kernel hangs after running program that uses a custom SIGSEGV handler

[Bruno Haible]

Stef O'Rear wrote:
> The bug is caused by mishandling of PROT_NONE (failing to distinguish
> between PROT_NONE and non-present pages)

Indeed, this sounds like a possible bug cause: clisp is one of the few
programs that uses mprotect not only with PROT_READ and PROT_READ_WRITE
but also occasionally with PROT_NONE.

Bruno