CVE-2026-89593

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

hugetlb: only adjust reservation during unmapping if mapcount is 0

Since df7a6d1f6405, __unmap_hugepage_range can adjust reservations.  In
the case of folio mapped in both a parent and a child, if the parent
unmaps the range first, the reservation adjustment will result in an
underflow of the reserved count.  Once the child unmaps the range, the
count is restored.  Change __unmap_hugepage_range() to check the mapcount
before adjusting the reservation.