cgroup_core02: Allocate child stack using mmap()

Some architectures like arm64 have strict requirements for stack alignment.
Statically allocated buffer may result in one of the test processes
getting killed by SIGBUS. Allocate child stack using mmap() to ensure
the requirements are met.

Link: https://lore.kernel.org/ltp/[email protected]/
Acked-by: Petr Vorel <[email protected]>
Reviewed-by: Cyril Hrubis <[email protected]>
Signed-off-by: Martin Doucha <[email protected]>

testcases/kernel/controllers/cgroup/cgroup_core02.c

@@ -32,6 +32,8 @@
 #include "tst_safe_file_at.h"
 #include "lapi/sched.h"
 
+#define STACK_SIZE 65536
+
 static struct tst_cg_group *cg_child_a, *cg_child_b;
 static uid_t nobody_uid;
 
@@ -51,7 +53,7 @@ static int lesser_ns_open_thread_fn(void *arg)
 static void test_lesser_ns_open(void)
 {
 	int i;
-	static char stack[65536];
+	char *stack;
 	pid_t pid;
 	int status;
 	struct lesser_ns_open_thread_arg targ = { .fds = {0}, .loops = -1};
@@ -63,14 +65,19 @@ static void test_lesser_ns_open(void)
 		SAFE_CG_PRINT(cg_child_a, "cgroup.procs", "0");
 		SAFE_CG_FCHOWN(cg_child_a, "cgroup.procs",  nobody_uid, -1);
 		SAFE_CG_FCHOWN(cg_child_b, "cgroup.procs",  nobody_uid, -1);
+		stack = SAFE_MMAP(NULL, STACK_SIZE, PROT_READ | PROT_WRITE,
+			MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
 		pid  = ltp_clone(CLONE_NEWCGROUP | CLONE_FILES | CLONE_VM | SIGCHLD,
-					lesser_ns_open_thread_fn, &targ, 65536, stack);
+					lesser_ns_open_thread_fn, &targ, STACK_SIZE, stack);
+
 		if (pid < 0)  {
 			tst_res(TFAIL, "unexpected negative pid %d", pid);
 			exit(1);
 		}
 
 		SAFE_WAITPID(pid, &status, 0);
+		SAFE_MUNMAP(stack, STACK_SIZE);
+
 		for (i = 0; i < targ.loops; i++) {
 			if (targ.fds[i] < 1) {
 				tst_res(TFAIL, "unexpected negative fd %d", targ.fds[i]);