Commit 29cc6fb7 authored Jun 02, 2025 by Kent Overstreet

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 <kent.overstreet@linux.dev>

parent 09fb85ae

fs/bcachefs/subvolume.c

+14 −4

Original line number	Diff line number	Diff line
		@@ -130,9 +130,19 @@ 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;
		/*
		* 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 {