kernel: Update k_wakeup()

This commit does two things to k_wakeup():

1. It locks the scheduler before marking the thread as not suspended.
As the the clearing of the _THREAD_SUSPENDED bit is not atomic, this
helps ensure that neither another thread nor ISR interrupts this
action (resulting in a corrupted thread_state).

2. The call to flag_ipi() has been removed as it is already being
made within ready_thread().

Signed-off-by: Peter Mitsis <[email protected]>
(cherry picked from commit 51ae993)

kernel/sched.c

@@ -1653,13 +1653,18 @@ void z_impl_k_wakeup(k_tid_t thread)
 		}
 	}
 
+	k_spinlock_key_t  key = k_spin_lock(&sched_spinlock);
+
 	z_mark_thread_as_not_suspended(thread);
-	z_ready_thread(thread);
 
-	flag_ipi();
+	if (!thread_active_elsewhere(thread)) {
+		ready_thread(thread);
+	}
 
-	if (!arch_is_in_isr()) {
-		z_reschedule_unlocked();
+	if (arch_is_in_isr()) {
+		k_spin_unlock(&sched_spinlock, key);
+	} else {
+		z_reschedule(&sched_spinlock, key);
 	}
 }