text: // 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 "ctree.h"
  #include "disk-io.h"
  #include "transaction.h"
  #include "locking.h"
  #include "tree-log.h"
  #include "inode-map.h"
  #include "volumes.h"
  #include "dev-replace.h"
  #include "qgroup.h"
  
  #define BTRFS_ROOT_TRANS_TAG 0
  
  static const unsigned int btrfs_blocked_trans_types[TRANS_STATE_MAX] = {
  	[TRANS_STATE_RUNNING]		= 0U,
  	[TRANS_STATE_BLOCKED]		=  __TRANS_START,
  	[TRANS_STATE_COMMIT_START]	= (__TRANS_START | __TRANS_ATTACH),
  	[TRANS_STATE_COMMIT_DOING]	= (__TRANS_START |
  					   __TRANS_ATTACH |
  					   __TRANS_JOIN),
  	[TRANS_STATE_UNBLOCKED]		= (__TRANS_START |
  					   __TRANS_ATTACH |
  					   __TRANS_JOIN |
  					   __TRANS_JOIN_NOLOCK),
  	[TRANS_STATE_COMPLETED]		= (__TRANS_START |
  					   __TRANS_ATTACH |
  					   __TRANS_JOIN |
  					   __TRANS_JOIN_NOLOCK),
  };
  
  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));
  		if (transaction->delayed_refs.pending_csums)
  			btrfs_err(transaction->fs_info,
  				  "pending csums is %llu",
  				  transaction->delayed_refs.pending_csums);
  		while (!list_empty(&transaction->pending_chunks)) {
  			struct extent_map *em;
  
  			em = list_first_entry(&transaction->pending_chunks,
  					      struct extent_map, list);
  			list_del_init(&em->list);
  			free_extent_map(em);
  		}
  		/*
  		 * 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;
  
  			cache = list_first_entry(&transaction->deleted_bgs,
  						 struct btrfs_block_group_cache,
  						 bg_list);
  			list_del_init(&cache->bg_list);
  			btrfs_put_block_group_trimming(cache);
  			btrfs_put_block_group(cache);
  		}
  		kfree(transaction);
  	}
  }
  
  static void clear_btree_io_tree(struct extent_io_tree *tree)
  {
  	spin_lock(&tree->lock);
  	/*
  	 * Do a single barrier for the waitqueue_active check here, the state
  	 * of the waitqueue should not change once clear_btree_io_tree is
  	 * called.
  	 */
  	smp_mb();
  	while (!RB_EMPTY_ROOT(&tree->state)) {
  		struct rb_node *node;
  		struct extent_state *state;
  
  		node = rb_first(&tree->state);
  		state = rb_entry(node, struct extent_state, rb_node);
  		rb_erase(&state->rb_node, &tree->state);
  		RB_CLEAR_NODE(&state->rb_node);
  		/*
  		 * btree io trees aren't supposed to have tasks waiting for
  		 * changes in the flags of extent states ever.
  		 */
  		ASSERT(!waitqueue_active(&state->wq));
  		free_extent_state(state);
  
  		cond_resched_lock(&tree->lock);
  	}
  	spin_unlock(&tree->lock);
  }
  
  static noinline void switch_commit_roots(struct btrfs_transaction *trans)
  {
  	struct btrfs_fs_info *fs_info = trans->fs_info;
  	struct btrfs_root *root, *tmp;
  
  	down_write(&fs_info->commit_root_sem);
  	list_for_each_entry_safe(root, tmp, &trans->switch_commits,
  				 dirty_list) {
  		list_del_init(&root->dirty_list);
  		free_extent_buffer(root->commit_root);
  		root->commit_root = btrfs_root_node(root);
  		if (is_fstree(root->root_key.objectid))
  			btrfs_unpin_free_ino(root);
  		clear_btree_io_tree(&root->dirty_log_pages);
  	}
  
  	/* We can free old roots now. */
  	spin_lock(&trans->dropped_roots_lock);
  	while (!list_empty(&trans->dropped_roots)) {
  		root = list_first_entry(&trans->dropped_roots,
  					struct btrfs_root, root_list);
  		list_del_init(&root->root_list);
  		spin_unlock(&trans->dropped_roots_lock);
  		btrfs_drop_and_free_fs_root(fs_info, root);
  		spin_lock(&trans->dropped_roots_lock);
  	}
  	spin_unlock(&trans->dropped_roots_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);
  }
  
  /*
   * 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 (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {
  		spin_unlock(&fs_info->trans_lock);
  		return -EROFS;
  	}
  
  	cur_trans = fs_info->running_transaction;
  	if (cur_trans) {
  		if (cur_trans->aborted) {
  			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 (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {
  		spin_unlock(&fs_info->trans_lock);
  		kfree(cur_trans);
  		return -EROFS;
  	}
  
  	cur_trans->fs_info = fs_info;
  	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);
  	init_waitqueue_head(&cur_trans->pending_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);
  	atomic_set(&cur_trans->pending_ordered, 0);
  	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->pending_chunks);
  	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);
  	cur_trans->num_dirty_bgs = 0;
  	spin_lock_init(&cur_trans->dirty_bgs_lock);
  	INIT_LIST_HEAD(&cur_trans->deleted_bgs);
  	spin_lock_init(&cur_trans->dropped_roots_lock);
  	list_add_tail(&cur_trans->list, &fs_info->trans_list);
  	extent_io_tree_init(&cur_trans->dirty_pages,
  			     fs_info->btree_inode);
  	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 reference
   * counted 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;
  
  	if ((test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
  	    root->last_trans < trans->transid) || force) {
  		WARN_ON(root == fs_info->extent_root);
  		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
  		 */
  		btrfs_init_reloc_root(trans, root);
  		smp_mb__before_atomic();
  		clear_bit(BTRFS_ROOT_IN_TRANS_SETUP, &root->state);
  	}
  	return 0;
  }
  
  
  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;
  
  	if (!test_bit(BTRFS_ROOT_REF_COWS, &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);
  	record_root_in_trans(trans, root, 0);
  	mutex_unlock(&fs_info->reloc_mutex);
  
  	return 0;
  }
  
  static inline int is_transaction_blocked(struct btrfs_transaction *trans)
  {
  	return (trans->state >= TRANS_STATE_BLOCKED &&
  		trans->state < TRANS_STATE_UNBLOCKED &&
  		!trans->aborted);
  }
  
  /* 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 ||
  			   cur_trans->aborted);
  		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_REF_COWS, &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_trans_handle *h;
  	struct btrfs_transaction *cur_trans;
  	u64 num_bytes = 0;
  	u64 qgroup_reserved = 0;
  	bool reloc_reserved = false;
  	int ret;
  
  	/* Send isn't supposed to start transactions. */
  	ASSERT(current->journal_info != BTRFS_SEND_TRANS_STUB);
  
  	if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state))
  		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) {
  		qgroup_reserved = num_items * fs_info->nodesize;
  		ret = btrfs_qgroup_reserve_meta_pertrans(root, qgroup_reserved,
  				enforce_qgroups);
  		if (ret)
  			return ERR_PTR(ret);
  
  		num_bytes = btrfs_calc_trans_metadata_size(fs_info, num_items);
  		/*
  		 * 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(root, &fs_info->trans_block_rsv,
  					  num_bytes, 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))
  				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;
  	h->root = root;
  	refcount_set(&h->use_count, 1);
  	h->fs_info = root->fs_info;
  
  	h->type = type;
  	h->can_flush_pending_bgs = true;
  	INIT_LIST_HEAD(&h->new_bgs);
  
  	smp_mb();
  	if (cur_trans->state >= TRANS_STATE_BLOCKED &&
  	    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:
  	btrfs_record_root_in_trans(h, root);
  
  	if (!current->journal_info)
  		current->journal_info = h;
  	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);
  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,
  					int min_factor)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	struct btrfs_trans_handle *trans;
  	u64 num_bytes;
  	int ret;
  
  	/*
  	 * We have two callers: unlink and block group removal.  The
  	 * former should succeed even if we will temporarily exceed
  	 * quota and the latter operates on the extent root so
  	 * qgroup enforcement is ignored anyway.
  	 */
  	trans = start_transaction(root, num_items, TRANS_START,
  				  BTRFS_RESERVE_FLUSH_ALL, false);
  	if (!IS_ERR(trans) || PTR_ERR(trans) != -ENOSPC)
  		return trans;
  
  	trans = btrfs_start_transaction(root, 0);
  	if (IS_ERR(trans))
  		return trans;
  
  	num_bytes = btrfs_calc_trans_metadata_size(fs_info, num_items);
  	ret = btrfs_cond_migrate_bytes(fs_info, &fs_info->trans_block_rsv,
  				       num_bytes, min_factor);
  	if (ret) {
  		btrfs_end_transaction(trans);
  		return ERR_PTR(ret);
  	}
  
  	trans->block_rsv = &fs_info->trans_block_rsv;
  	trans->bytes_reserved = num_bytes;
  	trace_btrfs_space_reservation(fs_info, "transaction",
  				      trans->transid, num_bytes, 1);
  
  	return trans;
  }
  
  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_nolock(struct btrfs_root *root)
  {
  	return start_transaction(root, 0, TRANS_JOIN_NOLOCK,
  				 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 differentia 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 be fully complete */
  static noinline void wait_for_commit(struct btrfs_transaction *commit)
  {
  	wait_event(commit->commit_wait, commit->state == TRANS_STATE_COMPLETED);
  }
  
  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);
  	btrfs_put_transaction(cur_trans);
  out:
  	return ret;
  }
  
  void btrfs_throttle(struct btrfs_fs_info *fs_info)
  {
  	wait_current_trans(fs_info);
  }
  
  static int should_end_transaction(struct btrfs_trans_handle *trans)
  {
  	struct btrfs_fs_info *fs_info = trans->fs_info;
  
  	if (btrfs_check_space_for_delayed_refs(trans))
  		return 1;
  
  	return !!btrfs_block_rsv_check(&fs_info->global_block_rsv, 5);
  }
  
  int btrfs_should_end_transaction(struct btrfs_trans_handle *trans)
  {
  	struct btrfs_transaction *cur_trans = trans->transaction;
  	int updates;
  	int err;
  
  	smp_mb();
  	if (cur_trans->state >= TRANS_STATE_BLOCKED ||
  	    cur_trans->delayed_refs.flushing)
  		return 1;
  
  	updates = trans->delayed_ref_updates;
  	trans->delayed_ref_updates = 0;
  	if (updates) {
  		err = btrfs_run_delayed_refs(trans, updates * 2);
  		if (err) /* Error code will also eval true */
  			return err;
  	}
  
  	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);
  	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;
  	u64 transid = trans->transid;
  	unsigned long cur = trans->delayed_ref_updates;
  	int lock = (trans->type != TRANS_JOIN_NOLOCK);
  	int err = 0;
  	int must_run_delayed_refs = 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;
  
  	if (!list_empty(&trans->new_bgs))
  		btrfs_create_pending_block_groups(trans);
  
  	trans->delayed_ref_updates = 0;
  	if (!trans->sync) {
  		must_run_delayed_refs =
  			btrfs_should_throttle_delayed_refs(trans);
  		cur = max_t(unsigned long, cur, 32);
  
  		/*
  		 * don't make the caller wait if they are from a NOLOCK
  		 * or ATTACH transaction, it will deadlock with commit
  		 */
  		if (must_run_delayed_refs == 1 &&
  		    (trans->type & (__TRANS_JOIN_NOLOCK | __TRANS_ATTACH)))
  			must_run_delayed_refs = 2;
  	}
  
  	btrfs_trans_release_metadata(trans);
  	trans->block_rsv = NULL;
  
  	if (!list_empty(&trans->new_bgs))
  		btrfs_create_pending_block_groups(trans);
  
  	btrfs_trans_release_chunk_metadata(trans);
  
  	if (lock && should_end_transaction(trans) &&
  	    READ_ONCE(cur_trans->state) == TRANS_STATE_RUNNING) {
  		spin_lock(&info->trans_lock);
  		if (cur_trans->state == TRANS_STATE_RUNNING)
  			cur_trans->state = TRANS_STATE_BLOCKED;
  		spin_unlock(&info->trans_lock);
  	}
  
  	if (lock && READ_ONCE(cur_trans->state) == TRANS_STATE_BLOCKED) {
  		if (throttle)
  			return btrfs_commit_transaction(trans);
  		else
  			wake_up_process(info->transaction_kthread);
  	}
  
  	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 ||
  	    test_bit(BTRFS_FS_STATE_ERROR, &info->fs_state)) {
  		wake_up_process(info->transaction_kthread);
  		err = -EIO;
  	}
  
  	kmem_cache_free(btrfs_trans_handle_cachep, trans);
  	if (must_run_delayed_refs) {
  		btrfs_async_run_delayed_refs(info, cur, transid,
  					     must_run_delayed_refs == 1);
  	}
  	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 clear_btree_io_tree()).
  		 */
  		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 clear_btree_io_tree()).
  		 */
  		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;
  }
  
  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);
  
  	clear_btree_io_tree(&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;
  
  	eb = btrfs_lock_root_node(fs_info->tree_root);
  	ret = btrfs_cow_block(trans, fs_info->tree_root, eb, NULL,
  			      0, &eb);
  	btrfs_tree_unlock(eb);
  	free_extent_buffer(eb);
  
  	if (ret)
  		return ret;
  
  	ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
  	if (ret)
  		return ret;
  
  	ret = btrfs_run_dev_stats(trans, fs_info);
  	if (ret)
  		return ret;
  	ret = btrfs_run_dev_replace(trans, fs_info);
  	if (ret)
  		return ret;
  	ret = btrfs_run_qgroups(trans);
  	if (ret)
  		return ret;
  
  	ret = btrfs_setup_space_cache(trans, fs_info);
  	if (ret)
  		return ret;
  
  	/* run_qgroups might have added some more refs */
  	ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
  	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);
  
  		if (root != fs_info->extent_root)
  			list_add_tail(&root->dirty_list,
  				      &trans->transaction->switch_commits);
  		ret = update_cowonly_root(trans, root);
  		if (ret)
  			return ret;
  		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, fs_info);
  		if (ret)
  			return ret;
  		ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
  		if (ret)
  			return ret;
  	}
  
  	if (!list_empty(&fs_info->dirty_cowonly_roots))
  		goto again;
  
  	list_add_tail(&fs_info->extent_root->dirty_list,
  		      &trans->transaction->switch_commits);
  
  	/* 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;
  }
  
  /*
   * 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))
  		list_add_tail(&root->root_list, &fs_info->dead_roots);
  	spin_unlock(&fs_info->trans_lock);
  }
  
  /*
   * update all the cowonly tree roots on disk
   */
  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;
  	int err = 0;
  
  	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];
  			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);
  			btrfs_update_reloc_root(trans, root);
  
  			btrfs_save_ino_cache(root, trans);
  
  			/* 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);
  			}
  
  			err = btrfs_update_root(trans, fs_info->tree_root,
  						&root->root_key,
  						&root->root_item);
  			spin_lock(&fs_info->fs_roots_radix_lock);
  			if (err)
  				break;
  			btrfs_qgroup_free_meta_all_pertrans(root);
  		}
  	}
  	spin_unlock(&fs_info->fs_roots_radix_lock);
  	return err;
  }
  
  /*
   * 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))
  			return PTR_ERR(trans);
  
  		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 commited.  Or, after comming
  	 * commit_fs_roots() and switch_commit_roots(), any dirty but not
  	 * recorded root will never be updated again, causing an outdated root
  	 * item.
  	 */
  	record_root_in_trans(trans, src, 1);
  
  	/*
  	 * We are going to commit transaction, see btrfs_commit_transaction()
  	 * comment for reason locking tree_log_mutex
  	 */
  	mutex_lock(&fs_info->tree_log_mutex);
  
  	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->transaction);
  	ret = btrfs_write_and_wait_transaction(trans);
  	if (ret)
  		btrfs_handle_fs_error(fs_info, ret,
  			"Error while writing out transaction for qgroup");
  
  out:
  	mutex_unlock(&fs_info->tree_log_mutex);
  
  	/*
  	 * 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)
  		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;
  	uuid_le new_uuid;
  
  	ASSERT(pending->path);
  	path = pending->path;
  
  	ASSERT(pending->root_item);
  	new_root_item = pending->root_item;
  
  	pending->error = btrfs_find_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(root,
  						     &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;
  	record_root_in_trans(trans, parent_root, 0);
  
  	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;
  	}
  
  	record_root_in_trans(trans, root, 0);
  	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);
  	uuid_le_gen(&new_uuid);
  	memcpy(new_root_item->uuid, new_uuid.b, BTRFS_UUID_SIZE);
  	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);
  	if (ret) {
  		btrfs_tree_unlock(old);
  		free_extent_buffer(old);
  		btrfs_abort_transaction(trans, ret);
  		goto fail;
  	}
  
  	btrfs_set_lock_blocking(old);
  
  	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_read_fs_root_no_name(fs_info, &key);
  	if (IS_ERR(pending->snap)) {
  		ret = PTR_ERR(pending->snap);
  		btrfs_abort_transaction(trans, ret);
  		goto fail;
  	}
  
  	ret = btrfs_reloc_post_snapshot(trans, pending);
  	if (ret) {
  		btrfs_abort_transaction(trans, ret);
  		goto fail;
  	}
  
  	ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
  	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 = parent_inode->i_ctime =
  		current_time(parent_inode);
  	ret = btrfs_update_inode_fallback(trans, parent_root, parent_inode);
  	if (ret) {
  		btrfs_abort_transaction(trans, ret);
  		goto fail;
  	}
  	ret = btrfs_uuid_tree_add(trans, new_uuid.b, 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;
  		}
  	}
  
  	ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
  	if (ret) {
  		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;
  	if (test_bit(BTRFS_FS_UPDATE_UUID_TREE_GEN, &fs_info->flags))
  		super->uuid_tree_generation = root_item->generation;
  }
  
  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;
  }
  
  /*
   * wait for the current transaction commit to start and block subsequent
   * transaction joins
   */
  static void wait_current_trans_commit_start(struct btrfs_fs_info *fs_info,
  					    struct btrfs_transaction *trans)
  {
  	wait_event(fs_info->transaction_blocked_wait,
  		   trans->state >= TRANS_STATE_COMMIT_START || trans->aborted);
  }
  
  /*
   * wait for the current transaction to start and then become unblocked.
   * caller holds ref.
   */
  static void wait_current_trans_commit_start_and_unblock(
  					struct btrfs_fs_info *fs_info,
  					struct btrfs_transaction *trans)
  {
  	wait_event(fs_info->transaction_wait,
  		   trans->state >= TRANS_STATE_UNBLOCKED || trans->aborted);
  }
  
  /*
   * commit transactions asynchronously. once btrfs_commit_transaction_async
   * returns, any subsequent transaction will not be allowed to join.
   */
  struct btrfs_async_commit {
  	struct btrfs_trans_handle *newtrans;
  	struct work_struct work;
  };
  
  static void do_async_commit(struct work_struct *work)
  {
  	struct btrfs_async_commit *ac =
  		container_of(work, struct btrfs_async_commit, work);
  
  	/*
  	 * We've got freeze protection passed with the transaction.
  	 * Tell lockdep about it.
  	 */
  	if (ac->newtrans->type & __TRANS_FREEZABLE)
  		__sb_writers_acquired(ac->newtrans->fs_info->sb, SB_FREEZE_FS);
  
  	current->journal_info = ac->newtrans;
  
  	btrfs_commit_transaction(ac->newtrans);
  	kfree(ac);
  }
  
  int btrfs_commit_transaction_async(struct btrfs_trans_handle *trans,
  				   int wait_for_unblock)
  {
  	struct btrfs_fs_info *fs_info = trans->fs_info;
  	struct btrfs_async_commit *ac;
  	struct btrfs_transaction *cur_trans;
  
  	ac = kmalloc(sizeof(*ac), GFP_NOFS);
  	if (!ac)
  		return -ENOMEM;
  
  	INIT_WORK(&ac->work, do_async_commit);
  	ac->newtrans = btrfs_join_transaction(trans->root);
  	if (IS_ERR(ac->newtrans)) {
  		int err = PTR_ERR(ac->newtrans);
  		kfree(ac);
  		return err;
  	}
  
  	/* take transaction reference */
  	cur_trans = trans->transaction;
  	refcount_inc(&cur_trans->use_count);
  
  	btrfs_end_transaction(trans);
  
  	/*
  	 * Tell lockdep we've released the freeze rwsem, since the
  	 * async commit thread will be the one to unlock it.
  	 */
  	if (ac->newtrans->type & __TRANS_FREEZABLE)
  		__sb_writers_release(fs_info->sb, SB_FREEZE_FS);
  
  	schedule_work(&ac->work);
  
  	/* wait for transaction to start and unblock */
  	if (wait_for_unblock)
  		wait_current_trans_commit_start_and_unblock(fs_info, cur_trans);
  	else
  		wait_current_trans_commit_start(fs_info, cur_trans);
  
  	if (current->journal_info == trans)
  		current->journal_info = NULL;
  
  	btrfs_put_transaction(cur_trans);
  	return 0;
  }
  
  
  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;
  	DEFINE_WAIT(wait);
  
  	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));
  
  	list_del_init(&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);
  	}
  	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(trans->root);
  
  	if (current->journal_info == trans)
  		current->journal_info = NULL;
  	btrfs_scrub_cancel(fs_info);
  
  	kmem_cache_free(btrfs_trans_handle_cachep, trans);
  }
  
  static inline int btrfs_start_delalloc_flush(struct btrfs_fs_info *fs_info)
  {
  	/*
  	 * We use 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.
  	 */
  	if (btrfs_test_opt(fs_info, FLUSHONCOMMIT))
  		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);
  }
  
  static inline void
  btrfs_wait_pending_ordered(struct btrfs_transaction *cur_trans)
  {
  	wait_event(cur_trans->pending_wait,
  		   atomic_read(&cur_trans->pending_ordered) == 0);
  }
  
  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;
  
  	/* Stop the commit early if ->aborted is set */
  	if (unlikely(READ_ONCE(cur_trans->aborted))) {
  		ret = cur_trans->aborted;
  		btrfs_end_transaction(trans);
  		return ret;
  	}
  
  	btrfs_trans_release_metadata(trans);
  	trans->block_rsv = NULL;
  
  	/* make a pass through all the delayed refs we have so far
  	 * any runnings procs may add more while we are here
  	 */
  	ret = btrfs_run_delayed_refs(trans, 0);
  	if (ret) {
  		btrfs_end_transaction(trans);
  		return ret;
  	}
  
  	cur_trans = trans->transaction;
  
  	/*
  	 * set the flushing flag so procs in this transaction have to
  	 * start sending their work down.
  	 */
  	cur_trans->delayed_refs.flushing = 1;
  	smp_wmb();
  
  	if (!list_empty(&trans->new_bgs))
  		btrfs_create_pending_block_groups(trans);
  
  	ret = btrfs_run_delayed_refs(trans, 0);
  	if (ret) {
  		btrfs_end_transaction(trans);
  		return ret;
  	}
  
  	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) {
  		spin_unlock(&fs_info->trans_lock);
  		refcount_inc(&cur_trans->use_count);
  		ret = btrfs_end_transaction(trans);
  
  		wait_for_commit(cur_trans);
  
  		if (unlikely(cur_trans->aborted))
  			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) {
  		prev_trans = list_entry(cur_trans->list.prev,
  					struct btrfs_transaction, list);
  		if (prev_trans->state != TRANS_STATE_COMPLETED) {
  			refcount_inc(&prev_trans->use_count);
  			spin_unlock(&fs_info->trans_lock);
  
  			wait_for_commit(prev_trans);
  			ret = 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);
  	}
  
  	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);
  
  	btrfs_wait_pending_ordered(cur_trans);
  
  	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);
  	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);
  
  	/* ->aborted might be set after the previous check, so check it */
  	if (unlikely(READ_ONCE(cur_trans->aborted))) {
  		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) {
  		mutex_unlock(&fs_info->reloc_mutex);
  		goto scrub_continue;
  	}
  
  	/*
  	 * 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) {
  		mutex_unlock(&fs_info->reloc_mutex);
  		goto scrub_continue;
  	}
  
  	ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
  	if (ret) {
  		mutex_unlock(&fs_info->reloc_mutex);
  		goto scrub_continue;
  	}
  
  	/*
  	 * 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);
  
  	/* btrfs_commit_tree_roots is responsible for getting the
  	 * various roots consistent with each other.  Every pointer
  	 * in the tree of tree roots has to point to the most up to date
  	 * root for every subvolume and other tree.  So, we have to keep
  	 * the tree logging code from jumping in and changing any
  	 * of the trees.
  	 *
  	 * At this point in the commit, there can't be any tree-log
  	 * writers, but a little lower down we drop the trans mutex
  	 * and let new people in.  By holding the tree_log_mutex
  	 * from now until after the super is written, we avoid races
  	 * with the tree-log code.
  	 */
  	mutex_lock(&fs_info->tree_log_mutex);
  
  	ret = commit_fs_roots(trans);
  	if (ret) {
  		mutex_unlock(&fs_info->tree_log_mutex);
  		mutex_unlock(&fs_info->reloc_mutex);
  		goto scrub_continue;
  	}
  
  	/*
  	 * 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);
  
  	/*
  	 * commit_fs_roots() can call btrfs_save_ino_cache(), which generates
  	 * new delayed refs. Must handle them or qgroup can be wrong.
  	 */
  	ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
  	if (ret) {
  		mutex_unlock(&fs_info->tree_log_mutex);
  		mutex_unlock(&fs_info->reloc_mutex);
  		goto scrub_continue;
  	}
  
  	/*
  	 * 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) {
  		mutex_unlock(&fs_info->tree_log_mutex);
  		mutex_unlock(&fs_info->reloc_mutex);
  		goto scrub_continue;
  	}
  
  	ret = commit_cowonly_roots(trans);
  	if (ret) {
  		mutex_unlock(&fs_info->tree_log_mutex);
  		mutex_unlock(&fs_info->reloc_mutex);
  		goto scrub_continue;
  	}
  
  	/*
  	 * The tasks which save the space cache and inode cache may also
  	 * update ->aborted, check it.
  	 */
  	if (unlikely(READ_ONCE(cur_trans->aborted))) {
  		ret = cur_trans->aborted;
  		mutex_unlock(&fs_info->tree_log_mutex);
  		mutex_unlock(&fs_info->reloc_mutex);
  		goto scrub_continue;
  	}
  
  	btrfs_prepare_extent_commit(fs_info);
  
  	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);
  
  	switch_commit_roots(cur_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_update_commit_device_size(fs_info);
  	btrfs_update_commit_device_bytes_used(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);
  
  	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;
  	}
  
  	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;
  
  	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);
  	clear_bit(BTRFS_FS_NEED_ASYNC_COMMIT, &fs_info->flags);
  
  	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(trans->root);
  
  	btrfs_scrub_continue(fs_info);
  
  	if (current->journal_info == trans)
  		current->journal_info = NULL;
  
  	kmem_cache_free(btrfs_trans_handle_cachep, trans);
  
  	return ret;
  
  scrub_continue:
  	btrfs_scrub_continue(fs_info);
  cleanup_transaction:
  	btrfs_trans_release_metadata(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_root *root)
  {
  	int ret;
  	struct btrfs_fs_info *fs_info = root->fs_info;
  
  	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, NULL, 0, 0);
  	else
  		ret = btrfs_drop_snapshot(root, NULL, 1, 0);
  
  	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_SET_INODE_MAP_CACHE;
  	if (prev & bit)
  		btrfs_set_opt(fs_info->mount_opt, INODE_MAP_CACHE);
  	prev &= ~bit;
  
  	bit = 1 << BTRFS_PENDING_CLEAR_INODE_MAP_CACHE;
  	if (prev & bit)
  		btrfs_clear_opt(fs_info->mount_opt, INODE_MAP_CACHE);
  	prev &= ~bit;
  
  	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);
  }
  