From 6426c7ad697df4bddf1d222685e6802e7616feaa Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Wed, 11 May 2016 12:53:52 -0700 Subject: [PATCH] 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: Qu Wenruo Reviewed-by: Josef Bacik Signed-off-by: Mark Fasheh Signed-off-by: David Sterba --- fs/btrfs/transaction.c | 129 +++++++++++++++++++++++++++++++++-------- 1 file changed, 105 insertions(+), 24 deletions(-) diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index 43885e51b882..d7172d7ced5f 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -311,10 +311,11 @@ loop: * 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: