+/*
+ * CPU-stall kthread. It waits as specified by stall_cpu_holdoff, then
+ * induces a CPU stall for the time specified by stall_cpu.
+ */
+static int __cpuinit rcu_torture_stall(void *args)
+{
+ unsigned long stop_at;
+
+ VERBOSE_PRINTK_STRING("rcu_torture_stall task started");
+ if (stall_cpu_holdoff > 0) {
+ VERBOSE_PRINTK_STRING("rcu_torture_stall begin holdoff");
+ schedule_timeout_interruptible(stall_cpu_holdoff * HZ);
+ VERBOSE_PRINTK_STRING("rcu_torture_stall end holdoff");
+ }
+ if (!kthread_should_stop()) {
+ stop_at = get_seconds() + stall_cpu;
+ /* RCU CPU stall is expected behavior in following code. */
+ printk(KERN_ALERT "rcu_torture_stall start.\n");
+ rcu_read_lock();
+ preempt_disable();
+ while (ULONG_CMP_LT(get_seconds(), stop_at))
+ continue; /* Induce RCU CPU stall warning. */
+ preempt_enable();
+ rcu_read_unlock();
+ printk(KERN_ALERT "rcu_torture_stall end.\n");
+ }
+ rcutorture_shutdown_absorb("rcu_torture_stall");
+ while (!kthread_should_stop())
+ schedule_timeout_interruptible(10 * HZ);
+ return 0;
+}
+
+/* Spawn CPU-stall kthread, if stall_cpu specified. */
+static int __init rcu_torture_stall_init(void)
+{
+ int ret;
+
+ if (stall_cpu <= 0)
+ return 0;
+ stall_task = kthread_run(rcu_torture_stall, NULL, "rcu_torture_stall");
+ if (IS_ERR(stall_task)) {
+ ret = PTR_ERR(stall_task);
+ stall_task = NULL;
+ return ret;
+ }
+ return 0;
+}
+
+/* Clean up after the CPU-stall kthread, if one was spawned. */
+static void rcu_torture_stall_cleanup(void)
+{
+ if (stall_task == NULL)
+ return;
+ VERBOSE_PRINTK_STRING("Stopping rcu_torture_stall_task.");
+ kthread_stop(stall_task);
+}
+