1 files changed, 1449 insertions, 584 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index b2acc79f1b3..5f379affdf2 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -17,79 +17,219 @@
  */
 
 #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 noinline void put_transaction(struct btrfs_transaction *transaction)
+static unsigned int btrfs_blocked_trans_types[TRANS_STATE_MAX] = {
+	[TRANS_STATE_RUNNING]		= 0U,
+	[TRANS_STATE_BLOCKED]		= (__TRANS_USERSPACE |
+					   __TRANS_START),
+	[TRANS_STATE_COMMIT_START]	= (__TRANS_USERSPACE |
+					   __TRANS_START |
+					   __TRANS_ATTACH),
+	[TRANS_STATE_COMMIT_DOING]	= (__TRANS_USERSPACE |
+					   __TRANS_START |
+					   __TRANS_ATTACH |
+					   __TRANS_JOIN),
+	[TRANS_STATE_UNBLOCKED]		= (__TRANS_USERSPACE |
+					   __TRANS_START |
+					   __TRANS_ATTACH |
+					   __TRANS_JOIN |
+					   __TRANS_JOIN_NOLOCK),
+	[TRANS_STATE_COMPLETED]		= (__TRANS_USERSPACE |
+					   __TRANS_START |
+					   __TRANS_ATTACH |
+					   __TRANS_JOIN |
+					   __TRANS_JOIN_NOLOCK),
+};
+
+void btrfs_put_transaction(struct btrfs_transaction *transaction)
 {
-	WARN_ON(transaction->use_count == 0);
-	transaction->use_count--;
-	if (transaction->use_count == 0) {
-		list_del_init(&transaction->list);
-		memset(transaction, 0, sizeof(*transaction));
+	WARN_ON(atomic_read(&transaction->use_count) == 0);
+	if (atomic_dec_and_test(&transaction->use_count)) {
+		BUG_ON(!list_empty(&transaction->list));
+		WARN_ON(!RB_EMPTY_ROOT(&transaction->delayed_refs.href_root));
+		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);
+		}
 		kmem_cache_free(btrfs_transaction_cachep, transaction);
 	}
 }
 
-static noinline void switch_commit_root(struct btrfs_root *root)
+static noinline void switch_commit_roots(struct btrfs_transaction *trans,
+					 struct btrfs_fs_info *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->objectid))
+			btrfs_unpin_free_ino(root);
+	}
+	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)
 {
-	free_extent_buffer(root->commit_root);
-	root->commit_root = btrfs_root_node(root);
+	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_root *root)
+static noinline int join_transaction(struct btrfs_root *root, unsigned int type)
 {
 	struct btrfs_transaction *cur_trans;
-	cur_trans = root->fs_info->running_transaction;
-	if (!cur_trans) {
-		cur_trans = kmem_cache_alloc(btrfs_transaction_cachep,
-					     GFP_NOFS);
-		BUG_ON(!cur_trans);
-		root->fs_info->generation++;
-		cur_trans->num_writers = 1;
-		cur_trans->num_joined = 0;
-		cur_trans->transid = root->fs_info->generation;
-		init_waitqueue_head(&cur_trans->writer_wait);
-		init_waitqueue_head(&cur_trans->commit_wait);
-		cur_trans->in_commit = 0;
-		cur_trans->blocked = 0;
-		cur_trans->use_count = 1;
-		cur_trans->commit_done = 0;
-		cur_trans->start_time = get_seconds();
-
-		cur_trans->delayed_refs.root.rb_node = NULL;
-		cur_trans->delayed_refs.num_entries = 0;
-		cur_trans->delayed_refs.num_heads_ready = 0;
-		cur_trans->delayed_refs.num_heads = 0;
-		cur_trans->delayed_refs.flushing = 0;
-		cur_trans->delayed_refs.run_delayed_start = 0;
-		spin_lock_init(&cur_trans->delayed_refs.lock);
-
-		INIT_LIST_HEAD(&cur_trans->pending_snapshots);
-		list_add_tail(&cur_trans->list, &root->fs_info->trans_list);
-		extent_io_tree_init(&cur_trans->dirty_pages,
-				     root->fs_info->btree_inode->i_mapping,
-				     GFP_NOFS);
-		spin_lock(&root->fs_info->new_trans_lock);
-		root->fs_info->running_transaction = cur_trans;
-		spin_unlock(&root->fs_info->new_trans_lock);
-	} else {
-		cur_trans->num_writers++;
-		cur_trans->num_joined++;
+	struct btrfs_fs_info *fs_info = root->fs_info;
+
+	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;
+		}
+		atomic_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 = kmem_cache_alloc(btrfs_transaction_cachep, 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
+		 */
+		kmem_cache_free(btrfs_transaction_cachep, cur_trans);
+		goto loop;
+	} else if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {
+		spin_unlock(&fs_info->trans_lock);
+		kmem_cache_free(btrfs_transaction_cachep, cur_trans);
+		return -EROFS;
 	}
 
+	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.
+	 */
+	atomic_set(&cur_trans->use_count, 2);
+	cur_trans->start_time = get_seconds();
+
+	cur_trans->delayed_refs.href_root = RB_ROOT;
+	atomic_set(&cur_trans->delayed_refs.num_entries, 0);
+	cur_trans->delayed_refs.num_heads_ready = 0;
+	cur_trans->delayed_refs.num_heads = 0;
+	cur_trans->delayed_refs.flushing = 0;
+	cur_trans->delayed_refs.run_delayed_start = 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->ordered_operations);
+	INIT_LIST_HEAD(&cur_trans->pending_chunks);
+	INIT_LIST_HEAD(&cur_trans->switch_commits);
+	list_add_tail(&cur_trans->list, &fs_info->trans_list);
+	extent_io_tree_init(&cur_trans->dirty_pages,
+			     fs_info->btree_inode->i_mapping);
+	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;
 }
 
@@ -99,39 +239,93 @@ static noinline int join_transaction(struct btrfs_root *root)
  * to make sure the old root from before we joined the transaction is deleted
  * when the transaction commits
  */
-static noinline int record_root_in_trans(struct btrfs_trans_handle *trans,
-					 struct btrfs_root *root)
+static int record_root_in_trans(struct btrfs_trans_handle *trans,
+			       struct btrfs_root *root)
 {
-	if (root->ref_cows && root->last_trans < trans->transid) {
+	if (test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
+	    root->last_trans < trans->transid) {
 		WARN_ON(root == root->fs_info->extent_root);
 		WARN_ON(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(&root->fs_info->fs_roots_radix_lock);
+		if (root->last_trans == trans->transid) {
+			spin_unlock(&root->fs_info->fs_roots_radix_lock);
+			return 0;
+		}
 		radix_tree_tag_set(&root->fs_info->fs_roots_radix,
 			   (unsigned long)root->root_key.objectid,
 			   BTRFS_ROOT_TRANS_TAG);
+		spin_unlock(&root->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;
 }
 
+
 int btrfs_record_root_in_trans(struct btrfs_trans_handle *trans,
 			       struct btrfs_root *root)
 {
-	if (!root->ref_cows)
+	if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state))
 		return 0;
 
-	mutex_lock(&root->fs_info->trans_mutex);
-	if (root->last_trans == trans->transid) {
-		mutex_unlock(&root->fs_info->trans_mutex);
+	/*
+	 * 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(&root->fs_info->reloc_mutex);
 	record_root_in_trans(trans, root);
-	mutex_unlock(&root->fs_info->trans_mutex);
+	mutex_unlock(&root->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.
@@ -140,203 +334,464 @@ static void wait_current_trans(struct btrfs_root *root)
 {
 	struct btrfs_transaction *cur_trans;
 
+	spin_lock(&root->fs_info->trans_lock);
 	cur_trans = root->fs_info->running_transaction;
-	if (cur_trans && cur_trans->blocked) {
-		DEFINE_WAIT(wait);
-		cur_trans->use_count++;
-		while (1) {
-			prepare_to_wait(&root->fs_info->transaction_wait, &wait,
-					TASK_UNINTERRUPTIBLE);
-			if (cur_trans->blocked) {
-				mutex_unlock(&root->fs_info->trans_mutex);
-				schedule();
-				mutex_lock(&root->fs_info->trans_mutex);
-				finish_wait(&root->fs_info->transaction_wait,
-					    &wait);
-			} else {
-				finish_wait(&root->fs_info->transaction_wait,
-					    &wait);
-				break;
-			}
-		}
-		put_transaction(cur_trans);
+	if (cur_trans && is_transaction_blocked(cur_trans)) {
+		atomic_inc(&cur_trans->use_count);
+		spin_unlock(&root->fs_info->trans_lock);
+
+		wait_event(root->fs_info->transaction_wait,
+			   cur_trans->state >= TRANS_STATE_UNBLOCKED ||
+			   cur_trans->aborted);
+		btrfs_put_transaction(cur_trans);
+	} else {
+		spin_unlock(&root->fs_info->trans_lock);
 	}
 }
 
-enum btrfs_trans_type {
-	TRANS_START,
-	TRANS_JOIN,
-	TRANS_USERSPACE,
-};
+static int may_wait_transaction(struct btrfs_root *root, int type)
+{
+	if (root->fs_info->log_root_recovering)
+		return 0;
+
+	if (type == TRANS_USERSPACE)
+		return 1;
+
+	if (type == TRANS_START &&
+	    !atomic_read(&root->fs_info->open_ioctl_trans))
+		return 1;
+
+	return 0;
+}
 
-static struct btrfs_trans_handle *start_transaction(struct btrfs_root *root,
-					     int num_blocks, int type)
+static inline bool need_reserve_reloc_root(struct btrfs_root *root)
 {
-	struct btrfs_trans_handle *h =
-		kmem_cache_alloc(btrfs_trans_handle_cachep, GFP_NOFS);
+	if (!root->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, u64 num_items, unsigned int type,
+		  enum btrfs_reserve_flush_enum flush)
+{
+	struct btrfs_trans_handle *h;
+	struct btrfs_transaction *cur_trans;
+	u64 num_bytes = 0;
+	u64 qgroup_reserved = 0;
+	bool reloc_reserved = false;
 	int ret;
 
-	mutex_lock(&root->fs_info->trans_mutex);
-	if (!root->fs_info->log_root_recovering &&
-	    ((type == TRANS_START && !root->fs_info->open_ioctl_trans) ||
-	     type == TRANS_USERSPACE))
+	/* Send isn't supposed to start transactions. */
+	ASSERT(current->journal_info != (void *)BTRFS_SEND_TRANS_STUB);
+
+	if (test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state))
+		return ERR_PTR(-EROFS);
+
+	if (current->journal_info) {
+		WARN_ON(type & TRANS_EXTWRITERS);
+		h = current->journal_info;
+		h->use_count++;
+		WARN_ON(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 > 0 && root != root->fs_info->chunk_root) {
+		if (root->fs_info->quota_enabled &&
+		    is_fstree(root->root_key.objectid)) {
+			qgroup_reserved = num_items * root->leafsize;
+			ret = btrfs_qgroup_reserve(root, qgroup_reserved);
+			if (ret)
+				return ERR_PTR(ret);
+		}
+
+		num_bytes = btrfs_calc_trans_metadata_size(root, num_items);
+		/*
+		 * Do the reservation for the relocation root creation
+		 */
+		if (unlikely(need_reserve_reloc_root(root))) {
+			num_bytes += root->nodesize;
+			reloc_reserved = true;
+		}
+
+		ret = btrfs_block_rsv_add(root,
+					  &root->fs_info->trans_block_rsv,
+					  num_bytes, flush);
+		if (ret)
+			goto reserve_fail;
+	}
+again:
+	h = kmem_cache_alloc(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(root->fs_info->sb);
+
+	if (may_wait_transaction(root, type))
 		wait_current_trans(root);
-	ret = join_transaction(root);
-	BUG_ON(ret);
 
-	h->transid = root->fs_info->running_transaction->transid;
-	h->transaction = root->fs_info->running_transaction;
-	h->blocks_reserved = num_blocks;
+	do {
+		ret = join_transaction(root, type);
+		if (ret == -EBUSY) {
+			wait_current_trans(root);
+			if (unlikely(type == TRANS_ATTACH))
+				ret = -ENOENT;
+		}
+	} while (ret == -EBUSY);
+
+	if (ret < 0) {
+		/* We must get the transaction if we are JOIN_NOLOCK. */
+		BUG_ON(type == TRANS_JOIN_NOLOCK);
+		goto join_fail;
+	}
+
+	cur_trans = root->fs_info->running_transaction;
+
+	h->transid = cur_trans->transid;
+	h->transaction = cur_trans;
 	h->blocks_used = 0;
-	h->block_group = 0;
-	h->alloc_exclude_nr = 0;
-	h->alloc_exclude_start = 0;
+	h->bytes_reserved = 0;
+	h->root = root;
 	h->delayed_ref_updates = 0;
+	h->use_count = 1;
+	h->adding_csums = 0;
+	h->block_rsv = NULL;
+	h->orig_rsv = NULL;
+	h->aborted = 0;
+	h->qgroup_reserved = 0;
+	h->delayed_ref_elem.seq = 0;
+	h->type = type;
+	h->allocating_chunk = false;
+	h->reloc_reserved = false;
+	h->sync = false;
+	INIT_LIST_HEAD(&h->qgroup_ref_list);
+	INIT_LIST_HEAD(&h->new_bgs);
 
-	if (!current->journal_info && type != TRANS_USERSPACE)
+	smp_mb();
+	if (cur_trans->state >= TRANS_STATE_BLOCKED &&
+	    may_wait_transaction(root, type)) {
 		current->journal_info = h;
+		btrfs_commit_transaction(h, root);
+		goto again;
+	}
 
-	root->fs_info->running_transaction->use_count++;
-	record_root_in_trans(h, root);
-	mutex_unlock(&root->fs_info->trans_mutex);
+	if (num_bytes) {
+		trace_btrfs_space_reservation(root->fs_info, "transaction",
+					      h->transid, num_bytes, 1);
+		h->block_rsv = &root->fs_info->trans_block_rsv;
+		h->bytes_reserved = num_bytes;
+		h->reloc_reserved = reloc_reserved;
+	}
+	h->qgroup_reserved = qgroup_reserved;
+
+got_it:
+	btrfs_record_root_in_trans(h, root);
+
+	if (!current->journal_info && type != TRANS_USERSPACE)
+		current->journal_info = h;
 	return h;
+
+join_fail:
+	if (type & __TRANS_FREEZABLE)
+		sb_end_intwrite(root->fs_info->sb);
+	kmem_cache_free(btrfs_trans_handle_cachep, h);
+alloc_fail:
+	if (num_bytes)
+		btrfs_block_rsv_release(root, &root->fs_info->trans_block_rsv,
+					num_bytes);
+reserve_fail:
+	if (qgroup_reserved)
+		btrfs_qgroup_free(root, qgroup_reserved);
+	return ERR_PTR(ret);
 }
 
 struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root,
-						   int num_blocks)
+						   int num_items)
 {
-	return start_transaction(root, num_blocks, TRANS_START);
+	return start_transaction(root, num_items, TRANS_START,
+				 BTRFS_RESERVE_FLUSH_ALL);
 }
-struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root,
-						   int num_blocks)
+
+struct btrfs_trans_handle *btrfs_start_transaction_lflush(
+					struct btrfs_root *root, int num_items)
 {
-	return start_transaction(root, num_blocks, TRANS_JOIN);
+	return start_transaction(root, num_items, TRANS_START,
+				 BTRFS_RESERVE_FLUSH_LIMIT);
 }
 
-struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *r,
-							 int num_blocks)
+struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root)
 {
-	return start_transaction(r, num_blocks, TRANS_USERSPACE);
+	return start_transaction(root, 0, TRANS_JOIN, 0);
 }
 
-/* wait for a transaction commit to be fully complete */
-static noinline int wait_for_commit(struct btrfs_root *root,
-				    struct btrfs_transaction *commit)
+struct btrfs_trans_handle *btrfs_join_transaction_nolock(struct btrfs_root *root)
 {
-	DEFINE_WAIT(wait);
-	mutex_lock(&root->fs_info->trans_mutex);
-	while (!commit->commit_done) {
-		prepare_to_wait(&commit->commit_wait, &wait,
-				TASK_UNINTERRUPTIBLE);
-		if (commit->commit_done)
-			break;
-		mutex_unlock(&root->fs_info->trans_mutex);
-		schedule();
-		mutex_lock(&root->fs_info->trans_mutex);
-	}
-	mutex_unlock(&root->fs_info->trans_mutex);
-	finish_wait(&commit->commit_wait, &wait);
-	return 0;
+	return start_transaction(root, 0, TRANS_JOIN_NOLOCK, 0);
+}
+
+struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root)
+{
+	return start_transaction(root, 0, TRANS_USERSPACE, 0);
 }
 
-#if 0
 /*
- * rate limit against the drop_snapshot code.  This helps to slow down new
- * operations if the drop_snapshot code isn't able to keep up.
+ * 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()
  */
-static void throttle_on_drops(struct btrfs_root *root)
+struct btrfs_trans_handle *btrfs_attach_transaction(struct btrfs_root *root)
 {
-	struct btrfs_fs_info *info = root->fs_info;
-	int harder_count = 0;
-
-harder:
-	if (atomic_read(&info->throttles)) {
-		DEFINE_WAIT(wait);
-		int thr;
-		thr = atomic_read(&info->throttle_gen);
-
-		do {
-			prepare_to_wait(&info->transaction_throttle,
-					&wait, TASK_UNINTERRUPTIBLE);
-			if (!atomic_read(&info->throttles)) {
-				finish_wait(&info->transaction_throttle, &wait);
-				break;
-			}
-			schedule();
-			finish_wait(&info->transaction_throttle, &wait);
-		} while (thr == atomic_read(&info->throttle_gen));
-		harder_count++;
+	return start_transaction(root, 0, TRANS_ATTACH, 0);
+}
+
+/*
+ * 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;
 
-		if (root->fs_info->total_ref_cache_size > 1 * 1024 * 1024 &&
-		    harder_count < 2)
-			goto harder;
+	trans = start_transaction(root, 0, TRANS_ATTACH, 0);
+	if (IS_ERR(trans) && PTR_ERR(trans) == -ENOENT)
+		btrfs_wait_for_commit(root, 0);
 
-		if (root->fs_info->total_ref_cache_size > 5 * 1024 * 1024 &&
-		    harder_count < 10)
-			goto harder;
+	return trans;
+}
+
+/* wait for a transaction commit to be fully complete */
+static noinline void wait_for_commit(struct btrfs_root *root,
+				    struct btrfs_transaction *commit)
+{
+	wait_event(commit->commit_wait, commit->state == TRANS_STATE_COMPLETED);
+}
+
+int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid)
+{
+	struct btrfs_transaction *cur_trans = NULL, *t;
+	int ret = 0;
 
-		if (root->fs_info->total_ref_cache_size > 10 * 1024 * 1024 &&
-		    harder_count < 20)
-			goto harder;
+	if (transid) {
+		if (transid <= root->fs_info->last_trans_committed)
+			goto out;
+
+		ret = -EINVAL;
+		/* find specified transaction */
+		spin_lock(&root->fs_info->trans_lock);
+		list_for_each_entry(t, &root->fs_info->trans_list, list) {
+			if (t->transid == transid) {
+				cur_trans = t;
+				atomic_inc(&cur_trans->use_count);
+				ret = 0;
+				break;
+			}
+			if (t->transid > transid) {
+				ret = 0;
+				break;
+			}
+		}
+		spin_unlock(&root->fs_info->trans_lock);
+		/* The specified transaction doesn't exist */
+		if (!cur_trans)
+			goto out;
+	} else {
+		/* find newest transaction that is committing | committed */
+		spin_lock(&root->fs_info->trans_lock);
+		list_for_each_entry_reverse(t, &root->fs_info->trans_list,
+					    list) {
+			if (t->state >= TRANS_STATE_COMMIT_START) {
+				if (t->state == TRANS_STATE_COMPLETED)
+					break;
+				cur_trans = t;
+				atomic_inc(&cur_trans->use_count);
+				break;
+			}
+		}
+		spin_unlock(&root->fs_info->trans_lock);
+		if (!cur_trans)
+			goto out;  /* nothing committing|committed */
 	}
+
+	wait_for_commit(root, cur_trans);
+	btrfs_put_transaction(cur_trans);
+out:
+	return ret;
 }
-#endif
 
 void btrfs_throttle(struct btrfs_root *root)
 {
-	mutex_lock(&root->fs_info->trans_mutex);
-	if (!root->fs_info->open_ioctl_trans)
+	if (!atomic_read(&root->fs_info->open_ioctl_trans))
 		wait_current_trans(root);
-	mutex_unlock(&root->fs_info->trans_mutex);
+}
+
+static int should_end_transaction(struct btrfs_trans_handle *trans,
+				  struct btrfs_root *root)
+{
+	if (root->fs_info->global_block_rsv.space_info->full &&
+	    btrfs_check_space_for_delayed_refs(trans, root))
+		return 1;
+
+	return !!btrfs_block_rsv_check(root, &root->fs_info->global_block_rsv, 5);
+}
+
+int btrfs_should_end_transaction(struct btrfs_trans_handle *trans,
+				 struct btrfs_root *root)
+{
+	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, root, updates);
+		if (err) /* Error code will also eval true */
+			return err;
+	}
+
+	return should_end_transaction(trans, root);
 }
 
 static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
 			  struct btrfs_root *root, int throttle)
 {
-	struct btrfs_transaction *cur_trans;
+	struct btrfs_transaction *cur_trans = trans->transaction;
 	struct btrfs_fs_info *info = root->fs_info;
-	int count = 0;
-
-	while (count < 4) {
-		unsigned long cur = trans->delayed_ref_updates;
-		trans->delayed_ref_updates = 0;
-		if (cur &&
-		    trans->transaction->delayed_refs.num_heads_ready > 64) {
-			trans->delayed_ref_updates = 0;
-
-			/*
-			 * do a full flush if the transaction is trying
-			 * to close
-			 */
-			if (trans->transaction->delayed_refs.flushing)
-				cur = 0;
-			btrfs_run_delayed_refs(trans, root, cur);
-		} else {
-			break;
-		}
-		count++;
+	unsigned long cur = trans->delayed_ref_updates;
+	int lock = (trans->type != TRANS_JOIN_NOLOCK);
+	int err = 0;
+	int must_run_delayed_refs = 0;
+
+	if (trans->use_count > 1) {
+		trans->use_count--;
+		trans->block_rsv = trans->orig_rsv;
+		return 0;
 	}
 
-	mutex_lock(&info->trans_mutex);
-	cur_trans = info->running_transaction;
-	WARN_ON(cur_trans != trans->transaction);
-	WARN_ON(cur_trans->num_writers < 1);
-	cur_trans->num_writers--;
+	btrfs_trans_release_metadata(trans, root);
+	trans->block_rsv = NULL;
+
+	if (!list_empty(&trans->new_bgs))
+		btrfs_create_pending_block_groups(trans, root);
 
+	trans->delayed_ref_updates = 0;
+	if (!trans->sync) {
+		must_run_delayed_refs =
+			btrfs_should_throttle_delayed_refs(trans, root);
+		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;
+	}
+
+	if (trans->qgroup_reserved) {
+		/*
+		 * the same root has to be passed here between start_transaction
+		 * and end_transaction. Subvolume quota depends on this.
+		 */
+		btrfs_qgroup_free(trans->root, trans->qgroup_reserved);
+		trans->qgroup_reserved = 0;
+	}
+
+	btrfs_trans_release_metadata(trans, root);
+	trans->block_rsv = NULL;
+
+	if (!list_empty(&trans->new_bgs))
+		btrfs_create_pending_block_groups(trans, root);
+
+	if (lock && !atomic_read(&root->fs_info->open_ioctl_trans) &&
+	    should_end_transaction(trans, root) &&
+	    ACCESS_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 && ACCESS_ONCE(cur_trans->state) == TRANS_STATE_BLOCKED) {
+		if (throttle)
+			return btrfs_commit_transaction(trans, root);
+		else
+			wake_up_process(info->transaction_kthread);
+	}
+
+	if (trans->type & __TRANS_FREEZABLE)
+		sb_end_intwrite(root->fs_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);
+
+	smp_mb();
 	if (waitqueue_active(&cur_trans->writer_wait))
 		wake_up(&cur_trans->writer_wait);
-	put_transaction(cur_trans);
-	mutex_unlock(&info->trans_mutex);
+	btrfs_put_transaction(cur_trans);
 
 	if (current->journal_info == trans)
 		current->journal_info = NULL;
-	memset(trans, 0, sizeof(*trans));
-	kmem_cache_free(btrfs_trans_handle_cachep, trans);
 
 	if (throttle)
 		btrfs_run_delayed_iputs(root);
 
-	return 0;
+	if (trans->aborted ||
+	    test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state)) {
+		wake_up_process(info->transaction_kthread);
+		err = -EIO;
+	}
+	assert_qgroups_uptodate(trans);
+
+	kmem_cache_free(btrfs_trans_handle_cachep, trans);
+	if (must_run_delayed_refs) {
+		btrfs_async_run_delayed_refs(root, cur,
+					     must_run_delayed_refs == 1);
+	}
+	return err;
 }
 
 int btrfs_end_transaction(struct btrfs_trans_handle *trans,
@@ -359,50 +814,23 @@ int btrfs_end_transaction_throttle(struct btrfs_trans_handle *trans,
 int btrfs_write_marked_extents(struct btrfs_root *root,
 			       struct extent_io_tree *dirty_pages, int mark)
 {
-	int ret;
 	int err = 0;
 	int werr = 0;
-	struct page *page;
-	struct inode *btree_inode = root->fs_info->btree_inode;
+	struct address_space *mapping = root->fs_info->btree_inode->i_mapping;
+	struct extent_state *cached_state = NULL;
 	u64 start = 0;
 	u64 end;
-	unsigned long index;
 
-	while (1) {
-		ret = find_first_extent_bit(dirty_pages, start, &start, &end,
-					    mark);
-		if (ret)
-			break;
-		while (start <= end) {
-			cond_resched();
-
-			index = start >> PAGE_CACHE_SHIFT;
-			start = (u64)(index + 1) << PAGE_CACHE_SHIFT;
-			page = find_get_page(btree_inode->i_mapping, index);
-			if (!page)
-				continue;
-
-			btree_lock_page_hook(page);
-			if (!page->mapping) {
-				unlock_page(page);
-				page_cache_release(page);
-				continue;
-			}
-
-			if (PageWriteback(page)) {
-				if (PageDirty(page))
-					wait_on_page_writeback(page);
-				else {
-					unlock_page(page);
-					page_cache_release(page);
-					continue;
-				}
-			}
-			err = write_one_page(page, 0);
-			if (err)
-				werr = err;
-			page_cache_release(page);
-		}
+	while (!find_first_extent_bit(dirty_pages, start, &start, &end,
+				      mark, &cached_state)) {
+		convert_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
+				   mark, &cached_state, GFP_NOFS);
+		cached_state = NULL;
+		err = filemap_fdatawrite_range(mapping, start, end);
+		if (err)
+			werr = err;
+		cond_resched();
+		start = end + 1;
 	}
 	if (err)
 		werr = err;
@@ -418,39 +846,22 @@ int btrfs_write_marked_extents(struct btrfs_root *root,
 int btrfs_wait_marked_extents(struct btrfs_root *root,
 			      struct extent_io_tree *dirty_pages, int mark)
 {
-	int ret;
 	int err = 0;
 	int werr = 0;
-	struct page *page;
-	struct inode *btree_inode = root->fs_info->btree_inode;
+	struct address_space *mapping = root->fs_info->btree_inode->i_mapping;
+	struct extent_state *cached_state = NULL;
 	u64 start = 0;
 	u64 end;
-	unsigned long index;
 
-	while (1) {
-		ret = find_first_extent_bit(dirty_pages, start, &start, &end,
-					    mark);
-		if (ret)
-			break;
-
-		clear_extent_bits(dirty_pages, start, end, mark, GFP_NOFS);
-		while (start <= end) {
-			index = start >> PAGE_CACHE_SHIFT;
-			start = (u64)(index + 1) << PAGE_CACHE_SHIFT;
-			page = find_get_page(btree_inode->i_mapping, index);
-			if (!page)
-				continue;
-			if (PageDirty(page)) {
-				btree_lock_page_hook(page);
-				wait_on_page_writeback(page);
-				err = write_one_page(page, 0);
-				if (err)
-					werr = err;
-			}
-			wait_on_page_writeback(page);
-			page_cache_release(page);
-			cond_resched();
-		}
+	while (!find_first_extent_bit(dirty_pages, start, &start, &end,
+				      EXTENT_NEED_WAIT, &cached_state)) {
+		clear_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
+				 0, 0, &cached_state, GFP_NOFS);
+		err = filemap_fdatawait_range(mapping, start, end);
+		if (err)
+			werr = err;
+		cond_resched();
+		start = end + 1;
 	}
 	if (err)
 		werr = err;
@@ -462,15 +873,23 @@ int btrfs_wait_marked_extents(struct btrfs_root *root,
  * 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
  */
-int btrfs_write_and_wait_marked_extents(struct btrfs_root *root,
+static int btrfs_write_and_wait_marked_extents(struct btrfs_root *root,
 				struct extent_io_tree *dirty_pages, int mark)
 {
 	int ret;
 	int ret2;
+	struct blk_plug plug;
 
+	blk_start_plug(&plug);
 	ret = btrfs_write_marked_extents(root, dirty_pages, mark);
+	blk_finish_plug(&plug);
 	ret2 = btrfs_wait_marked_extents(root, dirty_pages, mark);
-	return ret || ret2;
+
+	if (ret)
+		return ret;
+	if (ret2)
+		return ret2;
+	return 0;
 }
 
 int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
@@ -517,21 +936,24 @@ static int update_cowonly_root(struct btrfs_trans_handle *trans,
 		ret = btrfs_update_root(trans, tree_root,
 					&root->root_key,
 					&root->root_item);
-		BUG_ON(ret);
+		if (ret)
+			return ret;
 
 		old_root_used = btrfs_root_used(&root->root_item);
 		ret = btrfs_write_dirty_block_groups(trans, root);
-		BUG_ON(ret);
+		if (ret)
+			return ret;
 	}
 
-	if (root != root->fs_info->extent_root)
-		switch_commit_root(root);
-
 	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_root *root)
@@ -542,27 +964,53 @@ static noinline int commit_cowonly_roots(struct btrfs_trans_handle *trans,
 	int ret;
 
 	ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
-	BUG_ON(ret);
+	if (ret)
+		return ret;
 
 	eb = btrfs_lock_root_node(fs_info->tree_root);
-	btrfs_cow_block(trans, fs_info->tree_root, eb, NULL, 0, &eb);
+	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, root, (unsigned long)-1);
-	BUG_ON(ret);
+	if (ret)
+		return ret;
+
+	ret = btrfs_run_dev_stats(trans, root->fs_info);
+	if (ret)
+		return ret;
+	ret = btrfs_run_dev_replace(trans, root->fs_info);
+	if (ret)
+		return ret;
+	ret = btrfs_run_qgroups(trans, root->fs_info);
+	if (ret)
+		return ret;
+
+	/* run_qgroups might have added some more refs */
+	ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
+	if (ret)
+		return ret;
 
 	while (!list_empty(&fs_info->dirty_cowonly_roots)) {
 		next = fs_info->dirty_cowonly_roots.next;
 		list_del_init(next);
 		root = list_entry(next, struct btrfs_root, dirty_list);
 
-		update_cowonly_root(trans, root);
+		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;
 	}
 
-	down_write(&fs_info->extent_commit_sem);
-	switch_commit_root(fs_info->extent_root);
-	up_write(&fs_info->extent_commit_sem);
+	list_add_tail(&fs_info->extent_root->dirty_list,
+		      &trans->transaction->switch_commits);
+	btrfs_after_dev_replace_commit(fs_info);
 
 	return 0;
 }
@@ -572,12 +1020,12 @@ static noinline int commit_cowonly_roots(struct btrfs_trans_handle *trans,
  * a dirty root struct and adds it into the list of dead roots that need to
  * be deleted
  */
-int btrfs_add_dead_root(struct btrfs_root *root)
+void btrfs_add_dead_root(struct btrfs_root *root)
 {
-	mutex_lock(&root->fs_info->trans_mutex);
-	list_add(&root->root_list, &root->fs_info->dead_roots);
-	mutex_unlock(&root->fs_info->trans_mutex);
-	return 0;
+	spin_lock(&root->fs_info->trans_lock);
+	if (list_empty(&root->root_list))
+		list_add_tail(&root->root_list, &root->fs_info->dead_roots);
+	spin_unlock(&root->fs_info->trans_lock);
 }
 
 /*
@@ -592,6 +1040,7 @@ static noinline int commit_fs_roots(struct btrfs_trans_handle *trans,
 	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,
@@ -604,12 +1053,21 @@ static noinline int commit_fs_roots(struct btrfs_trans_handle *trans,
 			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_orphan_commit_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) {
-				switch_commit_root(root);
+				list_add_tail(&root->dirty_list,
+					&trans->transaction->switch_commits);
 				btrfs_set_root_node(&root->root_item,
 						    root->node);
 			}
@@ -617,140 +1075,60 @@ static noinline int commit_fs_roots(struct btrfs_trans_handle *trans,
 			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;
 		}
 	}
+	spin_unlock(&fs_info->fs_roots_radix_lock);
 	return err;
 }
 
 /*
- * defrag a given btree.  If cacheonly == 1, this won't read from the disk,
- * otherwise every leaf in the btree is read and defragged.
+ * defrag a given btree.
+ * Every leaf in the btree is read and defragged.
  */
-int btrfs_defrag_root(struct btrfs_root *root, int cacheonly)
+int btrfs_defrag_root(struct btrfs_root *root)
 {
 	struct btrfs_fs_info *info = root->fs_info;
-	int ret;
 	struct btrfs_trans_handle *trans;
-	unsigned long nr;
+	int ret;
 
-	smp_mb();
-	if (root->defrag_running)
+	if (test_and_set_bit(BTRFS_ROOT_DEFRAG_RUNNING, &root->state))
 		return 0;
-	trans = btrfs_start_transaction(root, 1);
-	while (1) {
-		root->defrag_running = 1;
-		ret = btrfs_defrag_leaves(trans, root, cacheonly);
-		nr = trans->blocks_used;
-		btrfs_end_transaction(trans, root);
-		btrfs_btree_balance_dirty(info->tree_root, nr);
-		cond_resched();
-
-		trans = btrfs_start_transaction(root, 1);
-		if (root->fs_info->closing || ret != -EAGAIN)
-			break;
-	}
-	root->defrag_running = 0;
-	smp_mb();
-	btrfs_end_transaction(trans, root);
-	return 0;
-}
-
-#if 0
-/*
- * when dropping snapshots, we generate a ton of delayed refs, and it makes
- * sense not to join the transaction while it is trying to flush the current
- * queue of delayed refs out.
- *
- * This is used by the drop snapshot code only
- */
-static noinline int wait_transaction_pre_flush(struct btrfs_fs_info *info)
-{
-	DEFINE_WAIT(wait);
-
-	mutex_lock(&info->trans_mutex);
-	while (info->running_transaction &&
-	       info->running_transaction->delayed_refs.flushing) {
-		prepare_to_wait(&info->transaction_wait, &wait,
-				TASK_UNINTERRUPTIBLE);
-		mutex_unlock(&info->trans_mutex);
-
-		schedule();
-
-		mutex_lock(&info->trans_mutex);
-		finish_wait(&info->transaction_wait, &wait);
-	}
-	mutex_unlock(&info->trans_mutex);
-	return 0;
-}
-
-/*
- * Given a list of roots that need to be deleted, call btrfs_drop_snapshot on
- * all of them
- */
-int btrfs_drop_dead_root(struct btrfs_root *root)
-{
-	struct btrfs_trans_handle *trans;
-	struct btrfs_root *tree_root = root->fs_info->tree_root;
-	unsigned long nr;
-	int ret;
 
 	while (1) {
-		/*
-		 * we don't want to jump in and create a bunch of
-		 * delayed refs if the transaction is starting to close
-		 */
-		wait_transaction_pre_flush(tree_root->fs_info);
-		trans = btrfs_start_transaction(tree_root, 1);
+		trans = btrfs_start_transaction(root, 0);
+		if (IS_ERR(trans))
+			return PTR_ERR(trans);
 
-		/*
-		 * we've joined a transaction, make sure it isn't
-		 * closing right now
-		 */
-		if (trans->transaction->delayed_refs.flushing) {
-			btrfs_end_transaction(trans, tree_root);
-			continue;
-		}
+		ret = btrfs_defrag_leaves(trans, root);
 
-		ret = btrfs_drop_snapshot(trans, root);
-		if (ret != -EAGAIN)
-			break;
+		btrfs_end_transaction(trans, root);
+		btrfs_btree_balance_dirty(info->tree_root);
+		cond_resched();
 
-		ret = btrfs_update_root(trans, tree_root,
-					&root->root_key,
-					&root->root_item);
-		if (ret)
+		if (btrfs_fs_closing(root->fs_info) || ret != -EAGAIN)
 			break;
 
-		nr = trans->blocks_used;
-		ret = btrfs_end_transaction(trans, tree_root);
-		BUG_ON(ret);
-
-		btrfs_btree_balance_dirty(tree_root, nr);
-		cond_resched();
+		if (btrfs_defrag_cancelled(root->fs_info)) {
+			pr_debug("BTRFS: defrag_root cancelled\n");
+			ret = -EAGAIN;
+			break;
+		}
 	}
-	BUG_ON(ret);
-
-	ret = btrfs_del_root(trans, tree_root, &root->root_key);
-	BUG_ON(ret);
-
-	nr = trans->blocks_used;
-	ret = btrfs_end_transaction(trans, tree_root);
-	BUG_ON(ret);
-
-	free_extent_buffer(root->node);
-	free_extent_buffer(root->commit_root);
-	kfree(root);
-
-	btrfs_btree_balance_dirty(tree_root, nr);
+	clear_bit(BTRFS_ROOT_DEFRAG_RUNNING, &root->state);
 	return ret;
 }
-#endif
 
 /*
  * new snapshots need to be created at a very specific time in the
- * transaction commit.  This does the actual creation
+ * 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_fs_info *fs_info,
@@ -760,93 +1138,254 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
 	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;
-	int ret;
+	struct timespec cur_time = CURRENT_TIME;
+	int ret = 0;
+	u64 to_reserve = 0;
+	u64 index = 0;
 	u64 objectid;
+	u64 root_flags;
+	uuid_le new_uuid;
+
+	path = btrfs_alloc_path();
+	if (!path) {
+		pending->error = -ENOMEM;
+		return 0;
+	}
 
 	new_root_item = kmalloc(sizeof(*new_root_item), GFP_NOFS);
 	if (!new_root_item) {
-		ret = -ENOMEM;
+		pending->error = -ENOMEM;
+		goto root_item_alloc_fail;
+	}
+
+	pending->error = btrfs_find_free_objectid(tree_root, &objectid);
+	if (pending->error)
+		goto no_free_objectid;
+
+	btrfs_reloc_pre_snapshot(trans, 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 no_free_objectid;
+	}
+
+	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;
+
+	dentry = pending->dentry;
+	parent_inode = pending->dir;
+	parent_root = BTRFS_I(parent_inode)->root;
+	record_root_in_trans(trans, parent_root);
+
+	/*
+	 * insert the directory item
+	 */
+	ret = btrfs_set_inode_index(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(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, root, ret);
 		goto fail;
 	}
-	ret = btrfs_find_free_objectid(trans, tree_root, 0, &objectid);
-	if (ret)
+	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, root);
+	if (ret) {	/* Transaction aborted */
+		btrfs_abort_transaction(trans, root, ret);
 		goto fail;
+	}
 
 	record_root_in_trans(trans, root);
 	btrfs_set_root_last_snapshot(&root->root_item, trans->transid);
 	memcpy(new_root_item, &root->root_item, sizeof(*new_root_item));
-
-	key.objectid = objectid;
-	/* record when the snapshot was created in key.offset */
-	key.offset = trans->transid;
-	btrfs_set_key_type(&key, BTRFS_ROOT_ITEM_KEY);
+	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);
-	btrfs_cow_block(trans, root, old, NULL, 0, &old);
+	ret = btrfs_cow_block(trans, root, old, NULL, 0, &old);
+	if (ret) {
+		btrfs_tree_unlock(old);
+		free_extent_buffer(old);
+		btrfs_abort_transaction(trans, root, ret);
+		goto fail;
+	}
+
 	btrfs_set_lock_blocking(old);
 
-	btrfs_copy_root(trans, root, old, &tmp, objectid);
+	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, root, ret);
+		goto fail;
+	}
 
-	btrfs_set_root_node(new_root_item, tmp);
-	ret = btrfs_insert_root(trans, root->fs_info->tree_root, &key,
-				new_root_item);
-	btrfs_tree_unlock(tmp);
-	free_extent_buffer(tmp);
-	if (ret)
+	/*
+	 * We need to flush delayed refs in order to make sure all of our quota
+	 * operations have been done before we call btrfs_qgroup_inherit.
+	 */
+	ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
+	if (ret) {
+		btrfs_abort_transaction(trans, root, ret);
 		goto fail;
+	}
 
-	key.offset = (u64)-1;
-	memcpy(&pending->root_key, &key, sizeof(key));
-fail:
-	kfree(new_root_item);
-	return ret;
-}
+	ret = btrfs_qgroup_inherit(trans, fs_info,
+				   root->root_key.objectid,
+				   objectid, pending->inherit);
+	if (ret) {
+		btrfs_abort_transaction(trans, root, ret);
+		goto fail;
+	}
 
-static noinline int finish_pending_snapshot(struct btrfs_fs_info *fs_info,
-				   struct btrfs_pending_snapshot *pending)
-{
-	int ret;
-	int namelen;
-	u64 index = 0;
-	struct btrfs_trans_handle *trans;
-	struct inode *parent_inode;
-	struct btrfs_root *parent_root;
+	/* see comments in should_cow_block() */
+	set_bit(BTRFS_ROOT_FORCE_COW, &root->state);
+	smp_wmb();
 
-	parent_inode = pending->dentry->d_parent->d_inode;
-	parent_root = BTRFS_I(parent_inode)->root;
-	trans = btrfs_join_transaction(parent_root, 1);
+	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, root, ret);
+		goto fail;
+	}
 
 	/*
-	 * insert the directory item
+	 * insert root back/forward references
 	 */
-	namelen = strlen(pending->name);
-	ret = btrfs_set_inode_index(parent_inode, &index);
-	ret = btrfs_insert_dir_item(trans, parent_root,
-			    pending->name, namelen,
-			    parent_inode->i_ino,
-			    &pending->root_key, BTRFS_FT_DIR, index);
+	ret = btrfs_add_root_ref(trans, tree_root, objectid,
+				 parent_root->root_key.objectid,
+				 btrfs_ino(parent_inode), index,
+				 dentry->d_name.name, dentry->d_name.len);
+	if (ret) {
+		btrfs_abort_transaction(trans, root, ret);
+		goto fail;
+	}
 
-	if (ret)
+	key.offset = (u64)-1;
+	pending->snap = btrfs_read_fs_root_no_name(root->fs_info, &key);
+	if (IS_ERR(pending->snap)) {
+		ret = PTR_ERR(pending->snap);
+		btrfs_abort_transaction(trans, root, ret);
 		goto fail;
+	}
 
-	btrfs_i_size_write(parent_inode, parent_inode->i_size + namelen * 2);
-	ret = btrfs_update_inode(trans, parent_root, parent_inode);
-	BUG_ON(ret);
+	ret = btrfs_reloc_post_snapshot(trans, pending);
+	if (ret) {
+		btrfs_abort_transaction(trans, root, ret);
+		goto fail;
+	}
 
-	ret = btrfs_add_root_ref(trans, parent_root->fs_info->tree_root,
-				 pending->root_key.objectid,
-				 parent_root->root_key.objectid,
-				 parent_inode->i_ino, index, pending->name,
-				 namelen);
+	ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
+	if (ret) {
+		btrfs_abort_transaction(trans, root, ret);
+		goto fail;
+	}
 
-	BUG_ON(ret);
+	ret = btrfs_insert_dir_item(trans, parent_root,
+				    dentry->d_name.name, dentry->d_name.len,
+				    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, root, ret);
+		goto fail;
+	}
 
+	btrfs_i_size_write(parent_inode, parent_inode->i_size +
+					 dentry->d_name.len * 2);
+	parent_inode->i_mtime = parent_inode->i_ctime = CURRENT_TIME;
+	ret = btrfs_update_inode_fallback(trans, parent_root, parent_inode);
+	if (ret) {
+		btrfs_abort_transaction(trans, root, ret);
+		goto fail;
+	}
+	ret = btrfs_uuid_tree_add(trans, fs_info->uuid_root, new_uuid.b,
+				  BTRFS_UUID_KEY_SUBVOL, objectid);
+	if (ret) {
+		btrfs_abort_transaction(trans, root, ret);
+		goto fail;
+	}
+	if (!btrfs_is_empty_uuid(new_root_item->received_uuid)) {
+		ret = btrfs_uuid_tree_add(trans, fs_info->uuid_root,
+					  new_root_item->received_uuid,
+					  BTRFS_UUID_KEY_RECEIVED_SUBVOL,
+					  objectid);
+		if (ret && ret != -EEXIST) {
+			btrfs_abort_transaction(trans, root, ret);
+			goto fail;
+		}
+	}
 fail:
-	btrfs_end_transaction(trans, fs_info->fs_root);
+	pending->error = ret;
+dir_item_existed:
+	trans->block_rsv = rsv;
+	trans->bytes_reserved = 0;
+no_free_objectid:
+	kfree(new_root_item);
+root_item_alloc_fail:
+	btrfs_free_path(path);
 	return ret;
 }
 
@@ -856,34 +1395,17 @@ fail:
 static noinline int create_pending_snapshots(struct btrfs_trans_handle *trans,
 					     struct btrfs_fs_info *fs_info)
 {
-	struct btrfs_pending_snapshot *pending;
-	struct list_head *head = &trans->transaction->pending_snapshots;
-	int ret;
-
-	list_for_each_entry(pending, head, list) {
-		ret = create_pending_snapshot(trans, fs_info, pending);
-		BUG_ON(ret);
-	}
-	return 0;
-}
-
-static noinline int finish_pending_snapshots(struct btrfs_trans_handle *trans,
-					     struct btrfs_fs_info *fs_info)
-{
-	struct btrfs_pending_snapshot *pending;
+	struct btrfs_pending_snapshot *pending, *next;
 	struct list_head *head = &trans->transaction->pending_snapshots;
-	int ret;
+	int ret = 0;
 
-	while (!list_empty(head)) {
-		pending = list_entry(head->next,
-				     struct btrfs_pending_snapshot, list);
-		ret = finish_pending_snapshot(fs_info, pending);
-		BUG_ON(ret);
+	list_for_each_entry_safe(pending, next, head, list) {
 		list_del(&pending->list);
-		kfree(pending->name);
-		kfree(pending);
+		ret = create_pending_snapshot(trans, fs_info, pending);
+		if (ret)
+			break;
 	}
-	return 0;
+	return ret;
 }
 
 static void update_super_roots(struct btrfs_root *root)
@@ -891,7 +1413,7 @@ static void update_super_roots(struct btrfs_root *root)
 	struct btrfs_root_item *root_item;
 	struct btrfs_super_block *super;
 
-	super = &root->fs_info->super_copy;
+	super = root->fs_info->super_copy;
 
 	root_item = &root->fs_info->chunk_root->root_item;
 	super->chunk_root = root_item->bytenr;
@@ -902,133 +1424,398 @@ static void update_super_roots(struct btrfs_root *root)
 	super->root = root_item->bytenr;
 	super->generation = root_item->generation;
 	super->root_level = root_item->level;
+	if (btrfs_test_opt(root, SPACE_CACHE))
+		super->cache_generation = root_item->generation;
+	if (root->fs_info->update_uuid_tree_gen)
+		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->new_trans_lock);
-	if (info->running_transaction)
-		ret = info->running_transaction->in_commit;
-	spin_unlock(&info->new_trans_lock);
+
+	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_root *root,
+					    struct btrfs_transaction *trans)
+{
+	wait_event(root->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_root *root,
+					 struct btrfs_transaction *trans)
+{
+	wait_event(root->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 btrfs_root *root;
+	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)
+		rwsem_acquire_read(
+		     &ac->root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
+		     0, 1, _THIS_IP_);
+
+	current->journal_info = ac->newtrans;
+
+	btrfs_commit_transaction(ac->newtrans, ac->root);
+	kfree(ac);
+}
+
+int btrfs_commit_transaction_async(struct btrfs_trans_handle *trans,
+				   struct btrfs_root *root,
+				   int wait_for_unblock)
+{
+	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->root = root;
+	ac->newtrans = btrfs_join_transaction(root);
+	if (IS_ERR(ac->newtrans)) {
+		int err = PTR_ERR(ac->newtrans);
+		kfree(ac);
+		return err;
+	}
+
+	/* take transaction reference */
+	cur_trans = trans->transaction;
+	atomic_inc(&cur_trans->use_count);
+
+	btrfs_end_transaction(trans, root);
+
+	/*
+	 * 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)
+		rwsem_release(
+			&root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
+			1, _THIS_IP_);
+
+	schedule_work(&ac->work);
+
+	/* wait for transaction to start and unblock */
+	if (wait_for_unblock)
+		wait_current_trans_commit_start_and_unblock(root, cur_trans);
+	else
+		wait_current_trans_commit_start(root, 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,
+				struct btrfs_root *root, int err)
+{
+	struct btrfs_transaction *cur_trans = trans->transaction;
+	DEFINE_WAIT(wait);
+
+	WARN_ON(trans->use_count > 1);
+
+	btrfs_abort_transaction(trans, root, err);
+
+	spin_lock(&root->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 == root->fs_info->running_transaction) {
+		cur_trans->state = TRANS_STATE_COMMIT_DOING;
+		spin_unlock(&root->fs_info->trans_lock);
+		wait_event(cur_trans->writer_wait,
+			   atomic_read(&cur_trans->num_writers) == 1);
+
+		spin_lock(&root->fs_info->trans_lock);
+	}
+	spin_unlock(&root->fs_info->trans_lock);
+
+	btrfs_cleanup_one_transaction(trans->transaction, root);
+
+	spin_lock(&root->fs_info->trans_lock);
+	if (cur_trans == root->fs_info->running_transaction)
+		root->fs_info->running_transaction = NULL;
+	spin_unlock(&root->fs_info->trans_lock);
+
+	if (trans->type & __TRANS_FREEZABLE)
+		sb_end_intwrite(root->fs_info->sb);
+	btrfs_put_transaction(cur_trans);
+	btrfs_put_transaction(cur_trans);
+
+	trace_btrfs_transaction_commit(root);
+
+	if (current->journal_info == trans)
+		current->journal_info = NULL;
+	btrfs_scrub_cancel(root->fs_info);
+
+	kmem_cache_free(btrfs_trans_handle_cachep, trans);
+}
+
+static int btrfs_flush_all_pending_stuffs(struct btrfs_trans_handle *trans,
+					  struct btrfs_root *root)
+{
+	int ret;
+
+	ret = btrfs_run_delayed_items(trans, root);
+	if (ret)
+		return ret;
+
+	/*
+	 * rename don't use btrfs_join_transaction, so, once we
+	 * set the transaction to blocked above, we aren't going
+	 * to get any new ordered operations.  We can safely run
+	 * it here and no for sure that nothing new will be added
+	 * to the list
+	 */
+	ret = btrfs_run_ordered_operations(trans, root, 1);
+
 	return ret;
 }
 
+static inline int btrfs_start_delalloc_flush(struct btrfs_fs_info *fs_info)
+{
+	if (btrfs_test_opt(fs_info->tree_root, FLUSHONCOMMIT))
+		return btrfs_start_delalloc_roots(fs_info, 1, -1);
+	return 0;
+}
+
+static inline void btrfs_wait_delalloc_flush(struct btrfs_fs_info *fs_info)
+{
+	if (btrfs_test_opt(fs_info->tree_root, FLUSHONCOMMIT))
+		btrfs_wait_ordered_roots(fs_info, -1);
+}
+
 int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 			     struct btrfs_root *root)
 {
-	unsigned long joined = 0;
-	unsigned long timeout = 1;
-	struct btrfs_transaction *cur_trans;
+	struct btrfs_transaction *cur_trans = trans->transaction;
 	struct btrfs_transaction *prev_trans = NULL;
-	DEFINE_WAIT(wait);
 	int ret;
-	int should_grow = 0;
-	unsigned long now = get_seconds();
-	int flush_on_commit = btrfs_test_opt(root, FLUSHONCOMMIT);
 
-	btrfs_run_ordered_operations(root, 0);
+	ret = btrfs_run_ordered_operations(trans, root, 0);
+	if (ret) {
+		btrfs_abort_transaction(trans, root, ret);
+		btrfs_end_transaction(trans, root);
+		return ret;
+	}
+
+	/* Stop the commit early if ->aborted is set */
+	if (unlikely(ACCESS_ONCE(cur_trans->aborted))) {
+		ret = cur_trans->aborted;
+		btrfs_end_transaction(trans, root);
+		return ret;
+	}
 
 	/* 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, root, 0);
-	BUG_ON(ret);
+	if (ret) {
+		btrfs_end_transaction(trans, root);
+		return ret;
+	}
+
+	btrfs_trans_release_metadata(trans, root);
+	trans->block_rsv = NULL;
+	if (trans->qgroup_reserved) {
+		btrfs_qgroup_free(root, trans->qgroup_reserved);
+		trans->qgroup_reserved = 0;
+	}
 
 	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();
 
-	ret = btrfs_run_delayed_refs(trans, root, 0);
-	BUG_ON(ret);
+	if (!list_empty(&trans->new_bgs))
+		btrfs_create_pending_block_groups(trans, root);
 
-	mutex_lock(&root->fs_info->trans_mutex);
-	if (cur_trans->in_commit) {
-		cur_trans->use_count++;
-		mutex_unlock(&root->fs_info->trans_mutex);
+	ret = btrfs_run_delayed_refs(trans, root, 0);
+	if (ret) {
 		btrfs_end_transaction(trans, root);
+		return ret;
+	}
 
-		ret = wait_for_commit(root, cur_trans);
-		BUG_ON(ret);
+	spin_lock(&root->fs_info->trans_lock);
+	if (cur_trans->state >= TRANS_STATE_COMMIT_START) {
+		spin_unlock(&root->fs_info->trans_lock);
+		atomic_inc(&cur_trans->use_count);
+		ret = btrfs_end_transaction(trans, root);
 
-		mutex_lock(&root->fs_info->trans_mutex);
-		put_transaction(cur_trans);
-		mutex_unlock(&root->fs_info->trans_mutex);
+		wait_for_commit(root, cur_trans);
 
-		return 0;
+		btrfs_put_transaction(cur_trans);
+
+		return ret;
 	}
 
-	trans->transaction->in_commit = 1;
-	trans->transaction->blocked = 1;
+	cur_trans->state = TRANS_STATE_COMMIT_START;
+	wake_up(&root->fs_info->transaction_blocked_wait);
+
 	if (cur_trans->list.prev != &root->fs_info->trans_list) {
 		prev_trans = list_entry(cur_trans->list.prev,
 					struct btrfs_transaction, list);
-		if (!prev_trans->commit_done) {
-			prev_trans->use_count++;
-			mutex_unlock(&root->fs_info->trans_mutex);
+		if (prev_trans->state != TRANS_STATE_COMPLETED) {
+			atomic_inc(&prev_trans->use_count);
+			spin_unlock(&root->fs_info->trans_lock);
 
 			wait_for_commit(root, prev_trans);
 
-			mutex_lock(&root->fs_info->trans_mutex);
-			put_transaction(prev_trans);
+			btrfs_put_transaction(prev_trans);
+		} else {
+			spin_unlock(&root->fs_info->trans_lock);
 		}
+	} else {
+		spin_unlock(&root->fs_info->trans_lock);
 	}
 
-	if (now < cur_trans->start_time || now - cur_trans->start_time < 1)
-		should_grow = 1;
+	extwriter_counter_dec(cur_trans, trans->type);
 
-	do {
-		int snap_pending = 0;
-		joined = cur_trans->num_joined;
-		if (!list_empty(&trans->transaction->pending_snapshots))
-			snap_pending = 1;
-
-		WARN_ON(cur_trans != trans->transaction);
-		prepare_to_wait(&cur_trans->writer_wait, &wait,
-				TASK_UNINTERRUPTIBLE);
-
-		if (cur_trans->num_writers > 1)
-			timeout = MAX_SCHEDULE_TIMEOUT;
-		else if (should_grow)
-			timeout = 1;
-
-		mutex_unlock(&root->fs_info->trans_mutex);
-
-		if (flush_on_commit) {
-			btrfs_start_delalloc_inodes(root, 1);
-			ret = btrfs_wait_ordered_extents(root, 0, 1);
-			BUG_ON(ret);
-		} else if (snap_pending) {
-			ret = btrfs_wait_ordered_extents(root, 0, 1);
-			BUG_ON(ret);
-		}
+	ret = btrfs_start_delalloc_flush(root->fs_info);
+	if (ret)
+		goto cleanup_transaction;
 
-		/*
-		 * rename don't use btrfs_join_transaction, so, once we
-		 * set the transaction to blocked above, we aren't going
-		 * to get any new ordered operations.  We can safely run
-		 * it here and no for sure that nothing new will be added
-		 * to the list
-		 */
-		btrfs_run_ordered_operations(root, 1);
+	ret = btrfs_flush_all_pending_stuffs(trans, root);
+	if (ret)
+		goto cleanup_transaction;
 
-		smp_mb();
-		if (cur_trans->num_writers > 1 || should_grow)
-			schedule_timeout(timeout);
+	wait_event(cur_trans->writer_wait,
+		   extwriter_counter_read(cur_trans) == 0);
+
+	/* some pending stuffs might be added after the previous flush. */
+	ret = btrfs_flush_all_pending_stuffs(trans, root);
+	if (ret)
+		goto cleanup_transaction;
 
-		mutex_lock(&root->fs_info->trans_mutex);
-		finish_wait(&cur_trans->writer_wait, &wait);
-	} while (cur_trans->num_writers > 1 ||
-		 (should_grow && cur_trans->num_joined != joined));
+	btrfs_wait_delalloc_flush(root->fs_info);
 
+	btrfs_scrub_pause(root);
+	/*
+	 * 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(&root->fs_info->trans_lock);
+	cur_trans->state = TRANS_STATE_COMMIT_DOING;
+	spin_unlock(&root->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(ACCESS_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(&root->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, root->fs_info);
-	BUG_ON(ret);
+	if (ret) {
+		mutex_unlock(&root->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, root);
+	if (ret) {
+		mutex_unlock(&root->fs_info->reloc_mutex);
+		goto scrub_continue;
+	}
 
 	ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
-	BUG_ON(ret);
+	if (ret) {
+		mutex_unlock(&root->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(root);
 
 	WARN_ON(cur_trans != trans->transaction);
 
@@ -1048,7 +1835,20 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 	mutex_lock(&root->fs_info->tree_log_mutex);
 
 	ret = commit_fs_roots(trans, root);
-	BUG_ON(ret);
+	if (ret) {
+		mutex_unlock(&root->fs_info->tree_log_mutex);
+		mutex_unlock(&root->fs_info->reloc_mutex);
+		goto scrub_continue;
+	}
+
+	/*
+	 * Since the transaction is done, we should set the inode map cache flag
+	 * before any other comming transaction.
+	 */
+	if (btrfs_test_opt(root, CHANGE_INODE_CACHE))
+		btrfs_set_opt(root->fs_info->mount_opt, INODE_MAP_CACHE);
+	else
+		btrfs_clear_opt(root->fs_info->mount_opt, INODE_MAP_CACHE);
 
 	/* commit_fs_roots gets rid of all the tree log roots, it is now
 	 * safe to free the root of tree log roots
@@ -1056,41 +1856,68 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 	btrfs_free_log_root_tree(trans, root->fs_info);
 
 	ret = commit_cowonly_roots(trans, root);
-	BUG_ON(ret);
+	if (ret) {
+		mutex_unlock(&root->fs_info->tree_log_mutex);
+		mutex_unlock(&root->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(ACCESS_ONCE(cur_trans->aborted))) {
+		ret = cur_trans->aborted;
+		mutex_unlock(&root->fs_info->tree_log_mutex);
+		mutex_unlock(&root->fs_info->reloc_mutex);
+		goto scrub_continue;
+	}
 
 	btrfs_prepare_extent_commit(trans, root);
 
 	cur_trans = root->fs_info->running_transaction;
-	spin_lock(&root->fs_info->new_trans_lock);
-	root->fs_info->running_transaction = NULL;
-	spin_unlock(&root->fs_info->new_trans_lock);
 
 	btrfs_set_root_node(&root->fs_info->tree_root->root_item,
 			    root->fs_info->tree_root->node);
-	switch_commit_root(root->fs_info->tree_root);
+	list_add_tail(&root->fs_info->tree_root->dirty_list,
+		      &cur_trans->switch_commits);
 
 	btrfs_set_root_node(&root->fs_info->chunk_root->root_item,
 			    root->fs_info->chunk_root->node);
-	switch_commit_root(root->fs_info->chunk_root);
+	list_add_tail(&root->fs_info->chunk_root->dirty_list,
+		      &cur_trans->switch_commits);
 
-	update_super_roots(root);
+	switch_commit_roots(cur_trans, root->fs_info);
 
-	if (!root->fs_info->log_root_recovering) {
-		btrfs_set_super_log_root(&root->fs_info->super_copy, 0);
-		btrfs_set_super_log_root_level(&root->fs_info->super_copy, 0);
-	}
+	assert_qgroups_uptodate(trans);
+	update_super_roots(root);
 
-	memcpy(&root->fs_info->super_for_commit, &root->fs_info->super_copy,
-	       sizeof(root->fs_info->super_copy));
+	btrfs_set_super_log_root(root->fs_info->super_copy, 0);
+	btrfs_set_super_log_root_level(root->fs_info->super_copy, 0);
+	memcpy(root->fs_info->super_for_commit, root->fs_info->super_copy,
+	       sizeof(*root->fs_info->super_copy));
 
-	trans->transaction->blocked = 0;
+	spin_lock(&root->fs_info->trans_lock);
+	cur_trans->state = TRANS_STATE_UNBLOCKED;
+	root->fs_info->running_transaction = NULL;
+	spin_unlock(&root->fs_info->trans_lock);
+	mutex_unlock(&root->fs_info->reloc_mutex);
 
 	wake_up(&root->fs_info->transaction_wait);
 
-	mutex_unlock(&root->fs_info->trans_mutex);
 	ret = btrfs_write_and_wait_transaction(trans, root);
-	BUG_ON(ret);
-	write_ctree_super(trans, root, 0);
+	if (ret) {
+		btrfs_error(root->fs_info, ret,
+			    "Error while writing out transaction");
+		mutex_unlock(&root->fs_info->tree_log_mutex);
+		goto scrub_continue;
+	}
+
+	ret = write_ctree_super(trans, root, 0);
+	if (ret) {
+		mutex_unlock(&root->fs_info->tree_log_mutex);
+		goto scrub_continue;
+	}
 
 	/*
 	 * the super is written, we can safely allow the tree-loggers
@@ -1100,21 +1927,27 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
 	btrfs_finish_extent_commit(trans, root);
 
-	/* do the directory inserts of any pending snapshot creations */
-	finish_pending_snapshots(trans, root->fs_info);
-
-	mutex_lock(&root->fs_info->trans_mutex);
+	root->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);
 
-	cur_trans->commit_done = 1;
+	spin_lock(&root->fs_info->trans_lock);
+	list_del_init(&cur_trans->list);
+	spin_unlock(&root->fs_info->trans_lock);
 
-	root->fs_info->last_trans_committed = cur_trans->transid;
+	btrfs_put_transaction(cur_trans);
+	btrfs_put_transaction(cur_trans);
 
-	wake_up(&cur_trans->commit_wait);
+	if (trans->type & __TRANS_FREEZABLE)
+		sb_end_intwrite(root->fs_info->sb);
 
-	put_transaction(cur_trans);
-	put_transaction(cur_trans);
+	trace_btrfs_transaction_commit(root);
 
-	mutex_unlock(&root->fs_info->trans_mutex);
+	btrfs_scrub_continue(root);
 
 	if (current->journal_info == trans)
 		current->journal_info = NULL;
@@ -1125,29 +1958,61 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 		btrfs_run_delayed_iputs(root);
 
 	return ret;
+
+scrub_continue:
+	btrfs_scrub_continue(root);
+cleanup_transaction:
+	btrfs_trans_release_metadata(trans, root);
+	trans->block_rsv = NULL;
+	if (trans->qgroup_reserved) {
+		btrfs_qgroup_free(root, trans->qgroup_reserved);
+		trans->qgroup_reserved = 0;
+	}
+	btrfs_warn(root->fs_info, "Skipping commit of aborted transaction.");
+	if (current->journal_info == trans)
+		current->journal_info = NULL;
+	cleanup_transaction(trans, root, ret);
+
+	return ret;
 }
 
 /*
- * interface function to delete all the snapshots we have scheduled for deletion
+ * 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_old_snapshots(struct btrfs_root *root)
+int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root)
 {
-	LIST_HEAD(list);
+	int ret;
 	struct btrfs_fs_info *fs_info = root->fs_info;
 
-	mutex_lock(&fs_info->trans_mutex);
-	list_splice_init(&fs_info->dead_roots, &list);
-	mutex_unlock(&fs_info->trans_mutex);
+	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);
 
-	while (!list_empty(&list)) {
-		root = list_entry(list.next, struct btrfs_root, root_list);
-		list_del(&root->root_list);
+	pr_debug("BTRFS: cleaner removing %llu\n", root->objectid);
 
-		if (btrfs_header_backref_rev(root->node) <
-		    BTRFS_MIXED_BACKREF_REV)
-			btrfs_drop_snapshot(root, 0);
-		else
-			btrfs_drop_snapshot(root, 1);
-	}
-	return 0;
+	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);
+	/*
+	 * If we encounter a transaction abort during snapshot cleaning, we
+	 * don't want to crash here
+	 */
+	return (ret < 0) ? 0 : 1;
 }