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, 3 insertions, 1 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 5cf3aa7b125c..a272bfd74ea0 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1276,8 +1276,10 @@ struct btrfs_root *btrfs_read_fs_root_no_radix(struct btrfs_root *tree_root,
         root->commit_root = btrfs_root_node(root);
         BUG_ON(!root->node);
 out:
-        if (location->objectid != BTRFS_TREE_LOG_OBJECTID)
+        if (location->objectid != BTRFS_TREE_LOG_OBJECTID) {
                 root->ref_cows = 1;
+                btrfs_check_and_init_root_item(&root->root_item);
+        }
 
         return root;
 }