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Commit 6426c7ad authored by Qu Wenruo's avatar Qu Wenruo Committed by David Sterba
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btrfs: qgroup: Fix qgroup accounting when creating snapshot 



Current btrfs qgroup design implies a requirement that after calling
btrfs_qgroup_account_extents() there must be a commit root switch.

Normally this is OK, as btrfs_qgroup_accounting_extents() is only called
inside btrfs_commit_transaction() just be commit_cowonly_roots().

However there is a exception at create_pending_snapshot(), which will
call btrfs_qgroup_account_extents() but no any commit root switch.

In case of creating a snapshot whose parent root is itself (create a
snapshot of fs tree), it will corrupt qgroup by the following trace:
(skipped unrelated data)
======
btrfs_qgroup_account_extent: bytenr = 29786112, num_bytes = 16384, nr_old_roots = 0, nr_new_roots = 1
qgroup_update_counters: qgid = 5, cur_old_count = 0, cur_new_count = 1, rfer = 0, excl = 0
qgroup_update_counters: qgid = 5, cur_old_count = 0, cur_new_count = 1, rfer = 16384, excl = 16384
btrfs_qgroup_account_extent: bytenr = 29786112, num_bytes = 16384, nr_old_roots = 0, nr_new_roots = 0
======

The problem here is in first qgroup_account_extent(), the
nr_new_roots of the extent is 1, which means its reference got
increased, and qgroup increased its rfer and excl.

But at second qgroup_account_extent(), its reference got decreased, but
between these two qgroup_account_extent(), there is no switch roots.
This leads to the same nr_old_roots, and this extent just got ignored by
qgroup, which means this extent is wrongly accounted.

Fix it by call commit_cowonly_roots() after qgroup_account_extent() in
create_pending_snapshot(), with needed preparation.

Mark: I added a check at the top of qgroup_account_snapshot() to skip this
code if qgroups are turned off. xfstest btrfs/122 exposes this problem.

Signed-off-by: default avatarQu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: default avatarJosef Bacik <jbacik@fb.com>
Signed-off-by: default avatarMark Fasheh <mfasheh@suse.de>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 72928f24

fs/btrfs/transaction.c

+105 −24
Original line number Diff line number Diff line
@@ -311,10 +311,11 @@ static noinline int join_transaction(struct btrfs_root *root, unsigned int type) 
 * when the transaction commits

 */

static int record_root_in_trans(struct btrfs_trans_handle *trans,

			       struct btrfs_root *root)

			       struct btrfs_root *root,

			       int force)

{

	if (test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&

	    root->last_trans < trans->transid) {

	if ((test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&

	    root->last_trans < trans->transid) || force) {

		WARN_ON(root == root->fs_info->extent_root);

		WARN_ON(root->commit_root != root->node);
@@ -331,7 +332,7 @@ static int record_root_in_trans(struct btrfs_trans_handle *trans, 
		smp_wmb();



		spin_lock(&root->fs_info->fs_roots_radix_lock);

		if (root->last_trans == trans->transid) {

		if (root->last_trans == trans->transid && !force) {

			spin_unlock(&root->fs_info->fs_roots_radix_lock);

			return 0;

		}
@@ -402,7 +403,7 @@ int btrfs_record_root_in_trans(struct btrfs_trans_handle *trans, 
		return 0;



	mutex_lock(&root->fs_info->reloc_mutex);

	record_root_in_trans(trans, root);

	record_root_in_trans(trans, root, 0);

	mutex_unlock(&root->fs_info->reloc_mutex);



	return 0;
@@ -1310,6 +1311,92 @@ int btrfs_defrag_root(struct btrfs_root *root) 
	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.

	 */

	mutex_lock(&fs_info->qgroup_ioctl_lock);

	if (!fs_info->quota_enabled) {

		mutex_unlock(&fs_info->qgroup_ioctl_lock);

		return 0;

	}

	mutex_unlock(&fs_info->qgroup_ioctl_lock);



	/*

	 * 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, src);

	if (ret)

		goto out;

	ret = btrfs_qgroup_prepare_account_extents(trans, fs_info);

	if (ret < 0)

		goto out;

	ret = btrfs_qgroup_account_extents(trans, fs_info);

	if (ret < 0)

		goto out;



	/* Now qgroup are all updated, we can inherit it to new qgroups */

	ret = btrfs_qgroup_inherit(trans, fs_info,

				   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, src);

	if (ret)

		goto out;

	switch_commit_roots(trans->transaction, fs_info);

	ret = btrfs_write_and_wait_transaction(trans, src);

	if (ret)

		btrfs_std_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.
@@ -1383,7 +1470,7 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans, 
	dentry = pending->dentry;

	parent_inode = pending->dir;

	parent_root = BTRFS_I(parent_inode)->root;

	record_root_in_trans(trans, parent_root);

	record_root_in_trans(trans, parent_root, 0);



	cur_time = current_fs_time(parent_inode->i_sb);
@@ -1420,7 +1507,7 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans, 
		goto fail;

	}



	record_root_in_trans(trans, root);

	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);
@@ -1516,6 +1603,17 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans, 
		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, parent_root,

				    dentry->d_name.name, dentry->d_name.len,

				    parent_inode, &key,
@@ -1559,23 +1657,6 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans, 
		goto fail;

	}



	/*

	 * account qgroup counters before qgroup_inherit()

	 */

	ret = btrfs_qgroup_prepare_account_extents(trans, fs_info);

	if (ret)

		goto fail;

	ret = btrfs_qgroup_account_extents(trans, fs_info);

	if (ret)

		goto fail;

	ret = btrfs_qgroup_inherit(trans, fs_info,

				   root->root_key.objectid,

				   objectid, pending->inherit);

	if (ret) {

		btrfs_abort_transaction(trans, root, ret);

		goto fail;

	}



fail:

	pending->error = ret;

dir_item_existed: