diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c
index 32c6ccc2a6be..8747ffef200f 100644
--- a/tools/testing/selftests/mm/cow.c
+++ b/tools/testing/selftests/mm/cow.c
@@ -6,7 +6,6 @@
  *
  * Author(s): David Hildenbrand <david@redhat.com>
  */
-#define _GNU_SOURCE
 #include <stdlib.h>
 #include <string.h>
 #include <stdbool.h>
diff --git a/tools/testing/selftests/mm/gup_longterm.c b/tools/testing/selftests/mm/gup_longterm.c
index 9423ad439a61..53c257f6159c 100644
--- a/tools/testing/selftests/mm/gup_longterm.c
+++ b/tools/testing/selftests/mm/gup_longterm.c
@@ -6,7 +6,6 @@
  *
  * Author(s): David Hildenbrand <david@redhat.com>
  */
-#define _GNU_SOURCE
 #include <stdlib.h>
 #include <string.h>
 #include <stdbool.h>
diff --git a/tools/testing/selftests/mm/hugepage-mmap.c b/tools/testing/selftests/mm/hugepage-mmap.c
index 267eea2e0e0b..edb46888222f 100644
--- a/tools/testing/selftests/mm/hugepage-mmap.c
+++ b/tools/testing/selftests/mm/hugepage-mmap.c
@@ -16,7 +16,6 @@
  * 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>
diff --git a/tools/testing/selftests/mm/hugepage-mremap.c b/tools/testing/selftests/mm/hugepage-mremap.c
index c463d1c09c9b..8e22822bb754 100644
--- a/tools/testing/selftests/mm/hugepage-mremap.c
+++ b/tools/testing/selftests/mm/hugepage-mremap.c
@@ -11,8 +11,6 @@
  * To make sure the test triggers pmd sharing and goes through the 'unshare'
  * path in the mremap code use 1GB (1024) or more.
  */
-
-#define _GNU_SOURCE
 #include <stdlib.h>
 #include <stdio.h>
 #include <unistd.h>
diff --git a/tools/testing/selftests/mm/hugetlb-madvise.c b/tools/testing/selftests/mm/hugetlb-madvise.c
index e74107185324..70c40c67bc5d 100644
--- a/tools/testing/selftests/mm/hugetlb-madvise.c
+++ b/tools/testing/selftests/mm/hugetlb-madvise.c
@@ -11,8 +11,6 @@
  * filesystem.  Therefore, a hugetlbfs filesystem must be mounted on some
  * directory.
  */
-
-#define _GNU_SOURCE
 #include <stdlib.h>
 #include <stdio.h>
 #include <unistd.h>
diff --git a/tools/testing/selftests/mm/hugetlb-read-hwpoison.c b/tools/testing/selftests/mm/hugetlb-read-hwpoison.c
index ba6cc6f9cabc..6b8b41b4f754 100644
--- a/tools/testing/selftests/mm/hugetlb-read-hwpoison.c
+++ b/tools/testing/selftests/mm/hugetlb-read-hwpoison.c
@@ -1,6 +1,4 @@
 // SPDX-License-Identifier: GPL-2.0
-
-#define _GNU_SOURCE
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 829320a519e7..d18bf400dae6 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1,4 +1,3 @@
-#define _GNU_SOURCE
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index 37de82da9be7..b0af40ddb0fb 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -6,7 +6,6 @@
  *
  * Author(s): David Hildenbrand <david@redhat.com>
  */
-#define _GNU_SOURCE
 #include <stdlib.h>
 #include <string.h>
 #include <stdbool.h>
diff --git a/tools/testing/selftests/mm/madv_populate.c b/tools/testing/selftests/mm/madv_populate.c
index ef7d911da13e..f2c8223ff3d4 100644
--- a/tools/testing/selftests/mm/madv_populate.c
+++ b/tools/testing/selftests/mm/madv_populate.c
@@ -6,7 +6,6 @@
  *
  * Author(s): David Hildenbrand <david@redhat.com>
  */
-#define _GNU_SOURCE
 #include <stdlib.h>
 #include <string.h>
 #include <stdbool.h>
diff --git a/tools/testing/selftests/mm/map_populate.c b/tools/testing/selftests/mm/map_populate.c
index 5c8a53869b1b..ff4d4079bd0e 100644
--- a/tools/testing/selftests/mm/map_populate.c
+++ b/tools/testing/selftests/mm/map_populate.c
@@ -4,8 +4,6 @@
  *
  * MAP_POPULATE | MAP_PRIVATE should COW VMA pages.
  */
-
-#define _GNU_SOURCE
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/mman.h>
diff --git a/tools/testing/selftests/mm/memfd_secret.c b/tools/testing/selftests/mm/memfd_secret.c
index 9a0597310a76..0ba721d45d35 100644
--- a/tools/testing/selftests/mm/memfd_secret.c
+++ b/tools/testing/selftests/mm/memfd_secret.c
@@ -4,8 +4,6 @@
  *
  * Author: Mike Rapoport <rppt@linux.ibm.com>
  */
-
-#define _GNU_SOURCE
 #include <sys/uio.h>
 #include <sys/mman.h>
 #include <sys/wait.h>
diff --git a/tools/testing/selftests/mm/mlock2-tests.c b/tools/testing/selftests/mm/mlock2-tests.c
index 7f0d50fa361d..99dc39bf2fec 100644
--- a/tools/testing/selftests/mm/mlock2-tests.c
+++ b/tools/testing/selftests/mm/mlock2-tests.c
@@ -1,5 +1,4 @@
 // SPDX-License-Identifier: GPL-2.0
-#define _GNU_SOURCE
 #include <sys/mman.h>
 #include <stdint.h>
 #include <unistd.h>
diff --git a/tools/testing/selftests/mm/mrelease_test.c b/tools/testing/selftests/mm/mrelease_test.c
index 100370a7111d..d78bf686e99f 100644
--- a/tools/testing/selftests/mm/mrelease_test.c
+++ b/tools/testing/selftests/mm/mrelease_test.c
@@ -2,7 +2,6 @@
 /*
  * Copyright 2022 Google LLC
  */
-#define _GNU_SOURCE
 #include <errno.h>
 #include <stdbool.h>
 #include <stdio.h>
diff --git a/tools/testing/selftests/mm/mremap_dontunmap.c b/tools/testing/selftests/mm/mremap_dontunmap.c
index 1d75084b9ca5..934fa6b441b2 100644
--- a/tools/testing/selftests/mm/mremap_dontunmap.c
+++ b/tools/testing/selftests/mm/mremap_dontunmap.c
@@ -5,7 +5,6 @@
  *
  * Copyright 2020, Brian Geffon <bgeffon@google.com>
  */
-#define _GNU_SOURCE
 #include <sys/mman.h>
 #include <linux/mman.h>
 #include <errno.h>
diff --git a/tools/testing/selftests/mm/mremap_test.c b/tools/testing/selftests/mm/mremap_test.c
index 1b03bcfaefdf..0d8dc16b63be 100644
--- a/tools/testing/selftests/mm/mremap_test.c
+++ b/tools/testing/selftests/mm/mremap_test.c
@@ -2,8 +2,6 @@
 /*
  * Copyright 2020 Google LLC
  */
-#define _GNU_SOURCE
-
 #include <errno.h>
 #include <stdlib.h>
 #include <stdio.h>
diff --git a/tools/testing/selftests/mm/mseal_test.c b/tools/testing/selftests/mm/mseal_test.c
index 41998cf1dcf5..d35ee37311a7 100644
--- a/tools/testing/selftests/mm/mseal_test.c
+++ b/tools/testing/selftests/mm/mseal_test.c
@@ -1,5 +1,4 @@
 // SPDX-License-Identifier: GPL-2.0
-#define _GNU_SOURCE
 #include <linux/mman.h>
 #include <sys/mman.h>
 #include <stdint.h>
diff --git a/tools/testing/selftests/mm/pagemap_ioctl.c b/tools/testing/selftests/mm/pagemap_ioctl.c
index 2d785aca72a5..50d6bfc8db05 100644
--- a/tools/testing/selftests/mm/pagemap_ioctl.c
+++ b/tools/testing/selftests/mm/pagemap_ioctl.c
@@ -1,5 +1,4 @@
 // SPDX-License-Identifier: GPL-2.0
-#define _GNU_SOURCE
 #include <stdio.h>
 #include <fcntl.h>
 #include <string.h>
diff --git a/tools/testing/selftests/mm/pkey-helpers.h b/tools/testing/selftests/mm/pkey-helpers.h
index 1af3156a9db8..37d6b01ce90a 100644
--- a/tools/testing/selftests/mm/pkey-helpers.h
+++ b/tools/testing/selftests/mm/pkey-helpers.h
@@ -1,7 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _PKEYS_HELPER_H
 #define _PKEYS_HELPER_H
-#define _GNU_SOURCE
 #include <string.h>
 #include <stdarg.h>
 #include <stdio.h>
diff --git a/tools/testing/selftests/mm/protection_keys.c b/tools/testing/selftests/mm/protection_keys.c
index 48dc151f8fca..9f7de92caeda 100644
--- a/tools/testing/selftests/mm/protection_keys.c
+++ b/tools/testing/selftests/mm/protection_keys.c
@@ -21,7 +21,6 @@
  *	gcc -mxsave      -o protection_keys    -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
  *	gcc -mxsave -m32 -o protection_keys_32 -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
  */
-#define _GNU_SOURCE
 #define __SANE_USERSPACE_TYPES__
 #include <errno.h>
 #include <linux/elf.h>
diff --git a/tools/testing/selftests/mm/seal_elf.c b/tools/testing/selftests/mm/seal_elf.c
index f2babec79bb6..0438695bc45a 100644
--- a/tools/testing/selftests/mm/seal_elf.c
+++ b/tools/testing/selftests/mm/seal_elf.c
@@ -1,5 +1,4 @@
 // SPDX-License-Identifier: GPL-2.0
-#define _GNU_SOURCE
 #include <sys/mman.h>
 #include <stdint.h>
 #include <unistd.h>
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index d3c7f5fb3e7b..ae6ac950d7a1 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -3,8 +3,6 @@
  * A test of splitting PMD THPs and PTE-mapped THPs from a specified virtual
  * address range in a process via <debugfs>/split_huge_pages interface.
  */
-
-#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdarg.h>
diff --git a/tools/testing/selftests/mm/thuge-gen.c b/tools/testing/selftests/mm/thuge-gen.c
index ea7fd8fe2876..28a5c31bd791 100644
--- a/tools/testing/selftests/mm/thuge-gen.c
+++ b/tools/testing/selftests/mm/thuge-gen.c
@@ -12,8 +12,6 @@
    ipcrm -m by hand, like this
    sudo ipcs | awk '$1 == "0x00000000" {print $2}' | xargs -n1 sudo ipcrm -m
    (warning this will remove all if someone else uses them) */
-
-#define _GNU_SOURCE 1
 #include <sys/mman.h>
 #include <stdlib.h>
 #include <stdio.h>
diff --git a/tools/testing/selftests/mm/uffd-common.h b/tools/testing/selftests/mm/uffd-common.h
index cc5629c3d2aa..abb44319264a 100644
--- a/tools/testing/selftests/mm/uffd-common.h
+++ b/tools/testing/selftests/mm/uffd-common.h
@@ -7,7 +7,6 @@
 #ifndef __UFFD_COMMON_H__
 #define __UFFD_COMMON_H__
 
-#define _GNU_SOURCE
 #include <stdio.h>
 #include <errno.h>
 #include <unistd.h>
