Re: [PATCH 01/10] hugetlb: fix metadata corruption inhugetlb_fault()

[Mel Gorman]

On Wed, Sep 08, 2010 at 10:19:32AM +0900, Naoya Horiguchi wrote:
> Since the PageHWPoison() check is for avoiding hwpoisoned page remained
> in pagecache mapping to the process, it should be done in "found in pagecache"
> branch, not in the common path.
> Otherwise, metadata corruption occurs if memory failure happens between
> alloc_huge_page() and lock_page() because page fault fails with metadata
> changes remained (such as refcount, mapcount, etc.)
> 
> This patch moves the check to "found in pagecache" branch and fix the problem.
> 
> ChangeLog since v2:
> - remove retry check in "new allocation" path.
> - make description more detailed
> - change patch name from "HWPOISON, hugetlb: move PG_HWPoison bit check"
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Signed-off-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>
> Reviewed-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>

Seems reasonable.

Acked-by: Mel Gorman <mel@xxxxxxxxx>

> ---
>  mm/hugetlb.c |   21 +++++++++------------
>  1 files changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git v2.6.36-rc2/mm/hugetlb.c v2.6.36-rc2/mm/hugetlb.c
> index cc5be78..6871b41 100644
> --- v2.6.36-rc2/mm/hugetlb.c
> +++ v2.6.36-rc2/mm/hugetlb.c
> @@ -2518,22 +2518,19 @@ retry:
>  			hugepage_add_new_anon_rmap(page, vma, address);
>  		}
>  	} else {
> +		/*
> +		 * If memory error occurs between mmap() and fault, some process
> +		 * don't have hwpoisoned swap entry for errored virtual address.
> +		 * So we need to block hugepage fault by PG_hwpoison bit check.
> +		 */
> +		if (unlikely(PageHWPoison(page))) {
> +			ret = VM_FAULT_HWPOISON;
> +			goto backout_unlocked;
> +		}
>  		page_dup_rmap(page);
>  	}
>  
>  	/*
> -	 * Since memory error handler replaces pte into hwpoison swap entry
> -	 * at the time of error handling, a process which reserved but not have
> -	 * the mapping to the error hugepage does not have hwpoison swap entry.
> -	 * So we need to block accesses from such a process by checking
> -	 * PG_hwpoison bit here.
> -	 */
> -	if (unlikely(PageHWPoison(page))) {
> -		ret = VM_FAULT_HWPOISON;
> -		goto backout_unlocked;
> -	}
> -
> -	/*
>  	 * If we are going to COW a private mapping later, we examine the
>  	 * pending reservations for this page now. This will ensure that
>  	 * any allocations necessary to record that reservation occur outside
> -- 
> 1.7.2.2
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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