Re: Hopefully a simple question on /proc/pid/mem

Stephen C. Tweedie
2001-05-01T09:36:31Z

Hi,

On Mon, Apr 30, 2001 at 07:13:53PM -0600, Eric W. Biederman wrote:

> > Hint: think about what happens if you make a shared mapping of a
> > private proc/*/mem region...
>
> Now that we have reusable swap cache pages we could make it work
> correctly, except for the case of the first write a private mapping of
> file. Not that we would want to...

Think about fork. If a parent forks and then touches a private page
before the child does, it's the parent which gets a new page. The
supposed shared mmap of the parent now points to the child's page, not
the parent's. COW basically just can't do the right thing if a page
is both shared and private at the same time.

--Stephen