Re: [criu] 1M guard page ruined restore

[Dmitry Safonov]

On 06/21/2017 08:31 PM, Oleg Nesterov wrote:
> On 06/21, Dmitry Safonov wrote:
> > The only question I have - how is it connected to guard page?
>
> Because with stack guard page do_page_fault() almost never needs to
> call expand_stack(), thus this check was almost never tested, I guess.
> Probably it should go away now.
>
> I'll write the changelog and patch tomorrow, unless someone does this
> before.

Ugh, maybe it's also worth now to update man 2 mmap.

At this moment, mmap() will no more return address one page lower
and "guard" is no more a page:

> MAP_GROWSDOWN
>        This flag is used for stacks. It indicates to the kernel virtual
>        memory system that the mapping should extend downward in       
>        memory. The return address is one page lower than the memory
>        area that is actually created in the process's virtual address
>        space. Touching an address in the "guard" page below the mapping
>        will cause the mapping to grow by a page. This growth can be
>        repeated until the mapping grows to within a page of the high end
>        of the next lower mapping, at which point touching the "guard"
>        page will result in a  SIGSEGV signal.

CC'ing Michael

--
             Dmitry