Re: [PATCH v3 4/5] use nth_page() in place of direct struct page manipulation.

[Zi Yan]

On 13 Sep 2023, at 16:12, Zi Yan wrote:

> From: Zi Yan <ziy@xxxxxxxxxx>
>
> When dealing with hugetlb pages, struct page is not guaranteed to be
> contiguous on SPARSEMEM without VMEMMAP. Use nth_page() to handle it
> properly.
>
> Fixes: 38c1ddbde6c6 ("hugetlbfs: improve read HWPOISON hugepage")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
>  fs/hugetlbfs/inode.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 7083fa0caaab..14d3d28e41b0 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -295,7 +295,7 @@ static size_t adjust_range_hwpoison(struct page *page, size_t offset, size_t byt
>  	size_t res = 0;
>
>  	/* First subpage to start the loop. */
> -	page += offset / PAGE_SIZE;
> +	page = nth_page(page, offset / PAGE_SIZE);
>  	offset %= PAGE_SIZE;
>  	while (1) {
>  		if (is_raw_hwpoison_page_in_hugepage(page))
> @@ -309,7 +309,7 @@ static size_t adjust_range_hwpoison(struct page *page, size_t offset, size_t byt
>  			break;
>  		offset += n;
>  		if (offset == PAGE_SIZE) {
> -			page++;
> +			page = nth_page(page, 1);
>  			offset = 0;
>  		}
>  	}
> -- 
> 2.40.1

Without the fix, a wrong subpage might be checked for HWPoison, causing wrong
number of bytes of a page copied to user space. No bug is reported. The fix
comes from code inspection.

--
Best Regards,
Yan, Zi

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