schedule(): do not preempt while holding spinlocks or while in offloaded syscall

kernel/cls.c

@@ -23,6 +23,7 @@
 extern int num_processors;
 
 struct cpu_local_var *clv;
+static int cpu_local_var_initialized = 0;
 
 void cpu_local_var_init(void)
 {
@@ -33,9 +34,22 @@ void cpu_local_var_init(void)
 
 	clv = allocate_pages(z, IHK_MC_AP_CRITICAL);
 	memset(clv, 0, z * PAGE_SIZE);
+	cpu_local_var_initialized = 1;
 }
 
 struct cpu_local_var *get_cpu_local_var(int id)
 {
 	return clv + id;
 }
+
+void preempt_enable(void)
+{
+	if (cpu_local_var_initialized)
+		--cpu_local_var(no_preempt);
+}
+
+void preempt_disable(void)
+{
+	if (cpu_local_var_initialized)
+		++cpu_local_var(no_preempt);
+}