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To:     Linux-MM <linux-mm@kvack.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        Muchun Song <songmuchun@bytedance.com>
From:   Miaohe Lin <linmiaohe@huawei.com>
Subject: [bug report] mm, hwpoison: memory_failure races with
 alloc_fresh_huge_page/free_huge_page
Message-ID: <3c542543-0965-ef60-4627-1a4116077a5b@huawei.com>
Date:   Tue, 2 Aug 2022 10:00:50 +0800
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Hi all:
    When I investigate the mm/memory-failure.c code again, I found there's a possible race window
between memory_failure and alloc_fresh_huge_page/free_huge_page. Thank about the below scene:

CPU 1							CPU 2
alloc_fresh_huge_page -- page refcnt > 0		memory_failure
  prep_new_huge_page					  get_huge_page_for_hwpoison
							    !PageHeadHuge -- so 2(not a hugepage) is returned
    hugetlb_vmemmap_optimize -- subpages is read-only
    set_compound_page_dtor -- PageHuge is true now, but too late!!!
							  TestSetPageHWPoison(p)
							    -- We might write to read-only subpages here!!!

Another similar scene:

CPU 1							CPU 2
free_huge_page -- page refcnt == 0 and not PageHuge	memory_failure
							  get_huge_page_for_hwpoison
							    !PageHeadHuge -- so 2(not a hugepage) is returned
							  TestSetPageHWPoison(p)
							    -- We might write to read-only subpages here!!!
  hugetlb_vmemmap_restore -- subpages can be written to now, but too late!!!

I think the above scenes are possible. But I can't found a stable solution to fix it. Any suggestions?
Or is it not worth to fix it as it's too rare? Or am I miss something?

Any response would be appreciated!

Thanks!