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 <mfasheh@xxxxxxx>
Signed-off-by: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
---
v2:
Fix a soft lockup caused by missing switch_commit_root() call.
Fix a warning caused by dirty-but-not-committed root.
v3:
Fix a bug which will cause qgroup accounting for dropping snapshot
wrong
v4:
Fix a bug caused by non-cowed btree modification.
To Filipe:
I'm sorry I didn't wait for your reply on the dropped roots.
I reverted back the version where we deleted dropped roots in
switch_commit_roots().
As I think as long as we called btrfs_qgroup_prepare_account_extents()
and btrfs_qgroup_account_extents(), it should have already accounted
extents for dropped roots, and then we are OK to drop them.
It would be very nice if you could point out what I missed.
Thanks
Qu
---
fs/btrfs/transaction.c | 117 +++++++++++++++++++++++++++++++++++++++----------
1 file changed, 93 insertions(+), 24 deletions(-)
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 43885e5..92f8193 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;
@@ -1311,6 +1312,80 @@ int btrfs_defrag_root(struct btrfs_root *root)
}
/*
+ * 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;
+
+ /*
+ * 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;
+}
