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Date:	Wed, 19 Nov 2014 17:07:30 -0800
From:	Linus Torvalds <>
To:	Andy Lutomirski <>
Cc:	Thomas Gleixner <>,
	"" <>,
	Arnaldo Carvalho de Melo <>,
	Peter Zijlstra <>,
	Frederic Weisbecker <>,
	Don Zickus <>, Dave Jones <>,
	"the arch/x86 maintainers" <>
Subject: Re: frequent lockups in 3.18rc4

On Wed, Nov 19, 2014 at 4:49 PM, Andy Lutomirski <> wrote:
> I thought so for a while, too, but now I disagree.  On PGE hardware,
> it seems entirely possible that the new stack would be in the TLB even
> if it's not visible via cr3.  Then, as soon as the TLB entry expires,
> we double-fault.

Ahh. Good point.

> I don't want vmalloc to avoid low-order allocations -- I want it to
> have guard pages.  The fact that a user-triggerable stack overflow is
> basically root right now and doesn't reliably OOPS scares me.

Well, if you do that, you would have to make the double-fault handler
aware of the stack issue anyway, and then you could just do teh same
PGD repopulation that a page fault does and return (for the case where
you didn't overflow the stack, just had the page tables unpopulated -
obviously an actual stack overflow should do something more drastic).

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