Re: arch_get_unmapped_area_topdown vs stack reservations

[Arjan van de Ven <arjanv@redhat.com>]

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On Tue, Aug 17, 2004 at 11:18:30PM -0700, Martin J. Bligh wrote:
> --Arjan van de Ven <arjanv@redhat.com> wrote (on Wednesday, August 18, 2004 08:11:21 +0200):
> 
> > On Tue, Aug 17, 2004 at 03:18:34PM -0700, Martin J. Bligh wrote:
> >> I worry that the current code will allow us to intrude into the 
> >> reserved stack space with a vma allocation if it's requested at
> >> an address too high up. One could argue that they got what they
> >> asked for ... but not sure we should be letting them do that?
> > 
> > well even the non-flexmmap code allows this...
> 
> Yeah, wasn't meant as a criticism of the new layout, just a general
> improvement, perhaps.
> 
> > what is the problem ?
> 
> Just that if they allocate right up to the stack, we'll go boom shortly
> afterwards. I guess the question is ... what exactly are the rules
> for stack space reservations?

well... unless you have a VERY good reason I would see it as rude to prevent
this, I mean, the user *asks* for this address. Posix and co I'm sure don't
allow you to deny it unless it's really busy. 
Or say the user unmaps the stack (after allocating a new one and changing
esp).... the kernel then would not allow a new area to be mapped there
either.... smells like something the kernel should not enforce to me.

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