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

In the Linux kernel, the following vulnerability has been resolved:

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.

[[email protected]: fix race, rename label per Miaohe]