sched: Constify function scope static struct sched_param usage

Function-scope statics are discouraged because they are
easily overlooked and can cause subtle bugs/races due to
their global (non-SMP safe) nature.

Linus noticed that we did this for sched_param - at minimum
make the const.

Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
LKML-Reference: Message-ID: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

Author: Peter Zijlstra

kernel/irq/manage.c

@@ -577,7 +577,7 @@ irq_thread_check_affinity(struct irq_desc *desc, struct irqaction *action) { }
  */
 static int irq_thread(void *data)
 {
-	static struct sched_param param = {
+	static const struct sched_param param = {
 		.sched_priority = MAX_USER_RT_PRIO/2,
 	};
 	struct irqaction *action = data;

kernel/kthread.c

@@ -148,7 +148,7 @@ struct task_struct *kthread_create(int (*threadfn)(void *data),
 	wait_for_completion(&create.done);
 
 	if (!IS_ERR(create.result)) {
-		static struct sched_param param = { .sched_priority = 0 };
+		static const struct sched_param param = { .sched_priority = 0 };
 		va_list args;
 
 		va_start(args, namefmt);

kernel/softirq.c

@@ -853,7 +853,7 @@ static int __cpuinit cpu_callback(struct notifier_block *nfb,
 			     cpumask_any(cpu_online_mask));
 	case CPU_DEAD:
 	case CPU_DEAD_FROZEN: {
-		static struct sched_param param = {
+		static const struct sched_param param = {
 			.sched_priority = MAX_RT_PRIO-1
 		};
 

kernel/trace/trace_selftest.c

@@ -558,7 +558,7 @@ trace_selftest_startup_nop(struct tracer *trace, struct trace_array *tr)
 static int trace_wakeup_test_thread(void *data)
 {
 	/* Make this a RT thread, doesn't need to be too high */
-	static struct sched_param param = { .sched_priority = 5 };
+	static const struct sched_param param = { .sched_priority = 5 };
 	struct completion *x = data;
 
 	sched_setscheduler(current, SCHED_FIFO, &param);