btrfs: create free space tree on ro->rw remount

When a user attempts to remount a btrfs filesystem with
'mount -o remount,space_cache=v2', that operation silently succeeds.
Unfortunately, this is misleading, because the remount does not create
the free space tree. /proc/mounts will incorrectly show space_cache=v2,
but on the next mount, the file system will revert to the old
space_cache.

For now, we handle only the easier case, where the existing mount is
read-only and the new mount is read-write. In that case, we can create
the free space tree without contending with the block groups changing
as we go.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 0d07643..a3e0065 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2898,6 +2898,17 @@ int btrfs_start_pre_rw_mount(struct btrfs_fs_info *fs_info)
                goto out;
        }
 
+       if (btrfs_test_opt(fs_info, FREE_SPACE_TREE) &&
+           !btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE)) {
+               btrfs_info(fs_info, "creating free space tree");
+               ret = btrfs_create_free_space_tree(fs_info);
+               if (ret) {
+                       btrfs_warn(fs_info,
+                               "failed to create free space tree: %d", ret);
+                       goto out;
+               }
+       }
+
        ret = btrfs_resume_balance_async(fs_info);
        if (ret)
                goto out;
@@ -3370,18 +3381,6 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
                }
        }
 
-       if (btrfs_test_opt(fs_info, FREE_SPACE_TREE) &&
-           !btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE)) {
-               btrfs_info(fs_info, "creating free space tree");
-               ret = btrfs_create_free_space_tree(fs_info);
-               if (ret) {
-                       btrfs_warn(fs_info,
-                               "failed to create free space tree: %d", ret);
-                       close_ctree(fs_info);
-                       return ret;
-               }
-       }
-
        ret = btrfs_start_pre_rw_mount(fs_info);
        if (ret) {
                close_ctree(fs_info);