From FreeBSD:

From FreeBSD:
> Fix a very rare error condition:  The code to free VM back to the kernel
> as done after a quasi-recursive call to free() had modified what we
> thought we knew about the last chunk of pages.
> This bug manifested itself when I did a "make obj" from src/usr.sbin/lpr,
> then make would coredump in the lpd directory.