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 current code first does prechecks roughly and then reconfirms after
taking refcount, but it's found that it makes code overly complicated,
so move the prechecks in a single hugetlb_lock range.

A newly introduced function, try_memory_failure_hugetlb(), always takes
hugetlb_lock (even for non-hugetlb pages).  That can be improved, but
memory_failure() is rare in principle, so should not be a big problem.

Link: https://lkml.kernel.org/r/20220408135323.1559401-2-naoya.horiguchi@linux.dev
Fixes: 761ad8d7 ("mm: hwpoison: introduce memory_failure_hugetlb()")
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reported-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>