smp: fix a race when starting / resuming multiple CPUs

cpu_start_fn is global, it's used by the initiator CPU to start or
resume secondary CPUs. However it's possible, that the initiator CPU
goes ahead and starts a second secondary CPU before the first one has
finished using the object. Fix this by creating a local copy of the
global object.

Signed-off-by: Guennadi Liakhovetski <[email protected]>

kernel/smp.c

@@ -109,7 +109,7 @@ static void wait_for_start_signal(atomic_t *start_flag)
 static inline void smp_init_top(void *arg)
 {
 	struct k_thread dummy_thread;
-	struct cpu_start_cb *csc = arg;
+	struct cpu_start_cb csc = arg ? *(struct cpu_start_cb *)arg : (struct cpu_start_cb){0};
 
 	/* Let start_cpu() know that this CPU has powered up. */
 	(void)atomic_set(&ready_flag, 1);
@@ -119,25 +119,25 @@ static inline void smp_init_top(void *arg)
 	 */
 	wait_for_start_signal(&cpu_start_flag);
 
-	if ((csc == NULL) || csc->invoke_sched) {
+	if ((arg == NULL) || csc.invoke_sched) {
 		/* Initialize the dummy thread struct so that
 		 * the scheduler can schedule actual threads to run.
 		 */
 		z_dummy_thread_init(&dummy_thread);
 	}
 
 #ifdef CONFIG_SYS_CLOCK_EXISTS
-	if ((csc == NULL) || csc->reinit_timer) {
+	if ((arg == NULL) || csc.reinit_timer) {
 		smp_timer_init();
 	}
 #endif
 
 	/* Do additional initialization steps if needed. */
-	if ((csc != NULL) && (csc->fn != NULL)) {
-		csc->fn(csc->arg);
+	if (csc.fn != NULL) {
+		csc.fn(csc.arg);
 	}
 
-	if ((csc != NULL) && !csc->invoke_sched) {
+	if ((arg != NULL) && !csc.invoke_sched) {
 		/* Don't invoke scheduler. */
 		return;
 	}