Patch "btrfs: don't go readonly on existing qgroup items" has been added to the 3.17-stable tree

[g***@linuxfoundation.org]

This is a note to let you know that I've just added the patch titled

btrfs: don't go readonly on existing qgroup items

to the 3.17-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
btrfs-don-t-go-readonly-on-existing-qgroup-items.patch
and it can be found in the queue-3.17 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,

From 0b4699dcb65c2cff793210b07f40b98c2d423a43 Mon Sep 17 00:00:00 2001

From: Mark Fasheh <***@suse.de>
Date: Mon, 18 Aug 2014 14:01:17 -0700
Subject: btrfs: don't go readonly on existing qgroup items

From: Mark Fasheh <***@suse.de>

commit 0b4699dcb65c2cff793210b07f40b98c2d423a43 upstream.

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 <***@suse.de>
Signed-off-by: Chris Mason <***@fb.com>
Signed-off-by: Greg Kroah-Hartman <***@linuxfoundation.org>

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

--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -551,9 +551,15 @@ static int add_qgroup_item(struct btrfs_
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_
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];


Patches currently in stable-queue which might be from ***@suse.de are

queue-3.17/btrfs-don-t-go-readonly-on-existing-qgroup-items.patch