btrfs: make clear_cache mount option to rebuild FST without disabling it

commit 1d6a4fc85717677e00fefffd847a50fc5928ce69 upstream.

Previously clear_cache mount option would simply disable free-space-tree
feature temporarily then re-enable it to rebuild the whole free space
tree.

But this is problematic for block-group-tree feature, as we have an
artificial dependency on free-space-tree feature.

If we go the existing method, after clearing the free-space-tree
feature, we would flip the filesystem to read-only mode, as we detect a
super block write with block-group-tree but no free-space-tree feature.

This patch would change the behavior by properly rebuilding the free
space tree without disabling this feature, thus allowing clear_cache
mount option to work with block group tree.

Now we can mount a filesystem with block-group-tree feature and
clear_mount option:

  $ mkfs.btrfs  -O block-group-tree /dev/test/scratch1  -f
  $ sudo mount /dev/test/scratch1 /mnt/btrfs -o clear_cache
  $ sudo dmesg -t | head -n 5
  BTRFS info (device dm-1): force clearing of disk cache
  BTRFS info (device dm-1): using free space tree
  BTRFS info (device dm-1): auto enabling async discard
  BTRFS info (device dm-1): rebuilding free space tree
  BTRFS info (device dm-1): checking UUID tree

CC: stable@vger.kernel.org # 6.1+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 18 insertions, 7 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 5b1b5e1a63c8f..acae82a5f8ee6 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3215,23 +3215,34 @@ int btrfs_start_pre_rw_mount(struct btrfs_fs_info *fs_info)
 {
 	int ret;
 	const bool cache_opt = btrfs_test_opt(fs_info, SPACE_CACHE);
-	bool clear_free_space_tree = false;
+	bool rebuild_free_space_tree = false;
 
 	if (btrfs_test_opt(fs_info, CLEAR_CACHE) &&
 	    btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE)) {
-		clear_free_space_tree = true;
+		rebuild_free_space_tree = true;
 	} else if (btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE) &&
 		   !btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE_VALID)) {
 		btrfs_warn(fs_info, "free space tree is invalid");
-		clear_free_space_tree = true;
+		rebuild_free_space_tree = true;
 	}
 
-	if (clear_free_space_tree) {
-		btrfs_info(fs_info, "clearing free space tree");
-		ret = btrfs_clear_free_space_tree(fs_info);
+	if (rebuild_free_space_tree) {
+		btrfs_info(fs_info, "rebuilding free space tree");
+		ret = btrfs_rebuild_free_space_tree(fs_info);
 		if (ret) {
 			btrfs_warn(fs_info,
-				   "failed to clear free space tree: %d", ret);
+				   "failed to rebuild free space tree: %d", ret);
+			goto out;
+		}
+	}
+
+	if (btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE) &&
+	    !btrfs_test_opt(fs_info, FREE_SPACE_TREE)) {
+		btrfs_info(fs_info, "disabling free space tree");
+		ret = btrfs_delete_free_space_tree(fs_info);
+		if (ret) {
+			btrfs_warn(fs_info,
+				   "failed to disable free space tree: %d", ret);
 			goto out;
 		}
 	}