Re: [PATCH] HWPOSION, hugetlb: lock_page/unlock_page does not match for handling a free hugepage

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

(Cced: Andrew)

On Sat, May 10, 2014 at 11:14:34AM +0800, Chen Yucong wrote:
> For handling a free hugepage in memory failure, the race will happen if
> another thread hwpoisoned this hugepage concurrently. So we need to
> check PageHWPoison instead of !PageHWPoison.
> 
> If hwpoison_filter(p) returns true or a race happens, then we need to
> unlock_page(hpage).
> 
> Signed-off-by: Chen Yucong <slaoub@gmail.com>
> Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

I tested this patch on latest linux-next, and confirmed that memory error
on a tail page of a free hugepage is properly handled.

Tested-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

And I think this patch should go into all recent stable trees, since this
bug exists since 2.6.36 (because of my patch, sorry.)

> ---
> mm/memory-failure.c |   15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 35ef28a..dbf8922 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1081,15 +1081,16 @@ int memory_failure(unsigned long pfn, int
> trapno, int flags)

This linebreak breaks patch format. I guess it's done by your email
client or copy and paste. If it's true, git-send-email might be helpful
to avoid such errors.

Thanks,
Naoya


>  			return 0;
>  		} else if (PageHuge(hpage)) {
>  			/*
> -			 * Check "just unpoisoned", "filter hit", and
> -			 * "race with other subpage."
> +			 * Check "filter hit" and "race with other subpage."
>  			 */
>  			lock_page(hpage);
> -			if (!PageHWPoison(hpage)
> -			    || (hwpoison_filter(p) && TestClearPageHWPoison(p))
> -			    || (p != hpage && TestSetPageHWPoison(hpage))) {
> -				atomic_long_sub(nr_pages, &num_poisoned_pages);
> -				return 0;
> +			if (PageHWPoison(hpage)) {
> +				if ((hwpoison_filter(p) && TestClearPageHWPoison(p))
> +				    || (p != hpage && TestSetPageHWPoison(hpage))) {
> +					atomic_long_sub(nr_pages, &num_poisoned_pages);
> +					unlock_page(hpage);
> +					return 0;
> +				}
>  			}
>  			set_page_hwpoison_huge_page(hpage);
>  			res = dequeue_hwpoisoned_huge_page(hpage);
> -- 
> 1.7.10.4
> 
> 
> 
> 
> 
> 
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