btrfs: keep orphans for subvolume deletion

Since we have the free space caches, btrfs_orphan_cleanup also runs for
the tree_root. Unfortunately this also cleans up the orphans used to mark
subvol deletions in progress.

Currently if a subvol deletion gets interrupted twice by umount/mount, the
deletion will not be continued and the space permanently lost, though it
would be possible to write a tool to recover those lost subvol deletions.
This patch checks if the orphan belongs to a subvol (dead root) and skips
the deletion.

Signed-off-by: Arne Jansen <sensille@gmx.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index f1c4bceed072..4a31493d97ac 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2158,6 +2158,38 @@ int btrfs_orphan_cleanup(struct btrfs_root *root)
                 if (ret && ret != -ESTALE)
                         goto out;
 
+                if (ret == -ESTALE && root == root->fs_info->tree_root) {
+                        struct btrfs_root *dead_root;
+                        struct btrfs_fs_info *fs_info = root->fs_info;
+                        int is_dead_root = 0;
+
+                        /*
+                         * this is an orphan in the tree root. Currently these
+                         * could come from 2 sources:
+                         *  a) a snapshot deletion in progress
+                         *  b) a free space cache inode
+                         * We need to distinguish those two, as the snapshot
+                         * orphan must not get deleted.
+                         * find_dead_roots already ran before us, so if this
+                         * is a snapshot deletion, we should find the root
+                         * in the dead_roots list
+                         */
+                        spin_lock(&fs_info->trans_lock);
+                        list_for_each_entry(dead_root, &fs_info->dead_roots,
+                                            root_list) {
+                                if (dead_root->root_key.objectid ==
+                                    found_key.objectid) {
+                                        is_dead_root = 1;
+                                        break;
+                                }
+                        }
+                        spin_unlock(&fs_info->trans_lock);
+                        if (is_dead_root) {
+                                /* prevent this orphan from being found again */
+                                key.offset = found_key.objectid - 1;
+                                continue;
+                        }
+                }
                 /*
                  * Inode is already gone but the orphan item is still there,
                  * kill the orphan item.