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

From: Naoya Horiguchi
Date: Mon Aug 10 2015 - 04:43:20 EST

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 <>
> ---
> 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.
I'll post some patch(es) to address this problem this week.

Naoya Horiguchi--
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