inode_attach_wb() was made a wrapper for __inode_attach_wb() and made generally available:

Linux commit v5.2-2705-g9b0eb69b75bc
cgroup, blkcg: Prepare some symbols for module and !CONFIG_CGROUP

Linux commit v6.12-rc1-25-g8182a8b39aa2
writeback: wbc_attach_fdatawrite_inode out of line

__inode_attach_wb() symbol is not exported making inode_attach_wb() unavailable.

Defer the check on attached wb inode until inode has wb attached (inode is marked dirty).