When MAP_HUGETLB memory is unmapped, the length must be hugepage aligned,
otherwise it fails with -EINVAL.

All tests currently behave correctly, but it's better to explcitly test
the return value for completeness and document the requirement,
especially if users copy map_hugetlb.c as a sample implementation.

Signed-off-by: David Rientjes <redacted>
---
 tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c | 8 ++++++--

diff --git a/tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c b/tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c
--- a/tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c
+++ b/tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c

@@ -21,9 +21,13 @@ static int test_body(void)
 		 * Typically the mmap will fail because no huge pages are
 		 * allocated on the system. But if there are huge pages
 		 * allocated the mmap will succeed. That's fine too, we just
-		 * munmap here before continuing.
+		 * munmap here before continuing.  munmap() length of
+		 * MAP_HUGETLB memory must be hugepage aligned.
 		 */
-		munmap(addr, SIZE);
+		if (munmap(addr, SIZE)) {
+			perror("munmap");
+			return 1;
+		}
 	}
 
 	p = mmap(addr, SIZE, PROT_READ | PROT_WRITE,