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SubjectRe: [PATCH v5] mm/hwpoison: fix race between hugetlb free/demotion and memory_failure_hugetlb()
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On 3/17/22 22:16, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@nec.com>
>
> There is a race condition between memory_failure_hugetlb() and hugetlb
> free/demotion, which causes setting PageHWPoison flag on the wrong page.
> The one simple result is that wrong processes can be killed, but another
> (more serious) one is that the actual error is left unhandled, so no one
> prevents later access to it, and that might lead to more serious results
> like consuming corrupted data.
>
> Think about the below race window:
>
> CPU 1 CPU 2
> memory_failure_hugetlb
> struct page *head = compound_head(p);
> hugetlb page might be freed to
> buddy, or even changed to another
> compound page.
>
> get_hwpoison_page -- page is not what we want now...
>
> The compound_head is called outside hugetlb_lock, so the head is not
> reliable.
>
> So set PageHWPoison flag after passing prechecks. And to detect
> potential violation, this patch also introduces a new action type
> MF_MSG_DIFFERENT_PAGE_SIZE.
>
> Reported-by: Mike Kravetz <mike.kravetz@oracle.com>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> Cc: <stable@vger.kernel.org>
> ---
> ChangeLog v4 -> v5:
> - call TestSetPageHWPoison() when page_handle_poison() fails.
> - call TestSetPageHWPoison() for unhandlable cases (MF_MSG_UNKNOWN and
> MF_MSG_DIFFERENT_PAGE_SIZE).
> - Set PageHWPoison on the head page only when the error page is surely
> a hugepage, otherwise set the flag on the raw page.
> - rebased onto v5.17-rc8-mmotm-2022-03-16-17-42

Thanks for all the updates!

I can not find any issues with these changes. However, this code is
very difficult to follow/understand.

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
--
Mike Kravetz

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