linux-kernel - Re: [PATCH v2] mm/memory-failure.c: recheck PageHuge() after hugetlb page migrate successfully

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Date:	Thu, 12 Dec 2013 21:32:29 -0500
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Jianguo Wu <wujianguo@...wei.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>, Mel Gorman <mgorman@...e.de>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Hanjun Guo <guohanjun@...wei.com>,
	qiuxishi <qiuxishi@...wei.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, gong.chen@...ux.intel.com
Subject: Re: [PATCH v2] mm/memory-failure.c: recheck PageHuge() after hugetlb
 page migrate successfully

On Fri, Dec 13, 2013 at 09:09:52AM +0800, Jianguo Wu wrote:
> After a successful hugetlb page migration by soft offline, the source page
> will either be freed into hugepage_freelists or buddy(over-commit page). If page is in
> buddy, page_hstate(page) will be NULL. It will hit a NULL pointer
> dereference in dequeue_hwpoisoned_huge_page().
> 
> [  890.677918] BUG: unable to handle kernel NULL pointer dereference at
>  0000000000000058
> [  890.685741] IP: [<ffffffff81163761>]
> dequeue_hwpoisoned_huge_page+0x131/0x1d0
> [  890.692861] PGD c23762067 PUD c24be2067 PMD 0
> [  890.697314] Oops: 0000 [#1] SMP
> 
> So check PageHuge(page) after call migrate_pages() successfully.
> 
> Tested-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Jianguo Wu <wujianguo@...wei.com>
> ---
>  mm/memory-failure.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index b7c1716..e5567f2 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1471,7 +1471,8 @@ static int get_any_page(struct page *page, unsigned long pfn, int flags)
>  
>  static int soft_offline_huge_page(struct page *page, int flags)
>  {
> -	int ret;
> +	int ret, i;
> +	unsigned long nr_pages;
>  	unsigned long pfn = page_to_pfn(page);
>  	struct page *hpage = compound_head(page);
>  	LIST_HEAD(pagelist);
> @@ -1489,6 +1490,8 @@ static int soft_offline_huge_page(struct page *page, int flags)
>  	}
>  	unlock_page(hpage);
>  
> +	nr_pages = 1 << compound_order(hpage);
> +
>  	/* Keep page count to indicate a given hugepage is isolated. */
>  	list_move(&hpage->lru, &pagelist);
>  	ret = migrate_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL,
> @@ -1505,10 +1508,16 @@ static int soft_offline_huge_page(struct page *page, int flags)
>  		if (ret > 0)
>  			ret = -EIO;
>  	} else {
> -		set_page_hwpoison_huge_page(hpage);
> -		dequeue_hwpoisoned_huge_page(hpage);
> -		atomic_long_add(1 << compound_order(hpage),
> -				&num_poisoned_pages);
> +		/* overcommit hugetlb page will be freed to buddy */
> +		if (PageHuge(page)) {
> +			set_page_hwpoison_huge_page(hpage);
> +			dequeue_hwpoisoned_huge_page(hpage);
> +		} else {
> +			for (i = 0; i < nr_pages; i++)
> +				SetPageHWPoison(hpage + i);

Why don't you set PageHWPoison only on the error raw page instead
of the whole error hugepage, or is there some problem of doing so?

Thanks,
Naoya

> +		}
> +
> +		atomic_long_add(nr_pages, &num_poisoned_pages);
>  	}
>  	return ret;
>  }
> -- 
> 1.8.2.2
> 
> 
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