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btrfs: don't go readonly on existing qgroup items

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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 <mfasheh@suse.de>
Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Mark Fasheh 2014-08-18 14:01:17 -07:00 committed by Chris Mason
parent b7831b20f3
commit 0b4699dcb6
1 changed files with 8 additions and 2 deletions
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10
fs/btrfs/qgroup.c
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@ -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];