[PATCH 0/2] btrfs: qgroup: stale qgroups related impromvents

[PATCH 0/2] btrfs: qgroup: stale qgroups related impromvents

[Qu Wenruo]

We have two problems in recent qgroup code:

- One can not delete a fully removed qgroup if the drop hits
  drop_subtree_threshold
  As hitting drop_subtree_threshold would mark qgroup inconsistent and
  skip all accounting, this would leave qgroup number untouched (thus
  non-zero), and btrfs refuses to delete qgroup with non-zero rfer/excl
  numbers.

  This would be addressed by the first patch, to allowing qgroup
  deletion as long as it doesn't have any child nor a corresponding
  subvolume.

- Deleted subvolumes leaves a stale qgroup until next rescan
  This is a long existing problem.

  Although previous pushes all failed, just let me try it again.

  The idea is commit current transaction (to sync qgroup numbers), then
  try to remove the subvolume qgroup if it's fully dropped.

Qu Wenruo (2):
  btrfs: slightly loose the requirement for qgroup removal
  btrfs: automatically remove the subvolume qgroup

 fs/btrfs/extent-tree.c |  9 +++++
 fs/btrfs/qgroup.c      | 76 ++++++++++++++++++++++++++++++++++++++----
 fs/btrfs/qgroup.h      |  2 ++
 3 files changed, 80 insertions(+), 7 deletions(-)

-- 
2.44.0

[PATCH 1/2] btrfs: slightly loose the requirement for qgroup removal

[Qu Wenruo]

[BUG]
Currently if one is utilizing "qgroups/drop_subtree_threshold" sysfs,
and a snapshot with level higher than that value is dropped, btrfs will
not be able to delete the qgroup until next qgroup rescan:

  uuid=ffffffff-eeee-dddd-cccc-000000000000

  wipefs -fa $dev
  mkfs.btrfs -f $dev -O quota -s 4k -n 4k -U $uuid
  mount $dev $mnt

  btrfs subvolume create $mnt/subv1/
  for (( i = 0; i < 1024; i++ )); do
  	xfs_io -f -c "pwrite 0 2k" $mnt/subv1/file_$i > /dev/null
  done
  sync
  btrfs subv snapshot $mnt/subv1 $mnt/snapshot
  btrfs quota enable $mnt
  btrfs quota rescan -w $mnt
  sync
  echo 1 > /sys/fs/btrfs/$uuid/qgroups/drop_subtree_threshold
  btrfs subvolume delete $mnt/snapshot
  btrfs subv sync $mnt
  btrfs qgroup show -prce --sync $mnt
  btrfs qgroup destroy 0/256 $mnt
  umount $mnt

The final qgroup removal would fail with the following error:

  ERROR: unable to destroy quota group: Device or resource busy

[CAUSE]
The above script would generate a subvolume of level 2, then snapshot
it, enable qgroup, set the drop_subtree_threshold, then drop the
snapshot.

Since the subvolume drop would meet the threshold, qgroup would be
marked inconsistent and skip accounting to avoid hanging the system at
transaction commit.

But currently we do not allow a qgroup with any rfer/excl numbers to be
dropped, and this is not really compatible with the new
drop_subtree_threshold behavior.

[FIX]
Instead of a strong requirement for zero rfer/excl numbers, just check
if there is any child for higher level qgroup, and for subvolume qgroups
check if there is a corresponding subvolume for it.

For rsv values, just do a WARN_ON() in case.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/qgroup.c | 48 ++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 41 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 9a9f84c4d3b8..e6fcce4372a4 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1736,13 +1736,38 @@ int btrfs_create_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
 	return ret;
 }
 
-static bool qgroup_has_usage(struct btrfs_qgroup *qgroup)
+static bool can_delete_qgroup(struct btrfs_fs_info *fs_info,
+			      struct btrfs_qgroup *qgroup)
 {
-	return (qgroup->rfer > 0 || qgroup->rfer_cmpr > 0 ||
-		qgroup->excl > 0 || qgroup->excl_cmpr > 0 ||
-		qgroup->rsv.values[BTRFS_QGROUP_RSV_DATA] > 0 ||
-		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PREALLOC] > 0 ||
-		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PERTRANS] > 0);
+	struct btrfs_key key;
+	struct btrfs_path *path;
+	int ret;
+
+	/* For higher level qgroup, we can only delete it if it has no child. */
+	if (btrfs_qgroup_level(qgroup->qgroupid)) {
+		if (!list_empty(&qgroup->members))
+			return false;
+		return true;
+	}
+
+	/*
+	 * For level-0 qgroups, we can only delete it if it has no subvolume
+	 * for it.
+	 * This means even a subvolume is unlinked but not yet fully dropped,
+	 * we can not delete the qgroup.
+	 */
+	key.objectid = qgroup->qgroupid;
+	key.type = BTRFS_ROOT_ITEM_KEY;
+	key.offset = -1ULL;
+	path = btrfs_alloc_path();
+	if (!path)
+		return false;
+
+	ret = btrfs_find_root(fs_info->tree_root, &key, path, NULL, NULL);
+	btrfs_free_path(path);
+	if (ret > 0)
+		return true;
+	return false;
 }
 
 int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
@@ -1764,7 +1789,7 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
 		goto out;
 	}
 
-	if (is_fstree(qgroupid) && qgroup_has_usage(qgroup)) {
+	if (!can_delete_qgroup(fs_info, qgroup)) {
 		ret = -EBUSY;
 		goto out;
 	}
@@ -1775,6 +1800,15 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
 		goto out;
 	}
 
+	/*
+	 * Warn on reserved space. The subvolume should has no child nor
+	 * corresponding subvolume.
+	 * Thus its reserved space should all be zero.
+	 */
+	WARN_ON(qgroup->rsv.values[BTRFS_QGROUP_RSV_DATA] ||
+		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PREALLOC] ||
+		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PERTRANS]);
+
 	ret = del_qgroup_item(trans, qgroupid);
 	if (ret && ret != -ENOENT)
 		goto out;
-- 
2.44.0

Re: [PATCH 1/2] btrfs: slightly loose the requirement for qgroup removal

[Qu Wenruo]

在 2024/4/19 16:20, Qu Wenruo 写道:
> [BUG]
> Currently if one is utilizing "qgroups/drop_subtree_threshold" sysfs,
> and a snapshot with level higher than that value is dropped, btrfs will
> not be able to delete the qgroup until next qgroup rescan:
> 
>    uuid=ffffffff-eeee-dddd-cccc-000000000000
> 
>    wipefs -fa $dev
>    mkfs.btrfs -f $dev -O quota -s 4k -n 4k -U $uuid
>    mount $dev $mnt
> 
>    btrfs subvolume create $mnt/subv1/
>    for (( i = 0; i < 1024; i++ )); do
>    	xfs_io -f -c "pwrite 0 2k" $mnt/subv1/file_$i > /dev/null
>    done
>    sync
>    btrfs subv snapshot $mnt/subv1 $mnt/snapshot
>    btrfs quota enable $mnt
>    btrfs quota rescan -w $mnt
>    sync
>    echo 1 > /sys/fs/btrfs/$uuid/qgroups/drop_subtree_threshold
>    btrfs subvolume delete $mnt/snapshot
>    btrfs subv sync $mnt
>    btrfs qgroup show -prce --sync $mnt
>    btrfs qgroup destroy 0/256 $mnt

My bad, the target qgroup show be 0/257.

Would update the commit message.

Thanks,
Qu
>    umount $mnt
> 
> The final qgroup removal would fail with the following error:
> 
>    ERROR: unable to destroy quota group: Device or resource busy
> 
> [CAUSE]
> The above script would generate a subvolume of level 2, then snapshot
> it, enable qgroup, set the drop_subtree_threshold, then drop the
> snapshot.
> 
> Since the subvolume drop would meet the threshold, qgroup would be
> marked inconsistent and skip accounting to avoid hanging the system at
> transaction commit.
> 
> But currently we do not allow a qgroup with any rfer/excl numbers to be
> dropped, and this is not really compatible with the new
> drop_subtree_threshold behavior.
> 
> [FIX]
> Instead of a strong requirement for zero rfer/excl numbers, just check
> if there is any child for higher level qgroup, and for subvolume qgroups
> check if there is a corresponding subvolume for it.
> 
> For rsv values, just do a WARN_ON() in case.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>   fs/btrfs/qgroup.c | 48 ++++++++++++++++++++++++++++++++++++++++-------
>   1 file changed, 41 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 9a9f84c4d3b8..e6fcce4372a4 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -1736,13 +1736,38 @@ int btrfs_create_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
>   	return ret;
>   }
>   
> -static bool qgroup_has_usage(struct btrfs_qgroup *qgroup)
> +static bool can_delete_qgroup(struct btrfs_fs_info *fs_info,
> +			      struct btrfs_qgroup *qgroup)
>   {
> -	return (qgroup->rfer > 0 || qgroup->rfer_cmpr > 0 ||
> -		qgroup->excl > 0 || qgroup->excl_cmpr > 0 ||
> -		qgroup->rsv.values[BTRFS_QGROUP_RSV_DATA] > 0 ||
> -		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PREALLOC] > 0 ||
> -		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PERTRANS] > 0);
> +	struct btrfs_key key;
> +	struct btrfs_path *path;
> +	int ret;
> +
> +	/* For higher level qgroup, we can only delete it if it has no child. */
> +	if (btrfs_qgroup_level(qgroup->qgroupid)) {
> +		if (!list_empty(&qgroup->members))
> +			return false;
> +		return true;
> +	}
> +
> +	/*
> +	 * For level-0 qgroups, we can only delete it if it has no subvolume
> +	 * for it.
> +	 * This means even a subvolume is unlinked but not yet fully dropped,
> +	 * we can not delete the qgroup.
> +	 */
> +	key.objectid = qgroup->qgroupid;
> +	key.type = BTRFS_ROOT_ITEM_KEY;
> +	key.offset = -1ULL;
> +	path = btrfs_alloc_path();
> +	if (!path)
> +		return false;
> +
> +	ret = btrfs_find_root(fs_info->tree_root, &key, path, NULL, NULL);
> +	btrfs_free_path(path);
> +	if (ret > 0)
> +		return true;
> +	return false;
>   }
>   
>   int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
> @@ -1764,7 +1789,7 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
>   		goto out;
>   	}
>   
> -	if (is_fstree(qgroupid) && qgroup_has_usage(qgroup)) {
> +	if (!can_delete_qgroup(fs_info, qgroup)) {
>   		ret = -EBUSY;
>   		goto out;
>   	}
> @@ -1775,6 +1800,15 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
>   		goto out;
>   	}
>   
> +	/*
> +	 * Warn on reserved space. The subvolume should has no child nor
> +	 * corresponding subvolume.
> +	 * Thus its reserved space should all be zero.
> +	 */
> +	WARN_ON(qgroup->rsv.values[BTRFS_QGROUP_RSV_DATA] ||
> +		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PREALLOC] ||
> +		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PERTRANS]);
> +
>   	ret = del_qgroup_item(trans, qgroupid);
>   	if (ret && ret != -ENOENT)
>   		goto out;

[PATCH 2/2] btrfs: automatically remove the subvolume qgroup

[Qu Wenruo]

Currently if we fully removed a subvolume (not only unlinked, but fully
dropped its root item), its qgroup would not be removed.

Thus we have "btrfs qgroup clear-stale" to handle such 0 level qgroups.

This patch changes the behavior by automatically removing the qgroup of
a fully dropped subvolume.

Link: https://bugzilla.suse.com/show_bug.cgi?id=1222847
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent-tree.c |  9 +++++++++
 fs/btrfs/qgroup.c      | 28 ++++++++++++++++++++++++++++
 fs/btrfs/qgroup.h      |  2 ++
 3 files changed, 39 insertions(+)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 023920d0d971..f4887f05a819 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5834,6 +5834,7 @@ int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref, int for_reloc)
 	struct btrfs_root_item *root_item = &root->root_item;
 	struct walk_control *wc;
 	struct btrfs_key key;
+	const u64 rootid = btrfs_root_id(root);
 	int err = 0;
 	int ret;
 	int level;
@@ -6064,6 +6065,14 @@ int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref, int for_reloc)
 	kfree(wc);
 	btrfs_free_path(path);
 out:
+	if (!err && root_dropped) {
+		ret = btrfs_qgroup_cleanup_dropped_subvolume(fs_info, rootid);
+		if (ret < 0) {
+			btrfs_warn_rl(fs_info,
+				      "failed to cleanup qgroup 0/%llu: %d",
+				      rootid, ret);
+		}
+	}
 	/*
 	 * We were an unfinished drop root, check to see if there are any
 	 * pending, and if not clear and wake up any waiters.
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index e6fcce4372a4..8690e212ba2a 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1838,6 +1838,34 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
 	return ret;
 }
 
+int btrfs_qgroup_cleanup_dropped_subvolume(struct btrfs_fs_info *fs_info,
+					   u64 subvolid)
+{
+	struct btrfs_trans_handle *trans;
+	int ret;
+
+	if (!is_fstree(subvolid) || !btrfs_qgroup_enabled(fs_info) ||
+	    !fs_info->quota_root)
+		return 0;
+
+	/* Commit current transaction to ensure the root item is removed. */
+	trans = btrfs_start_transaction(fs_info->quota_root, 0);
+	if (IS_ERR(trans))
+		return PTR_ERR(trans);
+
+	ret = btrfs_commit_transaction(trans);
+	if (ret < 0)
+		return ret;
+
+	/* Start new trans to delete the qgroup info and limit items. */
+	trans = btrfs_start_transaction(fs_info->quota_root, 2);
+	if (IS_ERR(trans))
+		return PTR_ERR(trans);
+	ret = btrfs_remove_qgroup(trans, subvolid);
+	btrfs_end_transaction(trans);
+	return ret;
+}
+
 int btrfs_limit_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid,
 		       struct btrfs_qgroup_limit *limit)
 {
diff --git a/fs/btrfs/qgroup.h b/fs/btrfs/qgroup.h
index 706640be0ec2..3f93856a02e1 100644
--- a/fs/btrfs/qgroup.h
+++ b/fs/btrfs/qgroup.h
@@ -327,6 +327,8 @@ int btrfs_del_qgroup_relation(struct btrfs_trans_handle *trans, u64 src,
 			      u64 dst);
 int btrfs_create_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid);
 int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid);
+int btrfs_qgroup_cleanup_dropped_subvolume(struct btrfs_fs_info *fs_info,
+					   u64 subvolid);
 int btrfs_limit_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid,
 		       struct btrfs_qgroup_limit *limit);
 int btrfs_read_qgroup_config(struct btrfs_fs_info *fs_info);
-- 
2.44.0