tests/cgroup: use cgroup.kill in cg_killall()

If cgroup.kill file is supported make use of it.

Link: https://lore.kernel.org/r/[email protected]
Cc: Tejun Heo <[email protected]>
Cc: [email protected]
Reviewed-by: Shakeel Butt <[email protected]>
Acked-by: Roman Gushchin <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>

Author: Christian Brauner

tools/testing/selftests/cgroup/cgroup_util.c

@@ -252,6 +252,10 @@ int cg_killall(const char *cgroup)
 	char buf[PAGE_SIZE];
 	char *ptr = buf;
 
+	/* If cgroup.kill exists use it. */
+	if (!cg_write(cgroup, "cgroup.kill", "1"))
+		return 0;
+
 	if (cg_read(cgroup, "cgroup.procs", buf, sizeof(buf)))
 		return -1;