profs open hook

I have done this little patch for the procfs_example.c

diff procfs_example.c kernels/linux-2.4.20/Documentation/DocBook/procfs_example.c 87,91d86
< static int open_qp(struct inode * inode, struct file * file)
< {
< printk("Open my node %p %p \n",inode,file);
< return -EINVAL;
< }
180c175
< foo_file->proc_fops->open=open_qp;
---

And when loading this module. The procfs gets broken. I get EINVAL for open on /proc/meminfo and all other procfs info. Why? Should procfs inodes don't have full filesematics? And it don't help to unload the module.