RE: [RFC 0/4] Fix machine check recovery for copy_from_user

[Luck, Tony]

> I have one scenario, may you take into account:
>
> If one copyin case occurs, write() returned by your patch, the user process may
> check the return values, for errors, it may exit the process, then the error page
> will be freed, and then the page maybe alloced to other process or to kernel itself,
> then code will initialize it and this will trigger one SRAO, if it's used by kernel,
> we may do nothing for this, and kernel may still touch it, and lead to one panic.

In this case kill_me_never() calls memory_failure() with flags == 0. I think (hope!)
that means that it will unmap the page from the task, but will not send a signal.

When the task exits the PTE for this page has the swap/poison signature, so the
page is not freed for re-use.

-Tony