mm, selftests: test return value of munmap for MAP_HUGETLB memory

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 <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Davide Libenzi <[e-mail]>
Cc: Luiz Capitulino <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Joern Engel <[e-mail]>
Cc: Jianguo Wu <[e-mail]>
Cc: Eric B Munson <[e-mail]>
Acked-by: Michael Ellerman <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c

···
 		 * 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,

tools/testing/selftests/vm/hugetlbfstest.c

···
 	int *p;
 	int flags = MAP_PRIVATE | MAP_POPULATE | extra_flags;
 	u64 before, after;
+	int ret;
 
 	before = read_rss();
 	p = mmap(NULL, length, PROT_READ | PROT_WRITE, flags, fd, 0);
···
 			!"rss didn't grow as expected");
 	if (!unmap)
 		return;
-	munmap(p, length);
+	ret = munmap(p, length);
+	assert(!ret || !"munmap returned an unexpected error");
 	after = read_rss();
 	assert(llabs(after - before) < 0x40000 ||
 			!"rss didn't shrink as expected");

tools/testing/selftests/vm/map_hugetlb.c

···
 	write_bytes(addr);
 	ret = read_bytes(addr);
 
-	munmap(addr, LENGTH);
+	/* munmap() length of MAP_HUGETLB memory must be hugepage aligned */
+	if (munmap(addr, LENGTH)) {
+		perror("munmap");
+		exit(1);
+	}
 
 	return ret;
 }