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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007 Oracle.  All rights reserved.
  */
 
 #include <linux/fs.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
 #include <linux/writeback.h>
 #include <linux/pagemap.h>
 #include <linux/blkdev.h>
 #include <linux/uuid.h>
 #include <linux/timekeeping.h>
 #include "misc.h"
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
 #include "locking.h"
 #include "tree-log.h"
 #include "volumes.h"
 #include "dev-replace.h"
 #include "qgroup.h"
 #include "block-group.h"
 #include "space-info.h"
 #include "zoned.h"
 
 #define BTRFS_ROOT_TRANS_TAG 0
 
 /*
  * Transaction states and transitions
  *
  * No running transaction (fs tree blocks are not modified)
  * |
  * | To next stage:
  * |  Call start_transaction() variants. Except btrfs_join_transaction_nostart().
  * V
  * Transaction N [[TRANS_STATE_RUNNING]]
  * |
  * | New trans handles can be attached to transaction N by calling all
  * | start_transaction() variants.
  * |
  * | To next stage:
  * |  Call btrfs_commit_transaction() on any trans handle attached to
  * |  transaction N
  * V
  * Transaction N [[TRANS_STATE_COMMIT_START]]
  * |
  * | Will wait for previous running transaction to completely finish if there
  * | is one
  * |
  * | Then one of the following happes:
  * | - Wait for all other trans handle holders to release.
  * |   The btrfs_commit_transaction() caller will do the commit work.
  * | - Wait for current transaction to be committed by others.
  * |   Other btrfs_commit_transaction() caller will do the commit work.
  * |
  * | At this stage, only btrfs_join_transaction*() variants can attach
  * | to this running transaction.
  * | All other variants will wait for current one to finish and attach to
  * | transaction N+1.
  * |
  * | To next stage:
  * |  Caller is chosen to commit transaction N, and all other trans handle
  * |  haven been released.
  * V
  * Transaction N [[TRANS_STATE_COMMIT_DOING]]
  * |
  * | The heavy lifting transaction work is started.
  * | From running delayed refs (modifying extent tree) to creating pending
  * | snapshots, running qgroups.
  * | In short, modify supporting trees to reflect modifications of subvolume
  * | trees.
  * |
  * | At this stage, all start_transaction() calls will wait for this
  * | transaction to finish and attach to transaction N+1.
  * |
  * | To next stage:
  * |  Until all supporting trees are updated.
  * V
  * Transaction N [[TRANS_STATE_UNBLOCKED]]
  * |                            Transaction N+1
  * | All needed trees are modified, thus we only    [[TRANS_STATE_RUNNING]]
  * | need to write them back to disk and update     |
  * | super blocks.                  |
  * |                            |
  * | At this stage, new transaction is allowed to   |
  * | start.                     |
  * | All new start_transaction() calls will be      |
  * | attached to transid N+1.               |
  * |                            |
  * | To next stage:                 |
  * |  Until all tree blocks are super blocks are    |
  * |  written to block devices              |
  * V                            |
  * Transaction N [[TRANS_STATE_COMPLETED]]      V
  *   All tree blocks and super blocks are written.  Transaction N+1
  *   This transaction is finished and all its       [[TRANS_STATE_COMMIT_START]]
  *   data structures will be cleaned up.        | Life goes on
  */
 static const unsigned int btrfs_blocked_trans_types[TRANS_STATE_MAX] = {
     [TRANS_STATE_RUNNING]       = 0U,
     [TRANS_STATE_COMMIT_START]  = (__TRANS_START | __TRANS_ATTACH),
     [TRANS_STATE_COMMIT_DOING]  = (__TRANS_START |
                        __TRANS_ATTACH |
                        __TRANS_JOIN |
                        __TRANS_JOIN_NOSTART),
     [TRANS_STATE_UNBLOCKED]     = (__TRANS_START |
                        __TRANS_ATTACH |
                        __TRANS_JOIN |
                        __TRANS_JOIN_NOLOCK |
                        __TRANS_JOIN_NOSTART),
     [TRANS_STATE_SUPER_COMMITTED]   = (__TRANS_START |
                        __TRANS_ATTACH |
                        __TRANS_JOIN |
                        __TRANS_JOIN_NOLOCK |
                        __TRANS_JOIN_NOSTART),
     [TRANS_STATE_COMPLETED]     = (__TRANS_START |
                        __TRANS_ATTACH |
                        __TRANS_JOIN |
                        __TRANS_JOIN_NOLOCK |
                        __TRANS_JOIN_NOSTART),
 };
 
 void btrfs_put_transaction(struct btrfs_transaction *transaction)
 {
     WARN_ON(refcount_read(&transaction->use_count) == 0);
     if (refcount_dec_and_test(&transaction->use_count)) {
         BUG_ON(!list_empty(&transaction->list));
         WARN_ON(!RB_EMPTY_ROOT(
                 &transaction->delayed_refs.href_root.rb_root));
         WARN_ON(!RB_EMPTY_ROOT(
                 &transaction->delayed_refs.dirty_extent_root));
         if (transaction->delayed_refs.pending_csums)
             btrfs_err(transaction->fs_info,
                   "pending csums is %llu",
                   transaction->delayed_refs.pending_csums);
         /*
          * If any block groups are found in ->deleted_bgs then it's
          * because the transaction was aborted and a commit did not
          * happen (things failed before writing the new superblock
          * and calling btrfs_finish_extent_commit()), so we can not
          * discard the physical locations of the block groups.
          */
         while (!list_empty(&transaction->deleted_bgs)) {
             struct btrfs_block_group *cache;
 
             cache = list_first_entry(&transaction->deleted_bgs,
                          struct btrfs_block_group,
                          bg_list);
             list_del_init(&cache->bg_list);
             btrfs_unfreeze_block_group(cache);
             btrfs_put_block_group(cache);
         }
         WARN_ON(!list_empty(&transaction->dev_update_list));
         kfree(transaction);
     }
 }
 
 static noinline void switch_commit_roots(struct btrfs_trans_handle *trans)
 {
     struct btrfs_transaction *cur_trans = trans->transaction;
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct btrfs_root *root, *tmp;
     struct btrfs_caching_control *caching_ctl, *next;
 
     /*
      * At this point no one can be using this transaction to modify any tree
      * and no one can start another transaction to modify any tree either.
      */
     ASSERT(cur_trans->state == TRANS_STATE_COMMIT_DOING);
 
     down_write(&fs_info->commit_root_sem);
 
     if (test_bit(BTRFS_FS_RELOC_RUNNING, &fs_info->flags))
         fs_info->last_reloc_trans = trans->transid;
 
     list_for_each_entry_safe(root, tmp, &cur_trans->switch_commits,
                  dirty_list) {
         list_del_init(&root->dirty_list);
         free_extent_buffer(root->commit_root);
         root->commit_root = btrfs_root_node(root);
         extent_io_tree_release(&root->dirty_log_pages);
         btrfs_qgroup_clean_swapped_blocks(root);
     }
 
     /* We can free old roots now. */
     spin_lock(&cur_trans->dropped_roots_lock);
     while (!list_empty(&cur_trans->dropped_roots)) {
         root = list_first_entry(&cur_trans->dropped_roots,
                     struct btrfs_root, root_list);
         list_del_init(&root->root_list);
         spin_unlock(&cur_trans->dropped_roots_lock);
         btrfs_free_log(trans, root);
         btrfs_drop_and_free_fs_root(fs_info, root);
         spin_lock(&cur_trans->dropped_roots_lock);
     }
     spin_unlock(&cur_trans->dropped_roots_lock);
 
     /*
      * We have to update the last_byte_to_unpin under the commit_root_sem,
      * at the same time we swap out the commit roots.
      *
      * This is because we must have a real view of the last spot the caching
      * kthreads were while caching.  Consider the following views of the
      * extent tree for a block group
      *
      * commit root
      * +----+----+----+----+----+----+----+
      * |\\\\|    |\\\\|\\\\|    |\\\\|\\\\|
      * +----+----+----+----+----+----+----+
      * 0    1    2    3    4    5    6    7
      *
      * new commit root
      * +----+----+----+----+----+----+----+
      * |    |    |    |\\\\|    |    |\\\\|
      * +----+----+----+----+----+----+----+
      * 0    1    2    3    4    5    6    7
      *
      * If the cache_ctl->progress was at 3, then we are only allowed to
      * unpin [0,1) and [2,3], because the caching thread has already
      * processed those extents.  We are not allowed to unpin [5,6), because
      * the caching thread will re-start it's search from 3, and thus find
      * the hole from [4,6) to add to the free space cache.
      */
     write_lock(&fs_info->block_group_cache_lock);
     list_for_each_entry_safe(caching_ctl, next,
                  &fs_info->caching_block_groups, list) {
         struct btrfs_block_group *cache = caching_ctl->block_group;
 
         if (btrfs_block_group_done(cache)) {
             cache->last_byte_to_unpin = (u64)-1;
             list_del_init(&caching_ctl->list);
             btrfs_put_caching_control(caching_ctl);
         } else {
             cache->last_byte_to_unpin = caching_ctl->progress;
         }
     }
     write_unlock(&fs_info->block_group_cache_lock);
     up_write(&fs_info->commit_root_sem);
 }
 
 static inline void extwriter_counter_inc(struct btrfs_transaction *trans,
                      unsigned int type)
 {
     if (type & TRANS_EXTWRITERS)
         atomic_inc(&trans->num_extwriters);
 }
 
 static inline void extwriter_counter_dec(struct btrfs_transaction *trans,
                      unsigned int type)
 {
     if (type & TRANS_EXTWRITERS)
         atomic_dec(&trans->num_extwriters);
 }
 
 static inline void extwriter_counter_init(struct btrfs_transaction *trans,
                       unsigned int type)
 {
     atomic_set(&trans->num_extwriters, ((type & TRANS_EXTWRITERS) ? 1 : 0));
 }
 
 static inline int extwriter_counter_read(struct btrfs_transaction *trans)
 {
     return atomic_read(&trans->num_extwriters);
 }
 
 /*
  * To be called after doing the chunk btree updates right after allocating a new
  * chunk (after btrfs_chunk_alloc_add_chunk_item() is called), when removing a
  * chunk after all chunk btree updates and after finishing the second phase of
  * chunk allocation (btrfs_create_pending_block_groups()) in case some block
  * group had its chunk item insertion delayed to the second phase.
  */
 void btrfs_trans_release_chunk_metadata(struct btrfs_trans_handle *trans)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
 
     if (!trans->chunk_bytes_reserved)
         return;
 
     btrfs_block_rsv_release(fs_info, &fs_info->chunk_block_rsv,
                 trans->chunk_bytes_reserved, NULL);
     trans->chunk_bytes_reserved = 0;
 }
 
 /*
  * either allocate a new transaction or hop into the existing one
  */
 static noinline int join_transaction(struct btrfs_fs_info *fs_info,
                      unsigned int type)
 {
     struct btrfs_transaction *cur_trans;
 
     spin_lock(&fs_info->trans_lock);
 loop:
     /* The file system has been taken offline. No new transactions. */
     if (BTRFS_FS_ERROR(fs_info)) {
         spin_unlock(&fs_info->trans_lock);
         return -EROFS;
     }
 
     cur_trans = fs_info->running_transaction;
     if (cur_trans) {
         if (TRANS_ABORTED(cur_trans)) {
             spin_unlock(&fs_info->trans_lock);
             return cur_trans->aborted;
         }
         if (btrfs_blocked_trans_types[cur_trans->state] & type) {
             spin_unlock(&fs_info->trans_lock);
             return -EBUSY;
         }
         refcount_inc(&cur_trans->use_count);
         atomic_inc(&cur_trans->num_writers);
         extwriter_counter_inc(cur_trans, type);
         spin_unlock(&fs_info->trans_lock);
         return 0;
     }
     spin_unlock(&fs_info->trans_lock);
 
     /*
      * If we are ATTACH, we just want to catch the current transaction,
      * and commit it. If there is no transaction, just return ENOENT.
      */
     if (type == TRANS_ATTACH)
         return -ENOENT;
 
     /*
      * JOIN_NOLOCK only happens during the transaction commit, so
      * it is impossible that ->running_transaction is NULL
      */
     BUG_ON(type == TRANS_JOIN_NOLOCK);
 
     cur_trans = kmalloc(sizeof(*cur_trans), GFP_NOFS);
     if (!cur_trans)
         return -ENOMEM;
 
     spin_lock(&fs_info->trans_lock);
     if (fs_info->running_transaction) {
         /*
          * someone started a transaction after we unlocked.  Make sure
          * to redo the checks above
          */
         kfree(cur_trans);
         goto loop;
     } else if (BTRFS_FS_ERROR(fs_info)) {
         spin_unlock(&fs_info->trans_lock);
         kfree(cur_trans);
         return -EROFS;
     }
 
     cur_trans->fs_info = fs_info;
     atomic_set(&cur_trans->pending_ordered, 0);
     init_waitqueue_head(&cur_trans->pending_wait);
     atomic_set(&cur_trans->num_writers, 1);
     extwriter_counter_init(cur_trans, type);
     init_waitqueue_head(&cur_trans->writer_wait);
     init_waitqueue_head(&cur_trans->commit_wait);
     cur_trans->state = TRANS_STATE_RUNNING;
     /*
      * One for this trans handle, one so it will live on until we
      * commit the transaction.
      */
     refcount_set(&cur_trans->use_count, 2);
     cur_trans->flags = 0;
     cur_trans->start_time = ktime_get_seconds();
 
     memset(&cur_trans->delayed_refs, 0, sizeof(cur_trans->delayed_refs));
 
     cur_trans->delayed_refs.href_root = RB_ROOT_CACHED;
     cur_trans->delayed_refs.dirty_extent_root = RB_ROOT;
     atomic_set(&cur_trans->delayed_refs.num_entries, 0);
 
     /*
      * although the tree mod log is per file system and not per transaction,
      * the log must never go across transaction boundaries.
      */
     smp_mb();
     if (!list_empty(&fs_info->tree_mod_seq_list))
         WARN(1, KERN_ERR "BTRFS: tree_mod_seq_list not empty when creating a fresh transaction\n");
     if (!RB_EMPTY_ROOT(&fs_info->tree_mod_log))
         WARN(1, KERN_ERR "BTRFS: tree_mod_log rb tree not empty when creating a fresh transaction\n");
     atomic64_set(&fs_info->tree_mod_seq, 0);
 
     spin_lock_init(&cur_trans->delayed_refs.lock);
 
     INIT_LIST_HEAD(&cur_trans->pending_snapshots);
     INIT_LIST_HEAD(&cur_trans->dev_update_list);
     INIT_LIST_HEAD(&cur_trans->switch_commits);
     INIT_LIST_HEAD(&cur_trans->dirty_bgs);
     INIT_LIST_HEAD(&cur_trans->io_bgs);
     INIT_LIST_HEAD(&cur_trans->dropped_roots);
     mutex_init(&cur_trans->cache_write_mutex);
     spin_lock_init(&cur_trans->dirty_bgs_lock);
     INIT_LIST_HEAD(&cur_trans->deleted_bgs);
     spin_lock_init(&cur_trans->dropped_roots_lock);
     INIT_LIST_HEAD(&cur_trans->releasing_ebs);
     spin_lock_init(&cur_trans->releasing_ebs_lock);
     list_add_tail(&cur_trans->list, &fs_info->trans_list);
     extent_io_tree_init(fs_info, &cur_trans->dirty_pages,
             IO_TREE_TRANS_DIRTY_PAGES, fs_info->btree_inode);
     extent_io_tree_init(fs_info, &cur_trans->pinned_extents,
             IO_TREE_FS_PINNED_EXTENTS, NULL);
     fs_info->generation++;
     cur_trans->transid = fs_info->generation;
     fs_info->running_transaction = cur_trans;
     cur_trans->aborted = 0;
     spin_unlock(&fs_info->trans_lock);
 
     return 0;
 }
 
 /*
  * This does all the record keeping required to make sure that a shareable root
  * is properly recorded in a given transaction.  This is required to make sure
  * the old root from before we joined the transaction is deleted when the
  * transaction commits.
  */
 static int record_root_in_trans(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root,
                    int force)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     int ret = 0;
 
     if ((test_bit(BTRFS_ROOT_SHAREABLE, &root->state) &&
         root->last_trans < trans->transid) || force) {
         WARN_ON(!force && root->commit_root != root->node);
 
         /*
          * see below for IN_TRANS_SETUP usage rules
          * we have the reloc mutex held now, so there
          * is only one writer in this function
          */
         set_bit(BTRFS_ROOT_IN_TRANS_SETUP, &root->state);
 
         /* make sure readers find IN_TRANS_SETUP before
          * they find our root->last_trans update
          */
         smp_wmb();
 
         spin_lock(&fs_info->fs_roots_radix_lock);
         if (root->last_trans == trans->transid && !force) {
             spin_unlock(&fs_info->fs_roots_radix_lock);
             return 0;
         }
         radix_tree_tag_set(&fs_info->fs_roots_radix,
                    (unsigned long)root->root_key.objectid,
                    BTRFS_ROOT_TRANS_TAG);
         spin_unlock(&fs_info->fs_roots_radix_lock);
         root->last_trans = trans->transid;
 
         /* this is pretty tricky.  We don't want to
          * take the relocation lock in btrfs_record_root_in_trans
          * unless we're really doing the first setup for this root in
          * this transaction.
          *
          * Normally we'd use root->last_trans as a flag to decide
          * if we want to take the expensive mutex.
          *
          * But, we have to set root->last_trans before we
          * init the relocation root, otherwise, we trip over warnings
          * in ctree.c.  The solution used here is to flag ourselves
          * with root IN_TRANS_SETUP.  When this is 1, we're still
          * fixing up the reloc trees and everyone must wait.
          *
          * When this is zero, they can trust root->last_trans and fly
          * through btrfs_record_root_in_trans without having to take the
          * lock.  smp_wmb() makes sure that all the writes above are
          * done before we pop in the zero below
          */
         ret = btrfs_init_reloc_root(trans, root);
         smp_mb__before_atomic();
         clear_bit(BTRFS_ROOT_IN_TRANS_SETUP, &root->state);
     }
     return ret;
 }
 
 
 void btrfs_add_dropped_root(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_transaction *cur_trans = trans->transaction;
 
     /* Add ourselves to the transaction dropped list */
     spin_lock(&cur_trans->dropped_roots_lock);
     list_add_tail(&root->root_list, &cur_trans->dropped_roots);
     spin_unlock(&cur_trans->dropped_roots_lock);
 
     /* Make sure we don't try to update the root at commit time */
     spin_lock(&fs_info->fs_roots_radix_lock);
     radix_tree_tag_clear(&fs_info->fs_roots_radix,
                  (unsigned long)root->root_key.objectid,
                  BTRFS_ROOT_TRANS_TAG);
     spin_unlock(&fs_info->fs_roots_radix_lock);
 }
 
 int btrfs_record_root_in_trans(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     int ret;
 
     if (!test_bit(BTRFS_ROOT_SHAREABLE, &root->state))
         return 0;
 
     /*
      * see record_root_in_trans for comments about IN_TRANS_SETUP usage
      * and barriers
      */
     smp_rmb();
     if (root->last_trans == trans->transid &&
         !test_bit(BTRFS_ROOT_IN_TRANS_SETUP, &root->state))
         return 0;
 
     mutex_lock(&fs_info->reloc_mutex);
     ret = record_root_in_trans(trans, root, 0);
     mutex_unlock(&fs_info->reloc_mutex);
 
     return ret;
 }
 
 static inline int is_transaction_blocked(struct btrfs_transaction *trans)
 {
     return (trans->state >= TRANS_STATE_COMMIT_START &&
         trans->state < TRANS_STATE_UNBLOCKED &&
         !TRANS_ABORTED(trans));
 }
 
 /* wait for commit against the current transaction to become unblocked
  * when this is done, it is safe to start a new transaction, but the current
  * transaction might not be fully on disk.
  */
 static void wait_current_trans(struct btrfs_fs_info *fs_info)
 {
     struct btrfs_transaction *cur_trans;
 
     spin_lock(&fs_info->trans_lock);
     cur_trans = fs_info->running_transaction;
     if (cur_trans && is_transaction_blocked(cur_trans)) {
         refcount_inc(&cur_trans->use_count);
         spin_unlock(&fs_info->trans_lock);
 
         wait_event(fs_info->transaction_wait,
                cur_trans->state >= TRANS_STATE_UNBLOCKED ||
                TRANS_ABORTED(cur_trans));
         btrfs_put_transaction(cur_trans);
     } else {
         spin_unlock(&fs_info->trans_lock);
     }
 }
 
 static int may_wait_transaction(struct btrfs_fs_info *fs_info, int type)
 {
     if (test_bit(BTRFS_FS_LOG_RECOVERING, &fs_info->flags))
         return 0;
 
     if (type == TRANS_START)
         return 1;
 
     return 0;
 }
 
 static inline bool need_reserve_reloc_root(struct btrfs_root *root)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
 
     if (!fs_info->reloc_ctl ||
         !test_bit(BTRFS_ROOT_SHAREABLE, &root->state) ||
         root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID ||
         root->reloc_root)
         return false;
 
     return true;
 }
 
 static struct btrfs_trans_handle *
 start_transaction(struct btrfs_root *root, unsigned int num_items,
           unsigned int type, enum btrfs_reserve_flush_enum flush,
           bool enforce_qgroups)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_block_rsv *delayed_refs_rsv = &fs_info->delayed_refs_rsv;
     struct btrfs_trans_handle *h;
     struct btrfs_transaction *cur_trans;
     u64 num_bytes = 0;
     u64 qgroup_reserved = 0;
     bool reloc_reserved = false;
     bool do_chunk_alloc = false;
     int ret;
 
     if (BTRFS_FS_ERROR(fs_info))
         return ERR_PTR(-EROFS);
 
     if (current->journal_info) {
         WARN_ON(type & TRANS_EXTWRITERS);
         h = current->journal_info;
         refcount_inc(&h->use_count);
         WARN_ON(refcount_read(&h->use_count) > 2);
         h->orig_rsv = h->block_rsv;
         h->block_rsv = NULL;
         goto got_it;
     }
 
     /*
      * Do the reservation before we join the transaction so we can do all
      * the appropriate flushing if need be.
      */
     if (num_items && root != fs_info->chunk_root) {
         struct btrfs_block_rsv *rsv = &fs_info->trans_block_rsv;
         u64 delayed_refs_bytes = 0;
 
         qgroup_reserved = num_items * fs_info->nodesize;
         ret = btrfs_qgroup_reserve_meta_pertrans(root, qgroup_reserved,
                 enforce_qgroups);
         if (ret)
             return ERR_PTR(ret);
 
         /*
          * We want to reserve all the bytes we may need all at once, so
          * we only do 1 enospc flushing cycle per transaction start.  We
          * accomplish this by simply assuming we'll do 2 x num_items
          * worth of delayed refs updates in this trans handle, and
          * refill that amount for whatever is missing in the reserve.
          */
         num_bytes = btrfs_calc_insert_metadata_size(fs_info, num_items);
         if (flush == BTRFS_RESERVE_FLUSH_ALL &&
             delayed_refs_rsv->full == 0) {
             delayed_refs_bytes = num_bytes;
             num_bytes <<= 1;
         }
 
         /*
          * Do the reservation for the relocation root creation
          */
         if (need_reserve_reloc_root(root)) {
             num_bytes += fs_info->nodesize;
             reloc_reserved = true;
         }
 
         ret = btrfs_block_rsv_add(fs_info, rsv, num_bytes, flush);
         if (ret)
             goto reserve_fail;
         if (delayed_refs_bytes) {
             btrfs_migrate_to_delayed_refs_rsv(fs_info, rsv,
                               delayed_refs_bytes);
             num_bytes -= delayed_refs_bytes;
         }
 
         if (rsv->space_info->force_alloc)
             do_chunk_alloc = true;
     } else if (num_items == 0 && flush == BTRFS_RESERVE_FLUSH_ALL &&
            !delayed_refs_rsv->full) {
         /*
          * Some people call with btrfs_start_transaction(root, 0)
          * because they can be throttled, but have some other mechanism
          * for reserving space.  We still want these guys to refill the
          * delayed block_rsv so just add 1 items worth of reservation
          * here.
          */
         ret = btrfs_delayed_refs_rsv_refill(fs_info, flush);
         if (ret)
             goto reserve_fail;
     }
 again:
     h = kmem_cache_zalloc(btrfs_trans_handle_cachep, GFP_NOFS);
     if (!h) {
         ret = -ENOMEM;
         goto alloc_fail;
     }
 
     /*
      * If we are JOIN_NOLOCK we're already committing a transaction and
      * waiting on this guy, so we don't need to do the sb_start_intwrite
      * because we're already holding a ref.  We need this because we could
      * have raced in and did an fsync() on a file which can kick a commit
      * and then we deadlock with somebody doing a freeze.
      *
      * If we are ATTACH, it means we just want to catch the current
      * transaction and commit it, so we needn't do sb_start_intwrite(). 
      */
     if (type & __TRANS_FREEZABLE)
         sb_start_intwrite(fs_info->sb);
 
     if (may_wait_transaction(fs_info, type))
         wait_current_trans(fs_info);
 
     do {
         ret = join_transaction(fs_info, type);
         if (ret == -EBUSY) {
             wait_current_trans(fs_info);
             if (unlikely(type == TRANS_ATTACH ||
                      type == TRANS_JOIN_NOSTART))
                 ret = -ENOENT;
         }
     } while (ret == -EBUSY);
 
     if (ret < 0)
         goto join_fail;
 
     cur_trans = fs_info->running_transaction;
 
     h->transid = cur_trans->transid;
     h->transaction = cur_trans;
     refcount_set(&h->use_count, 1);
     h->fs_info = root->fs_info;
 
     h->type = type;
     INIT_LIST_HEAD(&h->new_bgs);
 
     smp_mb();
     if (cur_trans->state >= TRANS_STATE_COMMIT_START &&
         may_wait_transaction(fs_info, type)) {
         current->journal_info = h;
         btrfs_commit_transaction(h);
         goto again;
     }
 
     if (num_bytes) {
         trace_btrfs_space_reservation(fs_info, "transaction",
                           h->transid, num_bytes, 1);
         h->block_rsv = &fs_info->trans_block_rsv;
         h->bytes_reserved = num_bytes;
         h->reloc_reserved = reloc_reserved;
     }
 
 got_it:
     if (!current->journal_info)
         current->journal_info = h;
 
     /*
      * If the space_info is marked ALLOC_FORCE then we'll get upgraded to
      * ALLOC_FORCE the first run through, and then we won't allocate for
      * anybody else who races in later.  We don't care about the return
      * value here.
      */
     if (do_chunk_alloc && num_bytes) {
         u64 flags = h->block_rsv->space_info->flags;
 
         btrfs_chunk_alloc(h, btrfs_get_alloc_profile(fs_info, flags),
                   CHUNK_ALLOC_NO_FORCE);
     }
 
     /*
      * btrfs_record_root_in_trans() needs to alloc new extents, and may
      * call btrfs_join_transaction() while we're also starting a
      * transaction.
      *
      * Thus it need to be called after current->journal_info initialized,
      * or we can deadlock.
      */
     ret = btrfs_record_root_in_trans(h, root);
     if (ret) {
         /*
          * The transaction handle is fully initialized and linked with
          * other structures so it needs to be ended in case of errors,
          * not just freed.
          */
         btrfs_end_transaction(h);
         return ERR_PTR(ret);
     }
 
     return h;
 
 join_fail:
     if (type & __TRANS_FREEZABLE)
         sb_end_intwrite(fs_info->sb);
     kmem_cache_free(btrfs_trans_handle_cachep, h);
 alloc_fail:
     if (num_bytes)
         btrfs_block_rsv_release(fs_info, &fs_info->trans_block_rsv,
                     num_bytes, NULL);
 reserve_fail:
     btrfs_qgroup_free_meta_pertrans(root, qgroup_reserved);
     return ERR_PTR(ret);
 }
 
 struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root,
                            unsigned int num_items)
 {
     return start_transaction(root, num_items, TRANS_START,
                  BTRFS_RESERVE_FLUSH_ALL, true);
 }
 
 struct btrfs_trans_handle *btrfs_start_transaction_fallback_global_rsv(
                     struct btrfs_root *root,
                     unsigned int num_items)
 {
     return start_transaction(root, num_items, TRANS_START,
                  BTRFS_RESERVE_FLUSH_ALL_STEAL, false);
 }
 
 struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root)
 {
     return start_transaction(root, 0, TRANS_JOIN, BTRFS_RESERVE_NO_FLUSH,
                  true);
 }
 
 struct btrfs_trans_handle *btrfs_join_transaction_spacecache(struct btrfs_root *root)
 {
     return start_transaction(root, 0, TRANS_JOIN_NOLOCK,
                  BTRFS_RESERVE_NO_FLUSH, true);
 }
 
 /*
  * Similar to regular join but it never starts a transaction when none is
  * running or after waiting for the current one to finish.
  */
 struct btrfs_trans_handle *btrfs_join_transaction_nostart(struct btrfs_root *root)
 {
     return start_transaction(root, 0, TRANS_JOIN_NOSTART,
                  BTRFS_RESERVE_NO_FLUSH, true);
 }
 
 /*
  * btrfs_attach_transaction() - catch the running transaction
  *
  * It is used when we want to commit the current the transaction, but
  * don't want to start a new one.
  *
  * Note: If this function return -ENOENT, it just means there is no
  * running transaction. But it is possible that the inactive transaction
  * is still in the memory, not fully on disk. If you hope there is no
  * inactive transaction in the fs when -ENOENT is returned, you should
  * invoke
  *     btrfs_attach_transaction_barrier()
  */
 struct btrfs_trans_handle *btrfs_attach_transaction(struct btrfs_root *root)
 {
     return start_transaction(root, 0, TRANS_ATTACH,
                  BTRFS_RESERVE_NO_FLUSH, true);
 }
 
 /*
  * btrfs_attach_transaction_barrier() - catch the running transaction
  *
  * It is similar to the above function, the difference is this one
  * will wait for all the inactive transactions until they fully
  * complete.
  */
 struct btrfs_trans_handle *
 btrfs_attach_transaction_barrier(struct btrfs_root *root)
 {
     struct btrfs_trans_handle *trans;
 
     trans = start_transaction(root, 0, TRANS_ATTACH,
                   BTRFS_RESERVE_NO_FLUSH, true);
     if (trans == ERR_PTR(-ENOENT))
         btrfs_wait_for_commit(root->fs_info, 0);
 
     return trans;
 }
 
 /* Wait for a transaction commit to reach at least the given state. */
 static noinline void wait_for_commit(struct btrfs_transaction *commit,
                      const enum btrfs_trans_state min_state)
 {
     struct btrfs_fs_info *fs_info = commit->fs_info;
     u64 transid = commit->transid;
     bool put = false;
 
     while (1) {
         wait_event(commit->commit_wait, commit->state >= min_state);
         if (put)
             btrfs_put_transaction(commit);
 
         if (min_state < TRANS_STATE_COMPLETED)
             break;
 
         /*
          * A transaction isn't really completed until all of the
          * previous transactions are completed, but with fsync we can
          * end up with SUPER_COMMITTED transactions before a COMPLETED
          * transaction. Wait for those.
          */
 
         spin_lock(&fs_info->trans_lock);
         commit = list_first_entry_or_null(&fs_info->trans_list,
                           struct btrfs_transaction,
                           list);
         if (!commit || commit->transid > transid) {
             spin_unlock(&fs_info->trans_lock);
             break;
         }
         refcount_inc(&commit->use_count);
         put = true;
         spin_unlock(&fs_info->trans_lock);
     }
 }
 
 int btrfs_wait_for_commit(struct btrfs_fs_info *fs_info, u64 transid)
 {
     struct btrfs_transaction *cur_trans = NULL, *t;
     int ret = 0;
 
     if (transid) {
         if (transid <= fs_info->last_trans_committed)
             goto out;
 
         /* find specified transaction */
         spin_lock(&fs_info->trans_lock);
         list_for_each_entry(t, &fs_info->trans_list, list) {
             if (t->transid == transid) {
                 cur_trans = t;
                 refcount_inc(&cur_trans->use_count);
                 ret = 0;
                 break;
             }
             if (t->transid > transid) {
                 ret = 0;
                 break;
             }
         }
         spin_unlock(&fs_info->trans_lock);
 
         /*
          * The specified transaction doesn't exist, or we
          * raced with btrfs_commit_transaction
          */
         if (!cur_trans) {
             if (transid > fs_info->last_trans_committed)
                 ret = -EINVAL;
             goto out;
         }
     } else {
         /* find newest transaction that is committing | committed */
         spin_lock(&fs_info->trans_lock);
         list_for_each_entry_reverse(t, &fs_info->trans_list,
                         list) {
             if (t->state >= TRANS_STATE_COMMIT_START) {
                 if (t->state == TRANS_STATE_COMPLETED)
                     break;
                 cur_trans = t;
                 refcount_inc(&cur_trans->use_count);
                 break;
             }
         }
         spin_unlock(&fs_info->trans_lock);
         if (!cur_trans)
             goto out;  /* nothing committing|committed */
     }
 
     wait_for_commit(cur_trans, TRANS_STATE_COMPLETED);
     btrfs_put_transaction(cur_trans);
 out:
     return ret;
 }
 
 void btrfs_throttle(struct btrfs_fs_info *fs_info)
 {
     wait_current_trans(fs_info);
 }
 
 static bool should_end_transaction(struct btrfs_trans_handle *trans)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
 
     if (btrfs_check_space_for_delayed_refs(fs_info))
         return true;
 
     return !!btrfs_block_rsv_check(&fs_info->global_block_rsv, 5);
 }
 
 bool btrfs_should_end_transaction(struct btrfs_trans_handle *trans)
 {
     struct btrfs_transaction *cur_trans = trans->transaction;
 
     if (cur_trans->state >= TRANS_STATE_COMMIT_START ||
         test_bit(BTRFS_DELAYED_REFS_FLUSHING, &cur_trans->delayed_refs.flags))
         return true;
 
     return should_end_transaction(trans);
 }
 
 static void btrfs_trans_release_metadata(struct btrfs_trans_handle *trans)
 
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
 
     if (!trans->block_rsv) {
         ASSERT(!trans->bytes_reserved);
         return;
     }
 
     if (!trans->bytes_reserved)
         return;
 
     ASSERT(trans->block_rsv == &fs_info->trans_block_rsv);
     trace_btrfs_space_reservation(fs_info, "transaction",
                       trans->transid, trans->bytes_reserved, 0);
     btrfs_block_rsv_release(fs_info, trans->block_rsv,
                 trans->bytes_reserved, NULL);
     trans->bytes_reserved = 0;
 }
 
 static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
                    int throttle)
 {
     struct btrfs_fs_info *info = trans->fs_info;
     struct btrfs_transaction *cur_trans = trans->transaction;
     int err = 0;
 
     if (refcount_read(&trans->use_count) > 1) {
         refcount_dec(&trans->use_count);
         trans->block_rsv = trans->orig_rsv;
         return 0;
     }
 
     btrfs_trans_release_metadata(trans);
     trans->block_rsv = NULL;
 
     btrfs_create_pending_block_groups(trans);
 
     btrfs_trans_release_chunk_metadata(trans);
 
     if (trans->type & __TRANS_FREEZABLE)
         sb_end_intwrite(info->sb);
 
     WARN_ON(cur_trans != info->running_transaction);
     WARN_ON(atomic_read(&cur_trans->num_writers) < 1);
     atomic_dec(&cur_trans->num_writers);
     extwriter_counter_dec(cur_trans, trans->type);
 
     cond_wake_up(&cur_trans->writer_wait);
     btrfs_put_transaction(cur_trans);
 
     if (current->journal_info == trans)
         current->journal_info = NULL;
 
     if (throttle)
         btrfs_run_delayed_iputs(info);
 
     if (TRANS_ABORTED(trans) || BTRFS_FS_ERROR(info)) {
         wake_up_process(info->transaction_kthread);
         if (TRANS_ABORTED(trans))
             err = trans->aborted;
         else
             err = -EROFS;
     }
 
     kmem_cache_free(btrfs_trans_handle_cachep, trans);
     return err;
 }
 
 int btrfs_end_transaction(struct btrfs_trans_handle *trans)
 {
     return __btrfs_end_transaction(trans, 0);
 }
 
 int btrfs_end_transaction_throttle(struct btrfs_trans_handle *trans)
 {
     return __btrfs_end_transaction(trans, 1);
 }
 
 /*
  * when btree blocks are allocated, they have some corresponding bits set for
  * them in one of two extent_io trees.  This is used to make sure all of
  * those extents are sent to disk but does not wait on them
  */
 int btrfs_write_marked_extents(struct btrfs_fs_info *fs_info,
                    struct extent_io_tree *dirty_pages, int mark)
 {
     int err = 0;
     int werr = 0;
     struct address_space *mapping = fs_info->btree_inode->i_mapping;
     struct extent_state *cached_state = NULL;
     u64 start = 0;
     u64 end;
 
     atomic_inc(&BTRFS_I(fs_info->btree_inode)->sync_writers);
     while (!find_first_extent_bit(dirty_pages, start, &start, &end,
                       mark, &cached_state)) {
         bool wait_writeback = false;
 
         err = convert_extent_bit(dirty_pages, start, end,
                      EXTENT_NEED_WAIT,
                      mark, &cached_state);
         /*
          * convert_extent_bit can return -ENOMEM, which is most of the
          * time a temporary error. So when it happens, ignore the error
          * and wait for writeback of this range to finish - because we
          * failed to set the bit EXTENT_NEED_WAIT for the range, a call
          * to __btrfs_wait_marked_extents() would not know that
          * writeback for this range started and therefore wouldn't
          * wait for it to finish - we don't want to commit a
          * superblock that points to btree nodes/leafs for which
          * writeback hasn't finished yet (and without errors).
          * We cleanup any entries left in the io tree when committing
          * the transaction (through extent_io_tree_release()).
          */
         if (err == -ENOMEM) {
             err = 0;
             wait_writeback = true;
         }
         if (!err)
             err = filemap_fdatawrite_range(mapping, start, end);
         if (err)
             werr = err;
         else if (wait_writeback)
             werr = filemap_fdatawait_range(mapping, start, end);
         free_extent_state(cached_state);
         cached_state = NULL;
         cond_resched();
         start = end + 1;
     }
     atomic_dec(&BTRFS_I(fs_info->btree_inode)->sync_writers);
     return werr;
 }
 
 /*
  * when btree blocks are allocated, they have some corresponding bits set for
  * them in one of two extent_io trees.  This is used to make sure all of
  * those extents are on disk for transaction or log commit.  We wait
  * on all the pages and clear them from the dirty pages state tree
  */
 static int __btrfs_wait_marked_extents(struct btrfs_fs_info *fs_info,
                        struct extent_io_tree *dirty_pages)
 {
     int err = 0;
     int werr = 0;
     struct address_space *mapping = fs_info->btree_inode->i_mapping;
     struct extent_state *cached_state = NULL;
     u64 start = 0;
     u64 end;
 
     while (!find_first_extent_bit(dirty_pages, start, &start, &end,
                       EXTENT_NEED_WAIT, &cached_state)) {
         /*
          * Ignore -ENOMEM errors returned by clear_extent_bit().
          * When committing the transaction, we'll remove any entries
          * left in the io tree. For a log commit, we don't remove them
          * after committing the log because the tree can be accessed
          * concurrently - we do it only at transaction commit time when
          * it's safe to do it (through extent_io_tree_release()).
          */
         err = clear_extent_bit(dirty_pages, start, end,
                        EXTENT_NEED_WAIT, 0, 0, &cached_state);
         if (err == -ENOMEM)
             err = 0;
         if (!err)
             err = filemap_fdatawait_range(mapping, start, end);
         if (err)
             werr = err;
         free_extent_state(cached_state);
         cached_state = NULL;
         cond_resched();
         start = end + 1;
     }
     if (err)
         werr = err;
     return werr;
 }
 
 static int btrfs_wait_extents(struct btrfs_fs_info *fs_info,
                struct extent_io_tree *dirty_pages)
 {
     bool errors = false;
     int err;
 
     err = __btrfs_wait_marked_extents(fs_info, dirty_pages);
     if (test_and_clear_bit(BTRFS_FS_BTREE_ERR, &fs_info->flags))
         errors = true;
 
     if (errors && !err)
         err = -EIO;
     return err;
 }
 
 int btrfs_wait_tree_log_extents(struct btrfs_root *log_root, int mark)
 {
     struct btrfs_fs_info *fs_info = log_root->fs_info;
     struct extent_io_tree *dirty_pages = &log_root->dirty_log_pages;
     bool errors = false;
     int err;
 
     ASSERT(log_root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID);
 
     err = __btrfs_wait_marked_extents(fs_info, dirty_pages);
     if ((mark & EXTENT_DIRTY) &&
         test_and_clear_bit(BTRFS_FS_LOG1_ERR, &fs_info->flags))
         errors = true;
 
     if ((mark & EXTENT_NEW) &&
         test_and_clear_bit(BTRFS_FS_LOG2_ERR, &fs_info->flags))
         errors = true;
 
     if (errors && !err)
         err = -EIO;
     return err;
 }
 
 /*
  * When btree blocks are allocated the corresponding extents are marked dirty.
  * This function ensures such extents are persisted on disk for transaction or
  * log commit.
  *
  * @trans: transaction whose dirty pages we'd like to write
  */
 static int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans)
 {
     int ret;
     int ret2;
     struct extent_io_tree *dirty_pages = &trans->transaction->dirty_pages;
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct blk_plug plug;
 
     blk_start_plug(&plug);
     ret = btrfs_write_marked_extents(fs_info, dirty_pages, EXTENT_DIRTY);
     blk_finish_plug(&plug);
     ret2 = btrfs_wait_extents(fs_info, dirty_pages);
 
     extent_io_tree_release(&trans->transaction->dirty_pages);
 
     if (ret)
         return ret;
     else if (ret2)
         return ret2;
     else
         return 0;
 }
 
 /*
  * this is used to update the root pointer in the tree of tree roots.
  *
  * But, in the case of the extent allocation tree, updating the root
  * pointer may allocate blocks which may change the root of the extent
  * allocation tree.
  *
  * So, this loops and repeats and makes sure the cowonly root didn't
  * change while the root pointer was being updated in the metadata.
  */
 static int update_cowonly_root(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root)
 {
     int ret;
     u64 old_root_bytenr;
     u64 old_root_used;
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_root *tree_root = fs_info->tree_root;
 
     old_root_used = btrfs_root_used(&root->root_item);
 
     while (1) {
         old_root_bytenr = btrfs_root_bytenr(&root->root_item);
         if (old_root_bytenr == root->node->start &&
             old_root_used == btrfs_root_used(&root->root_item))
             break;
 
         btrfs_set_root_node(&root->root_item, root->node);
         ret = btrfs_update_root(trans, tree_root,
                     &root->root_key,
                     &root->root_item);
         if (ret)
             return ret;
 
         old_root_used = btrfs_root_used(&root->root_item);
     }
 
     return 0;
 }
 
 /*
  * update all the cowonly tree roots on disk
  *
  * The error handling in this function may not be obvious. Any of the
  * failures will cause the file system to go offline. We still need
  * to clean up the delayed refs.
  */
 static noinline int commit_cowonly_roots(struct btrfs_trans_handle *trans)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct list_head *dirty_bgs = &trans->transaction->dirty_bgs;
     struct list_head *io_bgs = &trans->transaction->io_bgs;
     struct list_head *next;
     struct extent_buffer *eb;
     int ret;
 
     /*
      * At this point no one can be using this transaction to modify any tree
      * and no one can start another transaction to modify any tree either.
      */
     ASSERT(trans->transaction->state == TRANS_STATE_COMMIT_DOING);
 
     eb = btrfs_lock_root_node(fs_info->tree_root);
     ret = btrfs_cow_block(trans, fs_info->tree_root, eb, NULL,
                   0, &eb, BTRFS_NESTING_COW);
     btrfs_tree_unlock(eb);
     free_extent_buffer(eb);
 
     if (ret)
         return ret;
 
     ret = btrfs_run_dev_stats(trans);
     if (ret)
         return ret;
     ret = btrfs_run_dev_replace(trans);
     if (ret)
         return ret;
     ret = btrfs_run_qgroups(trans);
     if (ret)
         return ret;
 
     ret = btrfs_setup_space_cache(trans);
     if (ret)
         return ret;
 
 again:
     while (!list_empty(&fs_info->dirty_cowonly_roots)) {
         struct btrfs_root *root;
         next = fs_info->dirty_cowonly_roots.next;
         list_del_init(next);
         root = list_entry(next, struct btrfs_root, dirty_list);
         clear_bit(BTRFS_ROOT_DIRTY, &root->state);
 
         list_add_tail(&root->dirty_list,
                   &trans->transaction->switch_commits);
         ret = update_cowonly_root(trans, root);
         if (ret)
             return ret;
     }
 
     /* Now flush any delayed refs generated by updating all of the roots */
     ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
     if (ret)
         return ret;
 
     while (!list_empty(dirty_bgs) || !list_empty(io_bgs)) {
         ret = btrfs_write_dirty_block_groups(trans);
         if (ret)
             return ret;
 
         /*
          * We're writing the dirty block groups, which could generate
          * delayed refs, which could generate more dirty block groups,
          * so we want to keep this flushing in this loop to make sure
          * everything gets run.
          */
         ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
         if (ret)
             return ret;
     }
 
     if (!list_empty(&fs_info->dirty_cowonly_roots))
         goto again;
 
     /* Update dev-replace pointer once everything is committed */
     fs_info->dev_replace.committed_cursor_left =
         fs_info->dev_replace.cursor_left_last_write_of_item;
 
     return 0;
 }
 
 /*
  * If we had a pending drop we need to see if there are any others left in our
  * dead roots list, and if not clear our bit and wake any waiters.
  */
 void btrfs_maybe_wake_unfinished_drop(struct btrfs_fs_info *fs_info)
 {
     /*
      * We put the drop in progress roots at the front of the list, so if the
      * first entry doesn't have UNFINISHED_DROP set we can wake everybody
      * up.
      */
     spin_lock(&fs_info->trans_lock);
     if (!list_empty(&fs_info->dead_roots)) {
         struct btrfs_root *root = list_first_entry(&fs_info->dead_roots,
                                struct btrfs_root,
                                root_list);
         if (test_bit(BTRFS_ROOT_UNFINISHED_DROP, &root->state)) {
             spin_unlock(&fs_info->trans_lock);
             return;
         }
     }
     spin_unlock(&fs_info->trans_lock);
 
     btrfs_wake_unfinished_drop(fs_info);
 }
 
 /*
  * dead roots are old snapshots that need to be deleted.  This allocates
  * a dirty root struct and adds it into the list of dead roots that need to
  * be deleted
  */
 void btrfs_add_dead_root(struct btrfs_root *root)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
 
     spin_lock(&fs_info->trans_lock);
     if (list_empty(&root->root_list)) {
         btrfs_grab_root(root);
 
         /* We want to process the partially complete drops first. */
         if (test_bit(BTRFS_ROOT_UNFINISHED_DROP, &root->state))
             list_add(&root->root_list, &fs_info->dead_roots);
         else
             list_add_tail(&root->root_list, &fs_info->dead_roots);
     }
     spin_unlock(&fs_info->trans_lock);
 }
 
 /*
  * Update each subvolume root and its relocation root, if it exists, in the tree
  * of tree roots. Also free log roots if they exist.
  */
 static noinline int commit_fs_roots(struct btrfs_trans_handle *trans)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct btrfs_root *gang[8];
     int i;
     int ret;
 
     /*
      * At this point no one can be using this transaction to modify any tree
      * and no one can start another transaction to modify any tree either.
      */
     ASSERT(trans->transaction->state == TRANS_STATE_COMMIT_DOING);
 
     spin_lock(&fs_info->fs_roots_radix_lock);
     while (1) {
         ret = radix_tree_gang_lookup_tag(&fs_info->fs_roots_radix,
                          (void **)gang, 0,
                          ARRAY_SIZE(gang),
                          BTRFS_ROOT_TRANS_TAG);
         if (ret == 0)
             break;
         for (i = 0; i < ret; i++) {
             struct btrfs_root *root = gang[i];
             int ret2;
 
             /*
              * At this point we can neither have tasks logging inodes
              * from a root nor trying to commit a log tree.
              */
             ASSERT(atomic_read(&root->log_writers) == 0);
             ASSERT(atomic_read(&root->log_commit[0]) == 0);
             ASSERT(atomic_read(&root->log_commit[1]) == 0);
 
             radix_tree_tag_clear(&fs_info->fs_roots_radix,
                     (unsigned long)root->root_key.objectid,
                     BTRFS_ROOT_TRANS_TAG);
             spin_unlock(&fs_info->fs_roots_radix_lock);
 
             btrfs_free_log(trans, root);
             ret2 = btrfs_update_reloc_root(trans, root);
             if (ret2)
                 return ret2;
 
             /* see comments in should_cow_block() */
             clear_bit(BTRFS_ROOT_FORCE_COW, &root->state);
             smp_mb__after_atomic();
 
             if (root->commit_root != root->node) {
                 list_add_tail(&root->dirty_list,
                     &trans->transaction->switch_commits);
                 btrfs_set_root_node(&root->root_item,
                             root->node);
             }
 
             ret2 = btrfs_update_root(trans, fs_info->tree_root,
                         &root->root_key,
                         &root->root_item);
             if (ret2)
                 return ret2;
             spin_lock(&fs_info->fs_roots_radix_lock);
             btrfs_qgroup_free_meta_all_pertrans(root);
         }
     }
     spin_unlock(&fs_info->fs_roots_radix_lock);
     return 0;
 }
 
 /*
  * defrag a given btree.
  * Every leaf in the btree is read and defragged.
  */
 int btrfs_defrag_root(struct btrfs_root *root)
 {
     struct btrfs_fs_info *info = root->fs_info;
     struct btrfs_trans_handle *trans;
     int ret;
 
     if (test_and_set_bit(BTRFS_ROOT_DEFRAG_RUNNING, &root->state))
         return 0;
 
     while (1) {
         trans = btrfs_start_transaction(root, 0);
         if (IS_ERR(trans)) {
             ret = PTR_ERR(trans);
             break;
         }
 
         ret = btrfs_defrag_leaves(trans, root);
 
         btrfs_end_transaction(trans);
         btrfs_btree_balance_dirty(info);
         cond_resched();
 
         if (btrfs_fs_closing(info) || ret != -EAGAIN)
             break;
 
         if (btrfs_defrag_cancelled(info)) {
             btrfs_debug(info, "defrag_root cancelled");
             ret = -EAGAIN;
             break;
         }
     }
     clear_bit(BTRFS_ROOT_DEFRAG_RUNNING, &root->state);
     return ret;
 }
 
 /*
  * Do all special snapshot related qgroup dirty hack.
  *
  * Will do all needed qgroup inherit and dirty hack like switch commit
  * roots inside one transaction and write all btree into disk, to make
  * qgroup works.
  */
 static int qgroup_account_snapshot(struct btrfs_trans_handle *trans,
                    struct btrfs_root *src,
                    struct btrfs_root *parent,
                    struct btrfs_qgroup_inherit *inherit,
                    u64 dst_objectid)
 {
     struct btrfs_fs_info *fs_info = src->fs_info;
     int ret;
 
     /*
      * Save some performance in the case that qgroups are not
      * enabled. If this check races with the ioctl, rescan will
      * kick in anyway.
      */
     if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags))
         return 0;
 
     /*
      * Ensure dirty @src will be committed.  Or, after coming
      * commit_fs_roots() and switch_commit_roots(), any dirty but not
      * recorded root will never be updated again, causing an outdated root
      * item.
      */
     ret = record_root_in_trans(trans, src, 1);
     if (ret)
         return ret;
 
     /*
      * btrfs_qgroup_inherit relies on a consistent view of the usage for the
      * src root, so we must run the delayed refs here.
      *
      * However this isn't particularly fool proof, because there's no
      * synchronization keeping us from changing the tree after this point
      * before we do the qgroup_inherit, or even from making changes while
      * we're doing the qgroup_inherit.  But that's a problem for the future,
      * for now flush the delayed refs to narrow the race window where the
      * qgroup counters could end up wrong.
      */
     ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
     if (ret) {
         btrfs_abort_transaction(trans, ret);
         return ret;
     }
 
     ret = commit_fs_roots(trans);
     if (ret)
         goto out;
     ret = btrfs_qgroup_account_extents(trans);
     if (ret < 0)
         goto out;
 
     /* Now qgroup are all updated, we can inherit it to new qgroups */
     ret = btrfs_qgroup_inherit(trans, src->root_key.objectid, dst_objectid,
                    inherit);
     if (ret < 0)
         goto out;
 
     /*
      * Now we do a simplified commit transaction, which will:
      * 1) commit all subvolume and extent tree
      *    To ensure all subvolume and extent tree have a valid
      *    commit_root to accounting later insert_dir_item()
      * 2) write all btree blocks onto disk
      *    This is to make sure later btree modification will be cowed
      *    Or commit_root can be populated and cause wrong qgroup numbers
      * In this simplified commit, we don't really care about other trees
      * like chunk and root tree, as they won't affect qgroup.
      * And we don't write super to avoid half committed status.
      */
     ret = commit_cowonly_roots(trans);
     if (ret)
         goto out;
     switch_commit_roots(trans);
     ret = btrfs_write_and_wait_transaction(trans);
     if (ret)
         btrfs_handle_fs_error(fs_info, ret,
             "Error while writing out transaction for qgroup");
 
 out:
     /*
      * Force parent root to be updated, as we recorded it before so its
      * last_trans == cur_transid.
      * Or it won't be committed again onto disk after later
      * insert_dir_item()
      */
     if (!ret)
         ret = record_root_in_trans(trans, parent, 1);
     return ret;
 }
 
 /*
  * new snapshots need to be created at a very specific time in the
  * transaction commit.  This does the actual creation.
  *
  * Note:
  * If the error which may affect the commitment of the current transaction
  * happens, we should return the error number. If the error which just affect
  * the creation of the pending snapshots, just return 0.
  */
 static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
                    struct btrfs_pending_snapshot *pending)
 {
 
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct btrfs_key key;
     struct btrfs_root_item *new_root_item;
     struct btrfs_root *tree_root = fs_info->tree_root;
     struct btrfs_root *root = pending->root;
     struct btrfs_root *parent_root;
     struct btrfs_block_rsv *rsv;
     struct inode *parent_inode;
     struct btrfs_path *path;
     struct btrfs_dir_item *dir_item;
     struct dentry *dentry;
     struct extent_buffer *tmp;
     struct extent_buffer *old;
     struct timespec64 cur_time;
     int ret = 0;
     u64 to_reserve = 0;
     u64 index = 0;
     u64 objectid;
     u64 root_flags;
 
     ASSERT(pending->path);
     path = pending->path;
 
     ASSERT(pending->root_item);
     new_root_item = pending->root_item;
 
     pending->error = btrfs_get_free_objectid(tree_root, &objectid);
     if (pending->error)
         goto no_free_objectid;
 
     /*
      * Make qgroup to skip current new snapshot's qgroupid, as it is
      * accounted by later btrfs_qgroup_inherit().
      */
     btrfs_set_skip_qgroup(trans, objectid);
 
     btrfs_reloc_pre_snapshot(pending, &to_reserve);
 
     if (to_reserve > 0) {
         pending->error = btrfs_block_rsv_add(fs_info,
                              &pending->block_rsv,
                              to_reserve,
                              BTRFS_RESERVE_NO_FLUSH);
         if (pending->error)
             goto clear_skip_qgroup;
     }
 
     key.objectid = objectid;
     key.offset = (u64)-1;
     key.type = BTRFS_ROOT_ITEM_KEY;
 
     rsv = trans->block_rsv;
     trans->block_rsv = &pending->block_rsv;
     trans->bytes_reserved = trans->block_rsv->reserved;
     trace_btrfs_space_reservation(fs_info, "transaction",
                       trans->transid,
                       trans->bytes_reserved, 1);
     dentry = pending->dentry;
     parent_inode = pending->dir;
     parent_root = BTRFS_I(parent_inode)->root;
     ret = record_root_in_trans(trans, parent_root, 0);
     if (ret)
         goto fail;
     cur_time = current_time(parent_inode);
 
     /*
      * insert the directory item
      */
     ret = btrfs_set_inode_index(BTRFS_I(parent_inode), &index);
     BUG_ON(ret); /* -ENOMEM */
 
     /* check if there is a file/dir which has the same name. */
     dir_item = btrfs_lookup_dir_item(NULL, parent_root, path,
                      btrfs_ino(BTRFS_I(parent_inode)),
                      dentry->d_name.name,
                      dentry->d_name.len, 0);
     if (dir_item != NULL && !IS_ERR(dir_item)) {
         pending->error = -EEXIST;
         goto dir_item_existed;
     } else if (IS_ERR(dir_item)) {
         ret = PTR_ERR(dir_item);
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
     btrfs_release_path(path);
 
     /*
      * pull in the delayed directory update
      * and the delayed inode item
      * otherwise we corrupt the FS during
      * snapshot
      */
     ret = btrfs_run_delayed_items(trans);
     if (ret) {  /* Transaction aborted */
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
 
     ret = record_root_in_trans(trans, root, 0);
     if (ret) {
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
     btrfs_set_root_last_snapshot(&root->root_item, trans->transid);
     memcpy(new_root_item, &root->root_item, sizeof(*new_root_item));
     btrfs_check_and_init_root_item(new_root_item);
 
     root_flags = btrfs_root_flags(new_root_item);
     if (pending->readonly)
         root_flags |= BTRFS_ROOT_SUBVOL_RDONLY;
     else
         root_flags &= ~BTRFS_ROOT_SUBVOL_RDONLY;
     btrfs_set_root_flags(new_root_item, root_flags);
 
     btrfs_set_root_generation_v2(new_root_item,
             trans->transid);
     generate_random_guid(new_root_item->uuid);
     memcpy(new_root_item->parent_uuid, root->root_item.uuid,
             BTRFS_UUID_SIZE);
     if (!(root_flags & BTRFS_ROOT_SUBVOL_RDONLY)) {
         memset(new_root_item->received_uuid, 0,
                sizeof(new_root_item->received_uuid));
         memset(&new_root_item->stime, 0, sizeof(new_root_item->stime));
         memset(&new_root_item->rtime, 0, sizeof(new_root_item->rtime));
         btrfs_set_root_stransid(new_root_item, 0);
         btrfs_set_root_rtransid(new_root_item, 0);
     }
     btrfs_set_stack_timespec_sec(&new_root_item->otime, cur_time.tv_sec);
     btrfs_set_stack_timespec_nsec(&new_root_item->otime, cur_time.tv_nsec);
     btrfs_set_root_otransid(new_root_item, trans->transid);
 
     old = btrfs_lock_root_node(root);
     ret = btrfs_cow_block(trans, root, old, NULL, 0, &old,
                   BTRFS_NESTING_COW);
     if (ret) {
         btrfs_tree_unlock(old);
         free_extent_buffer(old);
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
 
     ret = btrfs_copy_root(trans, root, old, &tmp, objectid);
     /* clean up in any case */
     btrfs_tree_unlock(old);
     free_extent_buffer(old);
     if (ret) {
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
     /* see comments in should_cow_block() */
     set_bit(BTRFS_ROOT_FORCE_COW, &root->state);
     smp_wmb();
 
     btrfs_set_root_node(new_root_item, tmp);
     /* record when the snapshot was created in key.offset */
     key.offset = trans->transid;
     ret = btrfs_insert_root(trans, tree_root, &key, new_root_item);
     btrfs_tree_unlock(tmp);
     free_extent_buffer(tmp);
     if (ret) {
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
 
     /*
      * insert root back/forward references
      */
     ret = btrfs_add_root_ref(trans, objectid,
                  parent_root->root_key.objectid,
                  btrfs_ino(BTRFS_I(parent_inode)), index,
                  dentry->d_name.name, dentry->d_name.len);
     if (ret) {
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
 
     key.offset = (u64)-1;
     pending->snap = btrfs_get_new_fs_root(fs_info, objectid, pending->anon_dev);
     if (IS_ERR(pending->snap)) {
         ret = PTR_ERR(pending->snap);
         pending->snap = NULL;
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
 
     ret = btrfs_reloc_post_snapshot(trans, pending);
     if (ret) {
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
 
     /*
      * Do special qgroup accounting for snapshot, as we do some qgroup
      * snapshot hack to do fast snapshot.
      * To co-operate with that hack, we do hack again.
      * Or snapshot will be greatly slowed down by a subtree qgroup rescan
      */
     ret = qgroup_account_snapshot(trans, root, parent_root,
                       pending->inherit, objectid);
     if (ret < 0)
         goto fail;
 
     ret = btrfs_insert_dir_item(trans, dentry->d_name.name,
                     dentry->d_name.len, BTRFS_I(parent_inode),
                     &key, BTRFS_FT_DIR, index);
     /* We have check then name at the beginning, so it is impossible. */
     BUG_ON(ret == -EEXIST || ret == -EOVERFLOW);
     if (ret) {
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
 
     btrfs_i_size_write(BTRFS_I(parent_inode), parent_inode->i_size +
                      dentry->d_name.len * 2);
     parent_inode->i_mtime = current_time(parent_inode);
     parent_inode->i_ctime = parent_inode->i_mtime;
     ret = btrfs_update_inode_fallback(trans, parent_root, BTRFS_I(parent_inode));
     if (ret) {
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
     ret = btrfs_uuid_tree_add(trans, new_root_item->uuid,
                   BTRFS_UUID_KEY_SUBVOL,
                   objectid);
     if (ret) {
         btrfs_abort_transaction(trans, ret);
         goto fail;
     }
     if (!btrfs_is_empty_uuid(new_root_item->received_uuid)) {
         ret = btrfs_uuid_tree_add(trans, new_root_item->received_uuid,
                       BTRFS_UUID_KEY_RECEIVED_SUBVOL,
                       objectid);
         if (ret && ret != -EEXIST) {
             btrfs_abort_transaction(trans, ret);
             goto fail;
         }
     }
 
 fail:
     pending->error = ret;
 dir_item_existed:
     trans->block_rsv = rsv;
     trans->bytes_reserved = 0;
 clear_skip_qgroup:
     btrfs_clear_skip_qgroup(trans);
 no_free_objectid:
     kfree(new_root_item);
     pending->root_item = NULL;
     btrfs_free_path(path);
     pending->path = NULL;
 
     return ret;
 }
 
 /*
  * create all the snapshots we've scheduled for creation
  */
 static noinline int create_pending_snapshots(struct btrfs_trans_handle *trans)
 {
     struct btrfs_pending_snapshot *pending, *next;
     struct list_head *head = &trans->transaction->pending_snapshots;
     int ret = 0;
 
     list_for_each_entry_safe(pending, next, head, list) {
         list_del(&pending->list);
         ret = create_pending_snapshot(trans, pending);
         if (ret)
             break;
     }
     return ret;
 }
 
 static void update_super_roots(struct btrfs_fs_info *fs_info)
 {
     struct btrfs_root_item *root_item;
     struct btrfs_super_block *super;
 
     super = fs_info->super_copy;
 
     root_item = &fs_info->chunk_root->root_item;
     super->chunk_root = root_item->bytenr;
     super->chunk_root_generation = root_item->generation;
     super->chunk_root_level = root_item->level;
 
     root_item = &fs_info->tree_root->root_item;
     super->root = root_item->bytenr;
     super->generation = root_item->generation;
     super->root_level = root_item->level;
     if (btrfs_test_opt(fs_info, SPACE_CACHE))
         super->cache_generation = root_item->generation;
     else if (test_bit(BTRFS_FS_CLEANUP_SPACE_CACHE_V1, &fs_info->flags))
         super->cache_generation = 0;
     if (test_bit(BTRFS_FS_UPDATE_UUID_TREE_GEN, &fs_info->flags))
         super->uuid_tree_generation = root_item->generation;
 
     if (btrfs_fs_incompat(fs_info, EXTENT_TREE_V2)) {
         root_item = &fs_info->block_group_root->root_item;
 
         super->block_group_root = root_item->bytenr;
         super->block_group_root_generation = root_item->generation;
         super->block_group_root_level = root_item->level;
     }
 }
 
 int btrfs_transaction_in_commit(struct btrfs_fs_info *info)
 {
     struct btrfs_transaction *trans;
     int ret = 0;
 
     spin_lock(&info->trans_lock);
     trans = info->running_transaction;
     if (trans)
         ret = (trans->state >= TRANS_STATE_COMMIT_START);
     spin_unlock(&info->trans_lock);
     return ret;
 }
 
 int btrfs_transaction_blocked(struct btrfs_fs_info *info)
 {
     struct btrfs_transaction *trans;
     int ret = 0;
 
     spin_lock(&info->trans_lock);
     trans = info->running_transaction;
     if (trans)
         ret = is_transaction_blocked(trans);
     spin_unlock(&info->trans_lock);
     return ret;
 }
 
 void btrfs_commit_transaction_async(struct btrfs_trans_handle *trans)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct btrfs_transaction *cur_trans;
 
     /* Kick the transaction kthread. */
     set_bit(BTRFS_FS_COMMIT_TRANS, &fs_info->flags);
     wake_up_process(fs_info->transaction_kthread);
 
     /* take transaction reference */
     cur_trans = trans->transaction;
     refcount_inc(&cur_trans->use_count);
 
     btrfs_end_transaction(trans);
 
     /*
      * Wait for the current transaction commit to start and block
      * subsequent transaction joins
      */
     wait_event(fs_info->transaction_blocked_wait,
            cur_trans->state >= TRANS_STATE_COMMIT_START ||
            TRANS_ABORTED(cur_trans));
     btrfs_put_transaction(cur_trans);
 }
 
 static void cleanup_transaction(struct btrfs_trans_handle *trans, int err)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct btrfs_transaction *cur_trans = trans->transaction;
 
     WARN_ON(refcount_read(&trans->use_count) > 1);
 
     btrfs_abort_transaction(trans, err);
 
     spin_lock(&fs_info->trans_lock);
 
     /*
      * If the transaction is removed from the list, it means this
      * transaction has been committed successfully, so it is impossible
      * to call the cleanup function.
      */
     BUG_ON(list_empty(&cur_trans->list));
 
     if (cur_trans == fs_info->running_transaction) {
         cur_trans->state = TRANS_STATE_COMMIT_DOING;
         spin_unlock(&fs_info->trans_lock);
         wait_event(cur_trans->writer_wait,
                atomic_read(&cur_trans->num_writers) == 1);
 
         spin_lock(&fs_info->trans_lock);
     }
 
     /*
      * Now that we know no one else is still using the transaction we can
      * remove the transaction from the list of transactions. This avoids
      * the transaction kthread from cleaning up the transaction while some
      * other task is still using it, which could result in a use-after-free
      * on things like log trees, as it forces the transaction kthread to
      * wait for this transaction to be cleaned up by us.
      */
     list_del_init(&cur_trans->list);
 
     spin_unlock(&fs_info->trans_lock);
 
     btrfs_cleanup_one_transaction(trans->transaction, fs_info);
 
     spin_lock(&fs_info->trans_lock);
     if (cur_trans == fs_info->running_transaction)
         fs_info->running_transaction = NULL;
     spin_unlock(&fs_info->trans_lock);
 
     if (trans->type & __TRANS_FREEZABLE)
         sb_end_intwrite(fs_info->sb);
     btrfs_put_transaction(cur_trans);
     btrfs_put_transaction(cur_trans);
 
     trace_btrfs_transaction_commit(fs_info);
 
     if (current->journal_info == trans)
         current->journal_info = NULL;
     btrfs_scrub_cancel(fs_info);
 
     kmem_cache_free(btrfs_trans_handle_cachep, trans);
 }
 
 /*
  * Release reserved delayed ref space of all pending block groups of the
  * transaction and remove them from the list
  */
 static void btrfs_cleanup_pending_block_groups(struct btrfs_trans_handle *trans)
 {
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_block_group *block_group, *tmp;
 
        list_for_each_entry_safe(block_group, tmp, &trans->new_bgs, bg_list) {
                btrfs_delayed_refs_rsv_release(fs_info, 1);
                list_del_init(&block_group->bg_list);
        }
 }
 
 static inline int btrfs_start_delalloc_flush(struct btrfs_fs_info *fs_info)
 {
     /*
      * We use try_to_writeback_inodes_sb() here because if we used
      * btrfs_start_delalloc_roots we would deadlock with fs freeze.
      * Currently are holding the fs freeze lock, if we do an async flush
      * we'll do btrfs_join_transaction() and deadlock because we need to
      * wait for the fs freeze lock.  Using the direct flushing we benefit
      * from already being in a transaction and our join_transaction doesn't
      * have to re-take the fs freeze lock.
      *
      * Note that try_to_writeback_inodes_sb() will only trigger writeback
      * if it can read lock sb->s_umount. It will always be able to lock it,
      * except when the filesystem is being unmounted or being frozen, but in
      * those cases sync_filesystem() is called, which results in calling
      * writeback_inodes_sb() while holding a write lock on sb->s_umount.
      * Note that we don't call writeback_inodes_sb() directly, because it
      * will emit a warning if sb->s_umount is not locked.
      */
     if (btrfs_test_opt(fs_info, FLUSHONCOMMIT))
         try_to_writeback_inodes_sb(fs_info->sb, WB_REASON_SYNC);
     return 0;
 }
 
 static inline void btrfs_wait_delalloc_flush(struct btrfs_fs_info *fs_info)
 {
     if (btrfs_test_opt(fs_info, FLUSHONCOMMIT))
         btrfs_wait_ordered_roots(fs_info, U64_MAX, 0, (u64)-1);
 }
 
 /*
  * Add a pending snapshot associated with the given transaction handle to the
  * respective handle. This must be called after the transaction commit started
  * and while holding fs_info->trans_lock.
  * This serves to guarantee a caller of btrfs_commit_transaction() that it can
  * safely free the pending snapshot pointer in case btrfs_commit_transaction()
  * returns an error.
  */
 static void add_pending_snapshot(struct btrfs_trans_handle *trans)
 {
     struct btrfs_transaction *cur_trans = trans->transaction;
 
     if (!trans->pending_snapshot)
         return;
 
     lockdep_assert_held(&trans->fs_info->trans_lock);
     ASSERT(cur_trans->state >= TRANS_STATE_COMMIT_START);
 
     list_add(&trans->pending_snapshot->list, &cur_trans->pending_snapshots);
 }
 
 static void update_commit_stats(struct btrfs_fs_info *fs_info, ktime_t interval)
 {
     fs_info->commit_stats.commit_count++;
     fs_info->commit_stats.last_commit_dur = interval;
     fs_info->commit_stats.max_commit_dur =
             max_t(u64, fs_info->commit_stats.max_commit_dur, interval);
     fs_info->commit_stats.total_commit_dur += interval;
 }
 
 int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct btrfs_transaction *cur_trans = trans->transaction;
     struct btrfs_transaction *prev_trans = NULL;
     int ret;
     ktime_t start_time;
     ktime_t interval;
 
     ASSERT(refcount_read(&trans->use_count) == 1);
 
     /* Stop the commit early if ->aborted is set */
     if (TRANS_ABORTED(cur_trans)) {
         ret = cur_trans->aborted;
         btrfs_end_transaction(trans);
         return ret;
     }
 
     btrfs_trans_release_metadata(trans);
     trans->block_rsv = NULL;
 
     /*
      * We only want one transaction commit doing the flushing so we do not
      * waste a bunch of time on lock contention on the extent root node.
      */
     if (!test_and_set_bit(BTRFS_DELAYED_REFS_FLUSHING,
                   &cur_trans->delayed_refs.flags)) {
         /*
          * Make a pass through all the delayed refs we have so far.
          * Any running threads may add more while we are here.
          */
         ret = btrfs_run_delayed_refs(trans, 0);
         if (ret) {
             btrfs_end_transaction(trans);
             return ret;
         }
     }
 
     btrfs_create_pending_block_groups(trans);
 
     if (!test_bit(BTRFS_TRANS_DIRTY_BG_RUN, &cur_trans->flags)) {
         int run_it = 0;
 
         /* this mutex is also taken before trying to set
          * block groups readonly.  We need to make sure
          * that nobody has set a block group readonly
          * after a extents from that block group have been
          * allocated for cache files.  btrfs_set_block_group_ro
          * will wait for the transaction to commit if it
          * finds BTRFS_TRANS_DIRTY_BG_RUN set.
          *
          * The BTRFS_TRANS_DIRTY_BG_RUN flag is also used to make sure
          * only one process starts all the block group IO.  It wouldn't
          * hurt to have more than one go through, but there's no
          * real advantage to it either.
          */
         mutex_lock(&fs_info->ro_block_group_mutex);
         if (!test_and_set_bit(BTRFS_TRANS_DIRTY_BG_RUN,
                       &cur_trans->flags))
             run_it = 1;
         mutex_unlock(&fs_info->ro_block_group_mutex);
 
         if (run_it) {
             ret = btrfs_start_dirty_block_groups(trans);
             if (ret) {
                 btrfs_end_transaction(trans);
                 return ret;
             }
         }
     }
 
     spin_lock(&fs_info->trans_lock);
     if (cur_trans->state >= TRANS_STATE_COMMIT_START) {
         enum btrfs_trans_state want_state = TRANS_STATE_COMPLETED;
 
         add_pending_snapshot(trans);
 
         spin_unlock(&fs_info->trans_lock);
         refcount_inc(&cur_trans->use_count);
 
         if (trans->in_fsync)
             want_state = TRANS_STATE_SUPER_COMMITTED;
         ret = btrfs_end_transaction(trans);
         wait_for_commit(cur_trans, want_state);
 
         if (TRANS_ABORTED(cur_trans))
             ret = cur_trans->aborted;
 
         btrfs_put_transaction(cur_trans);
 
         return ret;
     }
 
     cur_trans->state = TRANS_STATE_COMMIT_START;
     wake_up(&fs_info->transaction_blocked_wait);
 
     if (cur_trans->list.prev != &fs_info->trans_list) {
         enum btrfs_trans_state want_state = TRANS_STATE_COMPLETED;
 
         if (trans->in_fsync)
             want_state = TRANS_STATE_SUPER_COMMITTED;
 
         prev_trans = list_entry(cur_trans->list.prev,
                     struct btrfs_transaction, list);
         if (prev_trans->state < want_state) {
             refcount_inc(&prev_trans->use_count);
             spin_unlock(&fs_info->trans_lock);
 
             wait_for_commit(prev_trans, want_state);
 
             ret = READ_ONCE(prev_trans->aborted);
 
             btrfs_put_transaction(prev_trans);
             if (ret)
                 goto cleanup_transaction;
         } else {
             spin_unlock(&fs_info->trans_lock);
         }
     } else {
         spin_unlock(&fs_info->trans_lock);
         /*
          * The previous transaction was aborted and was already removed
          * from the list of transactions at fs_info->trans_list. So we
          * abort to prevent writing a new superblock that reflects a
          * corrupt state (pointing to trees with unwritten nodes/leafs).
          */
         if (BTRFS_FS_ERROR(fs_info)) {
             ret = -EROFS;
             goto cleanup_transaction;
         }
     }
 
     /*
      * Get the time spent on the work done by the commit thread and not
      * the time spent waiting on a previous commit
      */
     start_time = ktime_get_ns();
 
     extwriter_counter_dec(cur_trans, trans->type);
 
     ret = btrfs_start_delalloc_flush(fs_info);
     if (ret)
         goto cleanup_transaction;
 
     ret = btrfs_run_delayed_items(trans);
     if (ret)
         goto cleanup_transaction;
 
     wait_event(cur_trans->writer_wait,
            extwriter_counter_read(cur_trans) == 0);
 
     /* some pending stuffs might be added after the previous flush. */
     ret = btrfs_run_delayed_items(trans);
     if (ret)
         goto cleanup_transaction;
 
     btrfs_wait_delalloc_flush(fs_info);
 
     /*
      * Wait for all ordered extents started by a fast fsync that joined this
      * transaction. Otherwise if this transaction commits before the ordered
      * extents complete we lose logged data after a power failure.
      */
     wait_event(cur_trans->pending_wait,
            atomic_read(&cur_trans->pending_ordered) == 0);
 
     btrfs_scrub_pause(fs_info);
     /*
      * Ok now we need to make sure to block out any other joins while we
      * commit the transaction.  We could have started a join before setting
      * COMMIT_DOING so make sure to wait for num_writers to == 1 again.
      */
     spin_lock(&fs_info->trans_lock);
     add_pending_snapshot(trans);
     cur_trans->state = TRANS_STATE_COMMIT_DOING;
     spin_unlock(&fs_info->trans_lock);
     wait_event(cur_trans->writer_wait,
            atomic_read(&cur_trans->num_writers) == 1);
 
     /*
      * We've started the commit, clear the flag in case we were triggered to
      * do an async commit but somebody else started before the transaction
      * kthread could do the work.
      */
     clear_bit(BTRFS_FS_COMMIT_TRANS, &fs_info->flags);
 
     if (TRANS_ABORTED(cur_trans)) {
         ret = cur_trans->aborted;
         goto scrub_continue;
     }
     /*
      * the reloc mutex makes sure that we stop
      * the balancing code from coming in and moving
      * extents around in the middle of the commit
      */
     mutex_lock(&fs_info->reloc_mutex);
 
     /*
      * We needn't worry about the delayed items because we will
      * deal with them in create_pending_snapshot(), which is the
      * core function of the snapshot creation.
      */
     ret = create_pending_snapshots(trans);
     if (ret)
         goto unlock_reloc;
 
     /*
      * We insert the dir indexes of the snapshots and update the inode
      * of the snapshots' parents after the snapshot creation, so there
      * are some delayed items which are not dealt with. Now deal with
      * them.
      *
      * We needn't worry that this operation will corrupt the snapshots,
      * because all the tree which are snapshoted will be forced to COW
      * the nodes and leaves.
      */
     ret = btrfs_run_delayed_items(trans);
     if (ret)
         goto unlock_reloc;
 
     ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
     if (ret)
         goto unlock_reloc;
 
     /*
      * make sure none of the code above managed to slip in a
      * delayed item
      */
     btrfs_assert_delayed_root_empty(fs_info);
 
     WARN_ON(cur_trans != trans->transaction);
 
     ret = commit_fs_roots(trans);
     if (ret)
         goto unlock_reloc;
 
     /*
      * Since the transaction is done, we can apply the pending changes
      * before the next transaction.
      */
     btrfs_apply_pending_changes(fs_info);
 
     /* commit_fs_roots gets rid of all the tree log roots, it is now
      * safe to free the root of tree log roots
      */
     btrfs_free_log_root_tree(trans, fs_info);
 
     /*
      * Since fs roots are all committed, we can get a quite accurate
      * new_roots. So let's do quota accounting.
      */
     ret = btrfs_qgroup_account_extents(trans);
     if (ret < 0)
         goto unlock_reloc;
 
     ret = commit_cowonly_roots(trans);
     if (ret)
         goto unlock_reloc;
 
     /*
      * The tasks which save the space cache and inode cache may also
      * update ->aborted, check it.
      */
     if (TRANS_ABORTED(cur_trans)) {
         ret = cur_trans->aborted;
         goto unlock_reloc;
     }
 
     cur_trans = fs_info->running_transaction;
 
     btrfs_set_root_node(&fs_info->tree_root->root_item,
                 fs_info->tree_root->node);
     list_add_tail(&fs_info->tree_root->dirty_list,
               &cur_trans->switch_commits);
 
     btrfs_set_root_node(&fs_info->chunk_root->root_item,
                 fs_info->chunk_root->node);
     list_add_tail(&fs_info->chunk_root->dirty_list,
               &cur_trans->switch_commits);
 
     if (btrfs_fs_incompat(fs_info, EXTENT_TREE_V2)) {
         btrfs_set_root_node(&fs_info->block_group_root->root_item,
                     fs_info->block_group_root->node);
         list_add_tail(&fs_info->block_group_root->dirty_list,
                   &cur_trans->switch_commits);
     }
 
     switch_commit_roots(trans);
 
     ASSERT(list_empty(&cur_trans->dirty_bgs));
     ASSERT(list_empty(&cur_trans->io_bgs));
     update_super_roots(fs_info);
 
     btrfs_set_super_log_root(fs_info->super_copy, 0);
     btrfs_set_super_log_root_level(fs_info->super_copy, 0);
     memcpy(fs_info->super_for_commit, fs_info->super_copy,
            sizeof(*fs_info->super_copy));
 
     btrfs_commit_device_sizes(cur_trans);
 
     clear_bit(BTRFS_FS_LOG1_ERR, &fs_info->flags);
     clear_bit(BTRFS_FS_LOG2_ERR, &fs_info->flags);
 
     btrfs_trans_release_chunk_metadata(trans);
 
     /*
      * Before changing the transaction state to TRANS_STATE_UNBLOCKED and
      * setting fs_info->running_transaction to NULL, lock tree_log_mutex to
      * make sure that before we commit our superblock, no other task can
      * start a new transaction and commit a log tree before we commit our
      * superblock. Anyone trying to commit a log tree locks this mutex before
      * writing its superblock.
      */
     mutex_lock(&fs_info->tree_log_mutex);
 
     spin_lock(&fs_info->trans_lock);
     cur_trans->state = TRANS_STATE_UNBLOCKED;
     fs_info->running_transaction = NULL;
     spin_unlock(&fs_info->trans_lock);
     mutex_unlock(&fs_info->reloc_mutex);
 
     wake_up(&fs_info->transaction_wait);
 
     ret = btrfs_write_and_wait_transaction(trans);
     if (ret) {
         btrfs_handle_fs_error(fs_info, ret,
                       "Error while writing out transaction");
         mutex_unlock(&fs_info->tree_log_mutex);
         goto scrub_continue;
     }
 
     /*
      * At this point, we should have written all the tree blocks allocated
      * in this transaction. So it's now safe to free the redirtyied extent
      * buffers.
      */
     btrfs_free_redirty_list(cur_trans);
 
     ret = write_all_supers(fs_info, 0);
     /*
      * the super is written, we can safely allow the tree-loggers
      * to go about their business
      */
     mutex_unlock(&fs_info->tree_log_mutex);
     if (ret)
         goto scrub_continue;
 
     /*
      * We needn't acquire the lock here because there is no other task
      * which can change it.
      */
     cur_trans->state = TRANS_STATE_SUPER_COMMITTED;
     wake_up(&cur_trans->commit_wait);
 
     btrfs_finish_extent_commit(trans);
 
     if (test_bit(BTRFS_TRANS_HAVE_FREE_BGS, &cur_trans->flags))
         btrfs_clear_space_info_full(fs_info);
 
     fs_info->last_trans_committed = cur_trans->transid;
     /*
      * We needn't acquire the lock here because there is no other task
      * which can change it.
      */
     cur_trans->state = TRANS_STATE_COMPLETED;
     wake_up(&cur_trans->commit_wait);
 
     spin_lock(&fs_info->trans_lock);
     list_del_init(&cur_trans->list);
     spin_unlock(&fs_info->trans_lock);
 
     btrfs_put_transaction(cur_trans);
     btrfs_put_transaction(cur_trans);
 
     if (trans->type & __TRANS_FREEZABLE)
         sb_end_intwrite(fs_info->sb);
 
     trace_btrfs_transaction_commit(fs_info);
 
     interval = ktime_get_ns() - start_time;
 
     btrfs_scrub_continue(fs_info);
 
     if (current->journal_info == trans)
         current->journal_info = NULL;
 
     kmem_cache_free(btrfs_trans_handle_cachep, trans);
 
     update_commit_stats(fs_info, interval);
 
     return ret;
 
 unlock_reloc:
     mutex_unlock(&fs_info->reloc_mutex);
 scrub_continue:
     btrfs_scrub_continue(fs_info);
 cleanup_transaction:
     btrfs_trans_release_metadata(trans);
     btrfs_cleanup_pending_block_groups(trans);
     btrfs_trans_release_chunk_metadata(trans);
     trans->block_rsv = NULL;
     btrfs_warn(fs_info, "Skipping commit of aborted transaction.");
     if (current->journal_info == trans)
         current->journal_info = NULL;
     cleanup_transaction(trans, ret);
 
     return ret;
 }
 
 /*
  * return < 0 if error
  * 0 if there are no more dead_roots at the time of call
  * 1 there are more to be processed, call me again
  *
  * The return value indicates there are certainly more snapshots to delete, but
  * if there comes a new one during processing, it may return 0. We don't mind,
  * because btrfs_commit_super will poke cleaner thread and it will process it a
  * few seconds later.
  */
 int btrfs_clean_one_deleted_snapshot(struct btrfs_fs_info *fs_info)
 {
     struct btrfs_root *root;
     int ret;
 
     spin_lock(&fs_info->trans_lock);
     if (list_empty(&fs_info->dead_roots)) {
         spin_unlock(&fs_info->trans_lock);
         return 0;
     }
     root = list_first_entry(&fs_info->dead_roots,
             struct btrfs_root, root_list);
     list_del_init(&root->root_list);
     spin_unlock(&fs_info->trans_lock);
 
     btrfs_debug(fs_info, "cleaner removing %llu", root->root_key.objectid);
 
     btrfs_kill_all_delayed_nodes(root);
 
     if (btrfs_header_backref_rev(root->node) <
             BTRFS_MIXED_BACKREF_REV)
         ret = btrfs_drop_snapshot(root, 0, 0);
     else
         ret = btrfs_drop_snapshot(root, 1, 0);
 
     btrfs_put_root(root);
     return (ret < 0) ? 0 : 1;
 }
 
 void btrfs_apply_pending_changes(struct btrfs_fs_info *fs_info)
 {
     unsigned long prev;
     unsigned long bit;
 
     prev = xchg(&fs_info->pending_changes, 0);
     if (!prev)
         return;
 
     bit = 1 << BTRFS_PENDING_COMMIT;
     if (prev & bit)
         btrfs_debug(fs_info, "pending commit done");
     prev &= ~bit;
 
     if (prev)
         btrfs_warn(fs_info,
             "unknown pending changes left 0x%lx, ignoring", prev);
 }

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