kernel: trace: preemptirq_delay_test: use offstack cpu mask

A CPU mask on the stack is broken for large values of CONFIG_NR_CPUS:

kernel/trace/preemptirq_delay_test.c: In function ‘preemptirq_delay_run’:
kernel/trace/preemptirq_delay_test.c:143:1: error: the frame size of 8512 bytes is larger than 1536 bytes [-Werror=frame-larger-than=]

Fall back to dynamic allocation here.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Song Chen <chensong_2000@189.cn>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20250620111215.3365305-1-arnd@kernel.org
Fixes: 4b9091e ("kernel: trace: preemptirq_delay_test: add cpu affinity")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: arndb

kernel/trace/preemptirq_delay_test.c

@@ -117,12 +117,15 @@ static int preemptirq_delay_run(void *data)
 {
 	int i;
 	int s = MIN(burst_size, NR_TEST_FUNCS);
-	struct cpumask cpu_mask;
+	cpumask_var_t cpu_mask;
+
+	if (!alloc_cpumask_var(&cpu_mask, GFP_KERNEL))
+		return -ENOMEM;
 
 	if (cpu_affinity > -1) {
-		cpumask_clear(&cpu_mask);
-		cpumask_set_cpu(cpu_affinity, &cpu_mask);
-		if (set_cpus_allowed_ptr(current, &cpu_mask))
+		cpumask_clear(cpu_mask);
+		cpumask_set_cpu(cpu_affinity, cpu_mask);
+		if (set_cpus_allowed_ptr(current, cpu_mask))
 			pr_err("cpu_affinity:%d, failed\n", cpu_affinity);
 	}
 
@@ -139,6 +142,8 @@ static int preemptirq_delay_run(void *data)
 
 	__set_current_state(TASK_RUNNING);
 
+	free_cpumask_var(cpu_mask);
+
 	return 0;
 }