Re: [PATCH 2/2] mm/hwpoison: fix refcount of THP head page in no-injection case

[Wanpeng Li]

On 8/10/15 4:35 PM, Naoya Horiguchi wrote:
> On Mon, Aug 10, 2015 at 02:32:31PM +0800, Wanpeng Li wrote:
> > Hwpoison injection takes a refcount of target page and another refcount
> > of head page of THP if the target page is the tail page of a THP. However,
> > current code doesn't release the refcount of head page if the THP is not
> > supported to be injected wrt hwpoison filter.
> >
> > Fix it by reducing the refcount of head page if the target page is the tail
> > page of a THP and it is not supported to be injected.
> >
> > Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> > ---
> >   mm/hwpoison-inject.c |    2 ++
> >   1 files changed, 2 insertions(+), 0 deletions(-)
> >
> > diff --git a/mm/hwpoison-inject.c b/mm/hwpoison-inject.c
> > index 5015679..c343a45 100644
> > --- a/mm/hwpoison-inject.c
> > +++ b/mm/hwpoison-inject.c
> > @@ -56,6 +56,8 @@ inject:
> >   	return memory_failure(pfn, 18, MF_COUNT_INCREASED);
> >   put_out:
> >   	put_page(p);
> > +	if (p != hpage)
> > +		put_page(hpage);
> Yes, we need this when we inject to a thp tail page and "goto put_out" is
> called. But it seems that this code can be called also when injecting error
> to a hugetlb tail page and hwpoison_filter() returns non-zero, which is not
> expected. Unfortunately simply doing like below
>
> +	if (!PageHuge(p) && p != hpage)
> +		put_page(hpage);
>
> doesn't work, because exisiting put_page(p) can release refcount of hugetlb
> tail page, while get_hwpoison_page() takes refcount of hugetlb head page.
>
> So I feel that we need put_hwpoison_page() to properly release the refcount
> taken by memory error handlers.

Good point. I think I will continue to do it and will post it out soon. :)

Regards,
Wanpeng Li

> I'll post some patch(es) to address this problem this week.
>
> Thanks,
> Naoya Horiguchi

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