Re: [patch][rfc] mm: have expand_stack honour VM_LOCKED

[Nick Piggin <npiggin@suse.de>]

On Fri, Oct 17, 2008 at 02:41:31PM +0900, KOSAKI Motohiro wrote:
> Hi Nick,
> 
> > Is this valid?
> > 
> > 
> > It appears that direct callers of expand_stack may not properly lock the newly
> > expanded stack if they don't call make_pages_present (page fault handlers do
> > this).
> 
> When happend this issue?
> 
> I think...
> 
> case 1. explit mlock to stack 
> 
>    1. mlock to stack
>         -> make_pages_present is called via mlock(2).
>    2. stack increased
>         -> no page fault happened.
> 
> case 2. swapout and mlock stack
> 
>    1. stack swap out
>    2. mlock to stack
>         -> the page doesn't swap in at the time.
>    3. page fault in the stack
>         -> the page swap in
>            (no need make_present_page())
> 
> 
> So, it seems this patch isn't necessary.

What if you you page fault the stack further than a single page down?

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