Commit 0b4699dc authored Aug 18, 2014 by Mark Fasheh Committed by Chris Mason Sep 17, 2014

btrfs: don't go readonly on existing qgroup items



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>

parent b7831b20

fs/btrfs/qgroup.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -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];

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