Btrfs: disallow 'btrfs {balance,replace} cancel' on ro mounts

For both balance and replace, cancelling involves changing the on-disk
state and committing a transaction, which is not a good thing to do on
read-only filesystems.

Cc: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 9dfe038015f7..5d7ea267d8ff 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3424,6 +3424,9 @@ int btrfs_pause_balance(struct btrfs_fs_info *fs_info)
 
 int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
 {
+        if (fs_info->sb->s_flags & MS_RDONLY)
+                return -EROFS;
+
         mutex_lock(&fs_info->balance_mutex);
         if (!fs_info->balance_ctl) {
                 mutex_unlock(&fs_info->balance_mutex);