btrfs_drop_snapshot() leaves subvolume qgroup items on disk after
completion. This can cause problems with snapshot creation. If a new
snapshot tries to claim the deleted subvolumes id, btrfs will get -EEXIST
from add_qgroup_item() and go read-only. The following commands will
reproduce this problem (assume btrfs is on /dev/sda and is mounted at
/btrfs)
mkfs.btrfs -f /dev/sda
mount -t btrfs /dev/sda /btrfs/
btrfs quota enable /btrfs/
btrfs su sna /btrfs/ /btrfs/snap
btrfs su de /btrfs/snap
sleep 45
umount /btrfs/
mount -t btrfs /dev/sda /btrfs/
We can fix this by catching -EEXIST in add_qgroup_item() and
initializing the existing items. We have the problem of orphaned
relation items being on disk from an old snapshot but that is outside
the scope of this patch.
Signed-off-by: Mark Fasheh <mfas...@suse.de>
---
fs/btrfs/qgroup.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index b497498..8477d33 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -551,9 +551,15 @@ static int add_qgroup_item(struct btrfs_trans_handle
*trans,
key.type = BTRFS_QGROUP_INFO_KEY;
key.offset = qgroupid;
+ /*
+ * Avoid a transaction abort by catching -EEXIST here. In that
+ * case, we proceed by re-initializing the existing structure
+ * on disk.
+ */
+
ret = btrfs_insert_empty_item(trans, quota_root, path, &key,
sizeof(*qgroup_info));
- if (ret)
+ if (ret && ret != -EEXIST)
goto out;
leaf = path->nodes[0];
@@ -572,7 +578,7 @@ static int add_qgroup_item(struct btrfs_trans_handle *trans,
key.type = BTRFS_QGROUP_LIMIT_KEY;
ret = btrfs_insert_empty_item(trans, quota_root, path, &key,
sizeof(*qgroup_limit));
- if (ret)
+ if (ret && ret != -EEXIST)
goto out;
leaf = path->nodes[0];
--
1.8.4.5
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
