Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardownof hugetlbfs shared page tables V2 (resend)

From: Michal Hocko
Date: Wed Aug 01 2012 - 04:20:38 EST


On Tue 31-07-12 22:45:43, Larry Woodman wrote:
> On 07/31/2012 04:06 PM, Michal Hocko wrote:
> >On Tue 31-07-12 13:49:21, Larry Woodman wrote:
> >>On 07/31/2012 08:46 AM, Mel Gorman wrote:
> >>>Fundamentally I think the problem is that we are not correctly detecting
> >>>that page table sharing took place during huge_pte_alloc(). This patch is
> >>>longer and makes an API change but if I'm right, it addresses the underlying
> >>>problem. The first VM_MAYSHARE patch is still necessary but would you mind
> >>>testing this on top please?
> >>Hi Mel, yes this does work just fine. It ran for hours without a panic so
> >>I'll Ack this one if you send it to the list.
> >Hi Larry, thanks for testing! I have a different patch which tries to
> >address this very same issue. I am not saying it is better or that it
> >should be merged instead of Mel's one but I would be really happy if you
> >could give it a try. We can discuss (dis)advantages of both approaches
> >later.
> >
> >Thanks!
>
> Hi Michal, the system hung when I tested this patch on top of the
> latest 3.5 kernel. I wont have AltSysrq access to the system until
> tomorrow AM.

Please hold on. The patch is crap. I forgot about
if (!vma_shareable(vma, addr))
return;

case so somebody got an uninitialized pmd. The patch bellow handles
that.

Sorry about that and thanks to Mel to notice this.
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