Red Hat: CVE-2024-39477: kernel: mm/hugetlb: do not call vma_add_reservation upon ENOMEM

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

mm/hugetlb: do not call vma_add_reservation upon ENOMEM

sysbot reported a splat [1] on __unmap_hugepage_range(). This is because
vma_needs_reservation() can return -ENOMEM if
allocate_file_region_entries() fails to allocate the file_region struct
for the reservation.

Check for that and do not call vma_add_reservation() if that is the case,
otherwise region_abort() and region_del() will see that we do not have any
file_regions.

If we detect that vma_needs_reservation() returned -ENOMEM, we clear the
hugetlb_restore_reserve flag as if this reservation was still consumed, so
free_huge_folio() will not increment the resv count.

[1] https://lore.kernel.org/linux-mm/[email protected]/T/#ma5983bc1ab18a54910da83416b3f89f3c7ee43aa