linux-kernel - Re: [PATCH] hide guard page for stacks that grow upwards

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Message-ID: <AANLkTin5mxbyH9BOcrGAW2nFiDBOeUE8=HsBR8U=x3bc@mail.gmail.com>
Date:	Tue, 24 Aug 2010 15:23:52 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org,
	linux-ia64@...r.kernel.org
Subject: Re: [PATCH] hide guard page for stacks that grow upwards

On Tue, Aug 24, 2010 at 3:03 PM, Luck, Tony <tony.luck@...el.com> wrote:
>
> This looks useful too ... but I can't see where the code is that
> made vm_start be PAGE_SIZE lower to begin with. I'd expect to have
> to make a matching change to make vm_end PAGE_SIZE higher for the
> VM_GROWSUP areas.

That's the fault path - the very check_stack_guard_page() logic itself.

In other words, nowhere do we _explicitly_ make the stack larger by
one page, but nowhere do we explicitly size the stack in the first
place! The stack grows by being populated, and every time a new page
is populated, check_stack_guard_page() will have expanded the stack
vma by one extra page.

                   Linus
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