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

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Fri, 2008-10-17 at 11:37 +0200, Nick Piggin wrote:
> 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,

Hmmm.  guess I should drain my inbox--not to mention a couple more cups
of coffee--before responding...

Lee

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