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/0000000000004096100617c58d54@google.com/T/#ma5983bc1ab18a54910da83416b3f89f3c7ee43aa

Link: https://lkml.kernel.org/r/20240528205323.20439-1-osalvador@suse.de


Fixes: df7a6d1f ("mm/hugetlb: restore the reservation if needed")
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reported-and-tested-by:  <syzbot+d3fe2dc5ffe9380b714b@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/linux-mm/0000000000004096100617c58d54@google.com/


Cc: Breno Leitao <leitao@debian.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>