Btrfs: Fix uninitialized root flags for subvolumes

root_item->flags and root_item->byte_limit are not initialized when
a subvolume is created. This bug is not revealed until we added
readonly snapshot support - now you mount a btrfs filesystem and you
may find the subvolumes in it are readonly.

To work around this problem, we steal a bit from root_item->inode_item->flags,
and use it to indicate if those fields have been properly initialized.
When we read a tree root from disk, we check if the bit is set, and if
not we'll set the flag and initialize the two fields of the root item.

Reported-by: Andreas Philipp <philipp.andreas@gmail.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Tested-by: Andreas Philipp <philipp.andreas@gmail.com>
cc: stable@kernel.org
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 255c7c5279c4..f9c93a9ed4a7 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -373,6 +373,10 @@ static noinline int create_subvol(struct btrfs_root *root,
         inode_item->nbytes = cpu_to_le64(root->leafsize);
         inode_item->mode = cpu_to_le32(S_IFDIR | 0755);
 
+        root_item.flags = 0;
+        root_item.byte_limit = 0;
+        inode_item->flags = cpu_to_le64(BTRFS_INODE_ROOT_ITEM_INIT);
+
         btrfs_set_root_bytenr(&root_item, leaf->start);
         btrfs_set_root_generation(&root_item, trans->transid);
         btrfs_set_root_level(&root_item, 0);