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

[Nick Piggin <npiggin@suse.de>]

On Fri, Oct 17, 2008 at 06:32:07PM +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?
> > 
> 
> I see. thanks.
> 
> But unfortunately, this patch conflicted against unevictable patch series.
> I'll make for -mm version patch few days after if you don't like do that.

Well, it's not a big deal. I just wanted to get some comments to see whether
the patch seems to be valid. Let's wait and see what gets merged in this
window, then I'll resubmit this patch unless anybody sees a problem with it.

Thanks for looking at it,

Nick

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