mm/memory-failure: fix hugetlb_lock AA deadlock in get_huge_page_for_hwpoison

mm/memory-failure: fix hugetlb_lock AA deadlock in get_huge_page_for_hwpoison

Two concurrent madvise(MADV_HWPOISON) calls on the same hugetlb page can
trigger a recursive spinlock self-deadlock (AA deadlock) on hugetlb_lock
when racing with a concurrent unmap:

  thread#0                              thread#1
  --------                              --------
  madvise(folio, MADV_HWPOISON)
    -> poisons the folio successfully
  madvise(folio, MADV_HWPOISON)         unmap(folio)
    try_memory_failure_hugetlb
      get_huge_page_for_hwpoison
        spin_lock_irq(&hugetlb_lock)    <- held
        __get_huge_page_for_hwpoison
          hugetlb_update_hwpoison()
            -> MF_HUGETLB_FOLIO_PRE_POISONED
          goto out:
            folio_put()
              refcount: 1 -> 0
              free_huge_folio()
                spin_lock_irqsave(&hugetlb_lock)
                  -> AA DEADLOCK!

The out: path in __get_huge_page_for_hwpoison() calls folio_put() to drop
the GUP reference while the hugetlb_lock is still held by the hugetlb.c
wrapper get_huge_page_for_hwpoison().  If concurrent unmap has released
the page table mapping reference, folio_put() drops the folio refcount to
zero, triggering free_huge_folio() which attempts to re-acquire the
non-recursive hugetlb_lock.

Fix this by moving hugetlb_lock acquisition from the hugetlb.c wrapper
into get_huge_page_for_hwpoison().  Place spin_unlock_irq() before the
folio_put() at the out: label so the folio is always released outside the
lock.

[akpm@linux-foundation.org: fix race, rename label per Miaohe]
Link: https://sashiko.dev/#/patchset/20260522010305.4099834-1-mawupeng1@huawei.com
Link: https://lore.kernel.org/f39f405e-4b4b-8f79-70fe-a2b5b62114eb@huawei.com
Link: https://lore.kernel.org/20260522010305.4099834-1-mawupeng1@huawei.com
Fixes: 405ce051236c ("mm/hwpoison: fix race between hugetlb free/demotion and memory_failure_hugetlb()")
Signed-off-by: Wupeng Ma <mawupeng1@huawei.com>
Acked-by: Oscar Salvador (SUSE) <osalvador@kernel.org>
Acked-by: Muchun Song <muchun.song@linux.dev>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>