selftests/vm: use memfd for hugepage-mmap test

This test was overlooked with a hard-coded mntpoint path in test when
we're removing the hugetlb mntpoint in commit 0796c7b8.  Fix it up so
the test can keep running.

Link: https://lkml.kernel.org/r/Y3aojfUC2nSwbCzB@x1n
Fixes: 0796c7b8 ("selftests/vm: drop mnt point for hugetlb in run_vmtests.sh")
Signed-off-by: Peter Xu <peterx@redhat.com>
Reported-by: Joel Savitz <jsavitz@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/vm/hugepage-mmap.c

@@ -16,14 +16,13 @@
  * range.
  * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
  */
-
+#define _GNU_SOURCE
 #include <stdlib.h>
 #include <stdio.h>
 #include <unistd.h>
 #include <sys/mman.h>
 #include <fcntl.h>
 
-#define FILE_NAME "huge/hugepagefile"
 #define LENGTH (256UL*1024*1024)
 #define PROTECTION (PROT_READ | PROT_WRITE)
 
@@ -67,16 +66,16 @@ int main(void)
 	void *addr;
 	int fd, ret;
 
-	fd = open(FILE_NAME, O_CREAT | O_RDWR, 0755);
+	fd = memfd_create("hugepage-mmap", MFD_HUGETLB);
 	if (fd < 0) {
-		perror("Open failed");
+		perror("memfd_create() failed");
 		exit(1);
 	}
 
 	addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0);
 	if (addr == MAP_FAILED) {
 		perror("mmap");
-		unlink(FILE_NAME);
+		close(fd);
 		exit(1);
 	}
 
@@ -87,7 +86,6 @@ int main(void)
 
 	munmap(addr, LENGTH);
 	close(fd);
-	unlink(FILE_NAME);
 
 	return ret;
 }