btrfs: allow BTRFS_IOC_SNAP_DESTROY_V2 to remove ghost subvolume

There is a report from the mail list that some subvolumes don't have any
ROOT_REF/BACKREF and has 0 ref.
But without an ORPHAN item.

Such ghost subvolumes can't be deleted by any ioctl but only rely on
btrfs-progs to add ORPHAN item.

Normally kernel only needs to gracefully abort/reject such corrupted
structure, but in this case we have all the needed infrastructures and
interface to allow BTRFS_IOC_SNAP_DESTROY_V2 to delete it.

So add the ability to delete such ghost subvolumes to
BTRFS_IOC_SNAP_DESTROY_V2.

Signed-off-by: Qu Wenruo <wqu@suse.com>
(cherry picked from commit 9de990fcc8864c376eb28aa7482c54321f94acd4)
(cherry picked from commit f6016879c1d2f2bdb7998c4649bb3accabf491b5)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index edc7816d682bfbba295cfa96e05d0124288eec8c..bd4cbf7f91206a466453e29064906bc848ab9765 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2931,6 +2931,81 @@ out:
        return ret;
 }
 
+/*
+ * Special case that some subvolume has missing ORPHAN_ITEM, but its refs is
+ * already 0 (without any ROOT_REF/BACKREF).
+ * In that case such subvolume is only taking space while unable to be deleted.
+ *
+ * No reproducer to reproduce such corruption, but it won't hurt to cleanup them
+ * as we can reuse existing code since we only need to insert an orphan item and
+ * queue them to be deleted.
+ */
+static int __cold remove_ghost_subvol(struct btrfs_fs_info *fs_info,
+                                     u64 rootid)
+{
+       struct btrfs_trans_handle *trans;
+       struct btrfs_root *root;
+       struct btrfs_path *path;
+       struct btrfs_key key;
+       int ret;
+
+       root = btrfs_get_fs_root(fs_info, rootid, false);
+       if (IS_ERR(root)) {
+               ret = PTR_ERR(root);
+               return ret;
+       }
+
+       /* A ghost subvolume is already a problem, better to output a warning */
+       btrfs_warn(fs_info, "root %llu has no refs nor orphan item", rootid); 
+       if (btrfs_root_refs(&root->root_item) != 0) {
+               /* We get some strange root */
+               btrfs_warn(fs_info,
+                       "root %llu has %u refs, but no proper root backref",
+                       rootid, btrfs_root_refs(&root->root_item));
+               ret = -EUCLEAN;
+               goto out;
+       }
+
+       /* Already has orphan inserted */
+       if (test_bit(BTRFS_ROOT_ORPHAN_ITEM_INSERTED, &root->state))
+               goto out;
+
+       path = btrfs_alloc_path();
+       if (!path) {
+               ret = -ENOMEM;
+               goto out;
+       }
+       key.objectid = BTRFS_ORPHAN_OBJECTID;
+       key.type = BTRFS_ORPHAN_ITEM_KEY;
+       key.offset = rootid;
+
+       ret = btrfs_search_slot(NULL, fs_info->tree_root, &key, path, 0, 0);
+       btrfs_free_path(path);
+       /* Either error or there is already an orphan item */
+       if (ret <= 0)
+               goto out;
+
+       trans = btrfs_start_transaction(fs_info->tree_root, 1);
+       if (IS_ERR(trans)) {
+               ret = PTR_ERR(trans);
+               goto out;
+       }
+
+       ret = btrfs_insert_orphan_item(trans, fs_info->tree_root, rootid);
+       if (ret < 0 && ret != -EEXIST) {
+               btrfs_abort_transaction(trans, ret);
+               goto end_trans;
+       }
+       ret = 0;
+       btrfs_add_dead_root(root);
+
+end_trans:
+       btrfs_end_transaction(trans);
+out:
+       btrfs_put_root(root);
+       return ret;
+}
+
 static noinline int btrfs_ioctl_snap_destroy(struct file *file,
                                             void __user *arg,
                                             bool destroy_v2)
@@ -2985,6 +3060,9 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
                                        vol_args2->subvolid, 0, 0);
                        if (IS_ERR(dentry)) {
                                err = PTR_ERR(dentry);
+                               if (err == -ENOENT)
+                                       err = remove_ghost_subvol(fs_info,
+                                                       vol_args2->subvolid);
                                goto out_drop_write;
                        }