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. Reported-by: Mark Fasheh <[email protected]> Signed-off-by: Qu Wenruo <[email protected]> --- fs/btrfs/transaction.c | 66 +++++++++++++++++++++++++++++++++++++------------- 1 file changed, 49 insertions(+), 17 deletions(-) diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index 43885e5..a3eb8ac 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -1516,6 +1516,55 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans, goto fail; } + /* + * Account qgroups before insert the dir item + * As such dir item insert will modify parent_root, which could be + * src root. If we don't do it now, wrong accounting may be inherited + * to snapshot qgroup. + * + * For reason locking tree_log_mutex, see btrfs_commit_transaction() + * comment + */ + mutex_lock(&root->fs_info->tree_log_mutex); + + ret = commit_fs_roots(trans, root); + if (ret) { + mutex_unlock(&root->fs_info->tree_log_mutex); + goto fail; + } + + btrfs_apply_pending_changes(root->fs_info); + + ret = btrfs_qgroup_prepare_account_extents(trans, root->fs_info); + if (ret < 0) { + mutex_unlock(&root->fs_info->tree_log_mutex); + goto fail; + } + ret = btrfs_qgroup_account_extents(trans, root->fs_info); + if (ret < 0) { + mutex_unlock(&root->fs_info->tree_log_mutex); + goto fail; + } + /* + * Now qgroup are all updated, we can inherit it to new qgroups + */ + ret = btrfs_qgroup_inherit(trans, fs_info, + root->root_key.objectid, + objectid, pending->inherit); + if (ret < 0) { + mutex_unlock(&root->fs_info->tree_log_mutex); + goto fail; + } + /* + * qgroup_account_extents() must be followed by a + * switch_commit_roots(), or next qgroup_account_extents() will + * be corrupted + */ + ret = commit_cowonly_roots(trans, root); + mutex_unlock(&root->fs_info->tree_log_mutex); + if (ret) + goto fail; + ret = btrfs_insert_dir_item(trans, parent_root, dentry->d_name.name, dentry->d_name.len, parent_inode, &key, @@ -1559,23 +1608,6 @@ 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: -- 2.8.0 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
