From 29cc6fb7c068c773049d3bde14b939033893eff4 Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Mon, 2 Jun 2025 19:48:27 -0400 Subject: [PATCH] bcachefs: Fix subvol to missing root repair We had a bug where the root inode of a subvolume was erronously deleted: bch2_evict_inode() called bch2_inode_rm(), meaning the VFS inode's i_nlink was somehow set to 0 when it shouldn't have - the inode in the btree indicated it clearly was not unlinked. This has been addressed with additional safety checks in bch2_inode_rm() - pulling in the safety checks we already were doing when deleting unlinked inodes in recovery - but the really disastrous bug was in check_subvols(), which on finding a dangling subvol (subvol with a missing root inode) would delete the subvolume. I assume this bug dates from early check_directory_structure() code, which originally handled subvolumes and normal paths - the idea being that still live contents of the subvolume would get reattached somewhere. But that's incorrect, and disastrously so; deleting a subvolume triggers deleting the snapshot ID it points to, deleting the entire contents. The correct way to repair is to recreate the root inode if it's missing; then any contents will get reattached under that subvolume's lost+found. Signed-off-by: Kent Overstreet --- fs/bcachefs/subvolume.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/fs/bcachefs/subvolume.c b/fs/bcachefs/subvolume.c index 60c10365c2857..020587449123b 100644 --- a/fs/bcachefs/subvolume.c +++ b/fs/bcachefs/subvolume.c @@ -130,10 +130,20 @@ static int check_subvol(struct btree_trans *trans, "subvolume %llu points to missing subvolume root %llu:%u", k.k->p.offset, le64_to_cpu(subvol.v->inode), le32_to_cpu(subvol.v->snapshot))) { - ret = bch2_subvolume_delete(trans, iter->pos.offset); - bch_err_msg(c, ret, "deleting subvolume %llu", iter->pos.offset); - ret = ret ?: -BCH_ERR_transaction_restart_nested; - goto err; + /* + * Recreate - any contents that are still disconnected + * will then get reattached under lost+found + */ + bch2_inode_init_early(c, &inode); + bch2_inode_init_late(c, &inode, bch2_current_time(c), + 0, 0, S_IFDIR|0700, 0, NULL); + inode.bi_inum = le64_to_cpu(subvol.v->inode); + inode.bi_snapshot = le32_to_cpu(subvol.v->snapshot); + inode.bi_subvol = k.k->p.offset; + inode.bi_parent_subvol = le32_to_cpu(subvol.v->fs_path_parent); + ret = __bch2_fsck_write_inode(trans, &inode); + if (ret) + goto err; } } else { goto err; -- 2.39.5