linux-kernel - Re: [PATCH v3 3/3] hugetlbfs: add swap entry check in follow_hugetlb

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Date:	Wed, 03 Apr 2013 16:01:53 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Michal Hocko <mhocko@...e.cz>,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/3] hugetlbfs: add swap entry check in follow_hugetlb_page()

On 04/03/2013 02:35 PM, Naoya Horiguchi wrote:
> With applying the previous patch "hugetlbfs: stop setting VM_DONTDUMP in
> initializing vma(VM_HUGETLB)" to reenable hugepage coredump, if a memory
> error happens on a hugepage and the affected processes try to access
> the error hugepage, we hit VM_BUG_ON(atomic_read(&page->_count) <= 0)
> in get_page().
>
> The reason for this bug is that coredump-related code doesn't recognise
> "hugepage hwpoison entry" with which a pmd entry is replaced when a memory
> error occurs on a hugepage.
> In other words, physical address information is stored in different bit layout
> between hugepage hwpoison entry and pmd entry, so follow_hugetlb_page()
> which is called in get_dump_page() returns a wrong page from a given address.
>
> We need to filter out only hwpoison hugepages to have data on healthy
> hugepages in coredump. So this patch makes follow_hugetlb_page() avoid
> trying to get page when a pmd is in swap entry like format.
>
> ChangeLog v3:
>   - add comment about using is_swap_pte()
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Reviewed-by: Michal Hocko <mhocko@...e.cz>
> Acked-by: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> Cc: stable@...r.kernel.org

Reviewed-by: Rik van Riel <riel@...hat.com>

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