshot(&root->root_item, trans->transid);
1204         memcpy(new_root_item, &root->root_item, sizeof(*new_root_item));
1205         btrfs_check_and_init_root_item(new_root_item);
1206 
1207         root_flags = btrfs_root_flags(new_root_item);
1208         if (pending->readonly)
1209                 root_flags |= BTRFS_ROOT_SUBVOL_RDONLY;
1210         else
1211                 root_flags &= ~BTRFS_ROOT_SUBVOL_RDONLY;
1212         btrfs_set_root_flags(new_root_item, root_flags);
1213 
1214         btrfs_set_root_generation_v2(new_root_item,
1215                         trans->transid);
1216         uuid_le_gen(&new_uuid);
1217         memcpy(new_root_item->uuid, new_uuid.b, BTRFS_UUID_SIZE);
1218         memcpy(new_root_item->parent_uuid, root->root_item.uuid,
1219                         BTRFS_UUID_SIZE);
1220         if (!(root_flags & BTRFS_ROOT_SUBVOL_RDONLY)) {
1221                 memset(new_root_item->received_uuid, 0,
1222                        sizeof(new_root_item->received_uuid));
1223                 memset(&new_root_item->stime, 0, sizeof(new_root_item->stime));
1224                 memset(&new_root_item->rtime, 0, sizeof(new_root_item->rtime));
1225                 btrfs_set_root_stransid(new_root_item, 0);
1226                 btrfs_set_root_rtransid(new_root_item, 0);
1227         }
1228         new_root_item->otime.sec = cpu_to_le64(cur_time.tv_sec);
1229         new_root_item->otime.nsec = cpu_to_le32(cur_time.tv_nsec);
1230         btrfs_set_root_otransid(new_root_item, trans->transid);
1231 
1232         old = btrfs_lock_root_node(root);
1233         ret = btrfs_cow_block(trans, root, old, NULL, 0, &old);
1234         if (ret) {
1235                 btrfs_tree_unlock(old);
1236                 free_extent_buffer(old);
1237                 btrfs_abort_transaction(trans, root, ret);
1238                 goto fail;
1239         }
1240 
1241         btrfs_set_lock_blocking(old);
1242 
1243         ret = btrfs_copy_root(trans, root, old, &tmp, objectid);
1244         /* clean up in any case */
1245         btrfs_tree_unlock(old);
1246         free_extent_buffer(old);
1247         if (ret) {
1248                 btrfs_abort_transaction(trans, root, ret);
1249                 goto fail;
1250         }
1251 
1252         /* see comments in should_cow_block() */
1253         root->force_cow = 1;
1254         smp_wmb();
1255 
1256         btrfs_set_root_node(new_root_item, tmp);
1257         /* record when the snapshot was created in key.offset */
1258         key.offset = trans->transid;
1259         ret = btrfs_insert_root(trans, tree_root, &key, new_root_item);
1260         btrfs_tree_unlock(tmp);
1261         free_extent_buffer(tmp);
1262         if (ret) {
1263                 btrfs_abort_transaction(trans, root, ret);
1264                 goto fail;
1265         }
1266 
1267         /*
1268          * insert root back/forward references
1269          */
1270         ret = btrfs_add_root_ref(trans, tree_root, objectid,
1271                                  parent_root->root_key.objectid,
1272                                  btrfs_ino(parent_inode), index,
1273                                  dentry->d_name.name, dentry->d_name.len);
1274         if (ret) {
1275                 btrfs_abort_transaction(trans, root, ret);
1276                 goto fail;
1277         }
1278 
1279         key.offset = (u64)-1;
1280         pending->snap = btrfs_read_fs_root_no_name(root->fs_info, &key);
1281         if (IS_ERR(pending->snap)) {
1282                 ret = PTR_ERR(pending->snap);
1283                 btrfs_abort_transaction(trans, root, ret);
1284                 goto fail;
1285         }
1286 
1287         ret = btrfs_reloc_post_snapshot(trans, pending);
1288         if (ret) {
1289                 btrfs_abort_transaction(trans, root, ret);
1290                 goto fail;
1291         }
1292 
1293         ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
1294         if (ret) {
1295                 btrfs_abort_transaction(trans, root, ret);
1296                 goto fail;
1297         }
1298 
1299         ret = btrfs_insert_dir_item(trans, parent_root,
1300                                     dentry->d_name.name, dentry->d_name.len,
1301                                     parent_inode, &key,
1302                                     BTRFS_FT_DIR, index);
1303         /* We have check then name at the beginning, so it is impossible. */
1304         BUG_ON(ret == -EEXIST || ret == -EOVERFLOW);
1305         if (ret) {
1306                 btrfs_abort_transaction(trans, root, ret);
1307                 goto fail;
1308         }
1309 
1310         btrfs_i_size_write(parent_inode, parent_inode->i_size +
1311                                          dentry->d_name.len * 2);
1312         parent_inode->i_mtime = parent_inode->i_ctime = CURRENT_TIME;
1313         ret = btrfs_update_inode_fallback(trans, parent_root, parent_inode);
1314         if (ret)
1315                 btrfs_abort_transaction(trans, root, ret);
1316 fail:
1317         pending->error = ret;
1318 dir_item_existed:
1319         trans->block_rsv = rsv;
1320         trans->bytes_reserved = 0;
1321 no_free_objectid:
1322         kfree(new_root_item);
1323 root_item_alloc_fail:
1324         btrfs_free_path(path);
1325         return ret;
1326 }
1327 
1328 /*
1329  * create all the snapshots we've scheduled for creation
1330  */
1331 static noinline int create_pending_snapshots(struct btrfs_trans_handle *trans,
1332                                              struct btrfs_fs_info *fs_info)
1333 {
1334         struct btrfs_pending_snapshot *pending, *next;
1335         struct list_head *head = &trans->transaction->pending_snapshots;
1336         int ret = 0;
1337 
1338         list_for_each_entry_safe(pending, next, head, list) {
1339                 list_del(&pending->list);
1340                 ret = create_pending_snapshot(trans, fs_info, pending);
1341                 if (ret)
1342                         break;
1343         }
1344         return ret;
1345 }
1346 
1347 static void update_super_roots(struct btrfs_root *root)
1348 {
1349         struct btrfs_root_item *root_item;
1350         struct btrfs_super_block *super;
1351 
1352         super = root->fs_info->super_copy;
1353 
1354         root_item = &root->fs_info->chunk_root->root_item;
1355         super->chunk_root = root_item->bytenr;
1356         super->chunk_root_generation = root_item->generation;
1357         super->chunk_root_level = root_item->level;
1358 
1359         root_item = &root->fs_info->tree_root->root_item;
1360         super->root = root_item->bytenr;
1361         super->generation = root_item->generation;
1362         super->root_level = root_item->level;
1363         if (btrfs_test_opt(root, SPACE_CACHE))
1364                 super->cache_generation = root_item->generation;
1365 }
1366 
1367 int btrfs_transaction_in_commit(struct btrfs_fs_info *info)
1368 {
1369         struct btrfs_transaction *trans;
1370         int ret = 0;
1371 
1372         spin_lock(&info->trans_lock);
1373         trans = info->running_transaction;
1374         if (trans)
1375                 ret = (trans->state >= TRANS_STATE_COMMIT_START);
1376         spin_unlock(&info->trans_lock);
1377         return ret;
1378 }
1379 
1380 int btrfs_transaction_blocked(struct btrfs_fs_info *info)
1381 {
1382         struct btrfs_transaction *trans;
1383         int ret = 0;
1384 
1385         spin_lock(&info->trans_lock);
1386         trans = info->running_transaction;
1387         if (trans)
1388                 ret = is_transaction_blocked(trans);
1389         spin_unlock(&info->trans_lock);
1390         return ret;
1391 }
1392 
1393 /*
1394  * wait for the current transaction commit to start and block subsequent
1395  * transaction joins
1396  */
1397 static void wait_current_trans_commit_start(struct btrfs_root *root,
1398                                             struct btrfs_transaction *trans)
1399 {
1400         wait_event(root->fs_info->transaction_blocked_wait,
1401                    trans->state >= TRANS_STATE_COMMIT_START ||
1402                    trans->aborted);
1403 }
1404 
1405 /*
1406  * wait for the current transaction to start and then become unblocked.
1407  * caller holds ref.
1408  */
1409 static void wait_current_trans_commit_start_and_unblock(struct btrfs_root *root,
1410                                          struct btrfs_transaction *trans)
1411 {
1412         wait_event(root->fs_info->transaction_wait,
1413                    trans->state >= TRANS_STATE_UNBLOCKED ||
1414                    trans->aborted);
1415 }
1416 
1417 /*
1418  * commit transactions asynchronously. once btrfs_commit_transaction_async
1419  * returns, any subsequent transaction will not be allowed to join.
1420  */
1421 struct btrfs_async_commit {
1422         struct btrfs_trans_handle *newtrans;
1423         struct btrfs_root *root;
1424         struct work_struct work;
1425 };
1426 
1427 static void do_async_commit(struct work_struct *work)
1428 {
1429         struct btrfs_async_commit *ac =
1430                 container_of(work, struct btrfs_async_commit, work);
1431 
1432         /*
1433          * We've got freeze protection passed with the transaction.
1434          * Tell lockdep about it.
1435          */
1436         if (ac->newtrans->type < TRANS_JOIN_NOLOCK)
1437                 rwsem_acquire_read(
1438                      &ac->root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
1439                      0, 1, _THIS_IP_);
1440 
1441         current->journal_info = ac->newtrans;
1442 
1443         btrfs_commit_transaction(ac->newtrans, ac->root);
1444         kfree(ac);
1445 }
1446 
1447 int btrfs_commit_transaction_async(struct btrfs_trans_handle *trans,
1448                                    struct btrfs_root *root,
1449                                    int wait_for_unblock)
1450 {
1451         struct btrfs_async_commit *ac;
1452         struct btrfs_transaction *cur_trans;
1453 
1454         ac = kmalloc(sizeof(*ac), GFP_NOFS);
1455         if (!ac)
1456                 return -ENOMEM;
1457 
1458         INIT_WORK(&ac->work, do_async_commit);
1459         ac->root = root;
1460         ac->newtrans = btrfs_join_transaction(root);
1461         if (IS_ERR(ac->newtrans)) {
1462                 int err = PTR_ERR(ac->newtrans);
1463                 kfree(ac);
1464                 return err;
1465         }
1466 
1467         /* take transaction reference */
1468         cur_trans = trans->transaction;
1469         atomic_inc(&cur_trans->use_count);
1470 
1471         btrfs_end_transaction(trans, root);
1472 
1473         /*
1474          * Tell lockdep we've released the freeze rwsem, since the
1475          * async commit thread will be the one to unlock it.
1476          */
1477         if (trans->type < TRANS_JOIN_NOLOCK)
1478                 rwsem_release(
1479                         &root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
1480                         1, _THIS_IP_);
1481 
1482         schedule_work(&ac->work);
1483 
1484         /* wait for transaction to start and unblock */
1485         if (wait_for_unblock)
1486                 wait_current_trans_commit_start_and_unblock(root, cur_trans);
1487         else
1488                 wait_current_trans_commit_start(root, cur_trans);
1489 
1490         if (current->journal_info == trans)
1491                 current->journal_info = NULL;
1492 
1493         put_transaction(cur_trans);
1494         return 0;
1495 }
1496 
1497 
1498 static void cleanup_transaction(struct btrfs_trans_handle *trans,
1499                                 struct btrfs_root *root, int err)
1500 {
1501         struct btrfs_transaction *cur_trans = trans->transaction;
1502         DEFINE_WAIT(wait);
1503 
1504         WARN_ON(trans->use_count > 1);
1505 
1506         btrfs_abort_transaction(trans, root, err);
1507 
1508         spin_lock(&root->fs_info->trans_lock);
1509 
1510         /*
1511          * If the transaction is removed from the list, it means this
1512          * transaction has been committed successfully, so it is impossible
1513          * to call the cleanup function.
1514          */
1515         BUG_ON(list_empty(&cur_trans->list));
1516 
1517         list_del_init(&cur_trans->list);
1518         if (cur_trans == root->fs_info->running_transaction) {
1519                 cur_trans->state = TRANS_STATE_COMMIT_DOING;
1520                 spin_unlock(&root->fs_info->trans_lock);
1521                 wait_event(cur_trans->writer_wait,
1522                            atomic_read(&cur_trans->num_writers) == 1);
1523 
1524                 spin_lock(&root->fs_info->trans_lock);
1525         }
1526         spin_unlock(&root->fs_info->trans_lock);
1527 
1528         btrfs_cleanup_one_transaction(trans->transaction, root);
1529 
1530         spin_lock(&root->fs_info->trans_lock);
1531         if (cur_trans == root->fs_info->running_transaction)
1532                 root->fs_info->running_transaction = NULL;
1533         spin_unlock(&root->fs_info->trans_lock);
1534 
1535         put_transaction(cur_trans);
1536         put_transaction(cur_trans);
1537 
1538         trace_btrfs_transaction_commit(root);
1539 
1540         btrfs_scrub_continue(root);
1541 
1542         if (current->journal_info == trans)
1543                 current->journal_info = NULL;
1544 
1545         kmem_cache_free(btrfs_trans_handle_cachep, trans);
1546 }
1547 
1548 static int btrfs_flush_all_pending_stuffs(struct btrfs_trans_handle *trans,
1549                                           struct btrfs_root *root)
1550 {
1551         int ret;
1552 
1553         ret = btrfs_run_delayed_items(trans, root);
1554         if (ret)
1555                 return ret;
1556 
1557         /*
1558          * running the delayed items may have added new refs. account
1559          * them now so that they hinder processing of more delayed refs
1560          * as little as possible.
1561          */
1562         btrfs_delayed_refs_qgroup_accounting(trans, root->fs_info);
1563 
1564         /*
1565          * rename don't use btrfs_join_transaction, so, once we
1566          * set the transaction to blocked above, we aren't going
1567          * to get any new ordered operations.  We can safely run
1568          * it here and no for sure that nothing new will be added
1569          * to the list
1570          */
1571         ret = btrfs_run_ordered_operations(trans, root, 1);
1572 
1573         return ret;
1574 }
1575 
1576 static inline int btrfs_start_delalloc_flush(struct btrfs_fs_info *fs_info)
1577 {
1578         if (btrfs_test_opt(fs_info->tree_root, FLUSHONCOMMIT))
1579                 return btrfs_start_all_delalloc_inodes(fs_info, 1);
1580         return 0;
1581 }
1582 
1583 static inline void btrfs_wait_delalloc_flush(struct btrfs_fs_info *fs_info)
1584 {
1585         if (btrfs_test_opt(fs_info->tree_root, FLUSHONCOMMIT))
1586                 btrfs_wait_all_ordered_extents(fs_info, 1);
1587 }
1588 
1589 int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
1590                              struct btrfs_root *root)
1591 {
1592         struct btrfs_transaction *cur_trans = trans->transaction;
1593         struct btrfs_transaction *prev_trans = NULL;
1594         int ret;
1595 
1596         ret = btrfs_run_ordered_operations(trans, root, 0);
1597         if (ret) {
1598                 btrfs_abort_transaction(trans, root, ret);
1599                 btrfs_end_transaction(trans, root);
1600                 return ret;
1601         }
1602 
1603         /* Stop the commit early if ->aborted is set */
1604         if (unlikely(ACCESS_ONCE(cur_trans->aborted))) {
1605                 ret = cur_trans->aborted;
1606                 btrfs_end_transaction(trans, root);
1607                 return ret;
1608         }
1609 
1610         /* make a pass through all the delayed refs we have so far
1611          * any runnings procs may add more while we are here
1612          */
1613         ret = btrfs_run_delayed_refs(trans, root, 0);
1614         if (ret) {
1615                 btrfs_end_transaction(trans, root);
1616                 return ret;
1617         }
1618 
1619         btrfs_trans_release_metadata(trans, root);
1620         trans->block_rsv = NULL;
1621         if (trans->qgroup_reserved) {
1622                 btrfs_qgroup_free(root, trans->qgroup_reserved);
1623                 trans->qgroup_reserved = 0;
1624         }
1625 
1626         cur_trans = trans->transaction;
1627 
1628         /*
1629          * set the flushing flag so procs in this transaction have to
1630          * start sending their work down.
1631          */
1632         cur_trans->delayed_refs.flushing = 1;
1633         smp_wmb();
1634 
1635         if (!list_empty(&trans->new_bgs))
1636                 btrfs_create_pending_block_groups(trans, root);
1637 
1638         ret = btrfs_run_delayed_refs(trans, root, 0);
1639         if (ret) {
1640                 btrfs_end_transaction(trans, root);
1641                 return ret;
1642         }
1643 
1644         spin_lock(&root->fs_info->trans_lock);
1645         if (cur_trans->state >= TRANS_STATE_COMMIT_START) {
1646                 spin_unlock(&root->fs_info->trans_lock);
1647                 atomic_inc(&cur_trans->use_count);
1648                 ret = btrfs_end_transaction(trans, root);
1649 
1650                 wait_for_commit(root, cur_trans);
1651 
1652                 put_transaction(cur_trans);
1653 
1654                 return ret;
1655         }
1656 
1657         cur_trans->state = TRANS_STATE_COMMIT_START;
1658         wake_up(&root->fs_info->transaction_blocked_wait);
1659 
1660         if (cur_trans->list.prev != &root->fs_info->trans_list) {
1661                 prev_trans = list_entry(cur_trans->list.prev,
1662                                         struct btrfs_transaction, list);
1663                 if (prev_trans->state != TRANS_STATE_COMPLETED) {
1664                         atomic_inc(&prev_trans->use_count);
1665                         spin_unlock(&root->fs_info->trans_lock);
1666 
1667                         wait_for_commit(root, prev_trans);
1668 
1669                         put_transaction(prev_trans);
1670                 } else {
1671                         spin_unlock(&root->fs_info->trans_lock);
1672                 }
1673         } else {
1674                 spin_unlock(&root->fs_info->trans_lock);
1675         }
1676 
1677         extwriter_counter_dec(cur_trans, trans->type);
1678 
1679         ret = btrfs_start_delalloc_flush(root->fs_info);
1680         if (ret)
1681                 goto cleanup_transaction;
1682 
1683         ret = btrfs_flush_all_pending_stuffs(trans, root);
1684         if (ret)
1685                 goto cleanup_transaction;
1686 
1687         wait_event(cur_trans->writer_wait,
1688                    extwriter_counter_read(cur_trans) == 0);
1689 
1690         /* some pending stuffs might be added after the previous flush. */
1691         ret = btrfs_flush_all_pending_stuffs(trans, root);
1692         if (ret)
1693                 goto cleanup_transaction;
1694 
1695         btrfs_wait_delalloc_flush(root->fs_info);
1696         /*
1697          * Ok now we need to make sure to block out any other joins while we
1698          * commit the transaction.  We could have started a join before setting
1699          * COMMIT_DOING so make sure to wait for num_writers to == 1 again.
1700          */
1701         spin_lock(&root->fs_info->trans_lock);
1702         cur_trans->state = TRANS_STATE_COMMIT_DOING;
1703         spin_unlock(&root->fs_info->trans_lock);
1704         wait_event(cur_trans->writer_wait,
1705                    atomic_read(&cur_trans->num_writers) == 1);
1706 
1707         /* ->aborted might be set after the previous check, so check it */
1708         if (unlikely(ACCESS_ONCE(cur_trans->aborted))) {
1709                 ret = cur_trans->aborted;
1710                 goto cleanup_transaction;
1711         }
1712         /*
1713          * the reloc mutex makes sure that we stop
1714          * the balancing code from coming in and moving
1715          * extents around in the middle of the commit
1716          */
1717         mutex_lock(&root->fs_info->reloc_mutex);
1718 
1719         /*
1720          * We needn't worry about the delayed items because we will
1721          * deal with them in create_pending_snapshot(), which is the
1722          * core function of the snapshot creation.
1723          */
1724         ret = create_pending_snapshots(trans, root->fs_info);
1725         if (ret) {
1726                 mutex_unlock(&root->fs_info->reloc_mutex);
1727                 goto cleanup_transaction;
1728         }
1729 
1730         /*
1731          * We insert the dir indexes of the snapshots and update the inode
1732          * of the snapshots' parents after the snapshot creation, so there
1733          * are some delayed items which are not dealt with. Now deal with
1734          * them.
1735          *
1736          * We needn't worry that this operation will corrupt the snapshots,
1737          * because all the tree which are snapshoted will be forced to COW
1738          * the nodes and leaves.
1739          */
1740         ret = btrfs_run_delayed_items(trans, root);
1741         if (ret) {
1742                 mutex_unlock(&root->fs_info->reloc_mutex);
1743                 goto cleanup_transaction;
1744         }
1745 
1746         ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
1747         if (ret) {
1748                 mutex_unlock(&root->fs_info->reloc_mutex);
1749                 goto cleanup_transaction;
1750         }
1751 
1752         /*
1753          * make sure none of the code above managed to slip in a
1754          * delayed item
1755          */
1756         btrfs_assert_delayed_root_empty(root);
1757 
1758         WARN_ON(cur_trans != trans->transaction);
1759 
1760         btrfs_scrub_pause(root);
1761         /* btrfs_commit_tree_roots is responsible for getting the
1762          * various roots consistent with each other.  Every pointer
1763          * in the tree of tree roots has to point to the most up to date
1764          * root for every subvolume and other tree.  So, we have to keep
1765          * the tree logging code from jumping in and changing any
1766          * of the trees.
1767          *
1768          * At this point in the commit, there can't be any tree-log
1769          * writers, but a little lower down we drop the trans mutex
1770          * and let new people in.  By holding the tree_log_mutex
1771          * from now until after the super is written, we avoid races
1772          * with the tree-log code.
1773          */
1774         mutex_lock(&root->fs_info->tree_log_mutex);
1775 
1776         ret = commit_fs_roots(trans, root);
1777         if (ret) {
1778                 mutex_unlock(&root->fs_info->tree_log_mutex);
1779                 mutex_unlock(&root->fs_info->reloc_mutex);
1780                 goto cleanup_transaction;
1781         }
1782 
1783         /* commit_fs_roots gets rid of all the tree log roots, it is now
1784          * safe to free the root of tree log roots
1785          */
1786         btrfs_free_log_root_tree(trans, root->fs_info);
1787 
1788         ret = commit_cowonly_roots(trans, root);
1789         if (ret) {
1790                 mutex_unlock(&root->fs_info->tree_log_mutex);
1791                 mutex_unlock(&root->fs_info->reloc_mutex);
1792                 goto cleanup_transaction;
1793         }
1794 
1795         /*
1796          * The tasks which save the space cache and inode cache may also
1797          * update ->aborted, check it.
1798          */
1799         if (unlikely(ACCESS_ONCE(cur_trans->aborted))) {
1800                 ret = cur_trans->aborted;
1801                 mutex_unlock(&root->fs_info->tree_log_mutex);
1802                 mutex_unlock(&root->fs_info->reloc_mutex);
1803                 goto cleanup_transaction;
1804         }
1805 
1806         btrfs_prepare_extent_commit(trans, root);
1807 
1808         cur_trans = root->fs_info->running_transaction;
1809 
1810         btrfs_set_root_node(&root->fs_info->tree_root->root_item,
1811                             root->fs_info->tree_root->node);
1812         switch_commit_root(root->fs_info->tree_root);
1813 
1814         btrfs_set_root_node(&root->fs_info->chunk_root->root_item,
1815                             root->fs_info->chunk_root->node);
1816         switch_commit_root(root->fs_info->chunk_root);
1817 
1818         assert_qgroups_uptodate(trans);
1819         update_super_roots(root);
1820 
1821         if (!root->fs_info->log_root_recovering) {
1822                 btrfs_set_super_log_root(root->fs_info->super_copy, 0);
1823                 btrfs_set_super_log_root_level(root->fs_info->super_copy, 0);
1824         }
1825 
1826         memcpy(root->fs_info->super_for_commit, root->fs_info->super_copy,
1827                sizeof(*root->fs_info->super_copy));
1828 
1829         spin_lock(&root->fs_info->trans_lock);
1830         cur_trans->state = TRANS_STATE_UNBLOCKED;
1831         root->fs_info->running_transaction = NULL;
1832         spin_unlock(&root->fs_info->trans_lock);
1833         mutex_unlock(&root->fs_info->reloc_mutex);
1834 
1835         wake_up(&root->fs_info->transaction_wait);
1836 
1837         ret = btrfs_write_and_wait_transaction(trans, root);
1838         if (ret) {
1839                 btrfs_error(root->fs_info, ret,
1840                             "Error while writing out transaction");
1841                 mutex_unlock(&root->fs_info->tree_log_mutex);
1842                 goto cleanup_transaction;
1843         }
1844 
1845         ret = write_ctree_super(trans, root, 0);
1846         if (ret) {
1847                 mutex_unlock(&root->fs_info->tree_log_mutex);
1848                 goto cleanup_transaction;
1849         }
1850 
1851         /*
1852          * the super is written, we can safely allow the tree-loggers
1853          * to go about their business
1854          */
1855         mutex_unlock(&root->fs_info->tree_log_mutex);
1856 
1857         btrfs_finish_extent_commit(trans, root);
1858 
1859         root->fs_info->last_trans_committed = cur_trans->transid;
1860         /*
1861          * We needn't acquire the lock here because there is no other task
1862          * which can change it.
1863          */
1864         cur_trans->state = TRANS_STATE_COMPLETED;
1865         wake_up(&cur_trans->commit_wait);
1866 
1867         spin_lock(&root->fs_info->trans_lock);
1868         list_del_init(&cur_trans->list);
1869         spin_unlock(&root->fs_info->trans_lock);
1870 
1871         put_transaction(cur_trans);
1872         put_transaction(cur_trans);
1873 
1874         if (trans->type & __TRANS_FREEZABLE)
1875                 sb_end_intwrite(root->fs_info->sb);
1876 
1877         trace_btrfs_transaction_commit(root);
1878 
1879         btrfs_scrub_continue(root);
1880 
1881         if (current->journal_info == trans)
1882                 current->journal_info = NULL;
1883 
1884         kmem_cache_free(btrfs_trans_handle_cachep, trans);
1885 
1886         if (current != root->fs_info->transaction_kthread)
1887                 btrfs_run_delayed_iputs(root);
1888 
1889         return ret;
1890 
1891 cleanup_transaction:
1892         btrfs_trans_release_metadata(trans, root);
1893         trans->block_rsv = NULL;
1894         if (trans->qgroup_reserved) {
1895                 btrfs_qgroup_free(root, trans->qgroup_reserved);
1896                 trans->qgroup_reserved = 0;
1897         }
1898         btrfs_warn(root->fs_info, "Skipping commit of aborted transaction.");
1899         if (current->journal_info == trans)
1900                 current->journal_info = NULL;
1901         cleanup_transaction(trans, root, ret);
1902 
1903         return ret;
1904 }
1905 
1906 /*
1907  * return < 0 if error
1908  * 0 if there are no more dead_roots at the time of call
1909  * 1 there are more to be processed, call me again
1910  *
1911  * The return value indicates there are certainly more snapshots to delete, but
1912  * if there comes a new one during processing, it may return 0. We don't mind,
1913  * because btrfs_commit_super will poke cleaner thread and it will process it a
1914  * few seconds later.
1915  */
1916 int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root)
1917 {
1918         int ret;
1919         struct btrfs_fs_info *fs_info = root->fs_info;
1920 
1921         spin_lock(&fs_info->trans_lock);
1922         if (list_empty(&fs_info->dead_roots)) {
1923                 spin_unlock(&fs_info->trans_lock);
1924                 return 0;
1925         }
1926         root = list_first_entry(&fs_info->dead_roots,
1927                         struct btrfs_root, root_list);
1928         list_del_init(&root->root_list);
1929         spin_unlock(&fs_info->trans_lock);
1930 
1931         pr_debug("btrfs: cleaner removing %llu\n",
1932                         (unsigned long long)root->objectid);
1933 
1934         btrfs_kill_all_delayed_nodes(root);
1935 
1936         if (btrfs_header_backref_rev(root->node) <
1937                         BTRFS_MIXED_BACKREF_REV)
1938                 ret = btrfs_drop_snapshot(root, NULL, 0, 0);
1939         else
1940                 ret = btrfs_drop_snapshot(root, NULL, 1, 0);
1941         /*
1942          * If we encounter a transaction abort during snapshot cleaning, we
1943          * don't want to crash here
1944          */
1945         BUG_ON(ret < 0 && ret != -EAGAIN && ret != -EROFS);
1946         return 1;
1947 }
1948 

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