On Wed, Apr 6, 2016 at 3:04 AM, Qu Wenruo <[email protected]> wrote: > 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().
btrfs_qgroup_accounting_extents() -> btrfs_qgroup_account_extents() just be -> just before > > However there is a exception at create_pending_snapshot(), which will > call btrfs_qgroup_account_extents() but no any commit root switch. "but no any commit root switch" -> without switching commit roots? > > 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. "there is no switch roots" -> there is no switch of commit 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]> Can we please get a test case for fstests? thanks > --- > 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 -- Filipe David Manana, "Reasonable men adapt themselves to the world. Unreasonable men adapt the world to themselves. That's why all progress depends on unreasonable men." -- 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
