btrfs: don't go readonly on existing qgroup items
diff mbox

Message ID
State Accepted
Headers show

Commit Message

Mark Fasheh Aug. 18, 2014, 9:01 p.m. UTC
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

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 <>
 fs/btrfs/qgroup.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff mbox

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.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,
-	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,
 	ret = btrfs_insert_empty_item(trans, quota_root, path, &key,
-	if (ret)
+	if (ret && ret != -EEXIST)
 		goto out;
 	leaf = path->nodes[0];