Filipe Manana wrote on 2016/04/06 10:20 +0100:
On Wed, Apr 6, 2016 at 3:04 AM, Qu Wenruo <quwen...@cn.fujitsu.com> 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
My English is really poor... :(
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 <mfas...@suse.de>
Signed-off-by: Qu Wenruo <quwen...@cn.fujitsu.com>
Can we please get a test case for fstests?
Test case will follow soon.
Thanks,
Qu
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
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