net/iucv: Avoid explicit cpumask var allocation on stack

For CONFIG_CPUMASK_OFFSTACK=y kernel, explicit allocation of cpumask
variable on stack is not recommended since it can cause potential stack
overflow.

Instead, kernel code should always use *cpumask_var API(s) to allocate
cpumask var in config-neutral way, leaving allocation strategy to
CONFIG_CPUMASK_OFFSTACK.

Use *cpumask_var API(s) to address it.

Signed-off-by: Dawei Li <dawei.li@shingroup.cn>
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Link: https://lore.kernel.org/r/20240331053441.1276826-2-dawei.li@shingroup.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/iucv/iucv.c

@@ -520,7 +520,7 @@ static void iucv_setmask_mp(void)
  */
 static void iucv_setmask_up(void)
 {
- cpumask_t cpumask;
+ static cpumask_t cpumask;
  int cpu;
 
  /* Disable all cpu but the first in cpu_irq_cpumask. */
@@ -628,23 +628,33 @@ static int iucv_cpu_online(unsigned int cpu)
 
 static int iucv_cpu_down_prep(unsigned int cpu)
 {
- cpumask_t cpumask;
+ cpumask_var_t cpumask;
+ int ret = 0;
 
  if (!iucv_path_table)
  return 0;
 
- cpumask_copy(&cpumask, &iucv_buffer_cpumask);
- cpumask_clear_cpu(cpu, &cpumask);
- if (cpumask_empty(&cpumask))
+ if (!alloc_cpumask_var(&cpumask, GFP_KERNEL))
+ return -ENOMEM;
+
+ cpumask_copy(cpumask, &iucv_buffer_cpumask);
+ cpumask_clear_cpu(cpu, cpumask);
+ if (cpumask_empty(cpumask)) {
  /* Can't offline last IUCV enabled cpu. */
- return -EINVAL;
+ ret = -EINVAL;
+ goto __free_cpumask;
+ }
 
  iucv_retrieve_cpu(NULL);
  if (!cpumask_empty(&iucv_irq_cpumask))
- return 0;
+ goto __free_cpumask;
+
  smp_call_function_single(cpumask_first(&iucv_buffer_cpumask),
  iucv_allow_cpu, NULL, 1);
- return 0;
+
+__free_cpumask:
+ free_cpumask_var(cpumask);
+ return ret;
 }
 
 /**