diff --git a/tools/testing/selftests/cgroup/cgroup_util.c b/tools/testing/selftests/cgroup/cgroup_util.c
index ce16a50ecff8..432db923bced 100644
--- a/tools/testing/selftests/cgroup/cgroup_util.c
+++ b/tools/testing/selftests/cgroup/cgroup_util.c
@@ -1,4 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0 */
+
+#define _GNU_SOURCE
+
 #include <errno.h>
 #include <fcntl.h>
 #include <linux/limits.h>
diff --git a/tools/testing/selftests/cgroup/test_core.c b/tools/testing/selftests/cgroup/test_core.c
index de8baad46022..a5672a91d273 100644
--- a/tools/testing/selftests/cgroup/test_core.c
+++ b/tools/testing/selftests/cgroup/test_core.c
@@ -1,4 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
+
+#define _GNU_SOURCE
 #include <linux/limits.h>
 #include <linux/sched.h>
 #include <sys/types.h>
diff --git a/tools/testing/selftests/cgroup/test_cpu.c b/tools/testing/selftests/cgroup/test_cpu.c
index 5a4a314f6af7..dad2ed82f3ef 100644
--- a/tools/testing/selftests/cgroup/test_cpu.c
+++ b/tools/testing/selftests/cgroup/test_cpu.c
@@ -1,4 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
 #include <linux/limits.h>
 #include <sys/sysinfo.h>
 #include <sys/wait.h>
diff --git a/tools/testing/selftests/cgroup/test_hugetlb_memcg.c b/tools/testing/selftests/cgroup/test_hugetlb_memcg.c
index 80d05d50a42d..856f9508ea56 100644
--- a/tools/testing/selftests/cgroup/test_hugetlb_memcg.c
+++ b/tools/testing/selftests/cgroup/test_hugetlb_memcg.c
@@ -1,4 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+
 #include <linux/limits.h>
 #include <sys/mman.h>
 #include <stdio.h>
diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
index 2e453ac50c0d..96693d8772be 100644
--- a/tools/testing/selftests/cgroup/test_kmem.c
+++ b/tools/testing/selftests/cgroup/test_kmem.c
@@ -1,4 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+
 #include <linux/limits.h>
 #include <fcntl.h>
 #include <stdio.h>
diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
index c871630d62a3..41ae8047b889 100644
--- a/tools/testing/selftests/cgroup/test_memcontrol.c
+++ b/tools/testing/selftests/cgroup/test_memcontrol.c
@@ -1,4 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
+#define _GNU_SOURCE
+
 #include <linux/limits.h>
 #include <linux/oom.h>
 #include <fcntl.h>
diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 8418a8d7439f..fa571bfd2432 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -1,4 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+
 #include <linux/limits.h>
 #include <unistd.h>
 #include <stdio.h>